DE102004006338A1 - Parking brake system for a motor vehicle has an operating element for locking/releasing a parking brake, an actuator, a control device and a device to determine braking force - Google Patents

Abstract

An actuator (25) adjusts braking force acting on a parking brake (12). A control device (7) triggers the actuator on demand. A device (26) determines braking force acting on the parking brake. The control device is set up so that the actuator is triggered by relying on the braking force determined, in order to lock or release the parking brake. An independent claim is also included for a method for operating a parking brake system for motor vehicles.

Description

The The invention relates to a parking brake system for motor vehicles according to the preamble of claim 1 and a method for driving such Parking brake system according to the preamble of claim 7.

modern Motor vehicles are increasingly common electrically operated Parking brakes, which by means of a control element, such. one Push button, pressed can be. A connected to the control unit detects the parking brake request and correspondingly controls an actuator, e.g. an electric motor or a hydraulic pump, to apply the parking brake or to solve. The parking brake includes a mechanical brake in addition to the actual brake Locking device, the brake calipers in the tightened Locked position. The locking device is usually also operated by hydraulic or pneumatic pressure. To do this e.g. a hydraulic pump and solenoid valves corresponding electrically driven.

1 shows a known from the prior art parking brake system in a schematic representation. The parking brake system essentially comprises an operating element 8th (Push button), a control unit 7 and a hydraulic unit 6 , Upon actuation of the operating element 8th controls the controller 7 the hydraulic unit 6 or a hydraulic pump contained therein such that they are in a hydraulic line 10 Build up brake pressure. The brake pressure is both for actuating the wheel brake 12 as well as for actuating the locking device 13 used. The parking brake further comprises a hydraulic valve 11 from the control unit 7 is controlled to the locking device 13 to lock or to release. The parking brake system is from the electrical system of a battery 9 (and the vehicle generator) powered.

According to the legal regulations, the vehicle must be held mechanically and without energy when the parking brake is applied. As a minimum requirement, ECE-R13 stipulates that a vehicle must be held at full load up to an incline of 18%. Known parking brake systems work with a time control of the hydraulic unit 6 that is, the hydraulic pump is driven for a predetermined amount of time that is long enough to meet the minimum requirement. Because of the high tolerances in the parking brake system, in particular due to different temperatures, wear, mechanical tolerances, etc., the force effect of the parking brake at the end of the time control is very different. In the worst case, the required minimum force effect is not achieved. To exclude this case, the pump running time is set as long as possible. However, this means high loads for the components involved.

It is therefore the object of the present invention, the control to optimize the actuator and thus the mechanical load the components as possible to keep low. The optimization should also be with as possible low sensory effort can be realized.

Is solved this task according to the invention by the features specified in claim 1 and in claim 7. Further embodiments of the invention are the subject of dependent claims.

One essential aspect of the invention is that of a parking brake actually acting Determine braking force and the actuator of the parking brake system (e.g., a hydraulic pump) in consideration of the determined ones To control braking force, at least until a predetermined braking force value is reached. To determine the braking force can optionally be a device (Sensor) be provided, by means of which the braking force measured, or a device (model), by means of which the braking force from others State variables is estimated. Under Cost aspects, it is advantageous to use the braking force by means of a mathematical algorithm (mathematical model) to estimate since In this case, no brake force sensor must be provided. By the measuring or estimating the braking force can accurately set a required minimum braking force so that the load on the components involved is minimal is. Furthermore can by monitoring the braking force a fault condition are relatively easily detected.

According to a first embodiment of the invention, the braking force is measured by means of a force sensor and the sensor signal is supplied to a control unit. The control unit can thus control the actuator (eg the hydraulic pump) for locking or releasing the parking brake until a predetermined braking force threshold is reached. The force sensor according to the invention can be realized, for example, as a strain gauge strip, force measuring cartridge or as a force switch. The force sensor is preferably arranged at a position at which upon actuation of the parking brake, a mechanical deformation takes place, from which the actually acting braking force can be derived. The force sensor can thus be arranged eg on the caliper, the brake piston, a wear compensation mechanism or at another location, where the braking force is effective.

