JPH05270426A - Electro-hydraulic power steering device for vehicle - Google Patents

Abstract

(57) [Summary] [Object] The present invention aims to enhance only the neutral tightness when traveling straight at high speed while maintaining the steerability at low and medium speeds depending on the vehicle speed and the steering angle and the steerability at high speed steering. The main feature. [Structure] A piston mechanism 12 for assisting the steering mechanism 1 is provided, and an electric hydraulic pump 22 and pressure receiving chambers 31a, 31b of the piston mechanism are connected via a supply / discharge valve 19 to generate an assist force according to steering. Circuit 3
4, the first circuit section 37 having discharge performance satisfying the neutral feeling during high-speed straight running and the second circuit section 37 having discharge performance satisfying the steering feeling based on the vehicle speed and the steering angle state.
And a circuit section 37 that operates the electric hydraulic pump according to the setting of the first circuit section during high-speed straight traveling, and otherwise operates the electric hydraulic pump according to the setting of the second circuit section.
Was established. This is to enhance the reaction force when traveling straight at high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicular electrohydraulic power steering system used to steer the front wheels of an automobile.

[0002]

2. Description of the Related Art An automobile (vehicle) is equipped with a hydraulic power steering device for steering with light operation. In such a power steering device, a structure using an oil pump that uses a running engine as a drive source is generally adopted.

Specifically, a steering mechanism for steering the front wheels (steering wheels) to the left and right according to the operation of the steering wheel,
Engine driven oil pump, rotary valve (supply / discharge valve), power cylinder device (piston mechanism)
A hydraulic circuit configured by connecting the valve to the power passage is used to supply the hydraulic pressure obtained by the rotary valve that is displaced by the rotation of the handle to the power cylinder device to generate the necessary assist force. It is being appreciated. However, the handle force cannot be properly controlled only by the displacement of the rotary valve.

Therefore, in a conventional power steering system using a running engine as a drive source, a reaction force mechanism for varying a steering reaction force and a control valve for controlling the reaction force mechanism are provided in a hydraulic circuit to provide an assist force. Variable,
This is controlled by using a sensor that detects the vehicle speed of the automobile and a sensor that detects the steering wheel angle to obtain appropriate steering characteristics. For example, when the steering wheel is stationary or in the low speed range, the assist force is appropriately increased to lighten the steering wheel force. On the contrary, when steering in the middle and high speed range, the assist force is appropriately reduced to increase the steering wheel force. There is.

However, although such an engine type power steering device can certainly control an appropriate steering force, it has a problem that it is structurally complicated because a reaction force mechanism and a control valve must be added. .. In addition, the load on the running engine is large, which is a factor that impairs the fuel efficiency of the automobile.

Therefore, recently, instead of the engine for running,
Controls the discharge performance of an electric hydraulic pump by using an electric hydraulic pump driven by an electric motor that operates with a battery and an alternator installed in an automobile as a power source, without using a reaction mechanism such as an engine type or a control valve. A power steering device, that is, an electro-hydraulic power steering device, is proposed in which the steering force is appropriately controlled just like the above engine type.

[0007]

However, this electro-hydraulic power steering system, like the engine-driven power steering system, reduces the steering force by increasing the discharge flow rate of the electro-hydraulic pump in the stationary and low speed range. However, since the discharge flow rate is reduced and the steering force is made heavier in the middle and high speed ranges, there is a problem that the neutral feeling in the high speed straight traveling state of the vehicle becomes ambiguous. This is because the power cylinder device is configured by providing a pair of chambers (pressure receiving chambers) on both sides of a reciprocating piston.

Here, like the engine-driven power steering device, when the power cylinder device is in a high-speed straight traveling state, the power cylinder device is provided in a pair of chambers on both sides of the power cylinder device from an electric hydraulic pump via a rotary valve. The discharged oil is supplied, the hydraulic pressure is evenly applied to both sides of the piston, and the neutral state of the steering mechanism (handle) is maintained from this neutral pressure to generate a neutral feeling, that is, a so-called neutral tight feeling.

