WO1996029222A1

WO1996029222A1 - Process and device for controlling or regulating a vehicle braking system

Info

Publication number: WO1996029222A1
Application number: PCT/DE1996/000329
Authority: WO
Inventors: Hermann Winner
Original assignee: Robert Bosch Gmbh
Priority date: 1995-03-23
Filing date: 1996-02-28
Publication date: 1996-09-26
Also published as: DE19510522C2; DE19510522A1

Abstract

The proposal is for a process and device for controlling or regulating the braking system of a vehicle in which the actuation of the brake pedal by the driver is detected by at least two measuring devices (12, 14) which detect different parameters (F, X), preferably with different measurement principles, and recognise faults in the brake pedal actuation detection field on the basis of said at least two parameters (F, X).

Description

Method and device for controlling or regulating the brake system of a vehicle

State of the art

The invention relates to a method and a device for controlling or regulating the brake system of a vehicle,

Such a method or such a device is known from US 5,230,549. There, a brake system with an electronic control unit is proposed, which actuates the wheel brakes depending on a driver specification (braking request). The actuation of a control element (brake pedal) is determined as the driver's specification. A first sensor for the actuating force of the brake pedal and a second sensor for the distance covered by the brake pedal are provided for detecting the pedal actuation. To determine the braking request, in particular to form a setpoint for a control circuit performing the brake actuation, either the actuation force signal or the travel signal is used, depending on the operating variables. The brake request is determined on the basis of the distance signal if the deceleration of the vehicle is less than a predetermined value, the distance covered by the brake pedal or the actuating force is less than a predetermined value. The function of the brake system depends on the electrically determined one If there is a braking request, an undesired situation can arise in the event of an error in the determination of the braking request, in particular in the event of an error in the pedal actuation detection. Measures for error detection and / or for availability in connection with the determination of the braking request are not described in US Pat. No. 5,230,549.

It is therefore an object of the invention to provide measures which improve a control or regulating system of a brake system of a vehicle with a view to fault states and / or to availability in the area of the determination of the brake request.

This is achieved through the features of the independent claims.

Advantages of the invention

Using at least two sensors for detecting the pedal actuation, which are based on a different measuring principle, the operational safety of the brake system is ensured. Error states in the area of the pedal actuation detection are reliably recognized. It is particularly advantageous to use the signal from a brake pedal switch, which can also be used to control the brake lights, as a third signal for checking the error.

Furthermore, the availability of the brake system is ensured even in the event of error states in the area of the brake request determination. This advantageously results in the possibility of localizing the error that has occurred and of continuing the braking function without restriction on the basis of the functional elements. If all the components function correctly, it is particularly advantageous to increase the accuracy of the braking request and thus the determination of the target value by evaluating the signals from at least two sensors which operate on different measuring principles.

The measures according to the invention are advantageously used in conjunction with all conceivable measuring principles for pedal force and pedal travel sensing and with all known brake systems, whether hydraulic, pneumatic or electrical, with and without emergency brake circuits.

Further advantages result from the following description of exemplary embodiments or from the dependent patent claims.

drawing

The invention is explained below with reference to the embodiments shown in the drawing. 1 shows a block diagram of a control system of a brake system, while FIG. 2 shows a diagram of the actuating force over the pedal travel for a preferred exemplary embodiment of a brake pedal characteristic. Preferred exemplary embodiments for determining errors and braking requests are shown with the aid of the flow diagrams in FIGS. 3 to 5.

Description of exemplary embodiments

Figure 1 shows an electronic control system for a vehicle brake system. In this case, 10 represents an operating element that can be actuated by the driver, preferably a brake pedal. This is with a measuring device 12 for detecting the actuating force F, a measuring device device 14 for detecting the distance traveled or angle X and, in an advantageous exemplary embodiment, connected to a switch 16 for binary detection of the brake pedal actuation BS. This pedal actuation detection unit generally comprises a mechanical unit, not shown, which offers the driver a progressive force curve, that is to say an actuating force that increases with increasing actuation. For this purpose, the pedal is connected to an elastic unit which yields to the force applied by the driver and has the characteristics outlined.

