JP2000170708A - Bleed-off control method using variable-displacement pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an engine stall by controlling the pump capacity with a discharge quantity instruction which is calculated with the subtraction value between a pump discharge pressure instruction and a pressure signal used as a parameter and is limited for its upper limit by a calculated value. SOLUTION: The discharge pressure Pp1 of a pump 2 detected by a pressure sensor 11 is inputted to the horse power calculating function of an arithmetic unit 12a, the given horse power signal of an engine 2a is divided by the pressure signal used as a constant to obtain a calculated value Qpp, it is used as the element for calculating a flow value Xa, and it is also used as the limit value of a variable limiter limiting the upper limit of the discharge quantity instruction multiplied by a gain to the deviation between the pump discharge pressure instruction and the fed-back pump actual discharge pressure. The calculated value Qpp is the pump maximum discharge quantity or below and is smaller than the pump discharge quantity Qp1 exceeding the engine horse power, the flow value Xa subtracted with the actuator flow from the horse power calculated result substituting the pump discharge quantity is reduced, and the pump discharge pressure instruction is reduced, thereby an engine stall can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bleed-off control method using a variable displacement pump applied to a machine such as a construction machine utilizing a bleed-off hydraulic system.

[0002]

2. Description of the Related Art Conventionally, in a hydraulic system of a construction machine such as a hydraulic shovel, a plurality of hydraulic actuators are driven by one hydraulic pump. One example is as shown in FIG. 1, in which a plurality of directional control valves c having a bleed-off passage (center bypass port) f are provided in a discharge circuit b of a fixed displacement pump a, and the directional control valves c are switched. , The bleed-off passage f gradually closes, and the discharge pressure of the pump a rises accordingly, and oil is introduced into the actuator d via the actuator ports g, g gradually opening opposite to the bleed-off passage f. And
The operating speed of the actuator d is controlled according to the opening area of the actuator port g. Focusing only on the meter-in circuit of the control valve c of the bleed-off hydraulic system, and further simplifying it by ignoring leakage and the like, a simplified control block diagram is as shown in FIG. In the figure, Kq is a flow coefficient, Cp is a pump pipe system compression coefficient, Co is a cylinder system compression coefficient, S is a Laplace operator, A is a cylinder area, M is a load system mass, eta is a viscous drag coefficient, and a valve. The horizontal axis of the bleed-off characteristics and metering characteristics is the manipulated variable,
The vertical axis indicates the opening area of the port such as a bleed-off port or an actuator port.

From FIG. 2, the bleed-off hydraulic system is:
It can be said that it has an operation block surrounded by a dotted line in FIG. This calculation block calculates a bleed-off flow rate from the operation amount and the pump discharge pressure, and calculates and outputs a difference flow rate obtained by subtracting a flow rate to the actuator (actuator flow rate) from the pump discharge rate. Since the differential flow rate calculated in the bleed-off calculation block compresses the pump pipe volume, which is a fluid in the pump pipe, and increases the pump discharge pressure, the bleed-off calculation eventually calculates and outputs the pump discharge pressure. Will be. In summary, it can be said that the bleed-off hydraulic system has a computing unit that inputs the operation amount, the pump discharge amount, the actuator flow rate, and the pump discharge pressure and outputs the pump discharge pressure.

[0004] The following relationship is established in the pre-matching section of the operation block in FIG. Pump discharge amount = actuator flow rate (Qa) + bleed-off flow rate (Qb) + differential flow rate The bleed-off characteristics are as follows: Ab = F (s), where s is the manipulated variable and Ab is the opening area of the bleed-off passage. And the following equation holds (Pp: pump discharge pressure). Qb = Kq × Ab × √Pp The pump in FIG. 1 is a fixed displacement pump and the discharge amount is Qmax.
The difference flow rate is almost zero, so if this is ignored, the following equation is established statically. Pp = {(Qmax−Qa) / (Kq × Ab)} ² (1) In such a bleed-off hydraulic system, a part of the pump discharge amount is returned to the tank via the bleed-off passage.
Since energy is wasted and the bleed-off passage is formed in the control valve, there are disadvantages such as the control valve becoming complicated, large and expensive, and when the bleed-off passage is opened and closed, fluid force is applied to the valve spool. The operability is also poor because a force that hinders the operability of the device works.

