Method for monitoring an electric motor, electronic control module, hydraulic brake system and storage medium

Abstract

A method for monitoring an electric motor of a hydraulic brake system for a motor vehicle, wherein a first torque and a second torque are calculated and compared with one another. A fault can be detected on the basis of the comparison. The invention also relates to an associated electronic control module, to an associated hydraulic brake system and to an associated non-volatile computer-readable storage medium.

Claims

1. A method for monitoring an electric motor of a hydraulic brake system for a motor vehicle, wherein the method comprises: determining a motor angular acceleration during operation of the electric motor; calculating a first torque of the motor during operation of the electric motor on the basis of one or more first values, the one or more first values including the motor angular acceleration, measuring a hydraulic pressure of the hydraulic brake system with a pressure sensor; calculating a second torque of the motor during the operation of the electric motor on the basis of one or more second values different from the one or more first values, the one or more second values including the measured hydraulic pressure, and detecting a malfunction on the basis of a comparison of the first torque and of the second torque.

2. The method as claimed in claim 1, wherein the first torque is a motor load torque.

3. The method as claimed in claim 1, wherein the first torque is calculated on the basis of an electrical motor torque, a moment of inertia and the motor angular acceleration.

4. The method as claimed in claim 3 wherein the first torque is calculated as follows: the electrical motor torque minus the moment of inertia multiplied by the motor angular acceleration.

5. The method as claimed in claim 3, wherein the motor angular acceleration is extracted by an observer.

6. The method as claimed in claim 1, wherein the second torque is calculated on the basis of at least each of the measured hydraulic pressure, a transmission ratio, an area of a linear actuator piston which is driven by the motor, and an efficiency constant.

7. The method as claimed in claim 6, wherein the second torque is calculated as follows: the product of the efficiency constant, the area of a linear actuator piston which is driven by the motor, the transmission ratio and the measured hydraulic pressure, divided by 2 and by n.

8. The method as claimed in claim 1, wherein the comparison comprises the following: calculating a difference between the first torque and the second torque, comparing the difference with a predetermined threshold value, and detecting a malfunction if the difference exceeds the predetermined threshold value.

9. The method as claimed in claim 1, wherein the method is executed if the motor is actuated by an electronic control module, without taking into account a user activation of a brake pedal or an activation request by a function which is executed in the electronic control module.

10. An electronic control module comprising a non-volatile computer-readable storage medium which contains instructions which, when executed by the electronic control module, cause the electronic control module to execute a method for monitoring an electric motor of a hydraulic brake system for a motor vehicle, including: determining a motor angular acceleration during operation of the electric motor; calculating a first torque of the motor during operation of the electric motor on the basis of one or more first values, the one or more first values including the motor angular acceleration, measuring a hydraulic pressure of the hydraulic brake system with a pressure sensor; calculating a second torque of the motor during the operation of the electric motor on the basis of one or more second values different from the one or more first values, the one or more second values including the measured hydraulic pressure, and detecting a malfunction on the basis of a comparison of the first torque and of the second torque.

11. A hydraulic brake system for a vehicle, wherein the brake system comprises: a linear actuator piston for generating hydraulic pressure, an electric motor which is designed to drive the linear actuator piston, a pressure sensor for measuring the hydraulic pressure, and an electric control module as claimed in claim 10.

12. A non-volatile computer-readable storage medium which contains instructions which, when executed by an electronic control module, cause the electronic control module to execute a method for monitoring an electric motor of a hydraulic brake system for a motor vehicle, including: determining a motor angular acceleration during operation of the electric motor; calculating a first torque of the motor during operation of the electric motor on the basis of one or more first values, the one or more first values including the motor angular acceleration, measuring a hydraulic pressure of the hydraulic brake system with a pressure sensor; calculating a second torque of the motor during the operation of the electric motor on the basis of one or more second values different from the one or more first values, the one or more second values including the measured hydraulic pressure, and detecting a malfunction on the basis of a comparison of the first torque and of the second torque.

13. The method as claimed in claim 2, wherein the first torque is calculated on the basis of an electrical motor torque, a moment of inertia and a motor angular acceleration.

14. The method as claimed in claim 4, wherein the motor angular acceleration is extracted by an observer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages will be gathered by a person skilled in the art from the exemplary embodiment described below with reference to the appended drawing. In the drawing:

(2) FIG. 1 shows a hydraulic brake system, and

(3) FIG. 2 shows an observer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) FIG. 1 shows a hydraulic brake system 5 according to an exemplary embodiment of the invention.

(5) The hydraulic brake system 5 has an electronic control module 10 according to an exemplary embodiment of the invention. This is designed, in particular, to execute a method according to an aspect of the invention. This will be discussed in more detail later on.

(6) The hydraulic brake system 5 has an electric motor 20 which is actuated by the electronic control module 10.

(7) The hydraulic brake system 5 has a shaft 30 which is driven by the motor 20 and has an external thread 35.

