JP5430548B2 - Working machine hydraulic system - Google Patents

Description

  The present invention relates to a hydraulic system for a working machine.

As a work implement, a swivel base is provided on the traveling device so as to be pivotable about the vertical axis, and a boom is swingable up and down at the front of the swivel base, and an arm is swingable up and down on the tip side of the boom ( There is an excavation work machine such as a hydraulic excavator that is pivotally attached to a dump and oyster, and a bucket is swingably provided on the tip side of the arm.
In this excavator, the boom, arm, and bucket are oscillated by a boom cylinder, an arm cylinder, and a bucket cylinder including hydraulic cylinders. These hydraulic cylinders are driven by pressure oil from a hydraulic pump, and the hydraulic pump is driven by an engine.

In the excavation work machine, when lowering the boom or arm (boom lowering operation, arm knucking operation), the boom and arm are lowered by their own weight, the bucket and its own weight are dropped by the bucket, etc. Therefore, there is a case where the amount of pressure oil supplied from the hydraulic pump to the boom cylinder or arm cylinder cannot catch up with the lowering operation of the boom or arm.
If the supply amount of pressure oil from the hydraulic pump to the boom cylinder and arm cylinder cannot catch up, there will be a shortage of pressure oil supply to the boom cylinder and arm cylinder, and the pressure oil supply side of the boom cylinder and arm cylinder will become negative pressure. A phenomenon called “breathing” occurs where the boom or arm stops instantaneously. When this “breathing” phenomenon occurs, there is a problem that operability is poor.

  Therefore, in order to prevent this “breathing” phenomenon, the conventional excavating work machine generally prevents breathing in the circuit on the return side of the boom cylinder and pressure oil from the arm cylinder when the boom and arm are lowered. By restricting the amount of pressure oil discharged from the boom cylinder and arm cylinder by inserting a restriction for the purpose, the “breathing” phenomenon is prevented from occurring (see Patent Document 1).

JP-A-5-44234

When the engine is running at low speed, such as when idling, the discharge flow rate of the hydraulic pump is small. Even when the engine is running at low speed, the opening of the throttle for preventing breathing is reduced so that the “breathing” phenomenon does not occur. It is set.
On the other hand, when the engine is rotating at high speed, such as near the maximum speed, the discharge flow rate of the hydraulic pump is larger than when the engine is rotating at low speed. Due to the restriction, there is a problem that wasteful pressure loss occurs and energy loss occurs.

  Accordingly, in view of the above problems, the present invention provides a hydraulic system for a working machine that can prevent the “breathing” phenomenon and that can efficiently operate a driven member that is driven by a hydraulic actuator. Let it be an issue.

The technical means taken by the present invention to solve the technical problems are characterized by the following points.
In the invention according to claim 1, a pump constituted by a variable displacement hydraulic pump driven by a drive source, a hydraulic actuator driven by pressure oil from the pump, and driven to swing up and down by the hydraulic actuator. A driven member, operating means for operating the driven member, a spool type control valve for controlling the hydraulic actuator, and a controller for controlling the spool of the control valve and the pump,
When the operation means is operated, an operation signal corresponding to the operation amount of the operation means is input to the controller, and the operation amount of the operation means is determined by a command signal output from the controller to the control valve based on the operation signal. The spool of the control valve is controlled in proportion to
In the controller, in order to send the discharge oil to the hydraulic actuator without returning a part of the discharge oil of the pump to the tank, a set discharge amount SQ which is an assumed discharge amount of the pump, an actual discharge amount Q of the pump, From the bleed-off area value B scheduled to be calculated from the operation signal of the operation means and the flow coefficient Kq, the target discharge pressure SP of the pump is obtained by the following formula,
SP = {(SQ−Q) / (Kq × B)} ²
In a hydraulic system for a working machine in which the discharge amount Q of the pump is controlled by a command signal calculated based on a deviation between the target discharge pressure SP and the actual discharge pressure of the pump,
When the operating means is operated so as to lower the driven member, a sign of insufficient pressure oil supply to the hydraulic actuator is detected, and when a sign of insufficient pressure oil supply is detected The control signal for returning the spool of the control valve is output from the controller to the control valve.