In order to solve these drawbacks and the like, the applicant has previously disclosed a plurality of actuators in a discharge circuit of a variable displacement pump having a pump displacement control device capable of externally adjusting the pump discharge amount by using a closed center type. It is connected via a direction control valve, detects a pressure signal based on the discharge pressure of the discharge circuit and an operation amount signal based on the operation amount of the operation lever of each direction control valve, and detects the control signal calculated by the controller. A method of operating a pump displacement control device to control the discharge amount of the pump to perform bleed-off has been proposed (Japanese Patent Application Laid-Open No. 10-47306). The controller is shown in FIG.
As shown in the figure, the planned bleed-off control amount Xb is calculated from the total value of the operation amount signals, and the bleed-off control amount is calculated from the maximum discharge amount of the variable displacement pump as the virtual pump discharge amount. The pump discharge pressure command is calculated from the flow value Xa obtained by subtracting the flow signal of
The pump displacement control device is operated by a discharge amount command calculated using the calculated value obtained by subtracting the pump discharge pressure command and the pressure signal as a parameter to control the pump displacement of the variable displacement pump. If a pump that cannot detect the flow rate actually flowing through the discharge circuit by a sensor or the like, that is, the actual discharge rate of the pump is used and the actuator flow rate Qa cannot be measured, as shown in FIG. The bleed-off control is performed by using the discharge amount command of the above as an estimated value. In this control method, in order to correspond to the fixed pump in FIG. 1, the pump maximum discharge amount is fixedly used as a virtual pump discharge amount for control calculation.

When the maximum pump discharge is fixedly used as the virtual pump discharge shown in FIG. 3, when the load increases and the load pressure rises from a certain steady state, pressure closed loop control works to reduce the pump discharge pressure. In order to meet the discharge amount command, the actual pump discharge amount decreases. In the steady state, the actual pump discharge amount is equal to the actuator flow rate. Therefore, when the actual pump discharge amount decreases due to an increase in the load, Xa increases. As a result, the pump discharge pressure command increases and the pump corresponding to the increase in the load pressure increases. The discharge pressure rises. That is, an increase in the load pressure causes a decrease in the flow rate of the pump and an increase in the discharge pressure. As described above, in the bleed-off control method, if the bleed-off control amount Xb is not zero, a decrease in the pump flow rate accompanies, and a rapid increase in the pump absorption horsepower tends to be avoided. However, when the operation amount s increases and the operation input increases, Xb decreases and eventually disappears, so that the decrease in the pump discharge amount also decreases and eventually becomes zero. In this state, since the actual discharge amount of the pump is the maximum discharge amount of the pump, an increase in the load is directly linked to an increase in the discharge pressure of the pump. When the variable displacement pump shown in FIG. The absorbed horsepower will exceed the engine horsepower. That is, engine stall occurs unless the operation amount is adjusted according to the magnitude of the load.

The present invention relates to a bleed-off control method using the above-mentioned variable displacement pump so that engine stalling does not occur even when the load changes without impairing the economy and good operability of the bleed-off control method. The purpose is to improve the method.

[0008]