(8) The hydraulic brake system 5 has a linear actuator 40 in which a piston 45 is arranged. The piston 45 is a linear actuator piston and is connected to the shaft 30 in such a way that when the shaft 30 rotates said piston can be moved owing to the external thread 35 and an internal thread (not illustrated) located within the piston 45 in the linear actuator 40.

(9) The hydraulic brake system 5 also has a pressure sensor 50 which senses a pressure in the linear actuator 40.

(10) The electronic control module 10 is designed to calculate a first torque and a second torque. For the first torque this is done according to the following formula:

(11) $M_1=M_e-J*\frac{d\omega }{dt}$
where M.sub.1 refers to the first torque, M.sub.e refers to an electrical motor torque which is determined on the basis of operating parameters of the motor 20, J refers to a moment of inertia of the system which is driven in its entirety by the motor 20, that is to say in particular the shaft 39 and rotatable components of the motor 20 which are connected thereto, ω refers to the angular speed of the shaft 30.

(12) The formula specified above therefore calculates the first torque M.sub.1 in such a way that the torque which occurs owing to the angular acceleration of rotatable parts is subtracted from the electrical torque which would typically arise in the load-free state.

(13) The angular acceleration

(14) $M_2=\frac{\eta *A*k}{2*\pi }*p$
can be obtained, for example, by means of an observer which is illustrated in FIG. 2. Details are not given on this circuit here in the description, but instead reference is made to the illustration in the circuit diagram. In particular, on the left, at the point marked by 1 a motor torque is input, and at the point marked by 2 a calculated mechanical speed is input. On the right, at a point 1 an estimated load torque is output, and at point 2 an estimated speed is output.

(15) The electronic control module 10 is also designed to calculate a second torque on the basis of the following formula:

(16) $\frac{d\omega }{dt}$
where: M.sub.2 refers to the second torque, η refers to an efficiency constant which represents an efficiency level of the system and which can be direction-dependent, A refers to the area of the piston 45 in the linear actuator 40, i.e. the area which generates a pressure in the linear actuator 40, k refers to the gradient of the external thread 35, p refers to the pressure which is measured by the pressure sensor 50.

(17) The second torque is therefore a torque which is recalculated on the basis of the actually generated pressure.

(18) After calculating the two torques M.sub.1, M.sub.2, the electronic control module 10 compares them with one another. For this purpose, the second torque M.sub.2 is subtracted from the first torque M.sub.1. The value which is obtained for the difference is compared with a predetermined threshold value. If the difference is greater than this threshold value, a malfunction is detected, since the motor has clearly generated significantly less torque than would be possible based on its design and its electrical actuation. This can indicate, in particular, increased friction or other problems. On the other hand, if the difference is below the threshold value, it is assumed that a malfunction is not present.

(19) It is to be understood that other possible sources of faults, such as for example faults in calculating amplification of a current measurement, an offset in a rotor position or even a fault in the pressure sensor 50 can influence the calculation. However, such faults can be detected with techniques which are known to a person skilled in the art, to be precise typically significantly more quickly than the detection of a fault in the motor or in the brake system on the basis of a comparison of torques, as described herein.

(20) The torque comparison described herein can be carried out, in particular, continuously and/or at defined times, which can occur, in particular, independently of the activation of a brake pedal by a user or some other way of triggering the brakes. This significantly increases the reliability when detecting faults.

(21) The mentioned steps of the method according to an aspect of the invention can be executed in the indicated order. However, they can also be executed in a different order as far as this is technically appropriate. In one of its embodiments, for example with a specific combination of steps, the method according to an aspect of the invention can be executed in such a way that no further steps are executed. However, in principle, further steps can also be executed, even steps of a kind which have not been mentioned.

(22) The claims that are part of the application do not represent any dispensing with of the attainment of further protection.

(23) If it turns out in the course of the method that a feature or a group of features is not absolutely necessary, the applicant aspires right now to formulate at least one independent claim which no longer has the feature or the group of features. This may be, by way of example, a subcombination of a claim available on the filing date or may be a subcombination of a claim available on the filing date that is limited by further features. Claims or combinations of features of this kind requiring rewording are intended to be understood to be covered by the disclosure of this application as well.

(24) It should further be pointed out that configurations, features and variants of aspects of the invention that are described in the various embodiments or exemplary embodiments and/or shown in the figures are combinable with one another in any way. Single or multiple features can be interchanged with one another in any way. Combinations of features arising therefrom are intended to be understood to be covered by the disclosure of this application as well.

(25) Back-references in dependent claims are not intended to be understood as dispensing with the attainment of independent substantive protection for the features of the back-referenced subclaims. These features can also be combined with other features in any way.

(26) Features that are disclosed only in the description or features that are disclosed in the description or in a claim only in conjunction with other features may fundamentally be of independent significance essential to aspects of the invention. They can therefore also be individually included in claims for the purpose of distinction from the prior art.