GB2267544A

GB2267544A - Improvements in hydraulic braking systems for vehicles.

Info

Publication number: GB2267544A
Application number: GB9307602A
Authority: GB
Inventors: Glyn Philip Reginald Farr
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1992-04-14
Filing date: 1993-04-13
Publication date: 1993-12-08
Anticipated expiration: 2013-04-13
Also published as: DE4312118C2; GB2267544B; DE4312118A1; GB9307602D0

Abstract

An hydraulic braking system for a vehicle provided with an intelligent cruise control system including a radar device (23), and an electronic control module (24) for differentiating cruise control signals and emitting electric currents, is disclosed. In the system an hydraulic pump (25) is operable in response to cruise control signals to pressurise the primary pressure space (8) of a master cylinder (1), whereby to apply the brakes on all the wheels by operating primary actuators (15, 17) directly and secondary actuators (19, 21) indirectly, following closure of an isolating valve (28) in a return line (12) from the primary pressure space (8) to the reservoir (10) of the master cylinder. A sensor (27) limits the rate of deceleration achieved by operation of the pump. Alternative embodiments include anti-lock and traction control. <IMAGE>

Description

2267544 IMPROVEMENTS IN HYDRAULIC BRAKING SYSTEMS FOR VEHICLES This

invention relates to hydraulic braking systems for vehicles comprising an hydraulic tandem master cylinder for applying the brakes on all wheels of a vehicle, the master cylinder having a primary pressure space, and a secondary pressure space, which are both normally fed from a reservoir for fluid through primary and secondary recuperation valves which are adapted to close when the master cylinder is operated by a pedal, in which the primary pressure space is connected to wheel primary brake actuators with which it forms a primary brake circuit, and the secondary pressure space is connected to wheel secondary brake actuators with which it forms a secondary brake circuit.

There is a requirement to apply automatically the brakes of a moving vehicle when it is equipped with an intelligent cruise control system to enable the vehicle automatically to follow another vehicle at a substantially constant time interval. Thus as the lead vehicle increases speed, the distance between the two vehicles lengthens automatically. Similarly when the lead vehicle slows down, the separation distance is shortened.

To provide automatic braking, the vehicle with the cruise control system must be equipped with automatic means to apply pressure to the -brakes automatically. This can be achieved with a special vacuum servo, for example as disclosed in EP-A-0 303 470. This ensures that all the brakes are applied with substantially equal pressures. This is achieved byapplying a force to the master cylinder to generate pressure in the 2 primary pressure space, in turn to act upon the secondary piston and provide a substantially equal pressure in the secondary chamber.

In use vacuum servo systems of the kind disclosed in EP-A-0 303 470 may cause undesirable pedal movement in operation.

According to our invention in an hydraulic system of the kind set forth for a vehicle provided with an intelligent cruise control system, and an electronic control module for differentiating cruise control signals and emitting electric currents, hydraulic pressure means is operable in response to cruise control signals to pressurise the primary pressure space of the master cylinder, whereby to apply the brakes on all the wheels by operating the primary actuators directly and the secondary actuators indirectly, following closure of an isolating valve in a return line from the primary pressure space to the reservoir of the master cylinder.

The brakes are therefore applied automatically in response to such signals whereby to maintain a desired braking distance between the vehicle and the lead vehicle for a given vehicle speed.

The isolating valve may comprise a solenoid-controlled valve disposed in the return line to the reservoir. Thus, when the pressure means is operated in response to an electric current emitted from the control module. the solenoid-controlled valve is also closed by the electric current to prevent fluid from being returned to the reservoir from the primary pressure space.

3 The hydraulic pressure means may comprise an hydraulic pump operable by energisation of an electric motor in response to an electric current emitted from the control module. In such a construction closure of the s olenoid- controlled valve prevents fluid from being returned to the reservoir through the return line as fluid is, itself, withdrawn from the reservoir by the pump through a supply line.

