JPS6125979A - On-off servomechanism available in variable displacement hydraulic pump - Google Patents

Abstract

PURPOSE:To perform the positional control of a servo piston in a stable manner, by making on-off valve train of position controlling solenoid valves adjustable to shorten its on-time according to reaction of the servo piston driving a displacement variable mechanism for a variable displacement hydraulic pump. CONSTITUTION:A servomechanism bearing the above caption operates a displacement variable mechanism (an angled axis or the like) 3 of a variable displacement hydraulic pump 2 through a servo piston 4, while a position of the servo piston 4 is controlled by a pair of solenoid valves 6a and 6b. These solenoid valves 6a and 6b are controlled a control unit 16 in accordance with a deviation between the output of a tilt variable detector of the mechanism 3 and an input value by an operating lever 10. In this case, reaction force to be imposed on the servo piston 4 is calculated from each output of a rotational frequency detector 17 for an input shaft of the pump 2 and a pressure detector 18 for discharge force of the pump 2, and according to size of the reaction force, an on-off pulse train for solenoid valve control is made adjustable to shorten its on-time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an on-off servo mechanism used in a variable displacement hydraulic pump installed in a hydraulic machine such as a hydraulic excavator.

[Background of the invention]

FIG. 6 is an explanatory diagram showing the configuration of an on-off servo mechanism used in a conventional variable displacement hydraulic pump. In this diagram,
1 is an engine, 2 is a variable displacement hydraulic pump driven by the engine 1, and 3 is a variable displacement mechanism of the variable displacement hydraulic pump 2, for example, a diagonal shaft. 4 is oblique axis 3
A servo piston 5 is connected to one oil chamber 4a of the servo piston 4, and is connected to the other oil m4b via a solenoid valve 6a. , and is also connected to a tank 8 via a relief valve 7. Note that the other oil chamber 4b of the servo pinton 4 is connected to the tank 8 via a solenoid valve 6b. Reference numeral 9 denotes a tilt amount detector connected to the oblique shaft 3 of the variable displacement hydraulic pump 2, which detects the amount of tilt of the oblique shaft 3 and outputs a signal. The signal from the tilt amount detector 9, that is, the output voltage Y, is proportional to the amount of displacement of the servo piston 4 with a practically acceptable error, and together with the signal input from the operating lever 10, that is, the input command voltage X. , is input to the trowel 12 of the control device 11. The adder 12 receives an input command voltage X
The difference between the output voltage Y of the tilt amount detector 9 and the deviation voltage g'? f: Not created. 13a.

13b+'j: A comparator connected to the adder 12. Of these, the comparator 13a operates when the value of the deviation voltage ε is larger than the preset value Δ, and sets the output Va to a high level and performs the comparison. The device 13b operates and outputs V when the value of the deviation voltage ε is less than the preset value - Δ.
Make b into HiRepe I. Then, the output V of the comparator 13a
a is the solenoid 15 of the solenoid valve 6a via the amplifier 14a.
aKJEj is obtained, and the output vb of the comparator 13b is output from the amplifier 1.
4b - using a fully closed configuration. In this case, when only the solenoid 15a of the solenoid valve 6a is energized, the servo piston 4 moves to the right in FIG.
When only the solenoid 15b is excited, the servo piston 4
moves to the left. Further, when neither the solenoid valves 6a and 6b are excited, the oil chambers 4a+4b are connected to the constant displacement hydraulic pump 5.
Since it is not connected to tank 8, servo piston 4
holds its position.

The operation of the on-off servo mechanism constructed in this way is as follows.

That is, in a state where ε>Δ, the solenoid 15a is excited, so the servo piston 4 moves to the right in FIG. Further, in the state of ε<-Δ, the solenoid 15b is excited, so the servo piston 4 moves to the left. In addition, in the state of -Δ〈Shield Δ, the solenoid 15a,
Since neither servo piston 15b is excited, the servo piston 4 maintains its position.

