EP0429550A1

EP0429550A1 - Hydraulic brake system with slip control

Info

Publication number: EP0429550A1
Application number: EP89912444A
Authority: EP
Inventors: Peter Volz
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1988-11-03
Filing date: 1989-11-01
Publication date: 1991-06-05
Also published as: DE3906529A1; JPH03503515A; US5152587A; WO1990005081A2; WO1990005081A3

Abstract

Système de freinage comprenant une unité de rappel grâce à laquelle on peut exercer sur la pédale une force de rappel. Comme la pédale actionne simultanément une soupape de commande (9) qui détermine la force du servomécanisme, tout rappel s'accompagne d'une diminution de la force du servomécanisme. La paroi (40) qui absorbe la force de rappel peut avantageusement être agencée dans le carter (5) du servomécanisme, entre le cylindre principal (1) et la paroi (6) du servomécanisme. Comme elle ne se déplace que sur des trajectoires beaucoup plus courtes que la paroi (6) du servomécanisme, il n'est pas besoin d'allonger de beaucoup le carter (5) du servomécanisme. La description contient d'autres modes de réalisation possibles.Braking system comprising a return unit by means of which a return force can be exerted on the pedal. As the pedal simultaneously actuates a control valve (9) which determines the force of the servomechanism, any return is accompanied by a reduction in the force of the servomechanism. The wall (40) which absorbs the restoring force can advantageously be arranged in the casing (5) of the servomechanism, between the main cylinder (1) and the wall (6) of the servomechanism. Since it only moves along much shorter paths than the wall (6) of the servomechanism, there is no need to lengthen the housing (5) of the servomechanism much. The description contains other possible embodiments.

Description

Hydraulic, slip-controlled braking system

The invention relates to a brake system as characterized in the preamble of claim 1. Such a brake system is described, for example, in DE-OS 33 17 629. The system essentially consists of a master cylinder and an amplifier which amplifies the pedal force acting on the master cylinder. The wheel brakes are each connected to the master cylinder via a check valve. The check valve is opened in its basic position so that there is a pressure medium connection between the master cylinder and the wheel brake cylinders. The rotational behavior of the wheels is continuously monitored so that it can be determined immediately if one of the wheels threatens to lock up during braking. If this occurs, a brake pressure reduction in the master brake cylinder is initiated, at the same time the blocking valves of the non-lock wheels switch into their locked position, so that only the wheel brake cylinder of the locked wheel is subjected to a reduced pressure. The pressure drop in the master brake cylinder is brought about by switching the; amplifier. Switching means that the chamber of the brake booster, which is connected to a high-pressure source to support the foot power, is now connected to a low-pressure source

is, while the chamber, which was previously connected to the low pressure source, is now connected to the high pressure source. This leads to a relief of the master brake cylinder and thus to a reduction in pressure in the brake circuits, since the foot forces are no longer supported but are compensated for.

As already described in GB-PS 15 11 254, there is the problem that the driving and thus also the retroactive force is determined by the effective area of the amplifier and the pressure difference between the high pressure source and the low pressure source. These are generally determined so that at full modulation, i.e. with a maximum possible pressure difference on the booster wall, a pressure is built up in the master brake cylinder, which leads to the wheels locking. In this case, an increase in the pressure in the master brake cylinder would not lead to a further increase in the vehicle deceleration, so that it is not necessary to support the foot force beyond the control point.

For the type of relief of the master cylinder described above, however, it may be necessary to compensate foot forces that are greater than the reinforcing forces that are reached at the control point. The restoring forces of the amplifier must therefore be much greater than the support forces. While the support staff can be turned to the blocking pressure, the

Restoring forces are matched to the pedal forces that the driver is able to apply. If the pedal forces are greater than the restoring forces, the pressure reduction in the master brake cylinder does not take place to a sufficient extent, so that no brake slip control can be carried out. In the aforementioned British patent, the problem is solved in that a second diaphragm plate is attached to the control sleeve of the brake valve, so that the effective area of the amplifier is increased in the case of brake slip control for resetting. The disadvantage here is that a corresponding movement space must be made available for the second membrane plate, which means that a considerable amount of space is required. Furthermore, additional valves are required which allow a corresponding inflow of pressure medium into the spaces delimited by the second diaphragm plate.

