CONTROL UNIT FOR AN ELECTROMETAL BRAKE

Abstract

System for providing motor control for an electromechanical brake when a motor control fails, wherein the system comprises the following: an electromechanical braking mechanism (110) comprising a permanent magnet synchronous machine (215), a rotor position sensor that is configured to to detect the position of a rotor of the permanent magnet synchronous machine (215), a motor current sensor and an electronic control (115) designed to: Determine if at least one of the rotor position sensor and the motor current sensor is malfunctioning. Generating a control signal to control the permanent magnet synchronous machine (215) and Activating the permanent magnet synchronous machine (215) using the generated control signal to generate a stator magnetic field to operate the rotor of the permanent magnet synchronous machine (215), where the control signal is a stator magnetic flux strength, includes a frequency of the stator magnetic field and a predetermined angular velocity of the stator magnetic field.

Description

[0001] Embodiments relate to systems and methods for providing limited control for an electromechanical brake when a control system fails. BACKGROUND

[0002] In modern braking systems, vacuum brakes are being replaced by electromechanical and vacuum-free brakes (e.g., the iBooster brake developed by Robert Bosch GmbH). Electromechanical and vacuum-free brakes only consume electrical energy when the brakes are applied, thus saving fuel and reducing the vehicle's CO2 emissions, as no energy from the combustion engine is required to apply more pressure to the brakes.

[0003] Electromechanical brakes are controlled based on sensor inputs (for example, from a brake pedal travel sensor, a rotor position sensor of a permanent magnet synchronous machine, a current sensor of a permanent magnet synchronous machine, and the like). An electronic control unit that operates the electromechanical brake receives feedback from the sensors to ensure correct operation. If the electronic control unit does not receive feedback or if it receives faulty signals from the sensors, the electromechanical brake may be controlled incorrectly or not activated at all.

[0004] From EP 3 187 385 A1, a system for providing motor control for an electromechanical brake when a motor control fails is known, comprising the system: an electromechanical braking mechanism that incorporates a permanent magnet synchronous machine, a rotor position sensor that is configured to to detect the position of a rotor of the permanent magnet synchronous machine, a motor current sensor and an electronic control unit designed to do the following: Determine if at least one of the rotor position sensor and the motor current sensor is malfunctioning. Generating a control signal to control the permanent magnet synchronous machine and Activating the permanent magnet synchronous machine using the generated control signal to generate a stator magnetic field to operate the rotor of the permanent magnet synchronous machine. SUMMARY

[0005] It is therefore an object of the present disclosure to provide a system for providing limited control of the electromechanical brake in the event of a sensor failure in a control system. This object is achieved by a system for providing motor control with the features of claim 1 and by a method for providing motor control with the features of claim 10. Advantageous embodiments are found in the dependent claims.

[0006] One embodiment provides a system that implements motor control for an electromechanical brake in the event of a motor control failure. The system includes an electromechanical braking mechanism comprising a permanent magnet synchronous machine, a rotor position sensor configured to detect the position of the rotor of the permanent magnet synchronous machine, a motor current sensor, and an electronic control configured to determine whether at least one of the rotor position sensor and the motor current sensor is malfunctioning, to generate a control signal for controlling the permanent magnet synchronous machine, and to activate the permanent magnet synchronous machine using the generated control signal to generate a stator magnetic field for operating the rotor of the permanent magnet synchronous machine.The control signal includes a stator magnetic flux strength, a frequency of the stator magnetic field, and a predetermined angular velocity of the stator magnetic field.

[0007] One embodiment provides a method for providing motor control for an electromechanical brake in the event of a motor control failure. The method comprises determining, by means of an electronic control, whether a rotor position sensor or a current sensor is malfunctioning; generating—by means of the electronic control—a control signal for controlling a permanent magnet synchronous machine; and activating—by means of the electronic control—the permanent magnet synchronous machine using the generated control signal to generate a stator magnetic field for operating the rotor of the electromechanical brake's permanent magnet synchronous machine. The control signal includes a stator magnetic flux strength, a frequency of the stator magnetic field, and a predetermined angular velocity of the stator magnetic field.

