METHOD FOR REDUCING VIBRATIONS IN A FRICTION BRAKE, AND BRAKING SYSTEM AND PROGRAM CODE

Abstract

The disclosure relates to a method for reducing unwanted vibrations in a friction brake. The friction brake has at least one friction surface and at least one brake lining associated with the friction surface. The method comprises the following steps: a) pressing the brake lining against the friction surface with a clamping force in order to convert a braking request into a braking force; and b) modulating a temporal fluctuation onto the clamping force in order to avoid or reduce the unwanted vibrations. A corresponding braking system together with the associated program code is also disclosed.

Claims

1. A method for reducing unwanted vibrations in a friction brake, wherein the friction brake has at least one friction surface and at least one brake lining associated with the friction surface, and wherein the method comprises the following steps: a) pressing the brake lining against the friction surface with a clamping force in order to convert a braking request into a braking force, and b) modulating a temporal fluctuation onto the clamping force in order to avoid or reduce unwanted vibrations.

2. The method according to claim 1, wherein the clamping force remains substantially unchanged by the modulated fluctuation on average over time.

3. The method according to claim 2, wherein the modulated fluctuation has a continuous curve.

4. The method according to claim 2 wherein the modulated fluctuation oscillates at a frequency of approximately 0.1 Hz to 250 Hz.

5. The method according to claim 4, wherein the frequency of the modulated fluctuation changes over time, and has alternating positive and negative chirps, as the clamping force increases.

6. The method according to claim 1, wherein an amplitude of the modulated fluctuation is at most 50% of the clamping force.

7. The method according to claim 1, wherein an amplitude of the modulated fluctuation changes as the clamping force increases.

8. The method according to claim 1, wherein the method further comprises the following steps: c) detecting a braking state which is susceptible to vibrations and in which unwanted vibrations can occur, and d) modulating the temporal fluctuation onto the clamping force when the braking state that is susceptible to vibrations is detected.

9. The method according to claim 8, wherein the detection of a braking state that is susceptible to vibrations includes evaluating a sensor signal from a sensor-.

10. The method according to claim 9, wherein the evaluation of the sensor signal includes a determination of the frequency, amplitude and/or phase position of dominant unwanted vibrations in the friction brake.

11. The method according to claim 1, wherein a curve of the modulated fluctuation is formed on the basis of the frequency, amplitude and/or phase position of one or more dominant unwanted vibrations in the friction brake.

12. The method for reducing unwanted vibrations in a friction brake pair having a first and a second friction brake, wherein the first and the second friction brake are each operated with the method for reducing unwanted vibrations according to claim 1, wherein the respective modulated fluctuations have an antiphase curve.

13. A braking system for a land vehicle, comprising a controller, an energy source and at least one friction brake with an associated actuator, wherein the actuator is designed to press a brake lining of the friction brake against an associated friction surface of the friction brake with a clamping force, wherein the energy source is designed to supply the actuator with energy, and wherein the controller is designed to control the actuator to a) cress the brake lining against the friction surface with a clamping force in order to convert a braking request into a braking force, and b) modulate a temporal fluctuation onto the clamping force in order to avoid or reduce unwanted vibrations.

14. The braking system according to claim 13, the at least one friction brake is associated with a sensor which provides a sensor signal, wherein the friction brake comprises the sensor.

15. The braking system according to claim 13, wherein the friction brake is an electromechanical brake.

16. A program code comprising commands which, when executed by a controller, cause a braking system to carry out the method according to claim 1.

17. The program code of claim 15, wherein the braking system comprising a controller, an energy source and at least one friction brake with an associated actuator, wherein the actuator is designed to press a brake lining of the friction brake against an associated friction surface of the friction brake with a clamping force, wherein the energy source is designed to supply the actuator with energy, and wherein the controller is designed to control the actuator

18. The method according to claim 3, wherein the curve of the modulated fluctuation is a continuous substantially sinusoidal curve.

19. The method according to claim 2, wherein the modulated fluctuation oscillates at a frequency of approximately 3 Hz to 70 Hz.

