JPH0885468A - Electric power steering device - Google Patents

Abstract

PURPOSE: To provide an electric power steering device capable of applying the optimum and stable assist torque. CONSTITUTION: A current limiting resistor 20 is provided between a battery 10 and a brush. An FET 21 is connected in parallel with the current limiting resistor 20. The gate voltage of the FET 21 is controlled by a controller 22. A tacho-generator 23 is fitted to an electric motor 9. The tacho-generator 23 can feed the voltage signal corresponding to the revolving speed of the electric motor 9 to the controller 22. The controller 22 controls the gate voltage of the FET 21 based on the voltage signal from the tacho-generator 23, i.e., the revolving speed of the electric motor 9.

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 which applies an assist torque according to a steering force by an electric motor.

[0002]

2. Description of the Related Art In a hydraulic power steering system utilizing hydraulic pressure, an assist force is obtained by supplying hydraulic pressure from a hydraulic pump to actuators such as hydraulic cylinders and hydraulic motors according to the operating state of steering. However, in this hydraulic power steering device, since the hydraulic pump is constantly operating, power loss is large, resulting in poor fuel economy.

In order to solve this, there is an electric power steering device such as that used in a light vehicle. This is provided with a control configuration as shown in FIG. 17, in which the torque sensor 50, 51 detects the twist angle of a torque transmission means such as a torsion bar interposed between the steering input shaft and the output shaft, The detected value is read by the controller 52 such as a microcomputer. The controller 52 calculates the assist torque value to be given from the signals from the torque sensors 50 and 51 while correcting with the control signals from the vehicle speed sensors 53 and 54, and the motor current according to the calculated assist torque value. Is supplied to the electric motor 56 via the motor drive circuit 55, thereby applying a predetermined assist torque to the output shaft to reduce the steering force.

However, in the electric power steering apparatus having the above structure, the torque sensors 50 and 51 fail during torque detection, the H-bridge FET forming the motor drive circuit 55 fails due to a short circuit, and the CPU 5
When a malfunction such as a runaway of the vehicle 7 occurs, the electric motor 56 may be operated and steered regardless of the driver's intention. Therefore, it is necessary to detect the failure of the FET, duplicate the torque sensors 50 and 51 and the CPU, and secure reliability. This leads to cost increase and device complexity.

As a conventional electric power steering device which solves this problem, there is, for example, one disclosed in Japanese Patent Publication No. 5-15592 (Japanese Patent Laid-Open No. 61-9371). In this, the steering input shaft and the output shaft are coaxially connected to each other via a bendable torque transmitting means.

A cylindrical body forming an iron core is coaxially fixed to the outer peripheral surface of the output shaft, and a conductor wire is wound around the outer peripheral surface of the cylindrical body to form a rotor winding. Further, a plurality of pairs of magnets are arranged at a position facing the rotor winding in the radial direction at predetermined intervals, and the magnet and the rotor winding form an electric motor. Rotating torque can be applied.

A cylindrical commutator is coaxially fixed to the outer circumference of the output shaft. The body of this commutator is made of an insulating member, and a pair of resistors are provided at symmetrical positions on the outer peripheral surface thereof. Each of the resistors has an arc shape by being extended along the circumferential direction, and the distance between the end portions of the pair of resistors is set to be equal. That is, the position between the end portions of the pair of resistors on the outer peripheral surface of the commutator is in an insulated state.

A pair of brushes is arranged at a position facing the commutator in the radial direction. Each brush is supported on the input shaft side and is urged toward the commutator by a spring, and follows the relative rotational displacement between the input shaft and the output shaft, and the outer circumference of the commutator. The surface is slidable in the circumferential direction. Then, in the initial state where no relative rotational displacement occurs between the input shaft and the output shaft, the brush is set in a state of sliding contact with the insulating portion between the pair of resistor end portions.

Further, the pair of resistors are connected to the ends of the rotor winding, and one brush is connected to a power source terminal such as a battery. When the steering wheel is not steered such as when the vehicle is running straight, the brush is in sliding contact with the insulating portion of the commutator, so that the motor current does not flow in the rotor winding that constitutes the electric motor. , The electric motor is not driven and the assist torque (rotation torque) is not applied to the output shaft.

Alternatively, when the steering wheel is steered, but the road surface resistance of the steered wheels is small and the torsional torque input between the input shaft and the output shaft is small, the torque between the input shaft and the output shaft is also small. Since the relative rotational displacement is small, the brush does not come into contact with the resistor, and the assist torque (rotation torque) is not applied to the output shaft. On the other hand, when the road surface resistance of the steered wheels is large, such as when the steering wheel is steered in a low speed operation, the steering torque becomes large, and the relative rotational displacement between the input shaft and the output shaft becomes large. As a result, the brush is brought into sliding contact with the resistor, and the motor current flows from the battery to the rotor winding through the brush and the resistor to generate current torque. As a result, a predetermined assist torque (rotational torque) is applied to the output shaft, and the steering torque is reduced.

