Method for controlling a hydraulic motor vehicle braking system and hydraulic motor vehicle braking system

Abstract

Method for controlling a motor vehicle braking system (100) comprising the following components: - front wheel brakes (110) and rear wheel brakes (120); - a master brake cylinder (140) comprising a pressure piston (141) actuated by means of a brake pedal (130) and an electromechanical brake booster (145); - a vehicle dynamics control module (150) comprising a hydraulic pump (151) and a separating valve (152) for separating the pre-pressure hydraulics from the wheel brake hydraulics; with the following steps: - Generating wheel brake pressure (p brems ) by pressing the brake pedal (130), whereby the electromechanical brake booster (145) generates an assisting force; - Increasing the wheel brake pressure (p brems ) using the hydraulic pump (151) of the vehicle dynamics control module (150), whereby the isolation valve (152) is closed, so that the pressure (p vor) of the pre-pressure hydraulics from the pressure (p brems ) the wheel brake hydraulics differs; - Preventing a reaction on the brake pedal (130) by adjusting the support force generated by the electromechanical brake booster (145) so that the brake pedal position (Pos. 1) is maintained, for which the following sub-steps are carried out: - Determining the pre-pressure prevailing in the master brake cylinder (140) (p vor ); - Calculating a pressure difference (Δp) between the determined pre-pressure (p vor ) and the pressure-volume characteristic curve that results for each brake pedal position (p (V) ) the resulting brake pressure of the motor vehicle braking system (100); - Reducing the support force generated by the electromechanical brake booster (145) by an amount corresponding to the calculated pressure difference (Δp).

Description

[0001] The invention relates to a method for controlling a hydraulic motor vehicle braking system, which comprises front and rear wheel brakes, a master brake cylinder with an electromechanical brake booster, and a vehicle dynamics control module, as explained in more detail below. The invention further relates to such a hydraulic motor vehicle braking system.

[0002] A hydraulic motor vehicle braking system (brake system) of this type is known, for example, from DE 20 2019 102 503 U1 (see in particular paragraph

[0014] ).

[0003] In such a hydraulic vehicle braking system, pressing a brake pedal generates brake pressure with an additional force provided by the electromechanical brake booster (in addition to the actuation force or driver's foot force). The relationship between brake pressure and actuation distance (of the brake pedal) is known to be determined by a system-specific pressure-volume characteristic (pV characteristic).

[0004] The nearest patent, DE 10 2010 002 406 A1, describes a method for operating a hydraulic braking system for a vehicle and a corresponding braking system comprising: - front and rear wheel brakes; - a master brake cylinder comprising a pressure piston (first piston and second piston) actuated by means of the brake pedal and input rod, and an electromechanical brake booster; - a so-called volume adjustment unit, by means of which the volume of brake medium or brake fluid present in a part of the hydraulic brake system can be increased and / or reduced by means of a piston (disc) guided in a cylinder and movable by a motor, and thereby the pressure in said part can be adjusted; and - a control unit or control device.

[0005] The volume adjustment unit enables active pressure build-up, particularly at each individual wheel, which can be used, among other things, in a vehicle stability program. The motor of the electromechanical brake booster is kept in the same position. This can be controlled / regulated via the control unit. The driver therefore does not perceive any change in the force required to hold the pedal in that position.

[0006] Regarding the state of the art, reference is also made to DE 10 2010 001 939 A1, which describes a brake booster as well as a method and a device for its operation, and also to DE 10 2013 218 330 A1, which describes a method for operating a brake booster, a control unit for carrying out the method and a brake system comprising the brake booster and the control unit.

[0007] One object of the invention is to demonstrate a way in which a comfortable reduction of the brake pedal travel can be achieved in a hydraulic motor vehicle braking system of the type mentioned above.

[0008] The problem is solved by the method according to the invention of claim 1. By the dependent claim, the invention also extends to a hydraulic motor vehicle braking system equipped with functionality corresponding to the method according to the invention. Further developments and embodiments of the invention are described analogously for both subject matters in the dependent claims, the following description of the invention, and the drawings.

[0009] The method according to the invention is intended for controlling a motor vehicle braking system (braking system) which comprises at least the following components: • front wheel brakes and rear wheel brakes; • a master brake cylinder comprising a hydraulic or pressure piston that can be actuated by means of a brake pedal or the like, and an electromechanical brake booster (eBKV); • a vehicle dynamics control module (ESC, ESP module) for driving situation-dependent control of the wheel brake pressure at each wheel brake, wherein this vehicle dynamics control module has (at least) a hydraulic pump (ESC, ESP pump) and (at least) a separating valve for separating the pre-pressure hydraulics from the wheel brake hydraulics (su).

