Method and device for detecting a rotation angle of a rotor in an electric motor by means of counters with opposite counting directions.

Abstract

Method for detecting a rotation angle of a rotor in an electric motor, in particular for a power steering device of a motor vehicle, with a sensor unit (MR) which is designed to generate a sensor signal (S_MR) which is representative of a rotation angle of the rotor, and at least two counting units (CU1, CU2) each having at least one counter (CNT1, CNT2), wherein the at least two counters (CNT1, CNT2) of the at least two counting units (CU1, CU2) are designed to either increment or decrement depending on the sensor signal, characterized in that depending on the sensor signal one of the counters (CNT1, CNT2) of the at least two counting units (CU1, CU2) is incremented and the other counter of the at least two counting units (CU1, CU2) is decremented, and that the sum of the counter readings (SUM_CNT) corresponds to a predefined reference value, in particular the maximum value of a counter range of the counters (CNT1, CNT2).

Description

[0001] The invention relates to a method and a device for detecting a rotation angle, in particular by means of the number of revolutions, of a rotor in an electric motor, in particular for a power steering device of a motor vehicle, according to the preamble of claims 1 and 6, as well as a steering system for a motor vehicle with a device according to the invention.

[0002] Modern power steering systems typically include electric power steering motors to assist the steering effort of a motor vehicle driver. The power steering motors assist the driver in achieving their intended steering direction as long as they apply the appropriate torque to a steering wheel connected to the steering system. The electric power steering motor in the steering system is typically controlled by a control and / or regulating unit.

[0003] To operate the control and / or regulating unit, the current position of the electric power steering motor's rotor is required, along with other state variables of the electric power steering motor. The rotor position is typically detected using a sensor that specifies an absolute angular position of the rotor within one full rotation of the rotor relative to a reference point. If the transmission ratio between rotations of the steering wheel and corresponding rotations of the electric power steering motor's rotor is specified over the entire steering angle range, and the number of rotor revolutions is known, the sensor used for the control and / or regulating unit can also be used to determine the absolute steering angle of the steering wheel and / or steerable wheels connected to the steering system.

[0004] Patents EP 2 050 658 B1 and EP 2 053 363 B1 disclose steering systems with a sensor unit configured to generate a sensor signal representative of a steering angle of the steering wheel, and an evaluation unit with two counter units for evaluating the sensor signal. The redundancy of the counter units provides increased reliability.

[0005] From the patent specification US 2005 / 0177338 A1, another method for detecting a rotation angle of a rotor is known, wherein counting units are provided which either increment or decrement a counter depending on a sensor signal.

[0006] However, there are still other types of errors that cannot be detected even with such a system. For example, it may happen that an error is present in one or both counter units, but the difference is still less than or equal to 1, and thus no error is detected in the system.

[0007] The invention was therefore based on the object of improving error detection in the known devices.

[0008] The problem is solved by a method of the type mentioned above, according to which, depending on the same sensor signal, one of the counters of the at least two counter units is incremented and the other of the at least two counter units is decremented. In contrast to the prior art, the simple redundancy of the counters is enhanced by having different counting directions, which enables more extensive counter verification. Thus, one sensor signal leads to different counts by the counters of the counting units.

[0009] The invention is based on the fundamental idea that errors in the counting unit are more clearly reflected in the counter values ​​when the counters have different target directions or count in opposite directions. The error type mentioned above can be identified using the method according to the invention.

[0010] It is preferred to implement the method such that the sum of the counter readings corresponds to a predefined reference value, in particular the maximum value of a counter range of the counters. For this purpose, the counters have a number range that they can map, e.g., 0 to 128. This typically depends on the bit depth with which the counters operate. The reference value corresponds to the maximum or highest value of the number range, e.g., 128.

[0011] The method according to the invention is advantageously further developed in that the counters (CNT1, CNT2) are set to different counter readings during initialization, in particular when a supply voltage is applied. This is necessary because the counter structures are normally permanently powered, and reinitialization of the counters is only necessary after an unforeseen disconnection from the current or voltage source. This can occur, for example, when replacing the vehicle battery. During this reinitialization of the counters, it is advantageous to set the counter readings so that the initial difference between the counters is as large as possible.

[0012] Therefore, it is particularly preferable to further develop the method such that one of the counters is set to the maximum value of the counter range and the other counter is set to the minimum value of the counter reading. The first counter is then set, for example, to the minimum value of 0 and the second counter to the maximum value of 128. The opposite counting method of the counters leads to intersecting counter readings, from which further checks of the counter readings can be performed.