However, since the discharge flow rate from the electric hydraulic pump in the high speed range decreases as the vehicle speed of the automobile increases (by increasing the steering wheel force in the high speed range), the neutral pressure is applied in the high speed straight traveling state. Is inevitably low, which inevitably results in a lack of reaction force, giving the driver a sense of lack of a so-called neutral tightness. Since this neutral tightness also determines the quality of high-speed straightness of an automobile, there is a strong demand for improvement.

The present invention has been made in view of the above circumstances, and its purpose is to maintain the steerability at low and medium speeds and the steerability at high speed steering depending on the vehicle speed and the steering angle state. An object of the present invention is to provide a vehicular electro-hydraulic power steering device capable of improving the neutral tightness during high-speed straight running.

[0011]

In order to achieve the above object, a vehicular electrohydraulic power steering apparatus of the present invention is provided with a steering mechanism for steering steered wheels in a steering direction according to an operation of a steering wheel, and an electric motor is a drive source. Is provided with an electric hydraulic pump driven as described above, pressure receptive chambers are provided on both sides of a reciprocating piston, and a piston mechanism for assisting the steering mechanism in the steering direction according to the displacement of the piston is provided. The pump and each pressure receiving chamber of the piston mechanism are connected via a supply / discharge valve that supplies / discharges according to the steering of the steering mechanism, and the assist force according to the steering of the steering mechanism is applied to each pressure. Discharge performance of the electric hydraulic pump that has a hydraulic circuit to generate in the receiving chamber and satisfies the neutral feeling when the vehicle travels straight at high speed When the vehicle is traveling straight at high speed, the first setting means is set, and the second setting means is set in which the discharge performance of the electric hydraulic pump that satisfies the steering feeling based on the vehicle speed and the steering angle state is set. Operates the electric hydraulic pump according to the setting performance of the first setting means,
Other than that, there is provided a means for operating the electric hydraulic pump according to the setting performance of the second setting means.

[0012]

According to the electric hydraulic power steering apparatus for a vehicle of the present invention, when the vehicle is operated at low and medium speeds and during high speed steering,
The electric hydraulic pump is controlled according to the discharge performance satisfying the steering feeling based on the vehicle speed of the vehicle and the steering angle state of the steering wheel set in the second setting means.

As a result, the assist force corresponding to the vehicle speed and the steering angle state is output to the pressure receiving chamber of the piston mechanism in both the low and medium speed range and the high speed steering state, and the steering force is controlled appropriately.

On the other hand, in the high-speed straight traveling state, the electric hydraulic pump is operated according to the first setting means in which the discharge performance satisfying the neutral feeling is set, not the discharge performance set in the second setting means. Will be controlled.

As a result, during high-speed straight traveling, control that emphasizes neutral feeling is performed instead of control that emphasizes steering. In other words, the feeling of reaction force is not insufficient, and a high neutral tightness is provided to the driver.

Therefore, while maintaining the good performance of the prior art such as the steerability at low and medium speeds and the steerability at high speed steering, it is possible to improve the neutral tightness during high-speed straight running, and Performance is improved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in FIGS.

FIG. 1 is a schematic view of an electrohydraulic power steering apparatus for an automobile (vehicle) to which the present invention is applied. In FIG. 1, reference numeral 1a is a rack and pinion type steering gear constituting the steering mechanism 1. ..

The steering gear 1a is constructed by incorporating a rack 3 extending in the vehicle width direction and a pinion gear 4 meshing with the rack 3 in a casing 2. The pinion gear 4 is connected to the input shaft 6 of the steering gear 1a via the torsion bar 5.

One end of the rack 3 is connected to the left front wheel 10 via a steering rod 7, a tie rod 8 and a knuckle 9. Similarly, the other end is connected to the right front wheel 10 via a steering rod 11, a power cylinder device 12 (corresponding to a piston mechanism), a tie rod 13, and a knuckle 14.

Input shaft 6 protruding from the upper part of casing 2
Is connected to a steering wheel 18 via a steering joint 16, for example, a two-part steering shaft 17. This allows the handle 18 to be operated (rotated)
Then, this displacement is transmitted to the knuckles 9 and 14 through the steering shaft 17, the torsion bar 5, the pinion gear 4, the rack 3, and the steering rods 7 and 11, and the left and right front wheels 10 and 10 are steered in the operated direction. ing. Incidentally, 17a is a steering column.
A rotary valve 19 (supply / discharge valve) is provided between the input shaft 6 of the steering gear 1 a and the pinion gear 4.