According to one special embodiment of the Invention, the braking force sensor is realized as a brake force switch, which changes its switching state when a characteristic braking force is reached. One Such brake force switch is particularly simple and inexpensive available. Furthermore the switching state can be easily evaluated by the control unit become. The brake force switch is preferably designed such that the characteristic braking force is about equal to the required Minimum braking force is.

According to one second embodiment The invention is a mathematical model for determining the braking force provided that the behavior of the wheel brake at different Brake pressure maps. The mathematical model determines e.g. from the one acting on the brake (hydraulic or pneumatic) brake pressure, taking into account other parameters (in particular the mechanical design and the elasticities brake pad and caliper), the prevailing braking force. As input is at This model only requires the brake pressure. To the temperature dependence the braking effect can be considered additionally the temperature measured or also by means of an algorithm estimated become. The estimation the braking force by means of a mathematical model has the advantage that no force-measuring sensor is required.

Of the for estimation required brake pressure can either by means of a pressure sensor measured or estimated using a mathematical model. In the case of a pressure measurement, the corresponding pressure sensor is preferred arranged after the hydraulic pump in the brake circuit.

in the Case of an estimate the braking pressure is preferably the follow-up behavior of the hydraulic pump evaluated to estimate the brake pressure. For this purpose, the hydraulic pump (or pneumatic pump) operated preferably clocked and after a falling edge of the clock signal, the trailing behavior of the Pump characterizing size, such as e.g. a tracking voltage, the pump is determined and evaluated. Optionally, could e.g. also the course of the speed of the pump can be evaluated. At higher Brake pressure results in principle, a faster drop in the Tracking voltage or pump speed, as the pump braked more is, and at lower brake pressure, a slower drop in the mentioned sizes, since the Pump is slowed down less. This can turn on the current brake pressure to be closed.

The Follow-up behavior of the hydraulic or pneumatic pump is in addition to the current brake pressure mainly depends on the current friction. Of the Friction fraction is again a function of the current temperature the pump. To calculate the friction component, it is preferable the trailing behavior of the pump at a known pressure, e.g. determined by means of a pre-pressure sensor determined. The following Examples are intended to clarify this: If the parking brake in activated in a situation in which the foot brake pedal is not actuated (pre-pressure = 0bar), Thus, the load calculated from the follow-up behavior corresponds to the beginning the friction component. This may be later during operation of the parking brake be calculated out. If the parking brake, however, in a Situation activated, in which the foot brake pedal is pressed (Form> 0bar), can be calculated from the follow-up behavior of the pump, e.g. based on a characteristic field, also the friction component can be determined. The friction component can thus later subtracted from the total load and the pressure component or the brake pressure be determined. An additional one Temperature sensor is not required in this case.

With the parking brake system according to the invention is it about it out possible, to recognize a malfunction of the system in a simple manner, as a Measuring or Estimated size for the braking force is present. When the braking force drops below a predetermined value, For example, the driver may warned visually or acoustically or it can an entry is made in a fault memory.

In addition, measures can to correct the error. Unless the parking brake can not properly locked after a lock request e.g. a renewed application of the parking brake can be automatically initiated.

The Invention will be exemplified below with reference to the accompanying drawings explained in more detail. It demonstrate:

1 a schematic view of a known from the prior art automatic parking brake;

2 a hydraulic brake system according to different embodiments of the invention;

3 a schematic representation of a mathematical model for braking force calculation;

4 a brake pressure / force characteristic of a vehicle brake;

5 a schematic representation of a mathematical model for pressure calculation;

6 an illustration of the follow-up behavior of a hydraulic pump at different brake pressure;

7 a flowchart of the essential steps in locking a parking brake with brake force switch; and

8th a flowchart of the essential steps in locking a parking brake with brake force estimation.

Regarding the explanation of 1 Reference is made to the introduction to the description.

2 shows a hydraulic brake system 30 , which is designed for vehicle dynamics control (eg ESP). The brake system comprises two brake circuits 28a . 28b in X-division, which are symmetrical. In the following, therefore, only on the part shown on the left in the figure 28a Referenced.