According to the present invention, in order to achieve the above object, a plurality of actuators are provided in a discharge circuit of a variable displacement pump driven by an engine and capable of adjusting a pump discharge amount from outside in a closed center type. Connected via a control valve, detecting a pressure signal based on the discharge pressure of the discharge circuit and an operation amount signal based on the operation amount of each direction control valve,
The controller calculates a predetermined bleed-off area value from the total value of the operation amount signals, and calculates a calculated value (Qli) obtained by dividing the horsepower signal of the engine by the pressure signal.
m), a pump discharge pressure command is calculated from a flow rate value obtained by subtracting the actuator flow rate from the m) and the bleed-off area value, and a pump displacement of the variable displacement pump is calculated by subtracting the pump discharge pressure command and the pressure signal. Is calculated as a parameter, and is controlled by a discharge amount command in which the upper limit is limited by the calculated value (Qlim). The valve bleed-off characteristic is input to the controller, the opening area of the bleed-off passage corresponding to the expected bleed-off characteristic is calculated from the total value of the operation amount signals, and the bleed is calculated by multiplying the opening area by the flow coefficient. The pump discharge pressure command is calculated by calculating the off characteristic value, dividing the flow rate value obtained by subtracting the actuator flow rate from the calculated value (Qlim) by the bleed off characteristic value, and squaring the value. The pump displacement of the pump is closed-loop controlled by a discharge amount command that is calculated using a calculated value obtained by subtracting the pump discharge pressure command and the pressure signal as a parameter and is limited by the calculated value (Qlim). If the actuator flow cannot be directly measured and the actual pump discharge cannot be detected, the pump discharge is estimated from the discharge command and used as the actuator flow.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG.
1 shows a hydraulic circuit applied to a hydraulic shovel or the like for controlling the operation of a hydraulic pump. These actuators 1 are connected to a discharge circuit 3 of a variable displacement pump 2 driven by an engine 2a via a closed center type directional control valve 4, 4. Is done. The variable displacement pump 2 is a known one such as an axial piston pump provided with a pump displacement control mechanism such as a swash plate. When the proportional solenoid 6 is excited by the solenoid drive amplifier 5, the pump control device 7 determines the magnitude of the excitation. The pump displacement control mechanism is operated in proportion to the control of the pump displacement, that is, the pump displacement, that is, the pump discharge amount. The directional control valve 4 includes a proportional solenoid 8 for moving a spool. When the solenoid drive amplifier 13 is operated by the electric joystick 9, the proportional solenoid 8 is excited to an intensity corresponding to the tilt angle of the electric joystick 9. The spool of the directional control valve 4 moves to a desired position, and the actuator port 1
0 and 10 are controlled to an opening area corresponding to the moving distance.

The discharge circuit 3 has a pressure sensor 11 for electrically detecting the discharge pressure of the pump 2 as a pressure signal.
Is provided. A command amount such as a tilt angle of an operation lever for operating each direction control valve 4 or a movement amount of a spool of each direction control valve 4 is electrically detected by a sensor, and the command amount or movement amount is detected by each direction control valve 4. In the illustrated example, a command electric signal from the electric joystick 9 to the solenoid drive amplifier 13 is used as the operation amount signal. The actuator flow rate is
Since the directional control valve 4 is actually an all-port closed valve having no bleed-off passage, if the slight leakage on the circuit is ignored, the discharge amount of the variable displacement pump 2 is substituted as a signal representing the flow rate of the actuator. This discharge amount can be controlled by a pump control device 7 for controlling the discharge amount of the pump 2.
Can be applied to the flow rate signal of the actuator flow rate, thereby eliminating the need for a special device for detecting the actuator flow rate. Become.

These electric signals are supplied to an A / D converter 12a,
Computation is performed by the controller 12 composed of a computing unit 12b and a D / A converter 12c, and the computing unit 12b composed of a microcomputer automatically executes the computation shown in the block diagram of FIG.

As described above, the bleed-off hydraulic system inputs a manipulated variable, a pump discharge volume, an actuator flow rate, and a pump discharge pressure and outputs a differential flow rate. Since the pump pipe volume is used as an arithmetic element in the above, the dynamic characteristic is obtained by the integral element, and there is actually a large error due to leakage. Therefore, it is not appropriate to handle the difference flow rate as it is. In order to simulate the bleed-off hydraulic system in the arithmetic unit, it is more appropriate to output the pump discharge pressure by the arithmetic unit.
In No. 2, the actual pump piping volume and leakage outside the computing unit were compensated, and a closed loop was formed so as to cancel out the computation, and the computation was automatically executed. The above formula (1) is applied to a part for generating a pump discharge pressure command.