The above-mentioned on-off servo mechanism is generally called a three-value on-off servo mechanism. That is, if the inertia of the servo piston 4 and the oblique shaft 3 and the compressibility of oil are ignored, the servo piston 4 has a positive maximum speed v1, a negative maximum speed -V2, and so on. This is because it can take only three states: and at rest. Now, in order to simplify the explanation, as mentioned above, we will ignore the inertia of the servo piston 4 and the oblique shaft 3 and the oil leakage, and the solenoid valves 6a, 6
Considering only the dead time τ caused by the delay in switching b, the stability condition for this servo mechanism is 2Δ> Vl・
τ (1) 2Δ>v2・τ
(2) It is expressed as

On the other hand, in Fig. 6, the positive maximum speed V when the servo piston 4 moves to the right and the negative maximum speed -v2 when it moves to the left ignore leakage A' in the hydraulic circuit. death,
The pressure receiving area of the servo piston 4 in the oil chamber 4b is A1,
The flow rate passing through the solenoid valve 6a and flowing into the oil chamber 4b is Q1% The flow rate flowing out from the oil chamber 4b and passing through the solenoid valve 6b is Q2
Then, Vl = Q t / A 1
(3)■2 =Q2/AI
(4) becomes. Generally, the same electromagnetic valves 6a and 6b are used, and their flow characteristics can be approximated as ΔP=RQ2 (5), where ΔP is the pressure difference before and after, and R is the coefficient.

Moreover, the pressure difference ΔP before and after the solenoid valve is determined by the balance of forces applied to the servo piston 4, and the equation for the force balance is given by the pressure receiving area of the servo piston 4 in the oil chamber 4a.
. , the pressure in the oil chamber 4a is P. , the pressure in the oil chamber 4b is Pl, the reaction force received from the variable displacement hydraulic pump 2 is F, and to simplify the explanation, ignoring the viscous resistance of the servo piston 4, PoA, -PlA, = F (6) Become. Therefore, the flow rate Q1 passing through the solenoid valve 6a is calculated by the formula (
5) From (6), the maximum positive speed V□ when the servo piston 4 moves to the right is from equation (3). Similarly, the flow rate Q2 passing through the electromagnetic valve 6b and the maximum negative speed v2 when the servo piston 4 moves leftward are as follows.

As described above, the maximum positive speed v1 when the servo piston 4 moves to the right is expressed as equation (8), and the reaction force F
As becomes larger, the maximum positive speed v8 becomes even larger,
Conversely, the maximum negative speed v2 when the servo piston 4 moves to the left is expressed by equation (10), and as the reaction force F increases, the maximum negative speed v2 becomes smaller. FIG. 7 is an explanatory diagram showing the relationship between such reaction force F and velocity 'V11V2. Here, the reaction force F is the variable displacement hydraulic pump 2
The force generated due to the structure of the engine generally depends on the engine speed N6 and the load pressure PL, and has characteristics as shown in FIG. 8, for example. In other words, when the engine speed Ne is constant, the reaction force F becomes stronger as the load pressure PL increases.
When the load pressure pL is constant, the lower the engine speed N8, the larger the reaction force F becomes.

In this way, in the conventional on-off servo mechanism shown in FIG. 6, the positive maximum speed v1 and the negative maximum speed v2 change depending on the reaction force F, but here, especially when the maximum speed becomes large, the servo billaton changes. 4 position may not be able to be accurately controlled. In other words, under the stability conditions of the on-off servo mechanism in equations (1) and (2), a dead zone 2Δ is set for a certain maximum speed, so as the maximum speed of the engine increases, equations (1) and (2) ) is not satisfied, and therefore stable control is not possible.

In order to solve this problem, it is conceivable to set the dead zone 2Δ to be thicker, but doing so will result in a reduction in the level of work.

[Purpose of the invention]

The present invention has been made in view of the actual situation in the prior art, and its purpose is to provide an on/off control system for use in a variable displacement hydraulic pump that can control the position of a servo piston in a completely stable manner without causing a decrease in work accuracy. The purpose is to provide a servo mechanism.

