DE19648195A1 - Electric brake system for vehicle - Google Patents

Abstract

The wheel brakes are operated by electric drives in response to control signals. The actual braking effort applied is controlled by monitoring the braking torque. If the wheel speed is below a set minimum level then the braking mode changes to be directly proportional to the force applied by the driver to the brake controls. The brakes are controlled in proportion to the level of control signals generated by the electronic control. Compact electric motors can apply the braking force directly to the wheel brakes. The control identifies the low speed, or parked setting and applies a holding force independent of the braking torque monitored on the wheel.

Description

State of the art

The invention relates to a method and a device for controlling a brake system of a vehicle, in particular re a brake system with electrical application, according to Preambles of the independent claims.

A brake system with electrical tensioning for vehicles is known for example from WO-A 94/24453. There is described a braking system in which the application force is generated by electric motors. An appropriate course of action way to operate these wheel brakes, especially in loading Range of vehicle standstill is not suggested gene.

It is therefore an object of the invention to provide measures for actuation of wheel brakes of a vehicle, particularly in the area of Standstill of the vehicle to be specified.

This is due to the characteristic features of the indep gene claims reached.  

Advantages of the invention

The solution according to the invention represents a suitable procedure way to actuate wheel brakes, especially in the area standstill of the vehicle. Special advantages shows this procedure when the wheel brake is actuated se as part of a braking torque control loop.

It is also advantageous that the Lö solution a clear strategy for the operational and / or fixed Parking brake is specified for operating areas in which no reliable about the braking torque exerted on the wheel statements are available.

It is particularly advantageous that based on the braking torque tensignals a clear standstill criterion for the Vehicle can be specified, which of standstill blockages of a wheel clearly differentiated.

By controlling the brake application in the area of The vehicle comes to a standstill in an advantageous manner Operation of the service brakes, similar to normal operation, maintained.

It is particularly advantageous that the inventive Solution a so-called "stopping ABS" can be realized by which will significantly improve the stopping process.

The solution according to the invention offers a further advantage for the control of a parking brake, which in some Be  drive situations controlled adaptively and / or individually for each wheel can be.

It is also advantageous to use the inventive Solution for wheel brakes with electrical application (electromotive brake).

Further advantages result from the following Be writing of exemplary embodiments or from the dependent ones Claims.

drawing

The invention is explained below with reference to the embodiments shown in the drawing. Fig. 1 shows an overview block diagram of a control device in a preferred embodiment of a brake system with electrical application. In Fig. 2, a procedure for actuating the wheel brakes with electrical application in and outside the area of the vehicle is at a standstill for the preferred embodiment based on a flow chart. In a selected operating situation, the mode of operation of this exemplary embodiment is illustrated in time diagrams in FIG. 3. The effectiveness of a "stopping ABS" is illustrated in the time diagrams in FIG. 4. Finally, the flow chart according to FIG. 5 shows the implementation of a parking brake control as a computer program.

