Method for starting up an electronically slip-controllable externally powered brake system for a motor vehicle, and electronic control unit for controlling the brake pressure of an externally powered brake system for a motor vehicle

Abstract

The invention relates to a method for starting up an electronically slip-controllable externally powered brake system (10) for a motor vehicle and to an electronic control unit (28) for controlling the brake pressure of an externally powered brake system (10). Known externally powered brake systems (10) are equipped with a piston / cylinder unit (32) for controlling the brake pressure in a brake circuit (A; B), wherein a piston (38) of said unit can be actuated by a motor (30) for a reciprocating translational movement within a cylinder (40). The motor control by an electronic control unit (28) requires knowledge of the position of the piston (38) inside the cylinder (40). For this purpose, a reference movement of the piston (38) to an end stop is carried out immediately after a start-up of the externally powered brake system (10). The reference movement causes a time delay from the start-up to a possible control of the brake pressure. According to the invention, immediately after the externally powered brake system (10) is started up, the brake pressure is controlled at a reduced piston speed until the piston position can be carried out on the basis of the reference movement at a more suitable later time after the brake pressure has been controlled.

Description

[0001] Disclosure of the invention

[0002] title

[0003] Method for commissioning an electronically controlled power brake system for a motor vehicle and electronic control unit for brake pressure control of a power brake system for a motor vehicle

[0004] The invention relates to a method for commissioning an electronically controlled power brake system for a motor vehicle according to the features of claim 1 and to an electronic control unit for brake pressure control of a power brake system for a motor vehicle according to the features of the preamble of the independent claim 7.

[0005] State of the art

[0006] Electronically controlled power brake systems are state-of-the-art and are used in modern motor vehicles for slip-dependent brake pressure control

[0007] By way of example, Figure 1 of this document shows the hydraulic circuit diagram of an external power brake system on which the invention is based and which is known from DE 10 2018 214 820 A1.

[0008] In contrast to conventional muscle-powered braking systems, with power-assisted braking systems the driver is decoupled from the actual brake pressure generation during normal operation of the system. They simply indicate a braking request by actuating a braking request input device, such as a foot-operated pedal or a hand-operated lever, which is then provided by a brake pressure generator driven by external power. The brake pressure generator is driven by an electric motor, hereinafter referred to as the motor, which is controlled by an electronic control unit with a control signal corresponding to the braking request. The brake pressure generator is a piston / cylinder unit with a piston that is slidably mounted in a cylinder and, together with the cylinder, defines a working chamber with a variable volume. The piston is actuated by the motor to perform a reciprocating translational movement.To build up brake pressure, the piston is driven in a first spatial direction and to reduce brake pressure, it is driven in a second spatial direction opposite to this first spatial direction.

[0009] When brake pressure builds up, the pressure fluid contained in the working chamber is displaced into a brake circuit connected to the brake pressure generator and connected to at least one wheel brake. When brake pressure decreases, pressure fluid flows from this brake circuit back into the working chamber. Accordingly, the volume of the working chamber decreases due to the piston movement when brake pressure builds up and increases again when brake pressure decreases.

[0010] The respective piston movement speed can be variably adjusted via the control signal to the motor. A power brake system is thus able to adapt the gradient with which the brake pressure changes in the brake circuit to the demand or desired braking action.

[0011] A prerequisite for electronic brake pressure control or for the electronic control unit to determine the actuation direction and / or actuation speed of the piston via the motor control signal is knowledge of the piston position within the cylinder. This information is obtained in the current state of the art by driving the piston on a reference run immediately after the vehicle brake system is started up. The piston is moved in the pressure reduction direction until it mechanically hits a design-specific, so-called inner end stop. Once it has reached the end stop, the current engine rotation angle is assigned to the piston position, and this assignment is stored in the electronic control unit. The engine rotation angle is recorded and evaluated by an engine rotation angle sensor.The disadvantage of this procedure is that the reference run immediately after the power brake system is put into operation takes a period of time during which no brake pressure control is available.