As is well known, the rotary valve 19 comprises a pinion gear 4 provided with a tubular outer valve 19a, and an input shaft 6 provided with a tubular inner valve 19b which is combined with the outer valve 19a. That is, when the torsion bar 5 is twisted by the handle force from the handle 18, the rotary valve 19 causes relative displacement between the outer valve 19a and the inner valve 19b.

An inflow port portion 20 formed in the rotary valve 19 is connected to a discharge portion of an electric hydraulic pump 22 via a flow passage 21, and an outflow port portion 23 is also provided.
Is connected to the suction section of the electric hydraulic pump 22 via the flow path 24.

That is, in the electric hydraulic pump 22, for example, the electric motor 22b for driving is directly connected to the pump portion 22a,
Further, it has a structure in which a reservoir 22c is connected to the suction portion of the pump portion 22a, the flow passage 21 is connected to the discharge port of the pump portion 22a, and the flow passage 2 is connected to the suction port of the reservoir 22c.
4 are connected.

Further, the electric motor 22b of the electric hydraulic pump 22 is connected to a power source circuit (not shown) constructed by connecting a battery mounted on the automobile and an alternator in parallel to each other. The electric hydraulic pump 22 is operated by using electric power as a power source. The pair of output port portions 26a, 26b formed in the rotary valve 19 are connected to the power cylinder device 12 via the flow paths 27a, 27b.

That is, the power cylinder device 12 includes a piston rod 28 connected to the steering rod 11.
Through a cylinder 29 fixed to a frame of an automobile or the like, and the cylinder 2 is partially attached to the piston rod 11.
Slidable piston 3 that divides the inside of 9 into left and right (vehicle width direction)
It is configured by providing 0.

The chambers 31a and 31 (pressure receiving chambers) on both sides (left and right) of the piston, which are partitioned by the piston 30, have a pair of input port portions 32a and 32b and flow paths 27a and 27b.
Is connected to the output port sections 26a and 26b through.

With the hydraulic circuit 34 thus constructed,
When the handle 18 is in the neutral state, the rotary valve 1
9, the hydraulic pressure generated by the electric hydraulic pump 22 is supplied to both chambers 31a and 31b as neutral pressure. When the steering wheel 18 is steered, the outer valve 1 of the rotary valve 19 corresponding to the steering is
9a and the inner valve 19b, the hydraulic pressure according to the relative displacement supply / discharge operation, that is, the hydraulic pressure corresponding to the steering (steering force and steering direction) is applied to the chamber 31a or the chamber 31b.
Is supplied to the front wheels 10, 10 while assisting the steering force with the hydraulic pressure generated in the chambers 31a, 31b.
To be able to steer.

The electric motor 22 of the electric hydraulic pump 22
A control unit 37 including a microcomputer and its peripheral circuits is connected to b via a drive circuit 36. This control unit 3
Reference numeral 7 denotes a vehicle speed sensor 38 for detecting the vehicle speed of the automobile, and a steering angle sensor 3 for detecting the steering angle of the steering wheel 18 by a pulse.
9 is connected. And, by the circuit configured by the connection of these electronic devices, when the high-speed straight running state, the power steering performance that emphasizes the neutral feeling is obtained, and other stationary installations,
Power steering performance that emphasizes steering is obtained during straight / steering in the low-medium speed range and steering in the high-speed range.

That is, in the control unit 37, a mode of "motor drive command value Mn according to vehicle speed" as shown in FIG. 4 is set as a map.
This map is set so that the steering force becomes optimal depending on the vehicle speed, and the discharge performance of the electric hydraulic pump 22 that satisfies the steering feeling based on the vehicle speed is set in this map. At the same time, M of the motor drive command value Mn of this map
The ax value is the value of the ejection performance that satisfies the neutral feeling during high-speed straight running.