Description of exemplary embodiments

Fig. 1 shows an electronic control unit 10 as an output circuit 16 includes an input circuit 12, a microcomputer 14, at least. These components are interconnected via a bus system 18 for data exchange. Furthermore, a control unit 20 is actuated which, in the preferred exemplary embodiment, actuates the electrical actuators, which are connected to the wheel brakes of the vehicle and which preferably comprise DC motors. To this control unit 20 , as exemplified for a wheel brake of the vehicle, the electric motor 26 (DC motor) is connected via electrical connecting lines 22 and 24 . Via a mechanical connection 28 , this is connected to the brake caliper 30 of the wheel 32 . When the electric motor 26 is actuated, the brake caliper 30 of the wheel brake is opened or closed depending on the direction of rotation of the motor. The actuating device is usually moved close to its rest position (open brake) when the motor is not powered. Furthermore, the actuating device comprises a controllable clutch which keeps the brake shoes at the value set by the electric motor in predetermined operating situations (e.g. parking brake function) even when not actuated. In the area of the actuating device, at least one sensor 34 is provided which, via a line 36 , supplies an actual value via the brake actuation of the control unit 10 , where it supplies the input circuit. The sensor 34 can be a braking force sensor, a braking torque sensor, a current sensor, etc. In the preferred exemplary embodiment, the braking torque acting on the wheel 32 is detected by the sensor 34 . In another embodiment, the braking torque z. B. estimated from braking force, average friction radius and coefficient of friction. The adjusting device is Untitled from the control unit 10 via an outgoing from the output circuit 16 output line 38 betae. In addition to the control of the wheel brake shown, the wheel brakes of the other vehicle wheels are controlled in a corresponding manner via output lines 40 , 42 and 44 and the input circuit 12 is supplied with further input lines 46 , 48 and 50 , which supply the control actual values of the other wheel brakes to the control unit 10 . Furthermore, the control unit 10 at least one input line 52 from egg ner measuring device 54 for detecting the brake pedal actuation (z. B. pedal travel, pedal force, etc.) and input lines 55 to 56 of measuring devices 58 to 60 are supplied. The latter record other operating parameters required to control the brake system, such as wheel speeds, possibly axle loads, yaw rates, etc.

In normal operation of the brake system, a setpoint for the individual wheel brakes is derived from the control unit 10 , there in the microcomputer 14 , from the degree of actuation of the brake pedal. This takes place, for example, taking into account the axle loads in accordance with specified characteristic curves, characteristic diagrams, tables or calculation steps. This setpoint value derived from the degree of actuation, which in the preferred embodiment represents a setpoint value for the braking torque to be exerted, is corrected, if necessary, in the context of an ABS and / or FDR control individually for the wheel in accordance with the wheel speeds, yaw rates, etc. The wheel-specific target value corrected in this way is then compared for each de wheel brake with the actual value for the braking torque measured on the corresponding wheel and the respective difference leads to the controller provided for the corresponding wheel. In accordance with the difference and a predetermined control strategy (e.g. PID), this forms a controller manipulated variable which is output to the control unit 20 via the output line. There, the control variable representing a current through the electric motor 26 is implemented by actuating the servomotor.

The described, wheel-specific braking torque control loops are implemented in another exemplary embodiment in the control device 20 , which also contains at least one microcomputer for this case.

In the range of low wheel speed, i.e. H. in the area of breastfeeding status of the vehicle, is (at least on the level) none Braking torque measurable. Therefore, when regulating one electrically controlled braking system based on the detected braking torque required in this operating range, in addition to the braking torque control to find additional solutions.

According to the invention, it is proposed to be very low in the range Wheel speed, especially in the area of the standstill Vehicle from the regulation to control the service brake to pass over. As explained in more detail below, the manipulated variable for each wheel according to the setpoint set. If the brake pedal position is changed to Brake force build-up or reduction is the manipulated variable for all wheels brake synchronously and with approximately the same timing different. As a suitable criterion for delimiting this tax range is in the area of low driving speeds ten (falling below a minimum value) a course of the Braking torque signal used. Through the transition to The brake pad comes to a standstill from sliding friction into the Overcome stiction. As a result, the braking torque ver a liability spike occur. In another out could also swing out the Bremsmo  ment course, caused by the spring-damped opening suspension of the vehicle, or a combination of both procedures serve as a criterion. So z. B. the standstill knows when a liability spike and a swinging out characteristic braking torque curve is present. With him When the machine is at a standstill, the braking torque control is exited and the manipulated variable for the brake actuators Provided a control. By pulling the Driving speed as a further criterion becomes an error Steady standstill detection avoided.

The pulses in the area of the braking torque signal, which at Stopping the vehicle from occurring can also improve stopping process. On a wheel for which such a standstill criterion is recognized switched from regulation to control and in the frame the brake released. Another braking is initiated at a time when a predetermined Number of wheels based on the criterion as stationary were known. There will be two, three or four different ones Wheels used to initiate re-braking.

