Method and device for detecting the locking of a wheel of a motor vehicle during a braking operation

Abstract

Method for detecting a locking of a wheel (12, 14, 16, 18) of a motor vehicle (10) during a braking operation, according to which a brake pressure at the wheel (12, 14, 16, 18) of the motor vehicle (10) is measured by means of a pressure sensor (20) during the braking operation and the brake pressure is used to detect the locking.

Description

[0001] The invention relates to a method for detecting the locking of a wheel of a motor vehicle during a braking operation, in particular after a failure of a wheel speed sensor assigned to the wheel, according to the type specified in patent claim 1 and to a device for carrying out the method according to patent claim 4.

[0002] To ensure vehicle stability and steerability even on slippery surfaces, information regarding wheel slip is necessary. Today's ABS / ESC systems use wheel speed information to determine which wheel is slipping and to what extent.

[0003] If one or more wheel speed sensors fail, the driver is notified (warning via the ABS / ESC light), and the driver is responsible for safely driving or parking the vehicle. Particularly with regard to piloted or (semi-)autonomous driving, this would mean that the piloted or (semi-)autonomous driving function would have to be deactivated temporarily, as the missing wheel speed signals could cause the vehicle to enter a safety-critical driving situation that the system could no longer control.

[0004] For some applications, however, the qualitative wheel speed signals do not need to be known; it is sufficient to detect whether one or more wheels lock during braking.

[0005] US Pat. No. 5,060,159 A discloses a method for controlling a braking system in which the pressure in the wheel brakes is measured and evaluated. Based on the measured values ​​thus determined, a wheel pressure model is derived that approximately represents the pressure curve in the wheel brakes and is taken into account in the brake pressure control.

[0006] A device and method for detecting and / or compensating for irregularities in a brake disc is disclosed in DE 100 26 125 A1. This involves evaluating changes in the control signals used to actuate the brake disc in order to detect any brake judder at an early stage.

[0007] A method for monitoring the pressure curve at a wheel brake of a pressure-operated vehicle brake system is known from DE 10 2014 225 984 A1. The pressure curve is recorded over a period of time using suitable sensors and evaluated in an electronic control unit for periodically recurring pressure pulses in order to detect brake disc runout.

[0008] The invention is based on the object of specifying a method by means of which replacement information about the grip situation (slip) of the wheels of the motor vehicle can be generated during a braking process - even in the event of a wheel speed sensor failure.

[0009] This problem is solved by the features of patent claim 1.

[0010] Subclaims 2 and 3 form advantageous developments of the method according to the invention.

[0011] According to the method for determining whether a wheel of a motor vehicle is locked during a braking operation, a brake pressure at the wheels of the motor vehicle is measured by means of pressure sensors during the braking operation and the measured brake pressure is used to determine whether one or more wheels of the motor vehicle are locked.

[0012] The method according to the invention is based on the finding that, due to tolerances in the brake disc, such as thickness and waviness, a rotating wheel influences the brake pressure in the hydraulic brake circuit of the motor vehicle. This influence on the brake pressure is now used according to the invention to generate substitute information regarding wheel locking in the event of a wheel speed sensor failure.

[0013] The method according to the invention now advantageously ensures that even in the event of a wheel speed sensor failure, redundant information about wheel locking is provided.

[0014] To determine locking, according to a particularly preferred embodiment of the method according to the invention, the brake pressure measured at the wheels is first evaluated with respect to pressure fluctuations using an evaluation unit. Subsequently, a determination of locking or non-locking is made based on the pressure fluctuations by determining that if pressure fluctuations are present, it is concluded that locking is not present, and that – if no pressure fluctuations can be sensed – it is concluded that the wheel is locked.

[0015] The invention is further based on the object of specifying a device for carrying out the method for detecting a locking of a wheel of a motor vehicle during a braking operation.

[0016] This problem is solved by patent claim 4.

[0017] Subclaims 5 to 6 represent advantageous developments of the device.

[0018] The device according to the invention for the method for detecting the locking of a wheel of a motor vehicle during a braking operation has a hydraulically actuated braking system, which, in a known manner, comprises a brake disc with an associated brake caliper assigned to each wheel of the motor vehicle. Furthermore, the device has a plurality of pressure sensors arranged in the braking system, with at least one pressure sensor assigned to each wheel. Furthermore, the device has an evaluation unit to which the output signals of the pressure sensors are provided as input signals. The evaluation unit is designed and / or configured to evaluate the input signals with respect to pressure fluctuations.

[0019] The device according to the invention again takes advantage of the fact that a rotating wheel causes pressure fluctuations in the hydraulic brake system due to tolerances in the brake disc, e.g., the waviness of a brake disc. Due to the now provided evaluation of the brake pressure for pressure fluctuations during a braking operation, a redundant statement about the rotational behavior, i.e., a statement about whether the wheel is rotating or whether it is locked, is now advantageously possible.

