Brake device, electromechanical brake system and method for operating electromechanical brake system

Abstract

The invention relates to an electromechanical brake system, in which the force required for the braking process is provided by means of an asynchronous motor. The asynchronous motor and especially the torque output by the asynchronous motor are adjusted by using the quasi-static rotor position of the rotor of the asynchronous motor.

Description

Technical Field

[0001] The invention relates to a brake device and an electromechanical brake system having such a brake device. The invention also relates to a method for operating an electromechanical brake system. Background Art

[0002] In order to brake or decelerate a motor vehicle, the motor vehicle has a brake system which can brake the wheels of the vehicle. At present, hydraulic brake systems are mainly used for this purpose. In addition, the application of electromechanical brake systems is also becoming more and more widespread.

[0003] Patent document WO 2000 / 29268 A1 describes, for example, an electrically actuatable parking brake device. Summary of the invention

[0004] The invention provides a brake device and an electromechanical brake system and a method for operating an electromechanical brake system having the features of the independent claims. Further advantageous embodiments are the subject matter of the dependent claims.

[0005] Accordingly, it is proposed that:

[0006] A brake device having a brake element, a transmission, an asynchronous motor and a control device. The brake element is designed to apply a force to a brake pad. In particular, the brake pad can be pressed against a brake disc when a force is applied to the brake pad. The transmission is designed to mechanically couple a drive shaft of the asynchronous motor to the brake element. The control device is designed to control the asynchronous motor. In particular, the control device can control the asynchronous motor with a quasi-stationary rotor position. In other words, when controlling the asynchronous motor, the control device assumes an at least approximately constant rotor position.

[0007] In addition, it is proposed that:

[0008] An electromechanical brake system has a brake device according to the invention, a brake disk and at least one brake pad. The at least one brake pad is designed to be pressed against the brake disk by the brake device.

[0009] Finally, it is proposed:

[0010] A method for operating an electromechanical brake system, in particular an electromechanical brake system controlled by an asynchronous motor. The method comprises the step of receiving a target value for a braking force to be set. Furthermore, the method comprises the step of controlling the asynchronous motor. In particular, the asynchronous motor can be controlled using the received target value for the braking force to be set and a quasi-stationary rotor position of the asynchronous motor.

[0011] Advantages of the present invention

[0012] The present invention is based on the recognition that an electric drive is needed to actuate an electromechanical brake. Here, a brushless motor, in particular a permanent-magnet synchronous motor, is preferably used in an electromechanical brake system.

[0013] However, the operation of the synchronous machine in a quasi-static state or at low rotational speeds necessarily requires the determination of the rotor position, for example with the aid of an additional rotor position sensor.

[0014] An idea of ​​the present invention is to take this knowledge into account and provide a drive that is as simple and robust as possible for an electromechanical brake system. In particular, an electromechanical brake system is to be provided that can be driven by a robust electric motor without a rotor position sensor.

[0015] For this purpose, it is proposed according to the invention to drive an electromechanical brake system by means of an asynchronous machine. Since the movement of the brake element, in particular the brake pad, during the braking process is relatively small, it can be assumed that the rotor of such an asynchronous machine exerts only very small rotational movements during the braking process. Accordingly, an at least approximately constant rotor position can be assumed for the control of the asynchronous machine. Thus, the asynchronous machine can also be controlled without an additional rotor position sensor for determining the rotational movement of the rotor of the asynchronous machine.

[0016] For controlling an asynchronous machine, it is sufficient to adjust the frequency of the phase voltage at the asynchronous machine based on the so-called slip, ie the speed difference between the rotor and the rotating magnetic field. The torque generated is proportional to the magnetic flux and the slip.

[0017] As already mentioned above, only very small movements are required to actuate the electromechanical brake. Accordingly, the rotational movement in the motor rotor is also very small. The torque to be set by the asynchronous motor used according to the invention can therefore be set based on an at least approximately stationary rotor. Therefore, no rotor position sensor is required to determine the rotational movement of the rotor.

[0018] According to one embodiment, the control device of the brake device is designed to receive a target value for the braking force to be adjusted. Accordingly, the control device on the asynchronous machine can use the received target value for the braking force to be adjusted to adjust the torque. Since the torque output by the asynchronous machine and the force exerted by the brake element on the brake pad are proportional to the magnetic flux and the slip in the asynchronous machine, the control device can adjust the braking force in a simple manner by assuming a quasi-stationary state of the rotor in the asynchronous machine, without requiring a rotor position sensor on the asynchronous machine.

[0019] According to one embodiment, the control device is designed to receive a sensor value from a rotation speed sensor. The rotation speed sensor can in particular detect the rotation speed of the wheel to be braked. The wheel to be braked can, for example, be mechanically coupled to a brake disc, which is braked by one or more brake pads, which are operated by a brake element of a braking device. Accordingly, the control device can also be designed to receive the torque at the asynchronous motor using the sensor value received from the rotation speed sensor. By evaluating the sensor value of the rotation speed sensor, the rotational movement of the wheel, more precisely the rotational movement of the brake disc, can be determined. Therefore, the deceleration, i.e. the reduction in the rotation speed, can be monitored during the braking process. Accordingly, the torque output by the asynchronous motor can be adjusted according to the determined rotation speed in order to apply a predetermined braking force. As an example, by monitoring the sensor value of the rotation speed sensor, the locking of the wheel can also be identified very quickly. Then, for example, the torque output by the asynchronous motor can be reduced in order to reduce the braking force and thereby avoid further locking of the wheel.

