JPH0988902A - Pump capacity control method and apparatus - Google Patents

Abstract

(57) Abstract: A pump capacity control method and apparatus for controlling the tilt angle of a pump in consideration of the pressure of a pump line in addition to the tilt angle of a variable displacement hydraulic pump. SOLUTION: From the deviation between the command value and the actual measurement value of the tilt angle of the variable displacement hydraulic pump 1, a tilt angle control amount such that this deviation becomes zero is obtained, and the discharge pressure of the variable displacement hydraulic pump 1 is tilted. The tilt angle is controlled to the target tilt angle by correcting this control amount in advance so as to cancel out the influence on the tilt angle control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pump displacement control method and device for a variable displacement axial pump.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a conventional pump displacement control device. In FIG. 5, the discharge amount of the pressure oil of the pump 1 per unit time is determined by the tilt angle of the pump 1, and the tilt angle is determined by the position of the piston 2a of the hydraulic cylinder 2. The position of the piston 2a of the hydraulic cylinder 2 is such that the supply and discharge of pressure oil from the pump line 5 to the oil chamber 3 and the electromagnetic switching valve
When the electromagnetic switching valve 7 is open to the pump line 5 side, the force acting from the oil chamber 4 to the piston 2a is controlled from the oil chamber 3 to the piston 2a.
Since the force acting on the pump 2 is exceeded, the piston 2a moves in the direction in which the tilt angle of the pump 1 increases. When the electromagnetic switching valve 7 is open to the drain tank 6 side, the force acting from the oil chamber 3 to the piston 2a exceeds, so that the piston 2a moves in the direction in which the tilt angle of the pump 1 decreases. When the electromagnetic switching valve 7 is controlled to the spool position where the amount of pressure oil supplied to and discharged from the oil chamber 4 is zero, the movement of the piston 2a is stopped and a desired tilt angle is obtained.

The electromagnetic switching valve 7 does not have a neutral point, and the flow rate from the pump line 5 to the electromagnetic switching valve 7 and the drain tank 6
To the oil chamber 4 at the spool position where the outflow rate to the
The amount of pressure oil supplied to and discharged from is kept at zero. As a result, if the spool position deviates from the position for keeping the amount of pressure oil supplied to and discharged from the oil chamber 4 to zero, the oil chamber 4 will be displaced depending on the degree of deviation.
The pressure oil is supplied and discharged to realize a highly responsive regulator.

A control signal 9B for controlling the spool position of the electromagnetic switching valve 7 is sent from the control device 8B to the electromagnetic switching valve 7, and a tilt angle detecting device 10 for detecting the tilt angle of the pump 1 is sent to the control device 8B. The signal representing the actual tilt angle θmes detected in step S1 and the signal representing the target tilt angle θref are input from the target tilt angle command device 12, respectively.
θ = θref−θmes is obtained. The control calculation unit 14 calculates the control signal 9B based on the deviation Δθ.
When the actual tilt angle θmes is larger than the target tilt angle θref, the control signal 9B is output to the electromagnetic switching valve 7 so that the oil chamber 4 is connected to the drain tank 6 side in order to reduce the tilt angle. On the other hand, when the actual tilt angle θmes is smaller than the target tilt angle θref, the control signal 9B is output to the electromagnetic switching valve 7 so that the oil chamber 4 is connected to the pump line 5 side in order to increase the tilt angle. The spool displacement amount of the electromagnetic switching valve 7 is calculated according to the deviation Δθ, and the piston 2a of the hydraulic cylinder 2 is calculated.
The moving speed of is proportional to the opening degree of the electromagnetic switching valve 7 according to the spool displacement amount. Actual tilt angle θmes and target tilt angle θre
When f is equal and the deviation Δθ is zero, the spool position control signal 9B that keeps the amount of pressurized oil supplied to and discharged from the oil chamber 4 to zero is output to the electromagnetic switching valve 7.

For example, consider a case where the actual tilt angle θmes of the pump detected by the tilt angle detection device 10 is smaller than the target tilt angle θref. As mentioned above, the solenoid switching valve 7
Is connected to the pump line 5 side, and the piston 2a of the hydraulic cylinder 2 moves in a direction in which the tilt angle of the pump 1 increases. When the tilt angle increases, the deviation Δθ becomes smaller accordingly, and the control signal 9B calculated again in response to this is output to the electromagnetic switching valve 7, and the passage cross-sectional area that connects the pump line 5 and the oil chamber 4 is communicated. Becomes smaller. When the tilt angle of the pump 1 finally reaches the target tilt angle by repeating such an operation, the deviation Δθ becomes zero, and the control signal 9B to the electromagnetic switching valve 7 changes the supply / discharge amount to / from the oil chamber 4. It becomes a control signal to make it zero. Then, the piston 2a of the hydraulic cylinder 2 does not move and the tilt angle is set to the target tilt angle. In this way, the tilt angle of the pump 1 is fed back and the pump 1
The pump capacity is controlled.

