JP5266913B2 - Control device for electric power steering device - Google Patents

Description

  The present invention relates to a control device for an electric power steering apparatus that applies a steering assist force by a motor to the steering of a vehicle, and in particular, reliably detects the state (normal or abnormal) of a current detection circuit that detects a motor current value. The present invention relates to a control device for an electric power steering device.

  An electric power steering device for energizing a vehicle steering device with an auxiliary load by a rotational force of a motor energizes an auxiliary load to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It is supposed to be. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist force). In the feedback control, the motor applied voltage is adjusted so that the difference between the current command value and the motor current detection value becomes small. Generally, the adjustment of the motor applied voltage is a duty of PWM (pulse width modulation) control. This is done by adjusting the tee ratio.

  Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. 7. The column shaft 2 of the handle 1 is connected to the tie rod 6 of the steering wheel via the reduction gear 3, the universal joints 4 a and 4 b, and the pinion rack mechanism 5. It is connected to. The column shaft 2 is provided with a torque sensor 10 that detects the steering torque of the handle 1, and a motor 20 that assists the steering force of the handle 1 is connected to the column shaft 2 via the reduction gear 3. A power is supplied from the battery 14 to the control unit 30 that controls the power steering device, and an ignition signal is input through the ignition key 11. The control unit 30 detects the steering torque Th detected by the torque sensor 10 and the vehicle speed. An assist command steering assist command value I is calculated based on the vehicle speed V detected by the sensor 12, and a current supplied to the motor 20 is controlled based on the calculated steering assist command value I.

  The control unit 30 is mainly composed of a CPU (including MPU and MCU), and FIG. 8 shows general functions executed by a program inside the CPU.

  The function and operation of the control unit 30 will be described with reference to FIG. 8. The steering torque Th detected by the torque sensor 10 is input to the steering assist command value calculation unit 32, and the vehicle speed V detected by the vehicle speed sensor 12 is also steered. This is input to the auxiliary command value calculation unit 32. The steering assist command value calculation unit 32 refers to the assist map stored in the memory 33 based on the input steering torque Th and the vehicle speed V, and the steering assist command is a control target value of the current supplied to the motor 20. Determine the value I. The steering assist command value I is input to the subtraction unit 30A and is also input to the feedforward differential compensation unit 34 for increasing the response speed, and the deviation (Ii) of the subtraction unit 30A is input to the proportional calculation unit 35. At the same time, it is input to the integral calculation unit 36 for improving the characteristics of the feedback system, and its proportional output is input to the addition unit 30B. The outputs of the differential compensator 34 and the integral compensator 36 are also added to the adder 30B, and the current control value E, which is the addition result of the adder 30B, is input to the motor drive circuit 37 as a motor drive signal. Electric power is supplied from the battery 14 to the motor drive circuit 37, the motor current value i of the motor 20 is detected by the motor current detector 38, and the motor current value i is input to the subtractor 30A and fed back.

  Further, a configuration example of the motor drive circuit 37 (in the case where the motor 20 is a two-phase motor) will be described with reference to the connection diagram of FIG. 9. The motor drive circuit 37 is based on the current control value E from the adder 30B. An FET gate drive circuit 371 for driving each gate of the transistors (FET) FET1 to FET4, an H bridge circuit composed of FET1 to FET4, a boost power source 372 for driving the high side of FET1 and FET2, and the like. The FET1 and FET2 are turned on / off by a PWM signal having a duty ratio D1 determined based on the current control value E, and the magnitude of the current flowing through the motor 20 is controlled. In the region where the duty ratio D1 is small, the FET3 and FET4 are driven by a PWM signal having a duty ratio D2 defined by a predetermined linear function equation (D2 = a · D1 + b where a and b are constants), and the duty ratio D1 is large. In the region, it is turned on / off according to the rotation direction of the motor determined by the sign of the PWM signal. For example, when the FET 3 is in a conductive state, the current flows through the FET 1, the motor 20, the FET 3, and the resistor Rp, and a current in the forward rotation direction flows through the motor 20. Further, when the FET 4 is in a conductive state, the current flows through the FET 2, the motor 20, the FET 4, and the resistor Rk, and a current in the reverse rotation direction flows through the motor 20. In this way, the current control value E from the adder 30 </ b> B is driven and controlled by the motor 20 via the drive circuit 37.

