DE102011078900B4 - Method for adjusting a parking brake in a vehicle - Google Patents

Abstract

In a method for adjusting a parking brake comprising an electromechanical braking device with an electric brake motor for generating a clamping force, the motor constant of the brake motor is determined as a function of the motor resistance and from measured current values to determine the clamping force.

Description

The invention relates to a method for adjusting a parking brake in a vehicle according to the preamble of claim 1.

State of the art

In the EN 10 2006 052 810 A1 A method is described for estimating the clamping force generated by an electric brake motor in a parking brake of a motor vehicle. The electric brake motor acts on a brake piston, which is the carrier of a brake pad, axially in the direction of a brake disc. To determine the clamping force, the current, the supply voltage of the brake motor and the motor speed are measured, then the clamping force is estimated taking into account the measured variables from a differential equation system that describes the electrical and mechanical behavior of the electric motor. A Hall sensor, for example, can be used to measure the motor speed, which is used to determine the motor constant required to determine the clamping force.

From the Scripture EN 10 2009 001 258 A1 A method is known for monitoring the thermal load of an electric motor that can be used in a parking or handbrake. To record the thermal load, at least the voltage, the current and, if applicable, the motor speed are measured.

Disclosure of the invention

The invention is based on the object of determining a motor characteristic in an electric brake motor of an electromechanical braking device using simple measures without using a speed sensor, wherein the electromechanical clamping force depends on the motor characteristic.

This object is achieved according to the invention with the features of claim 1. The subclaims specify expedient further developments.

The method according to the invention can be used in electromechanical parking brakes in vehicles which have an electric brake motor, via which a clamping force can be generated to immobilize the vehicle. In this case, the rotational movement of the rotor of the electric brake motor is transferred into an axial actuating movement of a spindle, via which a brake piston, which is the carrier of a brake pad, is subjected to axial force against a brake disk.

If necessary, the parking brake is equipped with an additional braking device in order to be able to provide an additional clamping force in addition to the electromechanical clamping force if required. For example, the additional braking device is the vehicle's hydraulic brake, the hydraulic pressure of which acts on the brake piston.

In the method according to the invention, the motor constant of the electric brake motor, which is required to determine the current braking force, is determined as a function of the motor resistance and from measured current values. If the motor constant is known, the value of which is temperature-dependent and can fluctuate relatively strongly within a motor series, the motor load torque can be calculated using the current motor current and from this the clamping force can be calculated using a gear reduction and an efficiency. This makes it possible to determine the currently effective clamping force even without a speed sensor. The only measured variables that need to be determined are the current and the voltage in the electric brake motor.

The motor constant depends on the motor resistance, which, according to an advantageous embodiment, is determined from the ratio of an applied operating voltage to a maximum current that prevails when the motor is at a standstill. The maximum current when the motor is at a standstill is in turn determined as a function of measured first and second current values, with an idle current also being taken into account. It is advantageous here that the time of the second current measurement value is twice as high as the time of the first current measurement value, with the times of the current measurements relating to the start of the current flow. Doubling the time period between the first current measurement point and the second current measurement point for determining the maximum current when the motor is at a standstill has the advantage that a relatively simple relationship is provided for determining the maximum current. In principle, however, measurement times for the current can also be selected which, in relation to the start of the current flow, have a ratio other than a factor of 2.

The motor constant is determined as a function of the motor resistance, whereby the moment of inertia of the rotor or armature of the brake motor, the no-load current, the already determined first current measurement value and an additional, third current measurement value are also taken into account. The third current measurement value is taken at a point in time that follows the point in time of the first current measurement value within a fixed period of time. This fixed period of time is expediently less than the electrical time constant of the brake motor and is in particular shortly after the first measurement time. If necessary, the measurement time for the third current measurement value is before the measurement time of the second current measurement value, which is required to determine the maximum current when the motor is at a standstill in order to calculate the motor resistance.

The method according to the invention runs in a control unit in the vehicle, which is expediently part of the parking brake system.

• 1 einen Schnitt durch eine elektromechanische Feststellbremse für ein Fahrzeug, bei der die Klemmkraft über einen elektrischen Bremsmotor erzeugt wird,
• 2 ein Schaubild mit dem zeitabhängigen Verlauf des Stroms, der Spannung und der Motordrehzahl beim Zuspannvorgang der Feststellbremse.