[0006]

However, as will be described below, the pump 1 is affected by the pressure of the pump line 5, and the control device 8B does not reflect this, so that accurate pump displacement control is possible. Not realized.

The influence of the pressure in the pump line 5 will be described below. FIG. 6 is a diagram modeling the conventional example of FIG. Meanings of symbols in FIG. 6 and the following formulas are as follows. Qin: Flow rate flowing from the pump line 5 to the electromagnetic switching valve 7 Qout: Flow rate flowing from the electromagnetic switching valve 7 to the drain tank 6 Qreg: Flow rate flowing from the electromagnetic switching valve 7 into the oil chamber 4 of the hydraulic cylinder 2 X: Spool displacement P1: Pressure of oil chamber 4 P2: Pressure of oil chamber 3 Ps: Pressure of pump line 5 α1, α2: Flow gain for spool displacement β1, β2: Flow gain for pressure difference S1: Oil chamber for piston 2a of hydraulic cylinder 2 Area on the 4th side S2: Area on the oil chamber 3 side of the piston 2a of the hydraulic cylinder 2 θmes: Tilt angle of the pump 1 y: Displacement of the piston 2a of the hydraulic cylinder 2 k: Spring constant K: Tilt return force of the pump 1 Constant C: coefficient

In FIG. 6, the flow rate Q and the differential pressure ΔP before and after the orifice are not exactly linear, but for simplicity of explanation, they are linearly approximated in the following description. The following formulas are obtained for each of the variable orifices that model the electromagnetic switching valve 7.

[Equation 1]

[Equation 2] Further, the following formula is obtained from the continuous formula around the hydraulic cylinder 2.

(Equation 3) Here, C is a coefficient that approximates the relationship between the movement of the piston 2a of the hydraulic cylinder 2 and the tilt angle of the pump 1 to a proportional type.
On the other hand, the following equation is obtained from the balance of the forces of the piston 2a of the hydraulic cylinder 2.

[Equation 4] In this equation, the first term on the left side is the spring force for holding the piston 2a at a certain position when the hydraulic cylinder 2 is in the initial state. The second term on the left side is the tilting return force of the pump 1 and is assumed to be proportional to the pressure of the pump line 5. For equation (4), ky << (S1 · P1),
Ignoring ky gives the following equation:

(Equation 5) Substituting equations (1), (2), and (5) into equation (3), the following relationship is obtained.

(Equation 6)

Thus, according to the equation (6), the tilt angle θ of the pump 1 is determined by the spool displacement X and the pressure Ps of the pump line 5.
It changes according to. FIG. 7 shows a conceptual diagram in which this is simplified by a block diagram. In FIG. 7, a signal 9B representing the amount of displacement X of the spool according to the deviation Δθ is output from the control device 14. A is a coefficient when the control signal 9B of the electromagnetic switching valve 7 is converted into the displacement of the spool to control the tilt angle of the pump 1, and B is the influence of the pump line pressure Ps on the control of the tilt angle of the pump 1. Is a coefficient to exert. That is, the tilt angle of the pump 1 is controlled by the expression represented by A · X + B · Ps.

As described above, the tilt angle of the pump 1 is affected by the pressure in the pump line 5. However, in the conventional control method, since only the actual tilt angle of the pump 1 is fed back to control the spool displacement of the electromagnetic switching valve 7, the tilt angle of the pump 1 cannot be accurately controlled by the pressure of the pump line 5. .

An object of the present invention is to provide a pump displacement control device for controlling the tilt angle of the pump in consideration of the pressure of the pump line in addition to the actual tilt angle.

