JPH09290763A - Electric pump type power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve several problems related to a relief valve and save energy by lowering impressed voltage to an electric motor when an electric pump discharge fluid pressure becomes the predetermined value or more so as to regulate a maximum discharge fluid pressure of the electric pump to a necessary maximum fluid pressure to a power cylinder. SOLUTION: A discharge fluid pressure P of an electric pump 18 is detected by means of a pressure sensor 31, and when the discharge fluid pressure P is the necessary maximum fluid pressure P0 set at the predetermined value or more, a duty ratio D/T, at which impressed voltage to an electric motor 14 is PWM (pulse width modulation) controlled in every sampling time when a computing process is executed, is lowered sequently from D/T0 (=100%), D/T1 ,... to D/T4 (=80%), so that the impression voltage is lowered from an ordinary impression voltage to the minimum impression voltage at which the maximum discharge fluid pressure P of the electric pump 18 is increased to the necessary maximum fluid pressure P0 at most.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering apparatus for a vehicle, and more particularly, to an electric pump for switching and supplying fluid pressure discharged from an electric pump to any fluid chamber of a power cylinder to obtain steering assist force. It is suitable for a power steering system.

[0002]

2. Description of the Related Art An electric pump type power steering apparatus for a vehicle as described above controls a control pump (electric pump) which is rotationally driven by an electric motor and a discharge fluid pressure of the electric pump, that is, steering force of a steering shaft, that is, When the discharge fluid pressure from the switching valve (control valve) for switching and supplying to the power cylinder according to the magnitude and direction of the steering input to the steering wheel and the electric pump is equal to or more than a predetermined value set in advance. And a relief valve that relieves the discharge fluid pressure. By the way, the control valve uses a conventional existing torsion bar or the like so that the steering assist force acts in the same direction as the steering input by the reaction force of the steering input in a magnitude corresponding to the steering input. The opening and closing of the flow path to each chamber to the power cylinder is mechanically adjusted. In addition, the electric pump is always operated with the same applied voltage so as to obtain a maximum discharge fluid pressure equal to or higher than a predetermined set value which is relieved by the relief valve, in order to compensate for the output of the entire device at the time of quick switching. Is driven to rotate.

[0003]

In the conventional electric pump type power steering apparatus, for example, when the steering wheel is steered to one of the steering wheels and held, the discharge fluid pressure of the electric pump is changed to the power cylinder. Is continuously supplied to any one of the chambers, and the fluid pressure from the electric pump to one of the chambers of the power cylinder approaches the maximum discharge fluid pressure. In reality, when the discharge fluid pressure reaches the predetermined set value, the relief valve operates and the discharge fluid pressure is maintained at the predetermined set value. However, in such a case, in the relief valve, the high-pressure fluid flows into the drain side from a slight opening portion, so that cavitation occurs here and causes abnormal noise. In order to eliminate this abnormal noise, that is, cavitation, various shapes of the inside of the relief valve have been devised, but at present, neither cavitation nor abnormal noise can be completely eliminated, and any relief valve was used. Even with the electric pump type power steering apparatus, there is a problem in that this abnormal noise is noticeable, especially in an electric vehicle in which no engine sound is generated while the vehicle is stopped. There is also a problem in that the relief of the discharge fluid pressure of the electric pump itself causes energy loss.

The present invention was developed in view of these problems. When the discharge fluid pressure of the electric pump exceeds a predetermined set value corresponding to the relief pressure, the voltage applied to the electric motor is changed. By lowering the discharge fluid pressure of the electric pump to the required maximum fluid pressure to the power cylinder to suppress or prevent energy loss, it is possible to prevent cavitation or abnormal noise even when using a relief valve. An object of the present invention is to provide a pump type power steering device.

[0005]

In order to solve the above problems, an electric pump type power steering apparatus according to claim 1 of the present invention is an electric pump rotatably driven by an electric motor, and the discharge of this electric pump. A control valve that switches the fluid pressure to the power cylinder according to the magnitude and direction of the steering input to the steering wheel and the discharge fluid pressure of the electric pump that is supplied to the power cylinder via this control valve are set to a predetermined value. A discharge fluid pressure detecting or estimating means for detecting or estimating whether the discharge fluid pressure is equal to or more than a value, and to the electric motor when the discharge fluid pressure of the electric pump is equal to or more than the predetermined set value by the discharge fluid pressure detecting or estimating means. Control means for lowering the applied voltage of the electric pump to regulate the maximum value of the discharge fluid pressure of the electric pump to the maximum required fluid pressure to the power cylinder. .

