JP2012137156A - Hydraulic system of working machine and hydraulic control method of working machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic system of a working machine and a hydraulic control method of the working machine, capable of heating up a control valve in advance to prevent any problem in operation of a spool, by flowing operating oil in the control valve by opening a drain oil path when the control valve is in the neutral position and the temperature of operating oil is predetermined temperature or below.SOLUTION: The hydraulic system includes a discharge circuit 4 of a variable displacement pump 3 whose pump discharge rate Q is adjustable, an actuator 6 connected with the discharge circuit 4 via a control valve 5, and a controller 7 for controlling pump discharge pressure of the variable displacement pump 3, and the controller 7 controls the discharge circuit 4 so that command discharge pressure corresponding to a predetermined bleed-off area value calculated from the operation amount of the control valve 5 is produced therefrom. The hydraulic system includes an oil flowing means 10 for flowing operating oil in the control valve 5 by opening a drain oil path 9 for discharging operating oil in the discharge circuit 4 through the control valve 5 to an operating oil tank 8, when the control valve 5 is in the neutral position and temperature of operating oil is predetermined temperature T or below.

Description

  The present invention relates to a variable displacement pump discharge circuit capable of adjusting a pump discharge amount in a work machine such as a backhoe or a tractor, and a bleed-off area where a pump discharge pressure of discharged hydraulic oil is calculated from an operation amount of a control valve The present invention relates to a working machine hydraulic system and a working machine hydraulic control method for controlling a command discharge pressure according to a value.

Conventionally, a method for controlling a hydraulic system of a working machine having a variable displacement pump is known.
This hydraulic system control method controls a hydraulic system in which a plurality of actuators are connected via a control valve to a discharge circuit of a variable displacement pump whose pump discharge amount can be adjusted from the outside. In this case, only the hydraulic oil necessary for operating the actuator is discharged from the variable displacement pump without flowing (bleeding) into the tank, thereby suppressing energy loss.

The conventional hydraulic system can detect the pressure signal based on the pump discharge pressure of the discharge circuit, the operation amount signal based on the operation amount of each control valve, and the flow signal of the actuator flow rate based on the pump discharge amount of the variable displacement pump, The controller calculates a planned bleed-off area value from the total value of the operation amount signals.
Further, the controller calculates a command discharge pressure from the bleed-off area value and a flow rate value obtained by subtracting the actuator flow rate based on the flow rate signal from the maximum discharge amount of the variable displacement pump, and the pump displacement of the variable displacement pump is set as the command discharge pressure. The hydraulic system is controlled by a discharge amount command calculated using a calculated value obtained by subtracting the discharge pressure signal as a parameter (see Patent Document 1).

Japanese Patent Laid-Open No. 10-047306

The conventional hydraulic system control method uses a control valve of a type (closed center type) that does not have a drain oil passage that communicates the discharge circuit and the hydraulic oil tank so as not to bleed waste hydraulic oil into the tank. Therefore, hydraulic oil does not flow inside the control valve when the control valve is neutral.
If the hydraulic oil does not flow, the temperature of the control valve will not rise. Especially in cold districts, the control valve will remain cold, which hinders the movement of the spool.

  In view of such problems, the present invention controls the discharge circuit of the variable displacement pump so that the pump discharge pressure becomes the command discharge pressure corresponding to the planned bleed-off area value calculated from the operation amount of the control valve. In this case, a drain oil passage is provided for draining the hydraulic oil of the discharge circuit to the hydraulic oil tank through the control valve, and the drain oil passage is opened when the control valve is neutral and the temperature of the hydraulic oil is equal to or lower than a predetermined temperature. An object of the present invention is to provide a hydraulic system for a work machine and a hydraulic control method for the work machine that can heat up the control valve in advance so that the operation of the spool is not hindered by opening and flowing hydraulic oil in the control valve. .

In order to achieve the above object, the hydraulic system for a working machine according to the present invention employs the following technical means.
First, the discharge circuit 4 of the variable displacement pump 3 capable of adjusting the pump discharge amount Q, the actuator 6 connected to the discharge circuit 4 via the control valve 5, and the hydraulic oil discharged from the variable displacement pump 3 A controller 7 for controlling the pump discharge pressure P of
The controller 7 is a hydraulic system for a working machine that controls the discharge circuit 4 so as to obtain a command discharge pressure SP corresponding to a planned bleed-off area value B calculated from the operation amount s of the control valve 5.
A drain oil passage 9 for draining the hydraulic oil of the discharge circuit 4 through the control valve 5 to the hydraulic oil tank 8;
The drain oil passage 9 is provided with oil flow means 10 that opens the drain oil passage 9 and allows the hydraulic oil to flow in the control valve 5 when the control valve 5 is neutral and the temperature of the hydraulic oil is equal to or lower than a predetermined temperature T. It is characterized by.

  Secondly, the oil flow means 10 is provided on the most downstream side of the drain oil passage 9, and a relief valve 11 that opens the drain oil passage 9 when the hydraulic oil in the discharge circuit 4 exceeds a predetermined relief pressure R. And a switching valve 12 that opens and closes the drain oil passage 9, and the controller 7 controls the discharge circuit 4 so that the command discharge pressure SP becomes higher than a predetermined relief pressure R when the control valve 5 is neutral. And the controller 7 controls the switching valve 12 so that the drain oil passage 9 is closed before the oil passage PC from the variable displacement pump 3 to the actuator 6 and the oil passage CT from the actuator 6 to the hydraulic oil tank 8 are opened. It is characterized by that.

