GB2262580A

GB2262580A - Hydraulic anti-lock braking systems for vehicles

Info

Publication number: GB2262580A
Application number: GB9226614A
Authority: GB
Inventors: Alfred Yardley; Glynn Ashman
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1991-12-20
Filing date: 1992-12-21
Publication date: 1993-06-23
Anticipated expiration: 2012-12-21
Also published as: GB2262580B; GB9226614D0

Abstract

A hydraulic anti-lock braking system comprises a solenoid-controlled valve (7) which is normally closed to isolate a brake (2) from an expander chamber (10), a cut-off valve (4) which is normally open to permit free communication between the master cylinder (3) and the brake, and a restricted flow path including an orifice (15) between the pump and the brake. Movement of the valve (7) into an open position in response to a suitable anti-lock signal, during an anti-lock control mode, places the brake in communication with the expander chamber (10) to relieve the brake pressure, and the anti-lock signal causes operation of the pump which in turn causes closure of the cut-off valve (4) to isolate the master cylinder (3) from the brake (2). At the termination of the anti-lock signal, the valve (7) will close and the pump (9) will continue to operate, whilst the system remains in its anti-lock control mode, so as to re-apply the brake at a rate determined by the restricted flow path. In an alternative system (Fig. 4) the pump can also be operated during a traction control mode. <IMAGE>

Description

IMPROVEMENTS IN HYDRAULIC SYSTEMS FOR VEHICLES This invention relates to hydraulic systems for vehicles of the kind comprising an hydraulic master cylinder for applying a brake on a wheel, a speed sensor for sensing the speed of rotation of the wheel, modulator means for modulating the supply of fluid from the master cylinder to the brakes, an electronic control module which receives signals from the speed sensor and is operative to actuate the modulator means in turn to control operation of the wheel depending upon the nature and duration of the said signal, and a motor driven pump adapted to make up the volume of fluid dumped from a brake to an.expander chamber during an anti-lock mode so that the brake can be re-applied at a rate determined by the modulator means.

In some known systems of the kind set forth the modulator means comprise a solenoid-controlled fluid flow control valve incorporating a first orifice of fixed area, and a second orifice of variable area and of which the area is determined by a pressure drop across the first orifice in response to operation of the solenoid by the control module. For normal brake operation there is unrestricted fiow through the flow control valve between the master cylinder and the brake. Upon receipt of a signal indication of an incipient lock of a braked wheel the flow control valve isolates the master cylinder from the brake and fluid is dumped from the brake to the expander chamber from which it is withdrawn by the pump and returned to the brake for brake re-application at the termination of the anti-lock signal and at a rate determined by the second orifice.When the pump delivers fluid at a rate higher than that required to re-apply the brake, the excess is returned to the master cylinder. This results in large brake pedal movements during anti-lock operation, and a high power requirement for the pump since it has to start, and work against, master cylinder pressure, possibly 200 bar.

Fluid flow control valves for such systems are complex in construction and expensive to produce due to the tolerances which have to be maintained and the number of individual components required to construct asingle valve.

According to our invention in an hydraulic system of the kind set forth for vehicles the modulator means comprises a solenoid-controlled valve which is normally closed to isolate the brake from the expander chamber, a cut-off valve which is normally open to permit free communication between the master cylinder and the brake, and means defining a restricted flow path including a connection between the pump and the brake, movement of the solenoid-controlled valve into an open position in response to signals from the wheel sensor placing the brake in communication with the expander chamber to relieve the brake pressure accompanied by closure of the cut-off valve to isolate the master cylinder from the brake and in response to operation of the pump to re-apply the brake at a rate determined by the restricted flow path upon closure of the solenoid-controlled valve at the termination of the anti-lock signal.

Our system therefore depends for its operation on two valves, each of which is simple in construction and cheap to produce. Since the master cylinder is isolated from the brake in an anti-lock mode, a relatively low power pump can be utilised since the pump has to start and work only against brake pressure, normally 100 bar maximum.

