JP2009090749A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of continuing the power assist for a predetermined time even when the difference between the main torque signal and the sub torque signal is large. <P>SOLUTION: In the electric power steering device having a torque sensor capable of outputting two torque signals, a motor, a steering assist command value computer, a motor drive circuit and a control device having a torque signal changing unit, the torque sensor has a first switching means for short-circuiting middle points of each arm of a torque detection bridge circuit. The control device has an abnormality diagnosis means which monitors the difference between the two torque signals, short-circuiting the first switching means when the period during which the difference exceeds the threshold is continued for a predetermined time, sets the torque signal from the torque sensor at that time to be the offset value of each torque signal, compares the offset values with each other, changes a changing unit so that the torque signal having the smaller offset value is input in the steering assist command value, and performs the control so as to open the first switching means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In particular, the present invention relates to an electric power steering device that can accurately detect an offset or drift failure that is an intermediate failure among signal failures of a torque sensor.

  An electric power steering device that biases an automobile or a vehicle steering device with an auxiliary load by the rotational force of a motor assists the steering shaft or rack shaft with a transmission mechanism such as a gear or a belt via a reduction gear. The load is energized. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist torque). In feedback control, the motor applied voltage is adjusted so that the difference between the current command value and the detected motor current value is small. Generally, the adjustment of the motor applied voltage is a duty ratio of PWM (pulse width modulation) control. It is done by adjusting.

Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. 6. The shaft 2 is provided with a torque sensor 10 that detects the steering torque of the steering handle 1, and a motor 20 that assists the steering force of the steering handle 1 is coupled to the shaft 2 via the reduction gear 3. . Electric power is supplied from the battery 14 via the ignition key 11 to the control unit 30 that controls the power steering device. The control unit 30 detects the steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12. The steering assist command value I _ref of the assist command is calculated based on the above, and the current supplied to the motor 20 is controlled based on the calculated steering assist command value I _ref .

  The control unit 30 is mainly composed of a CPU, and general functions executed by programs in the CPU are as shown in FIG.

The function and operation of the control unit 30 will be described. The steering torque T detected and inputted by the torque sensor 10 is phase-compensated by a phase compensator (not shown) in order to improve the stability of the steering system. The steering torque T is input to the steering assist command value calculator 32. The vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculator 32. The steering assist command value calculator 32 calculates a steering assist command value I _ref that is a control target value of the current supplied to the motor 20 based on the input steering torque T and vehicle speed V. The steering assist command value I _ref may be determined with reference to a characteristic map (lookup table) (not shown).

The steering assist command value I _ref is input to the subtractor 30A and is also input to the feedforward differential compensator 34 for increasing the response speed, and the deviation (I _ref -i) obtained by the subtractor 30A is proportionally calculated. The proportional output is input to the adder 30B and to the integration calculator 36 for improving the characteristics of the feedback system. The outputs of the differential compensator 34 and the integration calculator 36 are also added to the adder 30B, and the current command value E, which is the addition result of the adder 30B, is input to the motor drive circuit 37 as a motor drive signal. The motor current value i of the motor 20 is detected by the motor current detection circuit 38, and the motor current detection value i is input to the subtractor 30A and fed back.

  Here, conventionally, the torque sensor 10 that outputs a main torque signal TM and a sub torque signal TS is used. This is because safety measures are taken when the torque sensor 10 fails, and it is impossible to determine whether or not there is a failure with one signal output. Conventionally, the difference between the main torque signal TM and the sub torque signal TS is monitored, and when the difference continues for a predetermined time in a state where the difference is equal to or greater than a predetermined value, it is determined that the abnormality has been established, and the assist is turned OFF or limited. (See Patent Document 1).