According to the present invention, for example, when the discharge fluid pressure of the electric pump exceeds or exceeds a predetermined set value at which the relief valve operates, as described above, the steering wheel is steered to either one. Since it is in the state of being held, the maximum discharge fluid pressure of the electric pump itself is not required as in the case of the above-mentioned quick turning, and the maximum fluid pressure required for the power cylinder at that time is the relief pressure. It is equal to or almost equal to the predetermined set value at which the valve operates. Therefore, when the discharge fluid pressure detection or estimation means detects or estimates that the discharge fluid pressure of the electric pump is equal to or higher than the predetermined set value, the control means lowers the voltage applied to the electric motor. If the discharge fluid pressure of the pump is regulated to the maximum required fluid pressure to the power cylinder, it is not necessary to create unnecessary fluid pressure with the electric pump, energy loss is prevented and prevented, and energy saving is promoted. Even if the relief valve is provided on the discharge side of the electric pump, the relief valve does not need to relieve the discharge fluid pressure exceeding the predetermined set value, so that the conventional cavitation and abnormal noise are prevented. can do. In the present invention, the predetermined set value that is the threshold value for regulating the discharge fluid pressure of the electric pump does not necessarily have to be the relief pressure of the conventional relief valve, and the required maximum fluid pressure to the power cylinder. The same effect can be obtained even if the value is arbitrarily set smaller than.

In the electric pump type power steering apparatus according to a second aspect of the present invention, a pressure sensor for detecting the discharge fluid pressure of the electric pump is provided as the discharge fluid pressure detecting or estimating means, and the pressure sensor is provided. It is characterized in that it is provided with means for judging whether or not the discharge fluid pressure detection value from the sensor is equal to or more than the predetermined set value.

Further, in the electric pump type power steering apparatus according to a third aspect of the present invention, the discharge fluid pressure of the electric pump is a pressure at which the discharge fluid pressure is equal to or higher than the predetermined set value, as the discharge fluid pressure detecting or estimating means. A switch is provided, and means for determining whether or not the discharge fluid pressure of the electric pump is equal to or higher than a predetermined set value in accordance with a signal from the pressure switch is provided.

In the electric pump type power steering apparatus according to a fourth aspect of the present invention, a current detector for detecting a current value of the electric motor of the electric pump is provided as the discharge fluid pressure detecting or estimating means. , When the detected current value of the electric motor from the current detector is equal to or more than the electric current value of the electric motor corresponding to the discharge fluid pressure of the electric pump that is equal to or more than the predetermined set value, the discharge fluid pressure of the electric pump is set to the predetermined set value. It is characterized in that it is provided with means for estimating that the above is the case.

All of these are aspects of the embodiment of the discharge fluid pressure detecting or estimating means. Among them, in the invention according to claim 4, the current detection value of the electric motor from the current detector is the predetermined value. A means for estimating that the discharge fluid pressure of the electric pump is equal to or higher than a predetermined set value when the current value of the electric motor is equal to or higher than the discharge fluid pressure of the electric pump that is equal to or higher than the set value. The generated torque of an electric motor is generally proportional to its current value, and the generated torque of the electric motor is proportional to the discharge fluid pressure of the electric pump. Therefore, the discharge value of the electric pump is detected by detecting the current value of this electric motor. The pressure can be estimated. Therefore, as described above, when the detected current value of the electric pump is equal to or higher than the electric current value of the electric motor corresponding to the discharge fluid pressure of the electric pump equal to or higher than the predetermined set value, the discharge fluid pressure of the electric pump is equal to the predetermined value. It can be estimated that the value is equal to or larger than the set value.

[0011]

As described above, according to the electric pump type power steering apparatus according to the first aspect of the present invention, it is detected or estimated that the discharge fluid pressure of the electric pump is equal to or higher than the predetermined set value. In this case, it is necessary to reduce the applied voltage to the electric motor and regulate the discharge fluid pressure of the electric pump to the maximum required fluid pressure to the power cylinder, thereby creating an unnecessary fluid pressure with the electric pump. Energy consumption is suppressed and energy loss is suppressed and energy saving is promoted,
Even when the relief valve is provided on the discharge side of the electric pump, the relief valve does not need to relieve the discharge fluid pressure exceeding the predetermined set value, so that the conventional cavitation and abnormal noise are prevented. be able to.

Further, according to the electric pump type power steering apparatus according to the second to fourth aspects of the present invention, it is determined whether or not the discharge fluid pressure detection value from the pressure sensor is equal to or more than the predetermined set value. Judgment, whether or not the discharge fluid pressure of the electric pump is equal to or higher than a predetermined set value according to a signal from a pressure switch provided on the discharge side of the electric pump, or an electric motor from a current detector. When the detected current value of is equal to or higher than the current value of the electric motor corresponding to the discharge fluid pressure of the electric pump equal to or higher than the predetermined set value, it is estimated that the discharge fluid pressure of the electric pump is equal to or higher than the predetermined set value. Thus, it is possible to reliably detect or estimate that the discharge fluid pressure of the electric pump is equal to or higher than the predetermined set value.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an electric pump type power steering apparatus of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a first embodiment of an electric pump type power steering apparatus of the present invention.

In FIG. 1, a steering shaft 2 is fitted to a steering wheel 1, and the steering shaft 2 also rotates in the same phase by a rotational steering input of the steering wheel 1 by a driver.

The rotational movement of the steering shaft 2,
That is, the rotational steering input to the steering wheel 1 is transmitted to the torsion bar 4 via the upper joint 3a,
Further, it is transmitted to the pinion shaft 6 via the lower joint 3b. A pinion 7 is attached to the pinion shaft 6, and a rack 8 a of a rack shaft 8 is attached to the pinion 7.
Mesh with each other to form a so-called rack and pinion mechanism. This rack-and-pinion mechanism converts the rotational movement of the pinion 6 transmitted from the steering wheel 1 by the steering input as is known to the linear movement (translational movement) of the steering shaft 8 via the rack 8a. ,
It may be considered that the linear thrust force of the steering shaft 8 matches or substantially matches the axial direction.