The object of the invention is therefore to create a brake booster in which sufficiently large restoring forces can be made available with little valve outlay and at the same time being small in size.

The object is achieved in that a return wall is coupled to the pedal piston, the side remote from the pedal can be acted upon by a pressure which is formed according to the rotational behavior of the wheels to be braked.

The basic consideration is that the restoring forces act directly on the pedal piston. This has the advantage that only the pressure medium supply to the chamber, which is delimited by the side of the return wall remote from the pedal, has to be controlled for brake slip control. The valve effort is low. If the pedal piston is displaced under the action of the forces acting on the restoring wall, the brake valve is activated at the same time, so that the pressure difference on the booster wall is also influenced. The result of this is that, depending on the extent to which the pedal force is compensated, the force amplification is also reduced.

The reset unit can be represented both with the aid of an incompressible liquid, for example brake fluid, or with air as the pressure medium. If air is used as the pressure medium, it makes sense to arrange the rear wall between the main brake cylinder and the booster in the booster housing. Since the return wall is moved with the amplifier wall and only covers small control paths relative to the amplifier wall, the overall length of the device remains essentially unchanged compared to an amplifier of conventional design. The pedal piston is connected to the return wall via a shaft which is guided through the reaction element and a longitudinal channel in the tappet. The connection to the restoring wall is established by means of a cross pin which is inserted in a transverse bore of the ram

and is connected to a sleeve on the return wall.

Because e.g. when braking on black ice the pressure in the main cylinder has to be almost completely reduced, the reset unit must be designed so that it is able to generate a force that corresponds to the maximum force that a driver is able to to build up. The force that can be generated by the return unit depends on the one hand on the effective area of the wall. This is usually limited for design reasons. On the one hand, certain stability criteria have to be met, on the other hand, the installation space available for the reset unit is limited.

A second way is therefore to increase the maximum pressure difference on the movable wall.

To this end, the invention proposes that the modulator chamber be connected to a compressor via a check valve.

The compressor is able to generate a pressure that is above atmospheric pressure. A greater pressure difference can thus be generated at the resetting plate, so that it can be ensured at all times that the pedal force is completely compensated even in extreme cases. At the same time, the effective area, and thus the diameter of the reset plate, can be kept small, at least the diameter need not be larger.

as the amplifier plate of the vacuum amplifier.

The compressor can be represented in a wide variety of ways.

For example, For example, a separate compressor can be provided in the vehicle, which is designed as a piston or flow machine.

But it should also be remembered that existing compressors are integrated into the brake system. So it can be considered to use the turbocompressor to charge the internal combustion engine. It is also conceivable to use the exhaust gases from an internal combustion engine and to introduce them into the modulator room, that is to say to consider the exhaust system as a compressor. In this case, precautions may have to be taken so that the gases do not themselves get into the modulator chamber, but rather only the exhaust gas pressure is transmitted into the modulator chamber via an intermediate piston.

A further embodiment consists in that a reset unit is arranged between the pedal and the pedal piston. In this case, a control with incompressible liquid is particularly suitable, which is either made available by a memory or is pumped into the recovery room.

With these devices, traction slip can be easily

Carry out regulation, i.e. pressurizing the wheel brakes without pressing the pedal. The reset unit only has to be acted upon in the actuating line. This becomes particularly easy if the pump is driven by an electronically commutated electric motor and at the same time a pump is used that can deliver in both directions.

In the other cases, the pedal-near chamber of the reset unit is connected to a pressure source.

Exemplary embodiments for explaining the inventive idea are shown in FIGS. 1-5.

FIG. 1 shows a master cylinder 1 to which the wheel brakes, as shown in more detail in FIG. 2, are connected. The master cylinder 1 has two working spaces, which are formed by the push rod piston 2 and the floating piston 3, respectively. In front of the master cylinder is connected a vacuum brake booster 4, the housing 5 of which is divided by the booster plate 6 into a vacuum chamber 7 and a control chamber 8. The vacuum brake booster 4 further includes a control valve 9 which is arranged in a control sleeve 10 which is connected to the booster plate 6. A plunger 11, which is supported on the reaction disk 12 and transmits the pedal and pressure forces on the reaction plate 6 on the push rod piston 2 of the master cylinder 1.