  A torque sensor of a type that outputs the above-described main torque signal TM and sub torque signal TS is disclosed in Patent Document 2 below. FIG. 10 is a block diagram of a torque detection circuit of the torque sensor. The torque detection circuit 100 is connected to a control device (not shown) via a connector 129, and the power supply voltage V and the reference voltage Vref are supplied from the control device to each circuit element via the noise filter 128, and the detected main detection torque signal and A sub detection torque signal is output to the control device. The bridge circuit that detects torque includes a first arm in which a detection coil L1 and a resistor R1 are connected in series, and a second arm in which a detection coil L2 and a resistor R2 are connected in series. The oscillating unit 121 is supplied with the power supply voltage V and the reference voltage Vref and outputs an alternating voltage having a predetermined frequency. The output AC voltage is amplified by the current amplifying unit 122, and the amplified AC voltage Vosc is generated by the first arm of the bridge circuit including the detection coil L1 and the resistor R1, and the detection coil L2 and the resistor R2. It is supplied to the second arm of the constructed bridge circuit. The voltage signals appearing at both ends of the detection coil L1 and the detection coil L2 are converted and amplified and rectified by the main amplification / full wave rectification unit 123 into a difference signal between both detection coils, and further the main smoothing / neutral adjustment unit 126. After the output waveform is adjusted, the noise is output through the noise filter 128 to the control device as the main detection torque signal.

  Further, the voltage signals appearing at both ends of the detection coil L1 and the detection coil L2 are converted and amplified and rectified by the sub-amplification / full-wave rectification unit 124, and further sub-smooth / neutral adjustment. After the output waveform is adjusted by the unit 127, it is output to the control device as a sub detection torque signal via the noise filter 128.

  The torque detection circuit 100 is provided with two sets of a main amplification / full wave rectification unit 123 and a main smoothing / neutral adjustment unit 126, and a sub amplification / full wave rectification unit 124 and a sub smoothing / neutral adjustment unit 127, and two sets of detected torques. The reason why the signal is output is to detect a failure or the like of a circuit element by comparing these two sets of signals in a control circuit (not shown). In the torque detection circuit 100, a monitoring unit 125 is provided between the sub-amplification / full-wave rectification unit 124 and the sub-smoothing / neutral adjustment unit 127. The monitoring unit 125 detects a contact failure between the detection coil L1 or L2 and the resistor R1 or R2 by increasing the contact resistance.

JP 2002-225745 A Japanese Patent No. 3649057

  However, in the diagnosis based on the difference between the conventional main torque signal and the sub torque signal, the assist by the motor is stopped or limited even if either the main torque signal or the sub torque signal is normal. Therefore, in a vehicle with a heavy vehicle weight, if the assist is stopped by the above diagnosis, it is difficult to perform a stationary operation in a parking lot or a steering at a low vehicle speed only by a driver's steering force. There was a problem.

  The present invention has been made in view of such problems in the prior art, and provides an electric power steering device capable of continuing power assist for a certain period even when a difference between a main torque signal and a sub torque signal becomes large. For the purpose.

The present invention relates to an electric power steering apparatus capable of accurately detecting an offset or drift failure, and the above object of the present invention is to output two torque signals according to the steering torque applied to the steering. A torque sensor, a motor that applies a steering assist force to the steering mechanism, a steering assist command value calculator that calculates a steering assist command value based on a torque signal selected from the two torque signals, and the steering assist command value And a motor drive circuit that drives the motor based on a current command value calculated from the current detection value of the motor and a control unit that switches the torque signal input to the steering assist command value calculator In the electric power steering device comprising the device,
The torque sensor includes first switching means for short-circuiting the midpoints of the arms of the bridge circuit that detects a torque change as an electrical signal, and the control device further monitors a difference between the two torque signals, When a period in which the difference exceeds a predetermined threshold continues for a predetermined time, a signal for short-circuiting the first switching means is sent to the torque sensor to short-circuit the torque signal output from the torque sensor at that time. The switching unit is switched so that a torque signal having an offset value that is not larger than the offset values of the torque signals is input to the steering assist command value. This is achieved by providing abnormality diagnosis means for controlling the switching means to be opened.

