WO2011032754A1

WO2011032754A1 - Method for actuating a parking brake system in a vehicle

Info

Publication number: WO2011032754A1
Application number: PCT/EP2010/060561
Authority: WO
Inventors: Karsten Bieltz; Simon Hauber
Original assignee: Robert Bosch Gmbh
Priority date: 2009-09-17
Filing date: 2010-07-21
Publication date: 2011-03-24
Also published as: DE102009029525A1

Abstract

The invention relates to a method for actuating a parking brake system in a vehicle, comprising an electrically actuatable brake actuator and a hydraulic actuator, which can be controlled independently from each other. Initially, the required braking force is determined and then compared to the braking force which can be obtained by means of the electrically actuatable brake actuator, said hydraulic actuator only being actuated in a complimentary manner when the required braking force exceeds the braking force which can be obtained by the electric actuator.

Description

Description title

Method for actuating a parking brake system in a vehicle

The invention relates to a method for actuating a parking brake system in a vehicle.

State of the art

DE 10 2004 006 338 A1 describes a parking brake system in a vehicle which, as a brake actuator, comprises a hydraulic actuator with a pump for generating the desired brake pressure. For optimum actuation, a device is provided for determining the braking force acting on the parking brake, wherein the hydraulic actuator is actuated by actuating signals of a control device taking into account the determined braking force. In this way, a required minimum braking force can be set accurately, whereby the burden of the components involved is reduced.

Disclosure of the invention

The invention has for its object to provide a sufficiently high parking brake force in a parking brake system with minimized component load.

This object is achieved with the features of claim 1. The dependent claims indicate expedient developments.

The inventive method relates to an actuation of a parking brake system in a vehicle, wherein the parking brake system on the one hand an electrically actuated brake actuator and on the other

Hydraulic actuator and both via the electric brake actuator as Also, a braking force for setting the vehicle can be generated in each case via the hydraulic actuator. The electric brake actuator and the hydraulic actuator are basically independently controllable to generate a mechanical or hydraulic braking force, so that the respective proportions of mechanical and hydraulic braking force, which go back to the electric or hydraulic actuator, depending on the current situation can be set variably.

In the method according to the invention, the currently required braking force is preferred or set primarily via the electrically actuatable brake actuator.

The hydraulic actuator is operated in addition only in the event that the required braking force can not be applied by the operation of the electric brake actuator alone. To carry out the method, the currently required braking force is initially determined, which depends on ambient conditions, in particular on the gradient of the roadway on which the vehicle is currently located. In a following step, the currently required braking force is compared with the mechanical braking force, which can be maximally achieved with the electrically actuatable brake actuator. If this comparison shows that the maximum achievable mechanical braking force is less than the currently required braking force, so that alone the required braking force can not be provided by an operation of the electric brake actuator, the hydraulic actuator is additionally actuated to the remaining braking force, which the difference of currently required braking force and maximum possible mechanical braking force corresponds to provide as hydraulic braking force.

This approach has several advantages. Since the hydraulic braking force buildup is generated only supportive of the mechanical braking force, sufficient in a variety of cases, the control of the electrical alone

Brake actuator and to be provided via the electric brake actuator braking force. The connection of the hydraulic brake actuator takes place only in a smaller number of cases in which the mechanical braking force of the e lectric brake actuator is insufficient. In addition, only the differential braking force has to be generated via the hydraulic brake actuator, so that the It must also produce only a relatively small hydraulic brake pressure.

Due to the reduced activity of the hydraulic brake actuator has a longer life. Furthermore, via an actuation of the electric

Bremsaktuators faster braking force build-up possible, also the braking force can be adjusted with higher accuracy.

Another advantage is the lower noise level in an exclusive operation of the electric brake actuator compared to a

Actuation of the hydraulic brake actuator, resulting in higher customer acceptance.

