U.S. patent application number 14/649631 was filed with the patent office on 2015-12-03 for arrangement and procedure for pressurizing a cooling system to cool an internal combustion engine in a vehicle.
The applicant listed for this patent is SCANIA CV AB. Invention is credited to Hans WIKSTROM.
Application Number | 20150345365 14/649631 |
Document ID | / |
Family ID | 50934737 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150345365 |
Kind Code |
A1 |
WIKSTROM; Hans |
December 3, 2015 |
ARRANGEMENT AND PROCEDURE FOR PRESSURIZING A COOLING SYSTEM TO COOL
AN INTERNAL COMBUSTION ENGINE IN A VEHICLE
Abstract
An arrangement and procedure for pressurizing a cooling system
that cools an internal combustion engine (2) in a vehicle (1). The
cooling system includes a coolant pump (3) for circulating the
coolant in the cooling system, an expansion tank (12) allowing the
coolant in the cooling system to expand, and a pressure relief
valve (15) that releases air when a specific pressure is reached in
the cooling system. A compressed air-entraining device (17-21)
allows compressed air to be supplied to the cooling system by
supplying a continuous air flow to the cooling system while the
internal combustion engine (2) is operational, and to supplying an
air flow of a size at least equal to the estimated leakage from the
cooling system.
Inventors: |
WIKSTROM; Hans;
(Johanneshov, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCANIA CV AB |
Sodertalje |
|
SE |
|
|
Family ID: |
50934737 |
Appl. No.: |
14/649631 |
Filed: |
November 19, 2013 |
PCT Filed: |
November 19, 2013 |
PCT NO: |
PCT/SE2013/051357 |
371 Date: |
June 4, 2015 |
Current U.S.
Class: |
123/41.44 ;
415/1 |
Current CPC
Class: |
F01P 3/22 20130101; F01P
11/18 20130101; F01P 11/029 20130101; F01P 5/10 20130101 |
International
Class: |
F01P 3/22 20060101
F01P003/22; F01P 5/10 20060101 F01P005/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 10, 2012 |
SE |
1251396-6 |
Claims
1. An arrangement for pressurizing a cooling system that cools an
internal combustion engine in a vehicle, wherein the cooling system
contains: a coolant pump configured to circulate the coolant in the
cooling system; an expansion tank enabling the coolant in the
cooling system to expand when in operation; a pressure relief valve
configured to release air from the cooling system when a specific
pressure is reached and then exceeded in the cooling system; the
arrangement comprises a compressed air-entraining device configured
to allow compressed air to be supplied to the cooling system; the
compressed air-entraining device is set to provide a continuous air
flow to the cooling system during the entire time the internal
combustion engine is operational and to supply a constant air flow
at a rate of flow size equal to a maximum estimated air leakage
from the cooling system.
2. An arrangement in accordance with claim 1, further comprising
the compressed air-entraining device further containing a
compressed air source and a compressed air line attached to and
configured to continuously convey compressed air from the
compressed air source to the cooling system while the internal
combustion engine is in operation.
3. An arrangement in accordance with claim 2, further comprising
the compressed air source contains an accumulator tank configured
to store compressed air for an existing in-vehicle compressed air
system.
4. An arrangement in accordance with claim 2, further comprising
the compressed air line contains a throttle device that defines the
air flow to the cooling system.
5. An arrangement in accordance with claim 4, further comprising a
valve in the compressed air line , the valve being configured and
operable to being set in an open flow position when the internal
combustion engine is started to operation and in a closed no flow
position when the internal combustion engine is switched off.
6. An arrangement in accordance with claim 4, further comprising
the valve contains the throttle device.
7. An arrangement in accordance with claim 5, further comprising
the compressed air-entraining the device containing a control unit
which is settable to receive information indicating when the
internal combustion engine is started and when the engine is
switched off, and is settable to controlling the air valve with the
aid of this information.
8. An arrangement in accordance with claim 1, further comprising
the compressed air line is configured to convey compressed air from
the compressed air source to the expansion tank in the cooling
system.
9. An arrangement in accordance with claim 1, further comprising a
non-return valve for the expansion tank, and the non-return valve
is configured for ensuring that the pressure in the expansion tank
does not drop below the ambient pressure.
