JP2007205464A - Control method of variable displacement pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method of a variable displacement pump responding to bleed-off characteristics of each actuator, which uses the variable displacement pump and closed-center-type directional control valves, has good economic efficiency of a bleed-off control method, and a hydraulic circuit with good operability, and is capable of controlling an entire region of operation even during an emergency. <P>SOLUTION: In the hydraulic circuit in which the actuator 1 is connected to each of the variable displacement pump 2 driven by an engine which can adjust a pump discharge amount from the outside and to a plurality of the close-center-type directional control valves, control of the variable displacement pump 2 by electric operation is performed via a solenoid proportional valve so that the closed-center-type directional control valves replace center-bypass-type directional control valves. At the time of emergency where a signal to the solenoid proportional valve cannot be obtained, the actuators 1 are operated by making the discharge pressure of the variable displacement pump a predetermined value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control method for a variable displacement pump applied to a machine such as a construction machine using a bleed-off hydraulic system.

The applicant has proposed a control method in Patent Document 1 and Patent Document 2 in a case where a hydraulic system of a construction machine such as a hydraulic excavator is connected to a plurality of actuators via a control valve of a closed center.
However, when a plurality of actuators are actually connected through the control valve of the closed center, problems have occurred in the following points.

  First, the discharge pressure of the variable displacement pump is controlled in an electrically closed loop by a controller and a pressure sensor. Specifically, the control disclosed in Patent Document 2 will be described with reference to the block diagram of FIG. 7 and the block diagram of FIG. 8 in which the control is organized by function. When closed-loop pressure control calculation is performed, the pump discharge amount command Qpc after the variable limiter is electrically output to the pump, so a command such as a problem in the electrical system is not given to the pump. Under the circumstances, there is a problem that the discharge amount generally remains zero and the system cannot be moved.

Further, as shown in FIG. 7, the virtual discharge pressure P _idea is obtained based on the bleed-off flow rate Xa obtained by subtracting the limited virtual discharge amount Q ' _idea from the virtual discharge amount Q _idea and the operation amount. The virtual bleed-off characteristic value Xb of the actuator is used, and when the operation amount increases, the opening area Ab of the virtual bleed-off passage calculated as the virtual bleed-off characteristic value Xb normally converges to 0, and finally Thus, it becomes 0. Further, the limited virtual discharge amount Q ′ _idea increases with respect to the virtual discharge amount Q _idea , and the difference (that is, the virtual bleed-off flow rate Xa) finally becomes zero.
However, in order to calculate the discharge pressure, it is necessary to perform the calculation of (Xa / Xb) ² in order to use the following formula, and there is a limit even if it is terminated under appropriate conditions, such as where the result is the maximum pressure, A numerical value close to 0 may be divided by a numerical value close to 0, resulting in a problem that calculation error increases.
P _idea = {(Q _max -Q _a ) / (Kq × Ab)} ²
In the formula, Q _max is the maximum discharge amount of the pump, Kq is a flow coefficient, and Ab is the opening area of the bleed-off passage.

  In addition, the operation amounts of the plurality of actuators are summed up to calculate the opening area of the bleed-off passage corresponding to a predetermined bleed-off characteristic, but when a different bleed-off flow rate is required for each actuator, Was not effective.

Japanese Patent No. 3745038 Japanese Patent No. 3471636

  The present invention can configure a hydraulic circuit having excellent practicality and economy by using a variable displacement pump and a closed center type directional valve, and further, without damaging the good operability of the bleed-off control method. A variable displacement pump control method that can be moved even in an emergency, can be controlled over the entire operating range, and can be controlled according to the bleed-off characteristics of each actuator. It is intended to provide.