At this time, when the relative rotational displacement between the input shaft and the output shaft increases in proportion to the road surface resistance, that is, the magnitude of the steering torque, it increases in proportion to the relative rotational displacement angle. The contact area between the brush and the resistor is increased, and a current proportional to the contact area can be supplied to the rotor winding. This makes it possible to apply an assist torque linearly proportional to the magnitude of the steering torque to the output shaft.
That is, when the steering torque is small, the assist torque is small, and as the steering torque increases, the assist torque is increased and the steering force is reduced.

[0012]

In the electric power steering apparatus having the above-described structure, since the road surface resistance of the steered wheels is large in a situation such as stationary operation, the load input to the output shaft increases and steering The relative rotational displacement between the input shaft and the output shaft may be the maximum, and when the resistance value between the brush and the commutator becomes zero, the electric motor is directly connected to the battery and the motor rotation In the low speed region, the maximum current value allowed for the electric motor may be exceeded (see the dotted line portion in FIG. 9).

In order to prevent this, the resistance value between the brush and the commutator does not become zero even if the relative rotational displacement angle becomes maximum, or an overcurrent prevention is provided in the drive circuit. It is necessary to interpose a resistor for. However,
If such measures are taken, the motor current increases in proportion to the increase in the relative rotational displacement angle, and the torque is set to have the maximum capacity when the relative rotational displacement angle becomes maximum. Therefore (see the constant chain line in FIG. 9), the torque of the maximum capacity of the electric motor cannot be utilized until the relative rotational displacement angle is reached.

When the rotation speed (steering speed) of the motor increases during steering, the counter electromotive force of the electric motor increases in proportion to the increase, and the output torque decreases. As a result, there is a problem in that the change in the steering force input as a reaction force to the driver becomes large and the steering feeling deteriorates. The present invention has been made in view of the above problems, and an object of the present invention is to provide an electric power steering apparatus capable of providing an optimum and stable assist torque.

[0015]

In order to achieve the above object, an electric power steering apparatus according to the present invention has a structure as shown in FIG. 1 in which a steering input shaft and an output shaft are provided via a torsion bar. Is coaxially connected and an electric motor is connected to the output shaft so as to be intermittently connected. Further, when the relative rotational displacement angle between the input shaft and the output shaft becomes a predetermined rotational angle or more, The variable resistance means is interposed between the electric motor and the power supply, and the variable resistance means has a large relative rotational displacement angle. In the electric power steering device, which is set so that the resistance value is reduced proportionally, and which drives the electric motor with a current value corresponding to the relative rotational displacement angle to generate assist torque, in addition to the variable resistance means. , Above electric mode Current limiting resistor electrically interposed between the power source and the power source, resistance value changing means capable of changing the resistance value of the current limiting resistor, and speed detecting means for detecting the rotation speed of the electric motor. A resistance value control means for decreasing the resistance value of the current limiting resistor in proportion to an increase in the rotation speed of the electric motor through the resistance value changing means, based on the speed signal detected by the speed detecting means, It is characterized by having.

At this time, as described in claim 2, the resistance value control means reduces the rate of decrease of the resistance value of the current limiting resistor with respect to the increment of the rotation speed of the electric motor,
It is characterized in that the counter electromotive force of the electric motor generated by the increment of the rotation speed of the electric motor is set to a value that cancels it. Further, in addition to the configuration described in claim 1 or claim 2, as described in claim 3, the vehicle speed detection means for detecting the vehicle speed is provided, and the resistance value control means is set to decrease. A vehicle speed responsive correction means is provided for correcting the resistance value of the current limiting resistor so as to increase by an amount proportional to the vehicle speed based on the vehicle speed signal from the vehicle speed detection means.

Further, in addition to the structure described in claim 2 or claim 3, as described in claim 4, the vehicle speed detection means for detecting the vehicle speed is provided, and the vehicle by the vehicle speed detection means is provided. Resistance value correction means for setting and changing the rate of decrease of the resistance value of the current limiting resistor with respect to the increase of the rotation speed of the electric motor in the resistance value control means, in proportion to the magnitude of the vehicle speed, based on the speed signal Is provided.

Further, in contrast to the structure described in any one of claims 1, 3 and 4, as described in claim 5, in the resistance value control means of the electric motor. The reduction rate of the resistance value of the current limiting resistor with respect to the increase of the rotation speed is set to a value larger than a value capable of canceling the counter electromotive force of the electric motor generated by the increase of the rotation speed of the electric motor as an initial value. The feature is that it is set.

[0019]

By providing the current limiting resistor in the electric circuit that supplies current to the electric motor, the maximum allowable current value to the electric motor is limited, and overcurrent is prevented. Also,
When the rotation speed of the electric motor increases, the back electromotive force of the electric motor increases and the output torque (assist torque) decreases as it is. However, in the present invention, when the rotation speed of the electric motor increases, the output torque (assist torque) follows the increase. By reducing the resistance value of the current limiting resistor for preventing overcurrent, the output torque is prevented from decreasing.

