JP3055777B2 - Electric power steering device - Google Patents

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 device for reducing the steering force of a driver by applying the power generated by an electric motor to a steering system as a steering assist force, and more particularly, to calculating the temperature of electric motor driving means. The present invention relates to an electric power steering device that reduces a current flowing through a motor driving unit in accordance with the temperature.

[0002]

2. Description of the Related Art In a conventional electric power steering apparatus, a motor driving means for driving a motor is provided by four FETs.
(Field-effect transistor), and a FET (Pulse Width Modulation) signal from the control means.
Is configured to drive and control the motor to drive the motor with a desired motor current.

Further, as disclosed in Japanese Patent Application Laid-Open No. 63-263167, a conventional electric power steering apparatus detects a current value of motor driving means for driving a motor, and based on the current value, detects a motor value. There is also known a configuration in which an average value of a current supplied to the motor is calculated for a predetermined time, and a maximum value of the current supplied to the electric motor is limited according to the average value.

[0004]

The conventional electric power steering apparatus in which the motor drive control means for driving the motor is constituted by a bridge circuit composed of four FETs (field effect transistors) is provided by the four FETs of the motor drive means. When the current flowing through the FET is continuously used at the maximum current when controlling the driving of the FET, there is a problem in that the FET generates a large amount of heat and is damaged. In addition, there is a problem in that if it is made to withstand continuous use at the maximum current, the shape becomes large and the cost increases.

[0005] The conventional electric power steering apparatus disclosed in Japanese Patent Application Laid-Open No. 63-263167 discloses a steering assisting force (assist torque) by limiting the maximum current when the average current flowing through the motor exceeds a predetermined value. ) Suddenly decreases, and there is a problem that the steering feeling deteriorates.

The present invention has been made to solve such a problem, and an object thereof is to provide an FET for driving an electric motor.
The present invention provides an electric power steering apparatus in which a current flowing through a power steering device is reduced to prevent damage due to heat generation, and that a reduction in current caused by control does not affect a steering feeling as much as possible.

[0007]

An electric power steering equipment according to claim 1 of the present invention for solving the problems In order to solve the problems]
It includes a steering torque sensor for detecting steering torque of the steering system, an electric motor for adding a steering assist force to a steering system to detect a motor current flowing through the electric motor, and the motor current detecting means for outputting a motor current signal corresponding Target current setting means for setting a target current signal corresponding to a target current of a motor based on at least a signal from a steering torque sensor, and drive control means for determining a motor control signal based on a deviation between the target current signal and the motor current signal In an electric power steering apparatus including: a control unit having: and a motor driving unit that drives a motor by a motor control signal, the control unit calculates a temperature of the motor driving unit,
When the calculated temperature exceeds a first predetermined value, a motor first control signal for limiting the maximum value of the steering assist force, and the calculated temperature exceeds a second predetermined value larger than the first predetermined value. Sometimes, a motor second control signal for reducing and correcting the steering assist force,
Monodea with a fool-proof control means for generating a
You .

According to the electric power steering apparatus of the first aspect of the present invention, the current flowing through the motor driving means can be corrected and controlled in two stages. When the temperature is equal to or higher than the first predetermined value and equal to or lower than the second predetermined value, only the maximum value of the steering assist force is limited. Therefore, when the steering assist force is not so large, the steering assist force is not changed. Further, when the steering assist force is reduced and corrected to be equal to or more than the second predetermined value, the first predetermined value can be set to be relatively large.

[0009] The electric power steering apparatus according to claim 2 of the present invention, it is foolproof control means, electrostatic
The amount of heat generated by the switching element of the motive drive means
A calorific value calculation means for calculating from the signal, and a target current signal
Motor first control to limit the maximum value of motor control signal
Control signal comparing means for outputting a signal, and the calorific value calculated
Is estimated that the temperature of the motor driving means becomes the first predetermined value.
When the first heating value signal is larger than the
Switching to supply the control signal to the motor driving means,
The calculated calorific value depends on the temperature of the motor driving means.
Second estimated to be a second predetermined value larger than the fixed value
When the heat generation amount signal is larger, the motor second control signal
Switching means for switching to supply to the motor driving means
And characterized in that:

According to the electric power steering apparatus of the present invention , the temperature of the motor driving means can be estimated from the existing motor current detecting means, so that it is necessary to provide a new detecting means such as a thermometer. Absent.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the present invention provides a motor driving means (FET bridge circuit) based on a current flowing through the motor.
Is calculated and the calculated temperature is compared with two predetermined values to limit or reduce the current flowing through the motor driving means.