[0012]

The present invention will be described with reference to FIG. 1 showing an embodiment. In order to achieve the above object, the invention of claim 1 is applied to a pump displacement control method for controlling a tilt angle of a variable displacement hydraulic pump 1 to a target tilt angle, and a command value of the tilt angle and a tilt angle. Actual measurement value and pump 1
The tilt angle of the variable displacement hydraulic pump 1 is controlled so that the target tilt angle is achieved on the basis of the discharge pressure. The pump displacement control method according to claim 2 is applied to the pump displacement control method according to claim 1, and from the deviation between the command value and the actual measurement value, a control amount is obtained so that this deviation becomes zero, and the variable displacement hydraulic pump 1 The control amount is corrected so as to cancel the influence of the discharge pressure on the tilt angle. The pump displacement control device according to claim 3 includes a command device 12 for instructing a target tilt angle of the variable displacement hydraulic pump 1, a tilt angle detector 10 for detecting an actual tilt angle of the variable displacement hydraulic pump 1, and a variable angle detector 10. The pressure detector 15 that detects the discharge pressure of the displacement hydraulic pump 1, the tilting member drive devices 2 and 7 that drive the tilting member of the variable displacement hydraulic pump 1 to adjust the tilting angle, and the target tilting angle. , The actual tilt angle detected by the tilt angle detector 10, and the pressure detector 1
Based on the discharge pressure detected in 5, the signal generating device 8 that generates a signal for controlling the tilting member driving devices 2 and 7 so as to obtain the target tilting angle is provided. A pump displacement control device according to a fourth aspect is the pump displacement control device according to the third aspect, in which the signal generation device 8 obtains a control amount such that the deviation becomes zero from the deviation between the target tilt angle and the actual tilt angle. At the same time, a signal is generated by correcting the control amount so as to cancel the influence of the discharge pressure of the variable displacement hydraulic pump 1 on the tilt angle. Next, referring to FIG. 4, the pump displacement control device according to a fifth aspect of the invention is the variable displacement hydraulic pump 1.
Of the target displacement angle of the variable displacement hydraulic pump 1, the displacement angle detector 10 for detecting the actual displacement angle of the variable displacement hydraulic pump 1, and the displacement angle of the variable displacement hydraulic pump 1 by driving the displacement member. The tilt cylinder 2, the solenoid valve 7A that adjusts the amount of expansion and contraction of the tilt cylinder 2 to adjust the position of the tilt member, and the actual tilt detected by the target tilt angle and tilt angle detector 10. A valve control device 8A for controlling the displacement amount of the solenoid valve 7A so that the deviation from the turning angle is zero is provided, and the discharge pressure of the hydraulic pump 1 is controlled by the solenoid valve 7
The position of the solenoid valve 7A is controlled so as to act on A and cancel the influence of the discharge pressure on the tilt angle.

In the section of the means for solving the above problems, the explanation has been made in association with the drawings of the embodiments for the sake of easy understanding, but the present invention is not limited to the embodiments. .

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

-First Embodiment- A first embodiment will be described with reference to FIG. Here, the same parts as those in FIG. 5 are designated by the same reference numerals, and the differences are mainly described. The control device 8 includes the actual tilt angle θmes detected by the potentiometer 10 for detecting the tilt angle of the pump 1, the pressure Ps detected by the pressure sensor 15 for detecting the pressure of the pump line 5, and the target. Each signal corresponding to the target tilt angle θref commanded from the tilt angle command device 12 is input, and the control signal 9 is calculated based on these signals.

The control device 8 calculates a difference Δθ between the target tilt angle θref and the actual tilt angle θmes, and a control calculation for calculating the uncorrected control signal of the electromagnetic switching valve 7 from the difference Δθ. Part 14, a correction calculation part 17 for calculating a value for subtracting the influence of the pressure Ps of the pump line 5, and a deviation part for subtracting the value calculated by the correction calculation part 17 from the value calculated by the control calculation part 14. 13 and the output signal of the deviation unit 13 is output as the control signal 9 of the electromagnetic switching valve 7.

FIG. 2 is a block diagram similar to FIG.
The contents of calculation in the correction calculator 17 will be described with reference to this drawing. As described above in the section “Problems to be Solved by the Invention”, the coefficient A is a coefficient when the control signal 9 of the electromagnetic switching valve 7 is converted into displacement of the spool to control the tilt angle of the pump 1. B is a coefficient in which the pump line pressure Ps influences the control of the tilt angle of the pump 1. In the first embodiment, the influence of the pressure Ps on the control of the tilt angle of the pump 1 is converted into a spool displacement amount, and the value is subtracted in advance from the spool displacement amount obtained from the deviation Δθ, and the solenoid operated directional control valve. By generating the control signal 9 of 7, the actual pressure Ps
It is intended to cancel the influence of. Therefore, the correction calculator 17 obtains the spool displacement conversion amount from (B / A) · Ps.