In the present invention, the decrease of the assist torque is estimated from the rotation speed of the electric motor to control the resistance value of the current limiting resistor. At this time, a method of estimating the rotation speed of the electric motor from the steering speed of the steering wheel can be considered, but the relative rotational displacement angle between the steering input shaft and the output shaft, that is, the steering force, is changed due to changes in the road surface resistance of the wheels. Since there is no one-to-one correspondence between the rotation speed of the electric motor and the rotation speed of the electric motor, there is an error in estimating the rotation speed of the electric motor from the steering speed of the steering wheel or the like, and further estimating the fluctuation of the assist torque (the amount of back electromotive force). Seems large.

However, since the road surface resistance of the wheels is uniform when the vehicle is running on a constant road surface such as running on a paved road or stationary on the paved road, the rotational speed and steering of the electric motor are constant. There is a proportional relationship with the speed, and the above-mentioned action suppresses the change in the assist torque due to the change in the steering speed. As a result, the deterioration of the steering feeling due to the change in the rotation speed of the electric motor can be suppressed.

At this time, by adopting the configuration described in claim 2, the resistance value of the current limiting resistor is reduced by an amount corresponding to the increment of the counter electromotive force, and the steering speed or the rotation of the electric motor is reduced. Even if the speed increases, the fluctuation of the assist torque can be suppressed to zero or small. This also
Before the relative rotation displacement angle between the steering input shaft and the output shaft reaches the set maximum value, the maximum allowable electric current can be supplied to the electric motor, and the relative rotation The maximum capacity of the electric motor can be exhibited before the displacement angle becomes maximum.

The invention described in claim 3 is made in view of the fact that the steering torque input to the driver decreases as the vehicle speed increases, and the resistance value control follows the magnitude of the vehicle speed. By increasing the resistance value of the current limiting resistor controlled by the means, the assist torque is reduced according to the increase of the vehicle speed. As a result, a stable steering torque that suppresses the influence of the vehicle speed is applied to the driver.

In this case, the resistance value of the current limiting resistor is set to a value larger than the minimum resistance value for avoiding the overcurrent of the motor current, and the motor current is changed by the resistance value changing means. It is necessary to take measures such as initial setting to the minimum resistance value that avoids the overcurrent. Further, if the configuration described in claim 2 is adopted, it is set so that the amount of the assist torque does not change due to the change of the electric motor or the steering speed, but in this case, the damping component disappears, so that the vehicle speed is reduced. When the steering wheel is large, the convergence of the steering wheel to the neutral position is poor when the steering wheel is released from the hand, that is, when the steering wheel is released.

On the other hand, in the invention described in claim 4, when the vehicle speed increases, the reduction rate of the resistance value of the current limiting resistor with respect to the increase of the rotation speed of the electric motor decreases, and the electric motor The counter electromotive force generated with respect to the rotation speed or the increment of the steering speed of the steering device is not completely offset, but the assist torque value slightly decreases as the rotation speed of the electric motor increases. This decrease acts as a damping component to improve the convergence of the steering wheel to the neutral position in the released state. The above decrease is
The higher the vehicle speed, the greater the speed.

Next, the operation of the structure described in claim 5 will be described. Depending on the electric motor, the response delay of the motor torque may be large due to the control delay due to the delay component such as the inductance (L component), and the present invention described in claim 5 effectively works in such a case. . If there is a response delay, considering that the steering speed increases, the current value to be controlled, that is, the back electromotive force is larger than the back electromotive force obtained from the detected steering speed. In view of this, by setting the decrease rate of the resistance value of the current limiting resistor to be equal to or more than the counter electromotive force obtained from the steering speed is offset, it is possible to suppress the variation of the assist torque due to the control delay of the motor. You can

[0027]

Embodiments of the present invention will be described with reference to the drawings.
First, the structure will be described. As shown in FIG. 2, an upper end of a steering shaft 2 which is an input shaft is connected to a steering wheel 1, and the steering shaft 2 extends downward. The lower end of the steering shaft 2 is
It is connected to the pinion shaft 4, which is an output shaft, via the torque detection mechanism 3. The lower end of the pinion shaft 4 is
The rack 5 meshes with a horizontally extending rack 5, and the rack 5 and the pinion shaft 4 form a steering gear.

Both ends of the horizontally extending rack 5 are connected to knuckles and steered wheels 7 through tie rods 6, respectively, so that the rack 5 moves horizontally so that the left and right wheels 7 steer. It has become. Further, a reduction gear 8 is fixed to an upper portion of the pinion shaft 4, and a drive shaft of an electric motor 9 is intermittently connected to the reduction gear 8.

As shown in FIG. 2, at the connecting portion between the steering shaft 2 and the pinion shaft 4, the lower end portion of the steering shaft 2 and the upper end portion of the pinion shaft 4 are arranged coaxially, and between them. Torsion bar 1
1 is installed. The steering shaft 2 and the pinion shaft 4 and the torsion bar 11 are connected by, for example, pin connection.