10. A process to pressurize a cooling system for cooling an
internal combustion engine in a vehicle, wherein the cooling system
comprises a coolant pump connected with the coolant pump and
configured to circulate the coolant in the cooling system; an
expansion tank configured for enabling the coolant in the cooling
system to expand when the cooling system is operational; and a
pressure relief valve release air from the cooling system when a
specific pressure is reached in the cooling system; the method
comprising supplying a continuous and constant air flow to the
cooling system during the time the internal combustion engine is
operational, and supplying the constant air flow of a size equal to
at least a maximum estimated leakage from the cooling system.
11. An arrangement according to claim 4, wherein the throttle
device comprises a fixed throttle.
Description
BACKGROUND TO THE INVENTION AND PRIOR ART
[0001] The present invention relates to an arrangement and
procedure for pressurizing a cooling system to cool an internal
combustion engine in a vehicle according to the preamble of patent
claims 1 and 11.
[0002] The coolant circulating in a cooling system for cooling an
internal combustion engine generally has an operating temperature
of some 80-100.degree. C. When cold-started, the coolant in the
internal combustion engine is at a considerably lower temperature.
However, the coolant occupies a greater volume in the cooling
system when warm than when cold. In order to allow the volume of
the coolant to change in an operational state, the cooling system
includes an expansion tank. The expansion tank is made up of an
enclosed space containing air and coolant. The expansion tank is
fitted with a filler cap and a pressure relief valve which limits
the pressure in the latter as well as a non-return valve which
prevents underpressure occurring in the tank. As the coolant
expands during heating, the pressure in the tank rises. However,
the pressure cannot exceed a maximum permitted value defined by the
opening temperature of the pressure relief valve.
[0003] The expansion tank is normally connected to other parts of
the cooling system via a vertical pipe called a static line. The
height of the expansion tank is thus positioned at a certain level
above the coolant pump circulating the coolant in the cooling
system. By virtue of such a design a column of coolant is thus
formed, extending from the coolant pump up to an expansion tank,
thereby creating overpressure at the point of the coolant pump
intake, preventing the occurrence of cavitation whenever the
coolant pump is started.
[0004] However, the coolant pump's tendency to cavitate increases
with the temperature of the coolant. When the coolant has reached
operating temperature, the overpressure generated by the static
line column is not normally sufficient to eliminate the risk of
cavitation in the coolant pump. The coolant expands when heated up,
however, resulting in the creation of overpressure in the cooling
system. The volume of the expansion tank occupied by air and
coolant is dimensioned such that suitable overpressure arises when
the coolant expands. Together, this overpressure and the static
line create overpressure at the coolant pump intake, ensuring that
the coolant pump does not cavitate when the coolant is hot.
[0005] However, a cooling system is not altogether tight; rather,
there will invariably be minor leakage of both air and coolant from
the cooling system when the internal combustion engine is running
The fluid leakage occurs principally in the gland packing on the
coolant pump and the air leakage principally in the non-return
valve of the expansion tank. The leakage lowers the pressure level
in the cooling system when the internal combustion engine is
running. The leakage is so slight, however, that the pressure level
around the vehicle is lowered only negligibly when the vehicle is
operating normally with intervening periods when the coolant has a
chance to cool down to the ambient temperature.
[0006] Once the coolant cools down after a period of operation, it
resumes its original volume, thereby creating underpressure in the
cooling system equivalent to the leakage in the cooling system
during the period of operation. The non-return valve opens and
subsequently adjusts this leakage. A transport vehicle can
essentially run around the clock without intervening periods during
which the coolant cools down. Even if the air and coolant leakage
is very slight, the leakage during a long period of non-stop
operation can lower the overpressure to such a low level as to
create a risk of cavitation damage to the coolant pump.
[0007] DE 10 2007 058 575 shows a cooling system for an internal
combustion engine in which the pressure in the cooling system can
be regulated while the internal combustion engine is running In
this case a sophisticated pressure regulation system is used to
regulate the pressure in the cooling system to a desired level,
knowing the coolant's temperature and the operating state of the
internal combustion engine. Among other things, the pressure can be
raised to an extra-high level by quickly turning off a hot internal
combustion engine in order to avoid steam forming in the internal
combustion engine block. As a result, the expansion tank can be
made smaller, as it requires no extra volume to receive the copious
amount of steam otherwise formed when a hot internal combustion
engine is turned off quickly.
