DE3538330A1 - Hydraulic brake system for motor vehicles - Google Patents

Abstract

The hydraulic brake system comprises a brake pedal-operable tandem master cylinder (1) with two pressure chambers (5, 6), which are connected by way of pressure medium lines (I, II) to wheel brakes (7, 8, 9, 10). The wheel brakes (7, 8, 9, 10) have a first application unit (29), which when subjected to pressure produces a braking action on the vehicle. The brake system also has an external energy supply system, provided with a hydraulic pump (17), which system can be pressure-controlled as a function of the tandem master cylinder (1) and which correspondingly feeds additional pressure medium to the individual wheel brakes (7, 8, 9, 10). Individual wheel brakes (7, 8) and/or (9, 10) have a second hydraulic application unit (27, 30), which is dynamically acted upon by the pressure of the external energy supply system (17), whilst the first application unit (29, 38) of these individual wheel brakes (7, 8, 9, 10) is acted upon only by the pressure of the associated pressure chambers (5, 6) of the tandem master cylinder (1). <IMAGE>

Description

The invention relates to a hydraulic brake system for Motor vehicles with a master cylinder actuated by a brake pedal with pressure chambers over pressure medium lines are connected to wheel brakes, the wheel brakes being a first, one or more pressure chambers of the master cylinder have hydraulically actuated clamping unit, the braking effect on the vehicle when pressurized cause, and with a foreign energy supply system, which is pressure-controllable depending on the master cylinder and the additional according to the pressure in the pressure chambers Pressure medium feeds the individual wheel brakes.

Such a brake system is in the German patent application P 35 11 533.5. With this brake system become wheel brakes on the one hand from the pressure of the pressure chambers of the master cylinder and on the other hand from the pressure medium the external energy of the external energy supply system. The pressure of the foreign energy supply system is depending on the pressure of the pressure chambers a pressure control valve controlled. In one of the brake circuits a pedal travel simulator is connected to the brake system, who has the task, depending on the brake pressure correspondingly large way to effect on the brake pedal. If this pathway simulator were not available, then could be any high hydraulic with constant pedal travel Brake pressures are generated that one vehicle more or brake less strongly. This pedal travel simulator  leads to an increased effort of valves and power an increased swallowing volume of the brake system is required.

The object of the invention is therefore that described in the introduction to improve the mentioned brake system in such a way that with a minimum of valves and optimal safety of the brake system Brake pedal feel is made with the brake system has a low swallowing volume.

This object is achieved in that individual wheel brakes a second hydraulic application unit exhibit only from the pressure of the foreign energy supply system is dynamically loaded while the first Application unit of these individual wheel brakes only from Pressure of the associated pressure chamber of the master cylinder is applied becomes. When the master cylinder is actuated the first application unit the pressure medium from that with it connected pressure chamber of the master cylinder. The pressure medium flowing into the first application unit is from the associated pressure chamber of the master cylinder promoted, so that as a result Brake pedal gives a certain way. By building up pressure in the associated pressure chamber is a Reactive force on the brake pedal is exerted on the driver that gives the brake pedal feel common to master cylinders.

From the beginning or, if necessary, from a certain pressure level is additional pressure medium from the foreign energy supply system fed to the second application unit. The Ratio of the applied by the two application units  Braking torque is dependent on the one hand Area ratios of the clamping units and on the other hand of the area ratios of the control piston the valve seats of the pressure relief valve. The first Applying unit therefore functions as a simulator from that corresponding to the amount of the foreign energy supply system fed into the second application unit A corresponding path and a pressure medium corresponding reaction force on the brake pedal. By the integration of the simulator of the first clamping unit, in the wheel brake is advantageously achieved that not only dynamic pressure when braking, but there is also a static pressure on the wheel brake. This also means that in the event of failure the first application unit of the external power supply system at least from the one in the associated pressure chamber static pressure prevailing in the master cylinder is supplied with pressure medium, whereby a minimum braking of the vehicle is reachable. By the invention can use hydraulic braking systems with minimal Component effort can be realized.