Alternatively the hydraulic pressure means may comprise an hydraulic accumulator. In such a construction a normally-closed second solenoid-controlled supply valve is disposed in a line to the primary pressure space, and is operable 'in sequence with the isolating valve, which is normally open.

The fluid for the pressure means may be supplied directly into the primary space through the supply valve. Alternatively it may be supplied to the chamber in front of or behind the primary pressure space, to pressurise that chamber and the primary pressure space through a primary recuperation valve in the primary piston which remains open since the primary piston is held in a retracted position.

All the brakes are therefore applied simultaneously and independently of the pedal.

Operation of the pedal is sensed by an electrical switch which is operative to de-energise the pump and the solenoid-operated isolating valve and render the hydraulic pressure means inoperative. Operation of the pedal therefore overrides automatic application of the brakes by the hydraulic pressure means.

4 The response period for operating the brakes automatically is extremely small and brake application and release is substantially instantaneous upon receipt of an appropriate signal.

Since we pressurise the primary pressure space of the master cylinder to initiate operation of the master cylinder itself, the secondary or floating piston of the master cylinder acts to equalise the pressures in the two primary and secondary brake circuits in a similar manner to that which occurs when the master cylinder is operated by the pedal.

The pressure applied to each primary and secondary brake circuit by the hydraulic pressure means is adapted to increase up to a value determined by vehicle deceleration. This value is measured directly from a sensor sensing acceleration of the vehicle or, alternatively, indirectly from wheel speed information.

Our invention enables the brakes to be applied automatically whenever the time interval between the lead vehicle and the follower vehicle is reduced below predetermined limits.

When the hydraulic braking system is of the anti-lock (ABS) type the antilock pump may comprise the pump for automatically applying the brakes in response to cruise control signals. In such a system the solenoidcontrolled valve controlling the return line is closed whenever the brakes on the front wheels of the vehicle are being controlled. Thus surplus fluid from the front wheel brakes is pumped into the master cylinder and into the rear brakes to raise the pressure level so that fluid trapped within the annulus behind the primary piston of the master cylinder also rises and prevents an adverse pedal reaction at the driver's foot.

In the automatic braking system of the present invention the pressure levels in both primary and secondary brake circuits is raised to prevent brake intervention in combination with an anti-lock system which isolates or connects the relevant wheels in accordance with anti-lock signals emitted by sensors on the respective wheels.

Preferably the s olenoid- controlled isolating valve is spring-loaded to ensure a maximum generated pressure in the primary brake circuit. The solenoid-controlled isolating valve is therefore closed whenever a brake application immediately follows an automatic application in response to a signal from the brake pedal. Similarly the solenoid-controlled isolating valve is opened following a signal which indicates that manual actuation of the brakes by the pedal has been released.

The system is adapted to apply the brakes, or at least some of the brakes, whenever the vehicle is to be held on an upwardly facing hill. When the traction force exceeds the holding force, the brakes are released to enable the vehicle to be driven away.

During anti-lock control surplus fluid from the front wheel brakes is directly or indirectly utilised by the motor-driven pump to intensify the pressure applied to the rear wheel brakes.

Some embodiments of our invention are illustrated in the accompanying drawings in which:- 6 Figure 1 is a layout of an 'X'-split hydraulic braking system for a vehicle; Figure 2 is a layout similar to Figure 1 but showing a modification; Figure 3 is a layout similar to Figure 1 showing another modification; Figure 4 is a layout of an anti-lock hydraulic braking system for a four- wheel vehicle; Figure 5 is a detailed section through the solenoid-controlled valve of Figure 4; Figure 6 is a layout of a braking system similar to Figure 1 but showing a front/rear split; Figure 7 is a layout similar to Figure 4 but showing a fourchannel antilock system; Figure 8 illustrates a portion of a system similar to Figure 4 but showing a modification.

Figure 9 is similar to Figure 8 but showing a modification; and Figure 10 shows a portion of yet another system The hydraulic braking system illustrated in the layout of Figure 1 of the accompanying drawings is of the 'X' split type.