FIG. 1 is an overall configuration diagram of an electric power steering apparatus according to the present invention. In FIG. 1, an electric power steering apparatus 1 includes a universal joint 3 on a steering shaft 2 provided integrally with a steering wheel 17.
a manual steering force generating means 6 which is connected to a pinion 5a of a rack & pinion mechanism 5 provided in a steering gear box 4 via a connecting shaft 3 provided with a and a 3b.

The rack shaft 7 is provided with rack teeth 7a meshing with the pinion 5a, and reciprocates by these meshing.
Are connected to the left and right front wheels 9 as rolling wheels at both ends thereof via tie rods 8.

In this way, the steering wheel 1
At the time of steering, the front wheels 9 are rolled by manual steering via a normal rack and pinion type manual steering force generating means 6 to change the direction of the vehicle.

In order to reduce the steering force by the manual steering force generating means 6, an electric motor 10 for supplying a steering assist force is disposed coaxially with the rack shaft 7, and a ball screw mechanism 11 provided coaxially with the rack shaft 7. Is converted to thrust through the rack shaft 7
(Ball screw shaft 11a).

A steering torque sensor 12 for detecting the direction and magnitude of a driver's manual steering torque is disposed in the steering gear box 4, and an analog electric signal corresponding to the steering torque detected by the steering torque sensor 12 is steered. The torque signal Ts is provided to the control means 15. The vehicle speed sensor 14 detects an electric pulse signal having a frequency corresponding to the speed of the vehicle, and provides the control unit 15 with a vehicle speed signal Vs.

The control means 15 is composed of various arithmetic means, processing means, signal generating means, memory and the like based on a microprocessor, and uses a vehicle speed signal Vs as a parameter to control an electric motor control signal VO (for example, An ON signal, an OFF signal, and a hybrid signal of a PWM signal) are generated to drive and control the motor driving means 16.

The control means 15 includes foolproof control means, calculates the temperature of the motor driving means 16, and based on the calculated temperature, limits the motor 10 or the motor current IM flowing to the motor driving means 16 or controls the motor current IM. A motor control signal VO for correcting the decrease of the current IM is generated, and the driving of the motor driving means 16 is controlled.

The motor driving means 16 is constituted by a bridge circuit using four switching elements such as FETs (field effect transistors), for example. The motor control means comprises a switch-on / off signal and a PWM signal provided by the control means 15. In the signal VO, two pairs of Fs, each pair of two on the diagonal,
By driving and controlling each pair of ETs, the voltage value and the direction of the motor voltage VM to be supplied to the motor 10 are set. The direction of the motor voltage VM is determined according to the polarity of the motor control signal VO output from the control unit 15.

The motor current detecting means 19 differentially amplifies a voltage drop of the motor current IM flowing through a current detecting element (for example, a resistor) connected in series with the motor 10, and a motor current signal corresponding to the amplified output. The IMO is supplied to the control means 15.

The motor current detecting means 19 converts the motor current IM detected by a current detecting element (for example, a resistor) into a motor current signal IMO and feeds back to the control means 15 (negative feedback) to control the steering. Form the return path of the system.

FIG. 2 is a block diagram of a main part of an embodiment of an electric power steering apparatus according to the present invention. FIG.
, The control means 15 comprises a target current setting means 21, a deviation calculation means 22, a drive control means 23, and a foolproof control means 18.