In order to pull a vehicle when braking To avoid, it is provided according to the invention that the wheel brakes with the first and second application unit are arranged on a vehicle axle of a vehicle. But it is also possible that the wheel brakes with the first and second brake application on all braked Wheels of a vehicle are arranged.  

So if a pressure chamber of a master cylinder fails a residual braking effect can still be achieved on the vehicle, it is provided according to the invention that the first application units the wheel brakes assigned to a vehicle axle connected to a pressure chamber of the master cylinder are. If there is a pressure in the master cylinder pressure chamber is still a wheel brake on a vehicle axle operated. But it is also conceivable that the first Application units of a vehicle axle Wheel brake to a common pressure chamber of the master cylinder are connected. In this case falls in the event of failure the entire brake circuit in a pressure chamber of the master cylinder this vehicle axle, but it is still the second vehicle axle over the with the second pressure chamber of the master cylinder connected brake circuit fully effective.

A good brake pedal feel is also achieved when in addition to the wheel brakes with the first and second Clamping units on another vehicle axle Wheel brakes are arranged, which are only a first hydraulic Have application unit. This braking system offers especially when the braking force component is on the front axle is much higher than on the rear axle. Here are brakes on the front axle first and second application unit used while on the rear axle brakes with only a first application unit be used. The one with only one clamping unit Equipped wheel brakes can only be used here from the foreign energy supply system or from one Pressure chamber of the master cylinder are applied. To  But increasing the safety of this braking system is also conceivable that the wheel brakes with only a first application unit each with a separate pressure chamber of the master cylinder are connected.

The regulation of the foreign energy supply system too The pressure medium guided in the individual wheel brakes can be in a particularly simple manner by printing one or realize several pressure chambers of the master cylinder. Here According to the invention, the regulation of the pressure of the External energy supply system by a hydraulically operated Pressure control valve take place.

The brake system according to the invention can in particular Realize even with brake slip controlled brakes. This is achieved according to the invention in that the wheel brakes a release unit that reduces the braking effect have in certain operating conditions of the vehicle contrary to the first and / or. second clamping unit works. Because of the risk of the wheels locking up conveyed additional pressure medium into the release unit, so that the resulting loosening force counteracts the clamping force the first and second application unit acts and the braking effect of these wheel brakes is reduced. Here it is provided according to the invention that the release unit from the pressure-controlled energy supply system Pressure medium can be applied and that the time and the amount of pressure applied by a first valve arrangement takes place in the pressure medium line between the regulated pump pressure and the hydraulic release unit is regulated. The pressure control to the release unit  takes place here exclusively through the first valve arrangements, that is available in sufficient quantity Pressure medium of the external energy supply system dosed.

This enables a very precise and simple pressure control achieved that the first valve assembly from an electromechanical There is a cut-in valve if there is a tendency to block one or more wheels the pressure in each Release unit increased. Due to the pressure build-up in the release unit the application force of this wheel brake is reduced. increasing the risk of blocking this with the Release unit connected wheel is lowered.

So on the one hand, this release device in the non-actuated state with the expansion tank under atmospheric pressure is connected and secondly when actuated the first valve arrangement the connection to the expansion tank is blocked, the invention provides that to the fluid line between the first Valve arrangement and the release unit a connecting line is arranged to the expansion tank in which a second valve assembly is located when actuated the first valve arrangement can be closed. Hereby is achieved that when the first is not actuated Valve arrangement the release device no release force exerts on the first and second application unit.

A particularly simple training of the first and second Application unit is achieved in that it consists of one trained in a brake housing in a stepped bore Step piston with two ring surfaces, which with the brake housing two separate pressure chambers  forms, the stepped piston when pressurized one or both pressure chambers brake pads in frictional engagement with a friction disc rotatably connected to a wheel or friction drum brings. As soon as the stepped piston in the brake housing, it will indicated by a corresponding path on the brake pedal. The stepped piston can also be formed by two pistons be. Such a concept can be particularly wheel brakes formed by disc brakes realize. But it is also conceivable to use one Stepped piston in the brake housing of a wheel cylinder Arrange drum brake.