Further, the above-described object of the present invention is to provide a torque sensor capable of outputting two torque signals in accordance with a steering torque applied to the steering, a motor for providing a steering assist force to the steering mechanism, and one of the two torque signals. A steering assist command value calculator for calculating a steering assist command value based on the selected torque signal, and driving the motor based on a current command value calculated from the steering assist command value and a current detection value of the motor. An electric power steering apparatus comprising: a motor drive circuit; and a control device including a switching unit that switches the torque signal input to the steering assist command value calculator.
The torque sensor includes first switching means for short-circuiting the midpoints of the arms of the bridge circuit that detects a torque change as an electrical signal, and the control device further monitors a difference between the two torque signals, When a period in which the difference exceeds a predetermined threshold continues for a predetermined time, a signal for short-circuiting the first switching means is sent to the torque sensor to short-circuit the torque signal output from the torque sensor at that time. An abnormality diagnosing unit that controls each offset value of each torque signal, outputs one offset value selected in advance among the offset values as a correction value, and controls to open the first switching unit; It is arranged between the switching unit and the steering assist command value calculator, and is based on the offset value output from the abnormality diagnosis means. Is achieved by providing a correction means for correcting the torque signal.

  Further, the object of the present invention is to provide a torque signal input to the steering assist command value calculator immediately before the first switching means is short-circuited while the first switching means is short-circuited. This is effectively achieved by performing the assist control based on the stored value.

  Still further, the object of the present invention is to provide a second switching means for short-circuiting a predetermined impedance element of any one arm of the bridge circuit, and a first circuit for short-circuiting terminals at the midpoint of each arm. It is effectively achieved by confirming that the switching means normally returns to the open state by short-circuiting the second switching means.

  According to the electric power steering apparatus of the present invention, even if it is determined that the offset or drift is abnormal by the diagnosis based on the difference between the main torque signal and the sub torque signal, the assist torque is not immediately stopped and the torque with the smaller offset value is not generated. The assist control can be continued using a signal or using a torque signal corrected with the detected offset value (including drift amount).

  An electric power steering apparatus according to the present invention relates to an electric power steering apparatus capable of accurately detecting an offset or drift failure, which is an intermediate failure among signal failures of a torque sensor, and a main torque signal. And the sub-torque signal are monitored, and when a period in which the difference exceeds a predetermined value continues for a predetermined time, the detected voltage of the torque sensor (for example, appears at both ends of the detection coil L1 and the detection coil L2 in FIG. 10). The voltage signal) is forcibly made equal to artificially create a torque neutral state, the torque signal (main and sub) output as a result is regarded as an offset value (including drift), and the two are compared. The one with the larger offset value is regarded as abnormal, and the assist is continued using the torque signal with the larger offset value. Those were Unishi (Example 1).

  Further, the offset value of the main torque signal (or sub torque signal) is detected by the same method as described above, and the assist may be continued using the main torque signal (or sub torque signal) corrected by the offset value (implementation). Example 2). This is because even if it is assumed that the main torque signal (or sub torque signal) is abnormal, the main torque signal (or sub torque signal) is corrected (emergency) using the offset value at that time. This is because, as a result, the same level of assist is possible as in the normal case.

  Hereinafter, the above two embodiments will be specifically described with reference to the drawings.

  FIG. 1 shows an example of the output characteristics of a torque sensor used in the electric power steering apparatus according to the present invention. The cross characteristics of the main torque signal (Vtm) and the sub torque signal (Vts) change in opposite directions. An example is shown. At the time of shipment, the mechanical variation of the torque detection mechanism and the electrical variation of the elements of the detection circuit are corrected and adjusted so that the characteristic indicated by the dotted line in FIG.

  However, when it is actually operating, there is a deviation from the characteristics at the time of shipment due to an increase in the temperature drift of the circuit element due to the temperature of the usage environment or the deterioration of the characteristics due to aging, as shown by the solid line in the figure It is conceivable to shift to a correct value. Th = 0, that is, the torque signals (Vtm, Vts) in the torque neutral state are offset values (offs1, offs2).

FIG. 2 is a schematic diagram of a torque sensor 10 used in the electric power steering apparatus according to the present invention. The middle point of the first arm and the second arm of the bridge circuit of the conventional torque sensor shown in FIG. A first switching means is inserted between the two points, and a short circuit can be performed by an external switch short circuit signal SW1. In FIG. _{2, Z 11} to R1 in FIG. _{10, Z 12} to L1 of FIG. _10, the R2 of _{Z 21} is _{10, Z 22} respectively correspond to the L2 in FIG. 10. There is no fundamental difference in other configurations. As the first switching means, for example, a transistor, an FET, or the like can be used.

