U.S. patent application number 12/452088 was filed with the patent office on 2010-08-19 for power cutter.
This patent application is currently assigned to Black & Decker Inc.. Invention is credited to Wolfgang Emmerich, Willi Strauss.
Application Number | 20100206278 12/452088 |
Document ID | / |
Family ID | 38440346 |
Filed Date | 2010-08-19 |
United States Patent
Application |
20100206278 |
Kind Code |
A1 |
Emmerich; Wolfgang ; et
al. |
August 19, 2010 |
POWER CUTTER
Abstract
A power cutter including a two stroke internal combustion engine
mounted within a housing and a carburetor for providing aerated
fuel for the engine. The carburetor is capable of operating in at
least two modes of operation, a first mode when the engine is cold
and a second mode when the engine is hot. A temperature sensor is
mounted on the engine and provides an engine controller with a
signal which is a function of the temperature of the engine; the
carburetor comprising an electrically controlled cold start
mechanism which switches the carburetor between its two modes of
operation, wherein, when the electronic controller determines that
the engine is cold, it provides an electrical signal to the
electrically controlled cold start mechanism to cause it to change
the mode of operation of the carburetor to its first mode.
Inventors: |
Emmerich; Wolfgang;
(Sindelfingen, DE) ; Strauss; Willi; (Schoenaich,
DE) |
Correspondence
Address: |
THE BLACK & DECKER CORPORATION
701 EAST JOPPA ROAD, TW199
TOWSON
MD
21286
US
|
Assignee: |
Black & Decker Inc.
Newark
DE
|
Family ID: |
38440346 |
Appl. No.: |
12/452088 |
Filed: |
July 4, 2008 |
PCT Filed: |
July 4, 2008 |
PCT NO: |
PCT/EP2008/058727 |
371 Date: |
April 14, 2010 |
Current U.S.
Class: |
123/65R |
Current CPC
Class: |
Y02T 10/12 20130101;
F02M 1/10 20130101; F02M 31/13 20130101; F02M 1/12 20130101; F02B
63/02 20130101; Y02T 10/126 20130101; F01M 3/00 20130101; F02M
35/024 20130101; F01M 1/26 20130101; F02M 35/1017 20130101 |
Class at
Publication: |
123/65.R |
International
Class: |
F02D 9/00 20060101
F02D009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 4, 2007 |
GB |
0712928.1 |
Claims
1. A power cutter comprising: a housing; a two stroke internal
combustion engine mounted within the housing; a throttle switch by
which the engine can be accelerated when the engine is running; a
support arm mounted on the housing and which projects forward of
the housing; a blade mounting mechanism rotatably mounted on the
end of the support arm and which is capable of being rotationally
driven by the engine when the engine is running; a carburetor for
providing aerated fuel for the engine, the carburetor capable of
operating in at least two modes of operation, a first mode when the
engine is cold and a second mode when the engine is hot; an air
intake for providing air for the carburetor; an air filtration
mechanism to filter the air drawn in from the air intake for the
carburetor; a fuel tank for providing fuel to the carburetor; and
an exhaust through which the exhaust gases generated by the
operation of the engine are expelled from the engine; an electronic
controller which controls the operation of the engine; and an
electrical power supply for powering the electrical components of
the power cutter; wherein there is provided a temperature sensor
mounted on the engine and which provides an engine controller with
a signal which is a function of the temperature of the engine,
wherein the carburetor comprises an electrically controlled cold
start mechanism which switches the carburetor between the two modes
of operation, and wherein, when the electronic controller
determines that the engine is cold, it provides an electrical
signal to the electrically controlled cold start mechanism to cause
the electrically controlled cold start mechanism to change the mode
of operation of the carburetor to the first mode.
2. The power cutter as claimed in claim 1, wherein the electrically
controlled cold start mechanism maintains the carburetor in the
first mode of operation.
3. The power cutter as claimed in claim 1, wherein the electronic
controller provides a continuous electrical signal to the
electrically controlled cold start mechanism to maintain the mode
of operation of the carburetor to the first mode.
4. The power cutter as claimed in claim 1, wherein electrical power
from the electrical power supply is continuously supplied to the
electrically controlled cold start mechanism when the carburetor is
in the first mode of operation.
5. The power cutter as claimed in claim 4, wherein the electrically
controlled cold start mechanism changes the mode of operation of
the carburetor from the first mode of operation to the second mode
of operation when the continuous supply of electrical power is
stopped.
6. The power cutter as claimed in claim 1, wherein the electronic
controller provides an electrical signal to the electrically
controlled cold start mechanism to cause it to change the mode of
operation of the carburetor to the second mode.
7. The power cutter as claimed in claim 4, wherein no electrical
power is supplied to the electrically controlled cold start
mechanism when the carburetor is in the second mode of
operation.
8. The power cutter as claimed in claim 1, wherein the electrically
controlled cold start mechanism comprises a solenoid which is
activated when it receives a signal from the electronic
controller.
9. The power cutter as claimed in claim 8, wherein the solenoid
opens and closes passageways within the carburetor to control the
flow of at least one of air and fuel through said passageways in
order to change the mode of operation of the carburetor.
10. The power cutter as claimed in claim 8, wherein the electronic
controller provides a continuous electrical signal to the solenoid
in order for solenoid to keep the passageways at least one of open
and closed while the carburetor is operating in the first mode of
operation.
11. The power cutter as claimed in claim 8, wherein electrical
power is continuously supplied to the solenoid in order for
solenoid to keep the passageways at least one of open and closed
while the carburetor is operating in the first mode of
operation.
12. The power cutter as claimed in claim 10, wherein the solenoid
opens and closes the passageways to change the mode of operation of
the carburetor from the first mode of operation to the second mode
of operation when the continuous supply of electrical power is
stopped.
13. The power cutter as claimed in claim 8, wherein no electrical
power is supplied to the solenoid when the carburetor is in the
second mode of operation.
14. The power cutter as claimed in claim 1, wherein the
electrically controlled cold start mechanism comprises a heating
element.
15. The power cutter as claimed in claim 1, wherein there is
provided an oil tank for providing lubricating oil for the engine
and an electrically powered oil pump for pumping lubricating oil
from the oil tank to mix it with fuel, the electrical power to the
oil pump being controlled by the electronic controller, and
wherein, when the carburetor is operating in the first mode of
operation, the electronic controller switches the electrical power
to the oil pump off to reduce the amount of power drawn from the
electrical power supply.
16. The power cutter as claimed in claim 1, wherein the electrical
power supply is a generator driven by the engine.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a national stage filing under 35
U.S.C. .sctn.371 of PCT/EP2008/058727 filed Jul. 4, 2008, which
claims priority to GB 0712928.1 filed Jul. 4, 2007, both of which
are incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a power cutter.
[0004] 2. Description of the Related Art
[0005] A typical power cutter comprises a housing in which is
mounted a two stroke internal combustion engine. Attached to the
side of the housing is a support arm which extends forward of the
housing. Rotatably mounted on the end of the support arm is a
cutting blade, usually in the form of a grinding disk. The motor is
drivingly connected to the cutting blade via a drive belt. The
rotary output of the engine rotatingly drives the cutting blade via
the drive belt. The drive belt is driven via a centrifugal clutch
which enables the out drive spindle of the engine to disengage from
the belt when the engine is running at a slow speed, to allow the
engine to continue running, while disengaging any drive to the
cutting blade to allow the blade to be stationary.
[0006] Also mounted in the housing is a fuel tank which provides
fuel for the engine via a carburetor. An oil tank can also be
provided, which provides lubricating oil to mix with the fuel, to
lubricate the engine.
[0007] Mounted on the rear of the housing is a rear handle for
supporting the power cutter, which contains a trigger switch for
accelerating the engine upon depressing. Depression of the trigger
switch causes more of the aerated fuel/oil mixture to be injected
into the engine which in turn causes the speed of the engine to
accelerate.
[0008] GB2232913 and WO2005/056225 show examples of such power
cutters.
[0009] A known problem with all two stokes engines is the
lubrication of the crank shaft 114 (using the reference numbers
shown in FIG. 19) and piston 1000. This is due to the fact that the
fuel/air mixture first passes through a chamber 18 in the cylinder
120 below the piston 1000 before being forced into the chamber 122
above the piston 16 before being ignited. This prevents the use of
lubricating oil being pumped around the crank shaft 114 on the
underside of the piston 1000. Therefore, in existing designs of two
stoke engines, a mixture of aerated fuel and lubricating oil is
burnt within the engine, the oil providing lubrication for the
crank shaft 114 and piston 1000 prior to being burnt with the fuel
during the combustion cycle. A common problem with the use of two
stoke engines is that the operator forgets to add the oil to the
fuel or adds it in an inconsistent manner, thus resulting in damage
to the engine. This particularly so for power cutters as often
power cutters are often hired out to operators. As such, operators
are not familiar with using them; they are not in the operator's
possession for long; the operator does not know who had it
previously or how the previous operator used the power cutter; and,
as the operator does not own it, has less reason to care for the
long term maintenance of the power cutter. Therefore, it is
desirable that a mechanism is provided to prevent or limit damage
to the two stroke engine of the power cutter to ensure that
sufficient lubrication oil is included in the aerated fuel which
prior to entering the engine.
[0010] It is possible to add lubricating oil directly to the fuel
in the fuel tank. However, this relies on the operator ensuring
that the correct ratio of lubricating oil to fuel is achieved. This
can be difficult as it may be hard to determine how much fuel is
already in the fuel tank and how much lubricating oil has already
been added. Therefore, it is preferable to have a separate oil tank
which is filled with lubricating oil and which is then pumped from
the tank and mixed with the fuel. This enables the amount of oil be
added to the fuel to be controlled more accurately.
[0011] The two stroke engines of power cutters use a carburetor to
provide aerated fuel for powering the engine. A typical design of
such a carburetor is shown in FIG. 31. Referring the FIG. 31, the
carburetor comprises a housing 1002 through which is formed an air
passageway 1004 through which air can pass in the direction of
Arrow Q. The air passageway 1004 at its entrance and exit has the
same cross sectional area. However, formed part way along the
length of the air passageway 1004, is a restriction 1006 which
reduces the size of the cross sectional area of the air passageway
and which acts as a venturi; the air passageway 1004 narrowing and
then expanding as the air passes through it. This causes the rate
of flow of air through the narrow section 1008 of the air
passageway 1004 to increase.