As an electric brake actuator are all electrically adjustable actuators or actuators into consideration, in particular electric motors, but also electromagnetic actuators and other actuators that perform a mechanical adjusting movement when creating an e- lectric voltage that can be used to generate a braking force. According to an advantageous embodiment, it is provided that the currently achievable mechanical braking force, which is adjustable via the electrically actuatable brake actuator, is determined as a function of the maximum available current in the power supply of the electric brake actuator. This approach has the advantage that restrictions both in terms of the maximum available voltage and in terms of maximum

Current supply of other components of the parking brake can be considered. The maximum available current is in this case calculated, in particular, on the one hand from the ratio of battery voltage to ohmic resistance of the electric brake actuator, preferably including the supply lines. On the other hand, a component protection of various components in the parking brake system can be taken into account, which allows only an energization up to a maximum in order to avoid damage to the respective component, for example a relay. The maximum current available for the energization of the electric brake actuator is calculated from the minimum of the two aforementioned current values. In this way, both the

Limit over the maximum available, from the battery stam- Tension as well as the component protection are taken into account.

The maximum available current flows into the calculation of the achievable mechanical braking force of the electric brake actuator. By comparing the achievable mechanical braking force with the actually required braking force, the decision can be made whether the operation of the electrical brake actuator is sufficient or whether, in addition, the hydraulic actuator must be actuated.

It may be expedient to additionally take into account a lower gradient threshold value and possibly also an upper gradient threshold for the road gradient and to actuate the electrical or additionally the hydraulic actuator as a function of the gradient threshold values. For example, in the event that the actual slope value is below the lower slope threshold, only the electric brake actuator is actuated. On the other hand, if the actual slope is above the lower slope threshold, then a query is made as to whether the achievable mechanical braking force is less than that required to hold the vehicle at an upper, overlying gradient threshold. If so, the hydraulic actuator is additionally actuated; otherwise, the mechanical braking force will be at a level corresponding to holding the vehicle at the upper grade threshold so that the supplemental actuation of the hydraulic actuator may be dispensed with.

The inventive method runs in a control or control unit in the vehicle, which is part of the parking brake system.

Further advantages and expedient embodiments can be taken from the further claims, the description of the figures and the drawings. Show it:

1 shows a section through a braking device in a vehicle, with an electric motor for acting on a brake piston, which is additionally acted upon by hydraulic pressure, 2 is a schematic diagram of a brake system in a vehicle, each having a braking device on each wheel, wherein the brake devices are actuated on the rear wheels both by electric motor and by hydraulic pressure,

3 is a flowchart for actuating a parking brake system in a vehicle,

4 shows a further flowchart for actuating a parking brake system in a variant embodiment.

Fig. 1 shows a wheel brake 1 with a caliper 2, a brake piston 3 and an electric brake actuator 4, which acts on the brake piston 3 and adjusted in the direction of a pair of pliers 8 of the caliper 2. When braking, the free end face 9 presses with a braking force on a brake disc, which is overlapped by the caliper 2.

The brake piston 3 is adjusted axially by means of an electric brake actuator 4, which is designed in particular as an electric motor and an intermediate gear drives a spindle 5, the rotational movement is converted via a transmission element 6 in an axial adjusting movement, which adjusts the brake piston 3 in the braking position. The transmission element 6, which is provided with an internal thread and is seated on the external thread of the spindle 5, is located in the interior of the hollow cylindrical brake piston 3 and is connected to the brake piston 3.

Additionally or alternatively to the loading of the brake piston 3 via the electric brake actuator 4, the brake piston can also be acted upon by a hydraulic brake pressure in the braking position, wherein the hydraulic brake pressure at the electric brake actuator 4 facing end face 7 of the brake piston 3 acts.

In Fig. 2, a brake system 10 is shown in a vehicle with wheel brake 1 at the wheels of the rear axle and wheel brake 1 1 at the wheels of the front axle. To set the vehicle at a standstill, the brake system 1 can be used as a parking brake system. The bike Braking devices 1 on the rear axle are designed as described in FIG. 1 and each have a designed as an electric motor electric brake actuator 4, which acts on the respective brake piston. In addition, the wheel brake devices 1 1 at the rear axle via a Hydraulikak- tuator 12, which includes a hydraulic pump, and hydraulic lines 13 and 14 to apply hydraulic brake pressure.

The wheel brake devices 11 on the front axle of the vehicle can only be actuated via the hydraulic actuator 12 and hydraulic lines 15 and 16 with hydraulic brake pressure. The front wheel brake 1 1 have no electric brake actuator.