In the invention according to claim 2, when the operating means is operated so as to lower the driven member, the value of the target discharge pressure SP decreases and the value of the target discharge pressure SP falls below a predetermined value. In this case, a sign of insufficient pressure oil supply to the hydraulic actuator is detected, and in this case, the spool is controlled to return.
In the invention according to claim 3, when the operating means is operated so as to lower the driven member, the value of (SQ-Q) in the calculation formula decreases and the value of (SQ-Q) becomes zero. A sign that the pressure oil supply amount is insufficient is detected when the pressure falls below a nearby predetermined value, and in this case, control is performed to return the spool.

The present invention has the following effects.
According to the first aspect of the present invention, by detecting a sign that the hydraulic oil supply amount is insufficient with respect to the hydraulic actuator and returning the spool of the control valve before the pressure oil supply amount is insufficient, the “breathing” is performed. The phenomenon can be prevented and the driven member can be efficiently operated.
More specifically, in the hydraulic system of the present invention, when the operation means is operated, an operation signal corresponding to the operation amount of the operation means is input to the controller, and the control valve is controlled from the controller based on the operation signal. The spool of the control valve moves in proportion to the amount of operation of the operating means by the command signal output to.

  Then, when the descent of the driven member is detected, a command signal for returning the spool of the control valve is detected when a sign is detected that a hydraulic oil supply amount is insufficient for the hydraulic actuator that drives the driven member. Is output to the control valve and the spool is returned, and the opening area of the port of the control valve for supplying and discharging pressure oil to and from the hydraulic actuator is reduced.

At this time, in the hydraulic system of the present invention, the operation amount of the operation means does not change, the expected bleed-off area value is calculated from the operation signal of the operation means, and the set discharge amount SQ of the pump does not change. Therefore, the supply of the pressure oil to the hydraulic actuator is discharged from the pump at a flow rate corresponding to the operation amount of the operation means.
In other words, by returning the spool when an indication of insufficient supply of pressure oil to the hydraulic actuator is detected, the supply flow rate of pressure oil to the hydraulic actuator is substantially preserved and the discharge amount of pressure oil from the hydraulic actuator is reduced. Therefore, insufficient supply of pressure oil to the hydraulic actuator does not occur, and the “breathing” phenomenon can be prevented.

  In addition, since the “breathing” phenomenon can be prevented by controlling the spool by the controller, there is no need to provide a throttling for preventing breathing in the circuit on the return side of the pressure oil from the hydraulic actuator when the driven member is lowered. Or, even when a throttle is provided in the circuit on the return side of the hydraulic oil from the hydraulic actuator during the descending operation of the driven member, the opening area of the throttle can be increased. The member can be efficiently operated.

  According to the invention according to claim 2, since the sign that the pressure oil supply amount is insufficient due to the value of the target discharge pressure SP being lower than the predetermined value is detected, and according to the invention according to claim 3, Since a sign that the pressure oil supply amount is insufficient due to the value of (SQ-Q) falling below a predetermined value near zero is detected, it is necessary to provide a separate sensor to detect the sign that the pressure oil supply amount is insufficient It can be easily configured.

It is a side view of a working machine. It is a schematic block diagram of a hydraulic system. It is a block diagram of the principal part of a hydraulic system. It is a schematic block diagram of a pump pressure control part. It is a block diagram of a hydraulic system. It is a circuit diagram which shows a modification. It is a graph showing the spool stroke in the control valve of a hydraulic system, and the opening area of each oil path.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes a backhoe (work machine). The backhoe 1 includes a lower traveling body 2, and an upper revolving body 3 mounted on the traveling body 2 so as to be pivotable about a vertical pivot axis. And is composed mainly of.
The traveling body 2 includes a crawler-type traveling device 5 configured to circulate and rotate an endless belt-like crawler belt 4 in a circumferential direction by a traveling motor M1 including a hydraulic motor (traveling drive hydraulic actuator). Provided on both sides.