[0012] Fuel enters the carburetor via an inlet 1010 and fills a
first chamber 1012. The first chamber 1012 is connected to a second
chamber 1014 via a fuel passageway 1016. Fuel fills the second
chamber 1014 via the fuel passageway 1016.
[0013] An adjustable needle valve 1020, which has a pointed tip and
an elongate body, is mounted in the fuel passageway 1016 and which
can axially slide within the passage way 1016. The fuel passageway
1016 comprises a narrow section 1018. The tip of the adjustable
needle valve 1020 projects towards the narrow section 1018 and can
block the narrow section 1018 when the adjustable needle valve 1020
is moved towards it or open the narrow section 1018 when it is
moved away from it.
[0014] The rear end, remote from the tip, of the adjustable needle
valve 1020 projects into the second chamber 1014. Attached to the
rear end of the adjustable needle valve 1020 is a first lever 1022
which connects to a second lever 1024 via a pivot point 1026. One
of the walls of the second chamber 1014 is a flexible diaphragm
1032 which can move to adjust the volume of the second chamber
1014. A hollow chamber 1034 is formed on the other side of the
diaphragm 1032. The end of the second lever 1024 connects to the
diaphragm 1032. The second lever 1024 also connects to a solid wall
1028 of the second chamber 1014 via a spring 1030. The spring 1030
biases the second lever to a predetermine position, which in turn
biases the first lever 1022 to a predetermined angular position.
Flexing of the diaphragm 1032 causes pivotal movement of the first
and second levers against the biasing force of the spring 1030.
Movement of the first lever 1022 causes an axial sliding movement
of the adjustable needle valve 1020 moving its tip towards or away
from the narrow section 1018.
[0015] A first passageway 1036 connects to the second chamber 1014
via a high speed needle valve 1038. The other end of the first
passageway 1036 connects with the narrow section 1008 of the air
passageway 1004. A second passageway 1040 connects to the second
chamber 1014 via an idle needle valve 1042. The other end of the
second passageway 1040 connects via three small vents 1044 with the
air passageway 1004 down stream of the narrow section 1008. The
high speed needle valve 1038 is preset and limits the rate of flow
of fuel through the first passageway 1036. The idle needle valve
1042 is preset and limits the rate of flow of fuel through the
second passageway 1040.
[0016] Located in the air passageway 1004, ahead of the narrow
section 1008, is a first pivotal plate 1046 which acts as the choke
for the carburetor. The plate 1046 can be pivoted between an open
position (as shown) where it extends in the direction of the air
passageway 1004, allowing the maximum amount of air to enter the
passage 1004, to a closed position where it extends across the air
passageway 1004, substantially reducing the amount of air able
enter the air passageway 1004.
[0017] Located in the air passageway 1004, downstream of the narrow
section 1008, is a second pivotal plate 1048 which acts as the
throttle for the carburetor. The plate 1048 can be pivoted between
open and closed positions where it extends in the direction of the
air passage 1004, allowing the maximum amount of air to leave the
air passageway 1004, to a closed position where it extends across
the air passageway 1004, substantially reducing the amount of air
able to leave the air passageway 1004. The plate 1048 is shown half
way between its open and closed positions.
[0018] When the carburetor is in normal use, the first pivotal
plate 1046 is in its open position. Air is drawn through the air
passageway passing through the narrow section 1008 which causes it
to speed up. The movement of the air through the narrow section
1008 causes fuel to be drawn out of the first passageway 1036 into
the air flow and then pass through the air passageway 1004. The
amount of air, and hence the amount of fuel drawn out of the first
passageway 1036, is dependent on the angular position of the second
pivotal plate 1048. When it is in its open position, the maximum
amount of air is able to pass through the air passageway, drawing
out the maximum amount of fuel from the first passageway 1036. When
it is in its closed position, the minimum amount of air is able to
pass through the air passageway, drawing out the minimum amount of
fuel from the first passageway 1036. In order to ensure that
sufficient fuel enters the air flow in the air passageway 1004 when
the second pivotal plate 1048 is in its closed position, the second
passageway 1040 also provides fuel to the air flow. However, the
exit of the second passageway 1040 connects to the air passageway
down stream of the second pivotal plate 1048 to ensure that there
is always sufficient fuel entering the air flow.
[0019] As fuel is drawn out of the two passageways 1036; 1040, the
amount of fuel in the second chamber 1014 reduces. When the amount
of fuel reduces, the diaphragm 1032 flexes, to reduce the volume of
the second chamber 1014 to accommodate the loss of fuel. As the
diaphragm 1032 flexes, it moves the first and second pivotal levers
1024; 1022 against the biasing force of the spring 1030, which in
turn axially slides the adjustable needle valve 1020, moving its
tip away from the narrow section 1018, opening it up and allowing
fuel to flow from the first chamber 1012 into the second chamber
1014. As the second chamber 1014 fills up, the diaphragm 1032
flexes to accommodate the additional fuel, pivoting the levers and
moving the tip of the adjustable needle valve 1020 towards the
narrow section 1018 and reducing the amount of fuel flowing through
the fuel passageway. Movement of the diaphragm 1032 ensures
movement of the tip of the adjustable needle valve 1020 relative to
the narrow section 1018 is controlled to limit the amount of fuel
in the second chamber 1014.
[0020] When the engine is cold, the first pivotal plate 1046 is
placed in its closed position. This reduces the amount of air
entering the air passageway 1004 and therefore provides a higher
ratio of fuel to air in the air passageway to enable the cold
engine to run.
[0021] The angular position of the first pivotal plate 1046 is set
using a Bowden cable connected to a separate lever which is
adjusted manually by the operator of the power cutter. The angular
position of the second pivotal plate 1048 is set using a Bowden
cable connected to a trigger switch 1070 mounted on the handle
which is manually adjusted by the operator.
[0022] A problem with this design of carburetor on a power cutter
is that the operator has to be constantly adjusting the angular
position of the first pivotal plate when the engine is cold to
ensure the smooth operation of the engine. This is particularly
difficult if the operator is also trying to use the power
cutter.
SUMMARY OF THE INVENTION
[0023] Accordingly, there is provided a power cutter including a
housing; a two stroke internal combustion engine mounted within the
housing; a throttle switch by which the engine can be accelerated
when the engine is running; and a support arm mounted on the
housing and which projects forward of the housing. A blade mounting
mechanism is rotatably mounted on the end of the support arm and is
capable of being rotationally driven by the engine when the engine
is running. A carburetor provides aerated fuel for the engine and
is capable of operating in at least two modes of operation, a first
mode when the engine is cold and a second mode when the engine is
hot. An air intake provides air for the carburetor; an air
filtration mechanism filters the air drawn in from the air intake
for the carburetor; a fuel tank provides fuel to the carburetor;
and there is an exhaust through which the exhaust gases generated
by the operation of the engine are expelled from the engine. An
electronic controller controls the operation of the engine; and an
electrical power supply powers the electrical components of the
power cutter. A temperature sensor is mounted on the engine and
which provides the engine controller with a signal which is a
function of the temperature of the engine. The carburetor comprises
an electrically controlled cold start mechanism which switches the
carburetor between its two modes of operation. When the electronic
controller determines that the engine is cold, it provides an
electrical signal to the electrically controlled cold start
mechanism to cause it to change the mode of operation of the
carburetor to its first mode.
[0024] In the first mode of operation, the carburetor will provide
aerated fuel which richer in fuel to the engine than it would when
the carburetor is in its second mode of operation, where the
mixture is leaner. The richer mixture allows the engine to run
while it is cold. Once the engine has warmed up, the carburetor can
change to operate in its second mode of operation. The temperature
at which the engine is deemed to be hot or cold will vary depending
on the engine design. The electronic controller will compare the
signal provided by the temperature sensor with predetermine
parameters to determine if the engine is deemed to be hot or cold.
Based on this determination, the electronic controller will select
the mode of operation of the carburetor.
[0025] The electrical power supply will supply power at least to
electronic controller, the temperature sensor (either directly or
through the electronic controller) and the electrically controlled
cold start mechanism (either directly or through the electronic
controller).
[0026] The electrically controlled cold start mechanism can
maintain the carburetor in its first mode of operation.
[0027] The electronic controller can provide a continuous
electrical signal to the electrically controlled cold start
mechanism to maintain the mode of operation of the carburetor to
its first mode. Alternatively or in addition, electrical power from
the electrical power supply can be continuously supplied to the
electrically controlled cold start mechanism when the carburetor is
in its first mode of operation. In either case, the electrically
controlled cold start mechanism can changes the mode of operation
of the carburetor from its first mode of operation to its second
mode of operation when the continuous signal or continuous supply
of electrical power is stopped.
[0028] In some designs of carburetor, once a signal has been sent,
the carburetor will be maintained in the first mode with out any
further electrical signals being required from the electronic
controller. In such designs a second electrical signal needs to be
supplied by the electronic controller in order for the cold start
mechanism to change the mode of operation of the carburetor to its
second mode. Therefore, in such designs, the electronic controller
provides an electrical signal to the electrically controlled cold
start mechanism to cause it to change the mode of operation of the
carburetor to its second mode.
[0029] Ideally, no electrical power is supplied to the electrically
controlled cold start mechanism when the carburetor is in its
second mode of operation.
[0030] When the carburetor is working under normal conditions, it
will be in the second mode of operation as the engine will be warm.
The power cutter will be operated for the most of the time while
the carburetor is in its second mode of operation. Though
electrical power may be supplied, either directly from the power
supply or via the electronic controller as part of the signal, to
the electrically controlled cold start mechanism to change the
carburetor to its second mode of operation, it is desirable to
supply no electrical power at all to the electrically controlled
cold start mechanism once the carburetor is in its second mode of
operation to minimize the amount of power drawn from the power
supply while the power is being used.
[0031] Preferably, the electrically controlled cold start mechanism
comprises a solenoid which is activated when it receives a signal
from the electronic controller.
[0032] The solenoid can be used to activate or deactivate a number
of devices within the carburetor. For example is can be used to
control the first pivotal plate 1046 which acts as the choke for
the carburetor described with reference to FIG. 31. However, a
solenoid is most effective when
[0033] The solenoid may be utilized to open and close passageways
within the carburetor to control the flow of air and/or fuel
through those passageways in order to change the mode of operation
of the carburetor.