To implement the release unit is according to the invention provided that this from a in the brake housing on Step piston formed third ring step is formed which creates a third pressure chamber with the brake housing. Here is formed by the third ring stage Ring surface opposite to the direction of movement Step piston pressurized. The third ring stage can also from an additional, in the brake housing trained annular piston are formed.

Finally, it can be said that the invention elaborate valve arrangements in the master cylinder Regulation of the pressure of the external energy source while maintaining an optimal brake pedal feel is not required will.

Other features, advantages and possible applications the invention will become apparent from the following description of the attached figures, which are shown schematically in simplified representation of the most important components and  the hydraulic circuit of a brake system according to two Embodiments of the invention reproduces.

Show it:

Fig. 1 brake system with disc brakes formed on the front axles, which have a first and a second application unit and

Fig. 2 brake system with disc brakes, which has a first and second application unit and a release device.

For the purpose of Vereifachung be in FIGS. 1 and 2 used for the same mutatis mutandis the same components reference numerals.

The brake system shown in FIGS. 1 and 2 has a tandem master cylinder as the brake pressure sensor 1 . The pedal force F is transmitted to the push rod piston 3 and the intermediate piston 4 of the tandem master cylinder 1 via a brake pedal 2 . At the two working chambers 5 and 6 of the tandem master cylinder 1 , hydraulically actuated wheel brakes 7, 8, 9 and 10 are connected via two hydraulically separated pressure medium circuits I and II. In the exemplary embodiments described here, the front wheel brake 7 are connected to the working chamber 6 , the front wheel brake 8 to the working chamber 5 and the rear wheel brakes 9, 10 to the pump pressure circuit 11 regulated by the pump pressure. However, all other brake circuit divisions known in brake technology are also possible with this invention. At the working chambers 5, 6 , the two control chambers 12, 13 of an auxiliary pressure control valve, which is also called a pressure relief valve, and which is designated in its entirety by 14 . This pilot pressure is transmitted to a ball seat valve 16 via a shared control piston 16 inside the pressure-limiting valve 14, to the suction side of the pump 17 leading pressure fluid is inserted in turn in from the pressure side of a hydraulic pump 17 via the associated non-return valve 18 and via a line 19 and that determines the level of the regulated auxiliary pressure as a function of the pressure in the control chambers 12, 13 .

The suction side of the pump 17 opens into an expansion tank 20 . Likewise, the working chambers 5, 6 are connected to the compensating tank 20 via central valves 21, 22 formed in the pistons 3, 4 in the starting position of the tandem master cylinder 1 . Only when the tandem master cylinder 1 is actuated are these central valves 21, 22 closed, so that pressure can build up in the working chambers 5, 6 . The auxiliary pressure control valve 14 determines the level of the regulated auxiliary pressure as a function of the pressure in the control chambers 12, 13 .

In this exemplary embodiment according to FIG. 1, the brakes 7, 8 are designed with disc brakes with a piston arrangement 23 , as is usual with floating floating calipers. Here, a piston 26 is formed in a stepped bore 24 of the brake caliper housing 25 and forms the second hydraulic application unit 27 . A second application unit 27 is connected to the regulated pressure medium circuit 11 of the pump 17 . An annular piston 28 , which forms the first application unit 29 with the brake caliper housing 25, is guided concentrically to the piston 26 . The first application unit 29 is connected to the working chamber 6 of the tandem master cylinder 1 via the pressure medium line 30 . The first and second application units 29, 27 act upon hydraulic actuation on the friction lining 31 , which is then pressed against the brake disc 32 .