In order to solve the above problems, the inventors have found a solution as follows.
That is, the control method for a variable displacement pump according to the present invention includes a plurality of closed center type directional control valves in a variable displacement pump driven by an engine and having an adjustable pump discharge amount from the outside. In addition, in the hydraulic circuit to which each actuator is connected, the closed center type directional control valve is a method for controlling the variable displacement pump by electrical calculation so that it can replace the center bypass type directional control valve, Control of the discharge pressure of the variable displacement pump is performed via an electromagnetic proportional valve, and the actuator is controlled by setting the discharge pressure of the variable displacement pump to a predetermined value in an emergency when a signal to the electromagnetic proportional valve cannot be obtained. It is possible to operate.
Further, according to a second aspect of the present invention, in the variable displacement pump control method according to the first aspect, the tilt drive system of the variable displacement pump is a negative type in the emergency. .
According to a third aspect of the present invention, in the control method for the variable displacement pump according to the second aspect, in order to make the tilt drive system of the variable displacement pump a negative type, the electromagnetic proportional valve is a negative type. It is characterized by that.
According to a fourth aspect of the present invention, there is provided a hydraulic circuit in which an actuator is connected to a plurality of closed center type directional control valves to a variable displacement pump driven by an engine and capable of adjusting a pump discharge amount from the outside. The method of controlling the variable displacement pump by electrical calculation so that the closed center type directional control valve is substituted for a center bypass type directional control valve, the actual pump discharge amount of the variable displacement pump being And the operation amount of each directional control valve, the actual pump discharge amount as the actuator flow rate, a bleed-off flow rate is calculated based on the operation amount, and from the virtual pump discharge amount of the variable displacement pump, A flow rate value obtained by subtracting the actuator flow rate and the bleed-off flow rate is calculated, and the variable capacity pump is calculated based on the flow rate value. And determining a control command value.
According to a fifth aspect of the present invention, in the control method for the variable displacement pump according to the fourth aspect, the variable displacement pump is a swash plate type variable displacement pump, and the detection of the actual pump discharge amount is inclined. It is characterized by being performed by a rolling sensor.
According to a sixth aspect of the present invention, in the control method for a variable displacement pump according to the fourth or fifth aspect, the control command amount of the variable displacement pump is calculated based on a virtual piping system as a reference model. The virtual pump discharge pressure command is used.
According to a seventh aspect of the present invention, in the control method for a variable displacement pump according to any one of the fourth to sixth aspects, the bleed-off flow rate is multiplied by a square root of the discharge pressure by a flow coefficient of an orifice. It is characterized by obtaining by this.
The present invention described in claim 8 is the variable displacement pump control method according to claim 6 or 7, wherein the virtual discharge amount has an upper limit obtained by dividing the horsepower of the engine by the virtual discharge pressure command. It is limited as follows.
According to a ninth aspect of the present invention, there is provided a hydraulic circuit in which an actuator is connected to each of a plurality of closed center directional control valves to a variable displacement pump driven by an engine and capable of adjusting a pump discharge amount from the outside. The closed center type directional control valve is a method for controlling the variable displacement pump by electrical computation so that the closed center type directional control valve can replace the center bypass type directional control valve. Based on the individual bleed-off characteristics with respect to the manipulated variable signal (Sk), the opening area (Abk) of each directional control valve is calculated, the total bleed-off area value (Ab) is calculated based on the following formula, and the total bleed A virtual bleed-off flow rate of the closed center type directional control valve is determined based on an off area value (Ab), and a virtual discharge amount of the variable displacement pump Et on the basis of the virtual bleed-off flow rate value obtained by subtracting, and determines a control amount of the variable displacement pump.

As described above, according to the present invention, the electrical system is malfunctioning. For example, even when a control signal is not input to the variable displacement pump, the pump can be moved at a predetermined pressure such as the maximum pressure. It is possible to ensure the discharge flow rate required on the side. Further, if the required flow rate is adjusted by a control valve installed on the load side, engine stall can also be avoided.
Further, in the calculation process for determining the control amount of the variable displacement pump, a value close to 0 is not divided by a value close to 0. Therefore, even if the operation amount increases, the limited pump discharge amount increases with respect to the virtual discharge amount, and even if the difference (that is, the virtual bleed-off flow rate) finally becomes zero, the load Since the discharge pressure corresponding to the pressure can be output, there is no need for additional calculations such as aborting the calculation. In other words, since the hydraulic control system is simulated by calculation in a state close to the actual state, the pump is controlled by seamlessly calculating from the bleed-off control state until the operation amount increases until the bleed-off control state ends. Can do.
Furthermore, operability that matches the required characteristics of the individual actuators can be obtained.

