JP5267185B2 - Control device for electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an electric power steering device capable of continuing the overheat protection of a motor and a control unit, when there is no need to stop an assist of steering wheel steering, without reaching dangerous behavior by failure and abnormality of a motor current detecting part, by carrying out overheat protection by using a motor terminal voltage and a motor current estimate value, even when a current detecting part causes failure. <P>SOLUTION: This control device of the electric power steering device performs a steering assist by driving the motor by a motor driving circuit based on a motor current command value by arithmetically operating the motor current command value based on a detecting value of steering torque and a motor current, and includes a motor current abnormality detecting part for detecting abnormality of the current detecting part of the motor current, and a motor current estimate value arithmetic operation part for estimating a motor current estimate value when detecting abnormality of the current detecting part. When detecting the abnormality of the current detecting part, the motor current estimate value is used instead of the detection value of the motor current for carrying out the overheat protection of the motor and the control unit. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a control device for an electric power steering device in which a steering assist force by a motor is applied to a steering system of an automobile or a vehicle, and in particular, an abnormality or failure of a motor current detection unit necessary for motor control occurs and is normal. When the motor current cannot be detected, the motor current estimated value calculated by the voltage value between the motor terminals and the resistance value of the electric power steering device while continuing the steering assist is used instead of the motor current detected value. The present invention also relates to a control device for an electric power steering device that performs overheat protection of a control unit.

  An electric power steering device for energizing an automobile or vehicle steering device with an auxiliary load by the rotational force of a motor is an auxiliary load applied to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It comes to be energized. In addition, the conventional electric power steering apparatus performs feedback control of the 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 motor current command value and the detected motor current value is small. In general, the adjustment of the motor applied voltage is a duty of PWM (pulse width modulation) control. -Adjusting the tee ratio.

  Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. 3. The column shaft 2 of the steering handle 1 is connected to the steering wheel via the reduction gear 3, the universal joints 4 a and 4 b, and the pinion rack mechanism 5. Coupled to the tie rod 6. The column 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 connected to the column shaft 2 via the reduction gear 3. ing. The control unit 30 that controls the electric power steering apparatus is supplied with electric power from the battery 14 and also receives an ignition key signal from the ignition key 11. The control unit 30 calculates an assist command steering assist command value I based on the steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12, and the calculated steering assist command value I is calculated. Is used to control the current supplied to the motor 20.

  The control unit 30 is mainly composed of a CPU (including an MPU and MCU). A general configuration executed in the control unit 30 is shown in FIG.

  The function and operation of the control unit 30 will be described with reference to FIG. 4. The steering torque T detected and input by the torque sensor 10 is phase-compensated by the phase compensator 31 in order to improve the stability of the steering system. The phase-compensated steering torque TA is input to the steering assist command value calculation unit 32 and is also input to the feedforward differential compensation unit 34 for increasing the response speed, and the vehicle speed V detected by the vehicle speed sensor 12 is detected. Is also input to the steering assist command value calculator 32.

  The steering assist command value calculation unit 32 refers to the assist map in the memory 32A for the steering assist command value I, which is a control target value of the current supplied to the motor 20 based on the input steering torque TA and vehicle speed V. decide. The steering assist command value I is input to the subtraction unit 30A. The deviation (I-Is) of the subtractor 30A is input to the proportional calculator 35 and also to the integral compensator 36 for improving the characteristics of the feedback system. The outputs of the differential compensator 34 and the integral compensator 36 are also added to the adder 30B, and the motor current command value Im, which is the addition result of the adder 30B, is input to the motor drive circuit 37 as a motor drive signal.

  When the motor 20 is a two-phase motor, the motor drive circuit 37 is configured by an H bridge circuit in which four FETs as drive elements are connected in an H shape. The motor current detection value Is of the motor 20 is detected by the motor current detection circuit 38, and the motor current detection value Is is input to the subtraction unit 30A and fed back. In response to the ignition key signal from the ignition key 11, the control unit 30 drives the power supply relay 13 and power is supplied to the motor drive circuit 37. When the motor 20 is a three-phase motor, the motor drive circuit 37 has a three-phase bridge configuration in which six FETs are bridge-connected.