The target current setting means 21 has a memory such as a ROM, and stores correspondence data between a steering torque signal Ts and a target current signal IMS using a vehicle speed signal Vs set in advance as a parameter. Based on the detected vehicle speed signal Vs and the steering torque signal Ts detected by the steering torque sensor 12, a corresponding target current signal IMS is read and supplied to the deviation calculating means 22. The deviation calculation means 22 has a subtraction function, calculates a deviation between the target current signal IMS and the motor current signal IMO from the motor current detection means 19, and supplies a deviation signal ΔI to the drive control means 23.

The drive control means 23 includes a PID (proportional / integral / differential) controller and control signal generating means, and a deviation signal ΔI (= IMS) between the target current signal IMS supplied from the deviation calculating means 22 and the motor current signal IMO. -IMO) to PID
Control based on the signal subjected to the PID control.
A motor control signal VOO comprising a composite signal of the W signal VPWM, the ON signal VON and the OFF signal VOF is supplied to the foolproof control means 18.

The foolproof control unit 18 includes a calorific value calculating unit, a calorific value comparing unit, a control signal comparing unit, a correction coefficient setting unit, a switching unit, and the like.
Calorific value is calculated based on the motor current signal IMO from
The motor control signal VO supplied from the drive control means 23 is converted into a motor control signal VO for limiting or reducing the current flowing through the motor drive means 16 based on the calculated heat value, and the drive control of the motor drive means 16 is performed. .

The foolproof control means 18 receives the motor control signal VOO from the drive control means 23. If the heat generation amount of the switching element of the motor drive means 16 does not reach the predetermined value, the foolproof control means 18 receives the motor control signal VOO as it is. VO is output to the motor drive means 16 as a motor control signal VO.

FIG. 3 is a block diagram showing a main part of the foolproof control means according to the present invention. 3, the foolproof control unit 18 includes a calorific value calculating unit 31, a calorific value comparing unit 32, a calorific value table 33, a maximum value setting unit 34, a control signal comparing unit 35, a correction coefficient setting unit 36,
A multiplication unit 37 and a switching unit 38 are provided.

The calorific value calculating means 31 comprises various arithmetic circuits such as multiplication and integration, and memories such as ROM and RAM. When the motor current signal IMO is supplied from the motor current detecting means 19, the value of the motor current signal IMO is calculated. The value is converted into the value of the motor current IM stored in the ROM, and the calorific value Ch is calculated based on the on-resistance value Rh of the FET stored in the ROM and the converted value of the motor current IM. This heat value Ch is expressed by Equation 1.

[0029]

(Equation 1)

In the equation 1, Ch is the calorific value, and Rh is FE.
T is the ON resistance value, IM is the motor current value, t and T are time,
K represents a constant. The time T calculated by the calorific value calculating means 31 is a predetermined value, for example, 240 seconds, and the calorific value for 240 seconds immediately before the measurement is always calculated. At this time, the current calorific value Ch is an integrated value of the calorific value from 240 seconds before, for example, the calorific value after 60 seconds from now is 180
This is a value obtained by adding the value of the calorific value for 60 seconds from now to the calorific value before the second.

In equation (1), the constant K is fixed at all times. However, it is considered that the older the calorific value data is, the smaller the influence on the current temperature is. May be changed.

[0032]

(Equation 2)

In Equation 2, Ch is the heat value, and Rh is FE.
On-resistance of the T, IM _n is the motor current value after n seconds, t,
T is time, K _n is a constant after n seconds _{(K 0 <... <K n} -1 <K n)
Represents The calculated heat value Ch is supplied to the heat value comparison means 32 and the correction coefficient setting means 36.

The calorific value comparing means 32 is composed of a plurality of comparators.
Is compared with the first heating value signal Cf and the second heating value signal Cm in the heating value table 33, a switching signal Cd is supplied to the switching means 38, and the switching means 38 is switched to the switching points 1 and 2 by the switching signal Cd. , Or 3. That is, when the heat generation amount Ch is smaller than the first heat generation amount signal Cf, the switching signal Cd outputs the LH level of the 2-bit signal, and the switching unit 38 is in the state of the switching point 1.