A dozer device 7 is provided at the front portion of the track frame 6 and is driven to swing up and down by expansion and contraction of a dozer cylinder C1 composed of a hydraulic cylinder (hydraulic actuator).
The swivel body 3 is mounted on the swivel base 8, a swivel base 8 that is mounted on the track frame 6 so as to be rotatable about a swivel axis, an excavation device 9 that is mounted on the front of the swivel base 8, and the swivel base 8. The cabin 10 is provided.

The swivel base 8 is provided with an engine E, a hydraulic oil tank T (hereinafter simply referred to as a tank T), a battery Ba, a pump P, a radiator, a fuel tank, and the like. The swivel base 8 includes a hydraulic motor (hydraulic actuator). ) Is driven to turn by a turning motor M2.
Further, a support bracket 11 is provided at the front portion of the swivel base 8 so as to protrude forward from the swivel base 8, and the swing bracket 12 is swingable to the left and right around the vertical axis. It is supported. The swing bracket 12 is driven to swing left and right by a swing cylinder C2 including a hydraulic cylinder (hydraulic actuator).

  The excavator 9 includes a boom 13 (driven member) whose base side is pivotally connected to the upper part of the swing bracket 12 so as to be rotatable about a left and right axis, and can be swung up and down. An arm 14 (driven member) that is pivotally connected to be pivotable about an axis and can be swung up and down, and is pivotally connected to a distal end side of the arm 14 so as to be rotatable about a left and right axis to be rocked back and forth. It is mainly composed of a bucket 15 that is movable.

The boom 13 is driven to swing up and down by a boom cylinder C3 interposed between the boom 13 and the swing bracket 12, and the arm 14 is moved up and down by an arm cylinder C4 interposed between the arm 14 and the boom 13. The bucket 15 is driven to swing, and the bucket 15 is driven to swing by a bucket cylinder C <b> 5 interposed between the bucket 15 and the arm 14.
The boom cylinder C3, arm cylinder C4 and bucket cylinder C5 are constituted by hydraulic cylinders (hydraulic actuators).

Further, in the backhoe 1, for example, a hydraulic attachment such as a hydraulic breaker can be attached to the distal end side of the arm 14 instead of the bucket 15.
Next, the hydraulic system 16 for operating the various hydraulic actuators M1, M2, C1-5 installed in the backhoe 1 will be described with reference to FIGS.

  As shown in FIG. 2, the hydraulic system 16 includes the pump P, a pump pressure control unit 17 that controls the discharge pressure Pp (pump discharge amount Q) of the pump P, and the various hydraulic actuators M1, M2, and C1. To control valves V1 to 8 for controlling .about.5, operating means 18 for operating each of the control valves V1 to 8, controller 19 for electronically controlling the pump pressure controller 17 (pump P), each of the control valves V1 to 8 and the like Have

The pump P is composed of a variable displacement hydraulic pump (swash plate variable displacement axial pump) having a pump displacement control mechanism such as a swash plate, and is rotated by an engine E (a drive source such as).
As shown in FIG. 4, one end of the swash plate 20 of the pump P is connected to a piston rod 22 a of a pressing piston 22 incorporating a pump spring 21, and the other end of the swash plate 20 is connected to a piston rod of a pump actuator 23. 23a is connected, and is configured to press the swash plate 20 of the pump P by the self-pressure and the pump spring 21 in the direction of increasing the pump flow rate via the pressing piston 22, and to the pressing force of the pressing piston 22 The opposing force is applied to the swash plate 20 by the pump actuator 23, and the discharge amount Q of the pump P can be adjusted by moving the piston rod 23a of the pump actuator 23 back and forth.

When the engine E is stopped, the swash plate 20 has a maximum angle due to the urging force of the pump spring 21 of the pressing piston 22.
The pump pressure control unit 17 controls the discharge amount Q of the pump P via the pump actuator 23 so that the discharge pressure Pp of the pump P becomes the target discharge pressure SP. The input of the pump pressure control unit 17 is hydraulic oil from the discharge path 24 of the pump P and a pressure output signal D1 (command signal) output from the controller 19 based on the target discharge pressure SP described above. The hydraulic oil is supplied to the pump actuator 23.