[Flea of invention]

To achieve this object, the present invention provides a servo piston connected to a variable displacement mechanism of a variable displacement hydraulic pump, a solenoid valve that operates on and off to control the position of the servo piston, and a variable displacement mechanism. and a tilting amount detector for detecting the amount of tilting, and the variable capacity is configured to drive a solenoid valve according to a control deviation that is a deviation between the input amount and the signal for tilting 1 of the tilting amount detector. In an on-off servo mechanism used for a hydraulic pump, a detection means for detecting the rotation speed of the input shaft of the variable displacement hydraulic pump, a detection means for detecting the pressure in the discharge side circuit of the variable displacement hydraulic pump, and a detection means connected to the variable displacement hydraulic pump. At least one of the detection means for detecting the temperature of the pressure oil flowing through the circuit is provided, a calculation means for calculating the reaction force applied to the servo piston based on the output signal of the detection means, and one calculation means for the calculation means. And f
An adjustment means is provided for adjusting the on-time of the on-off pulse train to become scorching in accordance with the magnitude of the reaction force calculated in pL,
The solenoid valve is configured to be driven according to the ON time and interval adjusted by this adjusting means.

FIG. 1 is an explanatory diagram showing the configuration of an embodiment of an on/off servo mechanism used in a variable displacement hydraulic pump of the present invention.

In this figure, 17 is a detection means for detecting the input shaft rotation speed of the variable displacement hydraulic pump 2, that is, a rotation speed detector;
is a detection means, that is, a pressure detector, which detects the pressure in the discharge side circuit of the variable displacement hydraulic pump 2, and these rotation speed detector 17 and pressure detector 18 are connected to the function generator 1 of the control device 16.
Connect to the input side of 9. The function generator 19 generates a preset functional relationship, for example, the third
The reaction force Ft applied to the servo piston 4 is calculated according to the functional relationship shown in the figure, and its output is given to another function generator 20.

The function generator 20 generates a second ON pulse train (
The on time (hereinafter referred to as duty ratio) D in one cycle of the PVv'M signal (hereinafter referred to as the PVv'M signal) is determined by a preset functional relationship, for example, when the reaction force F is in a predetermined first range where it is small, 1 is output. However, when F exceeds the first range and reaches a predetermined second range where it is sufficiently large, a value that gradually becomes smaller than 1 is output, and when F is in the second range, the value becomes smaller than 1. Output according to a functional relationship that is set to output a small constant value.

The function generator 21 converts the PWM signal into an AN in accordance with the duty ratio output from the function generator 20 at a certain frequency.
Output to D element 22. When the AND element 22 receives both the PWM signal and the output of the comparator 13a, it outputs an excitation signal to the solenoid 15a of the electromagnetic valve 6a via the amplifier 14a.

The function generator 20.2i and the AND element 22 described above constitute an adjusting means that adjusts the on-time of the on-off pulse train to be shortened according to the magnitude of the reaction force F exerted by the function generator 19. There is.

The other configurations are the same as, for example, the configuration shown in FIG. 6 described above.

In this embodiment, when the pressure pL of the discharge side circuit of the variable displacement hydraulic pump 2 increases, the pump input shaft rotation speed Ne
decreases, the reaction force F applied to the servo piston 4 becomes
As shown in Fig. 7, the maximum positive speed v1 is fast and the maximum negative speed v2 is slow. The number Ne is detected, and the load pressure P is detected by the pressure detector 18.
L is detected, and the reaction force F is generated by the function generator 19 based on these pump input shaft rotational speed N6 and load pressure pL.
is calculated, and according to this reaction force F, the duty ratio is calculated by the function generator 20 to become smaller, and the on time of the PWM signal output from the function generator 21 is shortened according to this duty ratio. As a result, the on time of the driving current of the solenoid 15a outputted from the amplifier 14a is also shortened, and the flow rate Q passing through the electromagnetic valve 6a'z is reduced as shown in FIG. Note that if the duty ratio is set above a certain value, the flow will reach the maximum flow, and if it is set below another certain value, the flow will stop, so the duty ratio must be set within a controllable range.