When the heat generation amount Ch is smaller than the second heat generation amount signal Cm and larger than the first heat generation amount signal Cf, the switching signal Cd outputs the HL level of the 2-bit signal, and the switching means 38 switches the switching point 38 to the switching point 2 Switch to state. Further, the calorific value C
When h is greater than the second heating value signal Cm, the switching signal Cd outputs the HH level of the 2-bit signal, and the switching means 38 is switched to the state of the switching point 3 by this signal.

The heating value table 33 is composed of a memory such as a ROM and a RAM, and stores a first heating value signal Cf and a second heating value signal Cm when a motor current flows in advance. From the calculating means 31 to the calorific value comparing means 32,
Each time the calculated heat value Ch is input, the first heat value signal Cf and the second heat value signal Cm are output. At this time, the first heating value signal Cf is a heating value signal for which the temperature of the motor driving means 16 is estimated to be a first predetermined value, and the second heating value signal Cm is a signal indicating that the temperature of the motor driving means 16 is the second predetermined value. Is a heat generation amount signal estimated to be a predetermined value.

The maximum value setting means 34 is constituted by a memory such as a ROM or a RAM, and reads a predetermined value (for example, a current signal value of 70% of the maximum motor current) from the memory and outputs a limit signal C
The signal is output to the control signal comparing means 35 as s.

The control signal comparing means 35 is composed of a comparator, and the limit signal Cs from the maximum value setting means 34 and the VPWM of the motor control signal VOO supplied from the drive control means 23.
The comparison is made with the signal, and the smaller signal is supplied to the switching means 38 as the motor first control signal VO1.

The correction coefficient setting means 36 includes a multiplier, a ROM
And the like, and the calorific value C
h is supplied from the memory and corresponds to the heat value Ch,
Multiplier 37 reads out the correction coefficient and uses it as selection signal Cj.
To supply.

FIG. 4 is a characteristic diagram showing the relationship between the heat value and the correction coefficient. In this characteristic diagram, the vertical axis indicates the correction coefficient (selection signal C
In j), the horizontal axis represents the heat value, and the correction coefficient is 1 until the heat value is less than the second predetermined value. When the heat value is the second predetermined value, the correction coefficient becomes 0.7, and when the heat value further increases, the coefficient decreases until it becomes zero. This correction coefficient is stored in the memory of the correction coefficient setting means 36, and the heat value Ch
Is read out in response to.

The multiplication means 37 multiplies the selection signal Cj (correction coefficient) supplied from the correction coefficient setting means 36 by the motor control signal VOO supplied from the drive control means 23,
The switching means 38 uses the result of the multiplication as the second motor control signal VO2.
To supply. The motor control signal VOO is the ON signal V
The signal is a composite signal of the ON signal, the OFF signal VOF, and the PWM signal VPWM. The ON signal VON and the OFF signal VOF are not particularly controlled, and the multiplication is performed only on the PWM signal VPWM.

The multiplication means 37 multiplies the selection signal Cj (correction coefficient) supplied from the correction coefficient setting means 36 by the motor control signal VOO supplied from the drive control means 23. When the coefficient is 1, the motor control signal VO is attained. At this time, the switching means 38 does not switch to the switching point 3 state and is in the switching point 1 state or the switching point 2 state. Control signal VO2 is not output.

The switching means 38 has a switch function of software control, and the switching point is determined based on a two-bit LH level, HL level, and HH level switching signal Cd from the heat generation amount comparing means 32. (1) a state in which the motor control signal VOO from the drive control means 23 is directly output, a state in which the switching point is 2, and a state in which the motor first control signal VO1 supplied from the control signal comparing means 35 is output, Is 3,
The motor control signal VO, the motor first control signal VO1, or the motor second control signal VO2 is supplied to the motor drive means 16 by switching to the state of outputting the motor second control signal VO2 supplied from the multiplication means 37. It is supplied as a motor control signal VO.