An embodiment of the present invention will be described with reference to FIGS.
FIG. 1 shows a hydraulic circuit applied to a hydraulic excavator or the like for controlling the operation of a plurality of hydraulic actuators 1, which are closed to a discharge circuit 3 of a variable displacement pump 2 driven by a drive motor PM. They are connected via control valves 4 and 4 at the center.
The variable displacement pump 2 is a known one such as an axial piston pump having a pump displacement control mechanism such as a swash plate.

An output of the solenoid drive amplifier 5 as a command input and a discharge side pressure of the pump 2 as a feedback input are connected to the input side of the pump pressure control device 6, and a control piston 7 is connected to the output side of the pump pressure control device 6. Is connected.
The pump pressure control device 6 includes a control valve 6b and a negative electromagnetic proportional valve 6c. The actual pump discharge pressure P _real of the pump 2 and the elastic force of the spring 6d are negative at both ends of the spool of the control valve 6b. type electromagnetic proportional valve 6c pressure signal P ^'c is controlled such by, but on both ends of the spool are suitable Naru area difference is given, the control valve 6b is accordingly, they are controlled by their balance.
Negative solenoid proportional valve 6c the pressure signal P ^'c, and the controller 12, the signal P' of the input side facing the spring and to the proportional solenoid 6a is that in proportion to the control current input based _idea is variable Controlled by balance with generated force.
In this embodiment, as shown in the block diagram of FIG. 2, the virtual pump discharge pressure command P _idea obtained from the bleed-off characteristic calculation is subtracted from the maximum discharge pressure of the pump in order to perform negative control. The inverted signal P ′ _idea is transmitted to the proportional solenoid 6c of the negative electromagnetic proportional valve.
With the above configuration, the virtual pump discharge pressure command P _idea is inverted to the negative type, and then the proportional solenoid 6a of the pump pressure control device 6 is excited via the solenoid drive amplifier 5 and is excited via the negative type electromagnetic proportional valve. The control valve 6b is operated in inverse proportion to the size of the valve (and therefore in proportion to the virtual pump discharge pressure command P _idea ). As a result, the control piston 7 moves the pump displacement control mechanism, and the pump displacement, that is, the pump discharge. Control the amount large or small.
Then, even when the electrical system is malfunctioning, for example, even when a command to the variable displacement pump 2 is not input, the negative pressure can be closed-loop controlled, so that the pump 2 can move at a predetermined pressure such as the maximum pressure. Therefore, it is possible to ensure the discharge flow rate required on the actuators 1 and 1 side. Further, if the required flow rate is adjusted by the control valves 4 and 4 installed on the load side, engine stall of the prime mover PM can be avoided.
In the present specification, the “negative type” means that the output value gradually decreases with respect to the input value.

  In the example described, a proportional relief valve is used as the negative electromagnetic proportional valve 6c. However, the pressure reducing valve 16c shown in FIG. 3A or the flow control valve 16d and the variable throttle valve shown in FIG. The same purpose can be achieved by 16e. The same effect can be achieved by a negative tilt drive system as shown in FIG. In the present invention, the negative type tilt drive system means that the pump can be moved at a predetermined pressure such as the maximum pressure when no signal is obtained, and the output value gradually decreases when the signal is input. .

  The control valve 4 includes a proportional solenoid 8 for moving the spool. When the solenoid driving amplifier 13 is operated by the electric joystick 9 via the controller 12, the proportional solenoid 8 is changed according to the inclination angle of the electric joystick 9. When excited, the spool of the control valve 4 moves to a desired position, and the actuator ports 10 and 10 are controlled to the opening areas Ab1 and Ab2 corresponding to the moving distance.

