JP4736648B2 - Control device for electric power steering device - Google Patents

Description

  The present invention relates to a control device for an electric power steering device, and more particularly to a control device for an electric power steering device with improved reliability of operation of a motor drive circuit that drives a motor.

  In general, as an electric power steering apparatus, a motor control unit configured by a microcomputer or the like and a motor drive circuit for driving the motor are detected, and an operation amount acting on the steering system such as a steering torque and a steering rotational speed is detected. The motor control unit determines a motor control signal based on the detection signal, and the drive circuit controls driving of the motor based on this control signal, thereby improving the response performance of the motor and improving the steering feeling. A motor drive circuit for driving and controlling the motor is composed of a drive element (for example, FET) and is controlled by PWM control at a constant frequency.

  Here, an example of a conventional electric power steering device disclosed in Japanese Patent Publication No. 7-96387 (Patent Document 1) will be described with reference to FIG.

  In FIG. 10, the electric power steering apparatus includes a detection unit 1, a motor control unit 2 that determines a motor control signal based on an output signal of the detection unit 1, and a motor drive circuit 3 that drives a motor 4 that generates assist torque. And a power supply circuit 5 for supplying power.

  The detection unit 1 includes a steering torque sensor 11 that detects a steering torque applied to the steering system and a steering rotation sensor 12 that detects the number of steering rotations. The detection signals S1, S2, S3, and S4 are the interface circuit 13 and 14 to the motor control unit 2.

  The motor control unit 2 includes an A / D converter 21 and a microcomputer unit (MCU) 22, and calculates and outputs a control signal for the motor 4. That is, the MCU 22 reads the motor control duty DT stored in the memory (not shown) based on the steering torque detection signal T (T = | S1-S2 |), and reads the steering rotation speed N (N = | S3-S4). |), The motor speed control duty DN stored in the memory is read out, motor control signals T3 and T4 are determined based on these duties DT and DN, and the motor control signals T3 and T4 are input to the motor drive circuit 3. .

  The motor drive circuit 3 includes a drive unit 30 that generates a drive signal and an H-bridge circuit in which FETs 31b, 32b, 33b, and 34b serving as four drive elements are respectively connected to arms. The FETs 31b to 34b of the H-bridge circuit are vertically symmetrical with the first FET 31b and the second FET 32b forming the upper circuit, the third FET 33b forming the lower circuit, and the first FET 31b and the second FET 32b. The connection point of the first FET 31b and the second FET 32b is connected to the relay 54 of the power supply circuit 5 as a power supply terminal, and the connection point of the third FET 33b and the fourth FET 34b is the drive power supply. Grounded to the earth side. The connection point between the upper circuit and the lower circuit, that is, the connection point between the first FET 31b and the fourth FET 34b adjacent to each other, and the connection point between the second FET 32b and the third FET 33b are output terminals, and an output terminal. The motor 4 is connected between them via a relay 39. The current of the motor 4 is detected by the current detection circuit 40 and input to the MCU 22 as a digital value via the A / D converter 21. Then, the gates of the FETs 31 b to 34 b are turned on / off by the output signal of the drive unit 30 to operate the FETs 31 b to 34 b as switching elements, and the motor 4 is driven and controlled. The power supply circuit 5 supplies power from a power supply (battery) 50 to a relay 54 and a constant voltage circuit 55 via a key switch 52 such as an ignition switch. The relay 54 is for conducting or blocking power to the FETs 31b to 34b of the motor drive circuit 3, and the constant voltage circuit 55 is for operating the MCU 22 and the like.

  The connection relationship between the FETs 31b to 34b of the H bridge circuit, the relay 39, and the motor 4 is as shown in FIG. 11, and the motor 4 and the relay 39 are connected in series between the output terminals.

In the above-described electric power steering device, when one of the FETs 31b to 34b constituting the arm of the H bridge circuit of the motor drive circuit 3 breaks down and is always in a conducting state, this FET breakage is detected by the current detection circuit 40. Then, the MCU detects the abnormal state, and based on that, the MCU 22 sets the relay 39 in the cut-off state. As a result, a current due to the induced electromotive force of the motor 4 flows with respect to the external force that causes the motor 4 to rotate forward, and the formation of a closed circuit that acts as a braking circuit for the motor 4 can be avoided. No braking current will flow through.
Japanese Examined Patent Publication No. 7-96387 JP 2004-329552 A

  However, in the control device described in Patent Document 1, when at least one FET is turned on, the relay 39 is turned off for electromagnetic brake protection. Since the relay 39 is connected to the intermediate motor line, there is a problem that when the relay 39 is turned off, the assist is completely stopped and the steering wheel operation becomes heavy.