Also as part of the control system when the Vehicle realized a parking brake function. Because of the Loading possibility at standstill and the associated The control value for the actu size in the case of parking brake not effective from the last measured service brake setpoint are derived, esp especially if the axle loads are not recorded. Instead of In this case, a predetermined parking brake must be used value to be taxed due to stiction to the Brake pads can possibly be smaller than a Be  drive braking value. If the car is on the mountain, a party can take place parking brake torque can be measured. Depending on the value the This parking brake torque is a ra in one version individual increase of the manipulated value (adaptive Parking brake). The adaptive parking brake shows particularly well on the other hand in connection with a bivalent operation direction Advantages through adequate tensioning with limited energy consumption. In the case of a meterable actuator The device would be to use the adaptive holding brake connected with a standstill detection.

The solution according to the invention is the preferred embodiment example of a wheel brake with electrical application Darge poses. It also comes with the advantages mentioned above Brake systems with hydraulic or pneumatic actuators directions used for the wheel brakes. It is called Controller or control manipulated variable uses a variable with which Valve devices for controlling the pressure in the wheel brake cylinders are operated. This size will correspond chend the procedure according to the invention in the context of a Regulation, in special operating situations as part of a Control formed.

In Fig. 2 on the basis of a flow chart for the implementation of the scheme and the transition is shown for control. The program section described there is run through individually for each wheel brake at predetermined times when the brake pedal is actuated. A selected wheel brake is considered in FIG . Corresponding program parts are provided for the other wheel brakes. First, in step 100, the target value derived from the pedal actuation for the wheel brake under consideration and the vehicle speed V is detected. The actual value of the brake under consideration is then recorded in step 102. In the subsequent step 104, the controller manipulated variable Yi _R for the wheel brake under consideration is formed in accordance with a predetermined control strategy on the basis of the setpoint and actual value, possibly corrected by additional functions such as ABS, FDR, etc. The standstill criterion is checked in the subsequent query step 106. In one exemplary embodiment, this check takes place by evaluating corresponding marks, which are set when the speed falls below the speed threshold and when a liability peak occurs in the braking torque signal and / or a swinging braking torque curve on any wheel brake. If the standstill criterion is met, control is initiated in step 108. If the standstill criterion is not met, the controller manipulated variable Yi _R determined in step 104 is output in accordance with step 110. The program part is then repeated at a predetermined time with step 100.

A preferred embodiment of the controller 108 is set forth below.

The control variable Yi _S for the wheel brake is determined on the basis of the detected target value and a predetermined time function T, which is essentially the same for all wheel brakes. The time function changes the control variable when the setpoint changes. It ensures a braking force reduction (or the braking force build-up) that takes place essentially synchronously and with essentially the same time on all (braked) wheel brakes. When determining the control variable on the basis of the target value, a predetermined characteristic curve is provided, in which the control variable, depending on the target value and possibly the axle loads, is stored, a predetermined characteristic map, a predetermined table or suitable calculation steps are provided. The assignment is determined experimentally, so that on each wheel brake results in approximately the same braking force, braking torque or the same current. If a difference between the setpoint from one of the previous program runs and the current setpoint is determined, the control variable is changed from the old to the new value as part of the specified time function. The calculated control variable is then output to the brake control device.