[0010] Such a braking system, which includes both an electromechanical brake booster and a vehicle dynamics control module, can also be called a 2-box braking system.

[0011] The method according to the invention comprises at least the following steps, which are carried out in particular simultaneously or at least with temporal overlap: • Generating wheel brake pressure by actuating the brake pedal, whereby the electromechanical brake booster generates an assisting force (in addition to the actuating force or driver's foot force); • Intensifying or increasing the wheel brake pressure using the hydraulic pump of the vehicle dynamics control module, particularly with the aim of a shortened actuation distance, whereby the isolating valve is closed so that the pressure of the pre-pressure hydraulics differs from the pressure of the wheel brake hydraulics; • Preventing feedback to the brake pedal by adjusting the support force generated by the electromechanical brake booster so that the brake pedal position (achieved when the brake pedal is pressed) is maintained (su). Preferably, the latter two steps are performed automatically.

[0012] The method according to the invention provides that, when the brake pedal is depressed, additional pressure is built up by means of the hydraulic pump belonging to the vehicle dynamics control module. This hydraulic pump delivers an additional hydraulic volume to the wheel brakes or pumps it into the respective brake pressure lines to which the wheel brakes are connected to the vehicle dynamics control module. This allows the actuation travel of the brake pedal to be shortened, which improves the response, particularly with a flat pressure-volume characteristic curve. However, this leads to a change, and in particular a reduction, in the pre-pressure prevailing in the master brake cylinder. Without the adjustment of the support force generated by the electromechanical brake booster according to the invention, this would be noticeable by a change in the brake pedal position, in particular by the brake pedal noticeably moving away from the foot.By adjusting, in particular reducing, the support force according to the invention, such a feedback effect on the brake pedal is avoided by creating a new equilibrium of forces, which leads to a constant brake pedal position, provided that the actuating force or driver's foot force is not changed or eliminated. The method according to the invention thus achieves a comfortable reduction in the brake pedal travel for the driver without any noticeable or perceptible feedback effect on the brake pedal.

[0013] Preventing feedback to the brake pedal by adjusting the support force generated by the electromechanical brake booster includes the following steps, which are performed primarily automatically: • Determining the pre-pressure prevailing in the master brake cylinder, which results from or has been established due to the hydraulic pump feedback; • Calculating a pressure difference between the determined pre-pressure (in the master brake cylinder) and the brake pressure resulting for each brake pedal position from the (stored) pressure-volume characteristic curve of the motor vehicle braking system (meaning the basic characteristic curve of the overall braking system); • Reducing the support force generated by the electromechanical brake booster by an amount corresponding to the calculated pressure difference (delta force), which can be calculated, for example, via the pressure piston area.

[0014] These sub-steps can also be performed repeatedly, preferably in a control loop, especially depending on a changing brake pedal actuation.

[0015] The pre-pressure in the master brake cylinder can be measured (using a pressure sensor). However, the pre-pressure in the master brake cylinder can also be calculated, for example, using a (stored) mathematical pressure model and / or the measured wheel brake pressure and / or the delivery volume of the hydraulic pump, which can be determined, for example, via the pump runtime.

[0016] The vehicle dynamics control module has (at least) one isolating valve to separate the pre-pressure hydraulic system from the wheel brake hydraulic system. This isolating valve closes when the wheel brake pressure is increased, i.e., when the wheel brake pressure is amplified by the hydraulic pump. This facilitates controlled build-up and, if necessary, reduction of wheel brake pressure. By switching or closing this valve, two hydraulic subsystems are created whose pressures (pre-pressure and wheel brake pressure) differ from each other, as explained in more detail below.

[0017] Preferably, the hydraulic fluid (brake fluid) supplied by the hydraulic pump to increase the wheel brake pressure, while maintaining the brake pedal position, is drawn from a reservoir via (at least) a suitably designed cuff seal of the pressure piston (in the master brake cylinder).

