JP2002019635A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of maintaining ordinary carrying current to near to the overheat limit of an electric motor independent of the magnitude of the carrying current to the electric motor, and extremely reducing a feeling of physical disorder given in steering operation by early overload state judgment. SOLUTION: This electric power steering device has a fail-safe circuit J for reducing carrying current I to the electric motor M when an integrated value of a square value I2 of the carrying current I integrated with a current integration circuit F exceeds a limiter value LWR; and a timer circuit H for measuring integrated time in the current integration circuit F, and the limiter value LWR in the fail-safe circuit J is variably set so as to increase with increase in the integrated time of the carrying current I measured with the timer circuit H.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus, and more particularly, to a fail-safe technique for protecting an electric motor for assisting a steering force from burning due to continuous overload.

[0002]

2. Description of the Related Art As a conventional fail-safe technique of this kind, for example, a technique disclosed in Japanese Patent Application Laid-Open No. 5-254454 is disclosed. That is, in this conventional electric power steering apparatus, a current detecting means for detecting a current supplied to the electric motor and a current detecting means for detecting an electric current when the integrated value of the current detected by the current detecting means exceeds a predetermined threshold value. An overload estimating means for estimating that the electric motor is in an overloaded state, and when the overload estimating means estimates that the electric motor is in an overloaded state, by restricting supply of a current supplied to the electric motor, This is to protect the electric motor from burning due to continuation of the overload state.

[0003]

However, in the conventional electric power steering apparatus, as described above, the overload state of the electric motor is determined only by the integral value of the energizing current. Therefore, there were the following problems. That is, when the electric motor is driven with a small current, compared with the case where the electric motor is driven with a large current,
Since it takes a long time for the electric motor to overheat to the predetermined temperature, the integral value of the energizing current also becomes large, and therefore, when the electric motor is driven with a small current, the electric motor actually becomes overheated. Even though there is still enough margin, the overload state is determined when the integral value of the energizing current exceeds a predetermined threshold, and supply of the energizing current to the electric motor is limited. Therefore, the steering assist operation becomes uncomfortable due to a decrease in the steering assist force.

The present invention has been made in view of the above-mentioned conventional problems, and is intended to maintain a normal energizing current near the overheating limit of the electric motor irrespective of the magnitude of the energizing current to the electric motor. Accordingly, it is an object of the present invention to provide an electric power steering apparatus capable of minimizing the possibility of giving an uncomfortable feeling to a steering operation by an early overload state determination.

[0005]

In order to achieve the above object, an electric power steering apparatus according to a first aspect of the present invention detects an electric motor for assisting a steering force and a current supplied to the electric motor. Current detection means, current integration means for integrating the current supplied to the electric motor detected by the current detection means, and when the integrated value of the current supplied by the current integration means exceeds a predetermined threshold value Fail-safe means for reducing the current supplied to the electric motor, and integration time timer means for counting the integration time in the current integration means, wherein a predetermined threshold value in the fail-safe means is determined by the integration time timer means. The means is configured to be variably set in a direction to increase as the integration time of the energizing current measured by (1) increases.

According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, the current integrating means calculates a square value of a current supplied to the electric motor detected by the current detecting means. Means configured to accumulate.

According to a third aspect of the present invention, there is provided the electric power steering apparatus according to the first or second aspect, wherein the predetermined threshold value in the fail-safe means is counted by the accumulated time counting means. And a means that is variably set based on an approximate expression using a predetermined coefficient.

According to a fourth aspect of the present invention, there is provided the electric power steering apparatus according to the first or second aspect, wherein a predetermined threshold value in the fail-safe means is integrated by the current integrating means. Is configured to be variably set based on a map based on the integrated value of (i) and the integrated time measured by the integrated time measuring means.

[0009]

In the electric power steering apparatus according to the first aspect of the present invention, as described above, when the integrated value of the current supplied to the electric motor integrated by the current integrating means exceeds a predetermined threshold value, Although the current supplied to the electric motor is reduced in the fail-safe means, the predetermined threshold is variably set in a direction to increase as the integration time of the current supplied by the integration time timer increases.
It works as follows.

First, when the electric motor is driven by a large current, the integrated value of the energizing current rapidly increases in a short time. While the value is set to, the integrated value exceeds the threshold value in a short time to reduce the energizing current.

In addition, when the electric motor is driven with a small current, the integrated value of the energizing current gradually increases over time, so that the integrating time of the energizing current becomes long, that is,
The threshold value is variably set to a large value, which increases the time required for the integrated value to exceed the threshold value and reduce the energizing current, until the electric motor really overheats.
Normal current can be maintained.

Therefore, regardless of the magnitude of the current supplied to the electric motor, it is possible to maintain the normal current supplied to the vicinity of the overheating limit of the electric motor. Can be reduced as much as possible.