[0012] In safety-critical driving situations, the reference run is therefore performed with an increased reference movement speed of the piston in order to keep the required time and the time delay as short as possible. However, an increased piston speed results in greater kinetic energy in the piston and thus increased stress on the piston drive when the piston movement is braked to a standstill at the end stop. Over the service life of a power brake system, this can lead to premature damage to the components of the piston drive or even cause a total failure of the brake pressure generation.

[0013] In particular, if the power brake system has not been deactivated as intended beforehand, for example because the power supply to the electronic control unit was faulty and / or the piston has come to a standstill far from its inner end stop for mechanical reasons, the time delay in brake pressure control is particularly serious.

[0014] Advantages of the invention

[0015] In the method underlying this invention, the reference run of the piston immediately after commissioning of the power brake system is omitted and the brake pressure control is carried out virtually without any time delay, although at this point in time the position of the piston within the cylinder could not yet be determined.

[0016] According to the invention, brake pressure control is performed immediately after commissioning of the power brake system based on piston actuation at a dynamically adjustable, reduced speed. The position of the piston within the cylinder is determined based on the reference run at a later, more suitable time after the brake pressure control. A more suitable time after commissioning occurs, for example, when no brake pressure demand is expected.

[0017] The proposed method eliminates the need for a reference run of the piston immediately after commissioning the power brake system, thus eliminating any delay until brake pressure control or boosting is available. This eliminates piston movement at increased piston speed, and the aforementioned hard impact of the piston on one of its end stops and the resulting component stress are eliminated. This has a clearly positive effect on the availability of brake pressure control in a power brake system.

[0018] The invention consciously accepts that the speed range in which the piston is moved until a reference run is reduced compared to the speed range in which a brake pressure control takes place under normal conditions of the power brake system, i.e. with a known position of the piston within the cylinder, and that accordingly, until the reference run of the piston is carried out, brake pressure controls can only be implemented with lower pressure change gradients.

[0019] A determination of the reduced speed at which the piston is moved immediately after the vehicle brake system is put into operation in response to a given braking request is based on the piston position within the cylinder which the piston last assumed when the vehicle brake system was previously deactivated.

[0020] The method underlying the invention is used in particular when the power brake system has gone out of operation following a malfunction in the power supply of the electronic control unit and / or when, after the power brake system has been taken out of operation, the piston has not reached its intended starting position and is located far from its inner end stop. According to the invention, the method is carried out by a correspondingly configured electronic control unit of a hydraulic unit of the power brake system. Apart from the control electronics of the electronic control unit, no further changes to the individual components of the hydraulic unit or to the existing hydraulic circuit diagram of a system underlying the invention are therefore necessary.

[0021] A power brake system is required. Consequently, the invention can be easily and cost-effectively implemented in large-scale production and, if necessary, retrofitted by updating the control unit software.

[0022] Further advantages or advantageous developments of the invention may emerge from the following description.

[0023] drawing

[0024] The invention is illustrated by the drawing and is explained in detail in the following description.

[0025] Fig. 1 shows the hydraulic circuit diagram of a power brake system on which the invention is based and which is known from the prior art, and in the

[0026] Fig.2 shows the method underlying the invention in a simplified schematic form using a flow chart.

[0027] Description

[0028] Figure 1 shows the hydraulic circuit diagram of an electronically controlled slip-controllable power brake system 10 on which the invention is based. This hydraulic circuit diagram is part of the state of the art and is therefore only briefly explained below.

[0029] The electronically controlled power brake system 10 has a

[0030] braking request, for example, a pedal 18 actuated

[0031] Master brake cylinder 16. One of the pressure chambers of this master brake cylinder 16 is connected to a pedal feel simulator 20 via a simulator control valve 22. In normal operation, this simulator valve 22 is open, contrary to the illustration in Fig. 1, so that when the driver actuates the brake pedal 18, pressure fluid is displaced from the master brake cylinder 16 into a simulator chamber of the pedal feel simulator 20. A simulator piston is slidably received in the simulator chamber against the restoring force of a spring element and thus provides the driver with a haptic reaction on the pedal 18 that correlates with the pedal actuation.