An hydraulic master cylinder 1 comprises a housing 2 having a longitudinally bore 3 in which works a primary piston 4 adapted to be operated by a pedal 5, and a secondary or floating piston 6 disposed between 7 the inner end of the primary piston 4 and a closure or end wall 7 for the end of the bore 3 remote from the pedal 5. A primary pressure space 8 is defined in the bore 3 between the two pistons 4 and 6, and a secondary pressure space 9 is defined in the bore between the secondary or floating piston 6 and the end wall 7. The primary pressure space 8 is in communication in the off position of brake with a reservoir 10 for fluid through a normally-open recuperation valve 11 and a return line 12, and the secondary pressure space 9 is in communication with the reservoir through a normally-open recuperation valve 13.

The primary pressure space 8 is connected to an actuator 15 for a brake on one front wheel 16 of the vehicle and to an actuator 17 for a brake on the diagonally opposite rear wheel of the vehicle. The pressure space 8 and the two brakes defines a primary brake circuit.

The secondary pressure space 9 is connected to an actuator 19 for a brake on the other front wheel 20 of the vehicle, and to an actuator 21 of a brake on the diagonally rear wheel 22 of the vehicle. The secondary pressure space and the brake actuators 19 and 21 comprise a secondary brake circuit.

The system incorporates intelligent control means comprising a radar device 23 for sensing the distance and speed of a lead vehicle, and an acceleration/deceleration sensor 27. Signals from the device 23 and the sensor 27 are supplied to an electronic control module 24. The electronic control module is adapted to emit electrical energising currents in accordance with signals received from the radar device 23 and the sensor 27.

8 An hydraulic pump 25 is adapted to be driven by an electrical motor 26 in response to an electrical current from the electronic control module 24 in order to withdraw fluid from the reservoir 10 and pump it to the primary brake circuit including the primary pressure space 8.

An isolator valve comprising a solenoid-controlled valve 28 is located in the return line 12 in order to isolate the pressure space 8 from the reservoir and through the normally open recuperation valve 11 when the motor 26 is energised.

An electrical inhibit switch 29 is associated with the pedal 5.

When the brakes are operated normally for service braking, operation of the pedal advances the primary piston 4 in the bore initially to close the recuperation valve 11 to isolate the primary pressure space 8 from the reservoir 10. Further movement of the primary piston 4 in the same direction acts to advance the secondary piston 6 in the bore 3 and close the secondary recuperation valve 13 to isolate the secondary pressure space 9 from the reservoir. The brakes in both primary and secondary brake circuits are thereafter applied simultaneously and at equal pressures since the pressures are equalised by compensating movement of secondary piston 6 in the bore 3.

When the pedal is released the pistons 4, 6 return to their original operative positions by the effects of primary and secondary return springs, and return paths to the reservoir 10 are opened through the recuperation valves 11 and 13.

9 During normal operation of the master cylinder a signal from the switch 29 inhibits operation of the electronic control module 24 irrespective of whether it receives signals from the radar device 23 or the driver has selected auto-cruise. In consequence the isolator valve 28 is also deenergised and is held in an open position by a return spring to provide free communication through the return line 12 from the primary pressure space 8 to the reservoir 10.

When the vehicle is moving along a road and is in a position with a lead vehicle ahead of it and the driver selects automatically to follow, the relative speed of the lead vehicle and the distance between it and the following vehicle are sensed by the radar device 23 which sends a signal to the electronic control module 24. When the signal is recognised by the electronic control module 24 as being such that corrective action needs to be taken to maintain the relative speed and distance between the two vehicles within predetermined limits, an electrical current from the electronic control unit 24 energises the motor 26 and causes the solenoidcontrolled valve 28 to close. The pump 25 withdraws fluid from the reservoir 10 and pumps it into the primary brake circuit to raise the pressure in that circuit since the return line 12 to the reservoir 10 is closed by the solenoid- controlled valve 28. Specifically fluid is pumped to the actuators 15 and 17 and into the primary pressure space 8 through the normal outlet port connected to the actuators 15 and 17. An increase in pressure in the pressure space 8 is transmitted to the secondary or floating piston 6 which, in turn, is advanced in the bore 3 as described above to close the recuperation valve 30 and pressurise the fluid in the secondary pressure space 9 and the secondary brake circuit. The brakes on all four wheels are therefore applied simultaneously and at equal pressures due to the equalising effect of the secondary piston 6 as described above. The pressure in the pressure space 8 acts on the primary piston 4 to hold it against its back stop. Thus no reaction is transmitted to the pedal.

