Method for operating a brake booster, control unit for carrying out the method and a braking system comprising the brake booster and the control unit

Abstract

Method for controlling a brake booster (308) in a hydraulic brake system, comprising the steps - Determining a minimum partial pressure setpoint (p Target ) from at least three partial pressure setpoints (p Target-V , p Target-Wh , p Target-DRR ), - Setting the smallest partial pressure setpoint as the target pressure setpoint (p Target ) for the braking system, - Controlling the brake booster to set the target pressure setpoint (p Target ) by means of the brake booster.

Description

State of the art

[0001] German patent DE 20 2010 017 605 U1 describes a brake booster, a method, and a device for its operation. A control unit is described for controlling the brake booster. This control unit uses signals from a sensor device to determine the displacement of an input rod and signals from the brake booster's motor to control the booster. Optionally, the control unit can also evaluate signals from a differential displacement sensor to determine the relative deflection between the input rod and a booster body, or from a force sensor to determine the driver's force.

[0002] DE 10 2009 002 359 A1 discloses a method for operating a brake-assisted braking system of a vehicle and a control device for a brake-assisted braking system of a vehicle.

[0003] In driving situations involving braking, simultaneous brake pressure build-up by the driver, brake booster, and the ABS / ESP return pump can lead to high pressures in the brake system. These high pressures impair brake pedal feel and place unnecessary stress on the brake system. This disconcerts the driver, as they are unaccustomed to this deviation. The objective of the present method according to the invention is to control the pressure in the brake system appropriately in the case of ABS control, i.e., when the ABS / ESP return pump can return a large volume of fluid, in such a way that the brake pedal feel is perceived as pleasant, braking performance (minimal possible braking distance) is ensured, and the stress on the brake system is minimized to avoid overloading the brake system components.

[0004] The core of the invention is the determination of the necessary target pressure values ​​in the braking system based on the current driver behavior, the condition of the braking system, the road surface, and other driving situation parameters, such as vehicle speed. The target pressure value determined in this way is set by means of an electronic brake booster. In this way, the load on the braking system is limited according to the situation. Disclosure of the invention

[0005] The invention relates to a method for controlling a brake booster in a hydraulic brake system, which comprises several steps.

[0006] A minimum of three partial pressure setpoints is selected. This minimum setpoint is then defined as the target pressure for the braking system. The brake booster is controlled to achieve this target pressure. Based on the different partial pressure setpoints, a partial pressure setpoint can be queried from different areas of the braking system, thus allowing the current operating status of the braking system to be determined. Selecting the lowest of these available setpoints and controlling the brake booster to set this value as the target pressure ensures that the braking system operates smoothly and without any unexpected sensations for the driver.

[0007] In an advantageous embodiment of the method, the first partial pressure setpoint is determined as a function of a wheel brake pressure, the second partial pressure setpoint as a function of the driver's actuation of the braking system, and the third partial pressure setpoint as a function of the vehicle speed. Since, as described above, the partial pressure setpoints represent the current state of the braking system, it is advantageous to consider key characteristics of the current operating condition, such as the type of actuation by the driver or the prevailing wheel brake pressure, when determining the setpoints.

[0008] In one embodiment of the method according to the invention, the target pressure value determined in this way is compared with the pressure currently prevailing in the brake system. The pressure difference between the target pressure value and the prevailing pressure, determined from this comparison, is then regulated within the framework of the method according to the invention. This advantageously allows the extent to be determined how far the determined target pressure value deviates from the currently prevailing pressure value in the brake system. This establishes a control variable for the method. Furthermore, it is advantageous that the pressure difference is regulated by changing the gain of the brake booster, either by adjusting the target rotational speed of a brake booster motor or by adjusting the motor torque of the brake booster motor. In this way, the brake booster compensates for the determined pressure difference.

[0009] Advantageously, the target rotational speed of the motor (303) is determined as a function of the pressure differential and limited to a specific motor speed by a limiting factor. This limitation prevents the brake booster from operating at an excessively high motor speed. This provides a safety measure for the brake booster and prevents negative effects on the driver's pedal feel.

[0010] Furthermore, it is advantageous that, before activating the brake booster motor with the limited engine speed, a check is performed to determine whether activation should be carried out at the limited engine speed or at the engine speed specified by the driver's brake application. This prevents the brake booster motor speed, set by the driver through brake application, from being adjusted towards the limited engine speed when this is no longer necessary due to the situation.