The disc brake designated 8 in FIG. 1 corresponds in its embodiment to the disc brake 7 . For simplification, it is therefore only shown schematically here and is connected to the working chamber 5 of the tandem master cylinder 1 via the pressure medium circuit II. The wheel brakes 9, 10 can also be designed like the disc brakes 7, 8 , but they can also be simple disc brakes or drum brakes provided only with a piston. The wheel brakes 9, 10 are connected to the regulated pressure medium circuit 11 via the pressure medium line 33 .

The pump 17 is connected to an electric motor 34 which is switched on via an electrical switch 35 which can be actuated by the brake pedal. The electrical switch 35 is connected to the electric motor 34 via an electrical line 36 .

In FIG. 2, the wheel brakes 7, 8 ebenfals formed as disc brakes having disposed only on one side of piston assembly 37 are. Here, too, the wheel brake 8 is shown only schematically for simplification. As in the case of the piston arrangement 23 of the wheel brake 7 in FIG. 1, the piston arrangement 37 here also consists of a first and second application unit 39, 40 , but with an opposite diameter ratio compared to FIG. 1. Here, the piston 40 of the first application unit 38 has a smaller diameter than the piston 41 of the second application unit 39 . In contrast to FIG. 1, the pistons 40 and 41 are formed in one piece here. Another piston 42 connects to the piston 41 and forms the release unit 44 with the brake caliper housing 43 . In Fig. 2, therefore, the first brake application unit 38 is connected to the working chamber 5 of the tandem master cylinder 1. The second application unit 39 is connected to the regulated pressure medium circuit 11 of the pump 17 . The release unit 44 is connected to the regulated pressure medium circuit 11 via the pressure medium line 45 . At the same time, the pressure medium line 45 is connected to the expansion tank 20 via an expansion line 46 . An electromagnetic valve 47 is arranged in the pressure medium line 45 and, if necessary, supplies the regulated pump pressure to the release unit 44 . Between the electromagnetic valve 47 and the release unit 44 , a further electromagnetic valve 48 is formed in the compensating line 46 , which, when the electromagnetic valve 47 opens, closes the connection to the compensating tank 20 . This relatively complex embodiment of the disc brake 7 can be simplified in a system that is not slip-controlled, similar to the embodiment shown in FIG. 1.

The wheel brake 9, 10 , which can also be designed as a disc brake and also corresponding to the wheel brakes 7, 8 , but can also be simple disc brakes or drum brakes, are connected to the regulated pressure medium circuit 11 via the pressure medium line 49 .

The electromagnetic valves 47, 48 are controlled by an electronic circuit, not shown in the drawing, which triggers an actuation of the corresponding wheels when the wheels are slipping.

The operation of the brake system according to the invention according to FIGS. 1 and 2 is as follows:

When the tandem master cylinder 1 according to FIGS. 1 and 2 is actuated by the brake pedal 2 , hydraulic pressure builds up in the working chambers 5, 6 . In Fig. 1, the first application unit 29 is actuated statically via the pressure medium circuit I. The first application unit of the wheel brake 8 is also actuated statically by the pressure medium circuit 2 .

In FIG. 2, the first brake application of the wheel brake is pressurized 7 38 statically by the pressure medium circuit II, while the first brake application of the wheel brake is pressurized statically 8 from the pressure medium circuit I.

Due to the simultaneous pressurization of the auxiliary pressure control valves 14 , an auxiliary pressure proportional to the pedal force F arises at the seat of the ball valve 16 and thus at its connection 11 , which soon exceeds the pressure in the pressure medium circuits I and II. The pressure area at the ball seat valve 16 is decisive for the pressure ratio which is established in comparison with the (larger) pressure area at the pressure in the control chamber 13 . The control chamber 12 comes into operation if the brake circuit II fails.