Various measuring devices and various measuring principles are available for detecting the actuating force. For example, the actuating force can be determined via strain gauge bridges in front of the flexible unit on the basis of the pedal deflection or the compression of the connecting rod between the pedal and the flexible unit. Furthermore, the force can be detected at a support point in the flexible unit. Strain gauge bridges in particular are used to record the mechanical

Pressure of the connecting rod on the resilient element or used to detect the supporting force of the resilient element itself. If the flexible unit is a displacement piston (pneumatic or hydraulic), the pedal actuation force can be obtained by measuring the pressure in the flexible unit.

Almost all path or angle measuring methods are used to record the pedal travel. The use of potentiometers, non-contact induction and eddy current sensors, incremental sensors, etc. is particularly advantageous. The pedal angle, the displacement of the connecting rod to the flexible unit, the displacement of the support point of the connecting rod on the compliant unit or the displacement of the piston of the compliant unit is detected.

The measures described below for determining the brake request and for fault detection show the advantages indicated in connection with all the measuring devices and methods mentioned.

The operative connection between the brake pedal 10 and measuring devices 12, 14 and 16 is symbolized in FIG. 1 by a mechanical connection 18. Furthermore, a control unit 20, which has at least one microcomputer 22, is shown. This control unit 20 or the microcomputer 22 are supplied with the input line 24 from the measuring device 12, the input line 26 from the measuring device 14 and, if appropriate, the input line 28 from the switch 16. In addition, the control unit 20 or the microcomputer 22 are supplied with input lines 30 to 32 from further measuring devices 34 to 36 which detect selected operating variables of the brake system, the vehicle and / or its drive unit. Via the output lines 38 to 44, the control unit 20 or the microcomputer 22 is connected to control elements 46 to 52, which actuate the wheel brakes. In the preferred embodiment, the control elements are valve arrangements which control the pneumatic or hydraulic pressure in the wheel brake cylinders. The valve arrangements can each be assigned to a wheel brake and the wheel brakes to an axle. In the preferred exemplary embodiment, the control unit 20 actuates the wheel brakes in the context of a pressure control circuit, the setpoint of which is specified individually by the braking request. In an advantageous exemplary embodiment, the actuating elements 46 to 52 are electric motors which actuate the individual wheel brakes. The control unit 20 or the microcomputer 22 detects the actuating force F, the pedal travel X and, in an advantageous exemplary embodiment, the brake light signal state BS via its input lines. These signals are evaluated on the one hand for error detection, on the other hand for determining the braking request and thus for determining the setpoint for the control or regulation of the brake system. The determined braking request is converted into target values for the individual wheel brakes, taking into account further operating variables such as brake pad wear, axle loads, etc., in accordance with predetermined characteristic curves or fields. Depending on the type of control or regulation, these setpoints represent the brake pressure to be set, the braking torque to be set, the braking force, the vehicle deceleration, etc. They are then regulated in the context of one or more control loops.

The pedal actuation detection unit has a predetermined characteristic. This pedal characteristic is shown in FIG. 2 as pedal force F over path X.

Both values can be changed from the value 0 to a maximum value. With a path X0 of the pedal, the actuation force begins to differ from 0. As a rule, the course of the actuating force over the path X is progressive.

Both actuation force and pedal travel are suitable for determining the braking request. This places special security requirements. Accidental braking may not occur any more than strong braking when the pedal is stationary or the pedal is slightly depressed. The availability of the brake should also be ensured in the event of a fault. In the case of fully electronic brake systems without a mechano-hydraulic or mechano-pneumatic emergency function, this means that the setpoint determination must be designed to be fault tolerant. In a system with non-electrical trical no-run function, the setpoint acquisition must be at least fail-safe. In this context, it is also necessary to check the pedal travel-pedal force characteristic. In particular, due to a mechanical error, no counterforce can arise when the pedal is shifted, so that the actuating force for detecting the braking request is no longer a suitable variable.

The basic idea of the measures according to the invention is the use of measuring devices which record both the pedal force F and the pedal travel X. Since the pedal characteristic F (X) is known or can be determined, an error check is carried out on the basis thereof. For this purpose, the measured values F and X are compared with the known profile of the pedal characteristics and an error is detected in the event of impermissible deviations. It can be determined that one of the two sensors has failed or that the pedal characteristic is abnormal. This procedure is particularly suitable for brake systems with hydraulic or pneumatic emergency operation.

