Method for controlling a power-assisted braking system with electronically adjustable slip, in particular for a motor vehicle, and power-assisted braking system with electronically adjustable slip, in particular for a motor vehicle

Abstract

The invention relates to a method for controlling an electronically slip-adjustable power-assisted brake system (10), in particular for a motor vehicle, and an electronically slip-adjustable power-assisted brake system (10) controlled according to the method. The known power-assisted brake system (10) comprises an actuating device (14) loaded by muscle force, a master brake cylinder (12) coupled to the actuating device (14), a brake circuit (30a, b), wheel brakes (64a-d) connected to the brake circuit, and a brake pressure generator (50) actuable by force. The brake pressure generator (50) and the master brake cylinder (12) can be in contact with the brake circuit (30a, b) in parallel with each other. In addition, a pressure generator control valve (62a, b) for controlling a first pressure medium connection between the brake pressure generator (50) and the brake circuit (30a, b) and a brake circuit control valve (32a, b) for controlling a second pressure medium connection between the brake circuit (30a, b) and the master brake cylinder (12) are provided. The power-assisted brake system (10) can be operated in an operating state during which the pressure generator control valve (62a, b) assumes a breakthrough position, while no brake pressure prevails in the brake circuit (30a, b) and no brake pressure buildup occurs. It is proposed that during this operating state, the brake circuit control valve (32a, b) is electrically actuated by an electronic control unit (28) of the power-assisted brake system (10) so that it assumes the breakthrough position.

Description

Technical Field

[0001] The invention relates to a method for controlling an electronically slip-controlled power-assisted brake system, in particular for a motor vehicle, and to an electronically slip-controlled power-assisted brake system, in particular for a motor vehicle, which is controlled according to the method. Background Art

[0002] Power-assisted braking systems in motor vehicles that can be electronically adjusted in terms of slip belong to the prior art. The power-assisted braking systems differ from conventional muscle-powered braking systems in that, in the power-assisted braking systems, the driver does not participate in the construction of the brake pressure, but only predetermines the braking expectation, which is then set by a brake pressure generator driven by the power assist. Power-assisted braking systems are particularly suitable for use in modern vehicles with electric drives, in which the braking torques of multiple systems that interact with each other are superimposed on each other during the braking process. In addition, power-assisted braking systems are also used in vehicles that are equipped with electronic assistance systems and allow at least partially autonomous driving or braking operations, for example, in order to automatically adjust the distance to the vehicle traveling in front.

[0003] The advantage of decoupling the driver from the brake pressure buildup is that, for example, in the case of pressure changes due to wheel slip control during anti-lock brake control (ABS) or in the case of driving dynamics control (ESP mode), the driver does not receive any haptically perceptible feedback from the brake system itself. In addition, the power-assisted brake system improves driving comfort, since the pressure changes that occur do not generate any more noise that can be transmitted via the brake pedal into the interior of the vehicle.

[0004] A power-assisted brake system, on which the present invention is based, is known, for example, from DE 10 2014 205 431 A1.

[0005] In power-assisted brake systems, a distinction is made between passive and active operating states. During the passive operating state, there is no driver's braking desire and no brake pressure is built up in the brake circuit by the electronic controller. In contrast, in the active operating state, the braking process or brake pressure buildup occurs by a power-assisted brake pressure generator. In order to transition from the passive operating state to the active operating state, the electrical control of the various controllable valve components and brake pressure generator components of the power-assisted brake system is changed. In the prior art, noise is generated during the transition between operating states due to the large number of components to be controlled, which noise can be perceived by the vehicle's passengers in the vehicle interior and accordingly affects the vehicle's operating comfort. Summary of the invention

[0006] The object of the present invention is to improve the operating noise of a power-assisted brake system and to increase the driving comfort of a vehicle during the transition of operating states of the power-assisted brake system. This is achieved according to the present invention primarily by the following manner: during an operating state of the power-assisted brake system in which no brake pressure buildup occurs in the brake circuit, the brake circuit control valve is controlled by an electronic controller in such a way that it assumes a penetration position.