The reaction disc consists of a rubber disc that acts like a hydraulic cushion. Other types of reaction elements can also be provided, e.g. so-called lever systems.

The control valve 9 includes a valve piston 13, which forms a unit with the pedal rod 14. The valve piston 13, like the booster plate 6, is supported on the reaction disk 12. The control valve 9 has two switching positions. In the non-actuated position, there is a connection between the two rooms 7 and 8. When the brake pedal is actuated (ie when the pedal rod 14 is displaced in the direction of the arrow F), this connection is first interrupted and then a connection between the control chamber 8 and the atmosphere is established. The air flowing into the control chamber 8 pushes the booster plate 6 forward and actuates the master brake cylinder 1. The reset unit is connected between the symbolically indicated brake pedal and the control valve. It essentially consists of a reset piston 15 which is fastened to the pedal rod 14 and divides the housing 16 into two spaces 17 and 18. The rooms are filled with incompressible liquid and can be connected to a memory 19. The accumulator 19 is a piston accumulator with a piston 21, which is loaded by the pressure difference between the atmosphere and a vacuum source, which acts on a wall 23. With valves 20 ', 20 ", either

front room 17 or the rear room 18 can be connected to the memory. In addition, there is the possibility with valves 20 '"and 20" "to connect one of the rooms to the storage container.

The possibility of directly fastening the wall 23 to the rod 14 is not shown, so that the pressure differences between the atmosphere and the vacuum source become effective directly on the rod 14 without the interposition of a hydraulic transmission device.

The storage piston 21 delimits a storage chamber 31 which, in the basic position of the storage piston 21, is connected to a storage container 30 via a sniffing hole. By reversing the valve 32, the restoring wall 23 is displaced so that the piston 21 passes over the sniffing hole and a pressure is built up in the chamber 31.

The brake system just described works according to the following scheme.

To actuate the brake, the pedal is depressed so that the control valve 9 switches over and air flows into the control chamber 8. This moves the booster plate 6 to the left as shown, so that the push rod piston 2 is pushed into the master cylinder. A pressure builds up there, which applies to the wheel brakes.

is routed. The chamber 17 of the reset unit communicates via the open valve 20 'with the storage chamber 31 which is still connected to the storage container; the chamber 18 via the open valve 20 "" is also connected to the reservoir 30. The piston 15 can therefore be pushed back and forth almost without force.

The turning behavior of the wheels is continuously monitored. If the monitoring device determines that one of the wheels is threatening to block, valve 32 is actuated to pressurize wall 23. Pressure medium is displaced from the storage chamber into the chamber 17 so that a pressure is built up there, which is supported on the wall 15 and on the rod 14 on the pedal. The pedal force acting on the control valve 9 is thus reduced, which at the same time also reduces the pressure in the control chamber 8, since this is always set at the control valve 9 in accordance with the effective force.

Ultimately, the pressure in the master brake cylinder is also reduced, which is now passed on to the wheel brakes which are still connected to the master brake cylinder.

For renewed pressure build-up, the pressure in the accumulator is reduced by actuating valve 32, so that again larger parts of the pedal force at control valve 9 become effective and a corresponding pressure build-up takes place in the main brake cylinder.

With only a few additional valves, traction control can also be implemented with this system. If it should be determined that the driving forces or moments on the wheels are greater than those that can be transmitted between the tires and the road, the drive torque must be partially compensated for by a braking force. This is done in that after switching the valves 20 'to 20 "" the rear space 18 is connected to the memory 19, so that now instead of the pedal force a pressure force acts on the wall 15, and thus actuates the brake valve 9.

Basically, instead of the accumulator 19, a motor-driven pump 26 can also be connected to the chamber 17 (or chamber 18 in the case of traction control) (FIG. 2b). The pump delivers from the reservoir 30 into an open circuit; both valves 27a, 27b are opened. By closing the valve 27a, additional pressure medium enters the chamber 17 and generates a counterforce to the pedal force. The pressure can be reduced again by closing the valve 27b and opening the valve 27a again.

The embodiment according to FIG. 2a is even simpler. The pump is a gear pump 29 or another pump, the conveying direction of which is reversible. The pump 29 is driven by an electronically commutated motor, the direction of rotation of which can be changed quickly. In this way, pressure medium can be easily supplied or removed from the chamber 17.

