DE102011004772A1 - Method for adjustment of clamping force exercised by parking brake in vehicle, involves generating clamping force until mechanical clamping force of brake disk reaches threshold level that is determined as function of road gradient - Google Patents

Abstract

The method involves determining mechanical clamping force produced by a brake disk (10) by considering current and voltage of an electric brake motor (3) of the brake disk. Process for generating clamping force is performed until the mechanical clamping force of the brake disk reaches a threshold level, where the threshold level is determined as a function of road gradient. The clamping force is produced by an additional brake device such as hydraulic vehicle brake.

Description

The invention relates to a method for adjusting the force exerted by a parking brake clamping force in a vehicle.

State of the art

Are known parking or parking brakes in vehicles that are used to produce a stoppage the vehicle festsetzende clamping force. The DE 103 61 042 B3 discloses to use an electromotive parking brake with an electric brake motor as an actuator, upon actuation of a brake piston, the carrier of a brake pad, is axially adjusted in the direction of a brake disc. It must be ensured that a required nominal clamping force level is achieved.

Disclosure of the invention

The invention has for its object to set with simple measures, the required clamping force in a parking brake of a vehicle with sufficient accuracy.

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

The inventive method relates to an electromechanical parking brake in a vehicle with an electromechanical actuator, via which a stoppable the vehicle is generated clamping force, wherein the actuator comprises an electric brake motor, a gear and a spindle which axially displaces a brake piston, the Carrier of a brake pad is, which is pressed against a brake disc. The rotational movement of the brake motor is thereby transmitted in an axial adjusting movement of the brake piston,

To set a required nominal or clamping force clamping force generated by the electromechanical actuator during the application process, which represents the mechanical work, determined and compared with an associated threshold. When the clamping work of the actuator reaches the threshold value, the actually generated clamping force has reached the desired clamping force level, so that the clamping operation is completed; the electric brake motor can be switched off and the achieved clamping force level can be preserved.

This procedure has the advantage that the achievement of the nominal clamping force level is ascertained on the basis of the electrical work absorbed by the brake motor. Electrical parameters are used to determine the electrical work, in particular the current and the voltage of the electric brake motor, which are preferably determined directly or indirectly by sensors and present as measured values. From a known per se, the offset mechanical work of the electromechanical actuator can be determined by multiplying the current and voltage and integral formation over the considered period as well as further taking into account an overall efficiency. This takes place continuously during the application process of the parking brake, so that permanently the information about the currently deposited mechanical work of the actuator (MoC) is present and can be compared with the associated threshold value. When the threshold is reached, the desired clamping force is set.

The advantage here is that no position information about the current position of the adjustable part of the electric brake motor or the adjustable brake piston is required to set the desired clamping force. It can thus be dispensed with additional sensors for determining the position of the brake piston. Usually speed sensors are used in the prior art, from the signal can be closed to the current brake piston position. Even with a torque-based adjustment of the clamping force, a speed signal is needed in the prior art to determine the motor constant, which is used together with the current for calculating the engine torque. In the energy-based application process according to the invention, however, the engine torque for adjusting the clamping force is not necessarily required, so that no speed signal is required.

In the energy-based clamping force estimation according to the invention, it is assumed that the brake caliper of the brake device can receive and store potential energy in the manner of a spring. Upon actuation of the electric brake motor during the application process of the parking brake, the electrical energy absorbed by the brake motor is converted into potential energy of the brake caliper, minus a heat loss, which is described by the efficiency. The efficiency can be determined empirically and is determined by mechanical and electrical components. The efficiency is either as a fixed, constant, brake-specific size or is determined as a function of state or characteristics of the parking brake, for example as a function of temperature.

According to an advantageous embodiment, the electrical energy absorbed by the brake motor is taken into account from the time of the force increase of the clamping force. During the application process, the electric brake motor first passes through an idling phase until the brake piston or the brake disc, which are adjusted by the brake motor, comes into abutment against the brake disc and the force increase of the clamping force begins. From this point in time, which can be detected, for example, on the basis of the course of the current, the electrical work delivered by the brake motor is expediently taken into account.