[0007] Further advantages or advantageous developments of the invention will be found in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Exemplary embodiments of the invention are depicted in the drawings and will be explained in detail in the following description.

[0009] The accompanying drawings comprise a number of figures, among which:

[0010] FIG. 1 shows a hydraulic circuit diagram of a power-assisted brake device during a passive operating state;

[0011] FIG. 2 shows, in contrast, a hydraulic circuit diagram of a power-assisted brake system during an active operating state; and

[0012] · Figure 3 The invention is explained with reference to a hydraulic circuit diagram in which the power-assisted brake system is in an operating state which, in order to distinguish it from the operating states explained above, is referred to as an active operating state without brake pressure generation. DETAILED DESCRIPTION

[0013] 1 shows the power-assisted brake system, as mentioned, during a passive operating state. The power-assisted brake system assumes this operating state when there is no braking request or when no brake pressure buildup is taking place by the electronic control unit.

[0014] The known power-assisted brake device 10 is equipped with a master brake cylinder 12, which can be operated in order to predetermine the braking desire by the driver via an operating element 14. In FIG. 1, a brake pedal is shown as the operating element 14, but as an alternative to this, a brake lever can also be considered, for example. In the present embodiment, the operating element 14 is connected to one of the two master brake cylinder pistons 18a, b by way of a pressure tie rod 16. The master brake cylinder pistons 18a, b define assigned pressure chambers 22a, b in a common cylinder housing 20, respectively, which are supplied with hydraulic pressure medium by a pressure medium reservoir 24 coupled to the master brake cylinder 12. The pressure chamber 22a facing the operating element 14 is located between the two master brake cylinder pistons 18a, b and accommodates a first piston spring, by which the first master brake cylinder piston 18a is supported on the second master brake cylinder piston 18b. The second master brake cylinder piston 18b is supported at the bottom of the cylinder housing 20 by a second piston spring. Thus, as the driver applies pressure to the actuating element 14, the two master brake cylinder pistons 18a, b move forward in the direction of pressure buildup and thereby enter the interior of the cylinder housing 20. Here, the volume of the associated pressure chambers 22a, b decreases and the actuating element 14 performs an actuation distance. This actuation distance is detected by the displacement sensor 26 and converted into a voltage signal. This voltage signal is proportional to the braking desire and forms the main input variable for brake pressure regulation by the electronic controller 28, which is assigned to the power-assisted brake system 10.

[0015] One of the two brake circuits 30a, b of the power-assisted brake system 10 is respectively connected to the two pressure chambers 22a, b of the master brake cylinder 12 in a controllable manner. For control, a so-called circuit separation valve 32a, b is respectively provided in each brake circuit 30a, b. The circuit separation valve 32a, b is respectively a normally open 2 / 2 stroke switching valve, which can be switched from a penetration position to a blocking position by electrical control by an electronic controller 28 of the power-assisted brake system 10.

[0016] In the passive operating state of power-assisted brake system 10 shown, circuit disconnect valves 32 a, b assume their released position, as a result of which a hydraulic connection is established from master brake cylinder 12 to brake circuits 30 a, b.

[0017] In order to be able to realize the actuation distance of the actuating element 14 of the power-assisted brake system 10 even when the circuit clutch valves 32a, b are closed, i.e. during the active operating state of the power-assisted brake system 10 (FIG. 2), the pressure chamber 22a of the master brake cylinder 12 facing the actuating element 14 is connected to a pedal travel simulator 34. The pedal travel simulator 34 is a simulator piston 40 accommodated in a simulator cylinder 36 and loaded by an elastic element 38, which defines a simulator chamber 42 that can be filled with pressure medium from the pressure chamber 22a of the master brake cylinder 12. The elastic element 38 counteracts the inflow direction of the pressure medium into the simulator chamber 42 and is arranged on the back side of the simulator piston 40 for this purpose. The hydraulic connection of the pedal travel simulator 34 to the pressure chamber 22a of the master brake cylinder 12 can be implemented in a controlled manner again. For this purpose, there is a simulator control valve 44, which is implemented as a normally closed 2 / 2 stroke switching valve that can be controlled electrically.