However, in FIG. 4, the motor drive command value Mn
The relationship between the electric hydraulic pump 22 and the electric hydraulic pump 22 is such that the rotation speed of the electric motor 22b increases as the motor drive command value Mn increases, and the rotation speed of the electric motor 22b decreases as the motor drive command value Mn decreases. As a result, the pump discharge amount increases as the motor drive command value Mn increases, and the pump discharge amount decreases as the motor drive command value Mn decreases.

Further, the control unit 37 is set with a discriminant value of, for example, "80 km / h" of the vehicle speed as a set value for discriminating the vehicle speed range into each region, and the output from the vehicle speed sensor 38 can be read. Therefore, the vehicle speed range is discriminated into a low-medium speed range and a high-speed range with "80 km / h" as a boundary.

Further, the control unit 37 has a function of determining whether or not the handle 18 has been operated.
A function for determining the presence / absence of a pulse from the steering angle sensor 39 is set. In addition, the control unit 37 has, for example, a steering angle of “± 5 ° or less” as a function of determining which region the operated steering wheel 18 is.
Values for discriminating between “± 5 ° ± 20 °” and “± 20 ° or more” are set, and the operation of the handle 18 is “neutral band” according to the reading of the pulse output from the steering angle sensor 39. It is configured to determine which of the "small rudder angle range" and the "medium / large rudder angle range" the area corresponds to.

By means of the speed range and steering range discriminating functions, it is possible to detect the straight traveling state (the steering wheel 18 is in a neutral state) and the steering state in each of the low and medium speed regions and the high speed region. The control unit 37 is set with a value of a vehicle speed of "10 km / h" as a function for determining a state where steering is not performed in an extremely low speed range.

The control unit 37 is "10 km /
It is set to stop the electric motor 22b of the electric hydraulic pump 22 when the steering is not performed in the extremely low speed range of "h" or less.

Further, the control unit 37 displays "80".
When the vehicle is in the neutral zone or the steering zone in the low / medium speed range of "km / h or less", the "motor drive command value Mn depending on the vehicle speed" is calculated from the map of FIG.
And has a function of driving the electric motor 22b in accordance with the read motor drive command value Mn.

Further, the control unit 37 is
In the high speed range of "0 km / h or more" and in the steering range of "± 5 to ± 20 °", the value of "the motor drive command value Mn 'read according to the vehicle speed" is calculated according to the following formula. Originally,
It has a function of calculating the motor drive command value Mn according to the degree of steering angle, and the motor 22 is operated according to the calculated value.
b is driven. The discharge performance of the electric hydraulic pump 22 that satisfies the steering feeling based on the steering angle state is set by this mathematical expression. Mn = Max− (θh−5) · Max−Mn ′ / 15

In addition, the control unit 37 is
It has a function of driving the electric motor 22b in accordance with the motor drive command value Mn read from the map shown in FIG. 4 in the high speed range of “0 km / h or more” and the steering range of “± 20 ° or more”.

With such a function, the discharge flow rate of the electric hydraulic pump 22 is controlled with emphasis on the steering feeling in the neutral range and the steering range at low and medium speeds, and in the steering range at high speeds.

Further, the control unit 37 displays "80".
It has a function of reading the Max value of the motor drive command value Mn in the map of FIG. 4 and driving the electric motor 22b in accordance with the read Max value in the high speed range of “km / h or more” in the neutral zone. .. By this, in the neutral zone at high speed,
The power cylinder device 12 is provided with a high neutral pressure. In other words, the neutral belt at high speed is controlled with emphasis on the neutral feeling.

FIG. 5 shows steering characteristics for each speed (low speed, medium speed, high speed) of "motor drive command value Mn according to steering wheel angle" obtained by the function of the controller unit 37.

The control unit 37 uses a timer function to prevent the electric hydraulic pump 22 from activating and stopping hunting, and the electric hydraulic pump 22 is operated for a predetermined time, for example, 5 seconds, even after steering is completed. It is set to let. The flow charts shown in FIGS. 2 and 3 show the control operation in the control unit 37. Next, this control unit 3
The control operation in 7 will be described according to the flowchart. The controller unit 37 is activated by an ON signal of a switch of an automobile ignition key.