  A command amount such as an inclination angle of an operation lever for operating each control valve 4 or a movement amount of a spool of each control valve 4 is electrically detected by a sensor, and the command amount or movement amount is determined by operating each control valve 4. The operation amount signal S based on the amount is used, and in the example of FIG. 1, a command electric signal from the electric joystick 9 to the solenoid drive amplifier 13 via the controller 12 is used as the operation amount signal.

Since the control valve 4 is an all-port closed valve that does not actually have a bleed-off passage, the actuator flow rate Q _a is the actual discharge amount Q _real of the variable displacement pump 2 if the slight leak on the circuit is ignored. The flow rate Q _a can be substituted.
In this embodiment, the actuator flow rate Q _a is obtained by providing the variable displacement pump 2 with a discharge amount detection sensor 11 and multiplying the tilt amount detected by the discharge amount detection sensor 11 by the rotation speed of the pump 2. and to calculate the actuator flow rate Q _a.
As the discharge amount detection sensor, for example, when the variable displacement pump 2 is a swash plate type variable displacement pump or a radial pump, a potentiometer or the like can be used.

  These electric signals are calculated by a controller 12 including an A / D converter 12a, a calculator 12b, and a D / A converter 12c. The calculator 12b automatically performs the calculation shown in the block diagram of FIG. Run in a controlled manner.

In the controller 12, the virtual pump discharge pressure command P _idea is expressed by the following formula described in Patent Document 1,
P _idea = {(Q _max -Q _a ) / (Kq × Ab)} ²
Calculated by In the formula, Q _max is the maximum discharge amount of the pump, Kq is a flow coefficient, and Ab is the opening area of the bleed-off passage.

The computing unit (CPU) 12b simulates the inside of the dotted line in FIG. 2, and will be described below with reference to FIG.
First, as shown in FIG. 4 (a), receiving an input of an operation amount S _k of the plurality of control valves 4, their sum S ₁ + S ₂ + ··· take S _n, the operation amount signal of the sum S. At this time, each input may be weighted or an appropriate calculation process may be performed. Next, the opening area Ab of the bleed-off passage of the control valve corresponding to the scheduled bleed-off characteristic is obtained from the manipulated variable signal S, and the bleed-off characteristic value Xb is obtained by multiplying it by Kq (flow rate coefficient). Of course, the actual control valve 4 has a closed center without a bleed-off passage, and the opening area Ab is a value in calculation. The bleed-off characteristic is determined by determining in advance the relationship between the opening area Ab and the operation amount S.

Further, the virtual discharge amount Q _idea of the variable displacement pump 2 is set to a predetermined value.
At this time, since the maximum discharge amount of the variable displacement pump 2 is a known number, this value can also be used.
More preferably, as shown in FIG. 4 (b), it performs horsepower calculation, if to use a value obtained by dividing with the horsepower H _e of the engine in virtual pump discharge pressure command P _idea, the variable displacement pump 2 The engine stall can be avoided even if the absorption horsepower exceeds the engine horsepower.

The actuator flow rate, as described above, for example, from inputted as a flow rate signal from the actual pump discharge quantity Q _real, flow rate value Xa calculated by subtracting the actual pump discharge quantity Q _real virtual pump discharge quantity Q _idea bleed Corresponds to off flow rate. Dividing this Xa by Xb and calculating the square of the value, the virtual pump discharge pressure command P _idea is calculated. Then, based on the virtual pump discharge pressure command P _idea , the discharge pressure is closed-loop controlled. That is, the solenoid drive amplifier 5 receives the control signal based on the virtual pump discharge pressure command P _idea and increases or decreases the excitation of the electromagnetic proportional valve 6a, and subtracts the subtraction between the virtual pump discharge pressure P _idea and the actual pump discharge pressure P _real. The control piston 7 controls the pump discharge amount in accordance with a command from the control valve 6b, using the negative electromagnetic proportional valve 6c and the control valve 6b.