[0034] The electronic controller can provide a continuous
electrical signal to the solenoid in order for solenoid to keep the
passage ways open or closed while the carburetor is operating in
its first mode of operation. Furthermore, electrical power can be
continuously supplied to the solenoid in order for solenoid to keep
the passage ways or closed while the carburetor is operating in its
first mode of operation.
[0035] The solenoid can open or close the passageways to change the
mode of operation of the carburetor from its first mode of
operation to its second mode of operation when the continuous
signal or continuous supply of electrical power is stopped.
[0036] However, preferably, no electrical power is supplied to the
solenoid when the carburetor is in its second mode of
operation.
[0037] Alternatively, the electrically controlled cold start
mechanism comprises a heating element.
[0038] In order for a two stroke engine to operate without being
damaged, lubricating oil needs to be fed into the engine with the
aerated fuel. This can be achieved by adding the oil to the fuel in
the fuel tank, the fuel and oil mixture then being aerated as it
passes through the carburetor. However, on some power cutters there
is provided a separate oil tank for the lubricating oil. The
lubricating oil is pumped out of the tank and into the fuel,
typically after it has been aerated by being passed through the
carburetor.
[0039] Therefore, when there is provided an oil tank 128 for
providing lubricating oil for the engine and an electrically
powered oil pump 130 to pump lubricating oil from the oil tank to
mix it with fuel, the electrical power to the oil pump being
controlled by the electronic controller, and when the carburetor is
operating in its first mode of operation, the electronic controller
can switch the electrical power to the oil pump off to reduce the
amount of power drawn from the electrical power supply.
[0040] If the oil pump and the electrically controlled cold start
mechanism are run at the same time, it will require the power
cutter to generate larger quantities of electricity. The generation
of electricity on a power cutter is limited as the size of the
generator increases with as it is needed to produce more
electricity. As weight is an issue on a power cutter, as it has to
be supported above the ground by the operator, it is desirable to
minimize the size of the generator thus restricting the amount of
electricity available. It has been found that engine can run for a
short period of time without any substantial damage occurring when
no lubricating oil is added to aerated fuel supplied to the engine.
This period is longer that required to heat up the engine and thus
ensure the carburetor is working in its second mode of
operation.
[0041] The electrical power supply can be a generator driven by the
engine
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] A number of embodiments of the invention will now be
described with reference to accompanying drawings of which:
[0043] FIG. 1 shows a perspective view of the power cutter from a
first side;
[0044] FIG. 2 shows a side view of the power cutter from a second
side;
[0045] FIG. 3 shows a sketch of a horizontal cross section of the
belt drive and support arm;
[0046] FIG. 4 shows a sketch of the forward and rearward sections
of the support arm;
[0047] FIG. 5 shows a sketch of a horizontal cross sectional view
of the connection between the rearward and forward sections of the
support arm;
[0048] FIG. 6 shows the belt tensioner;
[0049] FIG. 7 shows a computerized drawing of the forward section,
driven wheel, blade and blade guard;
[0050] FIG. 8 shows a drawing of the blade and blade guard from the
opposite direction to that shown in FIG. 7;
[0051] FIG. 9 shows a drawing of a close up the blade and blade
guard;
[0052] FIG. 10 shows a drawing of a close up the blade and blade
guard without the holding nut;
[0053] FIG. 11 shows a drawing of a close up the blade and blade
guard without the first support disk;
[0054] FIG. 12 shows a drawing of forward support with the blade
guard;
[0055] FIG. 13 shows a drawing of a cut away view of the rotary
support mechanism from the side with the adapter in the first
position;
[0056] FIGS. 14 and 15 show drawings of a cut away views of the
rotary support mechanism from the side with the adapter in the
second position;
[0057] FIG. 16 shows a cut away view of the blade support;
[0058] FIG. 17 shows a drawing of a cut away view of the rotary
support mechanism from a first perspective;
[0059] FIG. 18 shows a drawing of a cut away view of the rotary
support mechanism from a second perspective;
[0060] FIG. 19 shows a sketch of the vertical cross section of the
body of a power cutter;
[0061] FIG. 20 shows a perspective view of the fuel cap;
[0062] FIG. 21 shows an exploded view of the fuel cap from a first
side;
[0063] FIG. 22 shows an exploded view from a second side;
[0064] FIG. 23 shows a sketch of a vertical cross section of the
part of the power cutter with the air filter;
[0065] FIG. 24 shows a computer generated drawing of the
filter;
[0066] FIGS. 25 and 26 show sketches of the cleaning action of the
filter;
[0067] FIGS. 27 to 29 show more computer generated drawings of the
filter;
[0068] FIG. 30 shows a second embodiment of an air filtration
system;
[0069] FIG. 31 shows a conventional design of a carburetor;
[0070] FIG. 32 shows a design of a capacitance sensor unit;
[0071] FIG. 33 shows a schematic view of the engine of the power
cutter;
[0072] FIG. 34 shows a sketch of the control system for the
engine;
[0073] FIG. 35 shows a design drawing of the oil pump;
[0074] FIG. 36 shows a sketch of the primer;
[0075] FIG. 37 shows the rotatable on/off switch;
[0076] FIG. 38 shows an exploded view of the switch;
[0077] FIG. 39A to 39E show the switch cam and micro switch;
[0078] FIG. 40 shows a cut away view of the switch;
[0079] FIG. 41 shows the underside of the knob;
[0080] FIG. 42 shows the knob, bolt and spring;
[0081] FIGS. 43 and 44 show rear views of the switch;
[0082] FIGS. 45A and 45B show the electric signal sent to the oil
pump from the electronic controller operating at two speeds, a slow
speed (FIG. 45A) and a high speed (FIG. 45B);
[0083] FIGS. 46A, 46B and 46C show the electric signals sent to the
oil pump from the electronic controller for the second embodiment
of the sensing mechanism;
[0084] FIG. 47 shows a carburetor with a solenoid; and
[0085] FIG. 48 shows a carburetor with a heating element.
[0086] Referring to FIGS. 1 and 2, the power cutter comprises a
body 2 in which is mounted a two stroke internal combustion engine
24, a front handle 4, a rear handle 6, a support arm 7, a cutting
blade 10, rotatably mounted on the support arm 7 and driven by the
engine 24 via a rubber belt 26 and a blade guard 22. A starter 12
is provided to activate the engine 24. A plastic cover 19 covers
the out side of the support arm 7 as shown in FIG. 2.
[0087] Referring to FIG. 3, the support arm 7 comprises two
sections, a forward section 8 and a rearward section 20. The
rearward section 20 is made from cast iron and is rigidly attached
to the side of the gear housing 32 using bolts (not shown). The
forward section 8 is made of cast iron and is slidably mounted on
the rearward section 20. The forward section can slide in the
direction of Arrow A. The method by which the forward section 8 is
slidably mounted on the rearward section 20 is described in more
detail below.
[0088] The engine 24 has an output shaft 28 on which is mounted a
drive wheel 30 for the rubber belt 26. The output shaft drives the
drive wheel 30 via a centrifugal clutch (not shown) in known
manner. A driven wheel 32 is rotatably mounted on the end of the
forward section 8 of the support arm. The driven wheel 32 is
connected to the cutting blade 10 which is also mounted on the
forward section 8 as described below. The belt 26 passes around the
rearward section 20, between the two wheels 30, 32 to transmit the
rotation of the engine to the cutting blade 10. The purpose of
enabling the forward section 8 to slide in relation to the rearward
section 20 is to enable the belt 26 to be tensioned as described
below. A hub 16 covers the drive wheel 30.
[0089] The Interconnection between rearward and forward sections of
the support arm 7 will now be described with reference to FIGS. 3,
4, 5 and 6.
[0090] Referring to FIGS. 3 and 4, the rearward section 20
comprises two elongate slots 40 formed through the width of the
rearward section 20. The elongate slots 40 are aligned with each
other, are of equal length, and run lengthways along rearward
section 20 of the support arm. Formed through the forward section 8
are two corresponding holes 46. The part of the forward section 8
with the holes 46 is located alongside of the part of the rear
section 20 with the elongate slots 40 so that the holes 46 align
with a corresponding slot 40. A bolt 42 passes through each hole 46
and corresponding slot 40. A nut 44 is screwed onto the bolt 42 to
sandwich the rearward and forward sections together and hold them
in place using friction. The slots 40 enable the bolts 42, and
hence the forward section 8, to slide relative to the rearward
section 20.
[0091] In order to slide the rearward section 20 relative to the
forward section 8, the nuts 44 are slackened so that the two can
move relative to each other. The forward section 8 is then slid
(using the belt tensioner described below) to the desired position,
and then the nuts 44 are tightened to sandwich the rearward section
20 to the forward section 8 to prevent movement between the
two.
[0092] The forward and rearward interconnection mechanism is
designed so that the forward section 8 can be located on either
side of the rearward section 20 as shown in FIG. 2. In normal
operation, the forward section 8 is located on the same side of the
rearward section 20 as the engine 24. This is indicated as position
B. In this position, the cutting blade 10 is located closer to the
central axis of the power cutter. However, it is sometimes
desirable to have the cutting blade located towards the edge of the
body 2 to enable it to cut near to a wall. The forward section 8
can then be moved to the other side of the rearward section 20 and
be rotated through 180 degrees about the longitudinal axis 48 of
the forward section 8 as indicated by Arrow D to the position C. In
both orientations, the driven wheel 32 locates in the same position
so that it can be driven by the belt 26.
[0093] The belt tensioner will now be described with reference to
FIGS. 4, 5 and 6
[0094] Referring to FIGS. 5 and 6, the belt tensioner comprises a
metal plate 50 having two holes 46 through which the bolts 42 pass
as seen in FIG. 4. The position of the plate 50 is fixed by the
position of the bolts 42. Formed on the metal plate 50 are two
hoops 52 which form apertures which are aligned. The shaft of an
elongate bolt 54 passes through the hoops 52. The elongate bolt 54
can freely rotate and axially slide within the hoops 52. Threadedly
mounted onto the bolt 54 is a nut 56. A spring 58 is sandwiched
between the nut 56 and one of the hoops 52. The spring 58 prevents
the nut from rotating. Therefore, as the bolt 54 is rotated, the
nut 56 travels along the length of the bolt 54 in a direction
dependent on the direction of rotation of the bolt 54. The position
of the nut 56 is fixed relative to the hoop 52 by the spring 58. A
stop 60 is integrally formed on the rearward section 20 of the
supporting arm.