When sufficient pressure has been generated by the pump 25, the motor 26 driving the pump stops.

After the brakes have been applied for a time sufficient to increase the distance between the vehicle and the lead vehicle to the required limit, the electronic control module 24 de-energises the motor 26. The brake applying pressure from the pump 25 ceases, and pressure from the brakes is relieved from the pressure spaces 8 and 9 and back to the reservoir 10 as a consequence of pulsing or opening the valve 28 to restore the return line 12.

During automatic application of the brakes in response to a signal from the radar sensing device 23, the acceleration/deceleration sensor 27 is operative to limit the rate of deceleration which is achievable.

In the braking system illustrated in the layout of Figure 2 a second solenoid-controlled valve 30, also operable in response to signals from the control module 24, is disposed in a supply line 31 between the reservoir and the inlet side of the pump 25.

In this system a solenoid-controlled valve 30 is normally open so that fluid can be withdrawn from the reservoir 10 and pumped to the primary brake circuit to apply the brakes automatically. However, as soon as pressure in the primary brake circuit has been increased by the pump to a given maximum value, the electronic control module 24 is operative to cause the solenoid-controlled valve 30 to close. This isolates the reservoir from the pump 25 and prevents fluid reaching the pump 25.

The construction and operation of the system illustrated in Figure 2 of the drawings is otherwise the same as Figure 1 and corresponding reference numerals have been applied to corresponding parts.

In the system illustrated in the layout of Figure 3 of the accompanying drawings, a solenoid-controlled valve 32 is located between the outlet from the pump 25 and the primary brake circuit, with a relief valve 33 located between the pump outlet and the reservoir 10.

In operation, upon the fluid in the primary brake circuit being pressurised to a given value, the solenoid-controlled valve 32 is closed by the electronic control module 24, and fluid from the pump outlet is returned to the reservoir 10 in a closed circuit following opening of the relief valve 33.

The construction and operation of the system of Figure 3 is otherwise the same as that of Figure 1 and corresponding reference numerals have been applied to corresponding parts.

The braking system illustrated in the layout of Figure 4 of the accompanying drawings is of the 'X'-split type and incorporates an antilock (ABS) modulator 40 of known construction and of the four-channel type.

12 As illustrated the modulator 4 comprises a solenoidoperated inlet valve 41,42,43,44 and a solenoid-operated exhaust valve 41a, 42a, 43a, 44a for controlling the operation of the brake on each wheel 20,16,18,22, respectively, an expander chamber 45 into which fluid can be released from a brake to relieve the pressure applied to that brake, and a pump 46 driven by an electric motor 47 for withdrawing fluid from the expander chamber 45 and pumping it back to re-apply a brake on a wheel following correction of the behaviour of that wheel.

A wheel speed sensor 50,51,52 and 53 is associated with each respective wheel 20,16,18,21.

As in the system of Figure 2 the solenoid-controlled valve 28 is incorporated in the line 12 and the second solenoid-controlled valve 30 is located between the reservoir 10 and the inlet to the pump 46.

The solenoid-controlled valve 28 is shown in detail in Figure 5 of the drawings. As illustrated a valve member 60 coupled to, and relatively moveable with respect to, an armature 61 is normally held away from a seating 62 leading to the primary pressure space 8 when a solenoid 63 surrounding the armature is de-energised. Thus, when the solenoid 63 is de-energised, the valve is held in an open position. When the solenoid 63 is energised the armature 61 is moved relatively towards the valve seat 62, in turn to urge the valve member 60 into engagement with the valve seat 62 thereby isolating the pressure space 8 from the reservoir 10. Any excess movement of the armature 61 towards the valve seat 62 is accommodated by relative movement between the armature 61 and the valve 13 member 60 itself due to compression of a lost-motion spring 64.