ABSTRACT OF THE INVENTION
[0008] The aim of the present invention is to provide an
arrangement that prevents cavitation damage to a coolant pump even
if the cooling system is primarily operated continuously for long
periods. Another aim is to provide an arrangement with a simple
design incorporating components that can be applied to an existing
cooling system with relative ease.
[0009] These aims are achieved with the type of cooling system
mentioned by way of introduction, characterized by the distinctive
features set out in the characterizing clause of patent claim 1.
When operational, a slight amount of air and fluid leakage thus
occurs in the cooling system. Such leakage results in a gradual
reduction in the overpressure in the cooling system as the cooling
system operates continuously with the hot coolant. It is possible
to estimate this leakage with a relatively high degree of accuracy,
however. In accordance with the invention an air flow is
continuously supplied to the cooling system whenever the internal
combustion engine is running The volume of air supplied is such as
always to be at least equal to the estimated leakage from the
cooling system. In this respect a designated overpressure can be
maintained in the cooling system, irrespective of how long the
internal combustion engine continues running for. The size of the
designated overpressure in the cooling system is such that,
together with the static line, it prevents cavitation arising in
the coolant pump. Thus, in order to create this arrangement,
components only need be added that continuously supply compressed
air to the cooling system in a suitable quantity. Such components
can be relatively simple in design and can also be beneficially
applied to an existing cooling system. The amount of compressed air
that needs to be supplied is so small as to be negligible compared
to the amount of compressed air consumed by other components in,
say, a heavy goods vehicle (HGV).
[0010] According to an embodiment of the invention, said compressed
air-entraining agent is geared to supplying a continuous air flow
of a size that exceeds the air flow estimated to escape from the
cooling system. Rather more air should preferably be supplied to
the cooling system than escapes. Essentially, all conventional
expansion tanks contain a pressure relief valve. In this case the
pressure in the cooling system will rise until it reaches the
overpressure defined by the pressure relief valve. When the opening
pressure on the pressure relief valve is reached, it opens and air
escapes, reducing the pressure in the cooling system. The pressure
relief valve thus ensures that the pressure level does not exceed a
maximum permitted level. In the process the pressure in the cooling
system is maintained at a basically constantly high level, which is
defined by the pressure relief valve's opening pressure as long as
the internal combustion engine is activated. Thus, the pressure
relief valve releases the difference here between the amount of air
supplied in the cooling system and the leakage from the cooling
system.
[0011] The compressed air supply should preferably exceed the
estimated leakage by a relatively small margin. Too great a flow of
compressed air to the cooling system results in very frequent
opening of the pressure relief valve and unduly great consumption
of compressed air. Although the leakage can be estimated with
relatively great accuracy, there still needs to be a certain margin
for error so that the influx of compressed air to the cooling
system is certain to equal the actual leakage. The leakage in the
cooling system is not constant but related to the size of the
overpressure in the cooling system. Maximum leakage occurs at the
maximum permitted overpressure thus prevalent in the cooling system
immediately prior to the pressure relief valve opening. It is an
advantage if the flow of compressed air supplied is basically
constant and equal to the maximum leakage. Thus the pressure rises
relatively quickly in the cooling system when there is low
overpressure and hence little leakage, whereas the pressure
increases considerably more slowly when there is greater
overpressure and hence greater leakage.
[0012] According to an embodiment of the invention, said
pressurizing agent includes a compressed air source and a
compressed air line, which conveys compressed air from the
compressed air source to the cooling system. Heavy vehicles
generally have access to compressed air at all times, which can
beneficially be exploited to this end. Said compressed air source
can be made up of an accumulator tank that stores compressed air
for an existing in-vehicle compressed air system. When a vehicle is
in operation, predetermined, relatively high air pressure is
usually maintained in an accumulator tank by a compressor that runs
off the internal combustion engine. Such accumulator tanks are
relatively tight so that compressed air can be stored at relatively
great overpressure for long periods of time even when the vehicle
is not operational. The accumulator tank, for example, can store
compressed air for an existing compressed air system for the
vehicle's brakes.
[0013] According to an embodiment of the invention, said compressed
air line contains a throttle device with regular throttling that
defines the air flow to the cooling system.