Then, first, as shown in step S1, the signal from the L terminal of the alternator (not shown) is read. Then, in step S2, it is determined whether or not the output from the L terminal is "Hi".

When the engine of the automobile is normally started by operating the ignition key, the alternator L
Since the "Hi" signal is output from the terminal, the process proceeds to step S3 when the engine is normally started.

In step S3, the initial setting is performed and the steering flag SFLG indicating that the steering wheel 18 is steered is set to "0" and the holding timer Tm is set to "0".

After that, step S4 and step S5
At, the vehicle speed V output from the vehicle speed sensor 38 and the steering wheel angle θH output in pulses from the steering angle sensor 39 are read. When the process proceeds to step S6, it is determined whether or not there is a pulse from the steering angle sensor 39.

At this time, if it is assumed that the vehicle has just started the engine and has not started (running) or operated the steering wheel, the steering angle sensor 39 does not output a pulse, so the steering wheel 18 is turned on. When it is determined that it is not operated (non-steering), the process proceeds to step S7. In this step S7, it is determined whether or not steering has been performed before that by determining whether or not the steering flag SFLG is "1". Here, the vehicle is in a state where the initial steering wheel operation has not been performed yet, so it is determined to be "non-steering" (no steering), and the process proceeds to step S8.
In step S8, it is determined whether the vehicle speed V is "10 km / h or less".

At this time, the vehicle is "1" as described above.
Since it is 0 km / h or less ", it is determined that the motor is stopped or at an extremely low speed, and the process proceeds to step S9 to stop the electric motor 22b of the electric hydraulic pump 22. Such processing is performed as long as the vehicle is stopped or at an extremely low speed, and as long as the steering is not performed. By this stop control, unnecessary operation of the electric hydraulic pump 22 is suppressed (the load on the power supply circuit of the automobile is reduced). On the other hand, it is assumed that the vehicle starts and the steering wheel 18 is steered.

Here, if the handle 18 is operated even within a playable range, the handle 18 is operated in step S6.
Is determined to have been operated. Since the steering at this time is a determination as to whether or not the steering wheel 18 is moved, the determination result includes the states of "neutral", "small rudder angle", and "medium / large rudder angle".

As a result of the above determination, the process proceeds to step S10,
In this step S10, the operation flag SFLG indicating that steering has been performed is set to "1". That is,
Steering is detected. Then, in step S11,
A holding timer Tm for holding the steering time after the steering detection is set, and then the process goes to step S12. In step S12, it is determined whether the vehicle speed V "exceeds 80 km / h".

At this time, if the vehicle speed V of the traveling automobile is not "exceeding 80 km / h", the state of the steering wheel 18, that is, "neutral", "small rudder angle", "medium and large rudder angle" Regardless of this, the process proceeds to steps S13 and S14, and the pump discharge amount of the electric hydraulic pump 22 is controlled to a predetermined value.

That is, in step S13, as shown in FIG.
The motor drive command value Mn corresponding to the current vehicle speed V of the automobile is read from the map of "vehicle speed-motor drive command value Mn" shown in FIG.

Then, in step S14, the read motor drive command value Mn 'is output to the drive circuit 36 to drive the electric motor 22b of the electric hydraulic pump 22 in accordance with the set performance of the map.

If the "motor drive command value Mn corresponding to the steering wheel angle" obtained by this processing is shown, the low speed region is M over the entire steering wheel angle as shown by the alternate long and short dash line in FIG.
The ax value is maintained, and the medium speed range has a characteristic that changes from the "small and medium steering angle" to the "large steering angle" as shown by the broken line in FIG. That is, the discharge flow rate of the electric hydraulic pump 22 is such that the vehicle speed V and the steering angle θH are low when the vehicle is running straight at low and medium speeds and steering.
The flow rate is controlled to satisfy the steering feeling based on the state of.

As a result, in the low speed range, the discharge flow rate of the electric hydraulic pump 22 is maximized over the entire steering wheel angle range, and in the medium speed range, the discharge flow rate of the electric hydraulic pump 22 decreases as the steering wheel angle increases. Then, an appropriate assist force is applied to the power cylinder device 12. Specifically, the assist force is generated as follows.