To control the wheel brake 1 and 1 1 at the rear or front of the vehicle, a control or control device 17 is provided, via which the hydraulic actuator 12 with control signals to build a desired

Brake pressure is controlled. The control unit 17 may be part of an electronic stability program (ESP).

The wheel brake 1 on the rear axle of the vehicle are also set on the electric brake actuators 4, which are acted upon by control signals of another control or control device 18, which is expediently part of the parking brake system. The control or control devices 17 and 18 communicate with each other, they may optionally also be combined to form a common control or control device.

The parking brake system is actuated manually by the driver via a switch 19, which supplies a corresponding control signal to the control or control device 18 for actuating the electric brake actuators 4 or to the control or control device 17 for actuating the hydraulic brake actuator 12. With the switching on of the parking brake system, a display unit 20 is actuated, which is designed, for example, as an optical display unit and via which the driver is informed about the activation of the parking brake system.

To power the electric brake actuators 4 in the wheel brake 1 on the rear axle, a battery 21 is provided. As can be seen from the flow chart of FIG. 3, in a first method step 30, it is first determined whether a parking request has been made by the driver. If this is the case, in the next method step 31, first of all, the required clamping force, with which the wheel brake devices have to be acted upon, on the basis of the current gradient of the roadway on which the vehicle is located, is determined, so that the vehicle is safely stopped.

In order to determine whether the currently required braking force F _br , _a ct can be provided exclusively via the electric brake actuator or whether the hydraulic actuator must additionally be actuated, the achievable mechanical braking force F _br , _e is first determined, which is a maximum below the current circumstances can be adjusted via the electrically actuated brake actuator. For this purpose, in the next method step 32 first engine parameters of the brake actuator designed as an electric brake motor are ascertained, in particular the motor constant k _eng , the motor resistance including the resistance of the supply lines R _mot and the no-load current or the idling torque M _R0 . These parameters are determined in method step 32.

In the next method step 33, the clamping force which can be achieved via the electric brake actuator is determined under existing conditions. The achievable

Braking force F _br , _e, which can be adjusted via the electric brake actuator, is calculated from the formula Ή ~ ^ Ro)

r determined. Here, r _{res is} the resulting radius of the electric brake actuator, Hmech is the mechanical efficiency of the electric brake actuator, k _{eng is} the engine constant, and M _{R0 is} the idle torque.

The achievable mechanical braking force F _br , _e is determined according to the aforementioned relationship from the maximum available current l _max , according to

from the minimum of the maximum permissible current load l _max , dev of the components in the parking brake system and the ratio of the battery voltage U _ba t and resistance R _mo t of the electric brake actuator is determined, via the resistor R _mo t additionally the resistance of the leads can be considered. About the maximum allowable current load l _max , dev component protection of existing in the parking brake system electronic components is achieved, for example, relays that may be acted upon only with a specific, component-specific maximum current. To ensure that this maximum current is not exceeded, the electric brake actuator is applied in the parking brake system with the limited in the aforementioned manner maximum current Lax.

After the achievable mechanical braking force F _{br, e has been determined} in method step 33, in the following method step 34 it is queried whether the achievable clamping force F _{br, e} for the current gradient level of the roadway is sufficient for setting the vehicle, which is based on a comparison of achievable Clamping force F _{br, e is performed} with the current required braking force F _{br act} . If the achievable mechanical braking force F _{br e is} sufficient, the Y-branching ("Y") is continued following the next method step 35, in which the electric brake actuator is subjected to the adjustment of the mechanical braking force A hydraulic braking force actuation is omitted in this case.

If the query in method step 34 shows that no sufficiently high braking force can be set solely by actuating the electric brake actuator, the no-branching ("N") is proceeded to method step 36, in which both the electric brake actuator and the hydraulic actuator This is preferably done in such a way that the maximum achievable mechanical braking force F _{br e applied} via the electric brake actuator and the hydraulic brake pressure is adjusted in addition to reach the currently required braking force.