[0095] In order to tension the belt 26, the elongate bolt is
rotated so that the nut moves towards the head 62 of the bolt 54.
As its position is fixed by the spring 58, the nut remains
stationary relative to the hoop 52 causing the bolt 54 to axially
move within the hoops 52 so that the end 64 of the bolt 54
approaches the stop 60. Upon engagement of the stop 60, the end 64
and hence the bolt 54, can not move further and therefore the nut
begins to move. The movement of the nut causes the spring 58 and
hence the hoop 52 to move towards the head 62 of the elongate bolt
54. This in turn results in the plate 50, the two bolts 42 and the
forward section 8 to move with the nut 56, the bolts 42 sliding
within the two slots 40. However, when the belt 26 becomes tight,
the forward section 8, and hence the bolts 42 and plate 50 are
prevented from moving further. However, if the elongate nut 54 is
further rotated, the nut 56 will continue to travel along its
length. Therefore, the spring 58 becomes compressed, applying a
force onto the hoop, and hence plate 50, which in turn transfers it
to the forward section 8. This tensions the belt 26. The more
compression of the spring 58, the more force is applied to the belt
26. An indicator 66 is added to the plate 50 to show when the
amount of the compression of the spring 58 is sufficient to apply
the correct amount of force to the belt 26.
[0096] The blade mount on the forward section 8 will now be
described.
[0097] Referring to FIG. 7, the driven wheel 32 is rotatably
mounted on the forward section 8. The driven wheel 32 is drivingly
connected to the cutting blade 10 via a spindle 70 as will be
described in more detail below. The blade guard 22 is pivotally
mounted around the spindle 70 as will be described in more detail
below. A grasp 72 is rigidly attached to the blade guard 22 which
can be held by an operator in order to pivot the blade guard
22.
[0098] FIGS. 12 to 18 show the mechanism by which the forward
support 8 rotatably supports the cutting blade 10.
[0099] Referring to FIGS. 17 and 18, the driven wheel 32 is rigidly
attached to the spindle 70 via a flanged nut 74. Rotation of the
driven wheel 32 results in rotation of the spindle 70. The spindle
70 is mounted in the forward section 8 using two ball bearing races
76, each comprising an inner track 78 rigidly connected to the
spindle 70, an outer track 80 rigidly connected to the forward
support 8, and a set of ball bearings 82 sandwiched between the two
tracks 78, 80 which allow the outer track 80 to rotate relative to
the inner track 78.
[0100] Formed along a part of the length of the spindle 70 are two
flat surfaces 84 (see FIG. 16). A second support disk 86 comprises
a central hole which is predominantly circular with the same
diameter of the spindle 70, but with two flat sides which
correspond in dimensions to the flat surfaces 84 of the spindle 70.
The second support disk 86 is mounted on the end of the spindle 70
and abuts against shoulders 88 on the spindle 70 formed by the two
flat surfaces 84. The flat surfaces 84 ensure that the second
support disk is rotationally fixed to the spindle 70 so that
rotation of the spindle 70 results in rotation of the second
support disk 86.
[0101] An adaptor 90 (described in more detail below) is mounted on
the spindle 70. The adaptor can freely rotate about the spindle 70.
The cutting blade 10 is mounted on the adaptor 90.
[0102] A first support disk 92 comprises a central hole which is
predominantly circular with the same diameter of the spindle 70,
but with two flat sides which correspond in dimensions to the flat
surfaces 84 of the spindle 70. The first support disk 92 is mounted
on the end of the spindle 70 and abuts against the cutting blade
10. The flat surfaces 84 ensure that the first support disk 92 is
rotationally fixed to the spindle 70 so that rotation of the
spindle 70 results in rotation of the first support disk 86.
[0103] A threaded hole 94 is formed in the end of the spindle 70
(see FIGS. 10 to 12). A second flanged nut 96 is screwed into the
hole 94. The flange of the nut 96 pushes the first support disk 92
against the blade 10 which in turn pushes the blade 10 against the
second support disk 86. The blade 10 becomes sandwiched between the
two support disks 86, 92. Rotation of the support disks 86, 92 by
the spindle 70 results in rotation of the blade due to the
frictional contact of the blade 10 being sandwiched between the two
disks 86, 92. By frictionally driving the blade 10, it allows
rotational movement of the blade 10 relative to the spindle 70 if
the blade becomes snagged during the operation of the power
cutter.
[0104] The automatic blade support adjustment mechanism will now be
described.
[0105] Cutting blades of different sizes can be used. Different
sized cutting blades 10 have different sized holes in their centers
through which the spindle 70 passes. It is intended that the
present power cutter will be able to fit cutting blades 10 having
two different sizes of hole through their centers. This is achieved
by the use of the adaptor 90.
[0106] Referring to FIGS. 17 and 18, the adaptor is mounted on the
spindle 70 between the two support disks 86, 92. As well as being
freely rotatable about the spindle 70, the adaptor 90 can axially
slide along the spindle 70 between the disks 86, 92.
[0107] The adaptor comprises a front section 98 and a rear section
100. The front section 98 has a first outer diameter, the rear
section 100 has a second larger outer diameter. The two sections
allow blades 10 with holes of different diameters to be mounted
onto the spindle 70. In FIGS. 14 to 18, it can be seen that a blade
10 with a central hole of a first diameter is mounted on the rear
section 100 of the adaptor 90. In FIG. 13, it can be seen that a
blade 10 with a central hole of a second diameter is mounted on the
front section 98 of the adaptor 90.
[0108] A spring 102 is sandwiched between the second support disk
86 and an inner shoulder 104 of the adaptor 90. The spring 102
biases the adaptor towards the first support disk 92. A circlip 106
is located around the spindle 70 which limits the maximum extent of
axial travel of the adaptor 90. When the adaptor 90 is allowed to
slide to its maximum extent and abut against the circlip 106, the
rear section 100 is located centrally between the support disks 86,
92.
[0109] When a blade 10, having a centre hole with the same diameter
of the rear section 100 of the adaptor is mounted onto the adapter,
it fits onto the rear section 100 of the adaptor as shown in FIGS.
14 to 18. As such, the blade 10 is centrally located between the
two support disks 86. 92. However, when a blade 10, having a centre
hole with the same diameter of the front section 98 of the adaptor
is mounted onto the adapter, it fits onto the front section 98 of
the adaptor as shown in FIG. 13. It is prevented from sliding onto
the rear section. In order for the blade 10 to be secured onto the
spindle 70 by the support disks 86, 92, it must be located
centrally between the two. When the first support disk 92 is
mounted onto the spindle 70 after the blade, it pushes the blade 10
and adaptor 90 against the biasing force of the spring 102, moving
the adaptor 90 towards the second support disk 86 as shown in FIG.
13. When the blade is securely mounted on the spindle 70, it is
centrally located between the support disks. The front section is
similarly mounted centrally. The adaptor enables two types of blade
10 to be used, it moving automatically in accordance with blade
size.
[0110] The pivotal blade guard 22 will now be described.
[0111] Referring to FIG. 15, the blade guard 22 is held by being
sandwiched between two pieces of rubber 108, 110. The blade guard
22 can pivot about the spindle 70. However, it is frictionally held
by the two pieces of rubber 108, 110. In order to pivot the guard
22, the operator must overcome the friction between the guard 22
and the rubber 108, 110.
[0112] A metal bracket 112 is attached to the forward section 8 via
four bolts 114. The bolts pass freely through the forward section 8
and threadedly engage with threaded holes formed in the bracket
112. A helical spring 116 is sandwiched between the head 118 of
each bolt 114 and the forward section 8, biasing the bolts 114 out
of the holes, pulling the bracket 112 towards the forward section.
Sandwiched between the bracket and the forward section 8 is a first
piece of rubber, 108, the guard 22, a second piece of rubber 110 to
form a rubber-guard-rubber sandwich. The strength of the spring 116
determines the amount of frictional force there is between the
rubber 108, 110 and the guard.
[0113] In order to pivot the guard the operator holds the grasp 72
and pivots the guard 22 by overcoming the frictional force between
the guard and the rubber 108, 110.
[0114] A first design of oil and fuel management system will now be
described with reference to FIG. 19.
[0115] The two stroke internal combustion engine comprises a
cylinder 120 in which is slidably mounted a piston 1000 which is
connected to a rotatable crank 114. The reciprocating motion of the
piston 100 in the cylinder 120 causes a rotational movement of the
crank shaft 114 in known manner. Movement of the piston is caused
by the burning of aerated fuel/oil mixture in the cylinder, the
ignition of which is caused by the ignition of a spark plug 730.
The engine burns the fuel in known manner to generate rotary motion
of its crank shaft 114, which connects to the output shaft 28. The
exhaust gases are then expelled from the engine 24 through an
exhaust 146 to the surrounding atmosphere. The speed of the engine
is determined by the amount of aerated fuel/oil mixture the
carburetor 126 provides to the engine which in turn is dependent on
the amount the operator depresses the trigger switch 1070.
[0116] The power cutter will comprise a fuel tank 124 in which is
located fuel for driving the two stroke internal combustion engine
24. Fuel will pass from the tank 124 via passageway generally
indicated by dashed lines 144 through the carburetor 126 which will
mix it with air prior to being forwarded to the cylinder 120 where
it will be burnt. Details of the supply of air, including its
filtration will be described in more detail below. A second tank
128 will also be mounted in the body 2 as shown, in which
lubricating oil will be contained. The oil will be pumped out of
the tank 128 via a standard design of oil pump 130, which is
mounted on the crank shaft housing which will be driven via a gear
arrangement (not shown) from the crank shaft 114. The oil pump 130,
will pump the oil through the oil passageways indicated by dashed
lines 142 from the oil tank 128 via the pump 130 into the
passageway 132 between the carburetor 126 and the cylinder 120, in
a suitable form, for example, as a liquid or as a spray or
atomized, and then mixing the oil with the air/fuel mixture
generated by the carburetor 126. It will inject oil at the ratio
1:50 in relation to the fuel.