In normal operation of the system of Figure 4 all the s olenoidcontrolled valves 28,30,41 to 44 and the motor 47 are normally de-energised. Unrestricted communication is therefore provided between the pressure spaces 8 and 9 and the brakes on the four wheels of the vehicle.

Should a wheel speed sensor, say the sensor 52, sense the approach of an incipient wheel lock condition, the signal from the sensor 52 causes the electronic control module 24 to emit an energising current. This operates the solenoid valve 43 in order to isolate the brake actuator 17 from the master cylinder, and the solenoid-operated valve 43a, to place the actuator in communication with the expander chamber 45 into which fluid from the brake is dumped. The pump 46 withdraws fluid from the expander chamber and, following operation of the solenoid-controlled valve 43 to re-connect the actuator 17 to the master cylinder at the termination of the anti-lock signal, is operative to make-up the volume of fluid dumped from the brake.

Whenever a driven wheel connected to the secondary pressure space 9, say the wheel 19, tends to spin, a signal from the wheel speed sensor 50 causes the electronic control module to close the solenoid- controlled valves 42,43 and 44 so the pressure from the master cylinder is applied to the brake actuator 19 in order to apply the brake on that wheel only for traction control. Following traction control, pressure is released from the actuator 19 to a secondary expander chamber (not shown) and a secondary 14 pump (not shown), returns fluid back to the second pressure space 9. When the front wheel 16 spins, fluid from the reservoir 10 is pumped into the primary pressure space 8. As the primary recuperation valve 11 remains open, no damage is incurred when the first solenoid-controlled valve opens to relieve primary circuit pressure when the wheel 16 is again fully controlled.

Should a wheel spin correction be immediately followed by a brake application with fluid still retained in the expander chamber 45, a positive pressure will still exist in the primary pressure space 8 when the brakes are released. To avoid damage to the primary recuperation valve 11, the first solenoid- controlled valve 28 is closed again should a brake application immediately follow a wheel spin correction. This is signalled from the brake light switch. On release, fluid trapped in an annular chamber 55 between the s olenoid- controlled valve 28 and the recuperation valve 11 flows via the recuperation valve 11 until the brake light is switched off. At this point the primary recuperation valve 11 is open and the metal seated first solenoid-controlled valve 28 can now be opened to release pressure. This sequence will permit the inclusion of a conventional rubber faced recuperation valve for the primary pressure space 8. Thus both primary and secondary brake circuits can incorporate preferred rubber faced recuperation valves 11 and 13.

With a conventional braking system, front wheels tend to lock before rear wheels so that in the event of an ABS failure, a sideways skid is prevented. This requirement under-utilises the contribution to stopping which can be made from the brakes on the rear wheels 18, 22, particularly when the average driver does not press harder to increase rear pressure when the pedal 5 vibrates whilst the front wheel 20, 16 are being controlled. The ability to trap f luid in the annular chamber 55 can be used beneficially in an anti-lock (ABS) mode.

When the brakes are applied in an emergency situation and the front wheel brakes are controlled by the ABS, the first solenoid- controlled valve 28 closes to trap fluid in the annular chamber 55. The motor driven pump 46 is energised and fluid, dumped into relevant expander chambers, is pumped back into the master cylinder 1. At the same time, fluid is admitted to re-apply the brakes on the front wheels 20, 16 but surplus fluid increases the pressure in the master cylinder 1 and the rear brakes. Thus fluid trapped in the annular chamber 55 is compressed. This acts as a buffer chamber between the master cylinder and the driver, and pedal feel is greatly improved. In addition the rear wheel brakes act as an accumulator to smooth out cyclic pulses of the pump 46.