That is, in the electrohydraulic power steering apparatus, when the handle 18 is rotated, the rotational displacement is the steering shaft 17 and the steering joint 1.
6, the input 6, and the torsion bar 5 are transmitted to the pinion gear 4 to drive the rack 3 in the direction in which the steering wheel 18 is steered.

At this time, the outer valve 19a and the inner valve 19b of the rotary valve 19 are displaced relative to each other according to the torsion bar 5 twisted by the resistance of the road surface.
Then, the controlled oil is supplied from the electric hydraulic pump 22 to the chamber 31a (right side) or the chamber 31b (left side) of the power cylinder device 12 according to the rotation difference between the outer valve 19a and the inner valve 19b. This room 3
By the assist force generated in 1a or the chamber 31b, the front wheels 10, 10 are driven in the direction steered by the steering wheel 18 to reduce the steering wheel force.

When the handle 18 is in the neutral zone, the controlled oil is uniformly supplied from the electric hydraulic pump 22 to both sides of the piston 30, and the neutral pressure generated at this time gives the handle 18 a neutral feeling. generate.

On the other hand, if the vehicle speed V of the automobile is "80 km / h or more", it is determined that the vehicle is traveling at high speed, and step S
Proceed to 18. Next, in step S18, it is determined whether or not the steering wheel angle θH is “± 5 ° or more”, and it is determined whether the high-speed traveling is in the steering state or in the straight traveling state (neutral zone). If the handle 18 is rotated more than the neutral band (± 5 ° or more), step S
20, the process proceeds to step S21.

In step S20, the motor drive command value Mn 'corresponding to the current vehicle speed V of the vehicle is read from the "vehicle speed-motor drive command value Mn" map shown in FIG. Then, in the subsequent step S21, the steering wheel angle θH of the currently operated steering wheel 18 is “20 °.
Or more ”is determined.

Such steps S18 and S
The handle 18 is set to “20 ° or more” by the determination process of 21.
It is determined whether the steering wheel has been operated to the medium or large steering angle or the small steering angle of "5 ° to 20 °". Here, when two requirements of "high speed running" and "small rudder angle" are determined, the process proceeds to step S22.

In step S22, the motor drive command value M corresponding to the deviation of the steering wheel angle θH is calculated based on the value of the motor drive command value Mn 'corresponding to the vehicle speed V.
n is calculated. Specifically, Mn ′ corresponding to the steering wheel angle θH is calculated from the Max value by using the above-described arithmetic processing.
The value is subtracted to obtain the Mn value. After that, the process proceeds to step S14, and the electric motor 22b of the electric hydraulic pump 22 is driven according to the calculated motor drive command value Mn, as in the case described above.

When the two requirements of "high speed running" and "medium / large steering angle" are discriminated, steps S21 to S1 are performed.
4, the electric motor 22b of the electric hydraulic pump 22 is driven in the same manner as described above according to the motor drive command value Mn 'read in step S20. Through such processing, during steering at high speed, the discharge flow rate of the electric hydraulic pump 22 is controlled to a flow rate that satisfies the steering feeling based on the vehicle speed V and the steering angle θH. On the other hand, if it is determined in step S18 that the range is within the neutral zone (within ± 5 °), the process proceeds to step S19. In this step S19, the Max value is set as the motor drive command value Mn. Then, the process proceeds to step S14, and according to the Max value, the electric motor 22 of the electric hydraulic pump 22 is driven as described above.
drive b.

Then, the oil of the maximum flow rate is uniformly supplied from the electric hydraulic pump 22 to both sides of the piston 30 in the neutral state of the power cylinder device 12. Then, due to the large neutral pressure generated at this time, a neutral feeling is generated in the handle 18. This eliminates the problem that the discharge flow rate of the electric hydraulic pump 22 decreases during high-speed straight traveling.

That is, if the obtained "motor drive command value Mn corresponding to the steering wheel angle" is shown, the "neutral band" is a value satisfying the neutral feeling, that is, Ma, as shown by the solid line in FIG.
The x value is set, and the “± 5 ° to ± 20 ° small steering angle range” is set to a value that satisfies the steering feeling, that is, the Mn value obtained based on the vehicle speed and the steering angle, and the “± 20 ° or more The "medium / large steering angle range" is also set to the Mn value that satisfies the steering feeling. That is, during high-speed straight traveling, the control emphasizes the neutral feeling.