The computing unit 12b simulates FIG. 5. First, it receives the input of the operation amounts of the plurality of closed center type directional control valves 4, takes the sum thereof, and sets the sum as an operation amount signal. At this time, each input may be weighted or an appropriate calculation process may be performed. Next, an opening area Ab of the bleed-off passage of the control valve corresponding to a predetermined bleed-off characteristic is obtained from the operation amount signal, and a bleed-off characteristic value Xb is obtained by multiplying this by Kq (flow coefficient). Of course, since the actual directional control valve 4 is a closed center having no bleed-off passage, the opening area Ab is a calculated value. The bleed-off characteristic is arbitrarily determined in advance using the opening area and the operation amount as parameters.

Then, the flow rate value Xa corresponding to the bleed-off flow rate is calculated in the arithmetic unit 12b by the bleed-off characteristic value X.
b, calculate the pump discharge pressure command by squaring the value, and then feed back the pump discharge pressure detected by the pressure sensor 11 of FIG. 4 installed in the actual piping system to close the pump. In order to form a loop control system, a pump discharge pressure command value and a feedback calculation of the discharge pressure are performed, and the calculated deviation is further multiplied by a gain (Gc) having a phase compensation function to obtain a pump 2.
Is output as a discharge amount command for

[0015] The flow value Xa is determined by the method proposed above.
The operation unit 12b subtracts the actuator flow rate substituted by the flow rate signal from the actual pump discharge rate (pump control device) from the pump discharge rate set at an appropriate value equal to or less than the maximum discharge rate of the variable displacement pump 2. As described above, there is a disadvantage that the absorption horsepower of the pump 2 exceeds the horsepower of the engine 2a and stalls unless the manipulated variable is adjusted as described above. Instead of the pump discharge amount set in the calculator 12a, a calculation value obtained by dividing a horsepower signal corresponding to the horsepower of the engine 2a by a pressure signal detected by the pressure sensor 11 is used,
The limit of the pump discharge amount command, specifically, the upper limit of the value obtained by multiplying the discharge amount command by the gain Gc having a phase compensation function is limited by a variable limiter so as not to exceed this calculated value, thereby solving the problem of engine stall. I tried to eliminate it. The engine 2
The horsepower and pump efficiency yp of a are stored in the ROM of the arithmetic unit 12a.

To explain this further, in the method proposed above, the actuator flow rate Qa0 (≒ actual pump discharge rate Qp
0), in the steady state at the pump discharge pressure Pp0,
If the pump discharge amount set to is the maximum pump discharge amount of the pump 2, if the load pressure increases due to an increase in load, the pump discharge pressure becomes Pp1, and the pump discharge amount changes to Qp1, Absorbed horsepower Hp = Pp1 × Qp1 / yp (yp: pump efficiency) In this case, if Hp exceeds engine horsepower, engine stalls unless horsepower control is performed.

On the other hand, according to the method of the present invention, the pump discharge pressure Pp1 detected by the pressure sensor 11 is input to the horsepower calculation function of the calculator 12a, and the pump discharge pressure Pp1 of the engine 2a is given as a constant. The calculated value Qpp is calculated by dividing by the horsepower signal of the engine horsepower He, and this Qpp is calculated as the flow rate value Xa
At the same time as the limit value of the variable limiter that limits the upper limit of the discharge amount command obtained by multiplying the gain Gc by the difference between the pump discharge pressure command and the fed-back pump actual discharge pressure. Is less than the pump maximum discharge rate, and is smaller than Qp1 which exceeds the engine horsepower. First, the flow rate value Xa for subtracting the actuator flow rate from the result of the horsepower calculation for substituting the pump discharge rate decreases. Since the pressure command is reduced, the pump discharge command is also reduced by the pressure closed loop control, so that even if the load pressure increases, it works in a direction to avoid excess horsepower, and engine stall is avoided. When the manipulated variable is large and Xb is small or zero, the square of 1 / Xb becomes an extremely large value. As a result, the calculated pump discharge pressure command is higher than the load pressure, and the pump discharge pressure is equal to the load pressure. , Pressure closed loop control is not established, and the actual pump discharge amount is at a maximum. In such a case, even if the load pressure increases, the pump discharge amount command is suppressed to Qpp by the variable limiter and does not increase further, so that engine stall can be completely avoided.