[0008] Further aspects, features and embodiments will become apparent from the detailed description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS The Fig. Figure 1 shows a vehicle having a braking system according to one embodiment. The Fig. Figure 2 shows an electromechanical braking mechanism according to one embodiment. The Fig. Figure 3 shows an electronic control system according to one embodiment. The Fig. Figure 4 shows a method for controlling an electromechanical braking mechanism according to one embodiment. The Fig. Figure 5 shows a method for controlling an electromechanical braking mechanism according to one embodiment. DETAILED DESCRIPTION

[0009] Before embodiments are explained in detail, it should be noted that this disclosure, when applied, is not limited to the design details and component arrangements set forth in the following description or illustrated in the following drawings. Embodiments may be designed differently and implemented in practice in various ways or executed differently.

[0010] To implement various embodiments, a variety of hardware- and software-based devices, as well as a variety of different components, can be used. Furthermore, embodiments may include hardware, software, and electronic components or modules, which for the purposes of discussion may be presented and described as if the majority of the components were implemented exclusively in hardware. However, a person skilled in the art will recognize from reading this detailed description that in at least one embodiment, the electronics-based aspects of the invention may be implemented in software executable by one or more processors (which is stored, for example, on a non-volatile, computer-readable medium).For example, the “control units” and “controls” described in the description may include one or more electronic processors, one or more memory modules with a non-volatile, computer-readable medium, one or more input / output interfaces, one or more application-specific integrated circuits (ASICs), and various connections (such as a system bus) that connect the different components.

[0011] The Fig. Figure 1 shows a vehicle 100 having a braking system 105. The braking system 105 comprises an electromechanical braking mechanism 110 and an electronic control unit 115. The electromechanical braking mechanism 110 is communicatively connected to the electronic control unit 115 and hydraulically connected to the brakes 120 to 123, which are designed to be applied to the wheels 125 to 128.

[0012] In the Fig. In the embodiment shown in Figure 1, the vehicle 100 is a four-wheeled vehicle, such as a car, a bus, and the like. However, it is understood that the braking system 105 can be implemented in other vehicles with more or fewer wheels (for example, in a motorcycle).

[0013] An example of the electromechanical braking mechanism 110 is in the Fig. 2 shown.

[0014] The electromechanical brake mechanism 110 includes an input rod 205, a position sensor 210, a permanent magnet synchronous machine 215, a gear system 220, a reinforcement element 225 and a master brake cylinder 230.

[0015] The input rod 205 receives inputs from a vehicle operator 100 to actuate the remaining electromechanical braking mechanism 110. For example, the input rod 205 can be connected to a brake pedal that is pressed by the operator of the vehicle 100 to decelerate the vehicle 100. The input rod 205 moves in response to user inputs. In self-driving vehicles, the input rod 205 can be moved without input from a user (for example, by receiving a braking request from a separate electronic control unit). Alternatively, the input rod 205 can be moved by a motor or not at all. If the input rod 205 is not moved at all, the electronic control unit 115 can receive the braking request from the separate electronic control unit to actuate the electromechanical braking mechanism 110.

[0016] The displacement sensor 210 detects the movement of the input rod 205. For example, the displacement sensor 210 detects how far the input rod 205 moves from a starting position. The displacement sensor 210 is connected to the electronic control unit 115 and transmits the distance traveled by the input rod 205 to the electronic control unit 115.

[0017] The electronic control unit 115 determines control signals for the permanent magnet synchronous machine 215 (and, for example, determines a torque of the permanent magnet synchronous machine 215 based on the distance traveled by the input rod 205, which is received by the position sensor 210). The permanent magnet synchronous machine 215 is configured to drive the gear system 220. The gear system 220 converts a torque from the permanent magnet synchronous machine 215 into amplifying force for the amplifying element 225. The amplifying element 225 then applies a force based on the amplifying force to the master cylinder 230, where the applied force is converted into hydraulic pressure for actuating the brakes 120 to 123.