In Fig. 1, the regulated pressure now passes into the second application unit 27 , which takes on the largest proportion of the application force due to the much higher regulated pressure compared to the static pressure. Due to the movement of the piston 26 , the annular piston 28 is also moved towards the brake disk 32 , as a result of which an increased path is also established on the brake pedal 2 . A pedal force F is also generated on the brake pedal by the pressure building up in the second application unit 29 . The path simulated in this way and the pedal force on the brake pedal simulated at the same time gives the driver an optimal brake pedal feeling. In this exemplary embodiment, however, this is only generated by the wheel brakes 7 and 8 , while the wheel brakes 9 and 10 are supplied by the regulated pressure medium of the pump 17 as a function of the pressure control. The mode of operation of the brake system shown in FIG. 1 also corresponds to the mode of operation of the brake system shown in FIG. 2. In FIG. 2, the blocking of the wheel brake 7, 8 when the brake pedal 2 is depressed is additionally prevented. During a normal braking operation, the electromagnetically actuable valve 47 is closed, while the electromagnetic valve 48 is open and the release unit 44 is thus relieved of pressure, so that when the pistons 40, 41 and 42 are moved, the pressure medium flows out of the release unit 44 to the expansion tank 20 or can flow from the expansion tank 20 to the release unit 44 . As soon as the wheels surrounding the wheel brakes 7, 8 show a tendency to lock, switching of the valves 47, 48 is caused by electronics, not shown. The valve 47 now opens while the valve 48 closes. Pressure medium can now flow into the release unit 44 , which generates a release force on the piston 42 , which acts counter to the clamping force generated on the pistons 40 and 41 . This reduces the friction torque of the wheel brakes 7, 8 , so that the tendency of the wheels to lock is reduced. As soon as the risk of blocking is eliminated, the valves 47 and 48 are moved back into their starting position by the electronics. This process can be repeated at very short intervals if necessary. The wheel brakes 9, 10 can also be connected to such electromagnetic valves if they are designed with the two application units and the release unit.

Claims (21)

