GB2344389A - A pneumatic actuator system - Google Patents

A pneumatic actuator system Download PDF

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Publication number
GB2344389A
GB2344389A GB9925496A GB9925496A GB2344389A GB 2344389 A GB2344389 A GB 2344389A GB 9925496 A GB9925496 A GB 9925496A GB 9925496 A GB9925496 A GB 9925496A GB 2344389 A GB2344389 A GB 2344389A
Authority
GB
United Kingdom
Prior art keywords
high pressure
reservoir
pressure reservoir
low pressure
actuator
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9925496A
Other versions
GB9925496D0 (en
Inventor
Michael Neil Basnett
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
MG Rover Group Ltd
Original Assignee
MG Rover Group Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by MG Rover Group Ltd filed Critical MG Rover Group Ltd
Publication of GB9925496D0 publication Critical patent/GB9925496D0/en
Publication of GB2344389A publication Critical patent/GB2344389A/en
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T17/00—Component parts, details, or accessories of power brake systems not covered by groups B60T8/00, B60T13/00 or B60T15/00, or presenting other characteristic features
    • B60T17/02—Arrangements of pumps or compressors, or control devices therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/24—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release the fluid being gaseous
    • B60T13/26—Compressed-air systems
    • B60T13/40—Compressed-air systems indirect, i.e. compressed air booster units indirect systems
    • B60T13/44—Compressed-air systems indirect, i.e. compressed air booster units indirect systems with two-chamber booster units
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/58—Combined or convertible systems
    • B60T13/581—Combined or convertible systems both hydraulic and pneumatic

Landscapes

  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Hydraulic Clutches, Magnetic Clutches, Fluid Clutches, And Fluid Joints (AREA)
  • Actuator (AREA)

Abstract

A pneumatic actuator system e.g. for vehicle brakes, is disclosed having an actuator assembly 20 having a housing defining a working chamber and an actuator member located within the working chamber. The actuator member is acted upon by high pressure gas on one side thereof supplied from a pressurised reservoir 13 and is exposed to a vacuum on its other side by connection to a low pressure reservoir 14. The low pressure reservoir 14 is connected to an inlet side of a compressor 11 and the high pressure reservoir 13 is connected to an outlet side of the same compressor.