  In such an electric power steering apparatus, since a relatively large current is applied to the motor 20, the heat generation amount of the motor 20 and the control unit 30 is large, and the motor 20 generates heat and emits smoke or breaks. May trigger.

  As an apparatus for solving such a problem, there is an apparatus disclosed in, for example, Japanese Patent Laid-Open No. 1-186468 (Patent Document 1). The device disclosed in Patent Document 1 is a motor current limiter that limits the maximum value of the motor current according to the magnitude of the average current of the motor current every predetermined time when a current flows through the motor continuously for a predetermined time or more. Means are provided. Further, the control device disclosed in Japanese Patent Application Laid-Open No. 63-180567 (Patent Document 2) detects an abnormal time such as when the power element is short-circuited due to the difference between the motor current target value and the motor current detection value. When an abnormality is detected, the motor current and the applied voltage of the electromagnetic clutch are cut off by the cut-off means. Furthermore, in the control device disclosed in Japanese Patent Application Laid-Open No. 2002-87304 (Patent Document 3), target determination means for predetermining a target value of a current flowing through the motor, motor current detection means for detecting the motor current, target value A first motor control process for closed-loop control of the motor current flowing to the motor according to the detected motor current, and a second motor control process for open-loop control of the motor current flowed to the motor according to the target value When the motor current control means and the target current are less than a predetermined value, it is determined whether or not the detected motor current is abnormal, and the abnormality detection is performed to switch the control of the motor current to the second motor control process when the abnormality is determined. Means.

Japanese Patent Laid-Open No. 1-186468 JP-A 63-180567 JP 2002-87304 A

  However, since the apparatus of Patent Document 1 is provided with motor current limiting means for limiting the maximum value of the motor current, it can prevent overheating due to excessive current, but measures are taken when the current detection means fails. Not. Further, in the device of Patent Document 2, the motor current is cut off at the time of abnormality such as when the power element is short-circuited, and the applied voltage of the electromagnetic clutch is cut off, so that abnormality such as when the power element is short-circuited Overheating based on can be prevented. However, when the motor current measuring means that detects a short circuit of the power element fails, there is a problem that overheating cannot be reliably prevented. Furthermore, in the apparatus described in Patent Document 3, the motor control process is switched based on the motor current abnormality determination. However, when the motor current detection value abnormality detecting means for determining the motor current abnormality fails. The motor may overheat.

  The operation of the electric power steering device when a current detection system such as a current detector is abnormal or fails will be described with reference to the flowchart of FIG. 5 and FIG.

  First, when the driver steers the steering wheel (starting steering), the steering torque T detected by the torque sensor 10 is input to the control unit 30, and the vehicle speed V from the vehicle speed sensor 12 is also input to the control unit 30. The control unit 30 calculates a motor current command value Im based on the input steering torque T and vehicle speed V (step S50), and drives the motor by flowing the motor current (step S51). As a result, assist is generated by driving the motor 20 (step S52), the motor current detection value Is flowing in the motor 20 is detected by the motor current detection circuit 38, and feedback control based on deviation from the motor current command value Im is performed. Done.

  Here, although the steering torque T and the vehicle speed V are constant, the current detection unit of the motor current detection circuit 38 breaks down, the motor current detection gain decreases, and the motor current detection circuit 38 It is assumed that the detection is small (step S53). Since the control unit 30 performs the feedback control, it is determined that the current of the motor 20 is small, and the motor current command value Im is increased (step S54). Since the motor 20 is driven with the increased motor current command value Im (step S55), the assist generated from the motor 20 becomes excessive assist (excessive assist) (step S56). In this way, under the condition of excessive assist, the driver inputs the steering torque T from the steering wheel. However, since the necessary steering force is reduced, the steering torque T is reduced (torque loss) (step S57). . Note that the motor current command value Im and the motor current detection value Is at this time are the same.

  Here, the motor current command value Im is calculated with the torque missing (step S58), and the motor is driven with the calculated motor current command value Im (step S59), resulting in insufficient assistance (step S60). Then, the steering torque T from the steering wheel increases due to insufficient assistance (step S61), the current detection unit of the motor current detection circuit 38 breaks down, the motor current detection gain decreases, and the current flowing through the motor 20 is reduced to the motor. Since the current detection circuit 38 detects a small value (step S53), the motor current command value Im is increased (step S54).