That is, if the value of the control signal 9 corresponding to the spool displacement of the electromagnetic switching valve 7 is X, the calculated value of the control calculation unit 14 is X1, and the calculated value of the correction calculation unit 17 is X2, X =
It is represented by X1-X2. X1 is represented by a function of f (Δθ), and this function f (Δθ) is determined by the performance of the electromagnetic switching valve 7. X2 is (B / A) · P as described above.
It is represented by s. Specifically, the value of the coefficient B / A is obtained by previously experimentally determining the spool displacement X at which the pump tilt angle is most stable for each pump line pressure by varying the pump line pressure Ps. This experimental result and the function f
It is determined by calculation from X1 obtained by (Δθ).

For example, if the tilt angle of the pump 1 is the target tilt angle θ
Consider a case where the pressure in the pump line 5 rises while being kept equal to ref. According to the conventional control method, from FIGS. 5 and 6, the front-rear pressure of the electromagnetic switching valve 7 fluctuates due to the increase of S2 · P2 and the increase of the tilt return force K · Ps due to the pressure increase of the oil chamber 3 of the hydraulic cylinder 2. However, at the spool position where the supply and discharge of pressure oil to and from the oil chamber 4 has been zero until now, the supply and discharge of pressure oil to and from the oil chamber 4 cannot be maintained at zero. Therefore, the piston 2a of the hydraulic cylinder 2 moves, which causes a deviation Δθ, and when the deviation Δθ occurs, the electromagnetic switching valve 7 is driven according to the deviation Δθ. Solenoid switching valve 7
Drive the piston 2a of the hydraulic cylinder 2 to move,
The tilt angle of the hydraulic pump 1 reaches the target tilt angle θref, and the deviation Δθ becomes zero. However, when the deviation Δθ becomes zero, the electromagnetic switching valve 7 is controlled so as to make the supply and discharge of the pressure oil to and from the oil chamber 4 zero, but the solenoid switching valve 7 is returned to the previous spool position that does not consider the pressure increase in the pump line 5. Therefore, the supply and discharge of the pressure oil to and from the oil chamber 4 cannot be maintained at zero, and the above operation is repeated.
As a result, the tilt angle of the pump 1 is not stable.

On the other hand, in the first embodiment of the present invention shown in FIGS. 1 and 2, the amount of pressure change in the pump line 5 is supplied to and discharged from the oil chamber 4 by the correction calculator 17. The signal 9 is corrected in a feed-forward manner by converting the spool position change amount to zero. Therefore, when the tilt angle of the pump 1 reaches the target tilt angle θref and the deviation Δθ becomes zero, the electromagnetic switching valve 7 returns to the spool position where the increase in the pressure Ps of the pump line 5 is corrected. ,
No pressure oil is supplied to or discharged from the oil chamber 4. As a result, the tilt angle of the pump 1 is stable without being affected by the pressure of the pump line 2. In addition, since the effect of pressure change is corrected by feedforward, the response is fast.

FIG. 3 shows data of an experiment verifying the effect of the present invention. The graph compares the frequency response of the tilt angle of the pump 1 under each condition between the case where the control method of the present invention is adopted and the case where the conventional control method is used. In the graph, the gain is the ratio of the actual tilt angle θmes detected by the tilt angle detection device (potentiometer) 10 to the target tilt angle θref. FIG. 3A shows the frequency response of both when the control gain is optimized. That is, it is a graph in which a certain optimum pump line pressure is specified and the pump line pressure is measured. Under this condition, both the conventional example and the device according to the present invention show substantially the same characteristics. FIG. 3B shows the measurement result when the pump line pressure is higher than the optimum condition, and FIG. 3C shows the measurement result when the pump line pressure is lower than the optimum condition. From these graphs, it is understood that the device of the present invention obtains more stable frequency characteristics than the device of the conventional example even if the pump line pressure changes.

-Second Embodiment- The second embodiment will be described with reference to FIG. The same parts as those in FIG. 1 of the first embodiment are designated by the same reference numerals and the description thereof will be omitted. In FIG. 4, the electromagnetic switching valve 7A is provided with a pump pressure Ps from the left by a pump line pressure detection line 18.
And the spring force of the spring 19 is applied from the opposite side. This is a method of directly adding to the electromagnetic switching valve 7 a calculation function of converting the influence of the pump line pressure Ps into the displacement of the spool in the first embodiment. That is, the pump line pressure Ps introduced to the pump line pressure detection line 18
Tries to move the spool of the electromagnetic switching valve 7A rightward against the spring 19. The amount of movement of this spool is the first
This corresponds to the displacement amount of the spool based on the calculation value calculated by the correction calculation unit 17 of the embodiment.