[0117] A sensor unit 140 will comprise a sensor which will be
mounted within the passageway 132 between the carburetor 126 and
cylinder 120, or in the oil passageways 142 adjacent the passageway
132. The sensor will measure a parameter of the flow of the oil
within the passageway and determine, using a signal processor
incorporated into the sensor unit, whether oil is being pumped
correctly in accordance with predetermined parameters in to the
passageway 132 either by checking the pressure of the oil as it
enters the passageway 132 or by detecting the presence of oil in
the passageway 132. Such a parameter could be the rate at which the
oil is pumped into the passageway 132.
[0118] The construction of one type of sensor unit will now be
described with reference to FIG. 32. The sensor unit comprises a
sensor consisting of two metal plates 1050; 1052 which are
connected via wires 1056 to a signal generator/signal processor
1054. The metal plates are located within the passageway 132
between the carburetor 126 and cylinder 120, down stream of the oil
passageways 142. The signal generator/signal processor 1054 sends a
signal to the plates 1050; 1052 to determine the capacitance of the
two plates. The capacitance is dependent on the material between
the plates 1050; 1052 which will consist of aerated fuel and
lubrication oil. As the amount of lubrication oil changes, the
capacitance of the plates changes. This capacitance will be
analyzed by the signal generator/signal processor 1054 which, if
the capacitance extends outside of a predetermined limit, will
provide a signal to an electronic ignition system.
[0119] The engine is controlled by the electronic ignition system.
The sensor unit 140 will provide signals to the electronic ignition
system about the amount of oil being pumped into the passageway
132. In the event that insufficient, excessive or no oil is pumped
into the passageway due to the fact that the oil tank is empty or
there is a blockage in an oil pipe 142 or there is a fault with the
pump, the sensor unit 140 will send the signal to the ignition
system. The ignition system will then either put the engine into an
idle mode or switch the engine off entirely, depending on the
settings of the ignition system. This will ensure that lubricating
oil is always added to the fuel in the correct amount prior to
combustion within the two stroke engine.
[0120] It will be appreciated by the reader that though the sensor
unit 140 has been described as having the signal generator/signal
processor 1054 incorporated in the sensor unit 140, the signal
generator/signal processor 1054 could be incorporated into the
electronic ignition system with the sensor unit only comprising the
sensor.
[0121] A second design of oil and fuel management system will now
be described with reference to Figures?
[0122] Referring to FIG. 33, the two stroke internal combustion
engine comprises a cylinder 120 in which is slidably mounted a
piston 1000 which is connected to a rotatable crank 114. The
reciprocating motion of the piston 100 in the cylinder 120 causes a
rotational movement of the crank shaft 114 in known manner.
Movement of the piston is caused by the burning of aerated fuel/oil
mixture in the cylinder, the ignition of which is caused by the
ignition of a spark plug 730. The engine burns the mixture in known
manner to generate rotary motion of its crank shaft 114, which
connects to an output shaft. The exhaust gases are then expelled
from the engine through an exhaust 146 to the surrounding
atmosphere. The engine is started using a pull cord in well know
manner. The speed of the engine is determined by the amount of
aerated fuel/oil mixture the carburetor 126 provides to the engine
which in turn is dependent on the amount the operator depresses the
trigger switch 1070.
[0123] The power cutter will comprise a fuel tank 124 in which is
located fuel for driving the two stroke internal combustion engine
24. Fuel will pass from the tank 124 via passageway 144 through the
carburetor 126 which will mix it with air from an air filter 890,
prior to being forwarded to the cylinder 120 where it will be
burnt. A second tank 128 will also be mounted in the body as shown
in which lubricating oil will be contained. The oil will be pumped
out of the tank 128 via an oil pump 700. The oil pump 700 will pump
the oil through the oil passageways indicated by lines 142 from the
oil tank 128 via the pump 130 into the passageway 132 between the
carburetor 126 and the cylinder 120, in a suitable form, for
example, as a spray or atomized, which is then mixed with the
air/fuel mixture generated by the carburetor 126.
[0124] A sensor 140 is mounted within the passageway 132 between
the carburetor 126 and cylinder 120. The sensor monitors the amount
of oil being added to the fuel/air mixture and sends a signal, via
an electric cable 701, indicative of the amount of oil in the
passageway 132 back to an electronic controller 716 (see FIG. 34).
The electronic controller comprises a signal processor which
processes the signal and determines whether it is in accordance
with a predetermined parameter or not. If the electronic controller
determines that the oil is not being supplied in sufficient
amounts, it places the engine in an idle mode or stops it
altogether.
[0125] Such a sensor can be of a capacitance type whereby the
sensor monitors the change in capacitance between two plates, the
capacitance being a function of the amount of oil there is in the
fuel/air mixture. Such a sensor has been described previously with
reference to FIG. 32.
[0126] The carburetor 126 will now be described with reference to
FIG. 47. The design of the carburetor is similar to that previously
described with reference to FIG. 31. Where the same features are
present the same reference numbers have been used.
[0127] The main difference between that disclosed in FIG. 31 and
that in FIG. 47 is that the first pivotal plate 1046 which acts as
the choke for the carburetor has been removed. Instead, a third
passageway 1100 has been added. The third passageway 1100 connects
to the second chamber 1014 via a solenoid valve 1102. The other end
of the third passageway 1100 connects with the air passageway 1004
down stream of the narrow section 1008. The solenoid valve 1102
comprises a solenoid 714 and a pin 1106. The pin can axially slide
(Arrow M) between a first position where the tip of the pin 1106
engages with a restriction 1108 in the third passageway 1100 to
block the third passageway 1100 and a second position where the tip
is located away from the restriction 1108 to open the third
passageway 1100. The pin 1106 is biased to its first position.
Activation of the solenoid by the provision of an electric current,
causes the pin 1106 to move against the biasing force from its
first position to its second position opening the third passageway
1100. Deactivation of the solenoid 714 by the removal of an
electric current, causes the pin 1106 to move under the influence
of the biasing force from its second position to its first
position, closing the third passageway 1100.
[0128] Under normal operation, the carburetor functions in the same
manner as that described with reference to FIG. 31. No current is
supplied to the solenoid 714, and the pin 1106 engages with the
restriction 1108 and blocks the third passage 1100. However, when
the engine is cold, a current can be supplied to the solenoid 714,
which causes the pin 1106 to slide away from the restriction,
unblocking the third passageway 1100 and allowing fuel to pass
through the third passageway 1100 and enter the air passageway
1004. This increases the amount of fuel relative to the amount of
air in the aerated fuel exiting the air passageway 1004 to enable
the engine to run smoothly while it is cold. Once the engine is
warm, the solenoid 714 can be switched off by removing the electric
current to it, allowing the pin 1106 to slide towards the
restriction 1108 to block the third passageway and prevent any
further fuel from passing through it.
[0129] In addition to the third passageway 1100, there is a fourth
passageway 1110 which connects between the hollow chamber 1034 and
the air passageway. This passageway provides an air passage between
the two. When there are increases or decreases in the air pressure
in the air passageway 1004, these are transmitted to the hollow
chamber 1034. These in turn are transmitted to the second chamber
1014 via the diaphragm 1032 which influences the flow of fuel into
the second chamber and into the air passageway 1004. The fourth
passageway 1110 acts as a feed back mechanism to improve
performance of the carburetor.
[0130] The solenoid is used when the engine is cold to provide an
air/fuel mixture which is richer in fuel to help start the engine.
When the engine is warm, the solenoid is switched off. The
temperature of the engine is measure using a sensor 710 located on
the engine block. The solenoid 714 is used to replace the choke on
exiting designs of carburetor whereby which an operator would
manually adjust the valve to start the engine when it is cold. The
electronic controller 716 operates the solenoid dependent on the
temperature of the engine.
[0131] An alternative design of carburetor which uses a solenoid in
a similar manner can be found in U.S. Pat. No. 7,264,230. This
could be used to replace that described previously with reference
to FIG. 47. The carburetor of U.S. Pat. No. 7,264,230 uses a
solenoid to open or close an air bleed passage. Through which flows
air.
[0132] A second alternative design will now be described with
reference to FIG. 48. The carburetor 126 will now be described with
reference to FIG. 48. The design of the carburetor is similar to
that previously described with reference to FIG. 31. Where the same
features are present the same reference numbers have been used.
[0133] The main difference between that disclosed in FIG. 31 and
that in FIG. 47 is that the first pivotal plate 1046 which acts as
the choke for the carburetor has been removed and has been replaced
by a heating element 1200. When the engine is cold, the heating
element 1200 is switched on and heats the air flow as it passes
through the carburetor. This provides heated aerated fuel which
enables the engine to run smoothly until it has achieved an
acceptable running temperature. The heating element 1200 would be
controlled by the electronic controller 716. This could be used to
replace that described previously
[0134] A third alternative design of carburetor 126 is to use the
carburetor previously described with reference to FIG. 31. However,
instead of controlling the movement first pivotal plate 1046, which
acts a choke, manually using a Bowden cable, it could be controlled
using a solenoid which in turn is controlled by the electronic
controller 716.
[0135] The engine ignition system is controlled by an electronic
controller 716, the function of which is described in more detail
below with reference to FIG. 34.
[0136] Mounted on the end of the end of the crank shaft 114 is a
fly wheel 702 which contains a number of metal fins 704 which form
an impeller. As the fly wheel 702 rotates, the impeller blows air
around the out side of the engine. Adjacent the impeller 702 are
two generators 706; 708. The two generators generate electricity
using magnets and the change of inductance caused by the rotating
flywheel 702. As the fly wheel 702 rotates, it causes the two
generators 706; 708 to produce electricity. The first generator 706
is used to provide electricity for the ignition system of the
engine and the electronic controller 716. The second generator 708
is used to provide electricity for the oil pump 700 and the
solenoid 714 in the carburetor. Both are connected to the
electronic controller 716 via cables 717.
[0137] Also mounted adjacent the flywheel are two sensors 710; 712.
The first sensor 710 monitors the temperature of the engine block
and sends a signal via an electric cable 711 indicative of the
temperature to the electronic controller 716. The second sensor 712
monitors the angular position of the flywheel 702 and sends a
signal via an electric cable 713 indicative of the angular position
of the flywheel 702 back to the electronic controller 716. This
signal can also be used by the electronic controller 716 to
determine the rate of rotation of the fly wheel 702, as well as its
angular position.