The cut-off valve may comprise a pressure or flow responsive member, working in a bore in a housing, a spring normally holding the member in a retracted position to establish unrestricted communication between the master cylinder and the brake through a passage in the wall of the bore, and a pump orifice of fixed area in the member which establishes a pressure drop across the member sufficient to urge it into an advanced position against the spring to close the passage and isolate the master cylinder from the brake in response to a pressure differential which develops after the solenoid-controlled valve has been opened to relieve brake pressure to the expander chamber.

The pressure-responsive member may comprise a spool working in the bore in the housing, or alternatively a piston working in the bore in the housing. The piston is conveniently provided with low-friction PTFE seals.

The pressure differential may be developed in response to pressure generated by the pump.

Alternatively it may be developed by the release of fluid in the brake to the expander chamber with the spool then being retained in its advanced position by the pressure generated by the pump.

The pump orifice may be located between the pump and the brake. Alternatively it may be located in the supply line to the pump in order to throttle the supply to the pump and possibly also to maintain a pressure drop during pumping to maintain the cut-off valve in the closed position.

A dump orifice through which fluid is dumped from the brake to the expander chamber may also be provided to control the rate at which fluid is released from the brake.

The dump orifice may be disposed at any convenient location in the system. However, preferably, the dump orifice is incorporated in the cut-off valve itself.

In such a construction the housing and the spool are.

adapted to include a dump line through which. fluid is dumped from the brake to the expander chamber, and through which fluid can be withdrawn from the expander chamber by the pump.

The solenoid-controlled valve and the cut-off valve may be separate from each other or they may be combined together in a single assembly, conveniently within a common housing.

The system can also be adapted to apply the brake from the pump independently of the master cylinder for traction control of a spinning driven wheel.

Some embodiments of our invention are illustrated in the accompanying drawings in which: Figure 1 is a layout of an hydraulic system for a vehicle; Figure 2 is a layout of another system; Figure 3 is a detail of a layout similar to Figure 2 but showing a modification; Figure 4 is a layout similar to Figure 2 but showing a modification; and Figure 5 is a layout of a four channel system.

The system illustrated in the layout of Figure 1 comprises an anti-lock hydraulic braking system for a wheel 1 of a vehicle. The wheel 1 is provided with a brake 2 adapted to be applied by fluid from a master cylinder 3 which is supplied to it through a normally-open pressure-responsive cut-off valve 4 defining modulating means.

An electronic control module 5 receives signals from a wheel speed sensor 6 sensing the behaviour of the wheel 1 and is adapted to emit energising currents to control operation of a normally-closed solenoid-controlled valve 7 and an electric motor 8 for driving an hydraulic pump 9, for example a suction pump. The pump 9 is adapted to withdraw fluid from an expander chamber 10 and return it to the brake 2 through the isolation valve 4.

As illustrated the cut-off valve 4 comprises a housing 12 provided with a longitudinally extending bore 13 in which works a valve member 14 in the form of a spool. The spool 14 is of hollow piston configuration formed in its crown with a pump orifice 15, and having a skirt 16 which is adapted to close an annular passage 17 in the wall of the bore 13 as the spool 14 is moved axially in the bore 13 relatively away from a connection 18 from the pump 9 and against the loading in a return spring 19. A radial port 20 leading into the annular passage 17 is connected to the master cylinder.

In the inoperative position shown in the drawing the spool 14 is held in a retracted position by the spring 19 to permit open communication between the master cylinder 3 and the brake 2. The solenoid-controlled valve 7 is closed, and the motor 8 is de-energised to prevent the pump 9 from operating.

The brake 2 can therefore be applied for normal service braking by unrestricted flow of fluid from the master cylinder 3 and through the bore 13.

