JP2008024242A - Control device of 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 protecting a motor and a control unit from overheat even when a motor current value detector is failed. <P>SOLUTION: The current control value E as a command signal to be output to a motor driving circuit 37 is monitored, the counter value CNT is incremented when the current control value E consisting of, for example, the duty ratio is ≥75%, and the counter value CNT is decremented when the current control value E is ≤25%. When the motor current value i is a predetermined value iHi or under, and its counter value CNT is a predetermined counter value CNT<SB>0</SB>or over, there is a possibility that the temperature of the motor is excessively raised, and an assist steering command value I forming a base of the current control value E is limited (stopped). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device for an electric power steering device that applies a steering assist force by a motor to a steering system of a vehicle, and is particularly suitable for protecting a motor from overheating.

As a control device for such an electric power steering device, for example, as in Non-Patent Document 1 exemplified below, the relationship between the current value flowing through the motor and the temperature rise of the motor is obtained in advance by calculation or experiment, and the motor A current detector detects the value of the current flowing through the motor to estimate the temperature rise of the motor. When the temperature rises above a predetermined value, for example, the command signal to the motor drive circuit is limited to actually flow into the motor. There are some that limit the current value to protect the motor from overheating.
Japanese Patent Publication No. 6-51474

However, the control device of the conventional electric power steering apparatus has a problem that the motor and the control unit cannot be protected from overheating when a failure occurs in the motor current detector or its output system.
The present invention has been made paying attention to the above problems, and controls an electric power steering apparatus that can reliably protect a motor and a control unit from overheating without monitoring a motor current value. The object is to provide an apparatus.

  In order to solve the above-mentioned problems, when the control device for the electric power steering apparatus according to claim 1 of the present invention outputs a command signal corresponding to the steering torque to the motor drive circuit, the drive signal is sent to the motor by the motor drive circuit. In the control device for the electric power steering apparatus, the command signal is added when the command signal to the motor drive circuit is higher than a predetermined value on the high side and the command signal to the motor drive circuit is lower than the predetermined value on the low side. The counter includes a counter to be subtracted at a certain time, and overheat protection means for limiting a command signal to the motor drive circuit when the value of the counter is equal to or greater than a predetermined value.

  A control device for an electric power steering device according to a second aspect of the present invention is the control device for an electric power steering device according to the first aspect, further comprising motor current value detecting means for detecting a current value of the motor, wherein the overheating is performed. The protection means limits the command signal to the motor drive circuit when the motor current value detected by the motor current value detection means is less than or equal to a predetermined value.

  Thus, according to the control device for the electric power steering apparatus according to the first aspect of the present invention, the value of the counter is added when the command signal to the motor drive circuit is higher than the predetermined value on the high side and the motor Subtraction is performed when the command signal to the drive circuit is lower than the predetermined value on the low side, and when the counter value is greater than or equal to the predetermined value, the command signal to the motor drive circuit is limited. It is possible to protect the motor and the control unit from overheating without monitoring.

  According to the control device for an electric power steering apparatus according to claim 2 of the present invention, when the motor current value detected by the motor current value detecting means is equal to or less than a predetermined value, a command to the motor drive circuit is given. Since the signal is limited, the motor and the control unit can be reliably protected from overheating even when overheating protection based on the motor current value is used together.

Next, an embodiment of a control device for an electric power steering apparatus of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an electric power steering apparatus. A steering shaft 2 connected to the steering wheel 1 is connected to a tie rod 8 of a steered wheel through a reduction gear 3, universal joints 4a and 4b, and a pinion rack mechanism 5. The steering shaft 2 is provided with a steering torque sensor 10 that detects the steering torque of the steering wheel 1, and a motor 20 that assists the steering force of the steering wheel 1 is connected to the steering shaft 2 via the reduction gear 3. ing.

  Electric power is supplied from the battery 14 via the ignition switch 11 to the control unit 30 that controls the electric power steering device, and the control unit 30 is detected by the steering torque T detected by the steering torque sensor 10 and the traveling speed sensor 12. The steering assist command value I of the assist command is calculated based on the travel speed V, and the supply current value to the motor 20 is controlled based on the calculated steering station command value I.

