GB2366341A

GB2366341A - Improving rapid reversal of an electric motor driven brake actuator having a brake lock

Info

Publication number: GB2366341A
Application number: GB0120575A
Authority: GB
Inventors: Axel Schumacher
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-09-02
Filing date: 2001-08-23
Publication date: 2002-03-06
Anticipated expiration: 2021-08-23
Also published as: GB2366341B; GB0120575D0; JP2002104170A; DE10043255A1

Abstract

A brake system (fig 1) for a motor vehicle has electric motor driven actuators. A lock of a parking or holding brake of each actuator is used during rapid reversal of the motor direction to give a fast response deceleration of the motor. A control device, process and computer program assumes the need for a high dynamic response upon detecting sudden/rapid change in a setpoint or demand value (broken line), or a sign change in the difference between a braking parameter target and an actual value (chain dotted line), and produces a control signal to actuate the lock while the motor decelerates (phases II and IV). The additional frictional forces from the lock slow the motor, in addition to forces from reversing the motor drive. When the motor speed (solid line) passes zero the lock is released. Thus the dynamic response of the brakes during anti-lock, stability, traction control or during motor acceleration is improved.

Description

2366341 Process and device for controlling an electric motor-driven wheel

brake

10 Prior Art

The invention concerns a process and a device for controlling an electric motor-driven wheel brake.

15 Such a process and such a device, respectively, is disclosed in DE-A 198 26 130. Here an electric motordriven wheel brake is driven within a control loop in accordance with a predetermined setpoint value, in particular a braking torque or braking force value, and a 20 corresponding actual value that is detected in the area of the wheel brake. In this case the clamping force of the wheel brake is provided by an actuator containing an electric motor. This electric motor is actuated by the controller by means of a drive signal related to the system 25 deviation between the setpoint value and the actual value. Moreover, the actuating device of the wheel brake additionally contains a holding brake, for example an electrically-operated disengaging device, which in the deenergised state locks the actuating device and/or the wheel 30 brake. The purpose of this holding brake is on the one hand to realise a parking brake function, on the other hand to make it possible to switch off the actuating motor if the position of the wheel brake is to be maintained at a specific value. This considerably reduces the energy 35 consumption.

In some operating modes of the wheel brake, in particular in the case of rapid dynamic engagement, such as under anti-lock control, traction-slip control, stability control, etc., a rapidly alternating build-up and decay of 5 the force at the wheel brake is necessary. For the actuating device this means that a rapid reversal of the direction of movement of the brake shoes, and thus of the drive motor of the electric motor-driven wheel brake, must be provided. It has been shown though that in some 10 exemplary embodiments the reversal times which can be achieved by reversing the drive to the electric motor are long in comparison to the conventional system, so that the dynamic performance is unsatisfactory.

15 An example to clarify this situation is illustrated in Figure 4 and uses the example of a special operating case. Figure 4 shows the time characteristic of the speed NMOT of the electric motor (solid line), the actual value IST, for example of an actual braking torque (chain-dotted line), as 20 well as the corresponding setpoint value SOLL (broken line). At the beginning of the operation illustrated in Figure 4, a specific setpoint value SOLL is set by the actuation of the brake pedal by the driver. A system deviation therefore occurs between the setpoint value and 25 the actual value, according to which a drive signal is generated for the electric motor. The latter is accelerated in the operating phase I in accordance with the system deviation. Actual value and speed of the motor increase. At a certain instant tO, the setpoint value jumps from the 30 existing value to the value 0, for example on engagement of an anti- lock control. This causes a sign reversal of the system deviation (deviation between setpoint value and actual value) and the output of a drive signal decelerating the motor or driving it in the opposite direction, respectively. The motor starts to decelerate in phase II until motor and brake shoes come to a standstill. This electromotive braking lasts more or less as long as the acceleration phase. This means that during phase II, 5 despite the deceleration of the motor due to its inertia, a reduction of the speed is indeed achieved, but an increase in the actual value also occurs. The reversal of drive begins to take effect only at the end of phase II and the motor is accelerated in the opposite direction (phase III).