[0018] In the passive operating state of the power-assisted brake system 10 shown, the simulator control valve 44 accordingly assumes its blocking position, so that no pressure medium can flow from the pressure chamber 22 a of the actuated master brake cylinder 12 into the simulator chamber 42 .

[0019] As mentioned, the elastic element 38 of the pedal travel simulator 34 is arranged in a rear chamber 46 on the back side of the simulator piston 40 in the simulator cylinder 36 facing away from the simulator chamber 42. The rear chamber 46 is also filled with hydraulic pressure medium and is also hydraulically connected to the second pressure chamber 22b of the master brake cylinder 12 away from the actuating element 14 and is also hydraulically connected in parallel to the pressure medium reservoir 24 of the power-assisted brake system 10. In order to detect the pressure in the second pressure chamber 22b of the master brake cylinder 12, the power-assisted brake system 10 is equipped with a pressure sensor 48. The pressure sensor provides a voltage signal to the electronic control unit 28, which corresponds to the brake pressure that prevails in the assigned brake circuit 30b. The pressure signal and the travel signal of the displacement sensor 26 constitute mutually redundant parameters for controlling the brake pressure in the brake circuits 30a, b.

[0020] Downstream of the circuit clutch valves 32a, b, a motor-driven brake pressure generator 50 is in contact with the brake circuits 30a, b in parallel with the master brake cylinder 12. The brake pressure generator 50 is a plunger device with a plunger piston 54 that can be operated by a drive motor 52, and the plunger piston is guided in an axially movable manner in a plunger cylinder 56. When the plunger piston is driven in the pressure building direction, the driven plunger piston 54 discharges the pressure medium from the plunger working space 58 into the brake circuits 30a, b, or when the plunger piston 54 is driven in the reverse or pressure unloading direction, the pressure medium is extracted from the brake circuits 30a, b. The volume of the plunger working space 58 gradually decreases in the pressure building direction and increases accordingly in the pressure unloading direction.

[0021] The actuation of the drive motor 52 is monitored by a motor sensor system. The sensors 55a, b of the drive motor generate a voltage signal proportional to the rotation angle of the drive shaft of the drive motor 52 and a voltage signal proportional to the motor current. These two voltage signals are also detected by the electronic control unit 28 and are mainly used to evaluate the brake pressure regulation.

[0022] The hydraulic line connection 60a, b of the brake pressure generator 50 and the brake circuit 30a, b can be controlled by a plunger control valve 62a, b. The plunger control valve 62a, b is a 2 / 2 stroke switching valve, which is closed in its initial position and is switched to the penetration position by the electronic controller 28 in the active operating state of the power-assisted brake system 10.

[0023] In the passive operating state shown, plunger control valves 62 a, b interrupt line connections 60 a, b to brake circuits 30 a, b. A brake pressure buildup in brake circuits 30 a, b is therefore not possible via brake pressure generator 50 .

[0024] Downstream of the location where the brake pressure generator 50 is coupled to the brake circuit 30a, b, the brake circuit 30a, b branches into two brake circuit branches 31a-d respectively. Each of these brake circuit branches 31a-d is, for example, supplied with a pressure medium under brake pressure when necessary to the connected wheel brake 64a-d. The wheel brakes 64a-d are, for example, arranged diagonally distributed on the vehicle, that is, one of the wheel brakes 64a, d of the front axle (FL and FR) of the vehicle and one of the wheel brakes 64b, c of the rear axle (RR, RL) are present in the brake circuits 30a, 30b, respectively. In addition, the two wheel brakes 64a and 64d or 64b and 64c of the axle are located on different sides of the vehicle.

[0025] Each wheel brake 64a-d is connected upstream of a brake pressure control valve arrangement. The brake pressure control valve arrangement comprises a pressure build-up valve 66a-d and a pressure relief valve 68a-d, which can be electrically controlled by the electronic control unit 28. The pressure build-up valves 66a-d are each designed as a normally open 2 / 2 stroke proportional valve, while the pressure relief valves 68a-d are each designed as a normally blocked 2 / 2 stroke switching valve.