Third, the control valve 5 is configured to close the drain oil passage 9 before the oil passage PC from the variable displacement pump 3 to the actuator 6 and the oil passage CT from the actuator 6 to the hydraulic oil tank 8 are opened. And
The oil flow means 10 includes a relief valve 11 that is provided on the most downstream side of the drain oil passage 9 and opens the drain oil passage 9 when the hydraulic oil in the discharge circuit 4 exceeds a predetermined relief pressure R. In addition, the controller 7 controls the discharge circuit 4 so that the command discharge pressure SP is higher than a predetermined relief pressure R when the control valve 5 is neutral.

Fourth, when the temperature of the hydraulic oil exceeds a predetermined temperature T, the oil flow means 10 causes the controller 7 to cause the discharge circuit 4 and the command discharge pressure SP to be lower than the predetermined relief pressure R when the control valve 5 is neutral. It is characterized by controlling as follows.
Fifthly, the oil flow means 10 has a switching valve 12 that opens and closes the drain oil passage 9, and the switching valve 12 is in the neutral state of the control valve 5 by the controller 7, and the temperature of the hydraulic oil is a predetermined temperature. Control is performed so that the drain oil passage 9 is opened when the temperature is equal to or lower than T, and the drain oil passage 9 is closed when the temperature of the hydraulic oil exceeds a predetermined temperature T.

Sixth, the oil flow means 10 has a temperature sensor 14 for detecting the temperature of the hydraulic oil in the hydraulic oil tank 8, and the controller 7 drains the hydraulic oil based on the temperature of the hydraulic oil detected by the temperature sensor 14. The opening of the oil passage 9 is controlled.
Seventh, the variable displacement pump 3 is an engine 2 drive type,
The oil flow means 10 opens the drain oil passage 9 even when the engine 2 is started.

In the hydraulic control method for a work machine according to the present invention, first, the discharge circuit 4 having the variable displacement pump 3 capable of adjusting the pump discharge amount Q and connected to the actuator 6 through the control valve 5. Is a hydraulic control method for a working machine that controls the pump discharge pressure P of the variable displacement pump 3 to be a command discharge pressure SP corresponding to a bleed-off area value B calculated from an operation amount s of the control valve 5. There,
When the control valve 5 is in a neutral position and the temperature of the hydraulic oil is equal to or lower than a predetermined temperature T, a drain oil passage 9 for draining the hydraulic oil from the discharge circuit 4 to the hydraulic oil tank 8 through the control valve 5 is opened. Then, hydraulic oil is caused to flow through the control valve 5.

Second, the variable displacement pump 3 is an engine 2 drive type,
The drain oil passage 9 is also opened when the engine 2 is started.

  According to the first aspect of the present invention, there is provided a hydraulic system for a work machine that controls a discharge circuit so as to obtain a command discharge pressure corresponding to a predetermined bleed-off area value calculated from an operation amount of a control valve by a controller. It has a drain oil passage that drains oil to the hydraulic oil tank through the control valve. When the control valve is neutral and the temperature of the hydraulic oil is lower than the specified temperature, the drain oil passage is opened and operated in the control valve. Equipped with oil flow means to flow oil, it is possible to heat up by flowing working oil inside before operating the control valve, and even in cold districts etc. even if the control valve is low temperature, spool operation Can reduce the effects of

  According to the second aspect of the present invention, the controller includes a relief valve that opens the drain oil passage when the hydraulic oil in the discharge circuit exceeds a predetermined relief pressure, and a switching valve that opens and closes the drain oil passage. By controlling so that the command discharge pressure is higher than the predetermined relief pressure when the control valve is neutral and the oil passage from the variable displacement pump to the actuator and the oil passage from the actuator to the hydraulic oil tank are opened, the drain oil passage is closed. Since it is only necessary to retrofit the relief valve and switching valve to control the command discharge pressure and switching valve when the control valve is neutral, the low-temperature control valve can be installed while simplifying the assembly and simplifying the control system. Heat up and spool operation can be smooth.

  According to the third aspect of the invention, the control valve is configured to close the drain oil passage before the oil passage from the variable displacement pump to the actuator and the oil passage from the actuator to the hydraulic oil tank are opened, and the hydraulic fluid in the discharge circuit In addition to having a relief valve that opens the drain oil passage when the pressure exceeds the predetermined relief pressure, the controller controls the command discharge pressure to be higher than the predetermined relief pressure when the control valve is neutral. By reducing the number of parts as much as possible and reducing the size of the system and controlling the command discharge pressure when the control valve is neutral, the control oil can flow inside and heat up.

According to the invention of claim 4, after the control valve is heated up by controlling the command discharge pressure to be lower than the predetermined relief pressure when the control oil is neutral when the temperature of the hydraulic oil exceeds the predetermined temperature. By simply controlling the command discharge pressure, it is not necessary to bleed hydraulic oil into the tank, and waste can be saved.
According to the fifth aspect of the present invention, the switching valve for opening and closing the drain oil passage is opened when the control oil is neutral by the controller and the temperature of the hydraulic oil is equal to or lower than the predetermined temperature. By controlling so that the drain oil passage is closed when the temperature exceeds a predetermined temperature, it is possible to heat up by flowing the working oil into the control valve even when the control valve is neutral.