When the amount of movement of the spool by the pump line pressure Ps is X3, the spring constant of the spring 19 is k1, and the pressure receiving area of the spool is D, X3 = (D / k1) · Ps, and the first embodiment In the form of X2 = (B / A) · Ps. The spring constant k1 of the spring 19 can be obtained by an experiment similarly to the coefficient B / A of the first embodiment. That is, the pressure Ps of the pump line 5 is variously changed, the spring constants with which the tilt angle is most stable for each pressure are obtained, and the best spring constant is selected and determined from these experimental results.

In this way, in the second embodiment as well as in the first embodiment, the tilt angle of the pump 1 can be controlled quickly and accurately even if the pressure in the pump line 5 changes. . The structure of the second embodiment is simpler than that of the first embodiment, and high-responsive control can be expected.

Since the present invention is configured as described above, it has the following effects. Since the pump tilt angle is controlled in consideration of the pump line pressure in addition to the pump tilt angle, the pump tilt angle can be accurately controlled even if the pump line pressure changes.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of a pump displacement control device according to the present invention.

FIG. 2 is a block diagram of the first embodiment of the pump displacement control device according to the present invention.

FIG. 3 is a graph of comparative experiment results of the first embodiment of the pump displacement control device according to the present invention and a conventional example.

FIG. 4 is a configuration diagram of a second embodiment of the pump displacement control device according to the present invention.

FIG. 5 is a configuration diagram of a conventional example of a pump displacement control device.

FIG. 6 is a modeled configuration diagram of a conventional example of a pump displacement control device.

FIG. 7 is a block diagram of a conventional example of a pump displacement control device.

[Explanation of symbols]

 1 Hydraulic Pump 2 Hydraulic Cylinder 2a Hydraulic Cylinder Piston 3, 4 Oil Chamber 5 Pump Line 6 Drain Tank 7, 7A Electromagnetic Switching Valve 8, 8A, 8B Control Device 9, 9A, 9B Control Signal 10 Potentiometer 11, 13 Deviation Section 12 Target tilt angle command device 14 Control calculation unit 15 Pressure detection device 17 Correction calculation unit 18 Pump line pressure detection line 19 Spring

Claims (5)

[Claims] 1. A pump displacement control method for controlling a tilt angle of a variable displacement hydraulic pump to a target tilt angle, wherein a tilt angle command value, a tilt angle measured value, and a discharge pressure of the pump are used. A pump displacement control method comprising controlling a tilt angle of the variable displacement hydraulic pump so as to achieve the target tilt angle. 2. A control amount such that the deviation becomes zero is obtained from the deviation between the command value and the actual measurement value, and the influence of the discharge pressure of the variable displacement hydraulic pump on the tilt angle is offset. The pump displacement control method according to claim 1, wherein the control amount is corrected as described above. 3. A command device for instructing a target tilt angle of the variable displacement hydraulic pump, a tilt angle detector for detecting an actual tilt angle of the variable displacement hydraulic pump, and a discharge pressure of the variable capacity hydraulic pump. A pressure detector for detecting, a tilting member driving device for driving a tilting member of the variable displacement hydraulic pump to adjust the tilting angle, a target tilting angle, and a tilting angle detected by the tilting angle detector. A signal generation device that generates a signal for controlling the tilting member driving device so as to achieve the target tilting angle based on the actual tilting angle and the discharge pressure detected by the pressure detector. A pump displacement control device characterized in that 4. The signal generating device obtains a control amount from the deviation between the target tilt angle and the actual tilt angle so that the deviation becomes zero, and the discharge pressure of the variable displacement hydraulic pump is adjusted to the above-mentioned value. 4. The pump displacement control device according to claim 3, wherein the control amount is corrected so as to cancel the influence exerted on the tilt angle and the signal is generated. 5. A command device for instructing a target tilt angle of a variable displacement hydraulic pump, a tilt angle detector for detecting an actual tilt angle of the variable displacement hydraulic pump, and a tilting member of the variable displacement hydraulic pump. A tilt cylinder that drives the tilt cylinder to adjust the tilt angle; a solenoid valve that controls the amount of expansion and contraction of the tilt cylinder to adjust the position of the tilt member; the target tilt angle and the tilt angle detection. A valve control device that controls the displacement amount of the solenoid valve so that the deviation from the actual tilt angle detected by the device is zero, and the discharge pressure of the hydraulic pump is applied to the solenoid valve. The pump displacement control device is characterized in that the position of the solenoid valve is controlled so as to cancel the influence of the discharge pressure on the tilt angle.