[0026] In the passive operating state of the power-assisted brake system 10 shown, the pressure-building valves 66 a - d and the pressure-relief valves 68 a - d each assume the illustrated starting position.

[0027] A common pressure medium return 70 is led from the pressure relief valve 68a-d back to the pressure medium reservoir 24. The pressure medium return 70 is in contact with the brake pressure generator 50 via two pressure medium branches 72a, b. The first pressure medium branch 72a merges into the plunger working space 58 in the range of the internal dead center of the position of the plunger piston 54 in the plunger cylinder 56, and the second pressure medium branch 72b is located in the range of the external dead center of the plunger piston 54. When the plunger piston 54 is actuated by the drive motor 52 in the pressure building direction, the second pressure medium branch 72b is controlled by the check valve 74, which prevents the pressure medium from being discharged from the plunger working space 58 toward the pressure medium reservoir 24. The pressure medium branch 72a is controlled according to the position of the plunger piston 54 in the plunger cylinder 56.

[0028] During the passive operating state of the power-assisted brake system 10 , the plunger piston 54 assumes a position in which the first pressure medium branch 72 a to the pressure medium return 70 or to the pressure medium accumulator 24 is open, as shown.

[0029] In the passive operating state of power-assisted brake system 10 , wheel brakes 64 a - d of brake circuits 30 a, b are hydraulically connected to non-actuated master brake cylinder 12 via open pressure build-up valves 66 a - d and further via likewise open circuit disconnect valves 32 a, b and are therefore not pressurized.

[0030] FIG. 2 illustrates the power-assisted brake system 10 according to FIG. 1 during an active operating state, wherein the valve components and pressure generator components mentioned above are provided with corresponding reference numerals for the sake of simplicity, although these components occupy different valve positions compared to FIG. 1. The transition to the active operating state occurs as soon as a braking request is present or as soon as a brake pressure is built up in the brake circuits 30 a, b by the electronic control unit 28 via the electrical actuation of the drive motor 52 of the pressure generator 50.

[0031] The power-assisted brake system 10 works in principle in the following manner:

[0032] If the brake pressure buildup occurs due to the driver's existing braking desire, the driver actuates the actuating element 14 of the power-assisted brake system 10 for this purpose. Subsequently, the master brake cylinder piston 18a, which is mechanically coupled to the actuating element 14 via the pressure tie rod 16, discharges the pressure medium from its assigned pressure chamber 22a into the simulator chamber 42 of the pedal travel simulator 34, and the actuating element 14 performs an actuation distance corresponding thereto. The latter (the actuation distance) is detected by the displacement sensor 26 and converted into a voltage signal, which is supplied to the electronic controller 28. The electronic controller derives the existing braking desire from the voltage signal and generates a control signal to the drive motor 52 of the brake pressure generator 50. The drive motor 52 drives the plunger piston 54 in the direction of the pressure buildup. Here, the pressure medium is discharged from the plunger working space 58 in the direction of the wheel brakes 64a-d and there results in the buildup of a brake pressure proportional to the actuation of the actuating element 14. As a result, the vehicle performs a braking process.

[0033] If the brake pressure at at least one wheel brake 64a-d of the vehicle is so high that the wheel assigned to the wheel brake 64a-d is close to locking, the wheel speed sensor 78 detects the risk of locking and forwards it to the electronic control unit 28. The electronic control unit thus controls the brake pressure valve control device so that the relevant pressure build-up valve 66a-d adopts the blocking position and the pressure relief valve 68a-d adopts the penetration position. The brake pressure is relieved wheel-by-wheel via the pressure medium return 70 toward the pressure medium reservoir 24 until the assigned wheel has a rotational speed that corresponds to the vehicle speed again. The brake pressure valve control device is then switched back to the explained initial state by the electronic control unit 28.

[0034] First, when transitioning to the active operating state, both circuit isolation valves 32a, b are actuated by electronic control unit 28 and switched to the blocking position illustrated in Fig. 2. Master brake cylinder 12 is thus decoupled from brake circuits 30a, b and thus also serves as a device for detecting a braking requirement.