[0013] The method according to the invention is advantageously further developed in that an error is detected as soon as the sum of the counter readings deviates from the reference value. Since one counter increments and the second counter decrements, the sum of the counters remains constant. If the sum deviates from the constant reference value, an error is detected.

[0014] According to a further development of the method, it is particularly preferred to indicate an error as soon as the sum of the counter readings deviates from the reference value by two increments or decrements. This embodiment is particularly advantageous when the counters count with a time offset from one another or when a larger tolerance range in the counter values ​​is acceptable.

[0015] The object is further achieved according to a second aspect of the invention by means of a device of the type mentioned above, in which the evaluation unit is designed such that the counters have opposite counting directions. In particular, the device according to the invention comprises counter units of the evaluation unit in which the counters are configured such that they have opposite counting directions.

[0016] The device according to the invention is further developed by an error detection unit which detects an error as soon as the sum of the counter readings of the counters deviates from a predetermined reference value.

[0017] An advantageous embodiment of the device according to the invention is particularly preferred, according to which an error is detected as soon as the sum of the counter readings of the counters deviates from the reference value by more than one increment or decrement.

[0018] The above-mentioned object is further achieved by means of a steering system for a motor vehicle with a device according to one of the above-mentioned embodiments.

[0019] Embodiments of the invention are explained in more detail below with reference to the schematic drawings. They show: Fig. 1 a schematic representation of an evaluation unit, Fig. 2 a temporal representation of sensor values ​​of a sensor, Fig. 3 a temporal representation of an increment signal and decrement signal of the first and second counter,

[0020] Elements of the same design or function are marked with the same reference symbols throughout the figures.

[0021] In Fig. 1 shows an evaluation unit ASIC which is known from the prior art from EP 2 050 658 B1 and is used in a steering system for a motor vehicle.

[0022] The ASIC evaluation unit is designed as an application-specific integrated component and is used to detect changes in the steering angle or the rotation angle of the rotor element. For redundancy reasons, the ASIC evaluation unit comprises a first counting unit CU1 and a second counting unit CU2, each of which is assigned a sensor signal S_MR from the MR sensor on the input side.

[0023] The sensor unit MR is designed to generate a sensor signal S_MR that is representative of the rotor's rotation angle. The evaluation unit ASIC comprises two counting units CU1, CU2, each of which has at least one counter CNT1, CNT2. The two counters CNT1, CNT2 of the counting units CU1, CU2 are designed to either increment or decrement depending on the sensor signal S_MR.

[0024] The MR sensor for detecting the position of the rotor of the electric power steering motor is typically designed as a magnetoresistive measuring sensor that delivers a sine and a cosine signal as the sensor signal S_MR to the evaluation unit ASIC. An applied sensor signal value of the sine and cosine signals can be directly assigned to an angle of the rotor of the electric power steering motor relative to a specified reference point.

[0025] Furthermore, the MR sensor is designed in such a way that multiple rotations of the rotor typically cannot be detected by the MR sensor itself. In principle, multiple MR sensors can also be used to detect the position of the rotor; for example, each MR sensor can be assigned to a counting unit. In an advantageous embodiment, the MR sensor can be controlled by the ASIC evaluation unit, e.g., continuously or intermittently. This allows the MR sensor to be operated with particularly low power consumption.

[0026] The first counting unit CU1 comprises a first analog unit AFE1, a first state machine SM1, and a first counter CNT1. The first analog unit AFE1 is assigned the sensor signal S_MR on the input side. On the output side, the first analog unit AFE1 is assigned to the first state machine SM1 via a first state signal S_STATE1. The first analog unit AFE1 can be viewed as the interface between the analog sensor signal S_MR and the digital first state signal S_STATE1.

[0027] The first state machine SM1 is assigned the first state signal S_STATE1 on the input side. Depending on this signal, the first state machine SM1 generates a first increment signal S_UP1 and a first decrement signal S_DOWN1 on the output side, which are assigned to the first counter CNT1 on the input side. The first counter CNT1 is designed as an up- and down-counter and increments its current counter reading depending on the first increment signal S_UP1 and decrements its current counter reading depending on the first decrement signal S_DOWN1. On the output side, the first counter CNT1 generates a first counter signal S_CNT1.

[0028] The second counting unit CU2 is designed in principle similarly to the first counting unit CU1. It comprises a second analog unit AFE2, a second state machine SM2, and a second counter CNT2. In contrast to the first counting unit CU1, the second counting unit CU2 has a state machine whose increment and decrement signals S_UP2 and S_DOWN2 are output in the opposite direction to the first state machine. The counters CNT1 and CNT2 therefore have opposite counting directions. Depending on the sensor signal S_MR, the first counter CNT1 of the first counting unit CU1 is incremented, while the second counter CNT2 of the second counting unit CU2 is decremented. The opposite counting direction can also be achieved by appropriately designing the second counter CNT2 itself.