The currently performed mechanical work of the actuator (MoC = engine to caliper) is continuously compared with the associated threshold, the clamping process or clamping force increase is terminated when the threshold is reached. The threshold value can either be specified as a fixed, constant variable or, according to an advantageous embodiment, be set as a function of state or characteristic variables of the brake system and / or ambient conditions, in particular as a function of the inclination of the road on which the vehicle is standing.

According to a further expedient embodiment, the parking brake is provided with an additional brake device, in order to be able to provide, in addition to the electromechanical clamping force of the actuator (MoC), a clamping force component which is generated via the additional brake device. The auxiliary brake device is, in particular, the hydraulic vehicle brake of the vehicle whose hydraulic pressure has a supporting effect on the brake piston.

The inventive method runs in a control or control unit in the vehicle, which is in particular 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 a section through an electromechanical parking brake for a vehicle, in which the clamping force is generated by an electric brake motor,

2 a diagram with the time-dependent course of the current, the voltage and the engine speed during the application process of the parking brake,

3 a flowchart with the process steps for energy-based adjustment of the clamping force.

In 1 is an electromechanical parking brake 1 for setting a vehicle at a standstill. The parking brake 1 includes a caliper 2 with a pair of pliers 9 , which is a brake disc 10 overlaps. As an actuator, the parking brake points 1 an electric motor as a brake motor 3 on, a spindle 4 rotatably drives, on which a spindle component 5 is rotatably mounted. With a rotation of the spindle 4 becomes the spindle component 5 axially adjusted. The spindle component 5 moves inside a brake piston 6 , the wearer of a brake pad 7 is which of the brake piston 6 against the brake disc 10 is pressed. On the opposite side of the brake disc 10 there is another brake pad 8th , which is fixed to the pliers 9 is held.

Inside the brake piston 6 can the spindle component 5 during a rotary movement of the spindle 4 axially forward in the direction of the brake disc 10 at or at an opposite rotational movement of the spindle 4 axially to the rear until reaching a stop 11 move. To generate a clamping force, the spindle component acts 5 the inner end of the brake piston 6 , causing the axially displaceable in the parking brake 1 mounted brake pistons 6 with the brake pad 7 against the facing end face of the brake disc 10 is pressed.

If necessary, the parking brake can be assisted by a hydraulic vehicle brake, so that the clamping force is composed of an electromechanical component and a hydraulic component. When hydraulic support is the brake motor facing the rear of the brake piston 6 subjected to pressurized hydraulic fluid.

In 2 is a graph showing the current waveform I, the voltage U and the speed curve n of the electric brake motor time-dependent for a Zuspannvorgang. At time t1, the application process begins by applying an electrical voltage and energizing the brake motor when the circuit is closed. At time t2, the voltage U and the engine speed n have reached their maximum. The phase between t2 and t3 represents the idle phase in which the current I moves to a minimum level. This is followed by the force build-up phase from the time t3 to the time t4, in which the brake pads bear against the brake disc and are pressed with increasing clamping force F against the brake disc. At the time t4, the switching off of the electric brake motor takes place by opening the electric circuit, so that in the further course the speed n of the brake motor drops to zero.

With the phase of the force build-up at time t3, the force rise point coincides. The force build-up or the course of the clamping force F can be determined, for example, based on the course of the current I of the brake motor, which basically has the same course as the electromechanical clamping force. Starting from the low level during the idle phase between t2 and t3, the current profile increases steeply at the beginning of time t3. This increase in current can be detected and used to determine the force rise point. In principle, however, the course of the force build-up can also be determined from the voltage or speed curve or from any combination of the signals current, voltage and rotational speed.

In 3 a flow chart is shown with the individual process steps for energy-based adjustment of the clamping force in the parking brake. In a first process step 20 First, the inclination of the road on which the vehicle is parked determined. From the slope value, an energy threshold E _lim can be determined, which is in the process step 22 the comparison with the mechanical work done by the actuator (MoC). The energy threshold E _lim is tilt-dependent, with increasing slope of the energy threshold E _lim increases.