20. The method according to claim 1, wherein an amplitude of the modulated fluctuation is at most 35% of the clamping force.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0036] The disclosure is explained below with reference to an exemplary arrangement which is shown in the accompanying drawings, in which:

[0037] FIG. 1 is a highly simplified schematic view of a braking system according to the disclosure, which is operated in accordance with the method according to the disclosure, and

[0038] FIG. 2 is a diagram showing a modulated clamping force schematically plotted against a (nominal) clamping force.

DETAILED DESCRIPTION

[0039] FIG. 1 shows a braking system 10 for a motor vehicle comprising a plurality of friction brakes 1a-1d. Each friction brake 1a-1d has at least one friction surface 2, for example on flanks of a brake disk. In addition, each friction brake comprises at least one brake lining 3. The brake linings 3 are also referred to as brake pads or friction linings, among other things.

[0040] In addition to the friction brakes 1a-1d, the braking system 10 comprises a controller 11, an energy source 12 and at least one actuator 5 associated with the relevant friction brake 1a-1d.

[0041] Each actuator 5 is designed to press the associated brake lining 3 of the friction brake 1a-1d against the corresponding friction surface 2 of the friction brake with a clamping force. The energy source 12 is designed to supply the actuator 5 with energy.

[0042] The friction brakes 1a-1d are electromechanical brakes, i.e. those in which an electric motor acts directly on the brake linings via a gear mechanism.

[0043] The controller 11 is designed to control the actuator 5 and to carry out the steps of the method according to the disclosure. The controller 11 can be a conventional controller in the true sense or can also provide the function of an open-loop controller with a corresponding feedback path.

[0044] A sensor 4 which provides a sensor signal can be associated with the friction brakes 1a-1d. The sensor signal is processed by the controller 11. One sensor 4 can be associated with a plurality of friction brakes 1a-1d. Alternatively, as shown here, each friction brake 1a-1d can be associated with its own sensor 4. In one exemplary arrangement, the sensors are acceleration sensors which are arranged directly on or in a component of the friction brake 1a-1d and can detect vibrations of the friction brake 1a-1d.

[0045] However, unwanted vibrations can also be detected by other suitable sensors, for example microphones or magnetic field sensors.

[0046] A program code 13 having commands is stored in a memory of the controller 11 and, when executed by the controller 11, causes the braking system 10 to carry out the method according to the disclosure.

[0047] FIG. 2 shows a diagram with the modulated clamping force F_mod plotted schematically over the nominal clamping force F_nenn. Along the diagonal between the nominal clamping force F_nenn and the modulated clamping force F_mod, the clamping force is thus represented as an average over time. The time t for the schematic representation of the oscillation is also plotted along the diagonal between the nominal clamping force F_nenn and the modulated clamping force F_mod. The amplitude of the fluctuation S or of the antiphase fluctuation S′ is plotted transversely to said diagonal.

[0048] In principle, the brake linings 3 are pressed against the friction surfaces 2 with a clamping force F in order to convert a braking request from the driver or an autopilot into a braking force. As the clamping force F increases, so does the braking force on the contact area of the tire.

[0049] Here, in a first range A with a very low nominal clamping force, the probability of an unwanted vibration is so low that it is not absolutely necessary to modulate a fluctuation onto the nominal clamping force. The actual clamping force thus corresponds to the nominal clamping force F_nenn.

[0050] In order to reduce unwanted vibrations in one of the friction brakes 1a-1d, it is first ascertained or detected whether a braking state at risk of vibrations is present, in which unwanted vibrations can occur. Unwanted vibrations are in particular those that cause annoying noises and/or vibrations.

[0051] A temporal fluctuation S is then modulated onto the damping force F as long as the braking state susceptible to vibrations is detected in order to avoid or reduce the unwanted vibrations.

[0052] For example, unwanted vibrations can occur in a second range B with a low nominal damping force. This is therefore an operating state that is susceptible to vibrations. As soon as a vibration is detected or is determined to be imminent, a temporal fluctuation S1 is therefore modulated onto the nominal damping force of a first friction brake 1a. The damping force F is substantially unchanged by the modulated fluctuation S on average over time. Small fluctuations cannot be avoided for technical reasons.

[0053] In one exemplary arrangement, the modulated fluctuation S has a continuous, substantially sinusoidal curve.

[0054] A temporal fluctuation S1′ with an antiphase curve is modulated onto the nominal damping force of a second friction brake.

