U.S. patent application number 12/528971 was filed with the patent office on 2010-03-18 for mobile work platform.
Invention is credited to Frank Roger Bowden.
Application Number | 20100068071 12/528971 |
Document ID | / |
Family ID | 37966050 |
Filed Date | 2010-03-18 |
United States Patent
Application |
20100068071 |
Kind Code |
A1 |
Bowden; Frank Roger |
March 18, 2010 |
MOBILE WORK PLATFORM
Abstract
A mobile work platform includes an operator platform (6), a base
(2) and a lift mechanism (4) for lifting the operator platform
relative to the base. A hydraulic drive system for the mobile work
platform includes an internal combustion engine (14), an electric
motor (24) and a hydraulic pump (26). The internal combustion
engine (14) and the electric motor (24) are constructed and
arranged so as to be capable of driving the hydraulic pump (26)
either separately or together.
Inventors: |
Bowden; Frank Roger;
(Tottenhoe, GB) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET, FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
37966050 |
Appl. No.: |
12/528971 |
Filed: |
March 6, 2008 |
PCT Filed: |
March 6, 2008 |
PCT NO: |
PCT/GB08/00786 |
371 Date: |
September 24, 2009 |
Current U.S.
Class: |
417/16 ; 417/316;
417/364; 417/374 |
Current CPC
Class: |
B66F 11/044
20130101 |
Class at
Publication: |
417/16 ; 417/364;
417/374; 417/316 |
International
Class: |
F04B 49/00 20060101
F04B049/00; F04B 17/05 20060101 F04B017/05; F04B 17/03 20060101
F04B017/03; F04B 9/02 20060101 F04B009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2007 |
GB |
0704353.2 |
Claims
1. A hydraulic drive system for a mobile work platform, the system
including an internal combustion engine, an electric motor and a
hydraulic pump, wherein the internal combustion engine and the
electric motor are capable of driving the hydraulic pump either
separately or together.
2. A hydraulic drive system according to claim 1, including a
clutch mechanism for disconnecting the internal combustion engine
from the pump.
3. A hydraulic drive system according to claim 1, further including
a battery for powering the electric motor.
4. A hydraulic drive system according to claim 3, wherein the
electric motor is operable as a generator to charge the
battery.
5. A hydraulic drive system according claim 1, further including a
control device for controlling the transfer of power between the
internal combustion engine, the electric motor and the hydraulic
pump.
6. A hydraulic drive system according to claim 5, wherein the
control device has a plurality of selectable operational modes,
including at least one of a mode selected from the group consisting
of an electric mode in which power is supplied to the pump
exclusively from the electric motor, an IC engine mode in which
power is supplied to the pump exclusively from the IC engine, and a
boost mode in which power is supplied to the pump from both the
electric motor and the IC engine.
7. A hydraulic drive system according to claim 6, wherein the
control device selects boost mode when the power requirement of the
pump exceeds a predetermined value.
8. A hydraulic drive system according to claim 6, wherein the
control device has a regeneration mode in which the electric motor
is driven by the IC engine and operates as a generator to charge a
battery.
9. A hydraulic drive system according to claim 8, in which the
control device controls the transfer of electric power between the
battery and the motor.
10. A hydraulic drive system according to claim 1, wherein the
internal combustion engine has a power in the range 5-50 kW.
11. A hydraulic drive system according to claim 1, wherein the
hydraulic pump is a variable displacement pump.
12. A hydraulic drive system according to claim 1, wherein the
internal combustion engine, the electric motor and the hydraulic
pump are arranged co-axially.
13. A hydraulic drive system according to claim 1, wherein the pump
and the electric motor are mounted on a common drive shaft, which
is offset from an output shaft of the internal combustion engine,
wherein the drive shaft and the output shaft are connected by a
drive transfer mechanism.
14. A mobile work platform comprising an operator platform, a base
and a lift mechanism for lifting the operator platform relative to
the base, and a hydraulic drive system according to claim 1 for
operating the lift mechanism.
15. A mobile work platform according to claim 14, wherein the
operator platform has a working height of 10 m or more and a load
capacity in the range 100-1000 kg.
Description
[0001] The present invention relates to a mobile work platform and
a drive system for a mobile work platform.