[0138] The oil pump 700 is an electrically powered oil pump 700,
the power for which is supplied by the electronic controller 716
via electric cable 715. The oil pump is shown in FIG. 35.
[0139] This type of oil pump is described in EP1236894. Referring
to FIG. 35, the oil pump comprises a piston 850 which can axially
slide within a housing 1202 over a limit range of axial movement
which is determine by a stop mechanism 1204. A spring 854 biases it
to a predetermined position. A chamber 852 is located below the
piston 850. A solenoid 1206 surrounds the piston and moves it
axially when an electric current is applied. The piston 850 is
biased in direction of Arrow R by a spring 854. Activation of the
solenoid moves the piston against the biasing force of the spring
854 in the opposite direction to Arrow R. A passageway 1208 is
formed through the piston 850. Oil is fed into the passageway via
an inlet 1210. A first valve comprising a ball bearing 1212 and
spring 1214 is located between the end of the passageway 1208 and
the chamber 852. A second valve comprising a ball bearing 1216 and
a spring 1218 is located between the base the chamber 852. When the
piston is moving in the direction of Arrow R due to the biasing
force of the spring 854, enlarging the chamber 852, the first valve
opens and the second valve closes, filling the chamber with oil.
When the piston is in the opposite direction of Arrow R due to
activation of the solenoid 1206, reducing the size the chamber 852,
the first valve closes and the second valve opens, expelling the
oil from the chamber 852 and through an outlet 1220.
[0140] The oil pump 700 is driven by the electronic controller 716
which sends a square shaped voltage signal 892 to the oil pump (see
FIG. 45A) When the voltage is at V1, it causes the piston 850 of
the pump to move, reducing the size of the oil chamber 852. This
causes a preset amount of oil to be pump out of the chamber 852.
When voltage is "0", the piston returns to its starting position
due to the spring 854, enlarging the chamber 852 and allowing the
chamber 852 to fill with oil. The higher the frequency of the
square shaped voltage signal 892, the more oil the oil pump 700
pumps per unit of time. The oil pump is capable of running at two
speeds (the first speed shown in FIG. 45A, the second speed being
shown in FIG. 45B where the frequency of the square shaped voltage
signal 892, and hence the movement of the piston 850, is double)
and its general operation is described in more detail below.
[0141] The spark plug 730 is connected to the electronic controller
716 via a cable 732. Ignition of the spark plug is controlled by
the electronic controller 716.
[0142] A primer 734 is mounted on the rear wall 736 of the housing
800 of the power cutter. The primer is a manual pump. A pipe 738
connects from the fuel tank 124 to the primer 734. A second pipe
740 connects from the primer to the carburetor 126. A brief
description of the principle of how the primer works will now be
described with reference to FIG. 36. The primer consists of two
valves 742; 744 located in series which allow the fuel to flow one
way through them only (indicated by Arrows A and B). Located
between the two valves 742; 744 is a chamber 750 having a rubber
dome 746 forming a wall which is accessible to the user of the
power cutter. One valve 742 only allowing fuel to enter the chamber
750, the other only allowing fuel to leave the chamber 750. In
order to use the primer, the operator, compresses the rubber dome
746 (shown as dashed lines 748). This reduces the amount of volume
in the chamber 750 formed between the valves and hence the amount
of space which can contain fuel. As such, fuel is ejected from the
primer through the one of the valves 744, as the second valve 742
remains closed, preventing fuel from leaving the chamber 750 via
that valve 742. When the operator releases the dome 746, the volume
of the chamber 750 increases, causing fuel to be sucked into the
chamber 750 through the second valve 742 as the first valve remains
closed 744 preventing fuel from entering the chamber 750 through
that valve 744. Repetitive compressing and releasing of the dome
746 results in the fuel being pumped through the primer 734. The
primer is arranged so that the operator can manually pump the fuel
from the tank 124 to the carburetor 126 through the pipes 738;
740.
[0143] The purpose of the primer is to enable the operator to place
fuel into the carburetor. Otherwise the operator has to spin the
engine a number of times using the pull cord before a sufficient
amount of fuel is sucked through into the carburetor 126.
[0144] A DECO valve 752 is mounted on the side of the cylinder 120.
The valve 752 is opened manually by the operator prior to starting
the engine. When opened, the DECO valve reduces the pressure within
the cylinder 120 prior to ignition. This enables the starting of
the engine using the pull cord to be made easier as the amount
compression of the fuel/air mixture required is reduced. When the
engine is started, the DECO valve automatically closes.
[0145] The electronic controller 716 has an on/off switch 754 in
the form of a rotatable knob 758. The switch is connected to the
electronic controller via an electric cable 756.
[0146] The knob 758 as a pointer 764 integrally formed on its
periphery. The rotatable knob 758 has two angular positions between
which it can rotate. In the first position, the switch is ON. In
this position, the pointer 764 points to an ON label 762 (see FIG.
1). In the second position, the switch is OFF. In this position,
the pointer 764 points to an OFF label 760. When the rotatable knob
is in the ON position, the operator can start the engine and use
the power cutter. When the rotatable knob 758 is in the OFF
position, the engine is prevented from being started. If the
rotatable knob 758 is moved from the ON to the OFF position when
the engine is running, the engine is automatically switched
off.
[0147] A operating button 766 is located in the centre of the knob
758. If the engine is running (i.e. the knob is in the ON
position), depression of the operating button 766 will result in
the engine being switched off. The knob 758 then automatically
returns to the OFF position. If the knob 758 is prevented from
returning to the OFF position after the operating button has been
depressed, the engine will not be able to be started until the knob
758 has been allowed to return to the OFF position.
[0148] The construction of the assembly for the ON/OFF switch 754,
which includes the knob 758 and operating button 766, will now be
described.
[0149] The ON/OFF switch assembly consists of the rotatable knob
758, a crank 768, a switch cam 770 and the operating button
766.
[0150] The crank 768 is rigidly fixed into the rear wall 736 of the
housing 800 and prevented from rotation. The crank 768 comprises a
socket 772 into which is rigidly mounted a micro switch 774 (see
FIG. 49C).
[0151] Rotatably mounted on the outside of the crank 768 is the
knob 758. Rotatably mounted on the inside of the crank 768 is the
switch cam 770. A bolt 778, which passes through the base of a
tubular recess 776 formed in the knob 758, screws into the switch
cam 770 and is rigidly attached to it. Sandwiched between the head
of the bolt 778 and the base of the recess 776 is a spring 780. The
bolt 778 and spring 780 hold the knob 758 and switch cam 770 onto
the crank 768, biasing them towards each other as the spring biases
the head of the bolt 778 away from the base of the recess 776. The
knob can rotate through a limited range of movement (between the ON
and OFF positions) relative to the crank 768. The range of
positions is limited by pegs 786 formed on the underside of the
knob engaging with recesses 788 formed in the edge of the rear wall
736 of the housing. The switch cam 770 can also rotate through a
limited range of movement relative to the crank 768. In addition,
the switch cam 770 can axially slide relative to the crank 768 in a
direction parallel to the longitudinal axis of the bolt 778 over a
limited range of movement, the range being limited by the length of
the bolt 778 within the recess 776. The bolt 778 rotates and slides
with the switch cam 770.
[0152] The operating button 766 is mounted within the tubular
recess 776 formed in the knob 758 and encloses the end of the bolt
778 located in the recess 776 and the spring 780 (see FIG. 40). The
operating button 766 can axially slide within the recess 776
towards or away from the switch cam 770. The range of outward axial
movement of the operating button is limited by stops 782 each
engaging with an inner step of the knob 758. The head of the bolt
778 directly abuts the underside of the operating button 766.
Depression of the operating button, causes the bolt 778 to be
pushed through the base, compressing the spring 780, moving the
switch cam 770 away from the crank 768 and knob 758.
[0153] Connected between the knob 758 and the crank 768 is a long
helical spring 784. The helical spring 784 locates in a circular
channel 790 formed on the underside of the knob 758 as best seen in
FIG. 41. One end abuts against a wall 792 at the end of the channel
790. The other end abuts against a stop (not shown) formed on the
crank 772. The spring 784 rotationally biases the knob 758 relative
to the crank to its OFF position.
[0154] Connected between the switch cam 770 and the crank 768 is a
leaf spring 794 as best seen in FIGS. 43 and 44. One end of the
leaf spring 794 is connected using a small bolt 796 to the switch
cam 770. The other end abuts a stop 798 on the crank 768. The leaf
spring 794 rotationally biases the switch cam 770 relative to the
crank to an OFF position.
[0155] Formed on the underside of the knob 758 are two ramps 820,
each ramp having a ramp end 822 as best seen in FIG. 41. Formed on
the side of the switch cam 770 which faces the knob 758 are ramp
recesses 824 which have ramp recess ends 826 as best seen in FIG.
9. When the switch assembly is in the OFF position i.e. when both
the knob 758 and the switch cam 770 in their OFF positions under
the biasing force of their respective springs 784; 794, each of the
two ramps 820 is located in a corresponding ramp recess 824 with
the ramp ends 822 of each ramp 820 abutting directly against the
ramp recess ends 826 of the corresponding ramp recess 824.
[0156] Formed on the underside of the crank 768 are two crank ramps
828, each ramp 828 having a crank ramp end 830 as best seen in FIG.
39C. Formed on the side of the switch cam 770 which faces the knob
758 are switch cam crank ramps 832 which have switch cam crank ramp
ends 834 as best seen in FIG. 40. When the switch assembly is in
the OFF position i.e. with both the knob and the switch cam 770 in
their OFF positions under the biasing force of their respective
springs 784; 794, each of the two switch cam crank ramps 832 are
located against the low end (the end of the crank ramp 828 away
from the crank ramp end 830) of the corresponding crank ramp 828 as
shown in FIG. 39C.
[0157] Formed around the edge of the switch cam 770 is a peripheral
cam 836 as best seen in FIGS. 39A and 39B. The micro switch 774
comprises a pin 838 which projects from the body of the micro
switch 774. The pin 838 is capable of sliding axially in or out of
the body of the micro switch 774 and biased to its outer most
position by a spring (not shown) inside the micro switch 774. The
pin 838 engages the peripheral cam 836. Rotation of the switch cam
770 causes the pin 838 to slide along the peripheral cam 836, which
causes it to be pushed into the body of the micro switch 774
against the biasing force of the spring, or allows it to slide out
of the body of the micro switch 774 under influence of the spring.