[0018] In a control system for the electromechanical braking mechanism 110, the electromechanical braking mechanism 110 can have sensors that detect the position of a rotor of the permanent magnet synchronous machine 215 (a rotor position sensor) and a sensor that detects a current of the permanent magnet synchronous machine (a motor current sensor). These sensors are used as feedback mechanisms for the electronic control 115, as described below.

[0019] In some embodiments, the master cylinder 230 also includes a master cylinder pressure sensor. The master cylinder pressure sensor detects the hydraulic pressure in the master cylinder. The master cylinder pressure sensor can be connected to the electronic control unit 115 for communication purposes and can also be configured to transmit the hydraulic pressure of the master cylinder 230 to the electronic control unit 115.

[0020] The Fig. Figure 3 shows the electronic control unit 115 according to one embodiment. The electronic control unit 115 has an input / output interface 310, an electronic processor 320 (such as a programmable electronic microprocessor, a microcontroller, and similar devices), and a memory 330 (for example, non-volatile, machine-readable memory). The electronic processor 320 is communicatively connected to the memory 330 and the input / output interface 310. The electronic processor 320 is configured, in coordination with the memory 330 and the input / output interface 310, to implement, among other things, the methods described herein.

[0021] It is understood that the electronic control 115 may have a variety of electrical and electronic components - not described here - which provide power, operational control and protection to the components and modules within the electronic control 115.

[0022] The electronic control 115 can be implemented in several independent controllers (for example, programmable electronic control units), each configured to perform specific functions or sub-functions. Additionally, the electronic control 115 can include submodules with additional electronic processors, memory, or application-specific integrated circuits (ASICs) for handling input / output functions, processing signals, and applying the methods described below. In further embodiments, the electronic control 115 has additional, fewer, or different components.

[0023] The Fig. Figure 4 shows a control system 400 for the electromechanical braking mechanism 110. The control system 400 is implemented using the electronic controller 115. For example, a master controller 405 can be implemented as a sub-controller or a microprocessor within the electronic controller 115, or as a set of software instructions stored in the memory 330. The master controller 405 receives a signal from the position sensor 210 indicating how far the input rod 205 has been moved. Depending on the distance traveled, the master controller 405 determines a target motor speed (“target motor speed”) for the permanent magnet synchronous machine 215.

[0024] The master controller 405 sends the target motor speed to a motor speed controller 410. Like the master controller 405, the motor speed controller 410 can be implemented as a sub-controller or microprocessor in the electronic control unit 115, or as software instructions stored in the memory 330. The motor speed controller 410 receives the target motor speed and determines a target motor torque based on the target motor speed.

[0025] The motor speed controller 410 sends the target motor torque (“target motor torque”) to a field-oriented controller 415 (which is implemented similarly to the higher-level controller 405). The field-oriented controller 415 relies on a voltage measurement 416 from a power supply, a motor current measurement 417 from the motor current sensor, and a rotor position measurement 418 from the rotor position sensor. The field-oriented controller 415 outputs a duty cycle that, depending on the target motor torque, the voltage measurement 416, the motor current measurement 417, and the rotor position measurement 418, specifies a target voltage for each of the three phases of the permanent magnet synchronous machine 215. The duty cycle of each of the three phases generates a stator voltage space vector that determines the motor torque and the rotation of the rotor.

[0026] The stator voltage space vector is sent to the permanent magnet synchronous machine 215, which applies the motor torque to the gear system 220, which in turn generates an output force and output stroke 420 at the amplifying element 225. This output force and output stroke 420 are applied to the master brake cylinder 230, thereby increasing the hydraulic pressure in the master brake cylinder 230 and applying the hydraulic pressure to the brakes 120 to 123 (at block 425).