[0020] According to one specific embodiment, the control device is designed to regulate the phase currents at the asynchronous machine using the torque to be regulated.

[0021] According to one embodiment of the electromechanical brake system, a rotation speed sensor is provided in the electromechanical brake system. The rotation speed sensor is designed to detect the rotation speed of the brake disk or the rotation speed of the wheel mechanically coupled to the brake disk. Accordingly, the control device is designed to control the asynchronous motor using the detected rotation speed. In this way, the deceleration of the wheel can be monitored. The braking force can then be adjusted by adjusting the torque output by the asynchronous motor. In particular, wheel locking can be detected very quickly, and the braking force can then be reduced in order to release the locked wheel again.

[0022] As long as it makes sense, the above-mentioned designs and improvements can be combined with each other arbitrarily. Other designs, improvements and implementations of the present invention also include combinations of features of the present invention described above or below for the embodiments that are not explicitly mentioned. In particular, those skilled in the art will also add various aspects as improvements or supplements to the corresponding basic forms of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Further features and advantages of the present invention are explained below with reference to the accompanying drawings, in which:

[0024] Figure 1 A schematic diagram of an electromechanical brake system having a brake device according to one embodiment is shown; and

[0025] Figure 2 A flow chart of a method for operating an electromechanical brake system according to one specific embodiment is shown. DETAILED DESCRIPTION

[0026] Figure 1 1 shows a schematic diagram of an electromechanical brake system 1 according to an embodiment. The electromechanical brake system 1 comprises a brake disc 50, which is mechanically coupled to a wheel 60 via a force-transmitting connection. A rotational speed sensor 61 can be arranged on the wheel 60 or, if necessary, on the brake disc 50. The rotational speed sensor 61 can detect the rotational movement of the wheel 60 and thus also the rotational movement of the brake disc 50 in a sensory manner and can provide a sensor signal D corresponding to the rotational speed.

[0027] In order to brake the rotating wheel 60, one or more brake pads 41, 42 can be pressed against the brake disk 50. Here, the rotation of the brake disk 50 is braked according to the force applied by the brake pads 41, 42.

[0028] In conventional braking systems, the brake pads 41, 42 are usually pressed against the brake disc 50 by means of a hydraulic system. Figure 1 In the electromechanical brake system shown, a brake device with an electric drive is provided. The functional principle of the electric drive is explained in more detail below.

[0029] In order to make the brake pads 41 and 42 apply a braking force to the brake disc 50, an asynchronous motor 10 is provided in the electromechanical brake system 1, which presses at least one brake pad 41 against the brake disc 50 via the transmission device 20. If necessary, a mechanical component 43 can also be provided, which makes it possible to evenly distribute the force output by the transmission device 20 to the two brake pads 41 and 42, so that the brake disc 50 can be braked from both sides via the brake pads 41 and 42. As an example, the force output by the transmission device 20 can first act on the brake element 30, and the brake pad 41 can be fixed to the brake element.

[0030] In the released (stationary) state, i.e. when the brake pads 41, 42 do not apply a braking force to the brake disc 50, there is only a small distance between the brake pads 41, 42 and the brake disc 50. Therefore, the brake pads 41, 42 only need to be slightly moved to apply a braking force to the brake disc 50. This means that the rotating shaft of the asynchronous motor 10 only needs to be slightly rotated, i.e., only rotated by a very small angle, in order to press one or more brake pads 41, 42 against the brake disc 50. Since the distance between the brake pads 41, 42 and the brake disc 50 is very small in the released state, even due to the speed ratio of the transmission 20, only a very small rotational movement of the drive shaft of the asynchronous motor 10 is required. This means that for the control of the asynchronous motor 10 described below, it can be assumed that the drive shaft of the asynchronous motor 10 is at least approximately stationary and therefore the rotor of the asynchronous motor is at least approximately stationary. This is referred to as the quasi-stationary rotor position below.

[0031] In order to adjust the predetermined braking force, the brake pads 41, 42 need to be pressed against the brake disk 50 with a force corresponding to the predetermined braking force. For this purpose, the asynchronous motor 10 must provide a corresponding torque at the input end of the transmission 20. The torque output by the asynchronous motor 10 is proportional to the magnetic flux and the slip (i.e., the speed difference between the rotor and the rotating magnetic field) in the asynchronous motor. Since, as explained above, a quasi-stationary rotor position can be assumed in the described brake system 1, the desired slip and thus the torque output by the asynchronous motor 10 can be adjusted only by the frequency of the phase voltage at the asynchronous motor. In this way, the braking force can be controlled without an additional rotor position sensor on the asynchronous motor 10.