[0035] In addition, plunger control valves 62a, b are also electrically controlled and switched into their penetration position as shown in Figure 2. Thus, a hydraulic connection of brake pressure generator 50 to brake circuits 30a, b is achieved, so that a corresponding brake pressure buildup can be carried out by brake pressure generator 50 by actuating drive motor 52.

[0036] In order to carry out this brake pressure buildup without a time delay and therefore with a high pressure buildup dynamics, the plunger piston 54 moves to a position in which the first pressure medium branch 72a of the plunger working space 58, which is configured at the internal dead center of the position of the plunger piston 54, is interrupted from the pressure medium reservoir 24 by the plunger piston 54. To this end, the plunger piston 54 is moved forward a certain distance in the pressure buildup direction starting from its internal dead center by electrical control of the drive motor 52.

[0037] Finally, when transitioning to the active operating state, the simulator control valve 44 is still actuated and switched to its penetration position. Thus, the pedal-side pressure chamber 22a of the master brake cylinder 12 is coupled to the pedal travel simulator 34, which is shown by means of the offset plunger piston 40 in FIG. 2 .

[0038] When power-assisted brake system 10 transitions from a passive to an active operating state, the electrical activation of the aforementioned components disadvantageously triggers operating noises that can be perceived by passengers in the interior of the vehicle and can impair driving comfort.

[0039] The present invention Figure 3 The invention relates to a method for controlling a power-assisted brake system 10. The proposed method aims to improve the operating noise and increase the comfort of the power-assisted brake system 10 by setting a changed switching position of the valve and the pressure generator assembly when the power-assisted brake system 10 is in an operating state without brake pressure buildup. This operating state is referred to as an active operating state without brake pressure buildup in order to distinguish it from the operating state described above.

[0040] According to the invention, it is proposed that during the operating state of the power-assisted brake system 10, the plunger piston 54 maintains its current position within the plunger cylinder 56 and thus blocks the first pressure medium connection 72a to the pressure medium return 70. In addition, at least one of the two circuit clutch valves 32a, b is electrically controlled so that it takes up a penetration position. Finally, the two brake circuits 30a, b are hydraulically connected to one of the pressure chambers 22a, b of the master brake cylinder 12 and thus to the pressure medium reservoir 24 via this at least one open circuit clutch valve 32a, b. For the brake circuit 30a, the hydraulic connection to the pressure medium reservoir 24 is achieved directly via the associated circuit clutch valve 32a, while for the corresponding other brake circuit 30b, the hydraulic connection is only implemented indirectly via the electrically actuated and therefore penetrated plunger control valve 62a, b, the intermediately connected plunger working space 58 of the brake pressure generator 50 and the circuit clutch valve 32a in the penetrated position.

[0041] At this point it should be pointed out that, as an alternative, instead of the return isolation valve 32 a , a correspondingly different return isolation valve 32 b can also be brought into the penetration position, or both return isolation valves 32 a , b can assume their penetration position.

[0042] During an active operating state without brake pressure buildup, any possible heating of the pressure medium in the brake circuits 30a, b and the resulting increase in volume of the pressure medium can therefore be reduced toward the pressure medium reservoir 24 and counteract the brake pressure buildup in the wheel brakes 64a-d or the occurrence of residual slip torque in the wheel brakes 64a-d, without the need to actuate the plunger piston 54 in the direction of pressure relief for this purpose.

[0043] By means of adapted electrical actuation of drive motor 52 of brake pressure generator 50 , the position of plunger piston 54 within plunger cylinder 56 is maintained during this operating state of power-assisted brake system 10 .

[0044] In order to transition from an active operating state without brake pressure buildup to an active operating state with brake pressure buildup, it is therefore only necessary to cancel the electrical control of one or more circuit clutch valves 32a, b. The electrical control of the plunger control valves 62a, b is unchanged and the plunger piston 54 also maintains its position within the plunger cylinder 56. The plunger working space 58 and the first pressure medium connection 72a of the pressure medium return 70 are then kept closed.

[0045] Finally, according to the invention, during the transition between operating states, fewer components involved are actuated and thus less operating noise is caused. As a result, the noise comfort of the vehicle is improved without changing the functionality of the power-assisted brake system 10 .