The outer circumference of the pinion shaft 4 is shown in FIG.
As shown in, an annular commutator 12 is coaxially fixed. The main body 12a of the commutator 12 is formed of an insulating member, and four electric resistors 17a, 17b, 18a, 18b are arranged at predetermined intervals along the circumferential direction on the outer peripheral surface side. These four electric resistors 17a, 1
7b, 18a, and 18b are each formed in an arc shape extending in the circumferential direction, and two adjacent two are paired,
Moreover, a pair of electric resistance bodies are formed at symmetrical positions. Then, a pair of electric resistors 17a, 17b, and 18
Adjacent ends of a and 18b are connected by a conductor 13.

A pair of brushes 14 is arranged at a position opposed to the commutator 12 in the radial direction. The pair of brushes 14 are fixed to the ends of the tubular portion 2a extending from the main body of the steering shaft 2 toward the pinion shaft 4 and are urged toward the commutator 12 side by an elastic body such as a spring or rubber (not shown). The pair of brushes 14 are electric resistors 17a, 17 which are not connected by the lead wire 13 of the commutator 12 in the initial state where the relative rotational displacement is not generated between the steering shaft 2 and the pinion shaft 4.
b and 18a, 18b are in sliding contact with a predetermined contact pressure on the insulating portion between the end portions (between the end portions of the electric resistor group). The pair of brushes 14 and the commutator 12 constitute variable resistance means.

The pair of brushes 14 are connected to the battery 10 as a power source via a slip ring (not shown). In addition, each of the electric resistors 17a, 17b, 18a,
The lead wires 13 connecting 18b are connected to an annular slip ring 15 fixed to the pinion shaft 4, and are connected to the electric motor 9 via the slip ring 15.

Further, a current limiting resistor 20 is interposed between the battery 10 and the brush 14. Further, in parallel with the current limiting resistor 20, a FET 21 that constitutes resistance value changing means is connected. The gate voltage of the FET 21 is controlled by the controller 22, and the current limiting resistor 20 and the FE are controlled by changing the gate voltage.
The combined resistance value T with T21 changes. That is, when the gate voltage is zero, the combined resistance value T is set to zero,
The current limiting resistor 2 is proportional to the rise of the gate voltage.
The combined resistance value T continuously increases up to the resistance value of 0 unit. In this way, the resistance value of the current limiting resistor 20 can be variably controlled equivalently. In the initial state, the gate voltage is initialized so that the combined resistance value T becomes the same as the resistance value of the current limiting resistor 20 alone.

A tacho generator 23 is attached to the electric motor 9. Tacho generator 2
3 detects the rotation speed of the electric motor 9 as a voltage value,
The detected voltage signal can be supplied to the controller 22. The controller 22 is, as shown in FIG.
With the microcomputer 25 and the drive circuit 26 as the main components, the gate voltage of the FET 21 is controlled based on the voltage signal from the tacho generator 23, that is, the rotation speed of the electric motor 9.

That is, the voltage signal from the tacho generator 23 can be supplied to the microcomputer 25 after being converted into a digital amount by the A / D converter 27. In the microcomputer 25, as shown in FIG. 6, first, a voltage signal which is a control signal is input (step 1), and the rotation speed of the electric motor 9 is based on the voltage signal input via the A / D converter 27. M is calculated (step 2), and the combined resistance value T of the current limiting resistor 20 and the FET 21 set by the arithmetic expression shown below is calculated (step 3).

T = -k ₁ × M + k ₂ (1) Here, k ₁ and k ₂ are proportional constants determined by the characteristics of the motor and the like, and k ₁ is relative to the increment of the rotation speed. The reduction rate of the resistivity of the current limiting resistor 20 is shown.
For example, the characteristics of the electric motor 9 of this embodiment are set as shown in FIG. 7, and the internal resistance value of the electric motor 9 is set to 0.282.
When the maximum allowable current is 30 A and the voltage of the battery 10 is 12 V, the minimum resistance value required for the current limiting resistor 20 to prevent overcurrent is 12 ÷ 30−0.282 = 0.118Ω. The proportional constant k ₂ is set to 0.118.

At this time, since the motor back electromotive voltage with respect to the rotation speed of the electric motor 9 is shown in FIG. 8, the proportional constant k is set to a value corresponding to the slope of the graph L shown in FIG. Decide ₁ In addition, the above (1)
It goes without saying that instead of an arithmetic expression such as an expression, it may be given in the form of a graph, or may be stored in the memory in the form of a table and processed.

Next, the microcomputer 25 can supply the drive circuit 26 with a command value corresponding to the calculated combined resistance value T (step 4). The microcomputer 25 is composed of an I / O interface section, a memory section, a control section, a clock generator, etc., and is capable of performing the above-mentioned operation based on the clock pulse of the crystal oscillation circuit 28.