  Further, the current detection circuit 38 detects the magnitude of the current in the forward rotation direction flowing through the motor 20 based on the voltage drop across the resistor Rp, and reverse rotation flows through the motor 20 based on the voltage drop across the resistor Rk. Detect the magnitude of the current in the direction. The motor current value i detected by the current detection circuit 38 is input to the subtraction unit 30A and fed back. A power source Vcc is connected to the motor 20 via a resistor Rn and a diode Di, and is grounded via a resistor Ro. The resistors Rn and Ro have a very large value compared to the inter-terminal resistor Rm of the motor 20, and a motor terminal voltage Vm is obtained.

  Thus, the drive control of the motor 20 performs feedback control based on the detection value from the current detection circuit 38, and when the current detection circuit 38 fails, the accurate motor current value i cannot be detected. In other words, when excessive current flows into the motor 20 and excessive steering assist force is generated, or when the necessary current is not supplied to the motor 20 and sufficient steering assist force cannot be output, or steering A situation where hunting occurs as the auxiliary command value increases can be considered. For this reason, the current detection circuit 38 is required to always obtain an accurate current detection value.

  As means for solving such a problem, there is an apparatus disclosed in, for example, Japanese Patent Application Laid-Open No. 2006-137280 (Patent Document 1). In the apparatus of Patent Document 1, when the output side of the operational amplifier of the motor current detection circuit is grounded (grounded) and a failure occurs, the output of the operational amplifier becomes zero. Using this, when the current detection circuit is normal and the current detection value is zero, the output of the operational amplifier is also zero and cannot be determined from the output signal. A failure of the detection circuit is detected. That is, the ground fault of the operational amplifier is determined by using an amplifier circuit in which the output signal has a reverse phase inversion characteristic with respect to the input signal of the current detection means.

In addition, in the control device for the electric power steering apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-88877 (Patent Document 2), in contrast to the failure of the current detection circuit, the failure of the motor current detection circuit is not directly detected. Instead, the abnormality in the current loop due to the parameter variation is detected to determine whether the motor drive circuit is normal or abnormal. If the motor drive circuit is normal, it is regarded as a failure of the current detection circuit. Further, the failure determination of the motor drive circuit is performed based on the value of the motor terminal voltage Vm when all the H bridges constituted by the FETs in the motor drive circuit are turned off. Furthermore, even if the current detection circuit of the motor is faulty, other parts, especially the motor drive circuit, may be normal. In this case, the motor is driven in an open loop even if the motor current control is not possible. I have to. That is, the control unit includes a motor current detection circuit and a failure detection circuit that detects a failure of the current detection circuit. When the failure detection circuit detects a failure of the current detection circuit, the control unit has a current that is higher than that of the feedback system. The system has been switched to an open loop system that suppresses the motor and drives the motor.
JP 2006-137280 A JP 2005-88877 A

  In the electric power steering apparatus, when an amplifier short-circuit failure occurs in the current detection circuit, hunting occurs due to control that increases the current command value. Therefore, in the initial diagnosis immediately after turning on the ignition key, a minute current is supplied to the motor to monitor whether the current detection circuit is operating normally.

  However, the devices of Patent Document 1 and Patent Document 2 are both unnecessary due to the influence of an oxide film generated in the motor commutator (commutator), and foreign object biting of a relay contact arranged in the motor control circuit. Contact resistance may occur and current may not flow easily, and the state of the current detection circuit may not be detected accurately. Therefore, the appearance of a highly reliable electric power steering device that can always accurately monitor the state of the current detection circuit is desired.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to apply a detection voltage directly to a current detection circuit in consideration of the influence of contact resistance due to an oxide film or a relay contact of a motor commutator. Thus, an object of the present invention is to provide a highly reliable control device for an electric power steering device that more reliably detects the state of a current detection circuit.

The present invention relates to an electric power steering that drives and controls a motor that applies a steering assist force to a steering system by a current command value calculated based on a steering torque and a vehicle speed by feedback control of a motor current value detected by a current detection circuit. The above-described object of the present invention relates to a control device for a device, and a detection voltage output for generating a detection voltage based on a detection signal for state detection and directly applying the detection voltage to an input portion of an amplifier in the current detection circuit. Means for generating the detection signal at the time of state detection and inputting a state detection voltage generated from the output of the amplifier based on the detection voltage to obtain a current detection value, and detecting the detection signal and the current detection State detection means for determining normality or abnormality of the current detection circuit based on the relationship of values, the state detection means for the detection signal Wherein the normal range of the corresponding region has an error range of the current detection value, as well as an outer abnormality range of the normal range, the error range is achieved by increases with increasing the detection signal increases The

Further, the object of the present invention is that the detection signal is a PWM control signal and the detection voltage is a signal whose duty is adjusted based on the PWM signal, or the detection voltage output means is a ladder resistor. It is constituted by a circuit and switching means, and the switching means is switched by a detection switching signal from the state detection means , or the current detection circuit is constituted by an amplifier having a high input impedance and a low output impedance. This is achieved more effectively.