When the switch cam 770 is in its OFF position, the pin is pushed
into the body of the micro switch 774 as shown in FIG. 8A. When
switch cam is rotated to its ON position, the pin 838 extends to
its outer most position as shown in FIG. 39B.
[0158] The way the assembly for the ON/OFF switch works will now be
described.
[0159] Initially, the knob 758 and the switch cam 770 are both
located in their OFF positions. The operator of the power cutter
desires to turn the unit on using the ON/OFF switch. The operator
uses their hand to rotate the knob 758 from its OFF position to its
ON position. When the knob 758 is rotated, it causes the cam switch
770 to rotate in unison as the rotary movement is transferred from
the knob 758 to switch cam 770 by the ramp ends 822 of each ramp
820 pushing the ramp recess ends 826 of each corresponding ramp
recess 824, against which it abuts, in the direction of Arrow M in
FIG. 40, to cause the switch cam 770 to rotate with the knob 758.
As the switch cam 770 rotates, the two switch cam crank ramps 832,
which are initially located against the low end of the crank ramps
828 (shown in FIG. 39C), ride up the crank ramps 828 (shown in FIG.
39D), which are stationary. As the switch cam crank ramps 832 ride
up the crank ramps 828 due to the rotation of the switch cam 770,
the switch cam 770 is forced to axially slide away from the knob
758 (direction of Arrow N in FIG. 40), causing the spring 780 to be
compressed and the head of the bolt 778 to move towards the base of
the recess 776. When the switch cam has rotated sufficiently that
the crank ramp ends 830 and the switch cam crank ramp ends 834
become aligned, the switch cam 770 axially slides under the biasing
force of the spring 780 towards the knob 758, ensuring that the
crank ramp end 830 and the switch cam crank ramp ends 834 abut
against each other as shown in FIG. 39E. When the crank ramp ends
830 and the switch cam crank ramp ends 834 abut each other as shown
in FIG. 39E, the switch cam 770 is in its ON position and is
prevented from returning to its OFF position, under the influence
of the leaf spring 794, as the crank ramp ends 830 and the switch
cam crank ramp ends 834 prevent relative movement as they are
jammed against each other. The knob 758 is prevented from returning
to its OFF position under the influence of the spring 784 by the
ramps 820 being held within the ramp recesses 824 by the action of
the spring 780 which overrides the spring 784. When the switch cam
770 rotates from the OFF position (see FIG. 39A) to the ON position
(FIG. 39B), the peripheral cam 836 rotates, which in turn allows
the pin 838 to extend from the body of the micro switch 774. This
in turn makes a connection which allows the electric controller 716
to activate the power cutter and allow it to start when the pull
cord is pulled.
[0160] As such, the assembly of the ON/OFF switch is now ON with
the knob 758 and the switch cam 770 both in their ON positions,
allowing the pin 838 to extend from the body of the micro switch
774. There are two way of switching the ON/OFF switch assembly to
its OFF position.
[0161] The first method comprises the depression of the operating
button 766. Depression of the operating button 766 causes the head
of the bolt 778 to slide towards the base of the recess 776 of the
knob 758, compressing the spring 780, which in turn causes the
switch cam 770 to axially slide away from the knob 758. As the
switch cam 770 axially slides, the switch cam 770 moves away from
the crank 768, which in turn causes the crank ramps 828 and the
switch cam crank ramps 832 to move away from each other, and thus
causes the crank ramp ends 830 and the switch cam crank ramp ends
834 to disengage. As such, the switch cam 770 can now rotate back
to its OFF position under the influence of the leaf spring 794. As
the knob is held in its ON position by the ramps 820 being held
within the ramp recesses 824, the knob 858 will also return to its
OFF position as the ramp recesses 824 rotate with the switch cam
770. Should the ramps 820 become disengaged from the ramp recesses
824 due to the sliding movement of the switch cam 770 relative to
the knob 758, the knob 758 will return to its OFF position under
the influence of the spring 784 between the knob 758 and the crank
768.
[0162] The second method of switching the ON/OFF switch assembly
OFF comprises the rotation of the knob 758. The operator rotates
the knob 758 to its OFF position. As the ramps 820 are held within
the ramp recesses 824, rotation of the knob 758 urges rotation of
the switch cam 770. However, the switch cam 770 is prevented from
rotating as the crank ramp ends 830 and the switch cam crank ramp
ends 834 abut each other. Therefore, the ramps 820 slide out of the
ramp recesses 824, the ramp ends 822 moving away from ramp recess
ends 826. As the ramps 820 slide out of the ramp recesses 824, the
switch cam 770, which is prevented from rotating, axially slides
away from the knob 858 by the camming action of the ramps 820 and
ramp recesses 824. When the switch cam 770 has slid sufficiently
far enough away from the knob 758, the crank ramp ends 830 and the
switch cam crank ramp ends 834, which are sliding away from each
other, become disengaged. Thus the switch cam 770 can rotate under
the influence of the leaf spring 794 to its OFF position. The knob
758 will move under the influence of the operator and/or the spring
784. As such, both the knob 758 and the switch cam 770 return to
their OFF position where they are held by the springs 784; 794.
[0163] When both the knob and switch cam 770 moved to their OFF
positions, the ramps 820 engage with the ramp recesses 824 so that
the switch can be used again to switch on the power cutter.
[0164] The operation of the power cutter will now be described.
[0165] The operator first activates the DECO valve 752 and then
pumps some fuel into the carburetor 126 using the primer 734. The
operator then switches the ON/OFF switch to ON by rotation of the
knob 758 to its ON position. The operator then pulls the pull cord
to rotate the crank 114 of the engine. As the crank 114 rotates,
the fly wheel 702 also rotates causing the two generators 706; 708
to produce sufficient electricity to operate the power cutter.
[0166] The electronic controller checks the temperature of the
engine using sensor 710. If the engine is cold, it uses the
electricity from the second generator 708 to power the solenoid 714
in the carburetor to set the "automatic choke". The second
generator 708 is not powerful enough to power both the oil pump 700
and solenoid 714 at the same time. Therefore, when the electronic
controller 716 is operating the solenoid 714, it switches off the
oil pump 700. It has been found that the period during which
lubricating oil is not required before the engine is damaged is
greater than that required to heat up the engine.
[0167] The electronic controller supplies the power to the spark
plug to cause combustion in the engine, the power being provided by
the first generator 706, the timing being determine by the
electronic controller 716 based on the signal provided by the
sensor 712 in relation to the angular position of the fly wheel
702.
[0168] Once the engine commences firing, the DECO valve
automatically closes. The electronic controller 716 continues to
monitor the engine temperature and when it has reached a
predetermine temperature, the electronic controller 716 switches
the solenoid 714 in the carburetor 126 off. The electronic
controller 716 then commences supplying a square shape voltage
signal to the oil pump to commence pumping oil. The electronic
controller monitors the speed of the engine using the signal
provided by the sensor 712 monitoring the angular position of the
fly wheel 702 to calculate the rotational speed. If the rotational
speed is below a predetermined value, the electronic controller 716
sends a signal (FIG. 35A) to the oil pump 700 to cause it to pump
at a slow speed. If the rotational speed is above a predetermined
value, the electronic controller 716 sends a signal (FIG. 35B) to
the oil pump 700 to cause it to pump at a higher speed. The speed
of the engine is dependent on the operator squeezing a trigger
switch which connects to the carburetor via a cable.
[0169] While the engine is running the electronic controller 716
monitors the oil being added to the fuel/air mixture using the
sensor 140. If the sensor 140 sends a signal that indicates that
the rate of flow of the oil being pumped by the oil pump 700 has
dropped below a predetermine amount (e.g. there is a blockage in
the oil pipe 142 or the tank 128 is empty), the electronic
controller places the engine into an idle mode using the ignition
system so that the engine runs, but at a minimal rate.
[0170] The engine controller can place the engine in idle mode by
altering the timing of the ignition of the spark plug relative to
the angular position of the crank shaft or the number of ignitions
of the spark plug relative to the number of rotations of the crank
shaft. The engine controller can ignite the spark ever two or three
rotations of the crank shaft, for example, providing only a half or
a third of the power than if the spark plug was ignited every
rotation, as would be the case during the normal operation of the
engine.
[0171] The operator can not speed up the engine using the trigger
switch 1070 until the sensor 140 detects the flow of oil. This
protects the engine from damage due to a lack of lubrication. It
has been found that the engine can run in idle mode for a
considerable period of time before damage to the engine
results.
[0172] It will be appreciated by the reader that, as an alternative
to placing the engine in an idle mode, it could switch it off
completely. In such a case, the electronic controller 716 would
ensure it could not be started until oil was detected again by the
sensor.
[0173] In order for the operator to stop the power cutter, the
operator either depresses the operating button 766 or rotates the
knob 758 to its OFF position.
[0174] An alternative system for sensing whether oil is being
provided to the aerated fuel to that described previously will now
be described. In the alternative design, it is intended to remove
the sensor 140 and, instead, monitor the current being supplied to
the oil pump 700 when it is running to determine if oil is being
pumped by the oil pump.
[0175] Referring to FIGS. 46A, 46B and 46C, FIG. 46A shows the
voltage supplied to the oil pump 700, FIG. 46B shows the current
supplied to the oil pump 700 when the oil pump is pumping but there
is no oil being pumped, and FIG. 46C shows the he current supplied
to the oil pump when the oil pump is pumping oil. The oil pump 700
running at the slow speed.
[0176] A square wave voltage V1 indicated by line 900 is supplied
to the oil pump as shown in FIG. 46A. When oil is being pumped
through the oil pump 700 (FIG. 46C), the current indicated by line
902 starts to rise from zero at t0, when the voltage applied rises
to V1 and increases towards I1. When it reaches I1 the amount of
current drops 904 before increasing 906 again to I1. The current
drops after t2 seconds before beginning to rise again at t3
seconds. The drop in current occurs when the piston 850 in the oil
pump 700 reaches its maximum amount of travel due to the solenoid
1206 and then bounces back slightly due to the piston's 850 impact
at its maximum distance of travel. However, when no oil is being
pumped by the oil pump 700, but the pump is still operating, the
speed of travel of the piston 850 in the oil pump increases as
there is less resistance. As such it reaches its maximum amount of
travel sooner. Therefore, as shown in FIG. 46B, it reaches a lower
value of current I2 before the value of current drops 908 and then
rises 910 again towards I1. Furthermore, it only takes less time
before the current drops 908 and rises 910 again than if the oil
pump 700 was pumping oil. The signal processor in the electronic
controller 716 can monitor when the current begins to drop versus
the start of the voltage pulse and the value of the current at this
point to determine whether the pump is pumping oil or not. If t is
not, the electronic controller can place the engine in idle
mode.