[0055] The second friction brake 1b can be located on the same front or rear axle as the first friction brake 1a.

[0056] The second friction brake can, however, also be the friction brake 1d diagonally opposite the first friction brake 1a, in order to achieve even greater driving stability. If, for example, a vibration is determined on the front left friction brake 1a, a fluctuation is modulated onto the rear right friction brake 1d with an antiphase.

[0057] Of course, it is also conceivable that the first friction brake 1a and the second friction brake 1c are arranged one behind the other on one side of a vehicle.

[0058] Unwanted vibrations can also occur in a third range C with an average nominal damping force. In principle, this range still involves comfort braking. This is also an operating state that is susceptible to vibrations. A temporal fluctuation S2 is therefore modulated onto the nominal clamping force of the first friction brake 1a. A complementary or antiphase fluctuation S2′ is likewise modulated onto the nominal damping force of the second friction brake 1b, 1c or 1d.

[0059] The damping force F is also substantially unchanged by the modulated fluctuation S on average over time here. In one exemplary arrangement, the modulated fluctuation S has a continuous, substantially sinusoidal curve.

[0060] For reasons of comfort, the maximum amplitude of the fluctuation S2,max or S2,min (as a percentage of the nominal clamping force F_nenn) in the third range C is selected to be lower than the maximum amplitude of the fluctuation S1,max or S1,min (also as a percentage of the nominal damping force F_nenn) in the second range.

[0061] The modulated fluctuation S oscillates at a frequency of approximately 0.1 Hz to 250 Hz, in particular at a frequency of 3 Hz to 70 Hz. In contrast with hydraulic/pneumatic brakes, electromechanical brakes can convert frequencies of more than 10 Hz without major problems.

[0062] The frequency in the second range B can be 30 Hz, for example.

[0063] Furthermore, the frequency can decrease as the damping force F increases. For example, the frequency in the third range C can be 10 Hz.

[0064] The amplitude of the modulated fluctuation S is at most 50% of the clamping force F, and in one exemplary arrangement, at most 35% of the damping force F.

[0065] In the second range B, the amplitude S1,max can be, for example, 20% of the nominal damping force.

[0066] The amplitude of the modulated fluctuation S decreases as the damping force F increases. The amplitude S2,max in the third range C is for example 15% of the nominal damping force and does not exceed a certain absolute value.

[0067] In one exemplary arrangement, the frequency of the modulated fluctuation S is changed over time. For example, it can in particular have alternating positive and negative chirps. In other words, the frequency can wobble in a chirp modulation between a minimum frequency and a maximum frequency. In one exemplary arrangement, the minimum frequency can be 20 Hz and the maximum frequency can be 40 Hz. The transition from the minimum to the maximum and back again to the minimum frequency can last for approximately 2 seconds in the second range B, for example at an amplitude F1,max of 35%. Correspondingly lower values are to be selected in the third range C, for example an amplitude of 20%, a maximum frequency of 25 Hz and a minimum frequency of 10 Hz.

[0068] In a fourth range D with a high nominal clamping force F_nenn, it is no longer a question of comfort braking in the true sense. The driver and passengers of a vehicle are usually distracted in such a situation and accordingly more tolerant of noise. It is therefore not absolutely necessary here to modulate a fluctuation onto the nominal clamping force F_nenn in this range. Also, if the clamping force F is sufficiently strong, strong unwanted vibrations are not expected. The actual clamping force therefore corresponds to the nominal clamping force F_nenn.

[0069] Deviating advantageous fluctuation curves over the nominal clamping force are conceivable, in particular those in which the amplitude, frequency and/or phase position of the fluctuation curve is determined dynamically.

[0070] Optionally, the detection of a braking state that is susceptible to vibrations includes evaluating a sensor signal from a sensor 4. As an example, the sensor is an acceleration sensor. However, other types of sensors can also be considered.

[0071] The evaluation of the sensor signal can include a determination of the frequency, amplitude and/or phase position of dominant unwanted vibrations in the friction brake or brakes 1a-1d.

[0072] The curve of the modulated fluctuation S is then formed on the basis of the frequency, amplitude and/or phase position of one or more dominant unwanted vibrations in the friction brake or brakes 1a-1d.