In the embodiment configured in this way, when the pump input shaft rotational speed N8 decreases and the load pressure pL increases and the reaction force F applied to the servo piston 4 increases, the solenoid valve 6
Since oil no longer flows through a, the maximum positive speed v1 can be reduced as shown in FIG. Note that the negative maximum speed v
2 is the same as in the configuration shown in FIG.

In the above, as shown in FIG. 8, the characteristics of the reaction force F acting on the servo piston 4 are dependent on the pump input shaft rotation speed N8 and the load pressure PL, but only the pump input shaft rotation speed N8 - It is also possible to adopt a configuration in which the driving of the solenoid valve 15a is controlled in relation to the load pressure PH or only in relation to the load pressure PH. Further, since the characteristics of the reaction force F also depend on the temperature, a configuration may be adopted in which the temperature of the hydraulic circuit is detected and the drive of the solenoid 15a of the electromagnetic valve 6a is controlled in relation to this detected value.

In addition, in the above, as shown in FIG. 7, the maximum speed of the servo piston 4 is always higher than the negative maximum speed V2, and as the reaction force F increases, However, the present invention is not limited to this, and the present invention is not limited to this, but the present invention is not limited to this, and the maximum speed of the servo piston 4 may be negative in a region where the reaction force F is small, as shown in FIG. 9, for example. It is also applicable to the servo piston 4 having the characteristics that the maximum speed v2 is faster and the positive maximum speed V becomes faster in a region where the reaction force F is large. FIG. 4 is an explanatory diagram showing the structure of another embodiment corresponding to such characteristics. Note that in FIG. 4, the same equipment as shown in FIG. 1 is designated by the same reference numeral.

In FIG. 4, 23 is a control device, and 24.25 is a function generator provided in this control temporary station 23 and connected to the function generator 19. Of these, the function generator 24 is a function generator shown in FIG. A function generator similar to the generator 20, with a duty ratio D'
t - For example, when the reaction force F is in a predetermined first range where it is small, the full output is 1, and when F exceeds the first range and reaches a sufficiently large second range, it outputs more than 1. The functional relationship is set to output a value that gradually decreases, and a constant value that is sufficiently smaller than 1 in the second range. Outputting a value that gradually increases toward 1 between exceeding the first range and reaching a sufficiently large predetermined second range;
The functional relationship is set so that 1 is output in the second range.

21.26 is a function generator connected to each of the function generators 24.25, the frequency is constant, and the function generator 24.2
The PWM signal is A depending on the tuteity ratio at which 5 is output.
ND Mizuko 22.27F (: Output. AND element 22 connects the PWM signal output from function generator 21 and comparator 13
When both the output of A and the output of
When the ND element 27 receives both the PWM signal output from the function generator 26 and the output of the comparator 13b, it outputs an excitation signal to the solenoid 15b of the electromagnetic valve 6b via the amplifier 14bt-.

The combination of the function generators 24, 21 and the AND element 22 and the combination of the function generators 25, 26 and the AND element 27 are activated by an on-off pulse train according to the magnitude of the reaction force F calculated by the function generator 19. Adjust so that the time of M! constitutes a means. The rest of the configuration is equivalent to that shown in FIG. 1, which has been described previously.

In this implementation history, the calculation result of the function generator 19 is
When the reaction force F becomes smaller than a preset value, that is, when the reaction force F is within the first range of the functional relationship set by the function generator 25, the P output from the function generator 26
The tute ratio of the WM signal becomes smaller, and the on time of the PWM signal output from the function generator 26 to the AND element 27 becomes shorter. Furthermore, when the reaction force F becomes larger than a preset value, that is, when the reaction force F is within the second range of the functional relationship set by the function setting device 24, the PWM signal output from the function generator 21 The duty ratio becomes smaller, and the on time of the PWM signal output from the function generator 21 to the AND element 22 becomes shorter. As a result, when the reaction force F is smaller than a preset value, the ON time of the drive current of the solenoid 15h output from the amplifier 14b is shortened, and the flow rate passing through the solenoid valve 6b is reduced, and the reaction force F is reduced in advance. If the value is larger than the set value, the ON time of the drive current of the solenoid 155 output from the amplifier 14α becomes shorter, the flow rate passing through the solenoid valve 6α decreases, and the reaction force F increases in advance as shown in FIG. If it is smaller than a preset value, the negative maximum speed v2 can be slowed down, and if it is larger than a preset value, the positive maximum speed v1 can be slowed down.