[0013] In the electric power steering apparatus according to the second aspect, as described above, the electric current integrating means integrates the square value of the current supplied to the electric motor detected by the electric current detecting means, so that the electric power steering apparatus is electrically driven. The heat generation state of the motor can be accurately determined. That is, the work W with respect to the load is originally represented by W = I ² R (I: conducting current, R: resistance). Therefore, when R is assumed to be constant, the work W = I ²
This is because the temperature of the electric motor can be obtained proportionally from the work amount W for the load.

According to the third aspect of the present invention, as described above, the predetermined threshold value is variably set based on an approximation formula based on the integration time measured by the integration time timer and a predetermined coefficient. This facilitates variable control of the threshold.

In the electric power steering apparatus according to the fourth aspect, as described above, the predetermined threshold value is calculated by integrating the current value integrated by the current integrating means with the integrated value of the current supplied by the integrating time measuring means. By variably setting based on a map based on time, it is possible to variably set an accurate threshold value suitable for an actual device.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. First, a configuration of an embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is an overall schematic view showing an electric power steering apparatus according to an embodiment of the present invention. As shown in FIG. 1, when a steering wheel SW is manually rotated, the rotation is performed by a rack L & pinion P. This is converted into a linear motion of the rack L, whereby the left and right front wheels TL, T
The direction of R can be changed (steered). The pinion P is configured to be rotatable by the electric motor M via the reduction gear G, so that the manual steering force is assisted.

The drive of the electric motor M is controlled by a microcomputer A incorporated in a control unit ECU mounted on the vehicle, based on a signal from a torque sensor TS for detecting a manual steering force.
Auxiliary control of the steering force is performed manually. Note that, in the figure, R is a fail-safe relay, and B is a vehicle-mounted battery.

FIG. 2 is a system block diagram showing an electric power steering apparatus according to an embodiment of the present invention. As shown in FIG.
In the figure, a control operation unit (microcomputer) A, a motor drive circuit C, a power supply circuit D, a motor current detection circuit (current detection means)
E, a fail-safe relay R and a shunt resistor SR are incorporated. The microcomputer A receives a vehicle speed signal s, an engine rotation signal r, a torque signal t from a torque sensor TS, and a self-diagnosis signal f.

The fail-safe relay R is interposed in a battery line connecting the electric motor M and the battery B. That is, the relay R is used to disconnect the battery line when the electric power steering apparatus is fail-safe, and is turned on and off by the microcomputer A.
F control is performed. In the drawing, I indicates an ignition switch, and FL indicates a fail lamp.

The shunt resistor SR is a resistor incorporated in series in the middle of the motor line ML for detecting a current flowing through the electric motor M. In the motor current detection circuit E, as shown in FIG. 3, a voltage measurement terminal portion 21 located at both ends of a resistance portion of the shunt resistor SR,
22, a voltage difference between both terminal portions 21 and 22 (ΔVn = V
1-V2), and this voltage difference (voltage drop value) ΔVn
The current value I is obtained from the current value by a current value conversion graph (function). V1 is the voltage of the upstream voltage measuring terminal 21 of the shunt resistor SR, and V2 is the voltage of the downstream voltage measuring terminal 22 of the shunt resistor SR.

Further, the microcomputer A has an electric current I to the electric motor M detected by the motor current detection circuit E.
Current integrating circuit F for integrating the squared value I ^{2 of the above} , a timer circuit (integrated time measuring means) H for counting the integration time in the current integrating circuit F, and an integrated value of the energized current integrated by the timer circuit H Fail-safe circuits J for reducing the current I to be supplied to the electric motor M when the current exceeds the limiter value (threshold value) LWR.

The limiter value LWR in the fail-safe circuit J is variably set in such a manner that the limiter value LWR increases as the integration time (timer value) TM of the square value I ² of the conduction current I measured by the timer circuit H increases. It is configured to be. That is, as shown in the following equation, the limiter value LWR is variably set based on a timer value TM measured by the timer circuit H and an approximate equation using predetermined coefficients a and b. The predetermined coefficients a and b are, for example,
It may be determined experimentally. LWR = a · TM + b

The reason why the limiter value LWR is variably set so as to increase as the timer value TM increases as described above will be described. FIG. 4 is a time chart showing an experimental result of measuring a temperature change of the electric motor M due to a difference in a current I supplied to the electric motor M. As shown in FIG. 4, the electric motor M was driven with a large current. In this case, the temperature of the electric motor M rises rapidly in a short time,
When driven by a small current, the temperature of the electric motor M gradually rises over time.