10 Only then does the actual value fall until it has reached the intended value 0 at the end of phase IV. Due to the large system deviation, the motor is accelerated in phase III, while in the following phase IV, due to the reducing system deviation, the magnitude of the drive 15 signal is reduced, so that electromotive braking of the actuator also takes place in phase IV and the actual value settles around the setpoint value.

With regard to the required dynamic response when anti-lock 20 control is engaged, engagement of traction-slip control or engagement of a stability control program, the situation as illustrated is unsatisfactory.

Advantages of the invention Due to the deliberate use of the existing holding brake, at least during dynamic braking action, the dynamic response of the actuator action is improved in an electric motordriven wheel brake. It is particularly advantageous that 30 the deceleration process is considerably shortened during a sudden change in the setpoint value. Advantageously, this allows improved, fast engagement of the wheel brake in conjunction with anti-locking controls, traction-slip controls, stability programs, etc.

Further advantages are revealed in the following descriptioft of exemplary embodiments or in the dependent claims. 5 Drawing

The invention is explained in more detail below with the aid of the embodiments illustrated in the drawing. Figure 1 10 shows a block diagram of a wheel brake with electromotive clamping, while the procedure for improved dynamic actuation of the electromotive actuating device is represented as a flowchart in Figure 2. This outlines a computer program of a computer unit controlling the 15 actuating device. Finally, in Figure 3 a mode of operation is illustrated with the aid of a time diagram. Figure 4 discussed above, shows a time diagram without use of the procedure for the dynamically improved actuation in a corresponding operating situation.

Description of exemplary embodiments

Figure 1 shows a block diagram of a braking system of a vehicle with electromotive clamping of one axle, for 25 example. Here 10 represents an electronic control unit which drives electric motors 16 and 18 via the output lines 12 and 14. In this case the electric motors are part of brake actuators 20 and 22, respectively, which act on the brake device 28 and 30, respectively, of the wheels 32 30 and 34, respectively, via mechanical links 24 and 26, respectively. A corresponding arrangement is to be found in an exemplary embodiment on the other axles of the vehicle. In the preferred exemplary embodiment, the electric motors 16 and 18, respectively, are DC motors, stepping motors or electronically commutated motors. Furthermore, force sensors 40 and 42, respectively, are provided, whose signals ar( fed to the control unit 10 via the lines 44 and 46, respectively. These force sensors determine the 5 support forces of the brake actuator and in this way determine a measure of the acting brake forces or brake torques. In the preferred exemplary embodiment, these sensors are wire strain gauges. In other advantageous exemplary embodiments the contact pressure of the brake 10 linings (for example piezo-electric sensors) or as an indirect measure of the brake force or the brake torques, respectively, the movement of the brake linings or of an actuating lever of the wheel brake (for example displacement sensors) is determined via sensors.

For the sake of completeness, Figure 1 shows input lines 48 to 50 which connect the control unit 10 to measuring devices 52 to 54. These record further operating parameters of the vehicle or of the braking system, respectively, such 20 as wheel speeds, the rotational speed of the drive unit, etc., that are necessary for the control of the braking system. Furthermore, an input line 56 is provided, which connects the control unit 10 to a measuring device 58 for recording the driver's wishes, in particular for detecting 25 the position of a brake pedal actuated by the driver.

Moreover, the actuating devices 20 and 22 contain the aforesaid holding brakes (disengaging devices, general locking device) 60 and 62, for example couplings that are 30 actuated, in particular are opened, by the control unit 10 via output lines 64 and 66, respectively, by means of a drive signal. Here the locking device locks the actuating device, either by locking the wheel brake or the actuating device itself.