According to the invention of claim 6, the hydraulic system automatically controls the degree of warming of the control valve by controlling the opening of the drain oil passage by the controller based on the temperature of the hydraulic oil detected by the temperature sensor in the hydraulic oil tank. It can be recognized, and it heats up when it cools without going through the driver, and can stop useless bleed when it gets warm.
According to the seventh aspect of the present invention, as a problem in the hydraulic system having the engine-driven variable displacement pump, a large current is supplied to the cell motor in a situation where the hydraulic oil does not escape to the tank and the hydraulic oil becomes high pressure when starting the engine. Since the engine was started by flowing the air, a load was applied to the battery that supplies current to the cell motor.However, when the engine was started, the drain oil passage was opened to drain the hydraulic oil into the tank and reduce the load on the cell motor. Since it is not necessary to provide a separate battery or the like for starting the engine, the battery can be reduced in size.

  According to the eighth aspect of the present invention, when control is performed so that the pump discharge pressure of the variable displacement pump becomes the command discharge pressure corresponding to the scheduled bleed-off area value calculated from the operation amount of the control valve, the control valve is neutral. When the temperature of the hydraulic oil is lower than the predetermined temperature, the drain oil passage for draining the hydraulic oil in the discharge circuit through the control valve to the hydraulic oil tank is opened and the hydraulic oil is allowed to flow in the control valve. The control valve, which has become low temperature in a cold region, can be heated up, and there is no hindrance to the spool operation.

  According to the ninth aspect of the present invention, even when the variable displacement pump is an engine drive type, the burden on the cell motor and the battery when starting the engine can be reduced by opening the drain oil passage, and the battery can be downsized.

1 is a hydraulic circuit diagram of a hydraulic system for a working machine according to the present invention. It is a block diagram of a hydraulic system. It is a graph showing the spool stroke in the control valve of a hydraulic system, and the opening area of each oil path.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a hydraulic system 1 according to the present invention. Reference numeral 21 in FIG. 1 denotes a work machine 21 such as a backhoe or a tractor provided with the hydraulic system 1, and the work machine 21 includes an engine 2 in the machine body. , Hydraulic oil tank 8, battery 22 and other auxiliary equipment.
1 is an actuator (hydraulic actuator), and the hydraulic actuator 6 swings and drives a boom, an arm, a bucket, and the like in an excavation work device of a work machine (backhoe) 21.

With reference to FIGS. 1 and 2, a hydraulic system 1 for operating several hydraulic actuators 6 installed in the work machine 21 will be described.
As shown in FIG. 1, the hydraulic system 1 is driven by the engine 2 and is capable of adjusting a pump discharge amount Q, a discharge circuit 4 of the variable displacement pump 3, and a control by the discharge circuit 4. It has a hydraulic actuator 6 connected via a valve 5 and a controller 7 for controlling the pump discharge pressure P of hydraulic oil discharged from the variable displacement pump 3.

Further, the hydraulic system 1 includes a drain oil passage 9 for draining the hydraulic oil of the discharge circuit 4 to the hydraulic oil tank 8, and oil flow means 10 (10A1, 10A2, 10B, 10C) that opens the drain oil passage 9 when the engine 2 is started. ) And a temperature sensor 14 for detecting the temperature of the hydraulic oil.
If the oil flow means 10 opens the drain oil passage 9 when the engine 2 is started, 10A1 (A-1 in FIG. 1), 10A2 (same A-2), 10B (same B), 10C ( Any of the examples shown in C) may be used. First, the oil flow means 10 includes a relief valve 11 provided at the most downstream side of the drain oil passage 9 and a switching valve 12 provided immediately before the relief valve 11. The case of 10A1 (A-1) including

The variable displacement pump 3 is a known pump such as an axial piston pump having the engine 2 as a drive source and a pump displacement control mechanism such as an inclined plate 17. When the engine 2 is stopped, the variable displacement pump 3 is connected to one end of the inclined plate 17. The inclined plate 17 is configured to have a predetermined angle (for example, the maximum angle) by the biasing of the connected pump spring 23.
This is because the variable displacement pump 3 secures a predetermined pump discharge amount Q and supplies the necessary hydraulic fluid to the hydraulic actuator 6 even in an emergency such as when the current from the battery 22 suddenly stops. This is to prevent it from going down.

The other end of the inclined plate 17 of the variable displacement pump 3 is connected to the rod 18a of the pump actuator 18, and the pump discharge amount Q of the variable displacement pump 3 can be adjusted by moving the rod 18a of the pump actuator 18 back and forth. .
The discharge circuit 4 includes a pump pressure control unit 24 that controls the pump discharge pressure P of the variable displacement pump 3.

  The pump pressure control unit 24 controls the pump discharge amount of the variable displacement pump 3 via the pump actuator 18 so that the pump discharge pressure P becomes the command discharge pressure SP. The inputs of the pump pressure control unit 24 are hydraulic oil from the discharge port 3a of the variable displacement pump 3 and the command discharge pressure SP from the controller 7 described above, and supply hydraulic oil to the pump actuator 18 as an output.

The pump pressure control unit 24 includes a pump control valve 25 that controls the flow of hydraulic oil to the pump actuator 18, and an electromagnetic relief valve 26 that establishes a predetermined pressure at one end of the spool 25 a of the pump control valve 25.
The electromagnetic relief valve 26 is a negative type in which the pump relief pressure Pr is lowered when the input current is increased. The electromagnetic relief valve 26 urges the valve body in the oil passage closing direction, and antagonizes the urging direction of the adjustment spring 26a. And a proportional solenoid 26b arranged to do so.