[0177] The construction of the fuel cap will now be described with
reference to FIGS. 20 to 23.
[0178] The fuel tank 124 will be mounted within the body of the
unit as generally indicated in FIG. 19. The tank 124 will be sealed
by a fuel cap 13 as shown on FIG. 2.
[0179] The fuel cap will comprise an inner cap 202, a clutch 204
and an outer cap 206. The inner cap is of a tubular construction
with one end 210 being sealed. Formed on the inside surface of a
side wall 212 is a thread 208. When the fuel cap is screwed onto
the fuel tank, the thread 208 slidingly engages with a thread
formed around the external surface of the neck of the fuel tank
124.
[0180] Located inside the inner cap 202 adjacent the end 210 is a
seal 214. When the fuel cap is screwed onto the fuel tank, the seal
214 ensures that no fuel can escape from the tank. The inner cap 2
locates within the outer cap 206. Sandwiched between the two is the
clutch 204. A clip 216 locates within a groove 218 of the inner cap
and also engages with an inner groove 220 formed within the outer
cap. The clip holds the inner cap inside the outer cap while
allowing it to freely rotate within the outer cap 206. The inner
cap comprises a number of teeth 222 integrally formed with the
inner cap. The teeth locate within corresponding slots 224 formed
within the clutch, thus rotation of the inner cap causes rotation
of the clutch 204. Formed on the clutch 204 are a plurality of
resilient arms 226 mounted on the ends of which are pegs 228. The
pegs 228 face towards the internal end wall 230 of the outer cap.
Formed on the wall are a plurality of ridges 232. The pegs on the
clutch are arranged to co-operate with the ridges 232 in the outer
cap.
[0181] Rotation of the outer cap 206 causes the ridges 232 to
engage with the pegs 228 resulting in rotation of the clutch 204,
which in turn rotates the inner cap 202 via the teeth 222. When the
fuel cap is screwed onto the fuel tank, the inner cap 202
threadingly engages with the neck of the fuel tank, the rotation of
the inner cap 202 being caused by rotation of the outer cap 6 via
an operator rotating it using a finger grip 234. When the seal 214
located within the inner cap engages with the end of the neck of
the fuel tank, the inner cap 202 is prevented from further
rotation. This in turn prevents further rotation of the clutch 204.
However as the operator continues to exert a rotational force on
the outer cap 206, the ridges 232 are caused to ride over the pegs
228, the movement of the pegs 228 being allowed by the resilient
arms 226 upon which they are mounted. In this way the operator can
rotate the outer cap while the inner cap remains stationary thus
preventing the operator from over-tightening the fuel cap onto the
neck of the fuel tank.
[0182] The air filtration mechanism for any of the carburetors 126
previously described will now be described.
[0183] The two stroke engine comprises a carburetor 126 which mixes
liquid fuel with air to generate a combustible mixture for powering
the engine. However, due to the operation of the power cutter, a
large amount of dust is generated which mixes with the surrounding
air. This results in dust laden air. In order to ensure that the
air entering the carburetor is free from dust it must pass through
a filter system to remove the dust.
[0184] The filter system will now be described with reference to
FIGS. 23 to 29.
[0185] Inside the body 2 is a filter unit 316 comprising a plastic
base 318 and filter paper 320 folded to form pleats. The filter
unit 316 is located within the body 2 so that the pleats 320 hang
vertically downwards when the power cutter is in a storage position
as shown in FIGS. 1 and 2.
[0186] Air will be sucked through the filter system by the
carburetor 126. Air enters slots 314 on the rear of the body 2. Air
passes (Arrow G) to a space 322 underneath the filter unit 316 and
then passes through the filter paper 320 to a space 324 above the
filter unit 316. Any dust entrained within the air is trapped by
the filter unit 316 and held within the pleats of the filter paper
320.
[0187] The clean air then passes from the space 324, through a hose
326 to the carburetor 126 located below the space 322 below the
filter unit 316.
[0188] In order to enable the operator to remove the dust trapped
within the pleats of the filter paper 320, a cleaning device is
provided. The cleaning device comprises a rubber flap 328, mounted
on the top of a plastic base 330, a brush 332 attached to the
bottom of the plastic base 330, a handle 334 attached to the
plastic base 330 via to rigid arms 338. The base 330 can slide
within the space 322 below the filter unit 316, widthways across
the body 2. Movement is caused by the operator pulling the handle
334 away from the side of the body 2. Two springs 336 bias the
handle 334 towards the side of the body 2.
[0189] In order to clean the filter unit, the operator pulls the
handle 334, to move the base 330 across the width of the body 2 in
the direction of Arrow H, and then releases it to allow it to
return in the opposite direction under the biasing force of the
springs 336.
[0190] As the base 330 slides across the width, the rubber flap 328
engage with the pleats 320, as best seen in FIG. 25, knocking the
dust of the pleats 320. The dust drops to the base 340 of the space
322 below the filter unit 316.
[0191] The brush 332 slidingly engages with the base 340 of the
space 322. The brush 332 brushes the dust to one side or the other,
depending on the direction of movement. An aperture 344 is formed
on one side of the body 2. As the brush approaches the side of the
body, it pushes the dust being swept along the base through the
apertures, expelling it from the body 2.
[0192] Though FIG. 4 shows the flap 28 moving perpendicularly to
the direction of the pleats 320, it will be appreciated by a person
skilled in the art that is possible to rotate the filter paper 320
so that the pleats run in parallel to the sliding movement of the
flap 328 as shown in FIG. 26. In such a scenario, the rubber flap
28 may be replaced by a plurality of brushes 342.
[0193] The construction of the rear handle will now be described
with reference to FIGS. 1 and 2.
[0194] The body of the power cutter is constructed in the form of a
plastic casing constructed from a number of plastic clamshell
rigidly connected together. The rear clam shell 430 connects to the
rear handle 6. In existing designs of power cutter, the rear handle
6 is integral with the rear clam shell 430. However, if the handle
6 is broken, the whole clam shell 430 needs to be replaced. As
handle breakage is common it is desirable to avoid this.
[0195] Therefore, the rear handle 6 in the present invention is
constructed as a separate item to that of the rear clam shell 430
(or body 2).
[0196] The rear handle 6 is constructed from a separate single clam
shell 431 which is joined at its top 432 at two points 434 and at
its bottom at a single point 436. Each of the three points 434, 436
is joined using a bolt which screws into the plastic clam shell
430. Vibration dampening material may be used in conjunction with
the bolts to reduce the amount of vibration transferred to the
handle 6 from the body 2. The use of such vibration dampening
material allows limited movement of the handle 6 relative to the
rear clam 430 at each of the three points. The movement could be
either linear or rotational. One such construction is to surround
the bolts with the dampening material in order to sandwich it
between the bolts and parts of the clam shell of the rear handle
6.
[0197] The top 432 of the handle 6 is in the form of a cross bar.
The shape is such that the bolts fastening the top 432 of the
handle to the rear of the clam shell 430 are aligned with each
other and thus provide a pivot axis 440 for the rear handle 6 about
which it can rotate by a limited amount.
[0198] A person skilled in the art will appreciate that the handle
may be constructed from a number of clam shell connect rigidly
together. Rubber soft grip over mold 442 may also be added to the
handle for additional comfort.
[0199] A second embodiment of an air filtration system will now be
described with reference to FIG. 30.
[0200] The filter device comprises a box 400 in which is mounted
filter paper 402 which is pleated and which hangs down from the top
section from inside the box. A space 404 is formed below the pleat.
A large aperture 406 is formed in the side of the box below the
filter paper and through which a drawer 408 can be slid. The drawer
comprises a receptacle 410 which locates in the space 404
immediately below the filter paper 402. The drawer 408 can be
fastened into place via a screw 412 which threadedly engages a
threaded hole 414 in the box. Air passes through slots 314 into the
box and into the receptacle 410 in the space 404 below the filter
paper 402 then through the filter paper 402 into a space 416 above
the filter paper 402 and then exits the space 416 above the filter
paper through a flexible tube 418 to the carburetor 126. Any dust
contained in the air entering the box 400 is blocked by the filter
paper 402.
[0201] A combination of two systems have been proposed to shake any
dust within the filter paper 402 off the filter paper 402 into the
drawer 408 so that the drawer 408 an be removed for emptying.
[0202] The first system is very similar to that disclosed in the
first embodiment described above and comprises a rubber flap 420
which is attached to the front end of the drawer 408. As the drawer
408 is inserted into the box 400 the rubber flap 420 engages with
the pleated filter paper 402. As the drawer 408 slides into the box
400 the rubber flap 420 successively hits the base of each pleat
causing any dust on the pleats to be knocked off and into the
drawer 408. As such the action of inserting or removing the drawer
408 into the box 400 causes dust on the filter paper 402 to be
loosened and allowed to be removed.
[0203] The second system relies on the starter cord 422 of the
start 12 for the two stroke engine 24 of the power saw. When the
engine is started, the power cord 422 needs to be pulled in order
to cause it to rotate. As the cord 422 is pulled, it rotates a
pulley wheel 424 which causes an eccentric pin 426 to rotate about
the axis 428 of the pulley 420. This causes one side of the box 400
to oscillate up and down as indicated by arrows Y. The other side
of the box 400 is pivotally attached about an axis 435 to the body
of the power cutter. The reciprocating motion of the box 400 causes
dust in the filter 402 to be shaken off the filter paper 402 and
into the drawer 408.
[0204] Each system cause dust trapped in the filter paper 402 to
fall into the drawer. When the operator first starts up the power
cutter, the action of pulling the starter cord cleans the filter
paper 402. Then, the operator can subsequently clean the filter
paper during the operation of the power cutter by inserting and
removing the drawing 408.
[0205] It will be appreciated by a person skilled in the art that
the two systems could be used separately, as well as in
combination, a power cutter having only one or the other
system.
* * * * *