The brake system includes a foot brake pedal 1 , a brake booster 2 with a master cylinder connected to it 4 on which a brake fluid reservoir 3 is arranged. Upon actuation of the foot brake pedal 1 gets into the main brake line 15a . 15b generates a corresponding pressure, via a switching valve 18a . 18b and the two intake valves 20a . 20b on the brakes 12 the wheels 14 acts. The path in which a brake pressure builds up when the foot brake pedal is actuated is indicated by arrows b. Upon actuation of the foot brake pedal 1 is a high pressure switching valve 17a closed.

When the parking brake is actuated by means of the push button 8th the brake pressure is built up automatically and on given wheels 14 (eg the wheels LR and RR) distributed. The brake system 30 includes for this purpose a hydraulic pump 19a coming from a control unit 7 is controlled. The changeover valve 18a is closed in this case and the high pressure switching valve 17a opened (inverse to the position shown). The hydraulic pump 19a then pumps the hydraulic fluid along the paths a to the parking brakes 12 wheels LR, RR. The hydraulic fluid thus flows out of the brake fluid reservoir 3 , through the main brake line 15a , the high pressure switching valve 7a , a suction pipe 16a , by the hydraulic pump 19a and continue through the intake valves 20a . 20b to the parking brakes 12 (the element 13 is not shown here). Short-term pressure peaks are in a surge tank 23a buffered.

To the hydraulic pump 19a or the associated engine 25 To optimally control and also to be able to monitor the functionality of the parking brake, is the on the parking brakes 12 . 13 (the wheels LR, RR) actually acting braking force F _Br determined. The braking force F _Br can be determined in different ways:
The at the wheel brake 12 acting braking force F _Br can be measured according to a first embodiment, for example by means of a sensor. For this purpose, a braking force sensor 26 provided, for example, as a strain gauge sensor, as a force measuring cartridge or as a force switch can be realized. The sensor 26 is eg on the caliper 12 or another part of the brake, which is mechanically reversibly deformed when the brake is actuated. The measuring signal is the control unit 7 fed.

During a locking process, the controller controls 7 the engine 25 the hydraulic pump 19a until the desired braking force is reached. After reaching the desired braking force F _Br is the locking device 13 locked and the hydraulic pump 19a shut down again (ie the brake pressure is reduced again). A malfunction of the parking brake can in a simple manner by monitoring the braking force F _Br on the brake force switch 26 determined and warned the driver if necessary.

To unlock (release) the parking brake 12 . 13 is the brake pressure by controlling the controller 7 again brought to a predetermined value, the locking device 13 unlocked and the brake pressure then reduced again.

Instead of a continuous measuring force sensor 26 It is also possible to provide a force switch which changes its switching state when a characteristic braking force is exceeded. The characteristic value preferably corresponds to the minimum requirement mentioned at the beginning of the braking force at an 18% gradient and fully loaded vehicle. After reaching the characteristic value of the brake pressure can be further increased, in particular mechanical setting effects on the parking brake 12 . 13 compensate. This is again the hydraulic pump 19a or their engine 25 from the control unit 7 controlled accordingly.

The main steps in locking a parking brake system using a brake force switch 26 are in 7 shown.

In step 40 is by controlling the hydraulic pump 19a initially built brake pressure p _Br . The current braking force F _Br is by means of a brake force switch 26 measured (step 41 ). about If the braking force F _Br exceeds a predetermined threshold value SW, the braking force switch changes 26 its switching state. This will be in step 42 recognized. Thereafter, the brake pressure p _Br is increased by an amount Δp (see 4 ) in order to prevent the braking force F _Br from falling below the required minimum value after the brake pressure p _{Br has} been reduced (step 43 ). In step 44 becomes the locking device 13 locked and in step 45 the brake pressure p _Br degraded again. This is due to the mechanical properties and the tolerances of the parking brake 12 to set effects, whereby the braking force slightly decreases (see 4 , ΔF). The amount .DELTA.p is therefore to be chosen so that after the reduction of the brake pressure p _Br the switching threshold of the brake force switch 26 not fallen below.

If the required minimum braking force SW is nevertheless fallen below after the pressure has been reduced, the locking procedure is repeated automatically, eg with a larger Δp value. A corresponding routine is preferably in the control unit 7 deposited.