[0032] For example, two brake circuits A; B are connected to the master brake cylinder 16, which in turn are each connected to two wheel brakes 12. The two connections of the master brake cylinder 16 to the brake circuits A; B are interrupted by valve devices 24 during normal operation of the power brake system 10. Thus, the driver is decoupled from the brake circuits A; B during normal operation and is unaware of the prevailing brake pressure in these brake circuits A; B.

[0033] In the event of a malfunction of the power brake system 10, a hydraulic connection can be created between the master brake cylinder 16 and the wheel brakes 12 by opening the valve devices 24. The driver is then able to build up braking pressure in these wheel brakes 12 using muscle power by operating the pedal 18 and decelerate the vehicle.

[0034] Master brake cylinder 16, brake circuits A; B and wheel brakes 12 are supplied with hydraulic pressure medium by a pressure medium reservoir 14.

[0035] A second valve device comprising a pair of controllable valves 42; 44 is assigned to each wheel brake 12 and enables, if required, individual wheel control of the brake pressures in the assigned wheels 12.

[0036] Brake pressure in brake circuits A; B is provided by a piston / cylinder unit 32, which is connected to these brake circuits A; B in parallel to the master brake cylinder 16. This piston / cylinder unit 32 comprises a piston 38 movably received in a cylinder 40, which, together with the cylinder 40, defines a working chamber. The piston 38 can be driven by an electronically controllable motor 30 via a downstream gear 36 to perform a translational movement in a pressure build-up direction or, in the opposite direction, in a pressure reduction direction. In the pressure build-up direction, the volume of the working chamber of the piston / cylinder unit 32 decreases, while in the pressure reduction direction, it increases.

[0037] A third valve device 34 provided in the power brake system 10 enables the piston / cylinder unit 32 to be decoupled from the brake circuits A; B if necessary. In the decoupled state, the piston / cylinder unit 32 is capable of recharging pressure medium from the pressure medium reservoir 14 through a supply channel 41 into the working chamber by actuating the piston 38 in the pressure reduction direction.

[0038] Finally, the power brake system 10 is equipped with an electronic control unit 28. This control unit 28 detects signals from sensors 26, 27, 29, 48, 50 for detecting pedal travel, motor rotation angle, motor current, wheel speed, and pressure. Depending on the signals, it controls the aforementioned valve devices 24, 34, 42, 44 as well as the motor 30 to actuate the piston / cylinder unit 32 for brake pressure control, e.g., to adjust the brake pressure as needed to the prevailing slip conditions at the vehicle's wheels. Brake pressure control processes can be carried out automatically, i.e., independently of an existing driver command, or driver-dependent, i.e., dependent on the actuation of the master brake cylinder 16.

[0039] In Figure 1, the electronically controllable components are shown in their non-actuated basic position.

[0040] Fig.2 illustrates, using a diagram, the sequence of the method underlying the invention.

[0041] This method begins with the commissioning of the vehicle brake system 10 by switching on the voltage supply of a motor vehicle, for example by unlocking or opening a vehicle access by a driver or passenger or by actuating a corresponding actuating device (step 60).

[0042] With commissioning, the electronic control unit 28 of the

[0043] Power brake system 10 is put in readiness to implement an existing brake pressure request by correspondingly controlling the motor 30 assigned to the piston / cylinder unit 32.

[0044] If a corresponding query 62 indicates that such a brake pressure request exists, the electronic control unit 28 sends a control signal to the motor 30 in step 64. This control signal is selected such that the piston 38 is moved at a piston speed that lies within a speed range that is lower than the piston speed range during a translational movement of this piston 38 to a brake pressure setting under normal conditions of the power brake system 10, i.e. when the position of the piston 38 within the cylinder 40 is already fixed or the position of the piston 38 is assigned to the motor rotation angle.

[0045] In the state in which the above-mentioned assignment has not yet been made, the electronic control unit 28 bases the determination of a control signal to the motor 30 on the position of the piston 38 within the cylinder 40 which was last known when the power brake system 10 went out of operation.

[0046] This prevents excessive stress on the components of the piston drive (motor 30; gear 36) if the piston 38 hits one of its end stops during the brake pressure generation process. The latter possibility cannot be ruled out with certainty due to a lack of knowledge of the exact position of the piston 38 within the cylinder 40 at this time.