A pump discharge pressure P (self-pressure) is applied to one end of the spool 25a of the above-described pump control valve 25 by hydraulic oil that reaches directly from the discharge port 3a of the variable displacement pump 3, and a pump control valve is connected to the other end of the spool 25a. An urging force by a spring 25 b provided to 25 and a pump relief pressure Pr controlled by an electromagnetic relief valve 26 are applied.
By electrically adjusting the pump relief pressure Pr (by a pressure output signal D1 described later), the controller 7 moves the rod 18a of the pump actuator 18 back and forth with the inflow / outflow of hydraulic oil to / from the pump actuator 18. The inclined plate 17 can be operated, the variable displacement pump 3 can be controlled so that the pump discharge pressure P becomes the command discharge pressure SP, and the pump discharge amount Q can also be controlled.

The pump pressure control unit 24 includes a tilt sensor 27 that electrically detects a tilt angle (a tilt input signal H1 described later) of the tilt plate 17 of the variable displacement pump 3. 3 pump discharge amount Q is converted.
The control valve 5 is a center open type (6-port) directional control valve that switches the exit / retreat direction of the hydraulic actuator 6, and each directional control valve has an oil passage for hydraulic oil supplied from the discharge circuit 4, respectively. This is a parallel type branching to the P port (see FIG. 1).

The control valve 5 includes an urging spring 5a that urges the spool 15 from one end side, and a proportional solenoid 5b that is arranged to antagonize the urging direction of the urging spring 5a.
As shown in FIG. 1, the proportional solenoid 5 b moves the spool 15 inside the control valve 5 when a current flows in proportion to the operation amount s (tilt angle) of the operation means 28 such as an operation lever. The oil passage PC from the variable displacement pump 3 to each oil chamber of the hydraulic actuator 6 is opened by an area corresponding to the amount (stroke) of the spool 15, and the operating speed of the hydraulic actuator 6 depends on the opening area. Be controlled.

The control valve 5 is configured so that the oil passage PC to the hydraulic actuator 6 is opened before the drain oil passage 9 is closed.
The operation means 28 is an operation sensor that electrically detects an operation amount s (operation input signal H2 described later) of the control valve 5, which is a command amount such as an inclination angle of the operation lever or a movement amount of the spool 15 of the control valve 5. 29.

The drain oil passage 9 described above communicates the discharge port 3a of the variable displacement pump 3 and the hydraulic oil tank 8 so that the hydraulic oil from the variable displacement pump 3 is directly drained (drained) into the hydraulic oil tank 8. However, it is provided so as to penetrate the center port (center port) of each control valve 5.
The drain oil passage 9 may pass through any of the control valves 5 such as a port on the side of the center port, even if it is not provided in the center port.

In the most downstream of the drain oil passage 9 (between the control valve 5 on the most downstream side and the hydraulic oil tank 8), the drain oil passage 9 is opened when the hydraulic oil from the discharge circuit 4 exceeds a predetermined relief pressure R. A relief valve 11 is provided, and a switching valve 12 that opens and closes the drain oil passage 9 is provided immediately before the relief valve 11 (between the relief valve 11 and the control valve 5 on the most downstream side).
The predetermined relief pressure R of the relief valve 11 is set higher than a neutral command discharge pressure SP ′ (= (SQ / Kq × B) ² ) described later. In the present embodiment, 40 (Kgf / cm ² ).

The switching valve 12 includes an urging spring 12b that urges the internal spool 12a toward the side where the drain oil passage 9 is closed, and an ON / OFF solenoid 12c that is arranged to antagonize the urging direction of the urging spring 12b. And have. The switching valve 12 opens the drain oil passage 9 only when a current is passed through the solenoid 12c by the controller 7 (open output signal D2 described later).
The temperature sensor 14 uses a semiconductor resistance temperature sensor or a metal temperature measuring resistor such as platinum, and is provided in the hydraulic oil tank 8. The temperature of the hydraulic oil in the tank 8 is electrically detected, and a temperature input signal H6 described later corresponding to the temperature is sent to the controller 7.

The hydraulic system 1 includes a pressure sensor 30 that electrically detects a pump discharge pressure P (a pressure input signal H3 described later) of the discharge port 3a of the variable displacement pump 3.
Further, the work implement 21 has an engine starting means 31 (starting input signal H4) such as an engine key used by the driver when the engine 2 is started.
The controller 7 includes an A / D converter, an arithmetic unit, a D / A converter, etc., and inputs the tilt angle of the tilt plate 17 of the variable capacity pump 3 as a tilt input signal H1 from a potentiometer, a rotary encoder, etc. The operation amount s of the control valve 5 is input from the operation sensor 29 as the operation input signal H2, and the pump discharge pressure P of the variable displacement pump 3 is input from the pressure sensor 30 as the pressure input signal H3.

In addition to the above, the controller 7 according to the present invention inputs the temperature of the hydraulic oil from the temperature sensor 14 as a temperature input signal H6.
Further, the output of the controller 7 is that the pump relief pressure Pr of the pump control valve 25 of the pump pressure control unit 24 is used as the pressure output signal D1, and the opening output signal D2 (or closed) which makes the spool 12a of the switching valve 12 open. A closing output signal D3) for position is also output.