Upon receiving the discharge amount command, the solenoid drive amplifier 5 controls the excitation of the proportional solenoid 6, and the pump controller 7 controls the pump discharge amount according to the command.

To further explain the method of the present invention, when the electric joystick 9 is not operated, the direction control valve 4 is in the neutral position, and zero is input to the controller 12 as the operation amount signal. Since no oil leaks to the actuator, the actuator flow rate is zero. In this case, the opening area of the bleed-off passage calculated by the controller 12 is maximized, and the bleed-off characteristic value Xb is maximized. Therefore, even when Xa is the maximum pump discharge amount, the pump discharge pressure command is It becomes a small value. The pump 2 performs discharge based on the pump discharge pressure command, but since the pump discharge pressure command is small, the discharge circuit of the pump piping system is compressed to the pump discharge pressure command, and after increasing the pressure, the actual pump discharge amount is increased. Requires only a small leakage of the circuit, the actuator speed or actuator flow is input as almost zero, and the variable displacement pump actually has a minimum discharge rate (ie, actuator flow rate ≒ 0), but a virtual maximum discharge rate. (Ie, Qpp is the maximum ejection amount). At this time, Xa = Qmax and the pump discharge pressure Pp = (Qmax
/ Kq × Ab). Since the denominator is large, Pp has a low value.

When the electric joystick 9 is operated and the direction control valve 4 is operated in the direction of the switching position, the opening area (bleed-off characteristic value) of the bleed-off passage calculated by the controller 12 is reduced, and The discharge pressure command is once set to a value at which the entire pump discharge amount returns to the tank from the narrowed bleed-off passage having a small area. The pump discharge pressure is equal to the value of the pump discharge pressure command because the closed loop control is performed. If the pump discharge pressure command value is higher than the load pressure, the actuator 1
And the oil starts to flow, the pump discharge flow rate increases to maintain the pump discharge pressure command value, and the actuator speed increases, so the bleed-off flow rate decreases, and therefore the pump discharge pressure command value and the pump discharge pressure also increase. As the actuator speed decreases, the acceleration of the actuator decreases, and gradually converges and balances with the pump discharge amount and discharge pressure that maintain the actuator speed corresponding to the operation amount. During this time, the bleed-off operation is performed only by calculation in the controller, and the actual pump discharge amount is limited to the amount supplied to the actuator 1 if the leakage on the circuit is ignored. Accordingly, there is no waste of energy because the bleed-off flow does not flow, and the bleed-off passage is unnecessary in the control valve, so that the configuration is simple and inexpensive, and the operability is improved. When the load increases while the electric joystick 9 is operated to operate the actuator, the excess horsepower is avoided as described above.

In the above description, the actuator flow rate is used as the estimated value of the discharge amount command. However, when the actuator flow rate can be measured directly, the measured value is used and the actuator flow rate or the pump flow rate is indirectly used. When the discharge amount can be measured, the actuator flow rate may be calculated from the measured value and used.

[0022]

4 and 5, when the electric joystick 9 is operated by an operator, the tilt angle or the like is converted into a voltage, and the voltage is converted into a plurality of control signals constituting a multi-section valve. At the same time as being transmitted to the proportional solenoid 6 of one of the control valves 4 via the solenoid drive amplifier 13, the controller 1
2 is input to the A / D converter 12a as an operation amount signal. Each of the control valves 4 is provided with an electric joystick 9, and the controller 12 is provided with a plurality of A / D converter input ports corresponding to the number.

The pressure sensor 11 provided in the discharge circuit 3 between the variable displacement pump 2 and the multi-section valve is
The pump discharge pressure is detected, converted into a voltage pressure signal, and input to the A / D converter 12a of the controller 12. In this embodiment, the discharge amount command is used for the flow rate signal.
The system from the pump to the pump discharge pressure in the block diagrams of FIGS. 5 and 3 shows the flow of control elements and signals until the actual pump discharge pressure is determined.