[0011] In an advantageous configuration, the check is performed based on the prevailing pressure in the braking system, the driver's brake application, and the presence of brake pressure modulation by a brake pressure modulation unit. This has the advantage that the current braking situation is re-evaluated, thus further validating the pending adjustment of the bog speed. This, in turn, ensures increased safety of the braking system.

[0012] Advantageously, the first, second, and third partial pressure setpoints are selected from an identical pressure range between the maximum and minimum pressure of the brake system. This ensures that for all three partial pressure values, a permissible pressure range cannot be exceeded by the brake booster control.

[0013] Advantageously, the first partial brake pressure setpoint is determined as a function of a wheel brake pressure by means of a signal from a wheel pressure modulation unit, wherein the signal corresponds to the highest of the currently available wheel brake pressure values ​​of the wheel brakes connected to the braking system. This signal transmission adequately conveys the current braking situation to the control unit of the brake booster.

[0014] Furthermore, the determination of the first partial brake pressure target value includes filtering and offset application, which ensures that a sufficiently high pressure is always present in the brake system.

[0015] Furthermore, the partial brake pressure setpoints are determined based on input variables (v vehicle , p Estmax , DRR) can be taken from characteristic maps or calculated using equations.

[0016] The present invention also relates to a control unit for carrying out the method according to the invention.

[0017] The braking system according to the invention comprises a brake booster which is operated by means of the method according to the invention and a control device for carrying out the method. Character description Fig. Figure 1 shows a flowchart of the inventive method for controlling a brake booster. Fig. Figure 2 shows the determination of partial pressure setpoints that are incorporated into the control of the brake booster. Fig. Figure 3 shows a schematic representation of a brake booster. Designs

[0018] In one embodiment of the invention, the braking system comprises a control unit 1 and a brake pressure modulation unit 2. The control unit 1 controls and / or regulates the brake booster 308 of the braking system.

[0019] Fig. Figure 3 schematically shows an electromechanical brake booster 308. The brake booster applies a force to a master brake cylinder 304, more precisely to an input piston of the master brake cylinder 304, via an output rod 305, in order to build up pressure in a hydraulic brake system in a known manner.

[0020] A reaction disc 306 is located between the output rod 305 of the brake booster 308 on the one hand and a booster body 301 and an input rod 302 on the other. The driver can transmit a force to the output rod 305 via the reaction disc 306 using the input rod 302. The booster body can be moved by means of a motor 303 via a gearbox 307, which converts the rotation of the motor. The gearbox 307 is a rotary-translation gearbox. Thus, the motor 303 moves the booster body 301 via the gearbox 307, and the booster body, in turn, can also apply force to the output rod 305 via the reaction disc 306.

[0021] The offset of the amplifier body 301 in relation to the amplifier housing 309 is defined as size s BB shown. The deflection of the entrance rod 302 from its rest position as a measure s IRThe brake booster 308 is controlled by various parameters, which will be discussed below. The description follows step-by-step, referring to the corresponding components of control unit 1.

[0022] To meet the pressure requirements of the braking system, a closed-loop control system is used. This involves a pressure sensor signal that corresponds to a measured pressure in the braking system. This signal can be fed into the system directly and / or indirectly. For example, the pressure sensor signal can be provided directly by installing a pressure sensor in the brake pressure modulation unit 2, or alternatively, by a separately installed pressure sensor that transmits the pressure sensor signal via a data line.

[0023] Likewise, the pressure sensor signal can be derived from other quantities, for example from load-relevant quantities such as the motor torque of the drive motor of the brake booster 308.

[0024] In Fig. Figure 1 shows how, starting from the brake pressure modulation unit 2, for example a known ESP system, a pressure sensor signal p is generated. ESP is passed on to control unit 2 of the brake booster.

[0025] This pressure sensor signal p ESP This is now used to control the brake booster 308. The brake force amplification of the brake booster is modified so that the actual pressure currently present in the brake system matches the determined brake pressure requirement p. Target will be adjusted.

[0026] For example, the route s BB of the amplifier body 301 (also called boostbody) of the brake booster 308 with predefinable rotational speed ω Motor shifted via the motor control using the motor 303 of the brake booster 308. In the first part of the tax procedure, the target pressure p is determined.Target The target pressure p Target This corresponds to the current pressure requirement of the brake system, which must be adjusted using the brake booster 308.