[0014] Most compressed air sources in a vehicle store compressed
air at considerably higher pressure than the pressure required to
pressurize the cooling system. Knowing the pressure in the
compressed air source and in the cooling system, the throttle
device can be dimensioned so as to convey the compressed air from
the accumulator tank to the cooling system in the quantity desired.
If the compressed air source is at a constant high pressure in
relation to the pressure in the cooling system, the air flow to the
cooling system obtained will basically be constant, since the
pressure changes in the cooling system are relatively slight.
[0015] According to an embodiment of the invention, the compressed
air line includes a valve arranged in said line which is set to the
open position when the internal combustion engine is started and to
the closed position when the internal combustion engine is switched
off. Thus the compressed air supply to the cooling system will
start as soon as the internal combustion engine starts and will
stop as soon as the internal combustion engine is switched off.
Said valve can include the throttle device. Such a valve can be
designed so as to reduce the compressed air pressure when in the
open position and hence reduce the air flow to the cooling system
to a desired level. In this case, when in the open position, the
valve has a relatively narrow flow duct for the compressed air.
Alternatively, the throttle device and the valve can comprise
separate components in the compressed air line.
[0016] According to an embodiment of the invention, said
pressurizing agent can include a control unit geared to receiving
information that indicates when the internal combustion engine is
turned on and switched off, and to controlling said valve with the
aid of this information. Such a control unit can constitute part of
an engine control unit or a separate control unit receiving
information from, say, a motor control unit. The valve can
beneficially be an electrically controlled valve such as a solenoid
valve. With the aid of such a valve the control unit can simply and
quickly open and shut off the supply of compressed air to the
cooling system.
[0017] In accordance with another embodiment of the invention, the
compressed air line conveys compressed air to the expansion tank in
the cooling system. Since an expansion tank already contains air in
an upper area, it is expedient to supply the compressed air to this
area of the expansion tank. The compressed air supplied raises the
air pressure in the area above the coolant in the expansion tank.
The air pressure thus acts with compressive force on the coolant in
the expansion tank so that it takes on corresponding pressure. The
pressure of the coolant in the expansion tank is transferred to the
coolant in other parts of the cooling system. Alternatively, the
air can be supplied to a static line or some other suitable point
in the cooling system. It is an advantage if the expansion tank
contains the pressure relief valve. The expansion tank can also
contain a safety valve. A safety valve is normally arranged in the
expansion tank cover. It can open and help lower the pressure in
the tank if the pressure relief valve does not have the capacity to
lower the pressure in a particular way desired.
[0018] In accordance with another preferred embodiment of the
invention the expansion tank contains a non-return valve which
ensures that the pressure in the expansion tank does not fall below
the pressure of the ambient air. Such a non-return valve is
generally an existing component of an expansion tank. The
non-return valve opens if the pressure in the expansion tank falls
below the pressure of the surroundings. The presence of such a
non-return valve guarantees that the pressure in the expansion tank
presents at least the air pressure of the surroundings after the
coolant in the cooling system has cooled down after operation.
[0019] The aim stated by way of introduction is also achieved with
the procedure in accordance with patent claim 11.
BRIEF DESCRIPTION OF THE DRAWING
[0020] By way of example, a preferred embodiment of the invention
is described below, with reference to the drawing attached, in
which:
[0021] FIG. 1 shows a cooling system in a vehicle according to an
embodiment of the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
[0022] FIG. 1 shows a schematic illustration of a vehicle 1
operated by a supercharged internal combustion engine 2. The
vehicle 1 can advantageously be a heavy vehicle. The internal
combustion engine 2 can be a diesel engine. The internal combustion
engine 2 is cooled by the coolant circulating in a cooling system.
A coolant pump 3 circulates the coolant in the cooling system and
through the internal combustion engine 2. After cooling the
internal combustion engine 2, the coolant is conveyed along a line
4 to a thermostat 5 in the cooling system. Before the coolant
reaches normal operating temperature, the thermostat 5 is set to
convey the coolant, via a line 6, to the coolant pump 3, which is
laid out in a line 7. Since the thermostat 5 conveys the coolant to
the coolant pump 3, the coolant is circulated in the cooling system
without cooling off. As soon as the coolant reaches a temperature
exceeding a predetermined operating temperature, the thermostat 5
conveys the coolant, via a line 8, to a coolant cooler 9 fitted to
a front section of the vehicle 1. The coolant is cooled by a
cooling stream of air in the coolant cooler 9. The cooling stream
of air is generated by a radiator fan 10 and by the vehicle's head
wind. After cooling in the coolant cooler 9, the coolant is
conveyed via a line 11 to the coolant pump 3 in the line 7.