The controller 12 calculates the horsepower calculation and bleed-off characteristics based on these A / D converted signals to simulate the bleed-off characteristics, D / A converts the result and outputs the result to the solenoid drive amplifier 5. I do. The solenoid drive amplifier 5 is connected to a controller 12 via a pump controller 7.
The variable displacement pump 2 is controlled so as to have a discharge flow rate corresponding to the command from. Then, a closed loop is formed by the controller 12, the solenoid drive amplifier 5, the proportional solenoid 6, the pump control device 7, the variable displacement pump 2, and the pressure sensor 11, and the arithmetic unit 12b in the controller 12
The pump discharge pressure is controlled by processing each input signal and controlling the pump control device 7 in accordance with a discharge amount command calculated and simulated to simulate a target bleed-off characteristic. Arithmetic unit 12a
The result of the horsepower calculation is stored for use as the limit value of the variable limiter, and when the value of the pump discharge amount command exceeds this limit value, this limiter value is output as the pump discharge amount command, and the engine is stopped. Is prevented.

[0025]

As described above, according to the present invention, a plurality of actuators are connected via a closed center type directional control valve to a discharge circuit of a variable displacement pump driven by an engine and capable of adjusting a pump discharge amount from outside. A method of controlling a bleed-off control by detecting a pressure signal based on a discharge pressure of the discharge circuit and an operation amount signal based on an operation amount of each directional control valve, and controlling a capacity of the pump by an output from a controller. A flow rate value obtained by calculating a predetermined bleed-off area value from a total value of the operation amount signals, and subtracting an actuator flow rate from a calculation value obtained by dividing a horsepower signal of the engine by the pressure signal; A pump discharge pressure command is calculated from the bleed-off area value, and the pump displacement of the variable displacement pump is calculated by subtracting the pump discharge pressure command and the pressure signal. The engine is controlled by a discharge amount command that has been calculated as a limiter and the upper limit is limited by the calculated value, so that the engine can be prevented from stalling due to an increase in load during bleed-off control, and bleed without actually flowing oil to the tank. OFF control can be performed, the control valve is small, simple and inexpensive, and there is an effect such that operability is improved because no fluid force is generated during bleed-off control.

[Brief description of the drawings]

FIG. 1 is a diagram of a conventional bleed-off control circuit;

FIG. 2 is a block diagram of bleed-off control in the circuit of FIG. 1;

FIG. 3 is a block diagram of the previously proposed bleed-off control method;

FIG. 4 is a diagram showing an embodiment of the present invention.

FIG. 5 is a control block diagram of the controller of FIG. 4;

[Explanation of symbols]

1 actuator, 2 variable displacement pump, 3 discharge circuit, 4 control valve, 7 pump control device, 11 pressure sensor, 12 controller,

Claims (2)

[Claims] A plurality of actuators are connected via a closed center type directional control valve to a discharge circuit of a variable displacement pump driven by an engine and capable of adjusting a pump discharge amount from the outside. The controller detects a pressure signal based on the pressure signal and an operation amount signal based on the operation amount of each directional control valve.The controller calculates a scheduled bleed-off area value from the total value of the operation amount signals. A pump discharge pressure command is calculated from a flow rate value obtained by subtracting the actuator flow rate from a calculation value obtained by dividing the horsepower signal of the engine, and the bleed-off area value, and the pump displacement of the variable displacement pump is calculated by the pump discharge pressure. A variable obtained by calculating a parameter obtained by subtracting the pressure signal from the command and the pressure signal, and controlling the discharge amount command with an upper limit limited by the calculated value. Bleed-off control method using a pump. 2. A valve bleed-off characteristic is inputted to the controller, an opening area of a bleed-off passage corresponding to a predetermined bleed-off characteristic is calculated from a total value of the operation amount signals, and a flow rate is calculated in the opening area. A bleed-off characteristic value is calculated by multiplying by a coefficient, a flow rate value obtained by subtracting the actuator flow rate from the calculated value is divided by the bleed-off characteristic value, and the value is squared to calculate a pump discharge pressure command. The pump capacity of the variable displacement pump is calculated by using a calculated value obtained by subtracting the pump discharge pressure command and the pressure signal as a parameter, and is controlled in a closed loop by a discharge amount command limited by the calculated value. The bleed-off control method using a variable displacement pump according to claim 1, wherein the flow rate is an actuator flow rate.