  Even if one of the driving elements of the H-bridge circuit breaks down, one-side assist is possible, and it is required from the aspect of steering reliability to continue the assist as much as possible instead of making a complete stop. Yes. Such a demand is particularly strong in a control device for a large-capacity, high-output electric power steering device of a large vehicle.

  Further, in Japanese Patent Application Laid-Open No. 2004-312952 (Patent Document 2), an increase in the required steering force due to an on failure of the FET and an incorrect connection of the battery polarity are prevented without causing an increase in the size of the control device or a decrease in reliability. Although protection is intended, it does not consider continuing assistance as much as possible.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to switch a relay or the like to an arm of an inverter circuit (H bridge circuit), particularly in a control device for a large capacity and high output electric power steering device. It is an object of the present invention to provide a control device for an electric power steering apparatus that can continue the assist control even if one of the drive elements breaks down by providing means so that only one side can be energized.

The present invention relates to a control device for an electric power steering apparatus configured to drive and control a motor via an inverter circuit based on a current command value and to apply an assist torque to a steering system. The purpose is to provide a main drive element, a sub drive element and a switching means in each of the lower arms of the inverter circuit or in each of the upper arms, and the main drive by the switching means when a failure of the inverter circuit is detected. The main drive element, the sub drive element, and the switching means are provided in all the arms of the inverter circuit by switching from the element to the sub drive element, and when a failure of the inverter circuit is detected, the main means is switched by the switching means. From the drive element to the sub drive element It is achieved by switching to.

  Further, the object of the present invention is to control the main drive element with a main CPU and control the sub drive element with a sub CPU, or to detect a failure of the inverter circuit, a current detection value of the motor, and a motor terminal. By determining based on the inter-voltage and the steering torque signal, it is achieved more effectively.

  According to the control device for the electric power steering apparatus according to the present invention, switching means such as a relay is connected to the arm between the upper drive element (FET) and the lower drive element (FET) of the inverter circuit (H bridge circuit). Therefore, even if one of the drive elements (FET) breaks down, only one side can be energized and the assist control can be continued, so that it is easy to retreat to the road shoulder or the like.

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

  FIG. 1 shows an example of an apparatus for determining a failure of each FET constituting a motor drive circuit. A steering torque signal T from a torque sensor 101 is input to a current command value calculation unit 103 and a failure determination unit 100. The vehicle speed V from the vehicle speed sensor 102 is input to the current command value calculation unit 103. The current command value calculation unit 103 calculates a current command value Ir based on the steering torque signal T and the vehicle speed V, and drives and controls the motor 4 via the current control unit 104 and the drive circuit 105 of the H bridge circuit. The current i flowing through the inverter circuit (H bridge circuit) of the drive circuit 105 is detected by the current detection unit 110, the terminal voltage v of the motor 4 is detected by the voltage detection unit 111, the current command value Ir, the current detection value i, and the motor The terminal voltage v is input to the failure determination unit 100. Here, the current detection unit 110 is connected to the lower stage of the inverter circuit.

  FIG. 2 shows a flowchart of failure determination when any of the lower stage FETs 33b and 34b has an off failure. First, determination is made as to whether the current command value Ir is equal to or greater than a predetermined value and the current detection value i is equal to or less than the predetermined value. (Step S11), and when the above conditions are not satisfied, it is determined that the condition is normal (step S12). On the other hand, when the current command value Ir is equal to or greater than the predetermined value, but the detected current value i is equal to or smaller than the predetermined value, the torque direction is determined based on the steering torque signal T. For example, the neutral voltage is 2.5V. In this case, it is determined whether or not the steering torque signal T is equal to or higher than the neutral voltage of 2.5 V (step S13). As a result, the failure determination unit 100 can determine which of the upper FETs has been turned off with the left / right assist. If the steering torque signal T is 2.5 V or more, which is the neutral voltage, it is a failure of the FET 32b that performs the right assist. At the same time, the relay 33a is turned off, and the reverse side continues to assist (step S14). On the other hand, when the steering torque signal T is less than the neutral voltage of 2.5 V, it is a failure of the FET 31b that assists the left side, and at the same time, the relay 34a is turned off and the assist continues on the opposite side (step S15).