[0023] The volume of the coolant in the cooling system varies with
the temperature of the coolant. For that reason the cooling system
contains an expansion tank 12 with an internal space that
accommodates the varying volume of the coolant. In this case the
expansion tank 12 is connected via a line 13 to the line 7 in a
position on the suction side of the coolant pump 3. In a top
section the expansion tank 12 contains a removable cover 14 to
allow the cooling system to be replenished with coolant. The cover
14 contains a schematically displayed pressure relief valve 15. The
pressure relief valve 15 opens when the pressure in the expansion
tank 12 exceeds a maximum acceptable pressure in the cooling
system. The pressure relief valve 15, for example, can open at an
overpressure of 0.9 bar. The expansion tank 12 also contains a
non-return valve 16. The non-return valve 16 ensures that the
pressure in the expansion tank 12 is at least equal to the pressure
of the ambient air. It thus opens and lets in air if underpressure
arises in the expansion tank 12 in relation to the
surroundings.
[0024] In this case the vehicle 1 is provided with a compressed air
source in the form of an accumulator tank 17. The accumulator tank
17 contains compressed air, which is used in a compressed air
system to activate the vehicle's compressed air brakes. When the
internal combustion engine 2 is in operation, a brake compressor
maintains predetermined, relatively high air pressure in the
accumulator tank 17. Given that an accumulator tank 17 has a very
tight structure, the air pressure in the accumulator tank can be
kept relatively constant for a long time after the vehicle's
internal combustion engine 2 is switched off. As a result, the
compressed air brakes can be utilized as soon as the vehicle 1 is
to be used. The accumulator tank 17 is connected with the expansion
tank 12 via a compressed air line 18. The compressed air line 18
contains an electronically controlled valve 19 such as a solenoid
valve, which can be adjusted to a closed position, in which it
prevents compressed air being conveyed from the accumulator tank 17
to the expansion tank 12, and to an open position, in which it
allows compressed air to be conveyed from the accumulator tank 17
to the expansion tank 12.
[0025] The compressed air line 18 also contains a throttle device
20 which provides regular throttling of the compressed air conveyed
from the accumulator tank 17 to the expansion tank 12. The air
ducted into the expansion tank 12 thus presents considerably lower
pressure than the air in the accumulator tank 17. In order to
throttle the air, the throttle device 20 contains a flow duct
having a small cross-sectional area, thereby also providing a
relatively small air flow from the accumulator tank 17 to the
expansion tank 12. Knowing the pressure in the accumulator tank and
the pressure in the expansion tank 12, the regular throttle device
20 can be dimensioned so as to receive the desired air flow from
the accumulator tank 17 to the expansion tank 12 with great
precision. The valve 19 and the throttle device 20 make up separate
units in this case. Alternatively, the valve 19 and the throttle
device 20 can be designed as one component in the form of a
throttle valve, which in the open position provides a flow duct to
give suitable throttling of the air conveyed from the accumulator
tank 17 to the expansion tank 12.
[0026] The cooling system contains a control unit 21. The control
unit 21 is set to receive information indicating when the internal
combustion engine 2 starts and when it is switched off. In this
case the control unit 21 receives information from a motor control
unit 22. The control unit 21 puts the valve body 19 into the open
position when the internal combustion engine 2 starts and into the
closed position when the internal combustion engine 2 is switched
off. The valve body 19 is always in the open position when the
internal combustion engine is activated and in the closed position
when not activated. When the control unit 21 receives information
indicating that the internal combustion engine 2 has been
activated, the valve body 19 then opens. In so doing, a continuous
flow of compressed air is conveyed from the accumulator tank 17 to
the expansion tank 12 whenever the internal combustion engine 2 is
activated.