The controller 7 may output a capacity output signal D1 ′ for instructing the pump discharge amount Q to the variable capacity pump 3 instead of the pressure output signal D1.
The controller 7 performs the following three controls C1 to C3.
First, when the drain oil passage 9 is closed, the command discharge pressure SP is calculated according to the operation amount s (stroke of the spool 15) of the control valve 5 and the required pump discharge pressure P is obtained. Is controlled (discharge pressure control C1).

In addition, there are control for opening the drain oil passage 9 (open / close control C2) and control for increasing the pump discharge pressure P to a predetermined value (pressure increase control C3). First, a method of calculating the command discharge pressure SP will be described below.
The command discharge pressure SP is determined based on the following formulas 1 to 4.

In Formula 1, the set discharge amount SQ is first obtained. This set discharge amount SQ is a set value with the maximum pump discharge amount Qmax as an upper limit, and is used for traveling of the work implement 21, boom swinging, and the like. It is calculated as the sum of the actuator flow rate Qa and the bleed-off flow rate Qb required depending on the state and the difference flow rate ΔQ that can be generated.
The bleed-off flow rate Qb in Equation 1 is a relational expression of Equation 2 using a flow coefficient Kq, a bleed-off area value B planned according to the use state, and a command discharge pressure SP according to the use state. I can express.

Here, the bleed-off area value B in Expression 2 is a value calculated by a function that is prepared in advance in the controller 7 and that receives the operation amount s of the control valve 5, and is an output value of this function. The opening area value of a passage (bleed-off passage) communicating with a certain hydraulic oil tank 8 is referred to.
If the differential flow rate ΔQ in Equation 1 is almost 0, and ignored, the command discharge pressure SP can be obtained statically by Equation 3 below.

  In Formula 3, when the drain oil passage 9 is closed, the hydraulic oil is not discharged into the tank 8, so if a slight leak on the circuit is ignored, the pump discharge amount Q (that is, the variable displacement pump 3) The tilt input signal H1) of the tilt plate 17 can be replaced with a signal representing the actuator flow rate Qa in the equations 1 and 3.

The discharge pressure control C1 will be described below. In Equation 4, the numerator in the right side is the flow rate value Xa (= SQ-Q), and the denominator is the bleed-off characteristic value Xb (= Kq × B).
As shown in the block diagram of FIG. 2, the controller 7 calculates the flow rate value Xa from the set discharge amount SQ set by the set discharge amount calculation unit 7 a according to the use state, and the gradient input signal H1 from the variable displacement pump 3. The pump discharge amount Q converted by the pump discharge amount conversion unit 7b is calculated.

Next, the controller 7 calculates the bleed-off characteristic value Xb by multiplying the scheduled bleed-off area value B corresponding to the operation amount s (operation input signal H2) of the control valve 5 by the flow coefficient Kq.
The flow rate value Xa described above is divided by the bleed-off characteristic value Xb, and the value is squared to obtain the command discharge pressure SP (see Equation 4).

Then, closed loop control of the pump discharge pressure P is performed based on the command discharge pressure SP. That is, the command discharge pressure SP and the pump discharge pressure P (pressure input signal H3) subtracts, multiplied by the gain (G _C) having a phase compensation function for the difference between the command discharge pressure SP and the pump discharge pressure P The pressure output signal D1 is output to the pump pressure control unit 24.
The pump pressure control unit 24 adjusts the pump relief pressure Pr of the electromagnetic relief valve 26 in accordance with the pressure output signal D1 and operates the inclined plate 17 via the pump actuator 18, whereby the pump discharge pressure P of the variable displacement pump 3. Is controlled to converge to the command discharge pressure SP.

By performing the closed loop control, it is possible to compensate for and cancel the pump pipe volume and leakage that affect the differential flow rate ΔQ in Equation 1.
When the control valve 5 is neutral, 0 is input to the controller 7 as the operation input signal H2. In this case, the bleed-off area value B calculated by the controller 7 is the maximum, that is, the bleed-off characteristic value Xb that is the denominator in the right side in Equation 4 is relatively larger than the flow rate value Xa that is the numerator. The value of the command discharge pressure SP is reduced.

Actually, the pump discharge amount Q requires only a small amount of leakage of the circuit, and the actuator speed (that is, the actuator flow rate Qa) is almost zero. Therefore, the variable displacement pump 3 has a minimum necessary neutral command. It is only necessary to maintain the pressure corresponding to the discharge pressure SP ′ (= (SQ / Kq × B) ² ), and energy waste is reduced.
In this embodiment, the value of the neutral command discharge pressure SP ′ is 35 (Kgf / cm ² ) in consideration of the pressure loss and leakage due to the spring 25b of the pump control valve 25 and the electromagnetic relief valve 26. The set discharge amount SQ may be set to be a value.

Further, when commanding the neutral command discharge pressure SP ′ to the variable displacement pump 3, since the electromagnetic relief valve 26 is a negative type, a signal having a current value of 0 may be sent as the pressure output signal D 1 from the controller 7.
When the control valve 5 is moved to the operation position, the bleed-off area value B on the controller 7 decreases and the value of the command discharge pressure SP increases once.

However, when the command discharge pressure SP becomes higher than the load pressure applied to the hydraulic actuator 6 and the piston of the hydraulic actuator 6 is pushed and hydraulic oil starts to flow into the oil chamber, the pump discharge amount is maintained to maintain the value of the command discharge pressure SP. Q (actuator flow rate Qa) increases and the operating speed of the hydraulic actuator 6 increases.
The increase in the pump discharge amount Q means that the flow rate value Xa (= SQ−Q), which is the numerator in the right side of Equation 4, is relatively smaller than the bleed-off characteristic value Xb, which is the denominator. Conversely, the value of the discharge pressure SP decreases.