[0018] The motor vehicle braking system (braking system) according to the invention comprises, in addition to the above-mentioned components, (at least) a control unit which is designed to automatically initiate or cause the following process steps: • Increasing the wheel brake pressure (with the brake pedal depressed) using the hydraulic pump of the vehicle dynamics control module and closing the isolation valve (as described above); and • Preventing feedback to the brake pedal by adjusting the support force generated by the electromechanical brake booster so that the brake pedal position is maintained (as described above) by performing the above sub-steps.

[0019] The motor vehicle braking system according to the invention has a separating valve for isolating the pre-pressure hydraulics from the wheel brake hydraulics, which is part of the vehicle dynamics control module (so). The control unit is also designed to control this separating valve accordingly.

[0020] The invention is explained in more detail below by way of example and in a non-limiting manner with reference to the drawing. Fig. Figure 1 shows a schematic representation of a motor vehicle braking system (braking system) according to the invention. Fig. Figure 2 shows an example of the pressure-volume diagram or pressure-volume characteristic curve of the entire braking system. Fig. 1.

[0021] The in Fig. The dual-circuit vehicle braking system 100 shown in Figure 1 includes, by way of example, two hydraulically actuated disc brakes 110 on the front axle (VA) and two hydraulically actuated drum brakes 120 on the rear axle (HA). The vehicle braking system 100 also includes a brake pedal 130, a master brake cylinder 140 with a pressure piston 141 (designed as a tandem piston) and an electromechanical brake booster 145 (coupled to the pressure piston 141 and / or the brake pedal 130), a vehicle dynamics control module 150 (e.g., a standard ESC hydraulic unit), and a control unit 170. Preferably, the master brake cylinder 140 and the electromechanical brake booster 145 are designed as a single unit. The control unit 170 can also be part of the vehicle dynamics control module 150 or the electromechanical brake booster 145.Furthermore, the vehicle dynamics control module 150 and the electromechanical brake booster 145 may each have their own control unit, which communicate with each other. The wheel brakes 110 and 120 are individually connected to the vehicle dynamics control module 150 via brake pressure lines 160.

[0022] The schematically shown vehicle dynamics control module 150 includes, among other things, a hydraulic pump (ESC pump) 151, a separating valve (USV switching valve) 152, and several control valves 153 for the individual wheel brakes 110 and 120, as simplified here for only one of the brake circuits. A separate separating valve may be provided for the other brake circuit. The hydraulic pump 151 can act on both brake circuits by, for example, having at least two pistons or the like, with which it can build up pressure separately in the brake circuits. The vehicle dynamics control module 150 may include further components or parts, as known from the prior art, which will not be discussed further here.

[0023] The invention provides that when the brake pedal 130 is depressed (the depressurization is effected by an assistance force generated by the brake booster 145), the wheel brake pressure is increased or amplified by means of the hydraulic pump 151 of the vehicle dynamics control module 150. This is controlled by the control unit 170. As shown in the diagram of the Fig. As illustrated in Figure 2, this allows for a reduction in brake pedal travel corresponding to the volume difference ΔV (brake pedal travel and hydraulic volume correlate via the pressure piston area). Here, the isolating valve 152 is closed (valve switching), resulting in two hydraulic subsystems: a first hydraulic subsystem (pre-pressure hydraulics) from the master brake cylinder 140 to the isolating valve 152 of the vehicle dynamics control module 150, in which a pre-pressure p is maintained. vorprevails and a second hydraulic subsystem (wheel brake hydraulics) between the hydraulic pump 151 and the wheel brakes 110, 120 in which a wheel brake pressure p brems prevails (as in Fig. 1 and Fig. 2 shown).

[0024] The hydraulic volume delivered by the hydraulic pump 151 towards the wheel brakes 110, 120 leads to a reduction in the pre-pressure p. vor , where the form p vor It may even assume a value of 0 bar. The resulting or established pre-pressure p vor can be measured or calculated as described above. By comparing the determined pre-form p vor Using the brake pressure resulting from the pressure-volume characteristic curve (basic characteristic curve) of the vehicle braking system for the relevant brake pedal position (Pos. 1), a pressure difference Δp can be determined, as shown in Fig. Figure 2 illustrates this. According to the hydraulic design of the master brake cylinder 140, a force (delta force) corresponding to this pressure difference Δp can be calculated, by which the support force generated by the brake booster 145 can be reduced so that the brake pedal position Pos. 1 is maintained. This is also controlled by the control unit 170.

