EP0734335A1

EP0734335A1 - Method and device for controlling a vehicle brake system

Info

Publication number: EP0734335A1
Application number: EP95928951A
Authority: EP
Inventors: Werner Stumpe
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1994-09-14
Filing date: 1995-08-19
Publication date: 1996-10-02
Also published as: JPH09505255A; US5702163A; WO1996008397A1; DE4432642A1

Abstract

Proposed is a method and device for controlling a vehicle brake system, the pressure in the brake system being adjusted by an electronic control device (20) to correspond to a reference value and the braking action and/or the onset of the braking action being determined by detecting the reaction of the vehicle body to the braking operation.

Description

Method and device for controlling a brake system of a vehicle

State of the art

The invention relates to a method and a device for controlling a brake system of a vehicle according to the Oberbegri fen of the independent claims.

Such a method or such a device is known for example from DE 41 12 845 AI. In the electrically controlled or regulated brake system described there, the application pressure of the individual wheel brakes and thus the start of braking is determined by evaluating the pressure curve over time when the brake is actuated. This contact pressure is used to correct a target pressure derived from the driver's request, which is used to regulate the pressure medium introduced into the individual wheel brake. The correction is carried out in the sense of producing a braking force of the same magnitude on all vehicle wheels or on the vehicle wheels of an axle. This compensates for the effects of wear, friction fluctuations, mechanical losses and tolerances on the individual wheel brakes. Furthermore, by determining the contact pressures, the simultaneous response of the individual Guaranteed wheel brakes so that the run-up forces between the towing vehicle and trailer are reduced. A determination of the braking response, the braking effect and the beginning of the braking effect is carried out using parameters of the braking system itself. This can be unsatisfactory in individual cases.

It is an object of the invention to provide measures for an improved detection of the braking reaction, the braking effect and the beginning of the braking effect.

This is achieved by the characterizing features of the independent claims.

From EP 149 137 A2 it is known to detect a signal corresponding to the static axle load and to take this into account in the brake pressure distribution of a brake force control system.

The evaluation of the determined braking torque in an electrically controlled or regulated brake system is known from EP 276 435.

Advantages of the invention

The procedure according to the invention allows the braking effect and the beginning of the braking effect to be recorded. As a result, the control of an electrically pneumatic or electrically hydraulic or purely electrical brake system can be improved.

It is particularly advantageous that the values of the Supporting forces or axle loads can be used for brake pressure distribution.

It is also of particular advantage that the braking torques applied to the individual wheels can be calculated from the values determined.

It is also advantageous that monitoring of the brake system is made possible by the procedure according to the invention.

The brakes are matched to one another by the procedure according to the invention, so that wear behavior and run-up forces between the towing vehicle and the trailer vehicle are significantly improved. Likewise, incorrect mechanical adjustments are corrected during operation by the automatic tuning of the brake system.

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

drawing

The invention is explained below with reference to the embodiments shown in the drawing. 1 shows an overview block diagram of an electrically controlled or regulated brake system, while FIG. 2 shows various alternatives for detecting the supporting forces on a wheel. Figure 3 shows the time course of the brake pressure and the support forces during braking, while Figure 4 shows the assignment of the support forces to the brake pressure. Figure 5 finally shows a flow chart in which the determination of the braking effect and the start of braking action is shown according to the procedure according to the invention.

Description of exemplary embodiments

Figure 1 shows an overview block diagram of an electronically controlled or regulated brake system, as is known from the prior art. Pneumatic or hydraulic emergency or auxiliary brake circuits are usually attached to this. FIG. 1 shows an encoder 10 which can be actuated by the driver and which is connected to an electronic control unit 20 via an electrical line 12. The electronic control unit 20 is connected to pressure control valves 50 and 60 via a communication system 22. For brake actuation, these control the pressure in the brake actuation devices 90 and 100 and, in addition to electronics for pressure control, have sensors 70, 80 for detecting the pressure input into the brake actuation devices 90 and 100, respectively. Furthermore, memories 30 and 40 are shown, which store the energy for brake actuation. The pressure control valves 50 and 60 shown are assigned to an axis in the preferred exemplary embodiment and control the pressure in the brake actuation devices of an axis. In other exemplary embodiments, such pressure control valves are assigned to each wheel brake or a combination axle / wheel brake. Furthermore, FIG. 1 schematically shows an axle 102 of the vehicle with a wheel 105 and two spring elements 110 and 120, on which the vehicle body 125 rests. A load sensing element 130 is shown to determine the support forces of the vehicle body on the vehicle axle. In a preferred embodiment, this detected the pressures in the two spring elements 110 and 120. Das Load sensing element 130 is connected to electronic control unit 120 via an electrical line 135 - in the preferred exemplary embodiment via communication system 22.