When the control module 5 receives a signal from the wheel speed sensor 6 which is indicative of an incipient lock of the wheel 1, the control module 5 emits current to energise the solenoid of the valve 7 to open the valve and simultaneously to energise the motor 8 to drive the pump 9. Fluid is released from the brake 2 to the expander chamber 10 and a pressure drop across the orifice 15 due to the difference in pressure between the fluid from the pump 9, which is withdrawn from the expander chamber, and the reducing brake pressure, urges the spool 14 into an advanced position against the force in the spring 19 to close the annular passage 17. This therefore isolates the master cylinder 3 from the brake.

Fluid is pumped by the pump 9 in a closed circuit at low pressure through the orifice 15, the valve 7 and the expander chamber 10 until the control module 5 senses that the wheel 1 has recovered. It then de-energises the solenoid to permit the valve 7 to close. This increases the pump pressure to re-apply the brake 2 at a rate determined by flow through the orifice 15.

The orifice 15 may be of a size suitable to achieve a pressure drop across the spool 14 sufficient for it to move into its advanced position. In a modification the orifice 15 may be smaller in size to enable the pump pressure to re-apply the brake 2 at a rate determined by flow through it. In such a modification a one-way valve set at a given valve controls a return line to the master cylinder 3 through which any excess fluid can be returned to the master cylinder 3.

So long as fluid is present in the expander chamber 10, the pump 9 will continue to deliver fluid through the pump orifice 15, until all the -fluid has been scavenged from the expander chamber 10. The stored energy in the spring 19 is released to return the spool 14 into its retracted position and re-establish communication between the master cylinder 3 and the brake 2. Additionally should the pump stop at any point during the cycle, the spring 19 will act in the manner described above.

Should the pump 9 cease to function for any reason, the spring 19 automatically re-sets the valve 4 to re-connect the master cylinder 3 to the brake 2.

In the system shown in the layout of Figure 2 the solenoid-controlled valve 7 and the cut-off valve 4, which is flow controlled, are combined into a single modulator valve assembly 30, and one-way valves 28 and 29 are located on the supply and delivery sides of the pump 9.

The modulator valve assembly 30 comprises a common housing 31 for the valve 7 and the valve 4.

The housing 31 has a longitudinally extending bore 32 in which a sleeve 33 is located, and a spool 34 is guided to slide in the bore of the sleeve 33 between retracted and advanced positions. The sleeve 33 is provided with axially spaced radial ports 35, 36 and 37 connected to the expander chamber 10, the master cylinder 3, and the brake 2, respectively. An external branch line 38 also connects the brake 2 to the inlet of the valve 7 through a passage 39 in the housing 31.

The spool 34 has a longitudinal through-bore 40 which connects with the passage 35 through a diametral passage 41 and an annular passage 42 in the wall of the spool 34. The spool 34 also has a second annular passage 43 in its wall which is spaced from the passage 42 by a land 47. The passage 43 interconnectsthe passage 36 and 37 when the spool 34 is held in the retracted position shown in engagement with a stop face 44 by the force in a return spring 45. The stop face 44 surrounds a central passage 46 which leads into the solenoid-controlled valve 7.

A pump orifice 50 and a dump orifice 51 are provided at opposite ends of the spool 34 in discs which otherwise close opposite ends of the through-bore 40, and the return spring 45 acts on the spool 34 through the disc containing the pump orifice 50.

A one-way valve 52 permits fluid to be returned to the master cylinder 3 from the brake 2 but prevents flow in the opposite direction.

When the spool 34 is in its retracted position unrestricted communication is provided between the master cylinder 3 and the brake 2 through the annular passage 43. In this position the solenoid-controlled valve 7 is closed.