The steering shaft 8 thus converted into translational motion
Is transmitted to the side rod (tie rod) 11 via the inner joint 21a, and the linear thrust applied to the side rod 11 is converted into a moment having the wheel support member 12 as an arm via the outer joint 21b.
The steered wheels 13 are steered by this moment. However,
In the present embodiment, since the power steering device is provided as described above, it can be considered that the linear thrust of the steering shaft 8 is generated by the assist force of the power cylinder described later,
It can be considered that the steering input substantially given to the steering wheel 1 by the driver is consumed by the force for twisting the torsion bar 4, that is, the torque.

The torsion bar 4 is a power cylinder.
Valve (control valve) 15 to control the fluid pressure to the
It is decorated in. This rotary valve 15 is a conventional
Like the existing one, the torsional displacement corresponding to the steering input is
A rotor (not shown) generated in the torsion bar 4
Corresponds to steering input between (valve body) and case
When a phase difference occurs, the flow path between the two becomes the steering input.
It opens and closes according to the opening. Therefore, this rotary valve
If the group 15 is represented in sequence, as shown in FIG.
Switching control is performed according to the torsional displacement of the torsion bar 4.
The three-position switching valve 15a is provided. This 3
The position switching valve 15a is a pump port in the normal position.
The fluid (fluid pressure in this case) supplied from P remains unchanged
Two output ports as well as return to return port R
C₁, C_TwoShut off together, and at any switching position,
Output of the fluid pressure supplied from the pump port P
Port C ₁Or C_TwoTo the output port of either
Card C_TwoOr C₁Return pressure from return to return port R
It becomes a fluid path.

The output fluid pressure from any output port C ₁ or C _{2 of the} rotary valve 15 is supplied to any input port P ₁ or P ₂ of the power cylinder 17. This power cylinder 17 has a piston 17a connected to the steering shaft 8 therein, and therefore, when fluid pressure is supplied to any one of the input ports P ₁ or P ₂ , the input port P ₁ or The internal pressure of the fluid chamber communicating with P ₂ increases, and the piston 17a tries to move to the side of the fluid chamber communicating with the other input port P ₂ or P ₁ , and this moving force causes the steering shaft 8 to move. It acts as a steering assist force, that is, an assist force. Here, the fluid pressure in the fluid chamber whose volume is reduced by the moved piston 17a is the other input port P ₂ communicating with the fluid chamber.
Alternatively, it is returned from P ₁ to the reservoir 16 through the drain port from the return port R via the other output port C ₂ or C ₁ of the rotary valve 15.

On the other hand, an electric pump 18 is interposed in the supply path between the reservoir 16 and the pump port P of the rotary valve 15. This electric pump 18
It is driven to rotate by the electric motor 14 and discharges a predetermined flow rate at a predetermined fluid pressure. The applied voltage of the electric motor 14 is duty ratio controlled by a PWM (Pulse Width Modulation) drive signal from a control unit described later. Further, a pressure sensor 31 is provided on the discharge side of the electric pump 18, and the discharge fluid pressure P of the electric pump 18 is detected and output to a control unit described later.

Also in this embodiment, as in the conventional case, the relief valve 19 is interposed between the discharge side of the electric pump 18 and the drain passage.
The relief pressure 9 is correspondingly larger than the conventional one, for example, between the normal maximum fluid pressure required for the power cylinder 17 and a considerably larger pressure than the normal maximum fluid pressure generated in the abnormal state of the fluid pressure device. Since the relief valve 19 is set to about the value, the relief valve 19 does not relieve the discharge fluid pressure during normal operation of the device, and is provided only to relieve the fluid pressure generated when the device is abnormal. ing. Further, if the relief valve 19 is used to relieve the fluid pressure generated at the time of abnormality as described above,
When an abnormality actually occurs, the relief valve 19 concerned
Cavitation occurs in the same manner as described above, and abnormal noise also occurs with it, which is also advantageous in that it is easy for the occupant to sense the abnormality.

The control unit 34 comprises a microcomputer 35 and a drive circuit 36. Among them, the microcomputer 35 includes an input interface circuit 35a having an A / D conversion function for reading the discharge fluid pressure P consisting of an analog signal from the pressure sensor 31 as a digital value, a microprocessor unit (MPU) and the like. Comprised of an arithmetic processing unit 35b configured to control and perform main arithmetic processing such as calculating and outputting a duty ratio to the electric motor, a ROM, a RAM, etc., to store a program of necessary arithmetic processing contents and necessary information. A storage device 35c for temporarily storing the output voltage, and an output interface circuit 35d having a D / A conversion function for converting the duty ratio of the digital value to the electric motor into a corresponding analog voltage signal. . Then, in the microcomputer 35, the duty ratio D / T to the electric motor is calculated based on the discharge fluid pressure P of the electric pump according to the calculation processing of FIG. 2 described later, and the calculated duty ratio D / T is output as a control signal. Execute the process. Further, the drive circuit 36 converts the duty ratio analog voltage signal to the electric motor output from the microcomputer 35 into a pulse signal by PWM, and further converts the voltage of the power supply device 37 including a battery into the pulse signal. It amplifies according to the signal and outputs a PWM drive signal to the electric motor.