[0047] After the brake pressure request has been met and if no further brake pressure request is present, the reference movement of piston 38 takes place in step 66. Piston 38 is also driven at a piston speed (= reference movement speed) that is reduced compared to the translational movement speed. The reference movement also takes place if no existing brake pressure request was detected in query 62.

[0048] During the reference run, the piston 38 of the piston / cylinder unit 32 is actuated by the motor 30 in the pressure reduction direction until it mechanically strikes the so-called inner end stop. The reference movement speed of the piston 38 lies in a speed range that, as mentioned, is below the speed range of a translational movement of the piston 38 during brake pressure control in normal operation of the power brake system 10.

[0049] When the piston 38 hits the inner end stop, the position of the piston 38 within the cylinder 40 is assigned to the current engine rotation angle and stored in the electronic control unit 28. Consequently, the electronic control unit 28 is now able, in the event of a subsequent brake pressure request or brake pressure control, to drive the piston 38 at a speed within a speed range of a translational movement without risking mechanical overload of the piston drive (30; 36). The speed range of translational movements of the piston 38 is intended to be above the speed range in which the reference movements of the piston 38 take place.

[0050] If a second query 68 indicates that a new brake pressure request exists, a control signal is sent from the electronic control unit 28 to the piston 38 at 70, with which this piston 38 is now driven at translational movement speed in order to fulfill the brake pressure request. Query 68 is repeated continuously until such a brake pressure request is detected.

[0051] Of course, changes or additions beyond this description are conceivable without deviating from the basic idea of ​​the invention claimed in the independent claims.

[0052] Finally, it should be explicitly pointed out again that the speed of the piston can be dynamically adapted to the respective brake pressure requirement during both translational movements and reference movements and that the speed range in which translational movements take place is above the speed range of ongoing reference movements.

Claims

Claims 1. A method for commissioning an electronically controlled slip-controllable power brake system (10) for a motor vehicle, which is equipped with a piston / cylinder unit (32) actuated by an electrically controllable motor (30) for brake pressure control in a brake circuit (A; B), wherein the piston / cylinder unit (32) has a piston (38) guided inside a cylinder (40) which can be driven by the motor (30) to perform a reciprocating translational movement, wherein the power brake system (10) has an electronic control unit (28) configured to send a variable electrical control signal to the motor (30), wherein the electrical control of the motor (30) is performed as a function of a position of the piston (38) within the cylinder (40), and the position of the piston (38) within the cylinder (40) is determined based on a reference run,in which the piston (38) is moved at a reference movement speed against a mechanical end stop and wherein the reference movement speed is reduced compared to a translational movement speed of the piston (38) during a brake pressure control, characterized in that immediately after commissioning of the power brake system (10), a brake pressure control is carried out by actuating the piston (38) at a speed which is lower than the, T ranslation movement speed reduced speed is carried out until the position of the piston (38) within the cylinder (40) is determined on the basis of a reference run and wherein the reference run of the piston (38) is carried out after the brake pressure control.

2. Method according to claim 1, characterized in that after the vehicle brake system (10) has been put into operation until the reference run of the piston (38) has been carried out, the position of the piston (38) within the cylinder (40) is used as the basis which the piston (38) had assumed during an immediately preceding decommissioning of the vehicle brake system (10).

3. Method according to claim 1 or 2, characterized in that after commissioning of the power brake system (10), the reference run for determining the position of the piston (38) within the cylinder (40) is carried out as soon as no brake pressure request is expected from the power brake system (10).

4. Method according to one of claims 1 to 3, characterized in that during the reference run the piston (38) is actuated in the direction of a brake pressure reduction until the piston (38) mechanically strikes an inner end stop.

5. Method according to one of claims 1 to 4, characterized in that the method is carried out after a fault has occurred in a voltage supply of the electronic control unit (28).

6. Method according to claim 4 or 5, characterized in that the method is carried out after decommissioning of the power brake system (10), in which the piston (38) is located away from the inner end stop.

7. Electronic control unit for brake pressure control of an external power brake system of a motor vehicle, characterized in that the electronic control unit (28) is designed to carry out a method according to one of claims 1 to 6.

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