  According to the control device for the electric power steering apparatus of the present invention, the detection voltage is directly applied to the amplifier input portion of the current detection circuit so as to make a diagnosis, so that the current detection circuit is not affected by contact resistance or the like. It is possible to reliably detect abnormalities and conditions. Further, according to the present invention, the input / output characteristics of the current detection circuit can be checked and gain correction can be performed, so that the detection accuracy can be further increased.

  Furthermore, according to the present invention, it is possible to detect an abnormality or state of the current detection circuit without passing a current through the motor drive circuit, so that the efficiency and quality of repair and production processes can be improved.

  A control device for an electric power steering apparatus according to the present invention comprises a detection voltage output means for outputting a detection voltage based on an arbitrary detection signal from a state detection means mainly composed of a CPU, and calculates a current detection circuit. A detection voltage is directly applied to the input section of the amplifier or differential amplifier, and the state (normal or abnormal) of the current detection circuit is detected based on the detection value and detection signal from the operational amplifier or differential amplifier at that time. As described above, since the detection voltage is directly applied to the current detection circuit to detect the normal or abnormal state of the current detection circuit, the state of the current detection circuit can be reliably detected without being affected by the contact resistance. .

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an example of the basic configuration of the present invention. A current detection circuit 38 is composed of a shunt resistor Rr, an operational amplifier 381, input resistors Ra and Rb, a ground resistor Rd, and a feedback resistor Rc. A shunt resistor Rr is connected to the drive circuit 37, the ground side of the shunt resistor Rr is input to the non-inverting input portion of the operational amplifier 381 via the input resistor Rb, and the drive circuit 37 side of the shunt resistor Rr is connected to the input resistor Ra. Then, it is input to the inverting input section of the operational amplifier 381 and the detection voltage Vk from the detection voltage output means 40 is applied. A ground resistance Rd is connected to the non-inverting input portion of the operational amplifier 381, a feedback resistor Rc is connected to the inverting input portion and the output portion, and a state detection voltage eod indicating a current value is input from the operational amplifier 381 to the state detection means 301. Thus, the current detection value If is obtained. Further, a detection signal CS for detecting a state is input from the state detection unit 301 to the detection voltage output unit 40, and a detection voltage Vk generated based on the detection signal CS is input to the current detection circuit 38. Then, the operational amplifier 381 amplifies the difference between the non-inverting input unit and the inverting input unit based on the ratio of Ra = Rb and Rc = Rd, and the state detection voltage eod is input to the state detection unit 301 and converted into a current. Thus, the current detection value If is detected, and the detection signal CS and the current detection value If are compared. That is, the state detection unit 301 applies the detection voltage Vk to the operational amplifier 381 that detects the current value of the drive circuit 37 using the shunt resistor Rr, and the state detection voltage eod that is the output of the operational amplifier 381. And the state of the current detection circuit 38 is detected based on the detection signal CS.

  In such a configuration, an example of the operation will be described with reference to the flowchart of FIG.

  The state detection unit 301 generates a predetermined detection signal CS (step S10), and inputs the detection signal CS to the detection voltage output unit 40 (step S11). The detection voltage output means 40 applies the detection voltage Vk generated based on the detection signal CS to the inverting input portion of the operational amplifier 381 (step S12), and the state detection voltage eod calculated by the operational amplifier 381 is the state detection means 301. (Step S13). The state detection unit 301 obtains the current detection value If based on the state detection voltage eod (step S14), and the current detection circuit 38 is “normal” or “from the relationship between the generated detection signal CS and the current detection value If. It is detected whether it is “abnormal” (step S15). If it is determined in step S15 that it is “normal”, normal processing is performed assuming that the current detection circuit 38 is normal (step S16). On the other hand, if it is determined as “abnormal” in step S15, there is an abnormality in the current detection circuit 38, and abnormality processing such as alarm output is performed (step S17).