  In this example, the neutral voltage is set to 2.5 V, but may be an arbitrary value depending on the driving voltage of the torque sensor 101.

  FIG. 3 shows a flowchart of failure determination when either of the lower FETs 33b and 34b is on-failed. First, is an overcurrent abnormality in which the detected current value i becomes larger than the current command value Ir established? Whether or not an overcurrent abnormality in which the current detection value i is large with respect to the current command value Ir is not established is determined (step S22). On the contrary, when an overcurrent abnormality in which the current detection value i becomes large with respect to the current command value Ir is established, the driving of all the FETs 31b to 34b is turned off (step S23). Then, it is determined whether or not the motor terminal voltage v is at the high level H (step S24). If the motor terminal voltage v is at the high level H, it is determined that the upper stage FET on that side is on failure, and the relay 33a and 34a are turned off (step S25). Further, it is determined whether or not the motor terminal voltage v is at a high level H (step 26). If the terminal voltage v is at a high level H, it is determined that the motor line has a power fault, and all relays 33a and 34a are turned off. The assist is ended (step S27). In step S26, when the motor terminal voltage v is not high level H but low level L, the reverse side continues to assist.

  On the other hand, if the motor terminal voltage v is both at the low level L in step S24, it is determined that the lower stage FET is on (step S28), but the upper stage FET on one side is turned on for several ms (for example, 4 ms) and the motor is turned on. It is determined whether or not the terminal voltage v is at a low level L (step S29). If the motor terminal voltage v is at a low level L, it is determined that the lower FET on that side is an on failure and the relay is turned off (step S30). ). Further, the FET on one side is turned on for several ms (for example, 4 ms) to determine whether or not the motor terminal voltage v is at the low level L (step S31). It is determined that there is a line ground fault, and the assist is ended by turning off all the relays (step S32).

  If the motor terminal voltage v is not the low level L but the high level H in step S29, and if the motor terminal voltage v is not the low level L but the high level H in step S31, the opposite side continues assisting.

  FIG. 4 shows an embodiment of the present invention corresponding to FIG. 11, and relays 31 a to 34 a as switching means are provided as driving elements to the first arm 31 to the fourth arm 34 of the upper and lower stages, respectively. The FETs 31b to 34b are inserted in series.

  FIG. 5 shows an inverter circuit corresponding to FIG. 11 in a control device for an electric power steering apparatus according to another embodiment of the present invention.

  In this example, the relay as a switching means is not connected between the arms of the motor 4, that is, between the output terminals, but the relay 33a is inserted into the arm of the lower FET 33b, and the relay 34a is inserted into the arm of the lower FET 34b. Here, the line of the FET 31b is the first arm 31, the line of the FET 32b is the second arm 32, the circuit in which the relay 33a and the FET 33b are connected in series is the third arm 33, and the circuit in which the relay 34a and the FET 34b are connected in series is the first. The first arm 31 and the second arm 32 are upper arms, and the third arm 33 and the fourth arm 34 are lower arms. In this circuit, for forward rotation of the motor 4, for example, the FET 31b of the first arm 31 is turned on, the FET 33b of the third arm 33 is PWM-driven, and the relay 33a is turned on. When the FET 33b is turned on and the relay 33a is turned off by this PWM control, since the relay 34a is connected to the inverter circuit, a current flows through the FETs 32b and 34b, and the left side of the FET 32b and the FET 34b. Assist, that is, assist on the side opposite to the failure side is possible. Thereby, retreating of a road shoulder etc. becomes easy. In addition, in order to reversely rotate the motor 4, the same operation may be executed for the FETs 32b and 34b.

  In the case of the embodiment of FIG. 5 described above, an electromagnetic brake is applied when any one of the upper arm FETs 31b and 32b fails to be on, but for each of the FETs 31b to 34b as in the embodiment of FIG. By interposing the relays 31a to 34a in series, the electromagnetic brake is protected by turning on / off the relays 31a to 34a, and one-side assist becomes possible.

  However, in consideration of cost, failure frequency, etc., the case of only the lower arm is the connection diagram shown in FIG. Further, in this example, only the side that has not failed, that is, the right turn or left turn of the steering wheel, is assisted. Naturally, normal operation is hindered, but emergency evacuation such as retreating to the road shoulder is facilitated.