FIG. 5 is a diagram for explaining the driving of the motor driving means according to the present invention. The electric motor driving means 16 is turned on by an ignition switch (IGSW) to supply a power Vc.
When the driver operates the steering wheel to the right with the (12V power supply) stabilized after the vehicle starts, the control means 15 sends the motor control signal VO to the FETs (field effect transistors) Q1 to Q4 constituting the switching elements of the motor drive means 16.
To supply.

In this state, the ON signal VON is supplied to the gate G1 of Q1, the OFF signal VOF is supplied to the gate G2 of Q2, the OFF signal VOF is supplied to the gate G3 of Q3, and the PWM signal VPWM is supplied to the gate G4 of Q4. Setting, Q2 and Q3 are set to OFF, Q4 is set to ON / OFF determined by the duty cycle of the PWM signal VPWM, and the motor current IM + is changed from the power supply Vc to Q1 to the current detecting element (resistance RD).
The electric motor 10 flows along a route of Q4 → body ground (GND). For example, the electric motor 10 is rotated forward to apply an auxiliary steering force to the steering system to steer the vehicle to the right.

At this time, when the heating value is equal to or less than the first predetermined value, the switching signal Cd from the heating value comparing means 32 is at the 2-bit LH level and the switching means 38 remains set at the switching point 1. Yes, Q1 is set to on, Q2 and Q3 are set to off, and Q4 is supplied to the motor drive means 16 as the motor drive signal VO as the motor drive signal VOO with the duty cycle of the motor current determined by the drive control means 23. .

When the heating value exceeds the first predetermined value and does not exceed the second predetermined value, the switching signal Cd from the heating value comparing means 32 becomes a 2-bit HL level and the switching means 38
Are set to switching point 2 and Q1 is set to ON, Q2 and Q
3 is an off setting, and Q4 is a smaller one of a duty cycle for limiting the current to 70% of the maximum motor current calculated based on the limit signal Cs and a duty cycle of the motor current determined by the drive control means 23. The motor first drive signal VO1, which is a cycle, is supplied to the motor drive means 16 as a motor drive signal VO.

Further, when the heating value exceeds the second predetermined value, the switching signal Cd from the heating value comparing means 32 becomes 2
The switching point 38 is switched to the switching point 3 by the HH level of the bit, Q1 is set to ON, Q2 and Q3 are set to OFF, and Q4 is selected from the correction coefficient setting means 36 to the motor current determined by the drive control means 23. A motor second drive signal VO2 having a duty cycle multiplied by the signal Cj is supplied as a motor control signal VO.

The FET (field effect transistor) Q1 is turned on, the FET Q4 is PWM driven, and the motor current I
In the state where M + flows, the voltage V + of the current detection element (resistor RD) is detected with a positive (+) polarity.

When the motor 10 is rotated in the reverse direction, F
The ON signal VON is applied to the gate G3 of the ETQ3, and the gate G of the
1, an off signal VOF, a gate G4 of Q4, an off signal VOF,
The PWM signal VPWM is supplied to the gate G2 of Q2, Q3 is set ON, Q1 and Q4 are set OFF, and Q2
Is set to ON / OFF determined by the duty cycle of the PWM signal VPWM, and the motor current IM− is set to the power supply Vc →
Q3 → Motor 10 → Current sensing element (resistance RD) → Q2 →
It flows on the path of the vehicle body ground (GND), for example, the electric motor 10
Is rotated in reverse to apply an auxiliary steering force to the steering system to steer the vehicle to the left. At this time, the FET (field effect transistor) Q3 is set to ON, and the FET Q2 is set to PWM.
When the motor is driven and the motor current IM- flows, the voltage V- of the current detecting element (resistor RD) is detected with a negative (-) polarity.

The positive (+) polarity and the negative (-) polarity detection voltages V corresponding to the motor currents IM + and IM-, respectively.
I is supplied to the motor current detecting means 19, where it is amplified and converted to output a motor current signal IMO corresponding to the motor currents IM + and IM-.