When the electric joystick 9 is not operated, the control valve 4 is in the neutral position, and zero is input to the controller 12 as the operation amount signal S. In this case, since the opening area of the bleed-off passage calculated by the controller 12 is maximized, the virtual pump discharge pressure P _idea becomes a small value. Pump 2 based on the virtual pump discharge pressure P _idea do discharge, but compresses the actual pump discharge pressure P _real discharge circuit of the pump piping system to a virtual pump discharge pressure P _idea, After boosts the actual pump The discharge amount requires only a small amount of leakage in the circuit, and the actuator speed, that is, the actuator flow rate is almost zero, and at this time, Xa = Q _max and the virtual pump discharge pressure P _idea = (Q _max / (Kq × Ab )) ²

When the electric joystick 9 is operated and the control valve 4 is operated in the switching position direction, the opening area of the bleed-off passage calculated by the controller 12 is reduced, and the virtual pump discharge pressure P _idea is once set to the pump discharge amount. The total amount is set to a value when returning to the tank from a narrowed bleed-off passage with a small area. Since the pump discharge pressure is closed-loop controlled, the actual pump discharge pressure P _real is substantially equal to the value of the virtual pump discharge pressure P _idea . If the actual pump discharge pressure P _real is higher than the load pressure, the actuator 1 is accelerated and the oil begins to flow. Therefore, the pump discharge amount is increased to keep the actual pump discharge pressure P _real at the virtual pump discharge pressure P _idea. However, as the actuator speed increases, the bleed-off flow rate decreases, so the virtual pump discharge pressure P _{idea and} consequently the actual pump discharge pressure P _real decreases, the actuator acceleration decreases, and the actuator speed gradually matches the operation amount. It converges and balances the pump discharge amount and discharge pressure to be maintained. During this time, the bleed-off operation is performed only by calculation within the controller, and the actual pump discharge amount Q _real is limited to the amount supplied to the actuator 1 if the leakage on the circuit is ignored. Therefore, there is no waste of energy because the bleed-off flow rate does not flow, and since the bleed-off passage is not required for the control valve, the configuration is simple and inexpensive, and the operability is improved.

Next, another embodiment of the present invention will be described using the block diagram of FIG.
In the present embodiment, with the same hydraulic circuit configuration as in FIG. 1, the calculation in the controller 12 is performed according to the block diagram shown within the range surrounded by the dotted line in FIG.

In the illustrated example, the bleed-off flow rate Q _b is multiplied by the square root of the virtual pump discharge pressure command P _idea by the bleed-off area value Ab obtained from the operation amount S of the actuator, and further multiplied by the flow coefficient Kq. By getting. The flow rate value ΔQ (ΔQ = Q _idea -Q _a -Q _b ) is obtained by subtracting the actuator flow rate Q _a and the bleed-off flow rate Q _b from the virtual pump discharge amount Q _idea , and ΔQ is obtained using a digital filter or the like. The virtual pump discharge pressure command P _idea is calculated by integrating and dividing by the pipe compression coefficient C ′ _p of the virtual pump piping system.
Note that the virtual pump discharge pressure command P _idea is not limited to the above example, and uses a control calculation function modeled on a piping system to be realized as a model, and inputs the flow rate value ΔQ into the function. Any model that can be obtained as an output can be used as a model of a control operation function, for example, a higher-order model that takes into account a control valve, an actuator, and a load system that act as feedback elements in an actual pump piping system, For example, a model in which a compensator is inserted may be applied.

If the variable displacement pump is controlled with the above configuration, the pump can be controlled by seamlessly calculating from the bleed-off control state until the operation amount increases and the bleed-off control state ends.
In the above example, for convenience of explanation, the calculation is made on the assumption that there is no leakage in the piping system. However, even if there is a leakage, it can be used as a matter of course.

Next, another embodiment of the present invention will be described using the block diagram of FIG.
In the present embodiment, the operation of the controller 12 is performed according to the block diagram shown in FIG. 6 with the same hydraulic circuit configuration as in FIG.
In the illustrated example, input of operation amounts S1, S2,..., Sk,..., Sn of the plurality of closed center type directional control valves 4 is received. For these, the opening area Ab of the bleed-off passage of the control valve corresponding to the planned bleed-off characteristic is obtained by the following equation. In the formula, Abk corresponds to Sk.