When the control module 5 receives a signal from the wheel speed sensor 6 which is indicative of an incipient lock of the wheel 1, the control module 5 opens the valve 7 and energises the motor 8 to drive the pump 9. Fluid is released from the brake 2 towards the expander chamber 10 through the branch line 38, the open valve 7, and the dump orifice 51. The pressure drop across the orifice 51 causes the spool 34 to move rapidly away from the stop face 44 against the load in the spring 45 and into a latched position in which the land 47 closes the passage 36 to isolate the master cylinder 3 from the brake 2. The spool 34 moves rapidly into the latched position because of the presence of fluid released from the brake 2 acting on the end of the spool 34 adjacent to the stop face 44 and the action of the pump 9.

The release or de-boost of a relatively small initial volume of f fluid, say 10% of the volume applied to the brake 2, is accommodated by the movement of the spool 34 away from the stop face 44.

Thereafter, after the spool 34 has reached the latched position, if necessary further fluid is released from the brake 2 to the expander chamber 10 through1 at a rate determined by, the orifice 51.

During this operation the pump 9 draws fluid from the through bore 40, through and at a rate determined by the pump orifice 50, the pressure drop across which augments the force holding the spool 34 in the latched position, and throttles the inlet side of the pump 9.

The withdrawn fluid is pumped back to the brake 2 and thence through the brake passage 38 to be returned to the through-bore 40 through the open valve 7.

When the control module 5 senses that the wheel 1 has recovered, it de-energises the element so that the valve 7 closes. Thereafter the pump 9 continues to withdraw fluid from the expander chamber 10 at a rate determined by the throttling of the inlet side of the pump 9 to apply the brake 2, and scavenges the expander chamber 10. When the expander chamber 10 is empty, the differential acting on the spool 34 disappears and the spool 34 is returned to its retracted position by the force in the spring 45, in turn re-connecting the master cylinder 3 to the brake 2.

Thus the dump rate is determined by flow through the dump orifice 51, and the re-application rate is determined by the throttling effect of the pump orifice 50.

Upon release; of the master cylinder 1, fluid can be returned to it through the one-way valve 52, irrespective of the position of the spool 34 in its bore.

The construction and operation of the system of Figure 2 is otherwise the same as that of Figure 1 and corresponding reference numbers have been applied to corresponding parts.

The system illustrated in the layout of Figure 3 is similar to that of Figure 2, but showing a modification to the modulator valve assembly.

In Figure 2, a sleeve 33 is located in a bore 32 and a spool 34 is guided to slide in the bore of the sleeve 33 between retracted and advanced pistons. In Figure 3, the spool has been replaced by a piston 53.

The piston is essentially of similar construction to the spool in terms of its connections and the like, however, instead of the sealing areas provided for by the spool, the piston is provided with low-friction PTFE seals 55 backed by elastomeric seals 56.

The construction and operation of the system of Figure 3 is otherwise the same as that of Figure 2 and corresponding reference numerals have been applied to corresponding parts.

The system illustrated in the layout of Figure 4 is similar to that of Figure 2 but has been adapted to provide traction control when the wheel 1 comprises a driven wheel of the vehicle and the brake 2 is to be operated independently of the master cylinder 3.

As illustrated in Figure 4 of the drawings a second solenoid-control valve 60 is located in the line between the master cylinder 3 and the passage 36. The inlet side of the valve 60 is also connected to the pump 9 through a one-way valve 61, which functions in a similar manner to the one-way valve in the return line as described above with reference to Figure 1 of the accompanying drawings. A pressure-responsive isolator valve 62 is located between the master cylinder 3 and the expander chamber 10. The isolator valve 62 is urged into a closed position when the master cylinder is operated. Normally the second solenoid-controlled valve 60 is open with the solenoid de-energised.

To apply the brake 2 for traction control when the wheel 1 is spinning, a signal from the control module 5 closes the valve 60 and starts the pump 9. Since the master cylinder 3 is not operated, the valve 62 is open. Since there is no fluid in the expander chamber 10 the pump 9 withdraws fluid from the reservoir for the master cylinder 3, through the master cylinder itself, through the open isolator valve 62, and the orifice 50. The pump 9 delivers fluid to the brake 2 to apply the brake and reverse flow to the master cylinder 3 is prevented by the closed valve 60.