The corresponding procedure is illustrated using the flow diagram according to FIG. 3. After starting the program part at predetermined times, the measured actuation force F and the measured pedal travel X are read in in the first step 100. The pedal force FX to be expected is then determined in step 102 in accordance with the known pedal characteristic as a function of the measured pedal travel X. In the subsequent query step 104, the amount of the difference between the measured pedal force F and the expected pedal force FX is compared with a tolerance value Δ. If the amount of the difference is less than or equal to the tolerance value, error-free operation is recognized according to step 106 and the error flag is set to the value 0. If the amount of the difference exceeds the tolerance value, an error must be hen. According to step 108, the error flag is then set to the value 1 and a warning is issued to the driver. After steps 106 and 108, the program part is ended.

Instead of converting the detected pedal travel into an expected pedal force, in another advantageous embodiment the pedal travel to be expected is determined on the basis of the measured pedal force using the pedal characteristic. The error check is then carried out by comparing the difference between the measured and the expected pedal travel with a predetermined tolerance amount.

The determination of the braking request and thus the setpoint for the brake system control is shown for a preferred embodiment using the flow chart according to FIG.

After the program part has started, actuation force F and pedal travel X are read in in the first step. A check is then made in query step 202 as to whether the error flag is set, that is to say whether an error state in the area of the brake request determination has been detected. If this is the case, a switch is made to emergency operation in step 204. In the case of a brake system with a hydraulic or pneumatic emergency brake circuit, this is done by switching to this emergency brake circuit.

If there is no error, the braking request is determined in step 206. In the preferred embodiment, this takes place on the basis of predetermined characteristic curves or fields from pedal force and / or path. In a preferred exemplary embodiment, the braking request is determined from the mean value of the two measured values, and weighted mean values can also be used. In other advantageous exemplary embodiments, depending on the operating range of the brake system, one or the other measured value can be used to determine the braking request. reasons lie. A minimum or maximum selection (depending on the operating range of the brake system) from the available measured values can also be advantageous.

After determining the braking request in step 206, this braking request value is emitted in the subsequent step 210 to determine the possibly wheel-specific target values and the program part is ended.

A further improvement in operational security and

Fault diagnosis, especially with regard to availability, is achieved by integrating the brake pedal switching signal. This measure can provide information about the source of the error and this knowledge can be taken into account when determining the braking request and thus the setpoint in the event of an error. The result is an error-tolerant brake request or setpoint acquisition.

A preferred exemplary embodiment for fault diagnosis using the brake pedal switching signal is shown in the flow chart according to FIG. 5.

After starting the program part at predetermined times, the signal values for the pedal force F, for the pedal travel X and the signal state of the brake pedal switching signal BS are read in in the first step 300. Analogously to step 202, the pedal force FX to be expected is then determined in step 302 from the pedal characteristic depending on the pedal travel X or the pedal travel to be expected on the basis of the pedal force. In the subsequent step 304, the difference between the measured and the expected value is compared with a first tolerance value Δl. If it is found in query step 304 that the difference is greater than the tolerance value, then in step 306 the pedal force signal is compared with the switching state of the brake pedal switch. If the immediately in step 304 that the signal state and the measured value contradict each other, the pedal force detection is recognized as faulty in step 308 and the target value for the brake system is determined in step 322 on the basis of the measured pedal travel. The warning lamp for indicating the error that has occurred is then activated in accordance with step 316 and the program part is ended.

If it was recognized in step 306 that the pedal force travel and the brake pedal switch state do not contradict each other, the

Step 310 performed the appropriate comparison of the pedal travel with the brake pedal switch. If the two values contradict each other, then according to step 312 the pedal travel detection is recognized as faulty, and in the subsequent step 314 the target value for the brake system is determined on the basis of the pedal force signal then assumed to be correct. After step 314, step 316 is performed. If the brake pedal switch signal and the pedal travel do not conflict according to step 310, a defect in the mechanical component of the pedal detection unit is determined in step 318. In particular, the path simulator used there is assumed to be too hard. The setpoint value determination is then expediently carried out in this error state on the basis of the pedal force signal according to step 314, since in this case this is a more precise measure of the braking request than the pedal travel.