Next, the arithmetic processing executed by the arithmetic processing unit 35b of the microcomputer 35 of the control unit 34 will be described with reference to the flowchart of FIG. This calculation process is executed as a timer interrupt process at every predetermined sampling time ΔT (for example, 10 msec.). It should be noted that this flowchart does not include a step for exchanging information, but the information necessary for the arithmetic processing is appropriately read from the storage device 35c, and the information that needs to be temporarily stored is the storage device 35c. Will be remembered at any time.

In this calculation process, first in step S1,
The discharge fluid pressure P of the electric pump 18 detected by the pressure sensor 31 is read. Next, in step S2, it is determined whether the discharge fluid pressure P read in step S1 is equal to or greater than a preset value P ₀ set in advance, and the discharge fluid pressure P is set to a predetermined value. If it is P ₀ or more, the process proceeds to step S3, and if not, the process proceeds to step S4. The predetermined set value P ₀ of the discharge fluid pressure is generated by the power cylinder 17 in order to generate a steering assist force corresponding to the steering input when the steering wheel 1 is steered and held in either direction. It corresponds to the maximum fluid pressure required by either chamber.

[0024] In step S3, it is determined whether the set state of the first duty ratio setting flag F ₁ is "1", the first duty ratio setting flag F ₁ is in the set state of "1" If so, the process proceeds to step S5, and if not, the process proceeds to step S6.

In step S6, the duty ratio D /
T is set to a preset first duty ratio D / T ₁ (for example, 95%), which is output as a control signal to the electric motor, and then the process proceeds to step S7 where the first duty ratio is set. The setting flag F ₁ is set to "1" and then the main program is restored.

On the other hand, in step S5, the second duty ratio setting flag F ₂ is equal to or a set state of "1", the set state of the second duty ratio setting flag F ₂ is "1" If so, the process proceeds to step S8, and if not, the process proceeds to step S9.

In step S9, the duty ratio D /
T is set to a preset second duty ratio D / T ₂ (for example, 90%), which is output as a control signal to the electric motor, and then the process proceeds to step S10, in which the second duty ratio is set. The setting flag F ₂ is set to "1" and then the main program is restored.

[0028] In step S8, the third duty ratio setting flag F ₃ is equal to or a set state of "1", the set state of the third duty ratio setting flag F ₃ is set to "1" If so, the process proceeds to step S11, and if not, the process proceeds to step S12.

In step S12, the duty ratio D
/ T is set to a preset third duty ratio D / T ₃ (for example, 85%), which is output as a control signal to the electric motor, and then the process proceeds to step S13. return from is set to a specific setting flag F ₃ "1" to the main program.

In step S11, the duty ratio D / T is set to the preset fourth duty ratio D / T.
₄ (for example, 80%) and outputs it as a control signal to the electric motor, and then proceeds to step S14 where the fourth duty ratio setting flag F ₄ is set to "1". Return to the main program.

On the other hand, in step S4, the second duty ratio setting flag F ₂ is equal to or a set state of "1", the second duty ratio setting flag F ₂
Is set to "1", the process proceeds to step S15, and otherwise, the process proceeds to step S16.

[0032] At the step S15, the third duty ratio setting flag F ₃ is equal to or a set state of "1", the third duty ratio setting flag F ₃ is in the set state of "1" If there is, the process proceeds to step S17, and if not, the process proceeds to step S18.

[0033] Then, in step S17, the fourth duty ratio setting flag F ₄ is determined whether the set state of "1", the fourth duty ratio setting flag F ₄
Is set to "1", the process proceeds to step S19, and otherwise, the process proceeds to step S20.

Of these, in step S19, the duty ratio D / T is set to the preset third duty ratio D / T ₃ , and this is output as a control signal to the electric motor, and then in step S21. Then, the fourth duty ratio setting flag F ₄ is reset to "0" and the main program is restored.

In step S20, the duty
Ratio D / T to the preset second duty ratio D / T
T_TwoAnd set it as a control signal to the electric motor.
Output, and the process proceeds to step S22, where the first
3 Duty ratio setting flag F _ThreeReset to "0"
To return to the main program.

Further, in step S18, the duty
Ratio D / T to the preset first duty ratio D / T
T₁And set it as a control signal to the electric motor.
Output, the process proceeds to step S23, where
2 Duty ratio setting flag F _TwoReset to "0"
To return to the main program.

Then, in step S16, the duty ratio D / T is set to the preset initial duty ratio D / T.
₀ (for example, 100%) is set, the signal is output as a control signal to the electric motor, and then the process proceeds to step S24 where the first duty ratio setting flag F ₁ is reset to “0”. Return to the main program.