In the drive circuit 26, based on the input command value, it is possible to supply the gate voltage of the combined resistance value T corresponding to the command value to the gate electrode of the FET 21.
The microcomputer 25 and the drive circuit 26
When the key switch of the ignition key is turned on, the operation starts using a predetermined battery 10 as a power source.

Next, the operation of the electric power steering apparatus having the above structure will be described. When the steering wheel 1 is not steered, such as when traveling straight ahead, or when the steering wheel 1 is slightly steered, the torsion torque applied to the torsion bar 11 interposed between the steering shaft 2 and the pinion shaft 4 is Zero or small.

In this state, since the relative rotational displacement angle between the steering shaft 2 and the pinion shaft 4 is small, the brush 14 is connected to the electric resistors 17a, 17b, 18a,
18b is not contacted and no electric current is applied to the electric motor 9. As a result, the assist torque is not applied to the pinion shaft 4 until the steering torque reaches or exceeds the predetermined value.

Further, when the steering wheel 1 is steered and the road surface resistance of the wheels is large and a steering torque of a predetermined value or more is generated, an amount proportional to the steering torque is applied between the steering shaft 2 and the pinion shaft 4. Relative rotational displacement occurs at. At this time, the brush 14 slides toward the one end of the electric resistors 17b and 18b in the extending direction and comes into sliding contact with the one end of the extending direction (position A in FIG. 3). As a result, a predetermined motor current is supplied to the electric motor 9 via the electric resistors 17b and 18b, and an assist torque corresponding to the motor current is applied to the pinion shaft 4 via the speed reducer 8 to allow the driver to operate. Steering is reduced.

At this time, the electric resistors 17b, 18b
Since a current flows from one end to the other end in the extending direction, the resistance value of the electric resistors 17b and 18b is large, that is, the motor current supplied to the electric motor 9 is small, and thus the assist torque is small. Subsequently, when the steering torque further increases from the above state, the brush 14 moves on the electric resistors 17b and 18b from one end to the other end in the extending direction.

As a result, the positions of the other ends of the electric resistors 17b and 18b and the brush 14 become closer to each other by the amount of the increase in the relative rotational displacement between the steering shaft 2 and the pinion shaft 4, and the battery 10 and the electric motor are moved. The resistance value between No. 9 and 9 decreases, and the motor current, that is, the assist torque increases. In this way, the assist torque proportional to the steering torque is applied. When the steering wheel is steered to the side opposite to the steering operation, the brush 14 slides on the electric resistors 17a and 18a and has the same operation and effect as described above.

At this time, the electric resistors 17a, 17b, 1
Depending on the physical distance between the other end in the extending direction of 8a, 18b and the brush 14, the electric resistances 17a, 17
b, 18a, 18b with variable resistance values, electric motor 9
Since the current value supplied to the steering wheel 1 is controlled, it is possible to suppress the influence on changes in temperature, humidity and the like to a smaller extent than before, and a desired assist torque corresponding to the steering force generated in the steering wheel 1 is output to the pinion which is the output shaft. It can be applied to the shaft 4.

By applying a motor current proportional to the steering torque to the electric motor 9 in this way, an assist torque proportional to the steering torque is generated. At this time, the assist torque is increased in accordance with the increase in the rotation speed of the electric motor 9. A counter electromotive force is generated and the assist torque is reduced. On the other hand, in the present embodiment, the rotation speed of the electric motor 9 is based on the signal input via the tacho generator 23, and the controller 2
2 is obtained by the controller 22 by the controller 22
By controlling the gate voltage of the current limiting resistor 2
The combined resistance value T of 0 and the FET 21 is decreased with the increase of the rotation speed, and the decrease of the output torque due to the back electromotive force of the electric motor 9 is suppressed.

As a result, the electric power steering apparatus of this embodiment has the assist torque characteristic shown by the solid line in FIG. 9, for example. Where, as above,
The characteristics of the electric motor 9 are set as shown in FIG. 7, the internal resistance value of the electric motor 9 is 0.282, and the maximum current is 30 A.
In addition, the voltage of the battery 10 is set to 12V, the resistance value of the current limiting resistor 20 is set to 0.118Ω, and the current limiting resistor 2 for the motor rotation speed is set.
This is a case where the reduction rate of the combined resistance value T of 0 and the FET 21 is set to a value (value that cancels back electromotive force) according to the graph L in FIG. Further, the gear ratio of the speed reducer 8 is set to 16.

In FIG. 9, the alternate long and short dash line indicates the case where the current limiting resistor 20 is provided to prevent overcurrent and the resistance value of the current limiting resistor 20 is constant as in the conventional case. The characteristics of the conventional assist torque are shown for comparison. The line indicated by the dotted line shows the characteristic of the assist torque when the current limiting resistor 20 for preventing overcurrent is not provided.

As can be seen from FIG. 9, the electric motor 9
By decreasing the gate voltage of the FET 21 (reducing the resistance of the FET 21) with the increase of the rotation speed of the, the resistance value of the current limiting resistor 20 is equivalently decreased, and the rotation speed of the motor is 1000 rpm, that is, the output. The steering speed input to the pinion shaft 4, which is the shaft, is 375 de
Up to g / sec, the assist torque can be set constant.