FIG. 6 is a block diagram of a main part of another embodiment of the control means according to the present invention. In the embodiment shown in FIG. 2, the motor control signal is limited or reduced as a method of limiting or decreasing the steering assist force. In the present embodiment, the target current signal is limited or reduced. 6, the control unit 51 includes a target current setting unit 21, a deviation calculation unit 22, a drive control unit 23, and a foolproof control unit 52. The control unit 51 shown in FIG. 6 is different from the foolproof control unit 18 shown in FIG. 2 only in the position where the foolproof control unit 18 is formed.

The foolproof control means 52 includes a calorific value calculating means for detecting a calorific value based on the motor current signal IMO from the motor current detecting means 19, and a maximum value for generating a coefficient for limiting and reducing the current flowing through the motor. Setting means, a correction coefficient setting means, and a multiplying means for calculating the generated coefficient. The target current signal IMS from the target current setting means 21 is multiplied or calculated. It is supplied to the deviation calculating means 22. That is, the foolproof control means 52 outputs the target current signal IMS
The current flowing through the motor driving means 16 is limited or reduced by an operation current signal IMH obtained by multiplying the current by 1 or a value less than 1.

FIG. 7 is a block diagram showing a main part of the foolproof control means according to the present invention. In FIG. 7, the foolproof control unit 52 includes a heat generation amount calculation unit 61, a heat generation amount comparison unit 62, a heat generation amount table 63, a maximum value setting unit 64, a control signal comparison unit 65, a correction coefficient setting unit 66,
A multiplication unit 67 and a switching unit 68 are provided.

The calorific value calculating means 61 is composed of various arithmetic circuits such as multiplication and integration, and memories such as ROM and RAM, and calculates the calorific value Ch based on the motor current signal IMO supplied from the motor current detecting means 19. The calorific value calculating means 6
1. The calorific value comparing means 62, the calorific value table 63, the maximum value setting means 64, and the correction coefficient setting means 66 are the calorific value calculating means 31, the calorific value comparing means 32, and the calorific value table 3 of FIG.
3, since they are the same as the maximum value setting means 34 and the correction coefficient setting means 36, the description is omitted.

The control signal comparing means 65 is composed of a comparator, and compares the limiting signal Cs from the maximum value setting means 64 with the target current signal IMS supplied from the target current setting means 21. The signal is the motor first control signal IO1
Is supplied to the switching means 68.

The multiplying means 67 multiplies the selection signal Cj (correction coefficient) supplied from the correction coefficient setting means 66 by the target current signal IMS supplied from the target current setting means 21 and outputs the multiplication result to the motor second. It is supplied to the switching means 68 as a control signal IO2.

The switching means 68 has a switch function of software control, and a switching point is determined based on a two-bit switching signal Cd of LH level, HL level and HH level from the heat generation amount comparing means 62. The state in which the target current signal IMS supplied from the first target current setting means 21 is output as it is, the state in which the switching point outputs the first motor control signal IO1 supplied from the control signal comparing means 65 having the second switching point, The motor second control signal I supplied from the multiplication means 67 having a point of 3
The target current signal IMS, the motor first control signal IO1, or the motor second control signal IO2 is supplied to the deviation calculating means 22 by switching to the state of outputting O2, respectively.
Supply as MH. In this way, the foolproof control unit 52 limits and corrects the motor current.

The limitation and correction of the motor current are required in the following situations. In other words, when the driver repeatedly steers the steering wheel to the left as in the case of steering the garage of the vehicle, then performs the full steering to the right, and then performs the full steering to the left. If the current IM flows and the full steering is repeatedly performed for a long time, the FET of the motor driving means generates a large amount of heat, which may lead to damage.

FIG. 8 is a graph showing the relationship between the motor current IM and the steering position. In FIG. 8, for example, in the vicinity of the steering wheel full right position or the left full steering position, the steering torque sharply increases, and the motor current IM flows through the maximum current of IMMAX. If the state in which full steering is repeated is continued for a long time, the FET of the motor driving means may be damaged by heat generation. Therefore, the maximum value of the motor current IM is limited from the maximum current IMMAX to the assist current value IMASI.