  Here, an example of the relationship between the detection signal CS and the current detection value If will be described with reference to the characteristic diagram of FIG.

FIG. 3 shows the relationship between the detection signal CS and the current detection value If obtained by converting the state detection voltage eod from the operational amplifier 381. The state detection means 301 sets the hatched portion in the figure to a “normal” range, The range other than is determined as “abnormal”. That is, the state detection unit 301 detects a normal or abnormal state of the current detection circuit 38 based on the relationship between the generated detection signal CS and the current detection value If. If the current detection circuit 38 is normal, the current detection value If (or the state detection voltage eod) output in response to the predetermined detection signal CS can be estimated. If the current detection circuit 38 is abnormal, an error from this estimated value is generated. Therefore, normality and abnormality are detected by determining the size of the error range with respect to the estimated value. That is, the state detection unit 301 sets a corresponding region having an error range of the current detection value If with respect to the detection signal CS as a normal range (shaded portion in FIG. 3), and an outside of the normal range as an abnormal range (see FIG. 3), and the error range increases as the detection signal CS increases, and the state detection unit 301 determines whether the current detection circuit 38 is normal or not based on the relationship of the current detection value If to the detection signal CS. Judge abnormalities.

  Next, a configuration example of the detection voltage output means 40 will be described with reference to the connection diagram of FIG.

  FIG. 4 is an example of a circuit that adjusts the detection voltage Vk by controlling the duty using a PWM signal as the detection signal CS. The detection PWM signal CSP (detection signal CS based on the PWM signal) from the state detection unit 301 is input to the amplifier circuit unit 41 via the resistor Re, and the detection voltage Vk is supplied from the amplifier circuit unit 41 to the shunt resistor Rr of the current detection circuit system. And input to the connection point of the input resistor Ra. Here, the amplifying circuit unit 41 is configured by a Darlington-connected NPN transistor Tr1 and a PNP transistor Tr2, and a resistor Rh is interposed between the collector of the transistor Tr1 and the base of the transistor Tr2. A resistor Rj is interposed between the emitter of the transistor Tr2 and the power source Vcc. In addition, a resistor Rg is inserted between the resistor Re and the base of the transistor Tr1, connected to the power source Vcc via the resistor Rf, and grounded via the capacitor C1. Then, the state detection voltage eod from the operational amplifier 381 is input to the state detection means 301, and “normal” or “abnormal” of the current detection circuit 38 is detected. The resistors Rf and Rj are pull-up resistors that suppress noise and malfunction. Although the amplifier circuit unit 41 is formed by using the transistor Tr1 and the transistor Tr2, it is also possible to configure the amplifier circuit unit by one transistor by inverting the ON / OFF logic of the PWM signal by software. That is, the detection voltage output means 40 may have any circuit configuration that can output a stable detection voltage Vk based on the detection PWM signal CSP from the state detection means 301.

  In this way, the detection PWM signal CSP with the voltage signal width changed using the PWM signal is input to the detection voltage output means 40 and the generated detection voltage Vk is applied, so that the state detection means 301 can detect the signal. The current detection circuit 38 can be monitored by checking the PWM signal CSP and the output detection voltage eod as described above.

  Next, another configuration example of the detection voltage output means 40 will be described with reference to the connection diagram of FIG.

FIG. 5 shows an example in which the detection voltage Vk is adjusted by switching the switching means SW1 to SW4 with the detection switching signals CSC1 to CSC4 using the ladder resistor circuit 42 for the detection voltage output means 40. As an example of the ladder resistor circuit 42, a description will be given using a ladder resistor circuit 42 in which the resistors R _L1 to R _L4 are configured in a ladder shape. Ladder resistor circuit 42, the switching means SW1~SW4 are connected to the connecting portions of the resistor _R L. 1 to the resistor _{R L} 4 which is grounded is connected in series. Further, the contacts a1 to a4 of the switching means SW1 to SW4 are connected to the current detection circuit 38, the contacts b1 to b4 are grounded, and the switching means SW1 to SW4 are detected by the detection switching signals CSC1 to CSC4 from the state detection means 301. SW4 contacts a1 to a4 and contacts b1 to b4 are switched.