  Such an event of excessive / insufficient assistance repeatedly occurs in a very short time, so that the driver recognizes that the steering wheel vibrates. This state is a state in which the current detection unit of the motor current detection circuit 38 has failed and the motor current detection gain has decreased, and the motor current detection circuit 38 has detected the current flowing in the motor 20 small. Since the actual motor current flows larger than the value Is, there is a problem that the motor 20 and the control unit 30 are overheated.

  The present invention has been made under the circumstances as described above. The object of the present invention is to provide a motor by performing overheat protection using the motor terminal voltage and the estimated motor current even when the current detection unit fails. If there is no dangerous behavior due to failure or abnormality of the current detection unit and it is not necessary to stop the steering assist, it is possible to continue the overheating protection of the motor and control unit. It is to provide a control device.

The present invention calculates a motor current command value based on a detected value of a steering torque and a motor current, drives a motor by a motor drive circuit based on the motor current command value, and controls an electric power steering device that performs steering assist. The present invention relates to an apparatus, wherein the object of the present invention is to detect abnormality of a current detection unit that detects the motor current based on the detected value of the motor current and the motor current command value, when the abnormality of the current detector is detected, and a motor current estimated value calculating unit that estimates, based the motor current estimated value to a minimum guaranteed temperature at the resistor voltage and the electric power steering system motor terminal , when the abnormality of the current detector is detected, the motor current estimated value in place of the detected value of the motor current, overheat protection Used as the current is achieved by performing a thermal protection of the motor and the control unit.

The above-described object of the present invention, when the front Symbol abnormality continues for a predetermined time, by the motor current abnormality detection unit determines that a failure of the current detection unit, or when the fault is determined, the motor This is achieved more effectively by cutting off the current and stopping the steering assist.

  According to the control device for the electric power steering device of the present invention, even when the motor current detection unit is abnormal or failed, the estimated motor current value calculated from the motor terminal voltage value and the resistance value of the electric power steering device is used. If the current detection unit including the motor current detection circuit does not cause dangerous behavior and there is no need to stop the steering assist, the motor and control Unit overheating protection can be continued.

It is a block diagram which shows an example of the control apparatus of the power steering apparatus by this invention. It is a flowchart which shows the example of control operation | movement of this invention. It is a figure which shows the structural example of a general power steering apparatus. It is a block diagram which shows an example of the motor control system in the conventional power steering apparatus. It is a flowchart which shows the operation example when abnormality generate | occur | produces in the motor current detection circuit in the conventional power steering apparatus.

  The control device for the electric power steering apparatus according to the present invention is a case where the current detection unit including the motor current detection circuit is abnormal or malfunctions and the motor current detection value is abnormal, and there is no dangerous behavior. When it is not necessary to stop the steering assist, overheat protection of the motor and the control unit is performed based on the voltage between the motor terminals and the resistance value at the minimum guaranteed temperature of the electric power steering device.

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

  FIG. 1 is a block diagram showing a configuration example of the present invention corresponding to FIG. 3. The same reference numerals are given to the same components, and the description thereof is omitted, but the motor current command value calculator 33 is described in FIG. A phase compensation unit 31, a steering assist command value computation unit 32, a memory 32A, a differential compensation unit 34, a proportional computation unit 35, an integral compensation unit 36, etc., and computes and outputs a motor current command value Im. . The motor current command value calculation unit 33 calculates a motor current command value Im based on the steering torque T, the vehicle speed V, the motor current detection value Is, and the overheat protection current Ih.

  In the present invention, a motor terminal voltage detection unit 39 that detects the terminal voltage Vmt of the motor 20 and a motor current abnormality detection unit 42 that detects a motor current abnormality based on the motor current command value Im and the motor current detection value Is. A motor current estimated value calculation unit 41 that calculates a motor current estimated value Ip based on the detected value abnormality signal DA from the motor current abnormality detection unit 42 and the motor terminal voltage Vmt, and a circuit from the motor current abnormality detection unit 42 A motor current cut-off unit 43 that cuts off the motor current and the like based on the failure signal CA, and a motor current limit calculation unit 44 that calculates the motor current command value Ims based on the detected motor current value Is and the estimated motor current value Ip are provided. ing.