The control unit 10 detects the driver's wishes via the line 56. By means of performance data that are preprogrammed for each wheel brake or groups of wheel brakes, 5 the control unit converts the driver's wishes into setpoint values for the individual wheel brakes. These setpoint values correspond, for example, to braking torques or braking forces to be set, which are set in a suitable control loop by driving the electric motors of the wheel 10 brakes. In this case in an advantageous exemplary embodiment the assignment of the driver's wishes to the setpoint values depends on parameters such as axle loads, brake lining wear, brake temperature, tyre pressure, etc., whose magnitudes are fed to the control unit 10 via the 15 lines 48 to 50. Furthermore, under special braking conditions, the control unit 10 carries out the well-known anti-locking control functions or traction-slip control functions or stability programs, on the basis of the operating parameters to be evaluated.

The drive for the electric motor is effected with the aid of a drive signal with variable parameter T, in particular with the aid of a pulsewidth-modulated signal. In this case in one embodiment a polarity reversal of the current 25 through the electric motor takes place to reverse the direction of rotation.

Here the de-energised, that is to say closed, disengaging device (locking device) locking the actuating device is 30 always activated, that is to say open, when a change in the position of the wheel brake is necessary, that is to say for example during control when (again) a system deviation other than zero occurs. During the activation of the locking device the friction in the area of the actuating device and/or the wheel brake is thus increased. Without limiting the generality, the locking device is described in the following as a holding brake.

5 The dynamic response of the control action as described is important, for example in the context of the stated antilock control. In order to improve the dynamic response of the electromotive brake actuator, which is unsatisfactory in individual cases, provision is made, at least where it 10 is necessary to decelerate the electric motor following one revolution in the direction of movement of the brake lining, to use the existing holding brake in support. During such deceleration phases of the electric motor the holding brake is closed, that is to say de-energised, in 15 the preferred exemplary embodiment. This results in very great friction in the actuator, which decelerates the rotor of the electric motor. The deceleration phase of the motor is therefore considerably shortened and the dynamic response of the reversal of the direction of movement is 20 improved.

Depending on the embodiment, the described procedure is generally active during a braking process if a deceleration phase of the motor follows; in other exemplary embodiments 25 only in special operating states; for example during an anti-lock control action, a traction-slip control action, engagement of a stability program and/or during a reversal in the direction of movement.

30 The de-energised, closed embodiment of the holding brake is also exemplary. In other embodiments the holding brake is made to close.

In the preferred exemplary embodiment the described procedure is designed as a program of a computer of the control unit 10. In this case a program as illustrated in the flowchart of Figure 2 is provided for each electric5 motor driven wheel brake of the vehicle. In a preferred exemplary embodiment these are exclusively the rear axle wheels, exclusively the front axle wheels or all four wheels of a vehicle.

10 The program illustrated in Figure 2 runs at predetermined time intervals during an active actuating process of the actuating device. After the program part is started on detection of an existing system deviation, in step 100 the holding brake is released, that is to say current- 15 energised. Following that, in step 102, the output variable of the drive signal T for controlling the actuating device of the electromotive wheel brake, is generated on the basis of the system deviation A in accordance with the intended control strategy. A check is made in the following step 104 20 whether a deceleration phase of the electric motor commences with a high dynamic response. This is then assumed, for example if a sudden change in the setpoint value, a rapid change in the setpoint value, a change in the sign of the system deviation has taken place very 25 rapidly or if a small system deviation is present at a high motor speed NMOT. If this is not the case, then a normal control action is present which has no particular dynamic requirements, so that when the drive signal is output at the value calculated in step 102, it is left at that.

30 Therefore in step 106 a check is made as to whether the system deviation has become 0, that is to say whether the control action has ended. If this is not the case, the program is repeated with step 102, otherwise the holding brake is actuated in step 108, that is to say de-energised, and the program ended until the next actuating action.