The pump pressure control unit 17 includes a pump control valve 25 that controls the flow of hydraulic oil to the pump actuator 23, and an electromagnetic relief valve 26 that establishes a predetermined pressure at one end of the spool of the pump control valve 25. Yes.
The electromagnetic relief valve 26 is a negative type in which the pump relief pressure Pr decreases when the input current to the proportional solenoid 28 output from the controller 19 increases, and the adjustment spring 27 urges the valve body in the oil passage closing direction. The circuit pressure on the upstream side of the electromagnetic relief valve 26 that opposes the biasing direction of the adjusting spring 27 is controlled by a balance between the force generated by the proportional solenoid 28 by the pressure output signal D1 output from the controller 19.

A pump discharge pressure Pp (self-pressure) is applied to one end of the spool of the pump control valve 25 by hydraulic oil that reaches directly from the discharge passage 24 of the pump P, and the other end of the spool is provided in the pump control valve 25. The urging force by the spring 29 and the pump relief pressure Pr controlled by the electromagnetic relief valve 26 are applied.
By adjusting the pump relief pressure Pr electrically (by the pressure output signal D1), the controller 19 causes the piston rod 23a of the pump actuator 23 to move back and forth with the inflow / outflow of the hydraulic oil to the pump actuator 23. The plate 20 can be operated, the pump P can be controlled so that the pump discharge pressure Pp becomes the target discharge pressure SP, and the pump discharge amount Q can also be controlled.

In addition, since the electromagnetic pressure relief valve 26 is a negative type, the pump pressure controller 17 can move the pump P at a predetermined pressure such as the maximum pressure even in an emergency such as when the current from the battery Ba suddenly stops. The pump P secures a predetermined pump discharge amount Q and supplies the necessary hydraulic oil to each of the hydraulic actuators M1, M2, C1-5, and does not bring down the hydraulic system 16.
The pump pressure control unit 17 includes an inclination sensor 30 that electrically detects an inclination angle (an inclination input signal H1 described later) of the swash plate 20 of the pump P. Based on this, the controller 19 converts the discharge amount Q of the pump P.

  Each of the control valves V1 to V8 is composed of a center bypass type direct acting spool type directional switching valve in which the direction of the pressure oil is switched by sliding from the neutral position to one or the other in the axial direction of the spool. Connected to the corresponding (actuated) hydraulic actuators M1, M2, and C1-5 via the pump port 31 through which pressure oil from P flows in, the tank port 32 communicating with the tank T, and the hydraulic lines 33a and 33b A pair of actuator ports 34a and 34b and a bypass passage 35 are provided.

  Each of the control valves V1 to 8 includes a biasing spring 36 that biases the spool from one end side, and a proportional solenoid 37 that moves the spool against the biasing force of the biasing spring 36. The degree of opening of each of the ports 31, 32, 34a, 34b and the bypass passage 35 can be arbitrarily set by sliding the spool in an unsuccessful manner in proportion to the value of the current supplied to the proportional solenoid 37 by the command signal D2 from 19. It is composed of an electromagnetic proportional valve that can

In the present embodiment, the operating means 18 has an operating lever 18a that is tilted back and forth or left and right, and is provided for each of the control valves V1-8.
Each operation means 18 is provided with an operation sensor 38. When the operation lever 18a is tilted from the neutral position to one or the other in the tilt direction, the operation sensor 38 determines the operation direction of the operation lever 18a and the operation amount s of the operation lever 18a. It is configured to be detected electrically.

  An operation signal H2 corresponding to the operation direction and the operation amount s is input to the controller 19, and the controller 19 outputs a command signal D2 to the proportional solenoids 37 of the control valves V1 to 8 to be operated based on the operation signal H2. To do. By this command signal D2, the spools of the control valves V1 to 8 to be operated are operated from the neutral position to one or the other in proportion to the operation amount s of the operation means 18 (corresponding in proportion to the operation amount s of the operation means 18). The spools of the control valves V1 to V8 are controlled).