3 shows a further embodiment. The resetting unit is integrated within the amplifier housing 5. It consists of an additional wall, namely the reset plate 40, which separates a further chamber 41 in the amplifier housing 5, which can either be connected to a vacuum source vac or an atmosphere at. The connection of the reset plate 40 to the pedal piston 14 is realized in the following way.

The reset plate 40 is connected or screwed to a sleeve 42 which slides sealingly on the plunger 11. The sleeve has a transverse bore 48 in which a pin. 47 is inserted, which penetrates the plunger 11 in a transverse bore 44. A longitudinal bore 43 opens into the transverse bore 44, in which a shaft 46 is guided, which is fastened to the valve piston 13 by means of an intermediate piece 45. The intermediate piece 45 is passed through the reaction disk. The shaft 46 abuts the pin 47.

The embodiment according to FIG. 3 works according to the following scheme. In the basic position, a vacuum is present both in the chambers 7 and 8 and in the chamber 41. When the pedal is actuated, the control valve 9 is activated and, as explained, air is introduced into the chamber 8. The inflowing air forces the amplifier plate 6 to the left as shown. The resetting plate 40 is carried along, with no resetting forces being effective since the pressures on the resetting plate 40 are balanced

are. For brake slip control, i.e. To relieve the master cylinder, air is introduced into the chamber 41 by switching the valves 51 ′, 51 ″, as a result of which a restoring force acts on the plate 40 The valve 9 is brought into its basic position for a short time, so that the rooms 7 and 8 are short-circuited again and the pressure in the chamber 8. The effect here is also that by activating a counterforce at the same time This embodiment can also be easily expanded into a system with traction control by connecting chamber 7 to the atmosphere so that air flows in. Wall 40 is pushed forward and loads the master cylinder At the same time the valve 9 is actuated so that air also flows into the chamber 8. The valve will adjust itself so that in the n chambers 7 and 8 there is a pressure equilibrium, so that the booster wall 6 is carried along without force.

Since the wall 40 runs only a short distance relative to the wall 6, the resetting plate 40 can be guided within the booster plate 6 in a modification of the embodiment example according to FIG. 3. For this purpose, the amplifier plate 6 has a cylindrical extension on the outer edge, in which the reset plate 40 is mounted in a sealing manner. Since there are only short relative paths, there is no need for a complex rolling membrane.

Such an embodiment is shown in Figures 4a and 4b. The amplifier plate 6 is guided in the usual manner by means of a membrane 60 in the housing 5. The outer edge of the membrane 60 is clamped between the two housing halves 5a and 5b. The plate 6 has a cylindrical extension 62 on its outer edge. The inside of this extension has a surface on which a seal 63 slides. The reset plate 40 is now arranged within the cylindrical extension 62 and carries on its outer edge a seal 63 which bears against the inner surface of the cylindrical extension 62 already mentioned. In this way, a very compact design is achieved. A complex roller membrane seal for the reset plate 40 can be dispensed with. The chamber 7 is acted upon by vacuum via a hose 61, which connects two connections in the amplifier wall 6 and in the housing part 5b.

This embodiment can be further simplified (FIG. 4b), in which the hose 61 is shown as an integral part of the membrane 60. The vacuum connection 64 leads between the two housing parts 5a and 5b to the outside. The membrane 60 can be addressed as a hose membrane 65.

The structure of the brake system according to FIG. 5 corresponds to that of FIG. 3, with an additional compressor

73 can be connected to the modulation chamber.

The reset unit 55 is designed as follows.

In the housing 5 there is also a modulator space 41 which is formed on the side of the restoring wall 40 which lies opposite the vacuum space 7. The modulator chamber 41 can be connected via a valve 70, 71, 72 either to a vacuum source vac, to the outside air atm or to the compressor 73. A wide variety of embodiments can be provided for the compressor. The valve 70, which is arranged in connection with the vacuum source, is normally open, so that the modulator chamber 41, like the vacuum chamber 7, is depressurized. No force is exerted on the restoring wall 40, so that this can be carried along without exerting force when the brake is actuated.