Here, since the steering speed at the time of stationary steering is about 360 deg / sec at the maximum, by setting as described above, the rotation speed of the electric motor 9 at the time of stationary steering, that is, the steering speed is increased. The decrease of the assist torque due to the rise is suppressed, and the stable steering force can be applied to the steering wheel 1, that is, the driver, and the steering feeling is stabilized.

On the other hand, in the prior art, as indicated by the alternate long and short dash line in FIG. 9, the assist torque decreases as the steering speed increases, and the faster the steering wheel 1 is rotated, the heavier the steering wheel 1 becomes. Although it is uncomfortable, this is avoided in this embodiment. In the above embodiment, the tacho generator 23 is used as the speed detecting means.
However, the present invention is not limited to this, and for example, the rotation speed of the electric motor 9 may be set to be calculated from the terminal voltage and current of the electric motor 9.

Although the current limiting resistor 20 is interposed between the brush 14 and the battery 10 in the above embodiment, it may be interposed between the commutator 12 and the electric motor 9. . Further, without providing the electric motor 9 as a separate body as in the above-described embodiment, as described in JP-A-61-9371, it is formed coaxially with the pinion shaft 4 and the reduction gear 8 is omitted. Good. That is, the electric motor 9 is not limited to the above configuration, and any other known configuration may be adopted as long as the rotational torque according to the motor current can be applied to the pinion shaft 4.

In the above embodiment, the brush 14 side is connected to the electric motor 9 and the electric resistors 17a and 17a are connected.
Although the b, 18a, 18b side is connected to the battery 10, the brush 14 side may be connected to the battery 10 and the electric resistor 17a, 17b, 18a, 18b side may be connected to the electric motor 9. Further, in the above embodiment, the FET 21 which is a power element is used as the resistance value changing means, however, a power element such as another transistor element may be adopted, or the current limiting resistor 20 itself may be a variable resistance means. And the resistance value changing means may be configured by a mechanical structure that moves the movable portion such as the brush 14.

Next, the second embodiment will be described. Second
The basic configuration of the embodiment is similar to that of the first embodiment, and the different configuration will be described below. First, the resistance value of the current limiting resistor 20 is set to the minimum resistance value for preventing overcurrent to the electric motor 9, that is, 0.11 in the above embodiment.
Set larger than 8Ω.

For example, in the electric motor 9 shown in FIG. 7, no rotational torque is generated when the motor current is 1 A or less. Therefore, the resistance value of the current limiting resistor 20 is set to the value when the resistance value of the variable resistance means is zero. Motor current becomes 1A 12 ÷
1−0.282 = 11.718Ω. And
In the initial setting state, the current limiting resistor 20 and the FET 2
F so that the combined resistance value T with 1 is 0.118Ω.
Initialize the gate voltage of ET21.

Further, in this embodiment, the vehicle speed sensor 30 constituting the vehicle speed detecting means for detecting the vehicle speed is provided (FIG. 5).
reference). The vehicle speed sensor 30 can supply a vehicle speed signal corresponding to the detected vehicle speed to the controller 22. The controller 22 can supply the vehicle speed signal from the vehicle speed sensor 30 to the microcomputer 25 via the A / D converter 31, and the microcomputer 25 calculates the vehicle speed V based on the input vehicle speed signal. To do.

At this time, the microcomputer 25 of the first embodiment calculates the rotation speed M of the electric motor 9 based on the input voltage signal, and sets the current according to the arithmetic expression as shown in the equation (1). Limiting resistor 20 and FE
Although the combined resistance value T calculated by T21 and T21 is calculated, in the present embodiment, the combined resistance value T to be obtained is calculated based on the vehicle speed.
A correction term for correcting is added to the above equation. That is,
The combined resistance value T is calculated by the following arithmetic expression to which a correction term that constitutes the vehicle speed sensitive correction means is added. T = −k ₁ × M + k ₂ + k ₃ (V) (2) where k ₁ and k ₂ are proportional constants determined by motor characteristics and the like, and k ₃ is an increment of vehicle speed. It is a proportional number indicating the increment of the resistance value increased by.

It should be noted that it may be given in the form of an individual map according to the vehicle speed instead of the above-mentioned arithmetic expression, or may be stored in the memory in the form of a table. There is no end. Here, the above k ₃ (V) is a function of the vehicle speed V, is set so as to increase in proportion to the increase of the vehicle speed V, and the combined resistance value calculated by the above equation (2). The graph showing T is set so as to change as L → L ₁ → L ₃ as shown in FIG. 10 as the vehicle speed increases.