[0046] It goes without saying that modifications or additions to the described exemplary embodiments are conceivable without departing from the basic idea of ​​the invention.

Claims

1. A method for controlling an electronically slip-adjustable power-assisted brake device (10), comprising: an operating device (14) for presetting a braking expectation, a master brake cylinder (12) coupled to the actuating device (14), at least one brake circuit (30a, b), wheel brakes (64a-d) connected to the brake circuits (30a, b) and a brake pressure generator (50) which can be actuated by power assistance, wherein the brake pressure generator (50) and the master brake cylinder (12) are in contact with the brake circuits (30a, b) in parallel with each other, Furthermore, a pressure generator control valve (62a, b) for controlling a first pressure medium connection between the brake pressure generator (50) and the brake circuit (30a, b), and A brake circuit control valve (32a, b) for controlling a second pressure medium connection between the brake circuit (30a, b) and the master brake cylinder (12), characterized in that: The power-assisted brake system (10) is operable in an operating state, during which the pressure generator control valve (62a, b) occupies a breakthrough position, while the brake pressure in the brake circuit (30a, b) is not dominant and no brake pressure build-up is carried out, and in the operating state of the power-assisted brake system (10), the brake circuit control valve (32a, b) is actuated in such a way that it occupies the breakthrough position.

2. The method according to claim 1, characterized in that During an operating state of the power-assisted brake system (10), an existing third pressure medium connection from a brake pressure generator (50) of the power-assisted brake system (10) to a pressure medium reservoir (24) is interrupted.

3. The method according to claim 2, characterized in that The brake pressure generator (50) of the power-assisted brake system (10) has a plunger piston (54) which can be driven by an electric motor and is guided axially displaceably in a plunger cylinder (56), and a third pressure medium connection from the brake pressure generator (50) to a pressure medium reservoir (24) is interrupted by corresponding positioning of the plunger piston (54) in the plunger cylinder (56).

4. The method according to any one of claims 1 to 3, in, The power-assisted brake device (10) is equipped with a first brake circuit (30a) and a second brake circuit (30b), and has a first brake circuit control valve (32a) assigned to the first brake circuit (30a) and a second brake circuit control valve (32b) assigned to the second brake circuit (30b). It is characterized in that During an operating state of the power-assisted brake system (10), at least one of the two brake circuit control valves (32a, b) is actuated.

5. The method according to any one of claims 1 to 3, in, The power-assisted brake equipment (10) is equipped with a travel simulator (34) capable of realizing the operating distance of the operating device (14), and The travel simulator (34) is controllably connected to the master brake cylinder (12) via an actuable simulator control valve (44). It is characterized in that During an operating state of the power-assisted brake system (10), the simulator control valve (44) is actuated in such a way that it assumes a penetration position.

6. The method according to claim 5, characterized in that The power-assisted brake device (10) is equipped with an electronic controller (28), and the electronic controller (28) controls the operation of the brake circuit control valve (32a, b), the plunger piston (54) and / or the simulator control valve (44).

7. The method according to claim 1, characterized in that The power-assisted brake equipment (10) is used in a motor vehicle.

8. A power-assisted brake device (10) capable of electronically adjusting slip, comprising: an operating device (14) for presetting a braking expectation, a master brake cylinder (12) coupled to the actuating device (14), at least one brake circuit (30a, b), Wheel brakes (64a-d) connected to the brake circuits (30a, b) and a brake pressure generator (50) which can be actuated by power assistance, wherein the brake pressure generator (50) and the master brake cylinder (12) are each controllably connected to the brake circuits (30a, b) and in parallel with each other, Furthermore, a pressure generator control valve (62a, b) for controlling a first pressure medium connection between the brake pressure generator (50) and the brake circuit (30a, b), and A brake circuit control valve (32a, b) for controlling a second pressure medium connection between the brake circuit (30a, b) and the master brake cylinder (12), characterized in that: The power-assisted brake system (10) is equipped with an electronic control unit (28) which is designed to control the power-assisted brake system (10) according to a method according to any one of claims 1 to 7.

Images