[0029] Since the two counter units CU1 and CU2, along with the associated state machines SM1 and SM2 and the two analog units AFE1 and AFE2, are permanently supplied with power, even when the ignition is off, they are capable of detecting rotary movements even when the ignition is off. More than two counter units can also be used.

[0030] The evaluation unit ASIC also comprises a signal processor SP, to which the first counter signal S_CNT1 and the second counter signal S_CNT2, as well as an angle signal S_A, which is representative of the currently valid sensor value of the sensor MR, are assigned on the input side. The signal processor SP comprises an error detection unit ERRD and a decision unit DU. The first and second counter signals S_CNT1 and S_CNT2 are assigned on the input side to the decision unit DU and the error detection unit ERRD. Furthermore, the angle signal S_A is assigned to the decision unit DU. The decision unit DU generates a signal with the number of revolutions S_CNT on the output side, which represents the number of revolutions; this information is necessary for determining the steering angle. The error detection unit ERRD generates an error status signal S_ERR on the output side.An error is detected as soon as the sum of the counter readings of counters CNT1 and CNT2 deviates from a specified reference value. An error can also be detected if the deviation lies outside a tolerance range, for example, if the sum of the counter readings of counters CNT1 and CNT2 deviates from the reference value by more than one increment or decrement.

[0031] The signal processor SP with the decision unit DU and the error detection unit ERRD is designed to be switched on or off by means of the ignition of the motor vehicle.

[0032] The evaluation unit ASIC is typically connected to the control unit of an electric power steering (EPS) via a communication interface. The communication interface is typically implemented as an SPI interface. The information from the ASIC is transmitted to the EPS ECU via the ASIC's communication interface. The control unit of the electric power steering (EPS) also has communication interfaces, enabling communication with the steering, ESP, and other vehicle control units via a CAN or other bus system, such as Flexray.

[0033] Based on the Fig. 2 and Fig. 3 the method according to the invention is explained in more detail.

[0034] In Fig. Figure 2 shows the angle signal S_A or sensor angle signal, which is representative of the currently valid sensor value of the sensor MR. The angle signal S_A represents the angle φ with values ​​between 0° and 360°, whereby the full measuring range of the sensor MR covers the entire scan from 0° to 360°. Typically, the absolute angle of the angle signal S_A is particularly easy to determine by calculating the arc tangent from the sine and cosine signals of the sensor signal S_MR. This arc tangent calculation also takes place in the signal processor SP. Fig. 2 shows three full revolutions of the sensor angle signal.

[0035] In addition to the angle signal S_A, three state cycles of the first state signal S_STATE1 are shown. The first state signal S_STATE1, generated by the first analog unit AFE1, can assume four different states: a state 0, a state 1, a state 2, and a state 3. Due to the four different states, the first state signal S_STATE1 is typically bivalent, meaning it is fed to the first state machine SM1 via two signal lines.

[0036] If, for example, the sensor angle signal S_A is angularly rotated by an angle φ between 0° and 90° relative to the specified reference point, the first state signal S_STATE1 is generated by the first analog unit AFE1 in such a way that state 3 is fed to the input side of the first state machine SM1. If, for example, the sensor angle signal S_A is rotated by an angle φ between 90° and 180° relative to the specified reference point, state 2 is fed to the first state machine SM1. For a position between 180° and 270°, state 0 is specified, and for a position between 270° and 360°, state 1 is specified. Typically, the first analog unit AFE1 comprises comparators and clock-controlled switching elements, such as flip-flops, to generate the four different states.

[0037] Thus, the four states of the first state signal S_STATE1 generated by the first analog unit AFE1 each represent a predetermined angular range of the rotor of the electric power steering motor.

[0038] If the angle information of the sensor angle signal S_A rotates in a predetermined first direction of rotation with ascending angle values, ie starting from the angle φ equal to 0° up to the angle φ equal to 360°, the states 3 2 0 1 are passed through one after the other. In an opposite second direction of rotation of the rotor, the states 1 0 2 3 are passed through one after the other.

[0039] The second analog unit AFE2 is designed analogously to the first analog unit AFE1 and ideally generates a second state signal S_STATE2 that is identical to the first state signal S_STATE1.