  FIG. 3 is a block diagram showing the configuration of the first embodiment of the electric power steering apparatus according to the present invention. 9 differs from the conventional electric power steering apparatus shown in FIG. 9 in that the torque sensor 10 is provided with the first switching means as described above, and the control unit (hereinafter referred to as a control apparatus) 30 has a torque sensor. 10 monitors the main torque signal (Vtm) and sub-torque signal (Vts) output from 10 and diagnoses whether or not an abnormality has occurred. If an abnormality has been diagnosed, the process proceeds to the offset diagnosis mode and the first switching is performed. An abnormality diagnosing means 41 that gives a switch short-circuit signal SW1 to the means, and gives a torque input switching signal for switching a torque signal to be input to the steering assist command value 32 to the switching unit 42 described later, A switching unit 42 for switching a torque signal input to the steering assist command value 32 by the torque input switching signal, and an In that a storage unit 43 for storing the main torque signal immediately before the transition to the set diagnostic mode. Since the other parts are the same, the same reference numerals as those in FIG. 9 are used.

  Next, the operation of the first embodiment of the electric power steering apparatus according to the present invention will be described with reference to the flowchart shown in FIG.

  When the ignition key of the vehicle is turned on, it is determined whether or not the offset diagnosis mode is set (step S1). Since the default is the normal mode, it is “NO”, so the process proceeds to step S2, and the abnormality diagnosis means 41 reads the main torque signal Vtm and the sub torque signal Vts at that time (steps S2 and S3). The difference is calculated (step S4).

If the time period during which the difference exceeds a predetermined value continues for a predetermined time (for example, 1 minute), it is diagnosed that some abnormality has occurred ("YES" in step S5), and shifts to the offset diagnosis mode (step S6). A torque input switching signal is given from the diagnosis unit 41 to the switching unit 42, the switch of the switching unit 42 is switched to the b side, and the main torque signal stored in the storage unit 43 is FIXed to the value immediately before switching. The offset diagnosis torque Vt _off is held (step S7). On the other hand, if “NO” in the step S5, the assist is continued as it is, and the abnormality diagnosis is performed by returning to the beginning.

When shifting to the offset diagnosis mode, “YES” is determined in the step S1, so the process proceeds to a step S8, where the steering assist command value calculator 32 is based on the offset diagnosis torque Vt _off stored in the storage unit 43. A command value is calculated and steering assist is controlled based on the command value.

  At the same time, a switch short circuit signal SW1 is output from the abnormality diagnosis means 41 to the torque sensor 10, and the first switching means is short-circuited (step S9). When the first switching means is short-circuited, the steering torque Th apparently becomes 0, so Vtm = offs1 and Vts = offs2. offs1 and offs2 are input to the abnormality diagnosing means 41 (step S10), average values for a plurality of cycles are calculated (this average value is referred to as "offset value"), and stored in a memory (not shown) in the abnormality diagnosing means 41. (Step S11). When the offset value is stored in the memory, the switch short circuit signal SW1 is turned OFF, the first switching means is opened (step S12), and the torque sensor 10 outputs Vtm and Vts as before. At the same time, the offset diagnosis mode is canceled (step S13), and offs1 and offs2 stored in the memory are compared (step S14). If offs1, which is the offset value of the main torque signal, is larger ("YES" in step S15), it is determined that a larger abnormality has occurred in the main torque signal, and assist control is performed using the sub torque signal (Vts). Therefore, the switch of the switching unit 42 is switched from the b side to the c side by a torque input switching signal (step S16). On the other hand, if offs1 is smaller, it is determined that an abnormality has occurred in the sub torque signal, and the switch of the switching unit 42 is switched by the torque input switching signal so as to perform assist control using the main torque signal (Vtm). Is switched from the b side to the a side (step S17).

  Since the above process is an emergency process, the driver is informed that an abnormality has occurred in the torque sensor system after switching to provisional assist control (step S18). Take measures such as sounding an alarm or blinking a lamp.