If step 104 has shown that a deceleration phase with high 5 dynamic requirements is starting at the actuating device, then the holding brake is actuated, that is to say deenergised, in step 110. A check is then made in step 112, whether this deceleration phase of the electric motor has ended, that is to say whether the actual value is no longer 10 changing or its change has brought about a reversal of direction, the motor has come to a standstill (rotational speed is zero), etc. If this is not the case, according to step 114, the value of the drive signal T is again generated on the basis of the current control deviation A, 15 this value is output and the program repeated with step 110.

If a completion of the deceleration phase was determined in step 112, then the holding brake is again released, that is 20 to say energised, in step 116 and the program is continued with step 106.

The mode of operation of the procedure represented in Figure 2 is illustrated with the aid of a time diagram in 25 Figure 3. Here the time graph of the setpoint value SOLL and that of the actual value IST of the control loop, as well as the time graph of the rotational speed NMOT of the electric motor, is shown in the representation of Figure 4. Here again an operating situation is initially assumed, in 30 which a predetermined setpoint value SOLL is present. Due to the prevailing deviation between setpoint value and actual value, the electric motor is accelerated during phase I. At the time tO the setpoint value returns to the value 0. This is associated with a rapid change in the sign of the system deviation, which leads to a corresponding change in the drive signal. There is thus a requirement for a fast-resonse actuating speed of the electric motor in the opposite direction of movement. The deceleration phase 5 commences. At time tO the holding brake is therefore deenergised, that is to say closed. Because of the increased friction, the motor speed falls rapidly (compare phase II). On reaching the value 0 of the motor speed, that is to say when the motor is at standstill, and/or there is a 10 different change in direction of the actual value, the holding brake is again energised, that is to say opened. The deceleration phase is ended. Due to the again prevailing large system deviation, current is passed through the electric motor, which causes the electric motor 15 to be accelerated in the opposite direction. At the end of phase III the electric motor has reached its maximum speed, so that a deceleration of the electric motor has to take place for proper adjustment of the actual value to the setpoint value. To this end, at the end of phase III the 20 holding brake is de-energised so that due to the increased friction a rapid fall in the motor speed to the value 0 occurs (compare phase IV). When the motor reaches standstill, the holding brake is again opened or kept closed, respectively, in the case where the control process 25 is completed.

A direct comparison between Figures 3 and 4 shows the clear shortening of the control process, in particular of the deceleration phase, and the considerable increase in the 30 dynamic response of the actuating speed.

Claims

1. Process for controlling an electric motor-driven wheel 10 brake, wherein an actuating device of the wheel brake, containing an electric motor, is actuated by means of a drive signal, wherein via a further drive signal a locking device is actuated which locks the actuating device of the wheel brake, characterised in that the locking device is 15 actuated.during deceleration phases of the electric motor of the actuating device, so that the friction is increased in the area of the actuating device and/or the wheel brake.

2. Process according to Claim 1, characterised in that 20 the locking device is closed when a highly dynamic actuating speed is required.

3. Process according to Claim 2, characterised in that the locking device is closed if a rapid change in the 25 setpoint value underlying the control of the wheel brake, a change of sign of the system deviation has taken place and/or if a high motor speed is present when there is no system deviation.

30

4. Device for controlling an electric motor-driven wheel brake, having a control unit which outputs drive signals for actuating an actuating device containing an electric motor, and for actuating a locking device of a wheel brake locking the actuating device, wherein the control unit 35 determines the drive signal in relation to a system deviation, so that acceleration phases and-deceleration phases of the electric motor of the actuating device occur during an actuating process, characterised in that the control unit generates a drive signal for the locking

5 device for increasing the friction in the area of the actuating device and/or the wheel brake during a deceleration phase of the electric motor of the actuating device.

10 S. Computer program with program code means in order to execute all steps of any one of the Claims 1 to 3, if the program is executed on a computer.

6. Computer program product with program code means which 15 are stored on a computer-readable data medium in order to implement the process according.to any one of the Claims 1 to 3, if the program product is executed on a computer.

7. Process substantially as hereinbefore described with 20 reference to Figures 1 to 3 of the accompanying drawings.

8. Device substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

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9. Computer program substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.