[0002] Mobile work platforms typically include a cage or platform
that is designed to receive one or more human operators. The cage
is mounted on a lift mechanism, such as a hydraulic boom or a
scissor lift mechanism, that allows its height to be adjusted. The
mobile work platform also includes a wheeled or tracked chassis,
which allows it to be moved easily to a desired location. Various
types of mobile work platform are available, including
self-propelled, self-drive, trailer and vehicle-mounted
platforms.
[0003] The present invention is concerned in particular, but not
exclusively, with larger mobile work platforms, for example having
a working height of 14 m or more (typically up to 30-40 m) and a
load carrying capacity of over 200 kg (typically up to 1000 kg).
However, it is also applicable to smaller mobile work platforms,
such as those with a load carrying capacity of less than 200 kg and
a working height in the range 9-12 m.
[0004] Most mobile work platforms have a hydraulic drive system. In
smaller platforms (for example those with a working height of less
than 15 m), it is common to use two fixed displacement hydraulic
pumps, one of which is driven by an internal combustion (IC) engine
(for example a diesel engine) and the other being driven by a DC
electric motor, powered from batteries. Either pump may be used to
operate the hydraulic drive system. For example, it may be
preferable to use the electrically driven pump when the mobile work
platform is being operated indoors, where the noise and exhaust
fumes of the internal combustion engine might be undesirable. At
other times, for example when the mobile work platform is being
operated outdoors, it may be preferable to use the pump driven by
the internal combustion engine, since this can provide continuous
operation for a much longer period of time than the battery powered
electric motor. When the IC engine is operating, it may also be
used to recharge the batteries, using its alternator.
[0005] With larger mobile work platforms (for example those with a
working height of 14 m or more and a load carrying capacity greater
than 200 kg), a more complicated variable displacement hydraulic
pump is generally required. Variable displacement pumps are much
more expensive than fixed displacement pumps and generally it is
not commercially viable to employ a two pump system as described
above. Larger platforms therefore usually have only one pump, which
is driven directly by an internal combustion engine. The internal
combustion engine must of course have sufficient capacity to meet
the peak power requirement of the hydraulic drive system. For
example, a mobile work platform with a carrying capacity of 200 kg
may typically require a peak input power of 10 kW. Most of the
time, the power requirement will be much lower than this. As IC
engines are inefficient when operating at low power or when idling,
this leads to unnecessarily high fuel consumption and high levels
of noise and exhaust emissions. Larger IC engines also have higher
capital cost and higher maintenance charges.
[0006] It is an object of the present invention to provide a mobile
work platform and a drive system for a mobile work platform that
mitigates at least some of the aforesaid disadvantages.
[0007] According to one aspect of the present invention there is
provided a hydraulic drive system for a mobile work platform, the
system including an internal combustion engine, an electric motor
and a hydraulic pump, wherein the internal combustion engine and
the electric motor are constructed and arranged so as to be capable
of driving the hydraulic pump either separately or together.
[0008] The system provides the advantage that it is possible to
select the drive motor according to the circumstances. Thus, for
example, the electric motor may be used to drive the pump during
indoor operation (when exhaust fumes may be unacceptable), and the
internal combustion engine may be used to drive the pump during
operation outdoors, or to recharge the batteries when the platform
is outside (for example during a break). Alternatively, for maximum
power, both the internal combustion engine and the electric motor
may be used in tandem to drive the pump. This means that a less
powerful internal combustion engine can be used, while still
meeting the peak power requirement of the pump. This provides
savings both in the capital and maintenance costs of the IC engine,
and in its fuel consumption. Exhaust emissions and noise may also
be reduced. Only one pump is required, providing further cost
savings.
[0009] Advantageously, the system includes a clutch mechanism for
disconnecting the internal combustion engine from the pump, so that
it can be driven by the electric motor when the IC engine is
inoperative. Preferably, the clutch is designed to disconnect the
IC engine automatically when it is inoperative.
[0010] The system may include a battery for powering the electric
motor. Advantageously, the electric motor is operable as a
generator to charge the battery. This allows any spare capacity of
the IC engine, for example when it is idling or the load on the
pump is low, to be put to useful purpose, so improving fuel
efficiency. The stored energy may subsequently be used to drive the
electric motor, so reducing the load on the internal combustion
engine or allowing it to be turned off.