Next, the present embodiment by the arithmetic processing of FIG.
The operation of the electric pump type power steering device in the normal state will be described.
You. In this calculation process, the ejection read in step S1
The fluid pressure P is the required maximum fluid pressure to the power cylinder 17.
P₀If the above is the case, first from step S2
After step S3, the duty ratio D / T is set to the first decrement in step S6.
Duty ratio D / T₁(= 95%), then output
At step S7, the first duty ratio setting flag F ₁Is “1”
Since it is set to, the performance of Fig. 2 at the next sampling time.
When the arithmetic processing is executed, the steps from step S5 are started.
And the second duty ratio D / T_Two(= 90
%) Duty ratio D / T, and then step S1
When 0, the second duty ratio setting flag F_TwoIs set to “1”
Is done. Then, at the next sampling time, the same step
Shift from step S8 to step S12 and the third duty ratio
D / T_Three(= 85%) duty ratio is output and
In the same step S13, the third duty ratio setting flag F_ThreeTo
Set it to “1” and set the same step at the next sampling time.
4th duty ratio D / T at step S11_Four(= 80%) de
The duty ratio D / T is output and at the same step S14
Fourth duty ratio setting flag F_FourIs set to "1"
Therefore, after that, the discharge fluid pressure P becomes the required maximum flow.
Body pressure P₀Even if it is more than the above, the fourth duty ratio D / T
_FourContinues to be output.

On the other hand, if the discharge fluid pressure P becomes smaller than the required maximum fluid pressure P ₀ to the power cylinder 17 from this state, the fourth duty ratio setting flag F ₄ is all set to "1". , Step S4 to Step S15, and then Step S17 to Step S19, where the third duty ratio D / T ₃ is output as the duty ratio D / T, and then the fourth duty ratio setting flag is set in Step S21. Since F ₄ is reset to “0”, at the next sampling time, the same step S17 is performed.
From step S20, the second duty ratio D
/ T ₂ is output as the duty ratio D / T, the third duty ratio setting flag F ₃ is reset to “0” in step S22, and at the next sampling time, the process proceeds from step S15 to step S18. The first duty ratio D / T ₁ is output as the duty ratio D / T, the second duty ratio setting flag F ₂ is reset to “0” in the same step S23, and after the next sampling time, the steps from the same step S4 are performed. In S16, the initial duty ratio D / T ₀ (= 100%) is continuously output as the duty ratio D / T, and in the same step S24, the first duty ratio setting flag F ₁ is continuously set to “0”. The flow is repeated.

Further, when the discharge fluid pressure P is repeatedly increased and decreased in the vicinity of the required maximum fluid pressure P ₀ to the power cylinder 17, that is, the discharge fluid pressure P becomes greater than or equal to the required maximum fluid pressure P _0. If the discharge fluid pressure P is equal to or higher than the required maximum fluid pressure P ₀ , the duty ratio D / T becomes the third duty ratio D /
When the discharge fluid pressure P becomes smaller than the required maximum fluid pressure P ₀ after being set to a small value up to T ₃ , the second duty ratio D / T ₂ and the first duty ratio D are obtained after the next sampling time.
/ T As such ₁ increases, the duty ratio D / T is the up to the initial duty ratio D / T _0, between the fourth duty ratio D / T ₄ at the minimum, D / T _0, D
Increase / decrease in the order of / T ₁ , D / T ₂ , D / T ₃ , D / T ₄ .

Next, the details of the operation of the arithmetic processing will be further described. First, various input / output characteristics of the electric motor 14 are represented as shown in FIG. Here, the electric motor 14
Within the rating of, the current I of the electric motor 14 and the generated torque T thereof linearly increase with each other, as shown by the one-dot chain line rising to the right in the figure. On the other hand, the electric motor 14
When the applied voltage E to the motor is constant, the torque T generated by the motor and the rotation speed N decrease linearly with the increase of the rotation speed N, as shown by the solid line in the lower right of FIG. . Of these, the torque T generated by the motor is proportional to the discharge fluid pressure P of the electric pump 18, and the rotation speed N of the motor is proportional to the discharge flow rate Q of the electric pump 18. Below, the general formula of the pump and the solution to prove it are described.