In this way, the command discharge pressure SP rises and falls and gradually converges to the pump discharge pressure P and the pump discharge amount Q that maintain the actuator speed corresponding to the operation amount s, and is calculated from the operation amount s of the control valve 5. The discharge circuit 4 can be controlled so as to obtain the required command discharge pressure SP according to the bleed-off area value B.
Therefore, the actual pump discharge amount Q is limited to the amount supplied to the hydraulic actuator 6 if leakage on the circuit is ignored, and waste of energy is reduced.

Along with the discharge pressure control C1, the hydraulic system 1 of the present invention performs the open / close control C2 of the drain oil passage 9 and the boost control C3 of the pump discharge pressure P.
As shown in the block diagram of FIG. 2, the opening / closing control C2 and the pressure increase control C3 are both performed when the working oil (and the control valve 5) is cold when the work machine 21 is used in a cold district or the like. Is called.

  These controls C2 and C3 are the operation sensors when the control valve 5 is neutral (that is, before the spool 15 is slid) and the temperature of the hydraulic oil is equal to or lower than a predetermined temperature T (for example, 0 ° C. to 20 ° C.). The operation input signal H2 indicating that the operation amount s of the control valve 5 sent from 28 is 0 and the temperature input signal H6 sent from the temperature sensor 14 are simultaneously input to the controller 7 (heat-up mode). .

Further, among the signals for starting the controls C2 and C3, the temperature input signal H6 may be separately input to the controller 7 by a driver's button operation (heat-up start means) or the like.
In the controller 7, input signals H2 and H6 are input to both the open / close command unit 7c and the boost command unit 7d. Among these, the opening / closing command unit 7c sends an opening output signal D2 (current that excites the ON / OFF solenoid 12c) to the switching valve 12 in the oil flow means 10A1, and sets the spool 12a of the switching valve 12 to the open position to drain. Open the oil passage 9.

In parallel with this, the pressure increase command unit 7d increases the command discharge pressure SP so that the pump discharge pressure P becomes higher than the relief pressure R (40 (Kgf / cm ² )) of the relief valve 11.
More specifically, the relief pressure R is obtained from the value (neutral command discharge pressure SP ′ = 35 (Kgf / cm ² )) obtained from the flow rate value Xa and the bleed-off characteristic value Xb when the control valve 5 is neutral based on Equation 4. The boost value α (for example, 15 (Kgf / cm ² )) is added so as to be higher.

The added value (neutral command discharge pressure SP ′ + pressure increase α = 50 (Kgf / cm ² )) is newly set as the command discharge pressure SP, and the difference between the command discharge pressure SP and the pump discharge pressure P is determined. A pressure output signal D1 multiplied by a gain (G _C ) having a phase compensation function is output to the pump pressure control unit 24.
Upon receiving the pressure output signal D1, the pump pressure control unit 24 has a variable capacity so as to increase the pump discharge pressure P to 50 (Kgf / cm ² ) of the command discharge pressure SP via the electromagnetic relief valve 26 and the pump actuator 18. Although the pump discharge amount Q of the pump 3 is increased, since the hydraulic oil leaks from the drain oil passage 9 to the tank 8, the pump discharge pressure P cannot be converged to 50 (Kgf / cm ² ).

As a result, even when neutral, the hydraulic oil continues to flow (flows) through the drain oil passage 9 in the control valve 5, and the control valve 5 is operated by the frictional heat due to the flow of the hydraulic oil. Prior to the heat-up, the influence on the operation of the spool 15 can be reduced.
Note that the warming of the control valve 5 can be determined if the temperature of the hydraulic oil is detected. Therefore, the temperature input signal H6 from the temperature sensor 14 may be monitored.

That is, when the temperature of the hydraulic oil exceeds the predetermined temperature T, the controller 7 ends the control C2 and C3 (releases the heat-up mode) and returns only to the discharge pressure control C1.
At the time of releasing the heat-up, the controller 7 stops adding the boost value α to the neutral command discharge pressure SP ′ at the boost command unit 7d, and the command discharge pressure SP when the control valve 5 is neutral is the original 35 (Kgf / cm ² ). It becomes.

If the actual pump discharge pressure P approaches 35 (Kgf / cm ² ) by closed loop control and falls below the relief pressure R40 (Kgf / cm ² ) of the relief valve 11, the flow of the hydraulic oil stops, and the hydraulic oil is wasted. Oil is not discharged into the tank 8.
When the control valve 5 is operated after heating up, the drain oil passage 9 is switched by the switching valve 12 before the oil passage PC from the variable displacement pump 3 to the actuator 6 and the oil passage CT from the actuator 6 to the hydraulic oil tank 8 are opened. Is closed, the command discharge pressure SP can be controlled similarly to the above-described discharge pressure control C1.

When closing the drain oil passage 9, it is only necessary to interrupt the output of the opening output signal D2 sent from the opening / closing command portion 7c to the solenoid 12c of the switching valve 12, and after the interruption, the biasing spring 12b is attached. Due to the force, the spool 12a of the switching valve 12 moves to the closed position, and the drain oil passage 9 is closed.
Further, the oil flow means 10A2 indicated by (A-2) in FIG. 1 is a modification of 10A1, and includes a relief valve 11 provided on the most downstream side of the drain oil passage 9 and immediately before the relief valve 11. And a switching valve 12 provided.