[0011] Advantageously, the hydraulic drive system includes a
control device for controlling the transfer of power between the
internal combustion engine, the electric motor and the hydraulic
pump. Preferably, the control device has a plurality of selectable
operational modes, including at least one of an electric mode in
which power is supplied to the pump exclusively from the electric
motor, an IC engine mode in which power is supplied to the pump
exclusively from the IC engine, and a boost mode in which power is
supplied to the pump from both the electric motor and the IC
engine. The control device may be constructed and arranged to
select boost mode when the power requirement of the pump exceeds a
predetermined value.
[0012] Advantageously, the control device has a regeneration mode
in which the electric motor is driven by the IC engine and operates
as a generator to charge the battery. Preferably, the control
device controls the transfer of electric power between the battery
and the motor.
[0013] Advantageously, the internal combustion engine has a power
in the range 5-50 kW, preferably approximately 10-20 kW.
[0014] The internal combustion engine may for example be a diesel
engine, a petrol engine or an engine that runs on liquified
petroleum gas (LPG).
[0015] The pump is preferably a variable displacement pump.
[0016] The internal combustion engine, the electric motor and the
hydraulic pump may be arranged co-axially. This provides a compact
and mechanically simple arrangement.
[0017] Alternatively, the pump and the electric motor may be
mounted on a common drive shaft, which is offset from an output
shaft of the internal combustion engine, the drive shaft and the
output shaft being connected by a drive transfer mechanism. This
arrangement may be preferred in certain circumstances, for example
when packaging requirements do not permit a coaxial
arrangement.
[0018] According to a further aspect of the invention there is
provided a mobile work platform that includes an operator platform,
a base and a lift mechanism for lifting the operator platform
relative to the base, and a hydraulic drive system according to any
one of the preceding claims for operating the lift mechanism.
[0019] The operator platform preferably has a working height of 10
m or more and a load capacity in the range 100-1000 kg, and more
preferably 200-500 kg, the drive system being particularly well
suited to larger mobile work platforms having a load carrying
capacity in this range.
[0020] Certain embodiments of the invention will now be described
by way of example, with reference to the accompanying drawings, in
which:
[0021] FIG. 1 is a block diagram illustrating the components of a
mobile work platform drive system according to a first embodiment
of the invention;
[0022] FIG. 2 is a block diagram of a mobile work platform drive
system according to a second embodiment of the invention, and
[0023] FIG. 3 is a front elevation of a mobile work platform
according to an embodiment of the invention, in various operating
configurations.
[0024] FIG. 3 shows a typical mobile work platform according to an
embodiment of the invention, which includes a wheeled base unit 2,
a lift mechanism comprising a hydraulically operated boom 4 and a
platform (or cage) 6 for a human operator 8. The boom 4, which is
shown here in various operating configurations, may be retracted
and folded onto the base unit 2 for transportation or storage.
Movement of the boom 4 is controlled by various hydraulic cylinders
10, which are connected by hydraulic hoses (not shown) to a
hydraulic drive system. Hydraulic motors may also be provided for
driving the wheels. The components shown in FIG. 3 are all
conventional and will not therefore be described in detail. It
should be understood that the mobile work platform may take various
alternative forms. For example, it may include a scissor lift
mechanism.
[0025] A hydraulic drive system according to a first embodiment of
the invention is shown in FIG. 1. This includes a support frame 12
on which is mounted an internal combustion (IC) engine 14, for
example a diesel engine, having an output shaft 16, which is
connected via a clutch 18 and a flexible coupling 20 to a drive
shaft 28, on which is mounted an electric motor/generator 24 and a
variable displacement hydraulic pump 26. The drive shaft 28 is
coaxial with the internal combustion engine output shaft 16. The
pump 26 is connected via hydraulic pipes (not shown) to other
components of the hydraulic system, which are all conventional.
[0026] The clutch 18 is designed to disengage the IC engine 14
automatically from the drive shaft 28 whenever the engine is
inoperative, to allow free rotation of the drive shaft. The
flexible coupling 20 is designed to absorb misalignments and
transient shocks when engaging or disengaging the clutch 18.
[0027] The electric motor/generator 24 may be used either as a
motor or as a generator, which can be used to generate electricity
by driving the rotor mechanically through the drive shaft 28. The
motor/generator 24 is electrically connected via a control device
30 to a battery 32 of electric cells. The control device 30
controls operation of the motor/generator 24, either supplying
electrical power to the battery 32 to recharge it when the
motor/generator is in generator mode, or supplying electrical power
from the battery 32 to the motor/generator 24 when it is in motor
mode. The control device 30 controls the voltage supply to the
battery 32 during recharging, and controls the speed of the motor
when it is being driven by electric power drawn from the battery
32. The control device 30 is preferably located adjacent the
motor/generator 24, while the battery 32 may be located
remotely.