As a result, the sense of reaction force does not become insufficient during high-speed straight traveling. According to the experiment, as a result of comparing the steering wheel force of the control that emphasizes steering with the steering wheel force of the control that emphasizes the neutral feeling, the steering wheel force of the control that emphasizes the steering indicated by the broken line as shown in the diagram of FIG. Rather, the steering wheel force of the control that emphasizes the neutral feeling shown by the solid line is smaller. Therefore, it is possible to provide the driver with a high neutral tightness.

Therefore, while maintaining good performance such as steerability at low and medium speeds and steerability at high speeds, it is possible to enhance the neutral tightness when traveling straight at high speed while maintaining the same performance as before. The overall performance of the device can be increased.

In the above operation, if the steering wheel 18 is operated during high-speed straight running, the process proceeds from step S18 to step S20, and the motor drive command value Mn is Max.
The value changes to the value based on the vehicle speed and the steering angle described above, and brings an appropriate assist force to the power cylinder device 12.
Further, in the above operation, when the steering operation of the steering wheel 18 is finished, it is determined whether or not the steering flag SFLG is "1" in step S7, the timer count of the holding timer Tm in step S15, and the timer count in step S16 are "5 seconds. Determination of whether or not it has passed,
By the process of resetting the steering flag SFLG to "0" in step S17, the electric hydraulic pump 2 is operated for a certain period of time.
The operation of No. 2 continues, and then stops (in order to reduce hunting for starting and stopping the electric hydraulic pump 22).

[0069]

As described above, according to the present invention,
It is possible to improve only the feeling of neutral tightness when traveling straight at high speed, while maintaining the steerability at low and medium speeds depending on the vehicle speed and the steering angle state and the steerability at high speed steering. Therefore,
The overall performance of the power steering device can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an electrohydraulic power steering device of the present invention together with a control system.

FIG. 2 is a flowchart showing steering control of the device.

FIG. 3 is a flowchart showing steering control subsequent to the flowchart in FIG.

FIG. 4 is a diagram showing a map of motor drive command values for an electric hydraulic pump according to vehicle speed.

FIG. 5 is a diagram showing a motor drive command value of an electric hydraulic pump according to a steering wheel angle.

FIG. 6 is a diagram showing a difference in magnitude of reaction force during high-speed straight line running in comparison between the conventional control and the control of the present invention.

[Explanation of symbols]

1 ... Steering mechanism, 10 ... Front wheel (steering wheel), 12 Power cylinder device (piston mechanism), 19 ... Rotary valve (supply / discharge valve), 22 ... Electric hydraulic pump, 22b ...
Electric motor, 22c ... Reservoir, 30 ... Piston, 31a,
31b ... Chamber (pressure receiving chamber), 34 ... Hydraulic circuit, 37 ... Control unit, 38 ... Vehicle speed sensor, 39 ... Steering angle sensor.

Claims (1)

[Claims] 1. A steering mechanism for steering steered wheels in a steering direction according to an operation of a steering wheel, an electric hydraulic pump driven by an electric motor as a drive source, and pressure receiving chambers provided on both sides of a reciprocating piston. ,
A supply / discharge mechanism that supplies / discharges a piston mechanism that assists the steering mechanism in the steering direction according to the displacement of the piston, and the electric hydraulic pump and each pressure receiving chamber of the piston mechanism according to the steering of the steering mechanism. A hydraulic circuit connected via a valve for generating an assist force in each pressure receiving chamber according to the steering of the steering mechanism, and an electric hydraulic pump satisfying a neutral feeling when the vehicle is traveling straight at high speed. A first setting means in which the discharge performance is set, a second setting means in which the discharge performance of the electric hydraulic pump satisfying the steering feeling based on the vehicle speed and the steering angle state of the vehicle is set; At the time, the electric hydraulic pump is operated according to the setting performance of the first setting means, and at other times, the electric hydraulic pump is operated according to the setting performance of the second setting means. An electrohydraulic power steering device for a vehicle, comprising: means for operating a pump.