When the driver presses the brake pedal, the transmitter 10 emits a brake control signal to the electronic control unit 20. This assigns the degree of actuation of the transmitter 10, which corresponds to the driver's request, to a pressure setpoint, which is fed via the data bus 22 to each pressure control valve. The setpoint is set by the pressure control valve as part of a pressure control circuit. In the electronic control unit 20, for each pressure control valve, that is to say for each axle or for each wheel brake, a characteristic curve of the target pressure versus the degree of actuation of the transmitter 10 is stored, which takes into account the individual differences in the wheel brakes. In particular, the characteristic curves are determined in such a way that the braking effect on all wheels starts approximately simultaneously. It is therefore crucial that the electronic control unit 20 recognizes the braking reaction, the braking effect and its beginning and corrects the characteristic curves accordingly. The pressure detected by the pressure sensors 70, 80 is transmitted via the communication system 22 to the electronic control unit 20 for evaluation. In addition to the electronically controlled brake function shown, an axle load-dependent pressure control known from the prior art and an anti-lock protection are provided.

To detect the braking effect and the beginning of the braking effect, the braking reaction in the spring elements 110 and 120 is evaluated with the load detection element 130 in the preferred exemplary embodiment. Various embodiments of this load sensing element 13 are shown in FIG. 2. A load sensing element 130 is described in FIG. 2a, which has two pressure sensors 140 and 150, which measure the pressures in the spring elements. In another advantageous exemplary embodiment, only a pressure sensor is provided, the signal of which can be sufficient to determine the braking action and the start of the braking action. FIG. 2b shows a load measuring element 130 with a pressure sensor 140 and a changeover valve 160. The pressure sensor is connected to a spring element 110 and can be acted upon by operating the changeover valve 160 from the electronic control unit 20 with a comparative pressure from the second error element 120, so that the pressure sensor both the pressure in the spring element 110 and the difference between the pressures in detected two spring elements. In this case, the changeover valve 160 is actuated by the electronic control unit 20 at predetermined measuring times. Furthermore, the switching valve 170 is combined with the existing check valve of the air suspension system in the exemplary embodiment according to FIG. 2c.

The load detection element 130 serves to detect the braking reaction by determining the support forces at at least one support point of the vehicle body. In an advantageous embodiment, the differential forces between individual spring elements are also determined. The support forces are determined by measuring the pressure in the spring elements. The control unit 20 reads in the values from the load detection element 130 in certain time steps and evaluates them to determine the braking reaction, the braking effect and the beginning of braking as shown below. FIG. 3 shows the course of the support forces or the pressure PLF in a spring element and the brake pressure PBR applied to the brake system of the corresponding wheel over time. The electronic control unit determines the respective pressure values at predetermined time steps. It shows that after actuation of the transmitter 10 beyond a certain position at the time TO pressure is controlled in the wheel brake cylinder. A reaction on the vehicle body, which becomes visible through a change in the pressure in the spring elements and thus the support forces, only takes place at Time Tl, since only then does a braking torque reaction occur, ie a braking effect. If one compares the brake and spring element pressure at the time steps, the behavior shown in FIG. 4 results. The spring element pressure PLF remains constant for a certain time in spite of the increase in the brake pressure PBR and increases at a point in time T1 in analogy to the increase in the brake pressure. The time Tl accordingly designates the start of the braking effect on the vehicle, which at this point in time has a reaction in the vehicle body to the braking torque applied. According to the invention, this reaction of the vehicle body is evaluated in order to determine the braking effect and the beginning. If there is a braking torque reaction on the vehicle body (time T1), the braking pressure that is then present is stored as the beginning of the braking action and evaluated in the context of the characteristic curves described above.

In the simplest case, the evaluation of the braking torque reaction based on the pressure in a bellows of the wheel suspension system of the vehicle is sufficient. In a preferred exemplary embodiment, however, the pressure difference between the pressures in both bellows is used, since this procedure improves the accuracy of the detection of Braking effect and the beginning of braking effect increased. It should be noted that the pressure difference shows a time profile comparable to that of FIG. 3a.