[0028] The hydraulic drive system has various operational modes,
including IC engine operation mode, electrical operation mode,
regeneration mode and boost mode. Each of these operational modes
will now be described.
[0029] During IC engine operation, the internal combustion engine
14 drives the pump 26 via the output shaft 16, the clutch 18 and
the drive shaft 28. The pump 26 provides hydraulic fluid to the
drive components (for example the hydraulic cylinders and motors)
of the system so as to operate the lift and drive functions of the
mobile work platform. During this operational mode, the rotor of
the electric motor/generator 24 rotates with the drive shaft 28 but
it does not generate electricity, this function being controlled by
the control device 30.
[0030] During electrical operation mode, the pump 26 is driven
directly by the electric motor/generator 24, which operates in
motor mode and draws power from the battery 32. The pump 26 thus
provides hydraulic fluid to operate the lift and drive functions of
the mobile work platform. The control device 30 controls the power
delivered to the motor. During electrical operation, the internal
combustion engine 14 is inoperative and the clutch 18 is
automatically disengaged to disconnect the output shaft 16 of the
IC engine 14 from the drive shaft 28.
[0031] During regeneration mode, the IC engine 14 drives the
electrical motor/generator 24 via the clutch 18 and the drive shaft
28, to generate electricity which is stored in the battery 32. The
control device 30 controls the delivery of current to the battery
32 and prevents overcharging. Regeneration may take place either
when the hydraulic system is idle and the pump 26 is inoperative,
or when the pump 26 is operating at a low output level. In the
latter case, the spare output capacity of the IC engine 14, beyond
that required to operate the pump 26, is used to generate
electricity. This excess energy is stored in the battery and saved
for later use during electric operation, thus improving fuel
efficiency.
[0032] In certain circumstances, more power may be required by the
hydraulic pump 26 than can be supplied individually by either the
IC engine 14 or the electric motor 24. In this case, the drive
system enters boost mode, in which the IC engine 14 and the
electric motor 24 operate in tandem to drive the pump 26. The
electric motor 24 therefore supplements the power output of the IC
engine 14, thereby providing a greater output power than can be
supplied by the IC engine 14 operating on its own. This in turn
allows a smaller capacity IC engine to be used, which is smaller
and lighter, less expensive, more economical and causes less noise
and pollution. The system may be designed to enter boost mode
automatically whenever the power requirement of the pump exceeds a
certain predetermined level.
[0033] A second embodiment of the invention is shown in FIG. 2. In
this embodiment, the hydraulic drive system is similar in most
respects to the first drive system described above, and where
appropriate like reference numbers have been used to indicate
equivalent components. The main difference is that the drive shaft
is divided lengthwise into two parts 28a, 28b. The first part 28a
of the drive shaft is coaxial with the output shaft 16 of the IC
engine and is connected to the clutch 18 and the flexible coupling
20. The second part 28b of the drive shaft carries the electric
motor/generator 24 and the pump 26, and is offset from the axis of
the IC engine output shaft 16 . Drive is transferred from the first
part 28a of the drive shaft to the second part 28b of the drive
shaft by a drive transfer mechanism 34, which in this case consists
of a drive belt mounted on a pair of pulleys.
[0034] Various alternative drive transfer mechanisms may of course
be used, including gears, toothed belts or a chain and sprockets,
and this mechanism may be located at different positions within the
drive chain, such as between the IC engine 14 and the clutch 18.
The second part of the drive shaft may also be set at an angle
relative to the first part of the shaft (for example, it may be
perpendicular). These arrangements may be useful where packaging
requirements prevent the use of the co-axial drive system of the
first embodiment described above. Operation of the second drive
system is essentially identical to that of the first drive system,
as described above.
[0035] Numerous modifications of the drive system are of course
possible. For example, the drive system may include a charging
circuit that is designed to recharge the battery 32 or operate the
electric motor 24 directly from a mains electricity supply, where
one is available. Various alternative kinds of clutch may be used
including, for example, an electrically actuated clutch. The system
may also be reconfigured, for example so that the pump is located
between the IC engine and the electric motor.
* * * * *