Method for adjusting the clamping force exerted by an electromechanical brake

1 . A method for adjusting a clamping force exerted by an electromechanical brake of a motor vehicle, the electromechanical brake comprising an electric motor provided with a rotating shaft which is intended to drive mechanical brake-application means, the electric motor being controlled by a PWM-type voltage control, comprising steps of:

estimating a motor resistance,

estimating a motor constant,

estimating a rotational speed of the electric motor from the estimate of the motor resistance and the estimate of the motor constant,

determining the clamping force from the estimate of the rotational speed of the electric motor,

adjusting the clamping force by applying the determined clamping force with the electromechanical brake,

wherein the estimate of the motor resistance is updated during an idle phase of the motor controller with no voltage control.

2 . The method according to claim 1 , in which the estimate of the motor resistance is updated using a polynomial function of order n, n being greater than or equal to 2, centered around a nominal value of the motor resistance expressed as an integer.

3 . The method according to claim 1 , in which the estimate of the motor resistance is updated according to a sampling interval less than 1 ms.

4 . The method according to claim 1 , wherein the clamping force is determined according to the estimate of the motor resistance that is updated during the idle phase, and an actuator controls the mechanical brake application means to apply the clamping force.

5 . The method according to claim 1 , wherein the estimate of the motor resistance is updated continuously, wherein the motor resistance is estimated at a given time from a previous estimate of the motor resistance using a relation describing the resistance of a solenoid in which a motor supply voltage is replaced by a difference between the motor supply voltage and a motor voltage.

6 . The method according to claim 5 , in which a relation is used describing the resistance of a solenoid in which an exponential function is replaced by a Taylor series of order n, n being greater than or equal to 2, centered around a nominal value of the motor resistance expressed as an integer.

7 . The method according to claim 6 , in which the estimate of the motor resistance is updated at the given time using the following relation:

R

[

n

]

=

V

bat

′

⁢

δ

i

[

n

]

+

(

i

[

n

-

1

]

⁢

R

[

n

-

1

]

i

[

n

]

-

V

bat

′

⁢

δ

i

[

n

]

)

⁢

(

a

.

R

[

n

-

1

]

2

+

b

.

R

[

n

-

1

]

-

c

)

where:

R[n]: motor resistance at interval n,

R[n−1]: motor resistance at interval n−1,

i[n]: motor current at interval n,

i[n−1]: motor current at interval n−1,

V′ bat δ=V bat δ−K*w: where Vbat is the motor supply voltage, K is the motor constant, and w is the rotational speed of the electric motor,

a: polynomial coefficient,

b: polynomial coefficient, and

c: polynomial coefficient.

8 . The method according to claim 7 , in which:

a=0.4523,

b=0.291, and

c=0.07027.

9 . The method according to claim 7 , wherein a, b and c are integers.

10 . The method according to claim 9 , in which:

a=3,

b=2037, and

c=490979.

11 . The method according to claim 10 , in which parameters of the relation for determining the motor resistance are expressed in uint32, after expressing the motor resistance in mΩ, the voltage value is expressed with a gain of 100000 and the current is expressed with a gain of 100.

12 . The method according to claim 11 , in which a gain of 7000000 is added.

13 . The method according to claim 5 , in which the motor voltage is determined by multiplying the motor constant by the rotational speed of the motor.

14 . A braking system adapted to implement the method according to claim 1 .

15 . The braking system according to claim 14 , comprising a braking electric motor, and a controller adapted to implement the method.

16 . The braking system according to claim 15 , in which a nominal resistance of the motor is 0.34Ω and an inductance of the motor is 0.000117 H, and in which the controller has a sampling time (t) of 100 ms.

17 . The braking system according to claim 16 , in which the controller is a 16-bit or 32-bit controller.

18 . A vehicle comprising the braking system according to claim 14 .