  Even if the short circuit release (open) signal is sent in step S12, the two inputs of the operational amplifier are always at the same potential when the first switching means is always short-circuited and the same as in the torque neutral state. Thus, there is a problem that normal assist cannot be performed, and at the same time, this state cannot be diagnosed as abnormal on the control device side. Therefore, it is necessary to confirm that the first switching means has been normally opened.

Therefore, as shown in FIG. 5, a second switching means connected in parallel to the load Z _11, after entering the signal SW1 to return the first switching means in the open state, the switch operation check to the second switching means giving a signal SW2 to short-circuit the Z _11, largely allowed collapsed deliberately balance impedance detector bridge circuit, by confirming that the normal use range of the torque output signal, normal first switching means It can be confirmed that it is open.

Incidentally, rather than in parallel the second switching means Z _11, series may attempt to redundancy UP and series arrangement of two-stage to the first switching means.

  Alternatively, the second switching means is not provided, and it is estimated that the torque is not neutral from the presence / absence of rotation of the motor of the electric power steering apparatus or the left / right difference in wheel speed, and the first switching means is normally opened. You may confirm that.

  FIG. 6 is a block diagram showing the configuration of Embodiment 2 of the electric power steering apparatus according to the present invention. The difference from the electric power steering apparatus of the first embodiment shown in FIG. 3 is that the main torque signal (Vtm) and the sub torque signal (Vts) output from the torque sensor 10 are monitored and the presence or absence of abnormality is diagnosed. When the occurrence is diagnosed, after shifting to the offset diagnosis mode and acquiring the offset value of the main torque signal, the correction means 44 for correcting the main torque signal by the offset value (correction value) is provided, and the corrected main torque signal The steering assist command value is calculated based on the above and assist control is performed.

  Next, the operation of the electric power steering apparatus according to the second embodiment of the present invention will be described with reference to the flowchart shown in FIG.

  When the ignition key of the vehicle is turned on, it is determined whether or not the offset diagnosis mode is set (step S21). Since the default is the normal mode, the answer is “NO”, so the process proceeds to step S22, and the main torque signal Vtm and the sub torque signal Vts at that time are read into the abnormality diagnosis means 41 (steps S22 and S23). The difference is calculated (step S24).

If the period in which the difference exceeds a predetermined value continues for a predetermined time (for example, 1 minute), it is diagnosed that some abnormality has occurred ("YES" in step S25), and the offset diagnosis mode is entered (step S26). A torque input switching signal is given from the diagnosis unit 41 to the switching unit 42, the switch of the switching unit 42 is switched to the b side, and the main torque signal stored in the storage unit 43 is FIXed to the value immediately before switching. The offset diagnosis torque Vt _off is held (step S27). On the other hand, if “NO” in the step S25, the assist is continued as it is, and the process returns to the beginning to perform an abnormality diagnosis.

When shifting to the offset diagnosis mode, “YES” is determined in the step S21, so that the process proceeds to a step S28, and the steering assist command value calculator 32 performs the steering assist based on the offset diagnosis torque Vt _off stored in the storage unit 43. A command value is calculated and steering assist is controlled based on the command value.

  At the same time, the switch short-circuit signal SW1 is output from the abnormality diagnosis unit 41 to the torque sensor 10, and the first switching unit is short-circuited (step S29). When the first switching means is short-circuited, the steering torque Th apparently becomes 0, so Vtm = offs1 and Vts = offs2. Although offs1 and offs2 are input to the abnormality diagnosis unit 41, in the case of this embodiment, only one is required, so for example, offs1 is acquired (step S30). This is sampled for a plurality of cycles to calculate an average value (step S31; this average value is referred to as “offset value”) and stored in a memory (not shown) in the abnormality diagnosis means 41 (step S32). When the offset value is stored in the memory, the switch short circuit signal SW1 is turned OFF, the first switching means is opened (step S33), and Vtm and Vts are output from the torque sensor 10 as before. At the same time, the offset diagnosis mode is canceled (step S34), the switch of the switching unit 42 is switched from the b side to the a side by the torque input switching signal, and offs1 stored in the memory is input to the correction means 44, and by the offs1 Assist control is performed based on the corrected main torque signal (Vtm) (step S35).