  The control unit 30 is mainly composed of an arithmetic processing unit such as a microcomputer, and FIG. 2 shows the functions of the arithmetic processing executed inside. For example, the phase compensator does not indicate a phase compensator as independent hardware, but indicates a phase compensation capability, that is, software as arithmetic processing executed by the arithmetic processing device. The function and operation of the control unit 30 will be described. The steering torque T detected by the torque sensor 10 is phase-compensated by the phase compensator 31 to increase the stability of the steering system, and the phase-compensated steering torque TA is steered. This is input to the auxiliary command value calculator 32. Further, the traveling speed V detected by the traveling 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 that is a control target value of the current supplied to the motor 20 based on the input steering torque TA and travel speed V. The steering assist command value calculator 32 is provided with a memory 33. The memory 33 stores a steering assist command value I corresponding to the steering torque TA with the traveling speed V as a parameter. A steering assist command value I is set based on the data thus obtained.

  The steering assist command value I is input to the subtractor 30A and is also input to the feedforward differential compensator 34 for increasing the response speed, and the output (I-i) of the subtractor 30A is input to the proportional calculator 35. The proportional output is input to the adder 30B and to the integral compensator 36 for improving the characteristics of the feedback system. The output of the differential compensator 34 and the output of the integral compensator 36 are also input to the adder 30 </ b> B, and the current control value E that is the output thereof is input to the motor drive circuit 37. The motor current value i of the motor 20 is detected by the motor current detection circuit 38, and the motor current value i is fed back via the subtractor 30A. In this embodiment, the current control value E input to the motor drive circuit 37 is handled as a command signal.

  A configuration example of the motor drive circuit 37 is shown in FIG. The motor drive circuit 37 is based on the current control value E from the adder 30B, and FET gate drive circuits 371, FET1 to drive field effect transistors (hereinafter referred to as FETs) FET1 to FET4 that are power switching elements. An H bridge circuit composed of FET4, a boosting 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 pulse width modulation (PWM) signal having a duty ratio D1 determined based on the current control value E, and the magnitude of the current Ir that actually flows through the motor 20 is controlled. 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) in a region where the duty ratio D1 is small, and a region where the duty ratio D1 is large. Then, it is turned ON / OFF according to the rotation direction of the motor 20 determined by the sign of the PWM signal.

  For example, when the FET 3 is in a conductive state, the current flows in the order of the FET 1, the motor 20, the FET 3, and the resistor R 1, and a positive current is generated in the motor 20. When the FET 4 is in a conductive state, the current flows in the order of the FET 2, the motor 20, the FET 4, and the resistor R 2, and a negative current is generated in the motor 20. Therefore, the current control value E output from the adder 30B is also a PWM output (duty ratio). The motor current detection circuit 38 detects the magnitude of the positive current based on the voltage drop across the resistor R1, and detects the magnitude of the negative current based on the voltage drop across the resistor R2. . The motor current value i detected by the motor current detection circuit 38 is input to the subtracter 30A and fed back.

  On the other hand, in the present embodiment, the control unit 30 is provided with an overheat protection device 39 that protects the motor 20 and thus the control unit 30 itself from overheating. The overheat protection device 39 receives the current control value E output from the adder 30 </ b> B and the motor current value i detected by the motor current detection circuit 38, and assists the steering assist command value calculation period 32. A restriction (stop) command for the command value I is output.

  This overheat protection device 39 is also constructed by arithmetic processing, like the other functional blocks. In FIG. 4, the flowchart of the arithmetic processing which comprises the overheat protection apparatus 39 is shown. This arithmetic processing is always executed by, for example, timer interruption at every predetermined sampling time from the initial abnormality diagnosis when the ignition switch (IG in the drawing) is turned on to the ignition switch being turned off. In this calculation process, first, in step S1, the current control value E is read.

Next, the process proceeds to step S2, where it is determined whether or not the duty ratio of the current control value E read in step S1 is equal to or higher than the high-side predetermined value E _Hi set to, for example, about 75%. If the control value E is equal to or higher than the high-side predetermined value E _Hi , the process proceeds to step S4, and if not, the process proceeds to step S3.
In step S3, it is determined whether or not the duty ratio of the current control value E read in step S1 is equal to or lower than the high-side predetermined value E _Lo set to, for example, about 25%, and the current control value E is high. If it is equal to or _smaller than the predetermined value E _Lo on the side, the process proceeds to step S5, and otherwise, the process proceeds to step S6.