In the oil release means modification 10A2, the switching valve 12 in the oil flow means 10A2 is configured so that the spool 12a is opened by the biasing spring 12b when there is no opening output signal D2 from the controller 7. When the drain oil passage 9 is closed, a closing output signal D3 is output from the opening / closing command section 7c to the solenoid 12c of the switching valve 12.
A modified example 10B of the oil flow means shown in FIG. 1B includes a relief valve 11 provided on the most downstream side of the drain oil passage 9 and a control valve, as in the other examples 10A1 and 10A2. 5 is configured so that the drain oil passage 9 is closed before the oil passage PC from the variable displacement pump 3 to the actuator 6 and the oil passage CT from the actuator 6 to the hydraulic oil tank 8 are opened. (See FIG. 4).

Therefore, the controller 7 does not need to control to close the drain oil passage 9 before the oil passage PC from the variable displacement pump 3 to the actuator 6 and the oil passage CT from the actuator 6 to the hydraulic oil tank 8 are opened. Can be simplified.
1C includes an electromagnetic proportional valve 13 that can adjust the opening degree of the drain oil passage 9 by the controller 7 at the most downstream side of the drain oil passage 9. Yes.

The electromagnetic proportional valve 13 opens the drain oil passage 9 by the opening output signal D2 from the opening / closing command part 7c when the control valve 5 is in the neutral state and the hydraulic oil is below the predetermined temperature T.
Similarly to the above-described modified examples 10A1, 10A2, and 10B, before the oil passage PC from the variable displacement pump 3 to the actuator 6 and the oil passage CT from the actuator 6 to the hydraulic oil tank 8 are opened (operation input signal H2 ) Or when the hydraulic oil exceeds a predetermined temperature T (temperature input signal H6), the drain oil passage 9 is closed by the closing output signal D3 from the opening / closing command section 7c.

Note that when the drain oil passage 9 is closed, the electromagnetic proportional valve 13 is gradually closed to prevent a surge pressure from being generated in the hydraulic system 1.
Further, instead of the electromagnetic proportional valve 13, a proportional valve based on pilot pressure or the switching valve 12 described above may be used. In the case of the switching valve 12, the timing of receiving the opening output signal D2 and the closing output signal D3 is the same as that of the electromagnetic proportional valve 13 described above.

The oil flowing means 10 described so far may open the drain oil passage 9 not only when the control valve 5 is heated up but also when the engine is started.
This is because when the engine is started in the conventional hydraulic system, the hydraulic oil does not escape to the tank and the hydraulic oil becomes high pressure, and a load is applied to the cell motor and the battery 22 for starting the engine. The load can be handled by the opening / closing control C2.

When the engine is started by the driver, the engine start means 31 is operated and a start input signal H4 is input to the controller 7. At this time, the controller 7 sends an opening output signal D2 to the oil flow means 10 to open the drain oil passage 9, and the hydraulic oil escapes from the drain oil passage 9 before the hydraulic oil in the hydraulic system 1 is boosted. The engine 2 can be started with force.
Therefore, since the load applied to the cell motor can be reduced, there is no need to increase the voltage capacity of the battery 22 or to provide another battery for starting the engine, and the battery 22 can be reduced in size.

If the drain valve 9 is provided with a relief valve 11 as in the modified examples 10A1, 10A2, and 10B in FIG. 1, the control valve 5 is neutral even if the switching valve 12 is in the open position after the engine is started. Since the neutral command discharge pressure SP ′ at the time is lower than the relief pressure R of the relief valve 11, the hydraulic oil is not wastefully discharged into the tank 8.
In addition, this invention is not limited to embodiment mentioned above. Each structure of the hydraulic system 1 etc. of a working machine, or the whole structure, a shape, a dimension, etc. can be suitably changed in accordance with the meaning of the present invention.

The hydraulic system 1 has the variable displacement pump 3 that uses the engine 2 mounted on the work machine 21 as a drive source, but may have the variable displacement pump 3 that uses the battery 22 as a drive source. Furthermore, the work machine 21 may be an electric work machine such as an electric backhoe or an electric tractor using the battery 22 as a whole drive source.
The variable displacement pump 3 is a hydraulic type in which the displacement is adjusted by adjusting the inclined plate 18 with a pump actuator 18 that moves back and forth by hydraulic pressure, but the driving force is transmitted from the engine 2 or the like by a mechanical transmission mechanism such as a gear. A mechanical type that adjusts the inclined plate 18 or an electric type that changes the capacity by an electric mechanism such as a linear drive actuator may be used.

Although the control valve 5 is a parallel type, it may be a tandem type in which the P port of the downstream control valve 5 branches sequentially from the center port output of the upstream control valve 5.
At this time, if the switching valve 12 described above is not between the control valves 5 in the drain oil passage 9, it is provided immediately after the discharge port 4a of the discharge circuit 4 or at the most downstream side of the drain oil passage 9 immediately after the relief valve 11. Also good.

The neutral command discharge pressure SP ′ was 35 (Kgf / cm ² ) and the predetermined relief pressure R of the relief valve 11 was 40 (Kgf / cm ² ), but the neutral command discharge pressure SP′30 (Kgf / cm ² ). On the other hand, the relief pressure R may be set higher than the neutral command discharge pressure SP ′, for example, the relief pressure R is set to 35 (Kgf / cm ² ).