FIG. 4 shows a variant embodiment in the control of the electrically actuatable brake actuator and of the hydraulic actuator in the event of immobilization of the vehicle at standstill. First, in method step 40, It is correct whether there is a parking request by the driver. If this is the case, a query is made in the next method step 41 as to whether the current roadway gradient exceeds a lower gradient threshold value, for example a gradient threshold value of 20%. If this is not the case, the no branch is followed, proceeding to method step 42, in which the parking brake force is set exclusively via the electric brake actuator, at a fixed braking force level which corresponds to the lower gradient threshold value. If the current roadway slope exceeds the lower gradient threshold, for example, 20%, the Yes branch is continued following the process step 43, in which motor parameters of the electric

Bremsaktuators are determined, in particular the motor constant, the motor resistance and the idling current and derived variables. In the method step 44, the mechanical braking force F _{br, e} achievable under the current conditions via the actuation of the electric brake actuator is determined analogously to the procedure described in FIG. In method step 45, another query is made as to whether the achievable mechanical braking force _{Fbr, e is} sufficient for a gradient level which corresponds to an upper gradient threshold value, for example a gradient threshold value of 30%. Is this the

If so, following the yes branch, proceed to step 46 and set a brake force corresponding to a 30% power level via the electric brake actuator, that is, sufficient to set the vehicle on a 30% grade roadway. An additional actuation of the hydraulic actuator can be dispensed with.

If the query in method step 45 shows that the currently achievable clamping force F _{br, e of} the electric brake actuator is not sufficient for a gradient level of 30%, the no-branching is proceeded to method step 47, in which both the electric brake actuator and the

Hydraulic actuator to be controlled. About the electric brake actuator, the maximum achievable braking force F _{br, e is} set, the difference up to the 30% -Bremskraftniveau is set in addition to the hydraulic actuator.

Claims

claims

1 . Method for actuating a parking brake system in a vehicle, wherein the parking brake system has an electrically operable Bremsaktua- tor (4) and a Hydraulikaktuator (12) independently for generating a mechanical or hydraulic braking force (Fbr, e, Fbr, h) controllable are, before the activation of the actuators (4, 12) first determines the currently required braking force (F _br , _a ct) and with the over the electrically actuated brake actuator (4) achievable mechanical braking force (F _{br, e} ) is compared and the Hydraulic actuator (12) is operated in addition only in the event that the required braking force (F _br , _a ct) exceeds the achievable mechanical braking force (F _{br, e} ).

2. The method according to claim 1, characterized in that the currently neces sary braking force (F _br , _a ct) is determined from the slope of the road.

3. The method according to claim 1 or 2, characterized in that the currently achievable mechanical braking force (F _{br e} ), which is adjustable via the electrically operable brake actuator (4), as a function of the maximum available current (l _max ) is determined ,

4. The method according to claim 3, characterized in that the achievable mechanical braking force (F _{br e} ) from the context

r

is determined, where

r _res the resulting radius of the electric brake actuator (4) Hmech the mechanical efficiency of the electric brake actuator (4)

k _closely the motor constant

MRO the idling torque designated.

5. The method according to claim 3 or 4, characterized in that the maximum available current (l _max ) from the rated current (l _ne nn) as a function of battery voltage (U _ba t) and resistance (R _mo t) of the electric brake actuator (4) is determined.

6. The method according to any one of claims 3 to 5, characterized in that the maximum available current (l _max ) from the maximum allowable current load (l _ma x, dev) of the components is determined in the parking brake system.

7. The method according to claim 5 and 6, characterized in that the maximum available current (l _max ) from the minimum of rated current (Lenn) and maximum allowable current load (l _ma x, dev) is determined.

8. The method according to any one of claims 1 to 7, characterized in that falls below a lower gradient threshold only the electric brake actuator (4) is actuated.

9. The method according to any one of claims 1 to 8, characterized in that in the event that the achievable mechanical braking force (F _{br, e} ) is smaller than required for holding the vehicle at an upper gradient threshold, the hydraulic actuator (12) is additionally operated.

10. regulating or control device (17, 18) for carrying out the method according to one of claims 1 to 9.

1 1. Parking brake system in a vehicle having a control unit (17, 18) according to claim 10.