To generate a restoring force, the valve 70 in the connection to the vacuum source is closed and either the valve 71 or 72, which represent the connections to the outside air or to the compressor, is opened. This creates an overpressure in the modulator chamber 41, which urges the return wall 40 to the right in the illustration according to the figure and loads the pedal piston 14. The non-positive connection between the booster wall 40 and the pedal piston 14 is established as follows. The Rück¬ partition wall 40 is attached to a sleeve 42 which slides sealingly on the plunger 11. The plunger itself has one

Cross bore 48 and a longitudinal bore 43. A transverse pin 47 is inserted into the sleeve 42 and runs through the transverse bore 48. A shaft 46 is arranged in the longitudinal bore 43, which extends through the reaction disk 12 via an intermediate piece 45 and is connected to the valve piston 13. The shaft 46 abuts the cross pin 47.

If the restoring wall 40 now moves to the right, it initially moves relative to the plunger 11, since the diameter of the transverse bore 48 is larger than the diameter of the pin 47. The forces which are exerted on the shaft 46 the restoring wall 40 act on the valve piston 13 and thus on the pedal rod 14. The pedal force is reduced in accordance with the force of the restoring force, as a result of which the brake valve 9 experiences a smaller control force. The gain is reduced in accordance with the reduced control force, i. H. Air is sucked out of the control chamber 8, so that the force on the master cylinder 1 decreases as a result.

The master cylinder is connected to the wheel brakes via brake lines. A lock valve 50 is arranged with each wheel brake, with which the respective brake line can be locked.

The brake system works in the following way. The brake is activated by moving the pedal rod 14 to the left as shown in the figure. This is done by means of a pedal, not shown. The

Brake valve 9 is operated in the manner described. The air flowing into the control chamber 8 forces the booster wall 6 to the left and actuates the master brake cylinder via the tappet 11. The pressure generated there is transferred to the wheel brakes via the brake lines and leads to vehicle deceleration.

If the pressure in the master brake cylinder increases excessively, there is a risk that the wheels will lock. As soon as it is determined with a wheel that sensors are decelerating and threatening to lock too much, the system switches to ABS mode. For this purpose the valve 70 is closed, so that the modulator chamber 41 is no longer connected to the vacuum source. Now the valve 71 is first opened to the outside air. The inflowing air shifts the return wall to the right and the pressure that builds up in the modulator chamber 41 compensates for the pedal force. As already explained, this results in a pressure reduction in the master brake cylinder 1 and thus in the wheel brake of the wheel at risk of locking. The valves 50, which belong to the wheels that are not at risk of locking, are closed during this process, so that the pressure reduction in the master cylinder does not take effect in these wheel brakes.

Now it can happen that even if the full atmospheric pressure is present in the modulator chamber 41, the force on the restoring wall 40 is not sufficient to compensate the foot force to a sufficient extent. In this

In this case, the valve 72 switches to the compressor 73, so that air flows into the modulator chamber 41 under an overpressure. There is now no longer the atmospheric pressure, but an overpressure which is greater than the atmospheric pressure and which is generally sufficient to compensate for the foot force.

By switching the valves 50 and by modulating the pressure in the modulator chamber 41, by opening and closing the valves 71 and 72, an optimal slip value can now be set on all wheels so that they transmit large braking forces and yet do not block.

As an alternative to the two-stage loading of the modulator chamber 41 first with atmospheric pressure and then with an overpressure, the atmosphere connection can be dispensed with under certain circumstances, in particular if a separate compressor is provided, and in the case of a brake slip control the compressor is immediately connected to the Modulator chamber 41 are connected.

= Master cylinder = push rod piston = floating piston = vacuum booster = housing = booster plate = vacuum chamber = control chamber = control valve = control sleeve = tappet = reaction disk = valve piston = pedal rod = return piston = housing = front chamber = rear chamber = pressure accumulator = valves = storage piston = vacuum housing = pressure wall = vacuum chamber - Atmosphere chamber - Pump = valves = motor = gear pump

= Storage container = storage chamber = valve = reset plate = modulator space = sleeve = longitudinal bore = cross bore = intermediate piece = shaft = cross pin = cross bore = check valves = valves = reset unit = rolling diaphragm =? Hose = seal = vacuum connection = hose membrane = valve = valve. = Valve = compressor

Claims

Claims:

1. Hydraulic, slip-controlled brake system for a motor vehicle with a pedal-operated master cylinder (1) and wheel brakes connected to it, at least one wheel brake being able to be temporarily disconnected from the master cylinder by means of a check valve, with an amplifier (4) to support the pedal force has a movable booster wall (booster plate 6) which, like the pedal piston (14), is supported on a plunger (11) via a reaction element (12), the plunger (11) on the push rod piston (2) of the master cylinder (1 ) is supported with a pedal-operated control valve (9) for controlling pressure medium on the side of the movable booster wall (6) near the pedal, characterized in that a return wall (15, 40) is coupled to the pedal piston (14), the side of the pedal remote from one Pressure can be applied, which is formed according to the rotational behavior of the wheels to be braked.

2. Brake system according to claim 1, characterized in that the return wall is represented by a piston (15) which is directly attached to the pedal piston (14).

3. Brake system according to claim 1, characterized in that the restoring wall is represented by a plate (40) which is arranged between the master cylinder (1) and the movable wall of the amplifier (6).

4. Brake system according to claim 3, characterized in that the resetting plate (40) and the booster plate (6) are guided in a common housing (5).

5. Braking system according to claim 4, characterized in that in the housing (5) three chambers (41, 7, 8) are formed, with at least the chamber (41) which delimits from the pedal-remote side of the reset plate (40) by means of modulation valves (51 ', 51 ") can be connected either to a vacuum source or to the atmosphere.

6. Brake system according to claim 3, characterized in that a shaft (46) is attached to the pedal piston (14), which in a

Longitudinal bore (43) of the plunger (11) is guided and abuts or is attached to a cross pin (47), which establishes the connection to the booster plate (40).

7. Brake system according to claim 6, characterized in that the amplifier plate (40) is fastened to a sleeve (42) into which the cross pin (47) is inserted and which surrounds the tappet (11).

8. Brake system according to claim 1, characterized in that the pressure difference between a vacuum source and the atmosphere is used to generate the counterforce, and that air forms the pressure medium.

9. Brake system according to claim 1, characterized in that an incompressible liquid is used as the pressure medium.

10. Brake system according to claim 9, characterized in that the pressure accumulator (19) has a piston (21) on which a movable wall (23) is supported, which adjoins the atmosphere with one wall side, and with the other Connects wall side to a vacuum source.

11. Brake system according to claim 8, characterized in that the pressure source is formed by a pump (26) which is driven by a motor (M).

12. Brake system according to claim 11, characterized in that the pump (24) has a reversible delivery direction.

13. Brake system according to claim 12, characterized in that the pump is driven by an electronically commutated electric motor (28).

14. Brake system according to claim 6, characterized in that the shaft (46) is passed through the reaction element (12).

15. Brake system according to one of the preceding claims, characterized in that pressure medium from the high-pressure source can be introduced into the chamber near the pedal (18, 7) of the reset unit by means of a valve unit for actuating the master brake cylinder independently of the pedal force.

16. Brake system according to claim 10, characterized in that the memory is connected in its inactive position to a reservoir (30).

17. Brake system according to claim 3, characterized in that the amplifier plate (6) has on its outer edge a sleeve-shaped extension in which the reset plate slides tightly.

18. Brake system according to claim 3, characterized in that the return actuator (6) is guided in the housing by means of a rolling membrane, and the pressure medium supply to the chamber (7) in front of the return plate is an integral part of the rolling membrane.

19. Brake system according to claim 5, characterized in that the pedal-distant chamber (41) is connected with the interposition of a valve (72) to a compressor (73) which generates a pressure in the pressure medium which is greater than atmospheric pressure.

20. Brake system according to claim 19, characterized in that the restoring plate (40) is in positive connection with the pedal.

21. Brake system according to claim 19, characterized in that the modulator chamber (41) has a lockable atmosphere connection (valve 71).

22. Brake system according to claim 19, characterized in that the modulator chamber (41) has a lockable vacuum connection

(Valve 70).

23. Brake system according to claim 19, characterized in that the compressor (73) is represented by the exhaust systems of the vehicle.

24. Brake system according to claim 19, characterized in that the compressor (73) is represented by a turbocharger.

25. Brake system according to claim 19, characterized in that the compressor (73) is represented by a blower.