[0027] This printing requirement depends, among other things, on • from the driver's behavior 202, i.e. whether the driver operates the brake pedal rather cautiously or strongly, with high force and / or speed, • of the road surface friction coefficient 203 (high-grip road surface or smooth road surface) • and of the vehicle speed 201 (high speed vs. standstill).

[0028] This will be demonstrated using Fig. 2 described in more detail.

[0029] Fig. 2 represents part of the calculation of the pressure requirement p Target dar.

[0030] For each of the listed criteria—driver behavior 202, road friction coefficient 203, and vehicle speed 201—a partial pressure target value is determined. The value for the respective partial pressure target value lies between a minimum pressure requirement (p Min ) and a maximum pressure requirement (p Max ) for driver braking request, for road friction coefficient, and for vehicle speed. The actual selection of the respective partial pressure setpoint can be done via characteristic maps or also via equations, especially linear equations.

[0031] The driver-dependent partial pressure setpoint p Target-DRR is based on a path difference DRR (see Fig. 3) between an entrance pole path S IR and the path of the booster body, calculated from the measured rotation angle of the brake booster motor. BBDetermined in the brake booster (DRR = Driver Brake Request Recognition). This is therefore the difference in travel between the input rod travel and the booster travel.

[0032] If this path difference is small, a small partial pressure setpoint p is used. Target-DRR Assuming the path difference is large, a larger partial pressure setpoint p is required. Target-DRR Assumed. The selection of the partial pressure setpoint p corresponding to the path difference. Target-DRR This is done using characteristic maps or equations, especially linear equations. The difference in travel distance represents a measure of the driver's application of the brakes.

[0033] The road friction coefficient-dependent partial pressure setpoint p Target-Wh is determined using estimated or measured values ​​based on the wheel brake cylinder pressures p RR , p RL , p FR and p FL Determined according to the four wheel brake cylinders of a vehicle. This is possible, for example, using a signal p. EstMaxof the pressure modulation unit 2. This value corresponds to the maximum pressure present at each sampling point of the data transmission between pressure modulation unit 2 and control unit 1, derived from the four brake pressures p. RR , p RL , p FR and p FL of the connected wheel brakes. The brake pressure modulation unit 2 determines the maximum pressure of the connected wheel brakes and transmits this to the control unit 1. The pressure value p EstMax A corresponding partial pressure setpoint p can then be determined. Wh The actual selection of the respective partial pressure setpoint can be done via characteristic curves or equations, especially linear equations.

[0034] Alternatively, a p Estmax The corresponding value can also be calculated based on the structural and internal parameters of the brake booster 308. This is done by multiplying the displacement of the brake booster s BBA partial volume is determined using the pressure-acting surface of the master brake cylinder 304. This partial volume is added to the dead volume V. Offset of the braking system. Based on the known pressure-volume characteristic curve of the braking system, a pressure value can then be determined, analogous to p EstMax a partial pressure setpoint pp Wh is assigned.

[0035] The road friction coefficient-dependent partial pressure setpoint p determined in one of these ways Wh In a further step, the value is filtered and increased using an offset. After this step, a corrected value is available: partial pressure setpoint p. Target-Wh This increase ensures that the pressure is always high enough (even in the event of a malfunction) to brake with maximum safety.

[0036] High wheel cylinder pressures are relatively rare during real-world driving; only low pressures are applied during typical comfort braking maneuvers. Even when ABS activates in low-friction mode, which can be relatively long and therefore generate relatively high loads, only a low wheel cylinder pressure is measured. This allows for a low pressure requirement for the braking system. Only in high-friction modes is a very high pressure required for ABS activation.

[0037] The vehicle speed-dependent partial pressure requirement p Target-V The braking system is designed for low vehicle speeds. vehicle Near standstill, the minimum values ​​are set to low. This reduces the load on the entire braking system during potentially prolonged vehicle standstill – e.g., in traffic jams. At higher speeds v vehicleIf the maximum value is exceeded, the pressure requirement is set to the maximum value. Further special cases can also be considered to additionally define the pressure requirement of the brake system at this point.

[0038] The same parameterization of the minimum and maximum permissible partial pressure setpoints (p) is used for all three criteria. m i n or p max ) specified.