In step S4, for example, the high-side predetermined count value CNT _Hi set to 1, for example, is added to the counter CNT, and then the process proceeds to step S6.
In step S5, for example, the low-side predetermined count value CNT _Lo set to 1, for example, is subtracted from the counter value CNT, and then the process proceeds to step S6.
In step S6, the motor current value i is read.
Next, the process proceeds to step S7, in which it is determined whether or not the magnitude of the motor current value i read in step S6 is equal to or lower than the high-side predetermined value _iHi , and the motor current value i is determined to be the high-side predetermined value _iHi. When it is below, it transfers to step S8, and when that is not right, it transfers to step S9.

In step S8, the counter value CNT is equal to or a predetermined value CNT ₀ or more, when the counter value CNT is a predetermined value CNT ₀ or more, the routine proceeds to step S10, otherwise to the main program Return.
In step S10, a restriction (in this case, stop) command for the steering assist command value I is output to the steering assist command value calculation period 32, and then the process returns to the main program.
In step S9, fail-safe control corresponding to an excessive motor current value is performed by an individual calculation process (not shown), for example, as in the prior art described above, and then the process returns to the main program.

According to this calculation process, even when the motor current value i is larger than the high-side predetermined value i _Hi , the fail-safe control corresponding to the excessive motor current value is performed as in the prior art, but the motor drive circuit 37 Even when the count value CNT added or subtracted according to the current control value E, which is a command signal to the control signal, is equal to or greater than the predetermined value CNT ₀ , a limit (stop) command for the steering assist command value I is output. The command signal to the drive circuit 37 is limited, and it is possible to protect the motor 20 and thus the control unit 30 itself from overheating.

If waste and response delay are ignored, the motor current value i, which is the load amount of the motor 20, and the temperature T have a linear relationship, and the motor current value i and the current control value E are in principle proportional to each other. FIG. 5 shows these scales together. For example, with respect to the true temperature T of the actual motor, the temperature T and the linear motor current value i are obtained by the motor current detection circuit 38 at time t ₁ . It is assumed that the device cannot be detected correctly due to a failure. Even in such a case, since the counter value CNT to reflect the magnitude of the current control value E increases with the true temperature T of the motor becomes a predetermined value CNT ₀ or at time t ₂ soon, this time t ₂ after that Thus, the steering assist command value I is limited (stopped), and the motor 20 and thus the control unit 30 can be protected from overheating.
The current control value E as a command signal to be monitored may be an average value within a predetermined time.

It is a schematic block diagram which shows one Embodiment of the control apparatus of the electric power steering apparatus of this invention. It is a functional block diagram of the control unit of FIG. FIG. 3 is a circuit diagram of the motor drive circuit of FIG. 2. It is a flowchart which shows the arithmetic processing performed with the overheat protection apparatus of FIG. It is explanatory drawing of the effect | action of the arithmetic processing of FIG.

Explanation of symbols

1 is a steering wheel 2 is a steering shaft 3 is a reduction gear 4a and 4b are universal joints 5 is a pinion rack mechanism 8 is a tie rod 39 is an overheat protection device

Claims (2)

  When a command signal corresponding to the steering torque is output to the motor drive circuit, in the control device for the electric power steering apparatus in which the drive signal is output to the motor by the motor drive circuit, the command signal to the motor drive circuit is high. A counter that is added when the value is equal to or greater than a predetermined value and is subtracted when a command signal to the motor drive circuit is equal to or less than a predetermined value on the low side; A control device for an electric power steering apparatus, comprising overheat protection means for restricting a command signal to the motor.   Motor current value detection means for detecting a current value of the motor, wherein the overheat protection means outputs the motor drive circuit to the motor drive circuit when the motor current value detected by the motor current value detection means is less than or equal to a predetermined value. 2. The control device for an electric power steering apparatus according to claim 1, wherein the command signal is limited.

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