That is, if the full steering is repeated for a long time, the heat generated by the FET of the motor driving means exceeds the first predetermined value, so that the maximum value of the motor current is limited from the maximum current IMMAX to the assist current value IMASI. . At this time, the steering feeling near the right full steering position or the left full steering position is deteriorated, but at other positions, for example, near the neutral position, the steering feeling is not particularly changed and has no influence.

Further, this assist current value I MASI can be reduced by driving the FET for a short period of time, but driving the FET with the assist current value I MASI for a long period of time increases the heat generation of the FET and may lead to damage. If the current is detected and becomes equal to or larger than the second predetermined value, the decrease correction is performed so that the current becomes smaller. The current is reduced by decreasing the correction coefficient with the increase in the amount of heat generation. The relation between the amount of heat generation and the correction coefficient converges to a certain value due to the relation with the ambient temperature and the heat radiation of the FET.

When the current is decreased by reducing the correction coefficient, the protection of the FET is prioritized. Therefore, even when the steering wheel is in the full steering position and other positions, the steering wheel steering becomes slightly heavy and the steering feeling decreases.

FIG. 9 is a graph showing changes in the motor current IM according to the elapse of time according to the present invention. In FIG. 9, the current limiting and reduction correction states of the present invention are shown by solid lines, and the conventional current correction is shown by dashed lines. In FIG. 9, the state of the present invention is such that the motor current is 40 mA at the maximum current IMMAX.
At the point A which flows for (seconds), the heat value is detected as the first predetermined value, and the motor current is limited to the assist current value IMASI.

At this time, for example, the assist current value IMASI is limited to 70% of the maximum current IMMAX. If the assist current value IMASI continues to flow after a further time has elapsed, the heat generation amount of the FET of the motor driving means increases. For example, the heat generation amount at the point C where the assist current value IMASI flows by about 200 S (seconds) becomes the second predetermined value. The motor current detected as a value decreases to a correction current IMMIN corrected by a constant coefficient with an increase in the amount of heat generation.

The correction current IMMIN is continuously reduced from 70% of the maximum current IMMAX to 0%. Note that the correction current IMMIN is a current value such that the heat generation amount and the heat radiation amount of the FET are balanced and the temperature does not change. On the other hand, in the conventional invention, since the calorific value is calculated by the moving average, the average value of the maximum current is detected at the point B as shown by the dashed line in FIG. 9, and the motor current is reduced to the correction current IMMIN. Is done.

As described above, by limiting the maximum value of the motor current based on the amount of generated heat and controlling the reduction current in two stages, the start timing of the reduction correction can be delayed by the limit of the maximum current value. , The start timing of the decrease of the assist force is delayed, and a good steering feeling can be obtained.

In the embodiment, as a method of calculating the temperature of the motor driving means, the heat value of the switching element is calculated based on the motor current signal from the motor current detecting means. However, the temperature of the motor driving means varies with the environmental temperature. Therefore, a thermometer may be provided in the motor driving means as a technique for obtaining the temperature accurately.

[0069]

As described above, according to the present invention ,
According to the electric power steering device of the first aspect , the electric motor driving means can be corrected and controlled in two stages. When the temperature is equal to or higher than the first predetermined value and equal to or lower than the second predetermined value, only the maximum value of the steering assist force is limited. Therefore, when the steering assist force is not so large, the steering assist force is not changed. Further, since the steering assist force is reduced and corrected at the second predetermined value or more, the first predetermined value can be set larger accordingly, and the steering becomes heavier at the first predetermined value because the driver becomes heavier at the first predetermined value. Is cut off to the end, and the current is further limited, so that excessive current flow can be prevented. In addition, operability can be obtained in which the correction is moderate and the feeling during traveling does not suddenly change.

According to the electric power steering apparatus of the second aspect of the present invention , since the foolproof control means estimates the temperature of the motor driving means from the existing motor current detecting means, a new detection such as a thermometer can be performed. There is no need to provide any means. Further, since heat generation can be suppressed and the motor and the FET do not increase in size, the cost of the control unit is reduced, the probability of deterioration and failure is reduced, and the reliability is improved.