Should the pressure exceed a given valve determined by the setting of the one-way valve 61, then the valve 61 will open so that any excess fluid can be returned to the master cylinder 3.

The construction and operation of the system of Figure 4 is otherwise the same as that of Figure 2 and corresponding reference numbers have been applied to corresponding parts.

Figure 5 of the drawings shows a layout of a 4-channel braking system showing how the system of Figure 2 can be adapted to provide independent control of each brake of a vehicle. Each channel is identified by FR and FL for the front right and front left wheels, and RR and RL for the rear right and rear left wheels, and appropriate reference numerals have been applied to the channel FR.

A single motor 70 is adapted to drive a pair of hydraulic pumps 71, 72, and each pump 71, 72 incorporates two independent pump chambers, each incorporated in the respective channel for a respective one of the two pairs of wheels.

If traction control is required, the channels for the driven wheels, say the channels FR and FL, will be adapted to correspond to the system shown in the layout of Figure 4.

The arrows A indicate flow to and from the brakes and the arrows B indicate flow to and from the master cylinder.

Claims

l. An hydraulic system of the kind set forth for vehicles in which the modulator means comprises a solenoid-controlled valve which is normally closed to isolate the brake from the expander chamber, a cut-off valve which is normally open to permit free communication between the master cylinder and the brake, and means defining a restricted flow path including a connection between the pump and the brake, movement of the solenoid-controlled valve into an open position in response to signals from the wheel sensor placing the brake in communication with the expander chamber to relieve the brake pressure accompanied by closure of the cut-off valve to isolate the master cylinder from the brake and in response to operation of the pump to re-apply the brake at a rate determined by the restricted flow path upon closure of the solenoid-controlled valve at the termination of the anti-lock signal.
2. A system as claimed in claim 1, in which the cut-off valve comprises a pressure or flow responsive member working in a bore in a housing, a spring normally holding the member in a retracted position to establish unrestricted communication between the master cylinder and the brake through a passage in the wall of the bore, and a pump orifice of fixed area in the member which establishes a pressure drop across the member sufficient to urge it into an advanced position against the spring to close the passage and isolate the master cylinder from the brake in response to a pressure differential which develops after the solenoid-controlled valve has been opened to relieve brake pressure to the expander chamber.
3. A system as claimed in claim 2, in which the pressure or flow responsive member comprises a spool working in the bore in the housing.
4. A system according to claim 2, in which the pressure or flow responsive member comprises a piston working in the bore in the housing.
5. A system according to claim 4, in which the piston.

is provided with low-friction PTFE seals.
6. A system as claimed in any preceding claim, in which the pressure differential is developed in response to pressure generated by the pump.
7. A system as claimed in any of claims 1 to 3, in which the pressure differential is developed by the release of fluid in the brake to the expander chamber with the member then being retained in its advanced position by the pressure generated by the pump.
8. A system as claimed in any preceding claim in which the pump orifice is located between the pump and the brake.
9. A system as claimed in any of claims 1 to 7, in which the pump orifice is located in the supply line to the pump in order at least to throttle the supply to the pump.
10. A system as claimed in claim 9, in which the pump orifice also maintains a pressure drop during pumping to maintain the cut-off valve in the closed position.
11. A system as claimed in any preceding claim in which a dump orifice through which fluid is dumped from the brake to the expander chamber is also provided to control the rate at which fluid is released from the brake.
12. A system as claimed in claim 11, in which the dump orifice is incorporated in the cut-off valve itself.
13. A system as claimed in claim 12, in which the housing and the spool are adapted to include a dump line through which fluid is dumped from the brake to the expander chamber, and through which fluid can be withdrawn from the expander chamber by the pump.
14. A system as claimed in any preceding claim in which the system is adapted to apply the brake from the pump independently of the master cylinder for traction control of a spinning driven wheel.