[0027] In some embodiments, the generated hydraulic pressure is measured by a master cylinder pressure sensor as a master cylinder hydraulic pressure measurement (430), which is then used as feedback by the higher-level controller 405. For example, the higher-level controller 405 can determine an expected hydraulic pressure as a function of the target engine speed. The higher-level controller 405 then compares the received master cylinder hydraulic pressure measurement 430 with the expected hydraulic pressure to determine whether the components of the electromechanical brake mechanism 110 are functioning correctly.

[0028] The motor speed controller 410 also receives the rotor position measurement 418. This enables a more accurate calculation of the target motor torque.

[0029] The field-oriented controller 415 relies on precise measurements, such as the rotor position measurement 418, from the various sensors from which it receives signals, to apply the correct amount of braking force received from a braking request (via the input rod 205 or another braking request). If, for example, the motor current sensor or the rotor position sensor malfunctions, the field-oriented controller 415 cannot supply the permanent magnet synchronous machine 215 with the correct duty cycles. This results in an incorrect amount of braking force being applied to the brakes 120 to 123.

[0030] To provide redundancy and a fail-safe system in case one or more sensors fail, a 500 control system is required. Such a 500 control system is available in the Fig. 5 shown.

[0031] The electronic control unit 115 is designed to determine whether one or more sensors (in particular the motor current sensor and the rotor position sensor) are malfunctioning. For example, the electronic control unit 115 is designed to determine when one or more sensors are not sending a signal to the electronic control unit 115. In another example, the electronic control unit 115 may receive feedback from the one or more sensors, but the one or more sensors send data back to the electronic control unit 115 which, when compared to an expected value (such as a value of the pressure in the master brake cylinder 230), are determined to be incorrect values.

[0032] The control system 500 continues to use the master controller 405 to determine a target motor speed for the permanent magnet synchronous machine 215, as described above. However, because one or more sensors (such as the motor current sensor or the rotor position sensor) are not functioning correctly, the motor speed controller 410 and the field-oriented controller 415 may not function correctly.

[0033] In the event that the motor speed control 410 and / or the field-oriented controller 415 malfunction, the electronic control 115 (using the higher-level controller 405) determines a target motor speed ("target motor speed") and sets a limit to the target motor speed gradient (block 505). Since the electronic control 115 does not receive feedback from the motor current sensor or the rotor position sensor, it sets a maximum speed limit and a maximum permissible speed change for the permanent magnet synchronous machine 215. As described below, if the target motor speed is too high (for example, outside the operating range of the stator magnetic field of the permanent magnet synchronous machine 215), the rotor of the permanent magnet synchronous machine 215 may rotate asynchronously with the stator magnetic field, resulting in incorrect braking behavior.

[0034] To operate the permanent magnet synchronous machine 215 when the motor current sensor and / or the rotor position sensor are not functioning, the electronic control unit 115 generates a control signal to control the permanent magnet synchronous machine 215 to generate a stator magnetic field. The stator magnetic field is generated at a predetermined angular velocity (an angular velocity specified by the electronic control unit 115).

[0035] When the stator magnetic field is generated by the permanent magnet synchronous machine 215, this causes the rotor of the permanent magnet synchronous machine 215 to rotate. The stator magnetic field rotates at the specified angular velocity, and the rotor of the permanent magnet synchronous machine 215 rotates synchronously with the stator magnetic field. When the permanent magnet synchronous machine 215 generates the stator magnetic field, the electronic control 115 operates the rotor of the permanent magnet synchronous machine 215 as a stepper motor. With each step change of one of the rotating field axis of the stator magnetic field, the rotor of the permanent magnet synchronous machine 215 changes its position relative to that position of the rotating field axis.

[0036] Due to inertial and frictional forces, the rotor of the permanent magnet synchronous machine 215 may follow the position of the rotating field axis with a delay. To prevent or minimize this delay, the rate of change of the angular velocity of the stator magnetic field (a frequency of the stator magnetic field) must be limited by limiting the target motor speed gradient 505.