  Accordingly, when the operation lever 18a is tilted from the neutral position to one side, the spools of the control valves V1 to 8 to be operated slide to one side from the neutral position, and when the operation lever 18a is tilted from the neutral position to the other, the control valve V1 to be operated. When the -8 spool slides from the neutral position to the other and the operation amount s from the neutral position of the operation lever 18a increases, the spool stroke from the neutral position of the control valves V1 to 8 to be operated increases.

  As shown in FIG. 2, the control valves V1 to V8 are, in this embodiment, a travel control valve V1 that controls one of the left and right travel motors M1, and a travel control valve V2 that controls the other travel motor M1. A swing control valve V3 for controlling the swing motor M2, a bucket control valve V4 for controlling the bucket cylinder C5, an arm control valve V5 for controlling the arm cylinder C4, and a boom control valve V6 for controlling the boom cylinder C3. The swing control valve V7 for controlling the swing cylinder C2 and the dozer control valve V8 for controlling the dozer cylinder C1 are arranged in order from the upstream side in the flow direction of the pressure oil.

Note that the arrangement order of the control valves V1 to V8 is not limited to this.
Further, the hydraulic system 16 includes a pressure oil supply passage 39 for supplying the pressure oil in the discharge passage 24 of the pump P to the control valves V1 to 8, and the control valves V1 to 8 from the discharge passage 24 of the pump P. A center bypass oil passage 40 extending through the tank T is provided.
The pressure oil supply path 39 is connected to the pump port 31 of the dozer control valve V8, which is the control valve V8 whose oil path end is connected to the discharge path 24 and whose oil path end is at the most downstream position, and each of the other control valves. The pump ports 31 of V1 to V7 and the pressure oil supply path 39 are connected via a branch oil path 41.

  The center bypass oil passage 40 is connected to one discharge control valve V1 from the discharge path 24 of the pump P, the other control valve V2, the turning control valve V3, the bucket control valve V4, the arm control valve V5, and the boom. This is an oil passage that reaches the tank T through the control valve V6 → the swing control valve V7 → the dozer control valve V8, and passes through the center passage 35 of each control valve V1-8.

A low pressure relief valve 42 is provided on the downstream side of the dozer control valve V8 which is the control valve V8 on the oil path end side of the center bypass oil path 40 and at the most downstream position.
The set pressure of the low-pressure relief valve 42 is set higher than the discharge pressure Pp (neutral target discharge pressure) of the pump P at the neutral time of all the control valves V1 to 8 during the rotation of the engine E, and the engine E is rotating. The control valve V1 is set so as not to open at the discharge pressure Pp of the pump P when the control valves V1 to 8 are neutral.

In the present embodiment, the discharge pressure Pp of the pump P at the neutral time of all the control valves V1 to 8 is mechanically 35 kgf / cm ² by the spring 29 of the pump control valve 25 and the adjustment spring 27 of the electromagnetic relief valve 26. The set pressure of the low pressure relief valve 42 is set to a pressure higher than the discharge pressure of the pump P at the neutral time of all the control valves V1 to 8, for example, 40 Kgf / cm ^2. The oil discharged from the pump P is not bleed into the tank T when the valves V1 to V8 are neutral.

A switching valve 43 that opens and closes the center bypass oil passage 40 is provided on the upstream side (or downstream side) of the low pressure relief valve 42 on the oil passage end side of the center bypass oil passage 40.
This switching valve 43 is switchable between an open position 43a that allows the flow of pressure oil and a closed position 43b that blocks the flow of pressure oil, and an urging spring 44 that urges in the direction of switching to the open position 43a. And an ON / OFF solenoid 45 arranged so as to antagonize the urging direction of the urging spring 44, and when the solenoid 45 is excited by the excitation signal D3 from the controller 19, it switches to the closed position 43b. When the solenoid is demagnetized, it is switched to the open position 43a by the biasing force of the biasing spring 44.