That is, the electric motor M was driven with a large current.
When driven by a small current, the electric motor
It takes a long time for the heater M to overheat to the predetermined temperature.
The square value I of the current I^Two The integral value of
And therefore the limiter value LWR is set to a constant value
The electric motor M actually
Is the square value of the conduction current I, although there is still enough room
I^Two Judgment of overload state when the integral value exceeds the limiter value LWR
And the supply of the current to the electric motor M is restricted.
Therefore, the steering assist is reduced due to the decrease in the steering assist force.
It will make the work uncomfortable. Therefore, the limiter value LW
R is the square value I of the conduction current I measured by the timer circuit H.
^Two Increases as the integration time (timer value) TM of
The above problems can be solved by setting
It can be turned off.

Next, the basis for deriving the above-described approximate expression for variably setting the limiter value LWR will be described. FIG. 5 shows that the electric motor M is supplied with a plurality of current values I (50 A, 40 A,
20A), and the electric motor M is driven at a plurality of temperatures (2
0 ° C, 30 ° C, 40 ° C, 50 ° C, 60 ° C, 70 ° C, 80 ° C
, 90 ° C.), which is an experimental result of measuring the time until the temperature reaches 90 ° C., that is, an integrated value-isothermal characteristic diagram of the square value I ² of the conduction current I. As is clear from this experimental result, each isothermal characteristic As the value of the current I decreases, the time required for the line to reach the predetermined temperature increases, and the integrated value of the square of the current I ² increases.

Therefore, constant coefficients a and b are obtained based on the gradient of the integrated value of the square value I ² of the conduction current I and the isothermal characteristic, and the limiter value LWR is calculated by using the constant coefficients a and b as the timer value. The above approximate expression is given by a linear expression so that the TM is variably set in a direction to increase as the TM becomes longer.

Next, the content of the variable setting control of the limiter value LWR in the fail-safe circuit J will be described with reference to the flowchart of FIG. First, in step 101, square value I ² of the energizing current I is equal to or less than the limit value LWR, when it is YES, the process proceeds to step 102, when it is NO, the process proceeds to step 106.

[0029] At step 102, 1 square value I ² of the period before the energization current I is equal to or less than the limit value LWR, counting the timer value TM proceeds to step 103 when a YES If NO, the process proceeds to step 105 to initialize the timer value TM to 1, and then proceeds to step 104.

In step 106, it is determined whether or not the square value I ^{2 of the} current I before one cycle is less than the limiter value LWR. If YES, the process proceeds to step 107 to proceed to the timer value TM. Is initially set to 1. If NO, the routine proceeds to step 108, where the timer value TM is counted up, and then the routine proceeds to step 104. And this step 10
In step 4, the limiter value LWR is calculated based on the approximate expression and variably set to the calculated value, thereby completing one flow.

In the embodiment of the present invention, since the fail-safe circuit J is configured as described above, first, when the electric motor M is driven with a large current, the square value I ^{2 of the} current I ² Because the integrated value of increases rapidly in a short time,
While the integration time of the conduction current I is short, that is, the limiter value LW
While R is set to a small value, control is performed in a direction in which the integrated value exceeds the limiter value LWR and the energizing current I is reduced in a short time.

Further, when the electric motor M is driven with a small current,
The square value I of the conducting current I ^Two Is slow.
, The integration time of the conduction current I
Becomes longer, that is, the limiter value LWR is
This causes the accumulated value to exceed the limiter value LWR
The time required to reduce the conduction current I becomes longer, and the electric motor
Until the motor M is really overheated.
Can be maintained.

Therefore, according to the embodiment of the present invention,
Irrespective of the magnitude of the current I flowing into the electric motor M, the normal current I can be maintained up to the vicinity of the overheating limit of the electric motor M, thereby making the steering operation uncomfortable due to the early overload state determination. The effect of being able to minimize giving is obtained.

Further, since the current integrating circuit F integrates the square value I ² of the current I supplied to the electric motor M detected by the motor current detecting circuit E, the heat generation state of the electric motor M is increased. Can be accurately determined.
That is, originally, the work amount W for the load is W = I ² R
(I: conduction current, R: resistance). Therefore, when R is considered to be constant, it can be considered that the work amount W = I ² ,
Further, the temperature of the electric motor M can be obtained in proportion to the work W with respect to the load.

Further, the limiter value LWR is variably set on the basis of an approximate expression based on the integration time TM measured by the timer circuit H and predetermined coefficients a and b, thereby enabling the variable setting control of the limiter value LWR. It will be easier.

Although the embodiments of the present invention have been described with reference to the drawings, the specific configuration is not limited to those embodiments of the present invention, and there are design changes and the like without departing from the gist of the present invention. Are also included in the present invention.

For example, in the embodiment of the present invention, the limiter value LWR is variably set based on the integration time TM measured by the timer circuit H and an approximate expression using predetermined coefficients a and b. May be variably set based on a map of the integrated value of the square value I ² of the conduction current I integrated by the current integrating circuit F and the integrated time TM measured by the timer circuit H. Can accurately set the limiter value LWR variably in accordance with the actual device.