Input work: La _(W) = N _(rpm) × T
_(kgfm) /673.8 Output work: La _(W) = P _{(kgf / cm2)} x Q _{(l / min)} / 61
1.8 Here, assuming that the specific discharge amount of the pump is D _{(cm3 / rev)} , the discharge flow rate: Q _{(l / min)} = D _{(cm3 / rev)} × N _(rpm) / 1
000 ∴Q∝N (End of certification) Next, by substituting the discharge flow rate Q _{(l / min)} , La _(W) = P _{(kgf / cm2)} × D _{(cm3 / rev)} × N _(rpm) /
(611.8 × 1000) Here, the efficiency of the input work La and the output work La is 100.
% (La ≠ Lb), but there is a proportional relationship with a certain efficiency η, N × T∝P × D × N (D = const.) ∴T∝P (end of proof) Therefore, the microcomputer 35 The electric motor 14 when the duty ratio D / T of the control signal calculated and output according to the above is the initial duty ratio D / T ₀ (= 100%).
The applied voltage to the motor is E ₁ , the generated torque T and the rotation speed N of the motor at the applied voltage E ₁ are expressed as shown by the solid line on the right side of the figure, and the duty ratio D / T is The applied voltage to the electric motor 14 when the duty ratio is 4 / D ₄ (= 80%) is E ₂ , and the applied voltage E
A motor for generating torque T in ₂ and rotational speed N is assumed to be expressed as shown by the solid line in the left side of FIG. here,
When the voltage applied to the electric motor 14 is E ₂ , the intercept T of the generated torque T when the rotation speed N is “0”.
₀ is the maximum fluid pressure P ₀ required for the electric pump 18 required in any chamber of the power cylinder 17 when the steering wheel 1 is steered and held by either one.
Is a value proportional to. On the other hand, the intercept of the generated torque T when the applied voltage to the electric motor 14 is E ₁ is set to a value larger than the intercept T ₀ proportional to the required maximum fluid pressure P ₀ at the applied voltage E ₂ . That is, when the normal applied voltage E ₁ is supplied to the electric motor 14, the electric pump 18 can generate a fluid pressure P larger than the required maximum fluid pressure P ₀ . This is, for example, when turning quickly
The fluid pressure P is supplied to one of the chambers of the power cylinder 17, and the fluid pressure P on the discharge side of the electric pump 18 is increased to a state close to that. If it is drained, the discharge fluid pressure P may drop too much, and it may take time to increase the fluid pressure P supplied to the other chamber of the power cylinder 17 to a desired value. So, to ensure responsiveness in this situation,
During normal use, even if the motor current value I is equivalent (that is, the equivalent duty ratio), the required maximum fluid pressure P ₀
Torque T higher than the motor torque curve that outputs only up to
Is obtained.

Incidentally, when the steering wheel 1 is not steered, such as when the vehicle is traveling straight, the rotary valve 15 is maintained in the neutral state of FIG. 1, and the discharge fluid pressure P of the electric pump 18 is basically unchanged. Since it is drained, the generated torque T required for the electric motor 14 may be a small value Ta, which is small enough that the discharge fluid pressure from the electric pump resists the resistance in the pipeline. However, when the generated torque T of the electric motor 14 is small as described above, the rotational speed N, that is, the discharge flow rate Q of the electric pump 18 is desired to be as large as possible. As a general characteristic of the electric pump 18 used in such a power steering apparatus, the steering assist force with respect to the steering input, that is, the characteristic of the discharge fluid pressure P becomes smaller as the discharge flow rate Q of the pump becomes smaller. This is because there is a characteristic that That is, during so-called light steering such as when traveling straight ahead, the discharge fluid pressure P of the electric pump 18 is also very small according to the small generated torque T of the electric motor 14 as described above. When the steering wheel 1 is turned off from the state and further increased, a large amount of fluid tries to flow into the power cylinder 17. However, at this time, if the discharge flow rate Q of the pump is small, the necessary fluid cannot be supplied to the power cylinder 17 and the steering assist force becomes small. Therefore, in order to ensure responsiveness in such a situation. As described above, when the generated torque T of the electric motor 14 is small, the rotational speed N, that is, the discharge flow rate Q of the electric pump 18 should be made as large as possible.

The electric motor and electric pump characteristics that satisfy the above conditions are the input / output characteristic curves in FIG. Therefore, for example, when the discharge fluid pressure P is equal to or higher than the required maximum fluid pressure P ₀ , the applied voltage to the electric motor 14 changes from the normal applied voltage E ₁ corresponding to the initial duty ratio D / T ₀ to the fourth value. Minimum applied voltage E corresponding to duty ratio D / T ₄
Assuming that the steering wheel is changed to ₂ , for example, consider a state where the steering wheel is steered to one of the straight running state and held. As described above, the motor generated torque T during straight traveling is about the torque Ta during straight traveling as shown in FIG. 3, and the discharge fluid pressure P of the electric pump 18 at that time is, of course, the required maximum fluid pressure P.
_{Since it is} smaller than ₀ , the applied voltage to the electric motor 14 becomes the normal applied voltage E ₁ , and the motor-generated torque T and the rotation speed N at that time are also at the point A on the TN curve when the applied voltage E ₁ is applied. Become. By the way, the motor current value I at this time
The point on the TI curve at the same torque is the motor current value I at that time, such as Ia in the figure.

On the other hand, if the steering wheel 1 is steered to either side from this state, the rotary valve 1
5, the discharge side of the electric pump 18 communicates with one of the chambers of the power cylinder 17, and the fluid pressure circuit is closed, so that the discharge fluid pressure P of the electric pump 18 gradually increases, and accordingly, the electric pump 18 is electrically driven. The generated torque T of the motor 14 increases while the rotation speed N decreases, and eventually reaches the point R on the TN curve when the applied voltage E _{1 is} applied. Then, since the point R is the generated torque value T ₀ corresponding to the required maximum fluid pressure P ₀ , the voltage E applied to the electric motor 14 is reduced to the minimum applied voltage E ₂ at that time. Therefore,
Since the discharge fluid pressure P required for the electric pump 18 is still the required maximum fluid pressure P ₀ , the electric motor 14 also
Since the generated torque value T ₀ corresponding to this is continuously generated,
Along with this, the motor-generated torque T and the rotational speed N shift to a point R ′ on the TN curve at the minimum applied voltage E ₂ . Of these points, the motor current value I does not change to I _R shown at the R point or the R ′ point, and the normal applied voltage E ₁ is larger than the minimum applied voltage E ₂ , so the product of the two is obtained. The power consumption, that is, the energy represented, is smaller in the latter case, and energy can be saved accordingly.