FIG. 5 shows a flow chart which illustrates the procedure according to the invention shown.

After starting the program part with a brake actuation, which can be derived from the actuation signal of the transmitter 10, the brake pressure PBR in the pressure control valve and the pressure in a spring element PLF1 are read in in a first step 200. In an advantageous further

In the exemplary embodiment, the pressure PLF2 is additionally read into the second spring element. A check is then made in step 202 as to whether the difference between the pressure currently read in the spring element PLF1 (n) and the pressure PLFl (n-l) read in the previous program run is greater than the difference value Δl. If this is the case, the currently measured brake pressure value PBR (n) is stored in step 204 as the pressure PO which indicates the start of the braking action. In the subsequent step 206, the stored value PO is corrected with tolerance values Δ2 and thus the pressure PA for the

Start of braking effect formed. In the subsequent step 208, the characteristic curve, which forms the target value Psoll on the basis of the actuation value BWG of the transmitter 10 and the pressure for the start of braking PA, is determined. The program section is then ended and repeated at the appropriate time.

In an advantageous exemplary embodiment, in addition to evaluating the pressure in a spring element for determining the braking action and the start of the braking action, the pressure PBR in the braking system is evaluated. For this purpose, a step 210 is introduced between step 200 and step 202, in the currently measured brake pressure PBR (n) is checked to determine whether it is greater than the brake pressure PBR (nl) measured in the previous program run. If this is the case, the process continues with step 202, while in the opposite case the program part is ended. Due to the inclusion of the brake pressure when determining the braking effect and the beginning of the braking effect, it is advantageously possible to monitor whether the applied braking pressures bring about the expected braking effect. If, after a certain filter time or after a predetermined number of similar results, no corresponding reaction is detected on the vehicle body when the brake pressure is increased in step 210 in step 202, it can be assumed that the applied brake pressure has no braking effect. In this case, according to step 212, the driver is warned by an optical or acoustic signal. After step 212, the program part is ended.

In a further advantageous exemplary embodiment, not only the pressure in one, but also the pressure in a second spring element or the differential pressure between the two spring elements is used to improve the accuracy of the detection of the braking action and the beginning of the braking action. For this purpose, in the exemplary embodiment shown in FIG. 5, the pressure PLF2 is read into the second spring element in step 200. In the subsequent step 214, the difference ΔPLF between the pressure PLF2 in the second and that in the first spring element (PLF1) is formed. After advantageous step 210, step 202 does not check the time profile of the pressure in the first spring element but rather the time profile of the differential pressure ΔPLF. For this purpose, the difference between the currently measured differential pressure ΔPLF (n) and that in the previous one Differential pressure ΔPLF (nl) measured in the program run is compared with a predetermined differential value Δ3. If the difference exceeds this value, the process continues with step 204, while in the opposite case the program part is terminated, possibly with the execution of step 212.

In addition to the illustrated evaluation of the differential pressure and the pressure in a spring element, it can be provided in an advantageous exemplary embodiment that both of the conditions mentioned must be present in step 202 in order to detect the start of the braking action.

If the load sensing element is designed such that it senses a value for the differential pressure between the two spring elements and a value for the pressure in a spring element, step 214 is dispensed with and values are read in in step 200.

The computer program shown in FIG. 5 is carried out for each wheel brake or for each axle of the vehicle to which a pressure control valve is assigned, and the characteristic curve for the pressure setpoint is formed accordingly.

In addition to applying the procedures according to the invention to air-sprung vehicles, this is also advantageously used in conjunction with leaf-sprung vehicles.

Furthermore, in an advantageous exemplary embodiment, the determination of the braking action and the beginning of the braking action according to the procedure according to the invention is carried out automatically during each or during braking operations selected during driving operation, for example on the basis of a time criterion certainly. In other exemplary embodiments, the procedure according to the invention is carried out additionally or alternatively as part of the diagnosis in service workshops. The axles or wheels can also be braked there one after the other.

It is particularly advantageous that not only the start of the braking action and the braking action, but also the braking torques actually acting on the road or the acting braking force can be calculated from the determination of the support forces during the braking process. The following equations can be derived for this.

A value for braking torque MB results when measuring the pressures in two spring elements from the pressure difference between these spring elements during braking (Δ p) and during unbraked travel (ΔpO):

MB = K * (deltap - deltapO)

where the constant K is a value which characterizes the geometric relationships of the axle and the wheel suspension of the vehicle.