[0032] By way of example, the asynchronous machine 10 can be controlled by means of a control device 11 . The control device 11 can provide the asynchronous machine 10 with phase currents and phase voltages which are suitable for outputting a desired torque via the asynchronous machine 10 to the transmission 20 .

[0033] For this purpose, for example, a target value S of the braking force can be predetermined on the control device 11. The control device 11 can use the target value S to adjust the appropriate current and voltage for the braking force to be adjusted on the asynchronous motor 10. For example, the corresponding correspondence between the predetermined braking force and the current or voltage to be adjusted can be stored in a memory in the control device 11. Alternatively, the relationship between the braking force to be adjusted and the current or voltage can be specified as a functional relationship, and the corresponding current or voltage can be calculated according to the predetermined braking force using this functional relationship. Of course, any other method for determining the current or voltage to be adjusted according to the target value S of the braking force to be adjusted is also feasible.

[0034] Furthermore, the control of the asynchronous motor 10 can also take into account the rotational speed of the wheel 60, more precisely the rotational speed of the brake disc 50. For this purpose, for example, the sensor value D provided by the rotational speed sensor 61 described above can be evaluated by the control device 11. As an example, based on the change in the rotational speed during the braking process, in particular the reduction in the rotational speed, the electromechanical brake system 1 can draw conclusions about the current deceleration. Accordingly, based on the current change in the rotational speed and the deceleration derived therefrom, the torque output by the asynchronous motor 10 or the phase current or phase voltage to be adjusted can also be further adjusted. In this way, the electromechanical brake system 1 can adjust the braking behavior very quickly.

[0035] In particular, it is also possible to detect, for example, a locking of a wheel 60 by evaluating the sensor signal D from the rotational speed sensor 61. In this case, i.e., when a locked wheel 60 is detected, the torque delivered by the asynchronous machine 10 can be reduced, and thus also the force with which the brake pads 41 and 42 act on the brake disk 50. The braking force can thus be reduced to such an extent that the wheel is no longer locked. In this way, the braking action can be intervened very quickly, so that a vehicle having such a brake system 1 is easier to control.

[0036] Figure 2 A flow chart is shown as a basis for a method for operating an electromechanical brake system 1 according to one embodiment. The electromechanical brake system can in particular be an electromechanical brake system described above with an asynchronous machine 10. Accordingly, the method can include any of the steps that have been described above in conjunction with the electromechanical brake system 1. Similarly, the electromechanical brake system 1 described above can also include the components required for implementing the method described below.

[0037] In step S1 , a target value S for the braking force to be adjusted can be received.

[0038] In step S2 , the asynchronous machine 10 of the electromechanical brake system can then be actuated using the received target value S. In this case, the asynchronous machine 10 is actuated using its quasi-stationary rotor position.

[0039] Furthermore, the control of the asynchronous machine can also take into account any other suitable parameters, such as the rotational speed of the wheel to be braked or the like.

[0040] In summary, the present invention relates to an electromechanical brake system. The force required for the braking process is provided by an asynchronous motor. The quasi-stationary rotor position of the rotor of the asynchronous motor is used to adjust the asynchronous motor and in particular the torque output by the asynchronous motor.

Claims

1. Braking device, having: a brake element (30) designed to apply a force to a brake pad (41); Asynchronous motor (10); a transmission device (20) designed to mechanically couple a drive shaft of the asynchronous motor (10) to the brake element (30); and A control device (11) is designed to control the asynchronous machine (10) using the quasi-stationary rotor position of the asynchronous machine (10).

2. The braking device according to claim 1, wherein: The control device (11) is designed to receive a target value (S) for a braking force to be set and to adjust a torque at the asynchronous machine (10) using the received target value (S) for the braking force to be set.

3. The braking device according to claim 1 or 2, wherein: The control device (11) is designed to receive a sensor value (D) from a rotation speed sensor (61) which detects the rotation speed of the wheel (60) to be braked, and Therein, the control device (11) is designed to adjust the torque at the asynchronous motor (10) using the received sensor value (D).

4. The braking device according to any one of claims 1 to 3, wherein: The control device (11) is designed to adjust the phase current on the asynchronous motor (10) with a predetermined torque.

5. An electromechanical braking system (1) having: The braking device according to any one of claims 1 to 4; a brake disc (50); and A brake shoe (41) is designed to be pressed against the brake disc (50) by the brake device.

6. The electromechanical brake system (1) according to claim 5, comprising a rotation speed sensor (61) which is designed to detect the rotation speed of the brake disc (50) or the rotation speed of a wheel (60) mechanically coupled to the brake disc (50), in, The control device (11) of the brake device is designed to control the asynchronous motor (10) using the detected rotational speed.

7. A method for operating an electromechanical brake system (1) actuated by an asynchronous motor (10), wherein: The method comprises the following steps: receiving ( S1 ) a target value (S) for a braking force to be adjusted; The asynchronous motor (10) is controlled (S2) using a target value (S) for the braking force to be set and a quasi-stationary rotor position of the asynchronous motor (10).

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