The relationship between the master cylinder pressure and the pressure in the annular chamber 55, assuming a front skid pressure of 15 bar and an applied pressure of 20 bar from an input force of 40 Newtons is shown below:- MASTER CYLINDER ANNULAR CHAMBER + INPUT (PRESSURE X AREA) (PRESSURE X AREA) (FORCE) x 2 0 X 1 + 40 x 2 20 x 1 + 40 x 2 40 x 1 + 40 16 For this example, the ratio of the areas of the master cylinder to annular chamber 55 is 2:1.

It will be noted that the master cylinder pressure and the pressure applied to the rear wheel brakes can increase from 20 to a maximum of 40 bar without any increase in input force. The front wheel brakes are controlled at 15 bar by ABS. The automatic increase in rear brake pressure when the fronts are controlled is beneficial because the available road friction is better utilised and more weight is transferred onto the more powerfully braked front wheels.

For holding a stationary vehicle on an upwardly faced hill the brakes, or the brakes on one axle, are automatically applied by the use of the intelligent cruise control system, as described above. The driver can now release the brake pedal 5 in readiness to move away. When the forward traction force exceeds the brake holding force, the first solenoidcontrolled valve 28 opens to release brake pressure.

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

The braking system illustrated in the layout of Figure 6 is a front/rear split with the brakes on the rear wheels 18, 22 being applied from the primary pressure space 8 with which they form the primary brake circuit, and the brakes on the front wheels 20 and 16 being applied from the secondary pressure space 9 and with which they form the secondary brake circuit.

As in the embodiment of Figure 1, the primary brake circuit can be pressurised to provide direct automatic vehicle retardation and with the brake on the front wheel 20 and 16 being applied indirectly from the second pressure space 9.

The construction and operation of the braking system of Figure 6 is otherwise the same as that of Figure 1 and corresponding reference numerals have been applied to corresponding parts.

The braking system illustrated in Figure 7 of the accompanying drawings is similar to Figure 6 except that it incorporates an anti-lock modulator assembly 80 similar in construction to the modulator assembly 40 of the system of Figure 4 of the accompanying drawings, with the system also incorporating the second solenoid-controlled valve 30.

The system provides intensification of pressure applied to the brakes on the rear wheels 18 and 22 when the front wheels 20, 16 are being subjected to anti-lock control.

In a modification, if the brakes on the front wheels 20 and 16 are incorporated into the primary circuit. the brakes on the rear wheels 18, 22 are intensified as before. However if the brakes on the front wheels 20 and 16 are connected to the secondary pressure space 19, as shown, the surplus fluid from the brakes on the front wheels 20, 16 is pumped into the secondary pressure space 9, and the secondary or floating piston 6 moves back towards the pedal 5 indirectly to intensify the pressure applied to the brakes on the rear wheels 18 and 22. The brake intervention as before is possible for front or rear 18 with single axle drive or front and rear with four wheel drive.

The construction and operation of the braking system of Figure 7 is otherwise the same as that of Figure 4 and corresponding reference numerals have been applied to corresponding parts.

Figure 8 of the accompanying drawings shows an hydraulic master cylinder similar to, and to replace, the master cylinder of the braking system of Figure 4, and appropriate control valves. Corresponding reference numerals have been applied to corresponding parts of the master cylinder.

In the system of Figure 8, the reservoir isolator valve 28 is disposed in a line between the reservoir 10 and a normal recuperation port 81, through which the primary pressure space 8 is supplied with fluid from the reservoir 10 through the recuperation valve 11, when it is open. A further solenoid-controlled accumulator valve 82 is disposed in a line between an hydraulic accumulator (not shown) and the port 81.

For normal brake operation the valve 28 is open and the valve 82 is closed.