However, the required maximum fluid pressure P
_{Using 0} as a single threshold value without so-called hysteresis, the normal applied voltage E ₁ (or the normal duty ratio D / T ₀ corresponding thereto) and the minimum applied voltage E ₂ (or the corresponding corresponding _value ) to the electric motor 14 are used. Fourth duty ratio D /
When a control for largely switching between T ₄ ) and T ₄ ) is executed, so-called control hunting is likely to occur. Therefore, in the present embodiment, as shown in the above and FIG. 4, the duty ratio D / T serving as the control signal to the electric motor 14 is set to the initial duty ratio D.
/ T ₀ , the first duty ratio D / T ₁ , the second duty ratio D / T ₂ , the third duty ratio D / T ₃ , and the fourth duty ratio D / T ₄ are changed little by little in this order. The applied voltage E to 14 is changed stepwise between the normal applied voltage E ₁ and the minimum applied voltage E ₂ .
Therefore, in FIG. 3, the vehicle is steered to the maximum from one of the straight traveling states (shifts from the point A to the point R to the point R ′) and then releases the steering wheel (returns from the point R ′ to the point A). 2) in a situation such as
The locus of the actual motor-generated torque T and the rotational speed N by the calculation process of is like that of connecting the points in FIG.
Among them, at the point R ′, the discharge fluid pressure P required for the power cylinder 17 and the required maximum fluid pressure P ₀ corresponding to the maximum torque T ₀ generated at the minimum applied voltage E ₂ are balanced, and as a result, Then, the electric motor 14 is stopped. However, from this state, even if rapid return steering such as releasing the steering wheel as described above is performed, the duty ratio D / T immediately increases as the discharge fluid pressure P decreases, and the electric motor 14 returns to rotation and the electric pump 1
Since No. 8 continues to secure the necessary discharge fluid pressure P, the response of the steering assist force (or the feeling to it) is
It does not decrease compared to the conventional case.

In the above description, the threshold value of the discharge fluid pressure P of the electric pump 18 which starts to change and set the applied voltage E to the electric motor 14 from the normal applied voltage E ₁ corresponds to the conventional relief pressure. Although the required maximum fluid pressure P ₀ is set, the threshold value of the discharge fluid pressure of the electric pump, that is, the predetermined set value of the present invention may be any value less than or equal to the required maximum fluid pressure P ₀ . Here, for example, in the motor generated torque transient characteristic diagram of FIG. 4, when an arbitrary predetermined set value P ₀ ′ lower than the required maximum fluid pressure P ₀ is set as the threshold value of the discharge fluid pressure P of the electric pump 18, The locus of the actual motor-generated torque T and the rotational speed N by the arithmetic processing of FIG. 2 is like that of connecting the points X in FIG. Also in this characteristic diagram, the discharge pressure transient characteristic of the electric pump, which is equivalent to the steering assist force, is not much different from the above-mentioned case, and as a result, the generated torque T passes through the R ′ point and returns to the A point again. There is a similar energy saving effect.

Although not shown, a pressure switch that operates at a predetermined set value such as the required maximum fluid pressure P ₀ is used instead of the pressure sensor, and a signal from this pressure switch is used as a threshold value. The applied voltage E to the electric motor may be set to be smaller than the normal applied voltage E ₁ and then set.

Next, the electric pump type power steering apparatus of the present invention
The second embodiment will be described. FIG. 5 shows the present embodiment.
FIG. 2 is a schematic view of the electric pump type power steering device of FIG.
However, this electric pump type power steering device is the same as the first embodiment.
It is very similar to that of
Are assigned the same reference numerals and detailed explanations thereof are omitted. this
The biggest difference between the embodiment and the first embodiment is
The current value I of the electric motor 14 is used instead of the pressure sensor 31.
The point is that a current detector 32 for detecting is detected. Also, this
Accordingly, the micro of the control unit 34 is
The performance performed by the arithmetic processing unit 35b of the computer 35.
The calculation process is shown in the flowchart of FIG. 6 from that shown in FIG.
Has been changed. However, the performance of this Figure 6
In the calculation process, step S1 of the calculation process of FIG.
Step S1 ', step S2 changed to step S2'
It is exactly the same except that it is described. Moreover, the same arithmetic processing
In step S1 ', the electric current from the current detector 32 is
The current value I of the motor 14 is read, and in the same step S2 '
This current value I is the required maximum fluid pressure P₀Equivalent to
Predetermined value of motor current I₀It is determined whether or not the above,
The current value I is a predetermined value I ₀If more than the above,
If not, go to step S4.
It's just a transition.