In Fig. 3, the mode of operation of the procedure outlined in Fig. 2 is shown on the basis of time profiles. Since in Fig. 3a shows the time course of the nominal value, Fig. 3b to the braking torque at a selected wheel, Fig. 3c shows the course of the controller output at this wheel, and Fig. 3d the course of the control command value. The driver operated on this wheel from the time t₁ the brake pedal to brake the vehicle. Accordingly, a braking torque according to FIG. 3b is built up on the wheels by a corresponding course of the controller manipulated variable ( FIG. 3c) up to the point in time t₂ as part of the braking torque control. From the time t₂ the driver holds the brake pedal in a constant position, so that the controller manipulated variable is aborted from time t₂ and the built-up braking torque is held in the actuator by closing the clutch. Between the times t₂ and t₃, interventions can take place when the setpoint changes, which braking force build up or break down. At the time t₃, the wheel speed drops towards 0, so that a peak can be seen at the moment. This course of the braking torque stems from the fact that at this point the friction between the brake disc and the brake pad changes from sliding friction to static friction. As a result, the braking torque on this wheel is measurably increased. The controller is forced to reduce the braking force due to the increased actual value. A negative controller manipulated variable between times t₃ and t₄ is the result. After the wheel has come to a standstill, the braking torque can no longer be measured, so that, according to FIG. 3b, no evaluable signal is available. The undershoot of the speed threshold and the peak liability of the braking torque signal are evaluated as a standstill criterion, so that after the time t₄ the vehicle standstill is recognized and switched to control. In the area of the instant t daher, a control manipulated variable is therefore specified, which is maintained in accordance with the setpoint until the instant t₅. This will keep the braking force built up on the wheel. Between the times t₅ and t₆ the driver lets go of the pedal, so that the control manipulated variable is controlled accordingly. This control takes place on all Radbrem sen essentially synchronously and with a similar course. Between the times t₃ and t₄ there may be fluctuations in the torque value around the zero point due to the swinging out of the vehicle suspension. This signal could also be used as an alternative or in addition to the peak liability to detect standstill.

In a further embodiment, the Control in the area of low wheel speeds a so-called Stop ABS realized, which an uncontrolled blocking of the wheels in the area of lowest speeds avoids. As a standstill criterion and thus as a basis for the transition to control in this case is according to step 106 the presence of sticking peaks in the braking torque  gnale of two, three or four wheels in addition to Fahrge speed threshold evaluated. This leads to due to the control function at first at a standstill passing wheels the brakes are released first. Is The standstill criterion is met in wheels Most brakes synchronously as part of the braking force control built up, on the others the controller manipulated variable by the Corresponding control manipulated variable replaced, possibly with an increase the braking force.

For synchronous braking, depending on the embodiment the standstill criterion for two, three or four wheels be filled.

This solution is illustrated in FIG. 4 on the basis of time diagrams. Here, FIGS. 4a to 4d the course of the control variable Yi _S versus time for the four wheel brakes of the vehicle, while in Fig. 4e the profile of the Bremsmomen tensignals is shown for three selected vehicle wheels. Before the time t ₁ all brakes are in re gelungsbetrieb. At the time t 1, the standstill criterion for the first wheel I was met (see FIG. 4e). According to FIG. 4a, this leads to a corresponding control which releases the brake as part of the control of the brake assigned to this wheel. At the time t₂ (see FIG. 4e) the standstill criterion for a second wheel II is known as fulfilled. Therefore, this brake is released according to Fig. 4b at time t₂. At the time t₃ the standstill criterion was met for a third wheel III. According to FIGS. 4a to 4d, this leads to the synchronous build-up of braking force on wheels I and II (cf. FIGS. 4a and 4b) as part of the control system, while for wheel III and IV, the braking force obtained from the control operation by corresponding Control variables are maintained. On the fourth wheel IV (standstill criterion has not yet been met), the brakes may increase.