The other structure is the same as that of the first embodiment. Next, the operation of the electric power steering system of the second embodiment will be described. When the vehicle speed V increases, the road surface resistance of the steered wheels decreases and the steering of the steering wheel 1 becomes lighter, but in this embodiment, in addition to the operation of the first embodiment, the current limiting resistor is used. 20 and F
Since the combined resistance value T due to ET21 increases in proportion to the increment of the vehicle speed V, the motor current decreases and the assist torque decreases as the vehicle speed V increases.
As shown in, the characteristic of the assist torque is changed to the position shown by the arrow in the figure as the vehicle speed increases.

This prevents the steering wheel 1 from being lightly steered even when the vehicle speed V is high, so that the driver can be provided with a stable steering feeling independent of the vehicle speed V. Next, a third embodiment will be described. The basic configuration of the third embodiment is similar to that of the second embodiment, and the following equation is adopted as an arithmetic expression for calculating the combined resistance value T in the microcomputer 25.

T = −k ₁ (V) × M + k ₂ + k ₃ (V) (3) That is, k ₁ which is a proportional constant showing the rate of decrease of the resistance value is taken as a function of the vehicle speed V, and FIG. As shown in FIG. 12, it is set so as to decrease in proportion to the increase of the vehicle speed V (moves in the direction of the arrow in FIG. 12). The k ₁ (V) constitutes resistance value correcting means.

Instead of the above-mentioned arithmetic expression, it may be given in the form of an individual graph according to the vehicle speed V, or may be stored in the memory in the form of a table. Needless to say. The other structure is similar to that of the first embodiment. In such an electric power steering system, when the third term (+ k ₃ (V) portion) of the above equation (3) is ignored, the higher the rotation speed of the electric motor 9 is, the more the electric power steering apparatus is compared with the first embodiment. As shown by the arrow in FIG. 13, the assist torque is set to decrease a little as the vehicle speed V increases without completely canceling out the counter electromotive force generated by the increase of the rotation speed. It

Since the reduced amount of the assist torque acts as a damping component, the so-called convergence of the steering wheel 1 to the neutral position at the time of high speed running is higher than that of the first embodiment. Improve. Further, considering the third term in the equation (3), the combined resistance value of the current limiting resistor 20 and the FET 21 is the vehicle speed V
As shown in FIG. 14, the steering wheel 1 is changed and controlled in the direction of the arrow in accordance with the increase of the vehicle speed V, and has the above-described effect and the effect of the second embodiment. The hand-release convergence is good, and the steering force is prevented from being weakened even when the vehicle speed V increases, and the driver can be provided with a stable steering feeling that is not affected by the vehicle speed V.

Next, a fourth embodiment will be described. Fourth
The electric power steering apparatus of the embodiment has the same configuration as that of the third embodiment, and in the arithmetic expression (3) calculated by the microcomputer 25 of the controller 22,
The initial value of the proportional constant k ₁ that represents the reduction rate of the resistance value is set to be larger than the value that cancels the counter electromotive force due to the increase in the rotation speed of the electric motor 9.

That is, the initial value of the combined resistance value of the current limiting resistor 20 and the FET 21 with respect to the rotation speed of the electric motor 9 is represented by the counter electromotive force due to the increase in the rotation speed of the electric motor 9, as shown in FIG. It is set to the corresponding value of the graph L ₄ having a larger inclination than the canceling graph L. As a result, in the initial state where the vehicle speed V is zero, as shown in FIG. 16, the assist torque is set to slightly increase as the rotation speed of the electric motor 9 increases.

This is because the response of the rotational torque is delayed by the control delay element such as the inductance (L component) of the electric motor 9. Therefore, by increasing the gain with respect to the increase of the rotational speed as described above, the response is increased. To compensate for the delay. Then, when the vehicle speed V increases,
As described in the third embodiment, the value of k ₁ is the vehicle speed V
15 becomes larger (shifted in the direction of L ₄ → L in FIG. 15) in proportion to the increment of, and has a damping effect, and the above k ₁ is toward a value that cancels back electromotive force according to the rotation speed. change. Further, when the vehicle speed V increases, the value is changed to a value smaller than the value for canceling the counter electromotive force according to the rotation speed (shift in the direction of L → L _{5 in} FIG. 15).

In all the above embodiments, for example, 10
An extremely low vehicle speed such as km / h or less may be regarded as "zero vehicle speed", and the dead zone may be provided as described above without completely making the operation for the vehicle speed component proportional to the vehicle speed.

[0068]

As described above, in the electric power steering apparatus of the present invention, by providing the current limiting resistor, the overcurrent to the electric motor can be prevented and
Even if the rotation speed of the motor increases, the reduction of the assist torque is suppressed to zero or small. Even if the rotation speed of the motor and the steering speed increase, the steering force input to the driver via the steering wheel. There is an effect that it is possible to prevent deterioration of steering feeling due to less change.

At this time, if the configuration described in claim 3 is adopted, the increase or decrease of the assist torque due to the change of the vehicle speed is suppressed, the stable assist torque is generated, and the change of the steering force due to the change of the vehicle speed is small. Therefore, there is an effect that it is possible to prevent deterioration of steering feeling due to a change in vehicle speed. Further, when the configuration described in claim 4 is adopted, there is an effect that it is possible to prevent deterioration of so-called hand-releasing convergence to the neutral position of the steering wheel when the vehicle speed is high.