Except this point, the same operation as that shown in FIG. 5 is performed.
If the variable displacement pump is controlled by the above configuration, operability in accordance with the required characteristics of the individual actuators can be obtained.

FIG. 1 is a hydraulic circuit diagram for explaining a control method for a variable displacement pump according to an embodiment of the present invention. Block diagram for explaining the control of FIG. (A)-(c) is a figure which shows the modification of FIG. The figure which shows the example of a calculation in the controller of FIG. 2 both (a) and (b). Block diagram for explaining another embodiment of the present invention Block diagram for explaining another embodiment of the present invention Block diagram for explaining a control method of a conventional variable displacement pump Block diagram of Fig. 7 organized by function

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Actuator 2 Variable displacement pump 3 Discharge circuit 4 Control valve 7 Control valve 11 Pressure sensor 12 Controller,

Claims (9)

  In a hydraulic circuit that is driven by an engine and has a variable displacement pump that can adjust the pump discharge amount from the outside, and a plurality of closed center directional control valves, each of which is connected to an actuator, the closed center directional control valve is A method of controlling the variable displacement pump by electrical calculation so as to replace a bypass type directional control valve, wherein the discharge pressure of the variable displacement pump is controlled via an electromagnetic proportional valve, and the electromagnetic A control method for a variable displacement pump, characterized in that the actuator can be operated by setting a discharge pressure of the variable displacement pump to a predetermined value in an emergency in which a signal to the proportional valve cannot be obtained.   2. The variable displacement pump control method according to claim 1, wherein the tilt drive system of the variable displacement pump is a negative type in the emergency.   3. The variable displacement pump control method according to claim 2, wherein the electromagnetic proportional valve is a negative type in order to make the tilt drive system of the variable displacement pump a negative type.   In a hydraulic circuit that is driven by an engine and has a variable displacement pump that can adjust the pump discharge amount from the outside, and a plurality of closed center directional control valves, each of which is connected to an actuator, the closed center directional control valve is A method of controlling the variable displacement pump by electrical calculation so as to replace a bypass type directional control valve, wherein an actual pump discharge amount of the variable displacement pump and an operation amount of each directional control valve are Detecting the actual pump discharge amount as the actuator flow rate, calculating the bleed-off flow rate based on the operation amount, and subtracting the actuator flow rate and the bleed-off flow rate from the virtual pump discharge amount of the variable displacement pump And a control command amount for the variable displacement pump is determined based on the flow rate value. Control method for a variable capacity pump to.   5. The variable displacement pump control method according to claim 4, wherein the variable displacement pump is a swash plate type variable displacement pump, and the actual pump discharge amount is detected by a tilt sensor.   6. The control method for a variable displacement pump according to claim 4, wherein the control command amount to the variable displacement pump is a virtual pump discharge pressure command calculated based on a virtual piping system as a reference model. .   8. The variable displacement pump control method according to claim 4, wherein the bleed-off flow rate is obtained by multiplying a square root of the virtual discharge pressure command by a flow coefficient of an orifice.   The control method for a variable displacement pump according to claim 6 or 7, wherein the virtual discharge amount is limited with an upper limit being a value obtained by dividing the horsepower of the engine by the virtual discharge pressure command. In a hydraulic circuit that is driven by an engine and has a variable displacement pump that can adjust the pump discharge amount from the outside, and a plurality of closed center directional control valves, each of which is connected to an actuator, the closed center directional control valve is A method of controlling the variable displacement pump by electrical calculation so as to replace a bypass type directional control valve, wherein individual bleed-off for an operation amount signal (Sk) based on an operation amount of each directional control valve Based on the characteristics, the opening area (Abk) of each directional control valve is calculated, the total bleed-off area value (Ab) is calculated based on the following formula, and the closed bleed-off area value (Ab) is calculated based on the closed bleed-off area value (Ab). Determine the virtual bleed-off flow rate of the center type directional control valve and subtract the virtual bleed-off flow rate from the virtual discharge rate of the variable displacement pump. Based on the value, the control method for a variable displacement pump, characterized in that to determine the control amount of the variable displacement pump.

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