  In such a configuration, the switching means SW1 to SW4 are normally connected to the contacts b1 to b4, and when any of the detection switching signals CSC1 to CSC4 is output, the corresponding switching means SW1 to SW4 are connected. The contacts a1 to a4 are turned on. As a result, the divided voltage from the ladder resistor circuit 42 is output as the detection voltage Vk, and the detection voltage Vk is applied to the current detection circuit 38.

  Since the detection voltage Vk can be applied by adjusting the detection voltage Vk using the ladder resistor 42 in this way, the state detection unit 301 compares the detection switching signal CSC with the output detection voltage eod. Thus, normality and abnormality of the current detection circuit 38 can be detected.

  Another configuration example of the present invention will be described with reference to FIG. If the FET gate drive circuit 371 turns off all of the FET1 to FET4 constituting the H bridge of the motor drive circuit 37 and the terminal voltage Vm of the motor 20 is not zero, the failure detection circuit 310 of the current detection circuit 38 that determines that there is an abnormality is provided. In addition, the detection voltage output means 40 and the state detection means 301 described above are provided so that the state of the current detection circuit 38 and the failure of the motor drive circuit 37 can be reliably detected.

  When the ignition key is turned on, an initial diagnosis is started. Based on the detection signal CS from the state detection means 301, the detection voltage Vk is generated by the detection voltage output means 41 and applied to the current detection circuit 38. Detect the state of. Further, the failure detection circuit 310 detects a failure. For example, when the detection voltage output means 41 applies the detection voltage Vk to the current detection circuit 38 and an abnormality is detected in the current detection value If based on the state detection voltage eod (in the case of step S17 in FIG. 2), the failure detection circuit The failure detection of the current detection means 38 is performed by 310. Thus, by detecting the state of the current detection circuit 38 in two stages by initial diagnosis or the like, the accuracy of the state detection of the current detection circuit 38 can be further increased. Note that the failure detection circuit 310 may perform fail-safe by open loop using a failure detection circuit and a motor model, as disclosed in Patent Document 2.

  In the above description, the current detection circuit 38 is configured using the operational amplifier (op-amp) 381. However, a differential amplifier or a comparator (comparator) having a high input impedance and a low output impedance may be used.

It is a block diagram which shows the basic structural example of the control apparatus which concerns on this invention. It is a flowchart which shows the operation example of this invention. It is a characteristic figure which shows the normal / abnormality of the detected value with respect to the abnormality detection signal of this invention. It is a connection diagram which shows another structural example of the control apparatus which concerns on this invention. It is a connection diagram which shows another structural example of the control apparatus which concerns on this invention. It is a connection diagram which shows another structural example of the control apparatus which concerns on this invention. It is a block diagram which shows the structural example of the conventional electric power steering apparatus. It is a block diagram which shows the structural example of the control unit of the conventional electric power steering apparatus. It is a connection diagram which shows an example of the conventional motor drive circuit.

Explanation of symbols

20 motor 30 control unit 37 drive circuit 38 current detection circuit 40 detection voltage output means 41 amplifying circuit section 42 ladder resistance circuit 300 CPU
301 state detection means 310 failure detection circuit 381 operational amplifier

Claims (4)

Control device for electric power steering device for driving and controlling motor for applying steering assist force to steering system by current command value calculated based on steering torque and vehicle speed by feedback control of motor current value detected by current detection circuit In
Detection voltage output means for generating a detection voltage based on a detection signal for state detection, and applying the detection voltage directly to an input portion of an amplifier in the current detection circuit ;
The detection signal is generated at the time of state detection, and the current detection value is obtained by inputting the state detection voltage from the output unit of the amplifier generated based on the detection voltage, and the relationship between the detection signal and the current detection value State detection means for determining normality or abnormality of the current detection circuit based on
Comprising
The state detecting means has an error range of the current detection value with respect to the detection signal and a corresponding region is a normal range, an outside of the normal range is an abnormal range, and the error range is the detection signal. A control device for an electric power steering device, wherein the control device increases as the value increases . The control device for an electric power steering apparatus according to claim 1, wherein the detection signal is a PWM control signal, and the detection voltage is a signal whose duty is adjusted based on the PWM signal. 2. The control device for an electric power steering apparatus according to claim 1, wherein the detection voltage output means includes a ladder resistor circuit and a switching means, and the switching means is switched by a detection switching signal from the state detection means . 4. The control device for an electric power steering apparatus according to claim 1, wherein the current detection circuit is constituted by an amplifier having a high input impedance and a low output impedance.

Images