1.Hydraulic brake system for motor vehicles with a master cylinder which can be actuated by a brake pedal and has pressure chambers which are connected to wheel brakes via pressure medium lines, the wheel brakes having a first application unit which bring about braking action on the vehicle and with an external energy supply system which can be pressure-controlled as a function of the master cylinder pressure and correspondingly the pressure in the pressure chambers supplies additional pressure medium to the individual wheel brakes, characterized in that individual wheel brakes ( 7, 8, 9, 10 ) have a second hydraulic application unit ( 27, 30 ) which is acted upon dynamically by the regulated pressure of the external energy supply system 17 , while the first application unit of these individual wheel brakes ( 7, 8, 9, 10 ) is only acted upon by the pressure of the associated pressure chamber ( 5, 6 ) of the master cylinder ( 1 ). 2. Hydraulic brake system according to claim 1, characterized in that the wheel brakes ( 7, 8, ) and / or ( 9, 10 ) with the first ( 29, 38 ) and second ( 27, 39 ) application unit arranged on a vehicle axle of a vehicle are. 3. Hydraulic brake system according to claim 1, characterized in that the wheel brakes ( 7, 8 ) and / or ( 9, 10 ) with the first ( 29, 38 ) and second ( 27, 39 ) application unit arranged on all braked wheels of a vehicle are. 4. Hydraulic brake system according to claim 2, characterized in that the first application units ( 22, 38 ) of the wheel brakes assigned to a vehicle axle ( 7, 8 ) are each connected to a pressure chamber ( 5, 6 ) of the master cylinder ( 1 ). 5. Hydraulic brake system according to claim 2, characterized in that the first application units ( 29, 38 ) of the wheel brakes assigned to a vehicle axle ( 7, 8 ) or ( 9, 10 ) to a common pressure chamber ( 5 or 6 ) of the master cylinder ( 1 ) are connected. 6. Hydraulic brake system according to claim 2, characterized in that in addition to the wheel brakes ( 7, 8 ) with the first ( 29, 38 ) and second ( 27, 39 ) application units on a further vehicle axle of a vehicle further wheel brakes ( 9, 10 ) are arranged, which have only a first hydraulic application unit ( 29, 38 ). 7. Hydraulic brake system according to claim 6, characterized in that the further wheel brakes ( 9, 10 ) are pressurized exclusively by the regulated external power supply system ( 17 ). 8. Hydraulic brake system according to claim 6, characterized in that the further wheel brakes ( 9, 10 ) with only one pressure chamber ( 5 or 6 ) of the master cylinder ( 1 ) are connected. 9. Hydraulic brake system according to claim 6, characterized in that the further wheel brakes ( 9, 10 ) are each independently connected to a separate pressure chamber ( 5, 6 ) of the master cylinder ( 1 ). 10. Hydraulic brake system according to one of the preceding claims, characterized in that the regulation of the pressure medium from the external energy supply system ( 17 ) to the wheel brakes ( 7, 8, 9, 10 ) from the pressure of one or more pressure chambers ( 5 or 6 ) or ( 5 and 6 ) of the master cylinder ( 1 ). 11. Hydraulic brake system according to claim 10, characterized in that the control is carried out by a hydraulically actuated pressure control valve ( 14 ). 12. A hydraulic brake system according to claim 1, characterized in that the wheel brakes ( 7, 8 ) and / or ( 9, 10 ) have a release unit ( 44 ) which reduces the braking action and which, in certain operating states of the vehicle, counteracts the first ( 29, 38 ) and / or. second ( 27, 39 ) application unit can be actuated. 13. Hydraulic brake system according to claim 12, characterized in that the release unit ( 44 ) from the external energy supply system ( 17 ) can be acted upon with pressure medium and that the time and the amount of pressure applied by a first valve arrangement ( 47 ) which takes place in the pressure medium lines ( 45 ) is arranged between the regulated pump pressure and the hydraulic release unit ( 44 ). 14. Hydraulic brake system according to claim 13, characterized in that the first valve arrangement ( 47 ) consists of an electromechanical connecting valve which increases the pressure in the respective release unit ( 44 ) when one or more wheels lock. 15. Hydraulic brake system according to claim 13 and / or 14, characterized in that a connecting line ( 46, 19 ) to the expansion tank ( 20 ) is arranged on the pressure medium line ( 45 ) between the first valve arrangement ( 47 ) and the release unit ( 44 ), in which there is a second valve arrangement ( 48 ) which can be closed when the first valve arrangement ( 47 ) is actuated. 16. Hydraulic brake system according to one of claims 1 to 11, characterized in that the first ( 29, 38 ) and second ( 27, 39 ) application unit from a in a brake housing ( 25, 43 ) in a stepped bore ( 24 ) formed stepped piston ( 26, 28 ) or ( 40, 41 ) with two annular surfaces which form two separate pressure chambers with the brake housing ( 25, 43 ), the stepped piston ( 26, 28 ) or ( 40, 41 ) when one or both pressure chambers are pressurized Brings brake pads ( 31 ) into frictional engagement with a friction disc ( 32 ) non-rotatably connected to a wheel. 17. Hydraulic brake system according to claim 16, characterized in that the stepped piston ( 26, 28 ) or ( 40, 41 ) consists of two pistons. 18. Hydraulic brake system according to claim 16, characterized in that the wheel brakes ( 7, 8, 9, 10 ) are disc brakes. 19. Hydraulic brake system according to claims 12 to 15, characterized in that the release unit ( 44 ) from a in the brake housing ( 43 ) on the step piston ( 40, 41 ) formed third ring stage ( 42 ) is formed, which with the brake housing ( 43 ) creates a third pressure chamber. 20. Hydraulic brake system according to claim 19, characterized in that the annular surface formed by the third ring step ( 42 ) opposite to the tensile direction of the step piston ( 40, 41 ) is pressurized. 21. Hydraulic brake system according to one of the preceding claims, characterized in that the piston area of the first application unit ( 29, 38 ) is smaller or larger than the piston area of the second application unit ( 27, 39 ) and that the sum of the piston areas of the first ( 29, 38 ) and second ( 27, 39 ) application unit is the same size or smaller than the piston area of the third application unit ( 44 ).