In the embodiment shown in FIG. 4, the servo piston 4
The above-mentioned method for stably controlling the position of the servo piston 4 no matter how the reaction force F applied to the servo piston 4 changes or how the maximum positive and negative speed v1%v2 changes due to the reaction force F. The stability conditions shown in equations (1) and (2) can be satisfied without changing the dead zone 2Δ.As shown in FIG. It is also possible to make the vzO values the same.

〔Effect of the invention〕

Since the on-off servo mechanism used in the variable displacement hydraulic pump of the present invention is configured as described above, the maximum speed of the servo piston is This has the effect of making it possible to control the position of the servo piston more stably than in the past.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration of an embodiment of the on-off servo mechanism used in the variable displacement hydraulic pump of the present invention, and FIG. 2 is a diagram showing the duty ratio of the PWM signal obtained in the embodiment shown in FIG. 1 and the electromagnetic valve. FIG. 3 is a characteristic diagram showing the relationship between the reaction force F applied to the servo piston and the speed ν of the servo piston obtained in the embodiment shown in FIG. The figure is an explanatory diagram showing the configuration of another embodiment of the present invention, and FIG. 5 is a characteristic diagram showing the relationship between the reaction force F applied to the servo piston and the speed ν of the servo piston obtained in the embodiment shown in FIG. , Fig. 6 is an explanatory diagram showing the configuration of an on-off servo mechanism used in a conventional variable displacement hydraulic pump, and Fig. 7 shows the reaction force F acting on the servo piston of the on-off servo mechanism shown in Fig. 6 and the speed υ of the servo piston. Figure 8 is a characteristic diagram showing the relationship between load pressure PL, pump input shaft rotation speed N, and reaction force F. Figure 9 is a servo piston of another conventional on-off servo mechanism. FIG. 3 is a characteristic diagram showing the relationship between the reaction force F and the speed υ of the servo piston. 2... Variable capacity hydraulic pump, 3... Oblique shaft (variable displacement mechanism), 4... Servo piston, 6α, 6h... Solenoid valve, 9...
・Tilt amount detector, 1o...operation lever, 13α
, 13b... Comparator, 14α, 14A...
...Amplifier, 16.23...Control device, 1
7...Rotation speed detector, 18...Pressure detector, 19.20.21.24.25.26...
・Function generator, 22.27...AND element. 20 3rd ↑ Reaction force F 51.31 9U; Figure 7 Figure 8 0 Load life force PL

Claims (1)

[Claims] (1) A servo piston connected to the variable displacement mechanism of the variable displacement hydraulic pump, a solenoid valve that operates on and off to control the position of the servo piston, and detects the amount of tilt of the variable displacement mechanism. an on-off servo used in a variable displacement hydraulic pump, which is equipped with a tilting amount detector and drives the solenoid valve according to a control deviation that is a deviation between an input amount and a tilting amount signal of the tilting amount detector. In the mechanism, a detection means for detecting the rotation speed of the input shaft of the variable displacement hydraulic pump, a detection means for detecting the pressure in the discharge side circuit of the variable displacement hydraulic pump, and a circuit connected to the variable displacement pump. At least one detection means of the detection means for detecting the temperature of the pressure oil is provided, and a calculation means for calculating the reaction force applied to the servo piston based on the output signal of the detection means, and the reaction force calculated by the calculation means is provided. and an adjusting means for adjusting the on-time of the on-off pulse train to be shortened according to the magnitude of the reaction force, and the solenoid valve is driven according to the on-time adjusted by the adjusting means. On-off servo mechanism used in variable displacement hydraulic pumps.