If it was determined in step 304 that the difference does not exceed the tolerance value .DELTA.l, it is determined in accordance with step 305 whether the difference falls below a second tolerance value .DELTA.2, in particular whether the difference has negative values. If this is the case, in step 320, the pedal force path is compared with the brake pedal switch signal analogously to step 306. If a contradiction between the two signals is detected, the pedal force detection is assumed to be faulty in accordance with step 308 and the Setpoint determination as shown above. If there was no contradiction between the two signals in step 320, the pedal travel signal is compared in step 324 in accordance with step 310 with the brake pedal switch. If there is a contradiction between the two signals, proceed to step 314. If the comparison did not reveal a contradiction between the two signals, a defect in the mechanical part of the pedal detection unit is assumed in accordance with step 326. The path simulator is assumed to be too soft, so that the target value determination in this case of error is carried out according to step 322 on the basis of the pedal travel signal.

If step 305 showed that the difference does not fall below the tolerance value Δ2, that is, if the difference lies within a tolerance range between the values Δl and the preferably negative value Δ2, then according to step 328 one of the signals is compared with the brake pedal switch signal. In the event of an objection, the brake pedal switch is assumed to be faulty in accordance with step 330 and in accordance with

Step 332 issued a warning signal to the driver. In this fault case, the setpoint determination and the function check according to FIGS. 3 and 4 are then carried out. The setpoint calculation in this error case is, just like in error-free operation, if the decision is positive

Step 328 according to step 334 is carried out analogously to FIG. 4, steps 206 and 210. The program section is then ended and repeated at the appropriate time.

As mentioned above, in other advantageous exemplary embodiments the pedal force is converted into a pedal travel and FIG. 5 is carried out accordingly. In a preferred embodiment, the two values Δl and Δ2 are equal in terms of amount. In the other exemplary embodiment, the person skilled in the art defines the tolerance values in accordance with the experimentally determined tolerance conditions of the pedal detection unit.

Claims

- 13 claims

1. A method for controlling or regulating the braking system of a vehicle, with at least two measuring devices for detecting the actuation of an operating element influencing the braking system by the driver, the two measuring devices representing at least two different quantities which represent the actuation. detect, characterized thereby, an error state is recognized if the at least two sizes deviate from one another in an impermissible manner.

2. The method according to claim 1, characterized in that the first variable represents the actuating force, the second variable represents the distance traveled by the control element.

3. The method according to claim 2, characterized in that a force / displacement characteristic is specified.

4. The method according to claim 3, characterized in that on the basis of the predetermined characteristic at least one size is converted into the other and the error detection is carried out by comparing the measured and the converted size.

5. The method according to claim 1, characterized in that a third measuring device for detecting the actuation is additionally provided.

6. The method according to claim 5, characterized in that the third measuring device is a switching element whose signal state indicates the actuation or non-actuation of the control element.

7. The method according to claim 5 or 6, characterized in that the error determination is carried out by a two-out-of-three selection of the three detected quantities.

8. The method according to claim 1, characterized in that the braking request or the braking setpoint for the brake system is determined on the basis of at least one of the detected quantities, in the event of a fault on the basis of the error-free quantities.

9. The method according to any one of the preceding claims, da¬ characterized in that the control element is a brake pedal and for detecting the actuating force, a measurement of the pedal deflection, the rod compression, the support forces of the rod on a flexible element, the supporting force of the flexible element or the pressure in a compressible volume of the brake pedal actuation measuring device, the pedal travel is carried out by detecting the brake pedal deflection, the displacement of the rod, the displacement of the support point of the rod on the flexible element or the displacement of pistons in the flexible element by displacement or angle measuring methods is determined.

10. The method according to any one of the preceding claims, characterized in that the at least two sizes by

Measuring devices are determined which carry out the measurement on the basis of different measuring principles.

11. Device for controlling or regulating the brake system of a vehicle, with an electronic control unit for controlling or regulating the brake system, with a measuring device for detecting the actuation of an operating element influencing the brake system by the driver, at least two different, variables representing the actuation are determined, characterized by an error detection unit which recognizes an error state in the area of the actuation detection if the at least two variables deviate from one another inadmissibly.