When the vehicle is at a standstill, a parking brake function is implemented by controlling the brake system. This is initiated when the driver actuates an appropriate control element (hand brake lever, foot brake, switching element, etc.) to activate the parking brake. A preferred exemplary embodiment is described as a program of a microcomputer in the flow chart according to FIG. 5, which is a more detailed illustration of the control after step 108 from FIG. 2. In the first step 1080, the control manipulated variable Yi _{S of} the wheel brake under consideration is calculated from the target torque of the brake pedal Mset and possibly a predetermined time function T. In the subsequent step 1081, the control manipulated variable Yi is _{permanently determined} for the parking brake. Because of the possible changes in the axle loads due to loading at standstill, this control manipulated variable in the event of a parking brake may not be derived from the most recently measured service brake setpoint Msetpoint. If an actual torque Mbrems greater than zero is also measured, this indicates a slope of the vehicle at a standstill. The downhill force is to be counteracted by means of an increased control voltage. Therefore, in step 1081, the control variable of the parking brake is calculated depending on the setpoint Mfestsoll of the parking brake actuation device and on the measured actual torque (Mbrems) (described above as an adaptive parking brake). In the following step 1085 it is checked whether the actual braking torque is constant. Due to the changing control Yi _{, this is} only the case when the vehicle is _stationary . If this is not the case, the control variables calculated in steps 1080 and 1081 are compared with one another in step 1082. The brake actuator is controlled by the larger of the two control manipulated variables in accordance with steps 1083 or 1084. If it is no longer possible to determine a change in the braking torque (step 1085), the clutch of the brake actuators is activated in accordance with steps 1086 and 1087 in the sense of closing and maintaining the braking force and the control actuating variables are set to zero. When the parking brake actuation device is released again (release), the clutch is opened and the vehicle is released.

Claims (12)

1. A method for controlling a braking system of a vehicle, an electrically actuable brake actuator being provided on at least one wheel brake, which is actuated as part of a control system as a function of a setpoint essentially specified by the driver, characterized in that in at least one operating range, in particular at low wheel speed, the control is switched to control of the brake actuator depending on the setpoint. 2. The method according to claim 1, characterized in that the control is a braking torque control, in which the Actual braking torque occurring on the wheel is detected and to that of Driver or additional functions such as ABS or FDR predefined Target braking torque to form a control signal for the Brake actuator is related. 3. The method according to any one of the preceding claims, since characterized in that the at least one Betriebsbe rich is an area in which that which occurs on the wheel Braking torque can no longer be reliably detected. 4. The method according to any one of the preceding claims characterized in that the at least one Betriebsbe rich is considered to be reached when the vehicle  speed falls below a predetermined limit and the braking torque signal for at least one wheel of liability shows pointed. 5. The method according to any one of the preceding claims characterized in that as part of the control of the brake a tax variable, depending on the Chen setpoint specified by the driver. 6. The method according to any one of the preceding claims, since characterized in that when the driver changes predetermined setpoint the change of the on the wheel practiced braking force on other wheels essentially synchronously and with similar timings. 7. The method according to any one of the preceding claims characterized in that the transition to control then takes place when the driving speed is a predetermined falls below the limit and the braking torque signal for a predetermined number of wheels on a liability tip shows. 8. Method for controlling a driver's braking system stuff, an electrically at least one wheel brake actuatable brake actuator is provided, which is in the frame a regulation dependent on one essentially by the driver predetermined setpoint is actuated, characterized in that that when a standstill is detected to produce a feast Parking brake function formed a predetermined control value becomes.   9. The method according to claim 8, characterized in that the control value essentially only from the setpoint specification depends on the actuating device or from the setpoint and other signals as an adaptive parking brake is calculated. 10. The method according to any one of the preceding claims characterized in that the braking system is a braking system is with electrical tension and the brake actuator Elek include tromotors. 11. Device for controlling a braking system of a driver stuff, with at least one electronic control unit, which is an electrically actuated actuating device little regulates at least one wheel brake as part of a control loop depending on a substantially specified by the driver Setpoint, characterized in that the electronic Control unit the brake control device as part of a Control operated depending on the setpoint, if at least a predetermined operating area, in particular an area lower wheel speeds is reached. 12. Device for controlling a braking system of a driver stuff, with at least one electronic control unit, which is an electrically actuated actuating device little regulates at least one wheel brake as part of a control loop depending on a substantially specified by the driver Setpoint, characterized in that the electronic Control unit the brake control device when recognized Standstill to establish a parking brake function driven with a predetermined control value.