[0038]

As described above, in the electric power steering apparatus according to the first aspect of the present invention, as described above, the electric motor for assisting the steering force and the current detection for detecting the current supplied to the electric motor are provided. Means, a current integrating means for integrating the current supplied to the electric motor detected by the current detecting means, and an electric motor when the integrated value of the current supplied by the current integrating means exceeds a predetermined threshold value. A fail-safe means for reducing the current supplied to the motor; and an integrating time measuring means for measuring the integration time in the current integrating means, wherein a predetermined threshold value in the fail-safe means is counted by the integrating time measuring means. Means that is configured to be variably set in a direction to increase as the integration time of the supplied current increases, the magnitude of the current supplied to the electric motor Regardless of this, the normal energizing current can be maintained up to the vicinity of the overheating limit of the electric motor, thereby minimizing the possibility of giving an uncomfortable feeling to the steering operation by the early overload state determination. The effect is obtained.

According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, the current integrating means calculates a square value of a current supplied to the electric motor detected by the current detecting means. With the means configured to perform the integration, the heat generation state of the electric motor can be accurately determined.

According to a third aspect of the present invention, there is provided the electric power steering apparatus according to the first or second aspect, wherein the predetermined threshold value in the fail-safe means is calculated by the integrated time counting means. And a means configured to be variably set based on an approximate expression using a predetermined coefficient, the variable control of the threshold value becomes easy.

According to a fourth aspect of the present invention, there is provided the electric power steering apparatus according to the first or second aspect, wherein a predetermined threshold value of the fail-safe means is a current supplied by the current integrating means. By means configured to be variably set based on a map of the integrated value of the integrated time and the integrated time measured by the integrated time measuring means, the variable setting of an accurate threshold suitable for an actual device can be performed. It becomes possible.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram showing an electric power steering device according to an embodiment of the present invention.

FIG. 2 is a system block diagram showing the electric power steering device according to the embodiment of the present invention.

FIG. 3 is a circuit diagram showing a shunt resistance portion of a motor current detection circuit in the electric power steering device according to the embodiment of the present invention.

FIG. 4 is a time chart showing an experimental result of measuring a temperature change of the electric motor due to a difference in current supplied to the electric motor in the electric power steering apparatus according to the embodiment of the present invention.

FIG. 5 is an integrated temperature-isothermal characteristic diagram of a square value of a supplied current in the electric power steering device according to the embodiment of the present invention;

FIG. 6 is a flowchart showing the content of variable setting control of a limiter value in the fail-safe circuit of the electric power steering device according to the embodiment of the present invention.

[Explanation of symbols]

 A microcomputer B battery C motor drive circuit D power supply circuit E motor current detection circuit (current detection means) ECU control unit FL failure lamp F current integration circuit G reduction gear H timer circuit (integration time measurement means) I ignition switch J fail safe circuit L Rack M Electric motor ML Motor line P Pinion R Fail safe relay SR Shunt resistance SW Steering wheel TL Left front wheel TR Right front wheel TS Torque sensor 21 Voltage measuring terminal 22 Voltage measuring terminal

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B62D 127: 00 B62D 127: 00 F term (Reference) 3D032 CC08 CC34 CC38 DA15 DA23 DA49 DA64 DA65 DA67 DD17 EA01 EC23 GG01 3D033 CA03 CA04 CA13 CA16 CA20 CA21 5H570 AA21 BB09 BB20 CC04 DD01 EE01 EE02 EE08 JJ03 JJ18 LL02 MM04 MM07 PP02

Claims (4)

[Claims] An electric motor for assisting a steering force; current detecting means for detecting a current supplied to the electric motor; current integrating means for integrating a current supplied to the electric motor detected by the current detecting means; Fail-safe means for reducing the current supplied to the electric motor when the integrated value of the current supplied by the current integration means exceeds a predetermined threshold value; and integration for measuring the integration time in the current integration means. Time counting means, wherein the predetermined threshold value in the fail-safe means is variably set in a direction to increase as the integration time of the current supplied by the integration time counting means increases. An electric power steering device characterized by: 2. The electric motor according to claim 1, wherein the current integrating means is configured to integrate a square value of a current supplied to the electric motor detected by the current detecting means. Power steering device. 3. The method according to claim 1, wherein the predetermined threshold value in the fail-safe means is variably set based on an approximate expression based on the integrated time measured by the integrated time measuring means and a predetermined coefficient. The electric power steering device according to claim 1 or 2, wherein: 4. A predetermined threshold value in the fail-safe means is variably set based on a map based on an integrated value of the supplied current integrated by the current integrating means and an integrated time counted by the integrated time timer. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is configured to be configured as follows.