According to a second embodiment is a mathematical model 31 provided, with which the braking force F _Br can be estimated. The braking force sensor or switch 26 can be saved in this case.

3 shows a block diagram of a mathematical model 31 for estimating the braking force F _Br , that in the control unit 7 is deposited. The mathematical model 31 depicts the behavior of the brake system and can thus determine the resulting braking force F _Br from a given brake pressure p _Br . The mathematical model 31 contains in particular information about the mechanical structure of the parking brake 12 . 13 , the elasticities of brake pad and caliper, the temperature dependence of the braking characteristics, etc ..

4 shows the relationship between braking force F and brake pressure p in the form of a diagram. After the start (time t1) of the hydraulic pump 19a the power buildup takes place in the brake 12 along the characteristic curve 33 , Because of the effects of temperature, mechanical tolerances and other mechanical properties of the brake, however, the resulting braking force F _Br can only be determined with relatively great inaccuracy. The estimation of the braking force F _Br is therefore relatively inaccurate.

The brake pressure p _Br can either by means of a pressure sensor 27 (please refer 2 ) or estimated using a mathematical model. 5 shows a schematic block diagram of a mathematical model 32 for estimating the brake pressure p _Br . The model 32 is capable of the brake pressure p _Br by evaluating the follow-up behavior of the hydraulic pump 19a appreciate. Because the follow-up behavior of the pump 19a Depending on the prevailing pressure changes, it can be estimated from the brake pressure p _Br .

6 shows the principal relationship between a lagging behavior of the pump characterizing size K (eg U, n) over time and different brake pressures p _Br . It can be seen that the tracking voltage or speed of the pump 19a in principle with increasing brake pressure p _Br decreases more. That means the pump 19a is braked at higher pressure p _Br stronger than at lower pressure. The current brake pressure can thus by evaluating the follow-up behavior of the pump 19a to be appreciated.

In order to evaluate the follow-up behavior of the pump, the hydraulic pump 19a operated clocked. After each falling edge of the clock signal becomes the mathematical model 32 one the follow-up behavior of the pump 19a characteristic size K supplied and the follow-up behavior of the pump 19a evaluated. The supervised variable K can be, for example, a regenerative follow-up voltage U of the pump 19a , a time duration or the rotational speed n.

To take into account the friction component in the evaluation, before the pump starts up 19a the currently prevailing pressure with the admission pressure sensor 29 measured and the follow-up behavior of the pump 19a evaluated at this pressure. If the initial pressure measurement results in a brake pressure of about 0 bar - ie the driver is not standing on the foot brake pedal 1 - The initially estimated brake pressure p _Br corresponds to the friction component. This can thus be considered below in the pressure estimation.

Unless the driver at the beginning of the foot brake pedal 1 operated, the friction component with knowledge of the current form p _{before can} also be determined and taken into account in the subsequent estimation of the brake pressure. This method has the significant advantage that an additional temperature sensor is not required.

8th shows the essential steps of a locking process with brake force estimation and brake pressure estimation.

After an actuation of the operating element 8th will be in step 40 the brake pressure p _Br by appropriate control of the hydraulic pump 19a elevated. The actual brake pressure p _Br is determined by means of a mathematical model 32 how about 5 was estimated (step 41 ). In addition, in step 46 the on a parking brake 12 . 13 acting braking force F _Br means of the model 31 appreciated as regards 3 has been described.

If the estimated braking force F _Br exceeds a predetermined threshold SW (query in step 42 ), the brake pressure p _{Br is} still an amount Ap (see 4 ) increases to the said setting effects after locking the parking brake 12 . 13 to compensate. In step 44 gets the brake 12 . 13 finally locked and in step 45 the pressure is reduced again.

This method has the significant advantage that in addition to the already existing form sensor 29 no further sensors 26 respectively. 27 needed.