Accordingly, it is possible to provide an electric power steering apparatus having a simple structure, excellent steering characteristics, and excellent reliability.

[Brief description of the drawings]

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

FIG. 2 is a block diagram of a main part of an electric power steering apparatus according to an embodiment of the present invention;

FIG. 3 is a block diagram of a main part of a foolproof control unit according to the present invention.

FIG. 4 is a characteristic diagram showing a relationship between a calorific value and a correction coefficient.

FIG. 5 is a drive explanatory diagram of a motor drive unit according to the present invention.

FIG. 6 is a block diagram showing a main part of another embodiment of the control means according to the present invention;

FIG. 7 is a block diagram of a main part of a foolproof control unit according to the present invention.

FIG. 8 is a graph showing a relationship between a motor current IM and a steering position.

FIG. 9 is a graph showing a change with time of the motor current IM according to the present invention;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering shaft, 3 ... Connection shaft, 3a, 3b ... Universal joint, 4 ... Steering gear box, 5 ... Rack & pinion mechanism, 5
a: pinion, 6: manual steering force generating means, 7: rack shaft, 7a: rack teeth, 8: tie rods, 9: left and right front wheels, 10: electric motor, 11: ball screw mechanism, 12: steering torque sensor, 14 ... Vehicle speed sensor, 15, 51 control means, 16 electric motor driving means, 17 steering wheel, 18, 52 full-proof control means, 19 electric motor current detecting means, 21 target electric current setting means, 22 deviation calculating means, 23: Drive control means, 31: Heat generation amount calculation means, 32: Heat generation amount comparison means, 33: Heat generation amount table, 3
4 ... Maximum value setting means, 35 ... Control signal comparing means, 36 ...
Correction coefficient setting means, 37 multiplication means, 38 switching means,
61: calorific value calculating means, 62: calorific value comparing means, 63 ...
Heat value table, 64: maximum value setting means, 65: control signal comparison means, 66: correction coefficient setting means, 67: multiplication means, 68: switching means

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masaaki Kono 1-4-1 Chuo, Wako-shi, Saitama Pref. Honda Technology Laboratory Co., Ltd. (56) References JP-A-6-144279 (JP, A) JP-A Heihei 7-112666 (JP, A) JP-A-8-207799 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 6/00 B62D 5/04

Claims (2)

(57) [Claims] 1. A steering torque sensor for detecting a steering torque of a steering system, a motor for applying a steering assist force to the steering system, and a motor current for detecting a motor current flowing through the motor and outputting a corresponding motor current signal. Detecting means; target current setting means for setting a target current signal corresponding to a target current of the motor based on at least a signal from a steering torque sensor; and determining a motor control signal based on a deviation between the target current signal and the motor current signal. An electric power steering apparatus comprising: a control unit having a drive control unit to perform the operation; and a motor driving unit that drives the electric motor by a motor control signal.The control unit calculates a temperature of the electric motor driving unit,
When the calculated temperature exceeds a first predetermined value, a motor first control signal for limiting the maximum value of the steering assist force, and the calculated temperature exceeds a second predetermined value larger than the first predetermined value. An electric power steering apparatus comprising: a foolproof control unit that generates a second motor control signal that reduces and corrects the steering assist force when the steering assist force decreases. 2. The motor according to claim 2, wherein the foolproof control means calculates a heat generation amount of a switching element of the motor drive means from a motor current signal, and a motor which limits a maximum value of a target current signal or a motor control signal. Control signal comparing means for outputting a control signal; and calculating the calorific value based on the temperature of the motor driving means.
When it is larger than the first calorific value signal estimated to be a fixed value
Supplies the motor first control signal to the motor driving means.
Switch so that the calorific value calculated is
The temperature of the means to a second predetermined value greater than the first predetermined value;
When it is larger than the second heating value signal estimated to be
A motor second control signal is supplied to the motor driving means.
2. The electric power steering apparatus according to claim 1, further comprising: a switching unit configured to switch the electric power steering.