[0037] When the permanent magnet synchronous machine 215 (using the gear system 220 and the amplifying element 225) applies hydraulic pressure to the master brake cylinder 230, it is subjected to a load torque. As the load torque increases, the rotor of the permanent magnet synchronous machine 215 may lag behind the rotating field axis and follow it at an angle. For example, while the rotor of the permanent magnet synchronous machine 215 still rotates synchronously with the rotating field axis, its position follows the position of the rotating field axis at an angle (such as 10 degrees behind the position of the rotating field axis) at the same angular velocity as the stator magnetic field. As long as the internal torque of the permanent magnet synchronous machine 215 is greater than the load torque, the rotor follows the rotating field axis synchronously, but at an angle.

[0038] To ensure that the internal torque of the permanent magnet synchronous machine 215 is always higher than a load torque (and thus to ensure that the rotor of the permanent magnet synchronous machine 215 is not asynchronous to the rotating axis of the stator magnetic field), the frequency and stator magnetic flux strength of the stator magnetic field are selected such that sufficient internal torque is available to meet the braking requirement. The electronic control 115 therefore determines the frequency of the stator magnetic field and a stator voltage space vector (at block 510) as a function of the specified stator magnetic flux strength used to operate the permanent magnet synchronous machine 215 and thus to control the internal torque of the permanent magnet synchronous machine 215.

[0039] Two different configurations enable the electronic control unit 115 to control the internal torque of the permanent magnet synchronous machine 215. The first configuration allows the electronic control unit 115 (in block 515) to receive a hydraulic pressure reading from the master brake cylinder 230 via a master brake cylinder pressure sensor. The hydraulic pressure is a measure of the pressure in the master brake cylinder 230, indicating the load placed on the permanent magnet synchronous machine 215 when pressure is applied to the master brake cylinder 230 (via the gear system 220 and the amplifying element 225). Based on the hydraulic pressure, the electronic control unit 115 determines the frequency and flux strength of the stator magnetic field, which is then generated by the permanent magnet synchronous machine 215.

[0040] The stator magnetic flux strength is determined based on a stator current space vector, which in turn is based on the length of a stator voltage space vector.

[0041] The second embodiment involves the electronic control 115 generating a stator voltage space vector of fixed length, which in turn determines the stator magnetic flux strength. For example, the length of the stator voltage space vector can be set such that the internal torque of the permanent magnet synchronous machine 215 is always greater than would be required by the pressure (load torque) of the master brake cylinder 230.

[0042] In some embodiments, when the target engine speed gradient reaches its limit, the electronic control unit 115 sets a flag (block 520) indicating that no higher engine speed should be requested. For example, once the target engine speed gradient has been determined, the electronic control unit 115 can request an engine speed below the limit (e.g., for a braking request that does not require a high engine speed). If the electronic control unit 115 receives a new braking request (e.g., if the input rod 205 is further depressed by a driver 100), the electronic control unit 115 can then request a higher engine speed. When the target engine speed gradient is reached, the electronic control unit 115 sets the flag at block 520. If a new braking request is received after the flag has been set, the electronic control unit 115 does not request a higher engine speed.A requirement for a rotational speed that is higher than the limit of the target motor speed gradient can cause the rotor of the permanent magnet synchronous machine 215 to become asynchronous with respect to the rotating field axis of the stator magnetic field generated by the permanent magnet synchronous machine 215.

[0043] In some embodiments, the electronic control 115 determines the limit of the target motor speed gradient partly based on a supply voltage from a power supply motor (in block 525). For example, if less power is available for the permanent magnet synchronous machine 215, the limit of the target motor speed gradient can be lower to compensate for the fact that less power is available to apply torque to the permanent magnet synchronous machine 215.

[0044] Thus, the embodiments described herein generally provide systems and methods for implementing motor control for an electromechanical brake when motor control fails.

[0045] Various features, advantages and embodiments are set forth in the claims below.