1

Driver brake pedal

2

Brake booster

3

Brake fluid reservoir

4

auptbremszylinder

5

magnetic valve

6

hydraulic unit

7

control unit

8th

operating element

9

battery

10

brake line

11

Valve

12

Brake / Brake Caliper

13

locking device

14

wheel

15

brake line

16

suction

17

High pressure switching valves

18

switchover

19

hydraulic pump

20

On-off

22

exhaust

23

surge tank

24

check valves

25

pump motor

26

force sensor

27

Brake pressure sensor

28

brake circuits

29

form sensor

30

hydraulic braking system

31

mathematical Brake force estimation model

32

mathematical Model for brake pressure estimation

33 34, 35

F _Br / p _Br characteristics

40-46

steps

F _Br

braking force

P _Br

brake pressure

Claims (12)

Parking brake system for a vehicle, in particular a motor vehicle, comprising a control element ( 8th ) for detecting and / or releasing the parking brake ( 12 . 13 ), an actuator ( 19 . 25 ) for adjusting the parking brake ( 12 . 13 ) acting braking force (F _Br ) and a control unit ( 7 ), which is the actuator ( 19 . 25 ) on request, characterized in that a device ( 7 . 26 . 31 ) for determining the parking brake ( 12 . 13 ) acting braking force (F _Br ) is provided, and the control unit ( 7 ) is arranged such that the actuator ( 19 . 25 ) in response to the determined braking force (F _Br ) is controlled to the parking brake ( 12 . 13 ) to lock or release. Parking brake system according to claim 1, characterized in that the device ( 7 . 26 . 31 ) for determining the braking force (F _Br ) as a force sensor ( 26 ) is realized. Parking brake system according to claim 1 or 2, characterized in that the device ( 7 . 26 . 31 ) for determining the braking force (F _Br ) is realized as a brake force switch. Parking brake system according to claim 1, characterized in that the device ( 7 . 26 . 31 ) for determining the braking force (F _Br ) as a mathematical model ( 31 . 32 ) realized in a control unit ( 7 ), the mathematical model ( 31 . 32 ) taking into account a brake pressure (p _Br ) on the parking brake ( 12 . 13 ) acting braking force (F _Br ) determined. Parking brake system according to claim 4, characterized in that a sensor ( 27 ) for measuring the parking brake ( 12 . 13 ) acting brake pressure (p _Br ) is provided. Parking brake system according to claim 4, characterized in that a mathematical model ( 32 ) is provided for estimating the brake pressure (p _Br ), wherein the mathematical model ( 32 ) the brake pressure (p _Br ) by evaluating the follow-up behavior of the actuator ( 19 . 25 ), taking into account a pre-pressure (p _pre ), which prevails before the start-up of the actuator ( 19 . 25 ) prevails in the brake system. Method for actuating a parking brake system for vehicles, in particular motor vehicles, having a control element ( 8th ) for detecting and / or releasing the parking brake ( 12 . 13 ), an actuator ( 19 . 25 ) for varying the brake pressure (p _Br ) and a control unit ( 7 ), which is the actuator ( 19 . 25 ) on request, characterized in that the on the parking brake ( 12 . 13 ) acting braking force (F _Br ) by means of a device ( 7 . 26 . 31 ) and the actuator ( 19 . 25 ) taking into account the determined braking force (F _Br ) from the control unit ( 7 ) is driven to the Parking brake ( 12 . 13 ) to lock or release. A method according to claim 7, characterized in that the on the parking brake ( 12 . 13 ) acting braking force (F _Br ) by means of a force sensor ( 26 ) is measured. A method according to claim 7 or 8, characterized in that the on the parking brake ( 12 . 13 ) acting braking force (F _Br ) by means of a mathematical model ( 31 ), wherein the mathematical model of the parking brake ( 12 . 13 ) Brake pressure (p _Br) acting taken into account to estimate the braking force (F _Br). A method according to claim 9, characterized in that the brake pressure (p _Br ) by means of a pressure sensor ( 27 ) is measured. Method according to Claim 9, characterized in that the brake pressure (p _Br ) is determined by means of a mathematical model ( 32 ), the one the follow-up behavior of the pump ( 19 ) evaluates the characteristic quantity (K) in order to estimate the brake pressure (p _Br ). A method according to claim 7 or 8, characterized in that the on the parking brake ( 12 . 13 ) acting braking force (F _Br ) by means of a brake force switch ( 26 ), and the actuator ( 19 . 25 ) after exceeding a switching threshold (SW) of the brake force switch ( 26 ), with a predetermined additional pressure (Δp) is applied.