  FIG. 6 shows another embodiment of the present invention, in which the relay 31a is inserted into the arm 31 of the upper FET main batt 31b and the sub FET 31b2, and the relay 32a is inserted into the arm 32 of the upper fet main FET 32b and the sub FET 32b2. The relay 33a is inserted into the arm 33 of the lower stage main FET 33b and the sub FET 33b2, and the relay 34a is inserted into the arm 34 of the lower stage main FET 34b and the sub FET 34b2.

  In this example, the sub FETs 31b2 to 34b2 connected in parallel to the main FETs 31b to 34b are not only the lower arm sub FETs 33b2 and 34b2, as shown in FIG. 6, but the upper arm sub FETs 31b2 and 32b2 are not limited to the upper arm main FET 31b. And 32b are connected in parallel to form a double system. When it is determined that the main FETs 31b to 34b are out of order, the relays 31a to 34b are switched to the sub FETs 31b2 to 34b2 connected in parallel with each other, so that it is possible to assist for the failure of all the main FETs 31b to 34b. Become. However, it is necessary to consider whether to use the configuration of FIG. 7 in the case of only the lower arm in consideration of cost, failure frequency, and the like.

  FIG. 7 shows an inverter circuit according to another embodiment of the present invention.

  In this example, the lower stage circuit is constituted by the main FET 33b, the sub FET 33b2, the main FET 34b, and the sub FET 34b2, and the relay 33a connected to either the main FET 33b or the sub FET 33b2 of the lower arm, and any one of the main FET 34b and the sub FET 34b2. And a relay 34a connected to the. Normally, the main FETs 33b and 34b are used, and if the main FET fails, the sub FETs 33b2 and 34b2 are used.

  In the embodiment of FIG. 5 described above, when the FET is in an on-failure, the one-side steering is assisted, but the assist on the other side (failure-side) is turned off. However, in this example, when the lower main FET 33b fails, the relay 33a is switched to the sub FET 33b2, and the assist is continued. In addition, when the lower main FET 34b fails, the relay 34a is switched to the sub FET 34b2 to continue the assist. If the motor line has a power fault, ground fault or short circuit, the abnormality cannot be resolved even if the main FET 33b or the main FET 34b is changed to the sub FET 33b2 or the sub FET 34b by switching the relay 33a or 34a. Since a fault, a ground fault, or a short circuit can be considered to be stochastically sufficiently lower than a failure of the main FET 33b of the motor drive circuit, the improvement is performed by specializing in the failure of the main FET 33b or the main FET 34b. be able to. Further, since it is not used except for the failure of the main FET 33b or the main FET 34b, the current tolerance of the sub FET may be smaller than that of the main FET 33b or the main FET 34b. As a result, for example, it is possible to cope with retreating to a road shoulder or moving to a repair shop.

  FIG. 8 shows an inverter circuit which is still another embodiment of the present invention.

  In this example, the relay 31a is connected to the first arm 31, the relay 32a is connected to the second arm 32, the relay 33a is connected to the third arm 33, the relay 34a is connected to the fourth arm 34, and the main FET 31b is connected to the first arm 31. And the sub FET 31b2 are connected to be switched by the relay 31a, the main FET 32b and the sub FET 32b2 are connected to be switched by the relay 32a, and the main FET 33b and the sub FET 33b2 are switched to the third arm 33 by the relay 33a. The main FET 34b and the sub FET 34b2 are connected to the fourth arm 34 so as to be switched by the relay 34a. The main FETs 31b to 34b are ON / OFF controlled by the main CPU 120, and the sub FETs 31b2 to 34b2 are ON / OFF controlled by the sub CPU 121. In this example, the main and sub FETs are connected to the upper and lower arms, respectively, and are turned on / off by the main CPU 120 and the sub CPU 121, respectively, so that more efficient control is possible. However, since the number of components increases, the cost increases, and it is desirable to use it in consideration of the failure frequency and the like. An example of the case of only the lower stage that does not increase the cost is the circuit diagram of FIG.

  FIG. 9 shows an H-bridge circuit which is still another embodiment of the present invention.

  In this example, the relay 33a is connected to the third arm 33 and the relay 34a is connected to the fourth arm 34, and the main FET 33b and the sub FET 33b2 switched by the relay 33a are provided in the third arm 33, and the main FET 34b switched by the relay 34a. The sub-FET 34b2 is provided on the fourth arm 34. The main FETs 33b and 34b are on / off controlled by the main CPU 120, and the sub FETs 33b2 and 34b2 are on / off controlled by the sub CPU 121.