[0040] Furthermore, the first and second increment signals S_UP1 and S_DOWN2 are shown for the case where the rotor of the electric motor rotates multiple times in one direction. Depending on a predetermined state transition of the first and second state signals S_STATE1 and S_STATE2, a positive pulse of the first increment signal S_UP1 is generated by the first state machine SM1, whereas a positive pulse of the second decrement signal S_DOWN2 is generated by the second state machine SM1. The first state machine SM1 generates the positive pulse of the first increment signal S_UP1 during a transition from state 3 to state 2, while the second state machine SM2 generates the positive pulse of the second decrement signal S_DOWN2 during a transition from state 0 to state 1.In principle, other state transitions are also conceivable, whereby it is advantageous to ensure that the relevant state transition of the first state machine SM1 differs from the relevant state transition of the second state machine SM2.

[0041] The first increment signal S_UP1 is thus angularly offset from the second decrement signal S_DOWN2. With this predefined first direction of rotation of the rotor, no positive pulse is generated from the first decrement signal S_DOWN1 and the second increment signal S_UP2.

[0042] If, however, a transition from state 2 to state 3 occurs with the second, opposite direction of rotation of the rotor, a positive pulse of the first decrement signal S_DOWN1 is generated (not shown), while a transition from state 1 to state 0 generates a positive pulse of the second increment signal S_UP2 (not shown). Analogous to the case of the first direction of rotation, the increment signals S_DOWN1 and S_UP2 are angularly offset from one another. With a given second direction of rotation of the rotor, no positive pulse of the first increment signal S_UP1 and the second decrement signal S_DOWN2 is generated.

[0043] Depending on the first and second increment signals S_UP1 and S_UP2 and the first and second decrement signals S_DOWN1 and S_DOWN2, the first and second counters CNT1 and CNT2 are also incremented or decremented in opposite counting directions.

[0044] By means of the decision unit DU in the signal processor SP of the evaluation unit ASIC in Fig. 1, after the ignition is switched on, a counter reading of the two counters CNT1 and CNT2 is selected depending on the angle signal S_A, which is transmitted via the communication interface to the steering or ESP control unit. As shown in Fig. 2 as hatched areas for the first and second counters CNT1 and CNT2, an incrementation time and thus also a decrementation time are not clearly specified, but can be shifted in time due to inaccuracies that can be attributed, for example, to component tolerances and noise components in the sensor signal S_MR. Reading out the respective counter reading in these ranges is therefore avoided. If, for example, the angle signal S_A specifies the angle φ between 0° and 180°, the decision unit DU selects the counter reading of the second counter CNT2 because no change in the counter reading occurs within this angular range. If the angle signal S_A specifies the angle φ between 180° and 360°, the decision unit DU selects and transmits the counter reading of the first counter CNT1 because no change in the counter reading occurs within this angular range.

[0045] Using the error detection unit ERRD in the signal processor SP, the counter readings of the two counters CNT1 and CNT2 are compared after the vehicle's ignition is switched on. The sum of the counter readings must correspond to a predefined reference value, regardless of the angular position. The reference value is equal to the maximum value of a counter range of the counters CNT1 and CNT2. The maximum value of the counter range varies depending on the bit depth of the counters CNT1 and CNT2.

[0046] An error is detected as soon as the sum of the counter readings of counters CNT1 and CNT2 deviates from the reference value. Alternatively, the method can also be configured so that an error is detected as soon as the sum of the counter readings of counters CNT1 and CNT2 deviates from the reference value by more than one increment or decrement.

[0047] In the event that a disconnection from the power source, e.g. vehicle battery, has occurred, after re-applying the supply voltage, the counters CNT1, CNT2 are set to different counter readings, with the first counter CNT1 being set to the minimum value of the counter range, i.e. 0, and the other counter CNT2 being set to the minimum value of the counter range.

[0048] The task of the decision unit DU and the error detection unit ERRD can also be implemented as a program in the signal processor SP and processed by this.

[0049] In Fig. Figure 3 shows the increment signals S_UP1, S_UP2 and the decrement signals S_DOWN1, S_DOWN2, an idealized counter change of the first and second counters CNT1, CNT2, and the sum of the counters SUM_CNT as a function of the rotor's rotation angle φ. The abscissa represents the time axis.