[0025] With the brake pedal position (Pos. 1) remaining constant, the hydraulic pump 151 can be used to increase the wheel brake pressure p. brems The hydraulic fluid supplied is drawn from a reservoir 180 via the sleeve seal of the pressure piston 141, as shown in Fig. 1 illustrated by the small arrow in the master brake cylinder 140. This applies in particular if the pre-pressure p vor The pressure has already been reduced to 0 bar (as shown). The sleeve seal is designed accordingly. Reference symbol list 100 Motor vehicle braking system (braking system) 110 front wheel brake(s) 120 rear wheel brake(s) 130 Brake pedal 140 master brake cylinders 141 pressure pistons 145 electromechanical brake booster 150 Vehicle dynamics control module 151 Hydraulic pump 152 Isolation valve 153 Control valve 160 brake pressure line(s) 170 Control unit 180 reservoirs (brake fluid) Rear axle rear right wheel brake HL rear left wheel brake M drive (electronic brake booster) VA front axle VR front right wheel brake Front left wheel brake p print Volume p (V) Pressure-volume characteristic curve p brems Brake pressure p vor form ΔV volume difference Δp pressure difference Position 1 Brake pedal position

Claims

[1] Method for controlling a motor vehicle braking system (100) comprising the following components: - front wheel brakes (110) and rear wheel brakes (120); - a master brake cylinder (140) comprising a pressure piston (141) actuated by means of a brake pedal (130) and an electromechanical brake booster (145); - a vehicle dynamics control module (150) comprising a hydraulic pump (151) and a separating valve (152) for separating the pre-pressure hydraulics from the wheel brake hydraulics; with the following steps: - Generating wheel brake pressure (p brems ) by pressing the brake pedal (130), whereby the electromechanical brake booster (145) generates an assisting force; - Increasing the wheel brake pressure (p brems ) using the hydraulic pump (151) of the vehicle dynamics control module (150), whereby the isolation valve (152) is closed, so that the pressure (p vor) of the pre-pressure hydraulics from the pressure (p brems ) the wheel brake hydraulics differs; - Preventing a reaction on the brake pedal (130) by adjusting the support force generated by the electromechanical brake booster (145) so that the brake pedal position (Pos. 1) is maintained, for which the following sub-steps are carried out: - Determining the pre-pressure prevailing in the master brake cylinder (140) (p vor ); - Calculating a pressure difference (Δp) between the determined pre-pressure (p vor ) and the pressure-volume characteristic curve that results for each brake pedal position (p (V) ) the resulting brake pressure of the motor vehicle braking system (100); - Reducing the support force generated by the electromechanical brake booster (145) by an amount corresponding to the calculated pressure difference (Δp). [2] Method according to claim 1, characterized by, that the pre-pressure prevailing in the master brake cylinder (140) (p vor ) is measured. [3] Method according to claim 1, characterized by , that the pre-pressure prevailing in the master brake cylinder (140) (p vor ) is calculated. [4] Method according to any of the preceding claims, characterized by , that with the brake pedal position (Pos. 1) maintained, the hydraulic pump (151) is used to increase the wheel brake pressure (p brems ) conveyed hydraulic fluid is drawn from a reservoir (180) via the sleeve seal of the pressure piston (141). [5] Motor vehicle braking system (100), comprising the following components: - front wheel brakes (110) and rear wheel brakes (120); - a master brake cylinder (140) comprising a pressure piston (141) actuated by means of a brake pedal (130) and an electromechanical brake booster (145); - a vehicle dynamics control module (150) with a hydraulic pump (151) and a separating valve (152) for isolating the pre-pressure hydraulics from the wheel brake hydraulics; and - a control unit (170) which is designed to initiate the following steps when the brake pedal (130) is pressed: - Increasing the wheel brake pressure (p brems ) using the hydraulic pump (1151) of the vehicle dynamics control module (150) and closing the isolation valve (152); and - Preventing a reaction on the brake pedal (130) by adjusting the support force generated by the electromechanical brake booster (145) so that the brake pedal position (Pos. 1) is maintained by performing the following sub-steps: - Determining the pre-pressure prevailing in the master brake cylinder (140) (p vor ); - Calculating a pressure difference (Δp) between the determined pre-pressure (p vor) and the pressure-volume characteristic curve that results for each brake pedal position (p (V) ) the resulting brake pressure of the motor vehicle braking system (100); - Reducing the support force generated by the electromechanical brake booster (145) by an amount corresponding to the calculated pressure difference (Δp).

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