  In the embodiment of FIG. 7 described above, the FETs 31b to 34b as the main FETs and the FETs 33b2 and 34b2 as the sub FETs are driven by the same CPU, so that the drive signal of the lower main FET 33b is fixed at the high level H. If a failure occurs, the sub-FET 33b2 continues to be on even if the relay 33a is switched. Therefore, in the embodiment of FIG. 9, the main FETs 33 b and 34 b are driven by the main CPU 120, and the sub FETs 33 b 2 and 34 b 2 are driven by the sub CPU 121. By driving the main FETs 33b and 34b and the sub FETs 33b2 and 34b2 by the separate main CPU 120 and the sub 121, respectively, the main FET 33b or the main FET 34b and the sub FET 33b2 or the sub FET 34b2 can be driven efficiently.

  In the example of FIGS. 6 and 8, since the assist is continued as usual even after the failure of the drive element, the driver can steer without feeling uncomfortable. When a drive element breaks down, the driver is notified by a fail lamp, an alarm, etc. so that the driver senses the abnormality. After the failure, the assist amount is intentionally halved and the handle is made heavier so that the dealer can go to repair. It may be encouraged.

  In each of the embodiments described above, the FET is used as the drive element of the inverter circuit. However, the present invention can also be applied to the case where the inverter circuit is configured by a diode element and a relay or transistor. Moreover, not only a relay but switching means such as an electronic switch having an equivalent function may be used. Furthermore, the present invention is not limited to the above motor and can be similarly applied to an inverter circuit of a three-phase brushless motor.

It is a block diagram which shows the structural example of the electric power steering apparatus which shows the operation example of the failure determination of the motor drive circuit which concerns on this invention. It is a flowchart which shows the operation example of the failure determination (off failure) of the motor drive circuit which concerns on this invention. It is a flowchart which shows the operation example of a failure determination (ON failure) of the motor drive circuit which concerns on this invention. It is a connection diagram of an inverter circuit and a motor showing one embodiment of the present invention. It is a connection diagram of an inverter circuit and a motor showing one embodiment of the present invention. It is the connection diagram of the inverter circuit and motor which show the other Example of this invention. It is the connection diagram of the inverter circuit and motor which show the other Example of this invention. It is the connection diagram of the inverter circuit and motor which show the other Example of this invention. It is the connection diagram of the inverter circuit and motor which show the other Example of this invention. It is a block diagram which shows the structural example of the conventional electric power steering apparatus. It is a connection diagram of the inverter circuit and motor in the control apparatus of the conventional electric power steering apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Detection part 2 Motor control part 3 Motor drive circuit 4 Motor 5 Power supply circuits 31-34 Arm 31a-34a which connected relay and FET, 39 Relay 31b-34b Main FET
31b2-34b2 sub-FET
50 Power supply (battery)
DESCRIPTION OF SYMBOLS 100 Failure determination part 101 Torque sensor 102 Vehicle speed sensor 103 Current command value calculating part 104 Current control part 105 Inverter circuit (H bridge circuit)
110 current detector 111 voltage detector 120 main CPU
121 Sub CPU

Claims (4)

In the control device of the electric power steering apparatus configured to drive and control the motor via the inverter circuit based on the current command value and apply the assist torque to the steering system, each of the lower arms of the inverter circuit, or Each of the upper arms is provided with a main drive element, a sub drive element, and switching means, and when the failure of the inverter circuit is detected, the switching means switches from the main drive element to the sub drive element. A control device for an electric power steering device. In a control device for an electric power steering apparatus that controls driving of a motor via an inverter circuit based on a current command value and applies assist torque to a steering system, a main drive element is provided to all arms of the inverter circuit. An electric power steering apparatus comprising: a sub drive element and a switching means, wherein the switching means switches the main drive element to the sub drive element when a failure of the inverter circuit is detected. Control device. The control device for an electric power steering apparatus according to claim 1 or 2 , wherein the main drive element is controlled by a main CPU, and the sub drive element is controlled by a sub CPU. 4. The control device for an electric power steering apparatus according to claim 1 , wherein a failure of the inverter circuit is determined based on a detected current value of the motor, a voltage between motor terminals, and a steering torque signal. .

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