In the following process step 21 the current I picked up by the electric brake motor or the voltage U is measured. These electrical parameters of the brake motor are the basis for the energy-based setting of the clamping force F _Kl . In the next step 22 a query is made as to whether the currently acting clamping force F _Kl , which is generated by the electric brake motor, is greater than zero. This can be detected on the basis of the current profile I by, as above 2 executed, the increase is determined at the beginning of time t3 in the course of the current. The beginning of the increase in the clamping force curve F _Kl represents the start time t _start for the energy consideration and the determination of the mechanical work done by the actuator (MoC). If in the method step 22 If it is determined that the clamping force increase has not yet been reached, the no-branch ("N") again becomes the method step 21 returned and measured at regular intervals again current and voltage in the brake motor and the query in the process step 22 go through whether there is a clamping force increase.

If a clamping force increase in the process step 22 is determined, following the Yes branch ("Y") to the next step 23 continued, in which the mechanical clamping work E _{Mot, Kl} , which is generated by the actuator (MoC), is checked for exceeding an associated energy threshold E _lim . The mechanical clamping work E _{Mot, Kl} is according to the relationship E _{Mot, kl} = ∫ (U · I · η _ges ) dt by integrating the product of current I and voltage U, the lower limit of the integral being determined by the start time t _start at which a clamping force increase has been detected. The upper limit of the integral coincides with the current time of comparison with the energy threshold E _lim .

In the determination of the mechanical clamping work also flows the entire efficiency η _{ges of} the electromechanical actuator with electric BremsmMotor, a transmission and a spindle, wherein on the efficiency η _ges heat losses in the brake motor and the mechanics (gear and spindle) can be considered. The efficiency η _ges represents either an empirically determined, constant variable or a dependent of parameters of the environment or the parking brake size, such as a temperature-dependent variable.

Returns the query in the process step 23 in that the mechanical clamping work E _{Mot, Kl} , which is performed by the actuator for generating the clamping force F _Kl , exceeds the associated energy threshold E _lim , becomes the method branch following the yes branch 24 continued and the application of the electric motor stopped. Otherwise, following the no-branching again becomes the beginning of the method step 21 returned and the entire process including the measurement of current and voltage through again.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10361042 B3 [0002]

Claims (10)

Method for adjusting the parking brake ( 1 ) exerted clamping force, which is at least partially generated by an electromotive braking device with an electromechanical actuator, characterized in that the mechanical clamping work generated by the actuator (E _{Mot, kl} ) determined and the application process for generating the clamping force (F _kl ) is performed so far, until the generated mechanical clamping work (E _{Mot, kl} ) reaches a threshold value (E _lim ). A method according to claim 1, characterized in that the mechanical clamping work (E _Mot ) taking into account current and voltage of an electric brake motor ( 3 ) of the actuator. A method according to claim 2, characterized in that current (I) and voltage (U) of the electric brake motor ( 3 ) are measured. A method according to claim 2 or 3, characterized in that the mechanical clamping work (E _{Mot, kl} ) taking into account current (I) and voltage (U) from the integral (E _{Mot, kl} ) = ∫ (U · I · η _ges ) dt is determined, where η _ges denotes the overall efficiency of the electromechanical actuator. Method according to one of claims 1 to 4, characterized in that the mechanical clamping work generated by the actuator (E _{Mot, kl} ) from the time of increase in force of the clamping force (F _kl ) is taken into account. Method according to one of claims 1 to 5, characterized in that the threshold value (E _lim ) is determined as a function of road gradient. Method according to one of claims 1 to 6, characterized in that the clamping force (F _kl ) is additionally generated by an additional brake device. A method according to claim 7, characterized in that a hydraulic vehicle brake is used as additional brake device. Control device for carrying out the method according to one of claims 1 to 8. Parking brake in a vehicle with a control or control device according to claim 9.

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