When the brakes are to be applied independently of pedal operation of the master cylinder for establishing and maintaining a desired distance between the vehicle and a vehicle in front of it, the valve 28 is energised to cause it to close, and the solenoid of the valve 82 is pulsed to apply fluid to the primary circuit comprising the actuators 17 and 21 through the open recuperation valve 11 and a primary supply port 83. At the same time the secondary piston 6 is advanced in the 19 bore 3 to apply the secondary circuit comprising the actuators 19 and 15 through a secondary supply port 84. The secondary piston 6 ensures that the pressures applied to both circuits are substantially equal.

When the correct distance to the lead vehicle is established, the valve 82 is closed and the valve 28 is opened or pulsed to release the braking force.

Should the driver apply the brakes during automatic braking, the accumulator valve 82 is closed and the reservoir valve 28 opens. Brake pressure is applied by the master cylinder as soon as the recuperation valve 11 closes against the secondary piston 6. This enables most of the surplus fluid (i.e. fluid not provided by the master cylinder) to escapeback to the reservoir. The secondary piston 6 supplies its own fluid to the secondary circuit, so it does not receive surplus fluid.

With existing hydraulically operated systems, both master cylinder pistons 8, 6 remain stationary when the surplus fluid is introduced, so that when brakes are applied manually by pedal operation of the master cylinder, the initial movement of the master cylinder pistons 8, 6 will close the recuperation valves 11, 13. This does not allow sufficient time for surplus fluid to escape from either braking circuit. A subsequent operation of the ABS may, therefore, force fluid back into the master cylinder and the recuperation valves 11, 13 may have to open (against the applied pressure) to release some or all of the surplus fluid. It is under these circumstances that damage to the recuperation valves will occur.

During automatic braking, the secondary piston 6 moves away from the primary recuperation valve 11 so that the primary pressure chamber 8 and reservoir chambers are connected. Thus the recuperation valve 11 remains open so that damage to it is avoided.

Similarly if one of the drive wheels starts to spin, because the vehicle is on an incline on a surface with differing friction beneath the drive wheels, the solenoids of the valves 28 and 82 are energised to apply both circuits. In this case, the ABS modulator 40 isolates the non-driven and the non-spinning wheel and connects pressure to the wheel which has started to spin. In consequence, useful torque is transmitted to the wheel on the better surface and the vehicle can be driven away.

The advantage of having the solenoid valves 78, 82 connected to the master cylinder tank inlet 81 is that they are both isolated from the hydrostatic braking system whenever the brakes are applied normally and the integrity of the braking system is not jeopardised. Another advantage is that the primary pistons 8 is held firmly on its backstop so that na movement occurs at the brake pedal.

As illustrated in the braking system of Figure 9, a separate inlet port 85 leading directly into the primary pressure space 8 from the valve 82 is provided.

In this system the pressure fluid is supplied to the port 83 directly from the pressure space 8, with an equal pressure applied to the secondary piston 6 though the open recuperation valve 11.

21 This system has the disadvantage that the accumulator valve 82 is not isolated from the primary circuit when the brakes are applied normally.

The construction and operation of the system of Figure 9 is otherwise the same as that of Figure 8 and corresponding reference numerals have been applied to corresponding parts.

The system of Figure 10 illustrates a master cylinder without an integral power source, namely an accumulator as in the system described above with reference to Figures 9. In this system the normal inlet 87 from the reservoir to the recuperation valve 11, instead of being connected to the pressure space 8 through the recuperation valve 11, is connected to a separate motor driven power source comprising a pump 88. In addition a single solenoid-controlled valve 89 is located between the reservoir and the normal reservoir inlet port 90 to the primary pressure space 8.

For automatic braking, the solenoid-control valve 89 is closed and the pump 88 is operated to deliver fluid to the primary circuit. At the same time the secondary piston 6 moves to apply the circuit. At the required vehicle deceleration the motor driven pump 88 is switched off.

If the driver applies the brakes normally, the solenoid-controlled valve 88 opens to connect the primary inlet 87 to the reservoir.

The construction and operation of the system of Figure 10 is otherwise the same as that of Figures 8 22 and 9, and corresponding reference numerals have been applied to corresponding parts.