If the pressure is only recorded in one spring element, the braking torque results from the difference between the pressure during unbraked travel PU and the pressure during braked travel PB:

MB = K (PB - PU)

where K is also a constant value derived from the geometric relationships of the axle and the wheel suspension. A comparison of the calculated values is given in advantageously used for diagnosis or monitoring of the brake system by comparing the values with permissible limit values and detecting an error if the values are exceeded or fallen below.

The existing braking torque or force gradients can then be determined from the calculated braking torque. Furthermore, in one exemplary embodiment, the braking torque determined is used to control the braking system in accordance with the prior art mentioned at the beginning.

In summary it can be stated that the procedure according to the invention determines the braking reaction on the vehicle body by determining the articulation of the spring elements. The braking reaction is measured at at least one support point and the support forces or the differential forces are recorded. The pressure which brings the associated brake or the associated brakes into effect can be determined by comparison with the controlled brake pressures. On the basis of this pressure value, the specifications are changed in the sense of compensation in such a way that the same effect occurs essentially simultaneously for all brakes. Determining the support forces opens up the advantageous possibility of using the values of the support forces for brake pressure distribution and for regulating the brake pressure distribution as in the prior art. Furthermore, the calculation of the actually acting braking torques or the braking force is advantageously possible by determining the support forces.

These values can advantageously be used to diagnose the braking effect of the individual brakes. Furthermore, the procedure according to the invention enables Monitoring whether the applied brake pressures also bring the expected braking effect, with a warning to the driver if the brake malfunctions. By targeted braking of the individual axles one after the other and evaluation of the braking effect on the vehicle, a targeted local assignment of cause and effect can be carried out.

Claims

Expectations

1. A method for controlling a brake system of a motor vehicle, wherein an electronic control unit, to which at least one value representing the driver's request is supplied, determines a setpoint to be regulated as a function of the driver's request for one or more wheel brakes and determines the braking effect or the beginning of the braking effect, characterized in that that the braking effect or the beginning of the braking effect is derived from the reaction of the vehicle body during the braking process.

2. The method according to claim 1, characterized in that the reaction of the vehicle body is derived by determining the support forces of the vehicle body on the axle during the braking process.

3. The method according to claim 2, characterized in that the supporting forces are derived from the pressure in at least one spring element of the vehicle.

4. The method according to any one of the preceding claims, characterized in that the pressure is determined in at least one spring element and the start of braking action is determined from the time course of the pressure in this spring element.

5. The method according to any one of the preceding claims, characterized in that the pressure is detected in at least one spring element and the differential pressure is formed between the pressures in both spring elements of a wheel and from the time behavior of the differential pressure and / or the pressure in the one spring element Beginning of the braking effect is derived.

6. The method according to any one of the preceding claims, characterized in that when the pressure in a spring element increases or the differential pressure increases during the braking process, the beginning of the braking effect is derived.

7. The method according to any one of the preceding claims, characterized in that on the basis of the brake pressure prevailing at the start of the braking action, the assignment of the driver's request to the desired value is corrected, so that the braking action starts essentially simultaneously for all wheel brakes.

8. The method according to any one of the preceding claims, characterized in that the braking torques actually acting on the wheel are calculated on the basis of the pressures in the spring elements or the differential pressure when braking and when braking.

9. The method according to any one of the preceding claims, characterized in that the functioning of the brake system is monitored by comparing the pressure values in a spring element or the differential pressure values and the controlled brake pressure values and a fault is output if necessary, a warning.

10. The method according to any one of the preceding claims, characterized in that the determined support forces are used to control the brake pressure distribution.

11. The method according to any one of the preceding claims, characterized in that the functioning of the brake system is monitored on the basis of the calculated braking torques.

12. Device for controlling a brake system for a motor vehicle, with an electronic control device (10), which is supplied with a signal representing the driver's request from an encoder (10) that can be actuated by the driver, with pressure control valves (50, 60), which corresponds to that of the electronic control device Set the supplied setpoint as a function of the driver's request, and and the electronic control device comprises means which detect the braking effect and / or the beginning of the braking action, characterized in that values are supplied to the electronic control device from which the reaction of the vehicle body during the braking process can be derived and from which the braking effect or the beginning of the braking effect is derived.