[0039] From the available partial pressure requirement values ​​p Target-V , p Target-Wh as well as p Target-DRR The smallest partial pressure requirement is determined as the setpoint p using a minimum selection process. Target selected for pressure regulation.

[0040] The signals are combined using a logical AND gate. Only when the driver applies the brakes forcefully (D RR > Max) AND the road surface has a high coefficient of friction (p EstMax > Max) AND the vehicle speed is high enough (v vehicleIf the maximum pressure (> Max) is reached, then the highest pressure in the braking system is also necessary. In other words, if, for example, the driver only lightly applies the brakes, OR the coefficient of friction of the road surface is low, OR the vehicle is stationary, a lower pressure may be sufficient. This comparison result p Target This is used for further adjustment of the brake force boost. This determines the pressure to be set in the brake system.

[0041] The aim of the regulation is to adjust the pressure p. Target via a targeted variation of the brake force assistance provided by the brake booster. This is achieved by a targeted reduction of the travel or force of the brake force assistance element in the form of the motor torque of the brake booster motor 303.

[0042] In a subsequent step 4 of the illustrated embodiment, the target pressure p is used for this purpose. TargetIn step 3, the pressure requirement of the brake system was derived from the prevailing actual pressure p. ESP subtracted, resulting in a differential pressure signal Δp control This differential pressure signal Δp is generated. Control is fed to a control algorithm 5 (pressure controller, e.g. a PID controller) which, in the present embodiment, determines and outputs a set motor speed of the brake booster motor as an output signal.

[0043] In the subsequent step 6 (limitation), this target motor speed of the brake booster motor is limited and expressed as ω. Target-lim This ensures that the driver and the brake booster do not experience excessive changes in the current operating point. This means that the existing brake booster must not change too drastically, so as not to distract the driver. This is a safety function of the brake booster.

[0044] In the following step 7 (Controller Coordination), it is ensured that the current control signal for the brake booster's electric motor matches the driver's behavior. This is done by checking whether the brake is still applied. Parameters that enable this include the current differential travel D. RR as well as the target motor speed ω Target which was originally specified according to the driver's braking request. From the signal of the input rod path s IR This original setpoint ω Target The engine speed is determined to ensure brake force amplification for all driving situations. This is done by calculating the differential travel DRR = s BB -s IR as difference from amplifier body path s BB and entrance pole path s IR and the temporal derivation of the entrance pole path s IRas a dynamic control signal feed-in, in the form of a feedforward signal. The query thus checks the driver's braking request via two redundant paths to rule out any malfunction of the control system.

[0045] Furthermore, it is checked whether the brake pressure modulation device – i.e., the ESP controller – is still in anti-lock braking mode (ABS). Active ), and high pressure values ​​continue to be present, which necessitate the pressure control according to the invention (ABS) Active ).

[0046] In addition, it is checked whether there is any concerning behavior of the brake system pressure p. ESP This is the case, i.e., whether the pressure sensor signals are showing high values. This can be determined by the magnitude of the value p. ESP determined and fed in as an input variable in step 7.

[0047] In step 7, a decision is made as to whether all three conditions – brake still applied, ABS active, and pressure still high – are met. If this is the case, the determined motor control value ω is used. Target-lim passed through as quantity ω Motor , otherwise the engine speed specified by the driver ω will be maintained. Target forwarded as ω Motor This ensures the plausibility of the target rotational speed ω transmitted to the motor. Motor depending on the current situation.

[0048] The output signal from step 7 is ω Motor , the target motor speed of the brake booster motor 303. This target value is passed to the motor control 9 (motor control), which, based on a comparison with the actual speed of the brake booster motor, controls the brake booster motor in step 10 so that the motor reaches the target motor speed ω Motor assumes.

[0049] In step 11, the rotary motion of the motor 303 is converted into a longitudinal motion of the amplifier body 301 by means of the gearbox 307 connected downstream of the motor 303, resulting in an offset of the amplifier body by s BB leads.

[0050] Together with the driver's entry pole path s IR The path s is mechanically determined by offsetting the input rod 302 via further constructive transmission elements such as the reaction disk 306. TMC of the master brake cylinder in step 13. The offset of the pistons of the master brake cylinder leads, in a known manner, to pressurizing the brake fluid and thus to pressure in the brake system on the two output lines of the master brake cylinder (p TMC1,2 ).