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Claims

An hydraulic braking system of the kind set forth for a vehicle, in which the vehicle is provided with an intelligent cruise control system, the system comprising an electronic control module for differentiating cruise control signals and emitting electric currents, and hydraulic pressure means operable in response to cruise control signals to pressurise the primary pressure space of the master cylinder, whereby to apply the brakes on all the wheels by operating the primary actuators directly and the secondary actuators indirectly, following closure of an isolating valve in a return line from the primary pressure space to the reservoir of the master cylinder.
2. A system according to claim 1, in which the isolating valve comprises a solenoid-controlled valve which is normally open but which is adapted to be closed by a signal from the control module as the hydraulic pressure means is operated, also by a signal from the control module, closure of the isolating valve preventing fluid from being returned to the reservoir for the master cylinder from the primary pressure space.
3. A system according to claim 2, in which the hydraulic pressure means comprises an hydraulic pump operable by energisation of an electric motor in response to an electric current emitted from the control module, in which closure of the solenoid-controlled valve prevents fluid from being returned to the reservoir through a return line as fluid is, itself, withdrawn from the reservoir by the pump through a supply line.

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4. A system according to claim 2, in which the hydraulic pressure means comprise an hydraulic accumulator, and a normally closed second so lenoidcontrolled supply valve is disposed in a line to the primary pressure space and is operable in sequence with the isolating valve, which is normally open.
5. A system according to any preceding claim, in which fluid for the pressure means is supplied directly into the primary pressure space through the supply valve.
6. A system according to any of claims 1-4, in which fluid from the pressure means is supplied to a chamber adjacent to the primary pressure space to pressurise that chamber and also the pressure space through a primary recuperation valve in the primary piston.
7. A system according to any preceding claim in which operation of a pedal for operating the master cylinder manually is sensed by an electrical switch, and operation of the switch is adapted to de-energise the valve and render the hydraulic pressure means inoperative.
8. A system according to any preceding claim, in which the pressure applied to each primary and secondary brake circuit by the hydraulic pressure means is adapted to increase up to a value determined by vehicle deceleration.
9. A system according to any preceding claim, in which the hydraulic braking system is of the anti-lock (ABS) type and the anti-lock pump comprises the pump for automatically applying the brakes in response to cruise control signals, in which the solenoid-controlled valve controlling the return line is closed whenever the brakes on the front wheels of the vehicle are being controlled.
10. A system according to any preceding claim, in which the pressure level in both primary and secondary brake circuits is raised to prevent brake intervention in combination with an anti-lock system which isolates or connects the relevant wheels in accordance with anti-lock signals emitted by sensors on the respective wheels.
11. A system according to any preceding claim, in which the solenoidcontrolled isolating valve is spring loaded into an open position.
12. A system according to any preceding claim, in which system is adapted to apply at least some of the brakes, whenever the vehicle is to be held on an upwardly facing hill when the traction force exceeds the holding force, the brakes are released to enable the vehicle to be driven away.
13. An hydraulic braking system substantially as described herein with reference to and as illustrated in Figure 1 of the accompanying drawings.
14. An hydraulic braking system substantially as described herein with reference to and as illustrated in Figure 2 of the accompanying drawings.
15. An hydraulic braking system substantially as described herein with reference to and as illustrated in Figure 3 of the accompanying drawings.

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16. An hydraulic braking system substantially as described herein with reference to and as illustrated in Figures 4 and 5 of the accompanying drawings.
17. An hydraulic braking system substantially as described herein with reference to and as illustrated in Figure 6 of the accompanying drawings.
18. An hydraulic braking system substantially as described herein with reference to and as illustrated in Figure 7 of the accompanying drawings.
19. An hydraulic braking system substantially as described herein with reference to and as illustrated in Figure 8 of the accompanying drawings.
20. An hydraulic braking system substantially as described herein with reference to and as illustrated in Figure 9 of the accompanying drawings.
21. An hydraulic braking system substantially as described herein with reference to and as illustrated in Figure 10 of the accompanying drawings.