Further advantages and practical embodiments can be found in the further claims, the description of the figures and the drawings. They show:

• 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 showing the time-dependent course of the current, the voltage and the motor speed during the application process of the parking brake.

In 1 an electromechanical parking brake 1 is shown for immobilizing a vehicle when stationary. The parking brake 1 comprises a brake calliper 2 with a caliper 9 which engages over a brake disk 10. The parking brake 1 has an electric motor as a brake motor 3 as an actuator, which drives a spindle 4 in rotation, on which a spindle component 5 designed as a spindle nut is rotatably mounted. When the spindle 4 rotates, the spindle component 5 is adjusted axially. The spindle component 5 moves within a brake piston 6, which is the carrier of a brake pad 7, which is pressed against the brake disk 10 by the brake piston 6. On the opposite side of the brake disk 10 there is another brake pad 8, which is held stationary on the caliper 9.

Within the brake piston 6, the spindle component 5 can move axially forwards in the direction of the brake disc 10 when the spindle 4 rotates, or axially backwards when the spindle 4 rotates in the opposite direction until it reaches a stop 11. To generate a clamping force, the spindle component 5 acts on the inner end face of the brake piston 6, whereby the brake piston 6, which is mounted axially displaceably in the parking brake 1, is pressed with the brake pad 7 against the facing end face of the brake disc 10.

If necessary, the parking brake can be supported by a hydraulic vehicle brake, so that the clamping force is made up of an electromotor component and a hydraulic component. With hydraulic support, the rear side of the brake piston 6 facing the brake motor is pressurized with hydraulic fluid.

In 2 is a diagram showing the current I, the voltage U and the speed n of the electric brake motor as a function of time for a brake application process. Furthermore, 2 the electromechanical clamping force F _KI generated by the electric brake motor and the distance s covered by the brake motor or an actuator actuated by the brake motor during the application process are entered.

The application process begins at time t1 by applying an electrical voltage and energizing the brake motor with a closed circuit. The start phase (phase I) lasts from time t1 to time t2. At time t2, the voltage U and the motor speed n have reached their maximum. The phase between t2 and t3 represents the idling phase (phase II), in which the current I is at a minimum level. This is followed from time t3 by the force build-up phase (phase III) up to time t4, in which the brake pads rest on the brake disc and are pressed against the brake disc with increasing clamping force F _KI . At time t4, the electric brake motor is switched off by opening the circuit, so that the speed n of the brake motor then drops to zero.

The force increase point coincides with the force build-up phase at time t3. The force build-up or the progression of the clamping force F _KI can be determined, for example, using the progression of the current I of the brake motor, which basically has the same progression as the electromechanical clamping force. Starting from the low level during the idle phase between t2 and t3, the current progression rises steeply at the beginning of time t3. This increase in current can be detected and used to determine the force increase point. In principle, the progression of the force build-up can also be determined from the voltage or speed progression or from any combination of the current, voltage and speed signals.

To determine the clamping force F _KI without using a speed sensor, the motor constant K _M and the motor resistance R _M are required as motor parameters, which are determined from the voltage and current curve of the electrical The current rises sharply when the brake motor is switched on, only slowed down by the armature inductance, and then falls again significantly more slowly due to the onset of rotation. In the falling branch, the current curve is essentially determined by the mechanical time constant of the motor, which is influenced by the mass inertia of the armature J, the motor constant K _M and the motor resistance R _M.

berechnet, wobei I₁, I₂ die zu den Zeitpunkten t_1,m bzw. t_2,m gemessenen Stromwerte bezeichnen.To determine the motor resistance R _{M ,} current values of the brake motor are measured at a standstill - with the armature blocked - at a time when the current has at least approximately reached its steady state. To do this, the current is measured in the falling branch after the inrush current peak has been exceeded at two times t _1,m and t _2,m and from this the theoretical maximum current I _max is calculated that would flow when the brake motor was at a standstill. Taking into account the no-load current I _L , which is determined in the phase after the inrush current surge, in which the speed is constant and the no-load current is only determined by the load or the friction of the motor, the maximum current I _max is determined according to the relationship $$I_{\text{Max}}=\frac{{\left(I_1-I_L\right)}^2}{{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="DE102011078900B4\_0007.png"\; state="\{\{state\}\}">I</figure-callout>}}_2-I_L}+I_L$$

where I ₁ , I ₂ denote the current values measured at times t _1,m and t _2,m respectively.