As described above, the discharge fluid pressure P of the electric pump 18 is in a proportional relationship with the generated torque T of the electric motor 14 and the simple increase of the generated torque T of the electric motor 14 and the current value I. Since there is a proportional relationship (see FIG. 3), the current value I of the electric motor 14 and the discharge fluid pressure P of the electric pump 18 also have a simple increase proportional relationship. Therefore, the current value I of the electric motor 14 is the predetermined value I of the motor current corresponding to the required maximum fluid pressure P ₀ to the power cylinder 17.
_When it is ₀ or more, the discharge fluid pressure P of the electric pump 18
Can be estimated to be above the required maximum fluid pressure P ₀ . Therefore, setting the predetermined value I ₀ of the motor current corresponding to the required maximum fluid pressure P ₀ as the threshold value of the current value I of the electric motor 14 means setting the threshold value of the discharge fluid pressure P of the electric pump 18 to the required maximum fluid pressure. This is substantially equivalent to applying P ₀ , and therefore, in the arithmetic processing of FIG. 6, the same action and effect as those shown in FIG. 2 of the first embodiment can be obtained. Of course,
The predetermined value I ₀ of the motor current is set to the power cylinder 1
It is needless to say that even if the motor current value corresponding to the predetermined value P ₀ ′ smaller than the required maximum fluid pressure P ₀ to 7 is set, the same effect as the first embodiment can be obtained.

In each of the above embodiments, the control valve for switching and supplying the fluid pressure to the power cylinder is described in detail only when it is composed of the rotary valve including the torsion bar. However, the structure of the control valve is as follows. The present invention is not limited to this. For example, an electromagnetic switching valve that can open and close the flow path and adjust the opening is used to detect the direction and magnitude of the steering input to the steering wheel, and the electromagnetic switching is performed accordingly. It is also possible to employ a device in which the control unit controls the opening and closing of the flow path of the valve and the adjustment of the opening degree.

In the above embodiment, the control unit including the microcomputer has been described in detail only in the case of controlling only the voltage applied to the electric motor for rotationally driving the electric pump. However, the control unit includes, for example, Of course, it is also possible to execute arithmetic processing for controlling the discharge fluid pressure of the electric pump in parallel so that the steering assist force is adjusted according to the vehicle speed.

Further, in the above-mentioned embodiment, only the case where the control unit is composed of a microcomputer has been described in detail, but it goes without saying that this control unit may be composed by combining appropriate arithmetic circuits and logic circuits. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of an electric pump type power steering apparatus for a vehicle of the present invention.

FIG. 2 is a flowchart of a calculation process executed by the control unit of FIG.

3 is an input / output characteristic diagram of an electric motor used in the electric pump of FIG.

FIG. 4 is an explanatory diagram of transient characteristics of electric motor generated torque by the arithmetic processing of FIG.

FIG. 5 is a schematic configuration diagram showing a second embodiment of an electric pump type power steering apparatus for a vehicle of the present invention.

6 is a flowchart of a calculation process executed by the control unit of FIG.

[Explanation of symbols]

 1 is a steering wheel 2 is a steering column shaft 3a, 3b is a joint 4 is a torsion bar 6 is a pinion shaft 7 is a pinion 8 is a steering shaft 11 is a side rod 12 is a wheel support member 13 is a steered wheel 14 is an electric motor 15 is a rotary Valve 16 Reservoir 17 Power cylinder 18 Electric pump 19 Relief valve 31 Pressure sensor 32 Current detector 34 Control unit 35 Microcomputer 36 Drive circuit 37 Power supply device

Claims (4)

[Claims] 1. An electric pump rotationally driven by an electric motor, and a control valve for switching and supplying the discharge fluid pressure of the electric pump to a power cylinder according to the magnitude and direction of a steering input to a steering wheel. Discharge fluid pressure detection or estimation means for detecting or estimating whether or not the discharge fluid pressure of the electric pump supplied to the power cylinder via the control valve is equal to or higher than a predetermined set value, and the discharge fluid pressure detection or estimation means. By the control, when the discharge fluid pressure of the electric pump is equal to or higher than the predetermined set value, the voltage applied to the electric motor is reduced to limit the maximum value of the discharge fluid pressure of the electric pump to the maximum required fluid pressure for the power cylinder. An electric pump type power steering apparatus comprising: 2. A pressure sensor for detecting the discharge fluid pressure of the electric pump is provided as the discharge fluid pressure detection or estimation means, and whether or not the discharge fluid pressure detection value from the pressure sensor is equal to or more than the predetermined set value. The electric pump type power steering apparatus according to claim 1, further comprising means for determining whether or not the electric pump type power steering apparatus is a power steering apparatus. 3. A pressure switch for operating the discharge fluid pressure of the electric pump at the predetermined set value or more is provided as the discharge fluid pressure detecting or estimating means, and the discharge of the electric pump is performed in response to a signal from the pressure switch. The electric pump type power steering apparatus according to claim 1, further comprising means for determining whether or not the fluid pressure is equal to or higher than a predetermined set value. 4. The discharge fluid pressure detection or estimation means,
An electric current detector for detecting the electric current value of the electric motor of the electric pump is provided, and the electric current of the electric motor corresponding to the discharge fluid pressure of the electric pump whose electric current detection value from the electric current detector is equal to or more than the predetermined set value. The electric pump type power steering apparatus according to claim 1, further comprising means for estimating that the discharge fluid pressure of the electric pump is equal to or more than a predetermined set value when the value is equal to or more than the value.