Description

A Pneumatic Actuator Svstem This invention relates to a pneumatic actuator system and in particular to a pneumatic actuator system for a motor vehicle.
It is well known to supply a motor vehicle with a pneumatic actuator system for assisting with the application of the brakes. Such a system normally includes a servo device having a large diaphragm operated upon by a vacuum. Such a vacuum servo system has the disadvantage that the size of the diaphragm has to be relatively large as the maximum available pressure is approximately one Bar. This can be a particular problem when used on a small vehicle where the available space to package the servo device is normally limited.
It is also known to supply a motor vehicle with a compressed air system to operate the brakes or suspension. Such pressurised systems have the advantage that they are not limited by the available pressure difference between normal atmospheric pressure and practically achievable levels of vacuum. The size of an actuator for such a pressurised system can therefore be considerably reduced relative to the size of an equivalent vacuum servo device.
However, such pressurised systems have a number of disadvantages which have to some extent limited their popularity particularly for use on passenger motor vehicles. These can be summarised as high noise levels due to compressor intake and exhaust flows and system exhaust or discharge flows, condensation within the system causing corrosion and icing, ingestion of debris and moisture laden air requiring filtration and drying equipment and low efficiency due to lost exhaust energy.
It is an object of this invention to provide an improved pneumatic actuator system.
According to a first aspect of the invention there is provided a pneumatic actuator system comprising an actuator assembly having a housing, an actuator member movably located within the housing to define a high pressure chamber and a low pressure chamber, a high pressure reservoir connectable to the high pressure chamber and a low pressure reservoir connectable to the low pressure chamber, and a pump having an inlet side connectable to the low pressure reservoir and an outlet side connectable to the high pressure reservoir.
Preferably the two reservoirs are formed in a single reservoir assembly and separated from each other by a common wall.
Preferably the pump is driven via a clutch controlled by the pressure in the high pressure reservoir.
Preferably the actuator member is a diaphragm sealingly connected to the housing.
The present invention further provides motor vehicle servo assisted braking system including a system according to any foregoing claim wherein the actuator member is arranged to assist in actuation of a vehicle brake.
The invention will now be described by way of example with reference to Fig. 1 of the accompanying drawing.
There is shown part of a motor vehicle servo assisted braking system including a pneumatic actuator system according to said first aspect of the invention.
A pump in the form of a compressor 11 has an outlet side connected by means of a conduit 34 to a high pressure reservoir 13 containing compressed gas. The high pressure reservoir 13 forms part of a reservoir assembly 12 which further includes a low pressure reservoir 14 separated from the high pressure reservoir 13 by a wall 15 and a valve assembly 16. A conduit 33 connects the low pressure reservoir 14 to an inlet side of the compressor 11.
An actuator assembly 20 is connected to the reservoir assembly 12 via the control valve assembly by means of a supply pipe 31 and a return pipe 32.
The actuator assembly 20 has a housing 22 defining a working chamber (not shown) an actuator member in the form of a diaphragm is located within the working chamber and is sealed around its periphery to the housing 22. The diaphragm divides the working chamber into two variable volume chambers disposed on opposite sides of the diaphragm.
A supply of compressed gas from the high pressure reservoir 33 is supplied to one of the variable volume chambers through an inlet port 26 and the other of said variable volume chambers is connected to the low pressure reservoir 14 by an outlet port 27.
A valve assembly (not shown) is provided to control the flow of gas into the inlet port and out of the outlet port so as to vary the servo effect supplied by the diaphragm to a master cylinder 21. The valve assembly is controlled by a push rod 24 connected to a driver operable lever in the form of a brake pedal 23. The brake pedal 23 is pivotally connected by means of a pivot pin 25 to part of the body structure of the motor vehicle of which the braking system forms a part.
The master cylinder 21 has a pair of outlet ports 21a, 21b to supply high pressure fluid to a number of brake assemblies (not shown) each of which is arranged to supply a braking effort to an associated wheel of the motor vehicle.
The compressor 11 is driven by a gearwheel 36 driven from an engine of the motor vehicle by a gearwheel 37. A clutch arrangement 30 is interposed between the gearwheel 36 and a drive shaft 36a driving the compressor 11.
The clutch 30 is controlled by pneumatic pressure and is connected to the high pressure reservoir by means of a conduit 35.
An air inlet pipe 38 is connected to the valve assembly 16 to provide a supply of atmospheric air upon initial charging of the actuator system and also to provide a top-up of air to replace any air lost through leakage from the system. A filter 39 is provided to filter the air entering the system via the pipe 38.
Operation of the system is as follows.
Initially, both of the reservoirs 13 and 14 and the housing 22 are all at atmospheric pressure and when the compressor 11 is first activated it operates so as to draw air from the low pressure reservoir 14 and supply it to the high pressure reservoir 13. During this operation, air is drawn out of the housing 22 via the outlet port 27 through the pipe 32 into the valve assembly 16 and is supplied to the inlet port 26 via the pipe 31. The compressor 11 continues pumping until the pressure in the high pressure reservoir 13 reaches a predetermined level which during initial charging of the system requires air to be drawn in through the inlet pipe 38 as the volume of air within the system prior to starting of the compressor 11 is not sufficient to produce the required pressure in the high pressure reservoir 13.
When the pressure in the high pressure reservoir 13 reaches the desired pressure the control valve assembly 16 is operable to close off the flow from the inlet pipe 38 and supply compressed gas through the pipe 35 to the clutch 30. The compressed gas in the pipe 35 causes the clutch 30 to be disengaged thereby stopping the pumping action of the compressor 11.
In this state, the high pressure reservoir 13 and the pipe 31 are at a predetermined pressure such as, for example, 5 Bar and the low pressure reservoir and the pipe 32 are both maintained at a pressure below normal atmospheric pressure. This condition will remain until the brake pedal 23 is actuated with any leakage from the system being made up via the inlet pipe 38 with subsequent re-compression and evacuation by means of the compressor 11.
When the brake pedal 23 is actuated the push rod 24 moves a valve member within the actuator assembly allowing pressurised gas to enter via the inlet port 26 and permitting air to be drawn out through the outlet port 27. The movement of the push rod 24 also produces compression of the fluid contained within the master cylinder 21 assisted by servo effect of the diaphragm located within the housing 22. The servo effect supplied from the diaphragm to the master cylinder is related to the surface area of the diaphragm and the pressure differential that exists between the inlet port 26 and the outlet port 27. Therefore, if the pressure in the high pressure reservoir is 5 Bar and the pressure in the low pressure reservoir is 0.1 Bar, the effective pressure differential is 4.9 Bar.
When the brake pedal 23 is released the valve within the actuator assembly first closes off the inlet port 26 and then connects the inlet side of the working chamber to the outlet side of the working chamber thereby equalising the pressure on both sides of the diaphragm. In this way, the servo effect of the diaphragm is reduced to zero by releasing the pressure upon the master cylinder 21.
The pressurised gas that has been discharged from the high pressure side of the diaphragm to the low pressure side is drawn out through the outlet port 27 and returns to the low pressure reservoir 14 thereby increasing the pressure within the low pressure reservoir 14. However, because the volume of the high pressure side of the working chamber is much smaller than the volume of the reservoir 14 only a small increase in pressure occurs in the low pressure reservoir 14. After a number of applications of the brakes brought about by movement of the driver operable lever 23 the pressure in the high pressure reservoir 13 will fall to such a level that re-pressurisation is necessary and the clutch 30 is re-engaged causing the drive shaft 36a to be rotated.
The compressor 11 then reduces the pressure in the low pressure reservoir 14 by drawing air out from the reservoir 14 through the pipe 33 and supplying it to the high pressure reservoir 13 through the pipe 34 thereby increasing the pressure in the high pressure reservoir 13. This pumping action will continue until the pressure in the high pressure reservoir 13 returns to the predetermined level of pressure required for the system.
If necessary, additional air can be drawn through the inlet pipe 38 but this will not be normally necessary there being sufficient gas trapped within the system to permit the high pressure reservoir to be returned to its normal working pressure.
As soon as the high pressure reservoir 13 reaches its normal working pressure the clutch 30 is once again actuated thereby stopping the compressor 11.
It can therefore be seen that the pneumatic actuator system is a closedloop system in which air is increased in pressure one side of the circuit and reduced in pressure on the other side of the circuit by a common compressor.
One of the features of this arrangement is that once the system is initially charged with air via the inlet pipe 38 very little additional air is required as it is re-circulated through the system. This greatly reduces the amount of moisture within the system as fresh air is not continually being drawn in via the inlet pipe 38.
In addition, the exhaust from the compressor 11 discharges into the high pressure reservoir 13 and not to atmosphere thereby greatly reducing the associated noise.
A further feature is that when the brake pedal 23 is released the high pressure air is discharged back through the pipe 32 to the low pressure reservoir 14 and not to atmosphere. Once again, this greatly reduces the noise of the escaping gas which is a common problem with conventional air braking systems.
When the motor vehicle is not in use the valve assembly 16 is arranged to isolate the two reservoirs 13 and 14 from the actuator assembly 20 thereby maintaining the reservoir pressure and vacuum while the vehicle is parked. As soon as the ignition of the motor vehicle is re-activated the valve assembly 16 is operable to re-connect the pipes 31 and 32 to the reservoirs 13 and 14.
If the compressor 11 should for any reason fail the difference in volume between the two reservoirs 13,14 and the working chamber defined by the housing 22 is such that a number of operations of the braking system can be achieved to allow the vehicle to be brought to a safe halt. This can be extended by combining volumes in a low pressure/high pressure system when low differential indicates compressor failure and then exhausting to atmosphere.
Although the invention has been described with particular reference to a servo assisted braking system employing a diaphragm servo actuator member it will be appreciated that the push/pull principle could be applied to other pneumatic actuator systems. For example, the actuator assembly could be an air suspension unit for a motor vehicle.
In addition, it will be appreciated that the diaphragm described here above could be replaced by a piston located in a cylinder exposed to pressure at one end and vacuum at the other.
The compressor can be driven by any convenient means such as a belt drive or chain drive or can be electrically driven by an electric motor with control achieved using simple pressure and/or differential switch logic.