[0050] The counter readings of counters CNT1 and CNT2 are assumed to be five. It is further assumed that the ignition is switched off with this predetermined counter reading. If, for example, the angle of rotation of the rotor is changed using the steering wheel, or if, for example, the vehicle rolls against a curb with its steerable wheels while the ignition is switched off, thereby changing the steering angle in the first direction of rotation, the ASIC evaluation unit, which is still switched on despite the ignition being switched off, detects a change in the steering angle and increments the first counter CNT1 to a count of six when a rising edge of the first increment signal S_UP1 is present. If the steering angle of the steerable wheels is changed further in the first direction of rotation, the first counter CNT1 is incremented to a count of seven when there is a further rising edge of the first increment signal S_UP1.If the steering angle of the steering wheel and / or the steerable wheels is now changed in the opposite second direction of rotation, the counter value is decremented by one to a value of six upon a rising edge of the applied first decrement signal S_DOWN1. Similarly, the second counter CNT2 is incremented or decremented using the increment signal S_UP2 or decrement signal S_DOWN2, respectively, with the counting direction of the second counter being opposite to the counting direction of the first counter.

[0051] The sum of the counter readings SUM_CNT remains within the range of the reference value, here 10, with a tolerance of, here ± 1. As soon as the sum of the counter readings SUM_CNT leaves this range, the error detection unit ERRD detects an error.

[0052] In addition to using the two counting units CU1 and CU2 of the evaluation unit when the vehicle's ignition is off, it is also possible to use the unit when the ignition is on. The steering angle determined by the evaluation unit ASIC can be used, for example, for plausibility monitoring.

[0053] In addition to using the MR sensor of the rotor of the electric power steering motor as a steering angle sensor, other sensors known to those skilled in the art are also conceivable for detecting the steering angle of the motor vehicle, in particular those that detect a change in the steering angle by means of the ASIC evaluation unit when the ignition is switched off. Particularly preferred in this case is the use of the device according to the invention with a rotation angle sensor device comprising a chip housing for accommodating integrated circuits and a sensor unit for detecting the rotor angle, wherein the sensor unit has two sensors that are arranged in the chip housing and detect the rotor angle independently of one another. This is preferably a sensor unit with a magnetoresistive sensor and / or a Hall sensor.

Claims

[1] Method for detecting a rotation angle of a rotor in an electric motor, in particular for a power steering device of a motor vehicle, with a sensor unit (MR) which is designed to generate a sensor signal (S_MR) which is representative of a rotation angle of the rotor, and at least two counting units (CU1, CU2) each having at least one counter (CNT1, CNT2), wherein the at least two counters (CNT1, CNT2) of the at least two counting units (CU1, CU2) are designed to either increment or decrement depending on the sensor signal, characterized bythat, depending on the sensor signal, one of the counters (CNT1, CNT2) of the at least two counter units (CU1, CU2) is incremented and the other counter of the at least two counter units (CU1, CU2) is decremented, and that the sum of the counter readings (SUM_CNT) corresponds to a predefined reference value, in particular the maximum value of a counter range of the counters (CNT1, CNT2). [2] Method according to one of the preceding claims, characterized by that the counters (CNT1, CNT2) are set to different counter values ​​during initialization, especially when a supply voltage is applied. [3] Method according to one of the claims, characterized by that one of the counters (CNT1) is set to the maximum value of the counter range and the other counter (CNT2) is set to the minimum value of the counter reading. [4] Method according to one of the preceding claims, characterized bythat an error is detected as soon as the sum of the counter readings (SUM_CNT) of the counters (CNT1, CNT2) deviates from the reference value. [5] Method according to one of the preceding claims, characterized by that an error is detected as soon as the sum of the counter readings of the counters (CNT1, CNT2) deviates from the reference value by more than one increment or decrement. [6] Device for detecting a rotation angle of a rotor in an electric motor, in particular for a power steering device of a motor vehicle, with a sensor unit (MR) which is designed to generate a sensor signal (S_MR) which is representative of a rotation angle of the rotor, and an evaluation unit (ASIC) for evaluating the sensor signal (S_MR) of the sensor unit (MR), wherein the evaluation unit (ASIC) has at least two counting units (CU1, CU2) each with at least one counter (CNT1, CNT2), wherein the at least two counters (CNT1, CNT2) of the at least two counting units (CU1, CU2) are designed to either increment or decrement depending on the sensor signal, characterized by that the evaluation unit (ASIC) is designed such that the counters (CNT1, CNT2) have opposite counting directions, and that the sum of the counter readings (SUM_CNT) corresponds to a predefined reference value, in particular the maximum value of a counter range of the counters (CNT1, CNT2). [7] Device according to claim 6, characterized by an error detection unit that detects an error as soon as the sum of the counter readings (SUM_CNT) of the counters (CNT1, CNT2) deviates from a specified reference value. [8] Device according to one of the preceding claims, characterized by that an error is detected as soon as the sum of the counter readings (SUM_CNT) of the counters (CNT1, CNT2) deviates from the reference value by more than one increment or decrement. [9] Steering system for a motor vehicle with a device according to one of claims 6 to 8.

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