  Since the above process is an emergency process, the driver is notified that an abnormality has occurred in the torque sensor system after switching to provisional assist control (step S36). Take measures such as sounding an alarm or blinking a lamp.

An example of the output characteristic of the torque sensor used for the electric power steering device according to the present invention is shown. 1 is a schematic diagram of a torque sensor used in an electric power steering apparatus according to the present invention. 1 is a block diagram illustrating a configuration of a first embodiment of an electric power steering apparatus according to the present invention. FIG. It is a flowchart of Example 1 of the electric power steering apparatus which concerns on this invention. It is a schematic diagram of 2nd Example of the torque sensor used for the electric power steering apparatus which concerns on this invention. It is a block diagram which shows the structure of Example 2 of the electric power steering apparatus which concerns on this invention. It is a flowchart of Example 2 of the electric power steering apparatus which concerns on this invention. It is a figure which shows the general structure of the conventional electric power steering apparatus. It is a figure which shows the general structure of the control unit of the conventional electric power steering apparatus. It is an example of the block diagram of the torque detection circuit of the conventional torque sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Torque sensor 12 Vehicle speed sensor 20 Motor 30 Control apparatus 32 Steering assistance command value calculator 37 Motor drive circuit 38 Motor current detection circuit 41 Abnormality diagnosis means 42 Switching part 43 Storage part 44 Correction means SW1 Switch short circuit signal SW2 Switch operation check signal

Claims (4)

A torque sensor capable of outputting two torque signals according to the steering torque applied to the steering;
A motor for providing steering assist force to the steering mechanism;
A steering assist command value calculator for calculating a steering assist command value based on a torque signal selected from the two torque signals, a current command value calculated from the steering assist command value and the detected current value of the motor A motor drive circuit that drives the motor based on the control device, and a control device that includes a switching unit that switches the torque signal input to the steering assist command value calculator;
In the electric power steering apparatus with
The torque sensor includes first switching means for short-circuiting the midpoints of the arms of the bridge circuit that detects a torque change as an electrical signal;
The control device further includes:
The difference between the two torque signals is monitored, and when a period in which the difference exceeds a predetermined threshold continues for a predetermined time, a signal for short-circuiting the first switching means is sent to the torque sensor to short-circuit, The torque signal output from the torque sensor is used as each offset value of each torque signal, and a torque signal having an offset value that is not large by comparing the offset values is input to the steering assist command value. An electric power steering apparatus comprising: an abnormality diagnosing unit that switches the switching unit and controls the first switching unit to be open.
A torque sensor capable of outputting two torque signals according to the steering torque applied to the steering;
A motor for providing steering assist force to the steering mechanism;
A steering assist command value calculator for calculating a steering assist command value based on a torque signal selected from the two torque signals, a current command value calculated from the steering assist command value and the detected current value of the motor A motor drive circuit that drives the motor based on the control device, and a control device that includes a switching unit that switches the torque signal input to the steering assist command value calculator;
In the electric power steering apparatus with
The torque sensor includes first switching means for short-circuiting the midpoints of the arms of the bridge circuit that detects a torque change as an electrical signal;
The control device further includes:
The difference between the two torque signals is monitored, and when a period in which the difference exceeds a predetermined threshold continues for a predetermined time, a signal for short-circuiting the first switching means is sent to the torque sensor to short-circuit, The torque signal output from the torque sensor is used as each offset value of each torque signal, and one of the offset values selected in advance is output as a correction value, and the first switching means is opened. An abnormality diagnosis means for controlling so that
A correction unit that is disposed between the switching unit and the steering assist command value calculator and corrects the torque signal by an offset value output from the abnormality diagnosis unit;
An electric power steering apparatus comprising:
While the first switching means is short-circuited, assist control is performed based on the stored value of the torque signal input to the steering assist command value calculator immediately before the first switching means is short-circuited. The electric power steering apparatus according to claim 1 or 2, characterized by the above.
  Second switching means for short-circuiting a predetermined impedance element of any one arm of the bridge circuit is provided, and the first switching means for short-circuiting terminals at the midpoints of the arms normally returns to the open state. The electric power steering apparatus according to claim 1 or 2, wherein this is confirmed by short-circuiting the second switching means.

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