  When the motor current abnormality detection unit 42 determines that the motor current value Is detected by the motor current detection circuit 38 is normal, the motor current detection value Is is set as the overheat protection current Ih = Is, and the motor current command value is set. It inputs into the calculating part 33 and performs normal assist operation | movement. In addition, when the motor current abnormality detection unit 42 determines that the motor current value Is detected by the motor current detection circuit 38 is abnormal, the current detection unit is further abnormal (about some component failure, Whether it is an assistable state) or a failure (assistless state) is determined by measuring elapsed time. The motor current abnormality detection unit 42 outputs a detection value abnormality signal DA when the current detection unit determines that there is an abnormality, and outputs a circuit failure signal CA when the current detection unit determines that there is a failure.

When the motor current abnormality detection unit 42 determines that the motor current detection unit is abnormal, the detection value abnormality signal DA is input to the motor current estimation value calculation unit 41, and the motor current estimation value calculation unit 41 calculates the motor terminal voltage Vmt and the motor. Based on the resistance value Rm at the minimum guaranteed temperature of the electric power steering device stored in the estimated current value calculation unit 41, the estimated motor current value Ip is obtained by the following equation (1).

Ip = Vmt / Rm (1)
When the resistance value at the minimum guaranteed temperature is set in consideration of variation, the resistance value Rm at the minimum guaranteed temperature is the motor line resistance (harness) at the minimum guaranteed temperature + the resistance between the motor terminals at the minimum guaranteed temperature.

The estimated motor current value Ip is input to the motor current command value calculation unit 33 as the overheat protection current Ih. That is, when the motor current abnormality detection unit 42 determines that the motor current is normal, the motor current detection value Is together with the motor current detection value Is is input to the motor current command value calculation unit 33 as the overheat protection current Ih to detect the motor current. When the motor current abnormality detection unit 42 determines that there is an abnormality together with the value Is, the motor current estimated value Ip is input to the motor current command value calculation unit 33 as the overheat protection current Ih. Although feedback control is always performed using the motor current detection value Is, overheat protection for preventing abnormal overheating of the motor and the control unit is disclosed in, for example, Japanese Patent Laid-Open No. 1-186468 (Patent Document 1). Although the method is based, in the present invention, the motor current detection value Is is used when normal, but the motor current estimated value Ip is used when abnormal.

  Further, when the motor current abnormality detection unit 42 determines that the current detection unit has failed, the circuit failure signal CA is input to the motor current cutoff unit 43, and the motor current cutoff unit 43 cuts off the current supply to the motor 20 and the like. And stop assist. For example, the relay contact 13 is turned off, and the current supply to the motor drive circuit 37 is interrupted.

  An operation example of the present invention will be described with reference to the flowchart of FIG.

  First, the steering torque T is input from the torque sensor 10 to the motor current command value calculation unit 33 by steering the steering wheel, and the vehicle speed V is also input from the vehicle speed sensor 12 (Step S10), and the motor current command value Im is calculated (Step S10). S11) The motor 20 is driven by the motor drive circuit 37, and the motor current detection value Is is detected by the motor current detection circuit 38 (step S12).

The motor current abnormality detection unit 42 determines whether or not the current detection system is abnormal based on the motor current command value Im and the motor current detection value Is according to the following equation (2) (step S13). Note that “A” in equation (2) is a predetermined value.

| Im-Is |> A (2)

If the above equation (2) does not hold, that is, if | Im−Is | ≦ A, the motor current detection value Is is normal, so the built-in motor current detection value abnormality counter is cleared (step S30), and further It is determined whether or not the motor current command value Im is equal to or greater than a predetermined value D (step S31). If the motor current command value Im is equal to or greater than the predetermined value D, the built-in overheat protection counter counts down “−1” (step S32), and the normal motor current detection value Is is set as the overheat protection current Ih = Is. The current command value calculation unit 33 is input (step S33), and the process returns. If the motor current command value Im is smaller than the predetermined value D in step S31, the normal motor current detection value Is is input as the overheat protection current Ih = Is to the motor current command value calculation unit 33 (step S31). S33), return. In this case as well, the motor current command value Im is calculated based on the steering torque T, the vehicle speed V, and the motor current detection value Is, thereby assisting (not including overheat protection).