[0027] The coolant receives overpressure in the line 7 on the
suction side of the coolant pump 3, which is defined by the height
of the static line column and the overpressure in the expansion
tank 17. When the coolant is cold, the static line column generates
adequate overpressure on the suction side of the coolant pump 3 to
prevent cavitation. When the internal combustion engine is in
operation, the coolant circulating in the cooling system is heated
up. Since the coolant has been heated, the coolant pump 3 has an
increased tendency to cavitate. However, hot coolant absorbs a
greater volume than cold coolant, creating overpressure in the
cooling system when the coolant is heated up. Together, this
overpressure and the static line create sufficiently high pressure
to prevent cavitation in the coolant pump 3 when the coolant is
hot. A cooling system is not completely tight. A certain amount of
fluid leakage occurs, for instance, at a gland packing on the
coolant pump 3 and some air leakage occurs, for instance, at the
non-return valve 16. The leakage is reduced by the overpressure in
the cooling system when the internal combustion engine is in
operation. Particularly if the vehicle is operated non-stop for a
very long period, there is a risk that the overpressure will be
substantially reduced owing to said leakage. There is also a risk
that the overpressure in the cooling system will be reduced by the
cover on the cooling system being opened when the coolant is
hot.
[0028] The air and coolant leakage experienced in a cooling system
can be estimated with relatively good accuracy. For example, the
non-return valve 16 contains particulars of maximum leakage. The
control unit 21 thus receives information from the engine unit 22
when the internal combustion engine 2 starts up. The control unit
thereby places the valve 19 in the open position. In as much as the
pressure in the accumulator tank 17 is higher than the pressure in
the expansion tank 12, an air flow is obtained from the accumulator
tank 17, via the compressed air line 18, to the expansion tank 12.
The throttle device 20 and the pressure differential between the
accumulator tank 17 and the expansion tank define the size of the
air flow. The throttle device 20 has been dimensioned so that the
size of the air flow supplied is such as to always be at least
equal to the leakage occurring from the cooling system. As such, a
designated overpressure in the cooling system can be maintained
regardless of how long the internal combustion engine 2 continues
to operate. This overpressure, with the static line, guarantees
that pressure is received at the intake to the coolant pump,
preventing cavitation.
[0029] The dimensions of the throttle device 20 are advantageous in
that it supplies a continuous flow of air to the expansion tank 17
of a size that exceeds the estimated leakage from the cooling
system. The pressure in the cooling system will thus increase until
it reaches the maximum permitted overpressure defined by the
pressure relief valve 15. When the opening pressure on the pressure
relief valve 15 is reached, it will open and release air, reducing
the pressure in the expansion tank 12. The pressure relief valve 15
thus ensures that the pressure level does not exceed a maximum
permitted level in the cooling system. The pressure in the cooling
system is thereby maintained at a basically constantly high level
as long as the internal combustion engine is activated. This
overpressure, together with the static line, guarantees that
sufficiently great pressure is obtained at the coolant pump intake
so as to avoid cavitation.
[0030] The compressed air supply should preferably exceed the
estimated leakage by a relatively small margin. Too great a flow of
compressed air to the cooling system will result in very frequent
opening of the pressure relief valve 15 and unduly great compressed
air consumption. Although the leakage at the gland packing on the
coolant pump and the non-return valve 16 can be estimated with
relatively high accuracy, there must nevertheless be a certain
margin for error so that the inflow of compressed air to the
cooling system is certain to be at least equal to the actual
leakage. The leakage in the cooling system is not constant but
related to the size of the overpressure in the cooling system.
Maximum leakage occurs at the maximum permitted overpressure thus
prevalent in the cooling system immediately prior to the pressure
relief valve 15 opening. It is an advantage if the flow of
compressed air supplied is basically constant and equal to the
maximum leakage. The pressure in the cooling system will thus
increase relatively quickly, as there is low overpressure and
little leakage, whereas the pressure rises considerably more slowly
when there is higher pressure and greater leakage.
[0031] A pressure relief valve 16 is found in essentially all
conventional expansion tanks. A compressed air source 17 is
generally found in at least a heavy vehicles 1. In order to supply
compressed air to the expansion tank 12, therefore, only a
compressed air line 18, a valve 19, a throttle device 20 and a
control unit 21 are needed. These components can also be
beneficially applied to an existing vehicle without any major
problems. The quantity of compressed air that needs to be supplied
is so small as to be negligible compared with the quantity of
compressed air consumed by other components in an heavy vehicle
1.
[0032] The invention is in no way confined to the embodiment
described in the drawing but can be varied at will within the
parameters of the patent claim.
* * * * *