Claims (7)

  1. CLAIMS 1. A pneumatic actuator system comprising an actuator assembly having a housing, an actuator member movably located within the housing to define a high pressure chamber and a low pressure chamber, a high pressure reservoir connectable to the high pressure chamber and a low pressure reservoir connectable to the low pressure chamber, and a pump having an inlet side connectable to the low pressure reservoir and an outlet side connectable to the high pressure reservoir.
  2. 2. A system according to claim 1 wherein the two reservoirs are formed in n a single reservoir assembly and separated from each other by a common wall.
  3. 3. A system as claimed in claim 1 or claim 2 in which the pump is driven via a clutch controlled by the pressure in the high pressure reservoir.
  4. 4. A system as claimed in any foregoing claim in which the actuator member is a diaphragm sealingly connected to the housing.
  5. 5. A motor vehicle servo assisted braking system including a system according to any foregoing claim wherein the actuator member is arranged to assist in actuation of a vehicle brake.
  6. 6. A pneumatic actuator system substantially as described herein with reference to the accompanying drawing.
  7. 7. A motor vehicle servo assisted braking system substantially as described herein with reference to the accompanying drawing.
GB9925496A 1998-11-07 1999-10-29 A pneumatic actuator system Withdrawn GB2344389A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GBGB9824382.7A GB9824382D0 (en) 1998-11-07 1998-11-07 A pneumatic actuator system