[0051] The brake pressure modulation device 2 has a return pump in a known manner, which is active in ABS operation and which, in the event of activity, provides additional pressure modulation by means of a volume flow q.Pump generated. The pump's flow rate, in combination with the pressure p present at the master cylinder outlet, leads to TMC1,2 to a new present print p ESP which in turn is incorporated into the regulation.

[0052] The brake pressure modulation unit 2 measures the brake system pressure at the master brake cylinder output and, as described earlier, displays this via data line as p ESP available.

[0053] The valve configuration in the hydraulic unit of the brake pressure modulation device determines the behavior of the wheel brake cylinder pressures at the front left wheel. FL , front right p FR , rear left p RL and rear right p RR The pressure modulation device 2 estimates or measures this effect using suitable means and calculates the current values ​​of the wheel brake cylinder pressures p. FL , p FR , p RL and p RRand provides the brake booster with the maximum wheel cylinder pressures as a signal p EstMax available to determine the road friction coefficient-dependent partial brake pressure requirement p as described in step 3 Target-Wh to determine.

Claims

[1] Method for controlling a brake booster (308) in a hydraulic brake system, comprising the steps - Determining a minimum partial pressure setpoint (p Target ) from at least three partial pressure setpoints (p Target-V , p Target-Wh , p Target-DRR ), - Setting the smallest partial pressure setpoint as the target pressure setpoint (p Target ) for the braking system, - Controlling the brake booster to set the target pressure setpoint (p Target ) by means of the brake booster. [2] Method according to claim 1, wherein - the first partial pressure setpoint (p Target-Wh ) depending on a wheel brake pressure (p Estmax ), - the second partial pressure setpoint (p Target-DRR ) depending on the driver's use of the braking system (DRR s BB ) and - the third partial pressure setpoint (p Target-V ) depending on the vehicle speed (v vehicle ) is determined. [3] Method according to claim 2, wherein the target pressure setpoint (p Target ) with the current pressure prevailing in the braking system (p ESP ) is compared and the pressure difference (Δp) control ) from target pressure setpoint (p Target ) and prevailing pressure (p ESP ) is regulated (4). [4] Method according to claim 3, characterized by , that the difference is due to a change in the gain of the brake booster (308): - by adjusting a target rotational speed (ω) Motor ) of a motor (303) of the brake booster (308) or - is regulated by adjusting the motor torque of the motor (303) of the brake booster (308). [5] Method according to claim 4, characterized by , that the target rotational speed (ω Motor ) of the motor (303) depending on the pressure difference (Δp control ) is determined and limited to a specific motor speed (W) by a limit for the motor rotational speedTarget-lim ) is limited (6). [6] Method according to claim 5, characterized by , that before the motor of the brake booster (308) is controlled with the limited motor rotational speed (W Target-lim ) is checked to see if control with the limited motor speed (W) Target-lim ) is to be carried out or at the engine speed specified by the driver's braking action (ω) Target ). [7] Method according to claim 6, characterized by , that the check is carried out based on the prevailing pressure in the brake system, the brake actuation by the driver and the presence of brake pressure modulation by a brake pressure modulation unit (2). [8] Method according to claim 2, characterized by , that the selection of the first, second and third partial pressure setpoints from an identical pressure range between maximum pressure (p max ) and minimum pressure (p min ). [9] Method according to claim 2, characterized by , that the first partial brake pressure setpoint (p Target-Wh ) depending on a wheel brake pressure by means of a signal (p EstMax ) of a wheel pressure modulation unit (2) is determined, wherein the signal (p EstMax ) the highest of the currently available wheel brake pressure values ​​(p FL , p FR , p RL , p RR ) of the wheel brakes of the braking system connected to the braking system. [10] Method according to claim 9, wherein the determination of the first partial brake pressure setpoint comprises filtering and offset application. [11] Method according to claim 2, characterized by , that to determine the partial brake pressure setpoints, these are based on input variables (v vehicle , p Estmax , DRR) can be taken from characteristic maps or calculated using equations. [12] Control unit for carrying out a method according to any of the preceding claims. [13] Brake system comprising a brake booster operated by means of a method according to one of claims 1-11 and a control device for carrying out the method according to one of claims 1-11.

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