Claims

[1] System for providing motor control for an electromechanical brake when a motor control fails, wherein the system comprises: an electromechanical braking mechanism (110) comprising a permanent magnet synchronous machine (215), a rotor position sensor that is configured to to detect the position of a rotor of the permanent magnet synchronous machine (215), a motor current sensor and an electronic control (115) designed to: Determine if at least one of the rotor position sensor and the motor current sensor is malfunctioning. Generating a control signal to control the permanent magnet synchronous machine (215) and Activating the permanent magnet synchronous machine (215) using the generated control signal to generate a stator magnetic field to operate the rotor of the permanent magnet synchronous machine (215), where the control signal is a stator magnetic flux strength, includes a frequency of the stator magnetic field and a predetermined angular velocity of the stator magnetic field. [2] System according to claim 1, further comprising a master brake cylinder pressure sensor. [3] System according to claim 2, wherein the electronic control (115) receives a master brake cylinder pressure from the master brake cylinder pressure sensor and adjusts a stator magnetic flux strength of the permanent magnet synchronous machine (215) depending on the master brake cylinder pressure sensor. [4] System according to claim 1, wherein a stator magnetic flux strength is set by means of the electronic control (115) by applying a stator voltage space vector. [5] System according to claim 1, wherein the rotor of the permanent magnet synchronous machine (215) rotates synchronously with the stator magnetic field of the permanent magnet synchronous machine (215). [6] System according to claim 1, wherein an internal torque of the permanent magnet synchronous machine (215) is controlled by the electronic control (115) such that it is higher than a load torque of the permanent magnet synchronous machine (215). [7] System according to claim 1, wherein the electronic control (115) limits a maximum permissible motor speed gradient to prevent the rotor of the permanent magnet synchronous machine (215) from becoming asynchronous to the stator magnetic field. [8] System according to claim 7, wherein the maximum permissible motor speed gradient is based on a maximum permissible frequency of the stator magnetic field. [9] System according to claim 7, wherein a maximum permissible motor speed gradient is based on a supply voltage. [10] Method for providing motor control for an electromechanical brake when a motor control fails, the method comprising: Determine – using an electronic control (115) – whether a rotor position sensor or a current sensor is malfunctioning, Generating – by means of the electronic control (115) – a generated control signal for controlling a permanent magnet synchronous machine (215), and Activate - by means of the electronic control (115) - the permanent magnet synchronous machine (215) using the generated control signal to generate a stator magnetic field to operate the rotor of the permanent magnet synchronous machine (215), wherein the generated control signal includes a stator magnetic flux strength, a frequency of the stator magnetic field and a predetermined angular velocity of the stator magnetic field. [11] Method according to claim 10, further comprising receiving a master brake cylinder pressure from a master brake cylinder pressure sensor by means of the electronic control (115). [12] Method according to claim 11, wherein a stator magnetic flux strength of the permanent magnet synchronous machine (215) is set by means of the electronic control (115) based on the master brake cylinder pressure sensor. [13] Method according to claim 10, further comprising adjusting a stator magnetic flux strength of the permanent magnet synchronous machine (215) by means of the electronic control (115) by applying a stator voltage space vector. [14] Method according to claim 10, wherein the rotor of the permanent magnet synchronous machine (215) rotates synchronously with the stator magnetic field of the permanent magnet synchronous machine (215). [15] Method according to claim 10, further comprising controlling an internal torque of the permanent magnet synchronous machine (215) by means of the electronic control (115) such that it is higher than a load torque of the permanent magnet synchronous machine (215). [16] Method according to claim 10, further comprising limiting a maximum permissible motor speed gradient by means of the electronic control (115) to prevent the rotor of the permanent magnet synchronous machine (215) from becoming asynchronous to the stator magnetic field. [17] Method according to claim 16, wherein the maximum permissible motor speed gradient is based on a maximum permissible frequency of the stator magnetic field. [18] Method according to claim 16, wherein a maximum permissible motor speed gradient is based on a supply voltage.

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