The times t _1,m and t _2,m refer to the beginning of the current flow. The time t ₂ is twice as far after the beginning of the current flow as the time t _1,m .

der Motorwiderstand R_M aus dem Verhältnis der Motor- bzw. Betriebsspannung U_B und dem theoretischen Maximalstrom I_max berechnet werden.Taking into account the additionally measured motor or operating voltage U _B, $$R_M=\frac{U_B}{I_{\text{Max}}}$$

the motor resistance R _M can be calculated from the ratio of the motor or operating voltage U _B and the theoretical maximum current I _max .

wobei für die Motorkonstante K_M neben dem Motorwiderstand R_M zusätzlich das Massenträgheitsmoment J des Ankers des Bremsmotors berücksichtigt wird.After determining the motor resistance R _{M ,} the motor constant K _M can be determined taking into account the measured value I ₁ at the measuring time t _1,M and a further, third current measured value I ₃ at the measuring time t _3,M : $$K_M=\sqrt{\frac{R_M\cdot J}{\Delta t}\cdot \frac{I_1-I_3}{I_1-I_L}},$$

where for the motor constant K _M in addition to the motor resistance R _M the mass moment of inertia J of the armature of the brake motor is taken into account.

The measurement time t _3,m is offset by the time period Δt after the first measurement time t _1,m . The time period Δt is expediently small, in particular it is smaller than the electrical time constant τ of the brake motor. If necessary, the measurement time t _3,M is before the measurement time t _2,M , at which the second current measurement value is determined, which is required to determine the theoretical maximum current when the motor is at a standstill. In principle, the time period Δt can also be so large that the measurement time t _3,M is after the measurement time t _2,M .

Using the method described above, the motor constant can be determined before each application of the electromechanical parking brake. A speed sensor is not required. This means that the value of the motor constant K _M , which varies greatly depending on production and the age of the brake motor and the temperature, is determined with sufficient accuracy. Taking the motor constant K _M into account, the currently effective motor load torque in the electric brake motor can be determined if the currently effective current is known. The clamping force F _KI can be determined from the motor load torque.

Claims (7)

Method for adjusting a parking brake (1) which comprises an electromechanical braking device with an electric brake motor (3) for generating an electromechanical clamping force (F _KI ), wherein, in order to determine the clamping force (F _KI ), the motor constant (K _M ) of the electric brake motor (3) is determined as a function of the motor resistance (R _M ) and from measured current values (I ₁ , I ₂ , I ₃ ), and wherein the motor resistance (R _M ) is determined from the ratio of the applied operating voltage (U _B ) and a maximum current (I _max ) when the motor is at a standstill: $$R_M=\frac{U_B}{I_{\text{Max}}},$$

and wherein the maximum current (I _max ) at engine standstill is determined as a function of measured current values (I ₁ , I ₂ ), characterized in that the maximum current (I _max ) at engine standstill is determined from the relationship $$I_{\text{Max}}=\frac{{\left(I_1-I_L\right)}^2}{I_2-I_L}+I_L$$

is determined, where I _L denotes the no-load current I ₁ , I ₂ measured current values at times t _1,m and t _2,1 respectively. Procedure according to Claim 1 , characterized in that the times t _1,m or t _2,1 refer to the beginning of the current flow and the time t _2,m is twice as far after the beginning of the current flow as the time t _1,m . Method according to one of the Claims 1 or 2 , characterized in that the motor constant (K _M ) is determined from the relationship $$K_M=\sqrt{\frac{R_M\cdot J}{\Delta t}\cdot \frac{I_1-I_3}{I_1-I_L}}$$

is determined, where J is the mass moment of inertia of the armature of the brake motor, I ₃ is a measured current value at time t _3,m = t _1,m + Δt, Δt is a time period following t _1,m . Procedure according to Claim 3 , characterized in that the time period Δt is smaller than the electrical time constant (τ) of the brake motor. Procedure according to Claim 3 or 4 , characterized in that the time t _3,m is before the time t _2,m . Control device for carrying out the method according to one of the Claims 1 until 5 . Parking brake in a vehicle with a control unit according to Claim 6 .

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