Furthermore, if the structure described in claim 5 is adopted, it is possible to absorb the response delay of the electric motor.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim according to the present invention.

FIG. 2 is an overall configuration diagram of an electric power steering device according to an embodiment of the present invention.

FIG. 3 is a schematic diagram showing a configuration of a connecting portion between a steering shaft and a pinion shaft according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a configuration of variable resistance means of an exemplary embodiment according to the present invention.

FIG. 5 is a diagram showing a configuration of a controller according to an embodiment of the present invention.

FIG. 6 is a diagram showing a processing procedure of a controller according to an embodiment of the present invention.

FIG. 7 is a diagram showing characteristics of the electric motor of the embodiment according to the present invention.

FIG. 8 is a diagram showing characteristics of a rotation speed, a back electromotive force, and a combined resistance value of an electric motor according to an embodiment of the present invention.

FIG. 9 is a diagram showing characteristics of assist torque according to the embodiment of the present invention.

FIG. 10 is a diagram showing characteristics of a combined resistance value according to the second embodiment of the present invention.

FIG. 11 is a diagram showing characteristics of assist torque according to the second embodiment of the present invention.

FIG. 12 is a diagram showing a characteristic of a combined resistance value according to a third embodiment of the present invention.

FIG. 13 is a diagram showing characteristics of assist torque according to the third embodiment of the present invention.

FIG. 14 is a diagram showing characteristics of a combined resistance value according to the third embodiment of the present invention.

FIG. 15 is a diagram showing characteristics of a combined resistance value according to a fourth example of the present invention.

FIG. 16 is a diagram showing a characteristic of assist torque according to a fourth embodiment of the present invention.

FIG. 17 is a diagram showing an example of a configuration of a control unit in a conventional electric power steering device.

[Explanation of symbols]

 1 Steering Wheel 2 Steering Shaft 4 Pinion Shaft 5 Rack 7 Steering Wheel 8 Reducer 9 Electric Motor 10 Battery (Power Source) 11 Torsion Bar 12 Commutator (Variable Resistance Means) 14 Brush (Variable Resistance Means) 20 Current Limiting Resistor 21 FET (resistance value changing means) 22 Controller (resistance value control means) 23 Tacho generator 25 Microcomputer 26 Drive circuit 30 Vehicle speed sensor (vehicle speed detection means)

Claims (5)

[Claims] 1. A steering input shaft and an output shaft are coaxially connected via a torsion bar, an electric motor is intermittently connected to the output shaft, and a relative rotational displacement between the input shaft and the output shaft is provided. The electric motor and the power supply are set to be electrically connectable when the angle becomes equal to or larger than a predetermined rotation angle, and variable resistance means is interposed between the electric motor and the power supply. The variable resistance means is set so that the resistance value decreases in proportion to an increase in the relative rotational displacement angle, and the electric motor is driven with an electric current value according to the relative rotational displacement angle to assist the electric motor. In an electric power steering apparatus that generates torque, a current limiting resistor electrically interposed between the electric motor and a power source, and a resistance value of the current limiting resistor, separately from the variable resistance means. Resistance value changing means that can change ,
Based on the speed detection means for detecting the rotation speed of the electric motor and the speed signal detected by the speed detection means, in proportion to the increase in the rotation speed of the electric motor via the resistance value changing means, An electric power steering apparatus comprising: a resistance value control unit that reduces a resistance value. 2. The back electromotive force of the electric motor, which is generated by the increase in the rotation speed of the electric motor, by the resistance value control means, and reduces the rate of decrease of the resistance value of the current limiting resistor with respect to the increase in the rotation speed of the electric motor. The electric power steering device according to claim 1, wherein the electric power steering device is set to a value that cancels out. 3. A vehicle speed detecting means for detecting a vehicle speed is provided, and a resistance value of a current limiting resistor which is set to be reduced by the resistance value controlling means is set to a vehicle speed based on a vehicle speed signal from the vehicle speed detecting means. The electric power steering apparatus according to claim 1 or 2, further comprising a vehicle speed responsiveness correction means for correcting the vehicle speed responsiveness so as to be increased by a proportional amount. 4. A vehicle speed detecting means for detecting a vehicle speed is provided, and based on a vehicle speed signal from the vehicle speed detecting means, the resistance of the current limiting resistor with respect to the increment of the rotation speed of the electric motor in the resistance value controlling means. 4. The electric power steering device according to claim 2, further comprising resistance value correcting means for setting and changing the rate of decrease of the value in proportion to the magnitude of the vehicle speed. 5. The resistance value control means generates a reduction rate of the resistance value of the current limiting resistor with respect to an increase of the rotation speed of the electric motor as an initial value by the increase of the rotation speed of the electric motor. 5. The electric power steering apparatus according to claim 1, wherein the counter electromotive force of the electric motor is set to a value larger than a cancelable value.