DESCRIPTION OF SYMBOLS 1 Hydraulic system of work machine 2 Engine 3 Variable capacity pump 4 Discharge circuit 5 Control valve 6 Actuator 7 Controller 8 Work oil tank 9 Drain oil path 10 Oil flow means 11 Relief valve 12 Switching valve 13 Electromagnetic proportional valve 14 Temperature sensor Q Variable capacity Pump discharge amount of the pump P Pump discharge pressure of the variable displacement pump s Operation amount of the control valve B Expected bleed-off area value SP Command discharge pressure PC Oil path from the variable displacement pump to the actuator CT Oil path from the actuator to the hydraulic oil tank T Predetermined temperature R Predetermined relief pressure

Claims (9)

A discharge circuit (4) of a variable displacement pump (3) capable of adjusting a pump discharge amount (Q), an actuator (6) connected to the discharge circuit (4) via a control valve (5), and the variable A controller (7) for controlling the pump discharge pressure (P) of hydraulic oil discharged from the capacity pump (3),
The controller (7) controls the discharge circuit (4) to have a command discharge pressure (SP) corresponding to a planned bleed-off area value (B) calculated from the operation amount (s) of the control valve (5). A hydraulic system of a working machine
A drain oil passage (9) for draining the hydraulic oil of the discharge circuit (4) through the control valve (5) to the hydraulic oil tank (8);
When the control valve (5) is neutral and the temperature of the hydraulic oil is equal to or lower than a predetermined temperature (T), the drain oil path (9) is opened to the drain oil path (9) in the control valve (5). A hydraulic system for a working machine, comprising oil flow means (10) for flowing hydraulic oil.   The oil flow means (10) is provided on the most downstream side of the drain oil passage (9), and when the hydraulic oil in the discharge circuit (4) exceeds a predetermined relief pressure (R), the drain oil passage (9 ) And a switching valve (12) for opening and closing the drain oil passage (9), and the controller (7) controls the discharge circuit (4) with the control valve (5). The command discharge pressure (SP) is controlled to be higher than a predetermined relief pressure (R) when neutral, and the switching valve (12) is changed from the variable displacement pump (3) to the actuator (6) by the controller (7). The drain oil passage (9) is controlled to close before the oil passage (PC) and the oil passage (CT) from the actuator (6) to the hydraulic oil tank (8) are opened. The hydraulic system of the working machine according to 1. The control valve (5) is configured to open the oil passage (PC) from the variable displacement pump (3) to the actuator (6) and the oil passage (CT) from the actuator (6) to the hydraulic oil tank (8). Configured to close the drain oil passage (9);
The oil flow means (10) is provided on the most downstream side of the drain oil passage (9), and when the hydraulic oil in the discharge circuit (4) exceeds a predetermined relief pressure (R), the drain oil passage (9 ) To open the discharge circuit (4) by the controller (7) and when the control valve (5) is neutral, the command discharge pressure (SP) is higher than the predetermined relief pressure (R). 2. The hydraulic system for a working machine according to claim 1, wherein the hydraulic system is controlled to be higher.   When the temperature of the hydraulic oil exceeds a predetermined temperature (T), the oil flow means (10) is configured so that the controller (7) sets the discharge circuit (4) to the command discharge pressure (SP) when the control valve (5) is neutral. The hydraulic system for a working machine according to claim 2 or 3, wherein the hydraulic system is controlled to be lower than a predetermined relief pressure (R).   The oil flow means (10) has a switching valve (12) for opening and closing the drain oil passage (9), and the switching valve (12) is neutralized by the controller (7) at the control valve (5). The drain oil passage (9) is opened when the hydraulic oil temperature is lower than the predetermined temperature (T), and the drain oil passage (9) is closed when the hydraulic oil temperature exceeds the predetermined temperature (T). The hydraulic system for a working machine according to claim 1, wherein the hydraulic system is a working machine.   The oil flow means (10) has a temperature sensor (14) for detecting the temperature of the hydraulic oil in the hydraulic oil tank (8), and based on the temperature of the hydraulic oil detected by the temperature sensor (14). The hydraulic system for a working machine according to any one of claims 1 to 5, wherein the opening of the drain oil passage (9) is controlled by the controller (7). The variable displacement pump (3) is engine (2) driven,
The hydraulic system for a working machine according to any one of claims 1 to 6, wherein the oil flow means (10) opens the drain oil passage (9) even when the engine (2) is started. A discharge circuit (4) having a variable displacement pump (3) capable of adjusting a pump discharge amount (Q) and connected to an actuator (6) via a control valve (5) is connected to the variable displacement pump (3 ) Pump discharge pressure (P) is controlled so as to be a command discharge pressure (SP) corresponding to a predetermined bleed-off area value (B) calculated from an operation amount (s) of the control valve (5). A hydraulic control method,
When the control valve (5) is neutral and the temperature of the hydraulic oil is equal to or lower than a predetermined temperature (T), the hydraulic oil in the discharge circuit (4) is passed through the control valve (5) to the hydraulic oil tank (8). A hydraulic control method for a working machine, wherein a drain oil passage (9) for draining oil is opened and hydraulic oil is allowed to flow into a control valve (5). The variable displacement pump (3) is engine (2) driven,
The hydraulic control method for a working machine according to claim 8, wherein the drain oil passage (9) is opened even when the engine (2) is started.

Images