[0020] A particularly advantageous embodiment provides for the brake disc to be designed in such a way that the occurrence of pressure fluctuations is amplified. This can be achieved, for example, by the brake discs having increased waviness compared to the prior art.

[0021] Further advantages and possible applications of the present invention will become apparent from the following description in conjunction with the embodiment shown in the drawing.

[0022] In the drawing means: Fig. 1 a schematic representation of a motor vehicle to illustrate the method for detecting a locking of a wheel of a motor vehicle during a braking operation.

[0023] Fig. Figure 1 shows a schematic representation of a motor vehicle, designated overall by reference numeral 10. The motor vehicle 10 has a hydraulic braking system 100—illustrated only schematically here—which, in a known manner, comprises brake discs 110 assigned to the wheels 12, 14, 16, 18 of the motor vehicle 10, as well as brake calipers 120. The brake calipers 120 are operatively connected to a control unit 140 via hydraulic lines 130.

[0024] How Fig. 1 further shows, each wheel 12, 14, 16, 18 of the motor vehicle 10 is assigned a pressure sensor 20 arranged in the hydraulic line 130. The output signals of the pressure sensors 20 are provided as input signals to an evaluation unit 24 via data lines 22.

[0025] As is well known, wheel speed sensors are installed in today's motor vehicles, which allow for a qualitative assessment of the slip of a vehicle's wheels. A qualitative assessment of slip is particularly important with regard to future functions, such as piloted or (semi-)autonomous driving. For reasons of clarity, the wheel speed sensors assigned to wheels 12, 14, 16, and 18 have been omitted here.

[0026] If the wheel speed sensors fail, it is consequently no longer possible to make a qualitative statement about the slip of wheels 12, 14, 16, 18.

[0027] In addition to the above-mentioned safety-relevant applications for which a qualitative statement about the slip is essential, there are applications for which it is sufficient to detect whether one or more wheels 12, 14, 16, 18 of the motor vehicle 10 lock during a braking operation.

[0028] This is exactly where the invention comes in: for the following analysis, it is assumed that due to a failure of the wheel speed sensors, a qualitative statement about the slip of the wheels is not available.

[0029] In order to nevertheless provide information about whether a wheel 12, 14, 16, 18 of the motor vehicle 10 is locking or not locking during a braking operation, the brake pressure at the wheels 12, 14, 16, 18 is measured during the braking operation using the pressure sensors 20. The values ​​measured by the pressure sensors 20 are fed to an evaluation unit 24 via data lines 22 and evaluated in the evaluation unit 24 with regard to pressure fluctuations.

[0030] The method according to the invention utilizes the fact that, when a wheel is rotating, pressure fluctuations occur in the hydraulic lines 130 due to tolerances in the brake disc, whereas a stationary wheel does not cause any pressure fluctuations. These pressure fluctuations are then used according to the invention to generate substitute information about a possible wheel locking during a braking operation—particularly after the failure of wheel speed sensors.

[0031] If the evaluation of the evaluation unit 24 now shows that, for example, pressure fluctuations occur at wheels 12, 14 and 18 and that no pressure fluctuations could be sensed at wheel 16, it is determined that during the braking process, wheel 16 is already blocked while wheels 12, 14, 18 are still rotating.

[0032] Thus, the method according to the invention now ensures that even in the event of a wheel speed sensor failure, redundant information about wheel locking is provided.

Claims

[1] Method for detecting a locking of a wheel (12, 14, 16, 18) of a motor vehicle (10) during a braking operation, according to which a brake pressure at the wheel (12, 14, 16, 18) of the motor vehicle (10) is measured by means of a pressure sensor (20) during the braking operation and the brake pressure is used to detect the locking. [2] Method according to claim 1, characterized by that the brake pressure measured at the wheel (12, 14, 16, 18) during the braking process is evaluated with regard to pressure fluctuations. [3] Method according to claim 2, characterized by that in the presence of pressure fluctuations it is concluded that the wheel (12, 14, 16, 18) is rotating and that in the absence of pressure fluctuations it is concluded that the wheel (12, 14, 16, 18) is blocked. [4] Device for detecting the locking of a wheel (12, 14, 16, 18) of a motor vehicle (10) during a braking operation, comprising a hydraulically actuated braking system (100), an evaluation unit (24), a brake disc (110) assigned to each wheel (12, 14, 16, 18) of the motor vehicle (10), a brake calliper (120) assigned to each wheel (12, 14, 16, 18) of the motor vehicle (10), and a pressure sensor (20) assigned to each wheel (12, 14, 16, 18) of the motor vehicle (10) and arranged in the braking system (100), the output signals of which are made available to the evaluation unit (24) as input signals, the evaluation unit (24) being designed to evaluate pressure fluctuations. [5] Device according to claim 4, characterized by that the brake discs (110) are designed in such a way that the occurrence of pressure fluctuations is increased during the braking process. [6] Device according to claim 5, characterized bythat the brake discs (110) are designed with increased waviness.

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