On the other hand, if the above equation (2) is satisfied in step S13, that is, if | Im−Is |> A, the motor current detection value Is is abnormal, so the motor current detection value abnormality counter is counted up. +1 "(step S14), and it is determined whether or not the count value of the motor current detection value abnormality counter is equal to or greater than a predetermined value B (step S15).

  If the count value of the motor current detection value abnormality counter is smaller than the predetermined value B in step S15, the overheat protection counter is incremented by "+1" (step S16) since the failure has not yet been determined. It is determined whether or not the count value of the overheat protection counter is equal to or greater than a predetermined value C (step S17). When the count value of the overheat protection counter is smaller than the predetermined value C, it is determined that the assist can be continued, and the process proceeds to step S33, where the assist is continued.

In step S17, when it is determined that the count value of the overheat protection counter is equal to or greater than the predetermined value C, the detected value abnormality signal DA is output and input to the motor current estimated value calculation unit 41 (step S18). The motor current estimated value calculation unit 41 further inputs the motor terminal voltage Vmt from the motor terminal voltage detection unit 39 (step S19), and inputs the resistance value Rm at the minimum guaranteed temperature stored in the memory (step S20). ), The motor current estimated value Ip is obtained by the following equation (3) (step S22).

Ip = Vmt / Rm (3)

The estimated motor current value Ip estimated by the above equation (3) is input to the motor current command value calculation unit 33 as the overheat protection current Ih = Ip (step S23), and then returns. In this case as well, the motor current command value Im is calculated based on the steering torque T, the vehicle speed V, and the motor current detection value Is, thereby assisting (not including overheat protection).

  On the other hand, if the count value of the motor current detection value abnormality counter is greater than or equal to the predetermined value B in step S15, it is determined that the current detection system has failed so that assist cannot be continued. Therefore, the motor current abnormality detection unit 42 outputs the circuit failure signal CA (step S40), operates the motor current cut-off unit 43 to cut off the motor current (step S41), and turns on the warning lamp (step S42). Further, the relay is turned off (step S43), and the assist is stopped (step S44).

DESCRIPTION OF SYMBOLS 1 Steering handle 3 Reduction gear 10 Torque sensor 12 Vehicle speed sensor 13 Power supply relay 14 Battery 30 Control unit 31 Phase compensation part 32 Steering assistance command value calculation part 33 Motor current command value calculation part 34 Differential compensation part 35 Proportional calculation part 36 Integral compensation Unit 37 motor drive circuit 38 motor current detection circuit 39 motor terminal voltage detection unit 41 motor current estimated value calculation unit 42 motor current abnormality detection unit 43 motor current cutoff unit 44 motor current limit calculation unit

Claims (3)

In a control device for an electric power steering apparatus that calculates a motor current command value based on a detected value of a steering torque and a motor current, drives a motor by a motor drive circuit based on the motor current command value, and performs steering assist.
A motor current abnormality detection unit for detecting an abnormality of the current detection unit for detecting the motor current based on the detection value of the motor current and the motor current command value ;
When the said current detector abnormality is detected, and a motor current estimated value calculating unit that estimates, based the motor current estimated value to a minimum guaranteed temperature at the resistor voltage and the electric power steering system motor terminal And
When the abnormality of the current detector is detected, the motor current estimated value in place of the detected value of the motor current, using as overheat protection current, to perform overheat protection of the motor and the control unit A control device for an electric power steering device. The control device for an electric power steering apparatus according to claim 1 , wherein when the abnormality continues for a predetermined time, the motor current abnormality detection unit determines that the current detection unit is faulty. The control device for an electric power steering apparatus according to claim 2 , wherein when the failure is determined, the motor current is cut off and the steering assist is stopped.

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