Publications (2)

Publication Number Publication Date
GB9925496D0 GB9925496D0 (en) 1999-12-29
GB2344389A true GB2344389A (en) 2000-06-07

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GB9925496A Withdrawn GB2344389A (en) 1998-11-07 1999-10-29 A pneumatic actuator system

Family Applications Before (1)

Application Number Title Priority Date Filing Date
GBGB9824382.7A Ceased GB9824382D0 (en) 1998-11-07 1998-11-07 A pneumatic actuator system

Country Status (1)

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GB (2) GB9824382D0 (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102004047291A1 (en) * 2004-09-28 2006-03-30 Bayerische Motoren Werke Ag Braking force reinforcement system for motor vehicle, has brake booster utilizing pressure difference between lower pressure chamber and upper pressure chamber, where both chambers are provided by same pumping device
DE102008045713A1 (en) 2008-09-04 2010-03-18 Knorr-Bremse Systeme für Nutzfahrzeuge GmbH Compressed air unit for vehicle, has collector implemented in such manner that its pressure chamber stands under exhaust pressure from exhaust of valve unit
US20140144128A1 (en) * 2012-11-26 2014-05-29 Ford Global Technologies, Llc Brake booster assistance
WO2015092472A1 (en) 2013-12-18 2015-06-25 Volvo Truck Corporation Pneumatic actuator system and method for controlling such as system
IT201600132414A1 (en) * 2016-12-29 2018-06-29 Vhit S P A Soc Unipersonale Power unit for braking system

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB747216A (en) * 1953-03-04 1956-03-28 Bendix Westinghouse Automotive Improvements in or relating to fluid pressure supply systems, particularly for operating vehicle brakes
GB750999A (en) * 1954-03-17 1956-06-20 Westinghouse Brake & Signal Improvements relating to fluid pressure braking systems
WO1995031362A1 (en) * 1994-05-16 1995-11-23 Itt Automotive Europe Gmbh Brake system for motor vehicles with pneumatic brake booster

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB747216A (en) * 1953-03-04 1956-03-28 Bendix Westinghouse Automotive Improvements in or relating to fluid pressure supply systems, particularly for operating vehicle brakes
GB750999A (en) * 1954-03-17 1956-06-20 Westinghouse Brake & Signal Improvements relating to fluid pressure braking systems
WO1995031362A1 (en) * 1994-05-16 1995-11-23 Itt Automotive Europe Gmbh Brake system for motor vehicles with pneumatic brake booster

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102004047291A1 (en) * 2004-09-28 2006-03-30 Bayerische Motoren Werke Ag Braking force reinforcement system for motor vehicle, has brake booster utilizing pressure difference between lower pressure chamber and upper pressure chamber, where both chambers are provided by same pumping device
DE102008045713A1 (en) 2008-09-04 2010-03-18 Knorr-Bremse Systeme für Nutzfahrzeuge GmbH Compressed air unit for vehicle, has collector implemented in such manner that its pressure chamber stands under exhaust pressure from exhaust of valve unit
DE102008045713B4 (en) * 2008-09-04 2012-10-31 Knorr-Bremse Systeme für Nutzfahrzeuge GmbH Compressed air device of a vehicle with closed compressed air circuit
US20140144128A1 (en) * 2012-11-26 2014-05-29 Ford Global Technologies, Llc Brake booster assistance
US9663090B2 (en) * 2012-11-26 2017-05-30 Ford Global Technologies, Llc Brake booster assistance
WO2015092472A1 (en) 2013-12-18 2015-06-25 Volvo Truck Corporation Pneumatic actuator system and method for controlling such as system
IT201600132414A1 (en) * 2016-12-29 2018-06-29 Vhit S P A Soc Unipersonale Power unit for braking system

Also Published As

Publication number Publication date
GB9925496D0 (en) 1999-12-29
GB9824382D0 (en) 1998-12-30

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732E Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977)
WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)