  This switching valve 43 is in the open position 43a when none of the operating means 18 is operated after the engine E is started, and closed when the excitation signal D3 is output from the controller 19 when at least one operating means 18 is operated. The position is switched to the position 43b (or the excitation signal D3 may be output from the controller 19 immediately after the engine E is started to switch to the closed position 43b).

Accordingly, there is no bleed of pressure oil from the center bypass oil passage 40 to the tank T when the operation means 18 is operated.
The hydraulic system 16 includes a pressure sensor 46 that electrically detects the discharge pressure Pp of the pump P, and the controller 19 includes an A / D converter, a calculator, a D / A converter, and the like. Is done.

As shown in FIG. 3, the boom control valve V6 and the arm control valve V5 are switchable between neutral positions 47A and 47B, raised positions 48A and 48B, and lowered positions 49A and 49B.
In the control valves V6, V, the actuator ports 34a, 34b are closed and the center passage 35 is opened at the neutral positions 47A, 47B.

  When the boom control valve V6 is switched to the raised position 48A, the pump port 31 communicates with one actuator port 34a, pressure oil is supplied to the bottom side of the boom cylinder C3 via one pipe line 33a, and the tank port 32 communicates with the other actuator port 34b, the pressure oil on the rod side of the boom cylinder C3 is drained through the other conduit 33b, the boom 13 is raised, and the boom control valve V6 is switched to the lowered position 49A. The pump port 31 communicates with the other actuator port 34b, pressure oil is supplied to the rod side of the boom cylinder C3 via the other conduit 33b, and the tank port 32 communicates with one actuator port 34a. The pressure oil on the bottom side of the boom cylinder C3 is drained through the one pipe line 33a. Boom 13 is operated downward.

  Further, when the arm control valve V5 is switched to the lowered position 49B, the pump port 31 communicates with one actuator port 34a and pressure oil is supplied to the bottom side of the arm cylinder C4 through one pipe line 33a. The tank port 32 communicates with the other actuator port 34b, and the pressure oil on the rod side of the arm cylinder C4 is drained through the other conduit 33b, so that the arm 14 is lowered, and the arm control valve V5 is raised to a position 48B. , The pump port 31 communicates with the other actuator port 34b, pressure oil is supplied to the rod side of the arm cylinder C4 via the other conduit 33b, and the tank port 32 communicates with one actuator port 34a. Then, the pressure oil on the bottom side of the arm cylinder C4 is drained through the one pipe line 33a. By the arm 14 is operated increases.

The controller 19 receives the tilt angle of the swash plate 20 of the pump P as a tilt input signal H1 from a potentiometer, a rotary encoder, etc., and inputs the operation amount s of each control valve V1-8 as an operation signal H2 from the operation sensor 38. Then, the discharge pressure Pp of the pump P is input from the pressure sensor 46 as the pressure input signal H3.
Further, the controller 19 outputs the pump relief pressure Pr of the pump pressure control unit 17 as a pressure output signal D1. The controller 19 also outputs an excitation signal D3 that closes the switching valve 43.

The controller 19 may output a capacity output signal D1 ′ for instructing the pump discharge amount Q to the pump P instead of the pressure output signal D1.
The controller 19 performs the following control.
In this control, when the center bypass oil passage 40 is closed, the target discharge pressure SP is calculated according to the operation amount s (spool stroke) of the control valves V1 to V8, and the pump P is adjusted so that the required discharge pressure Pp is obtained. Control.

First, a method for calculating the target discharge pressure SP will be described below.
The target discharge pressure SP is determined based on the following formulas (1) to (4).
SQ = Qa + Qb + ΔQ (1)
SQ: Set discharge amount of pump P (assumed discharge amount of pump P)
Qa: Actuator flow rate Qb: Bleed-off flow rate ΔQ: Differential flow rate In equation (1), the set discharge amount SQ is first obtained. This set discharge amount SQ is set with the maximum discharge amount Qmax of the pump P as the upper limit. This value is calculated as the sum of the actuator flow rate Qa and the bleed-off flow rate Qb required according to the use state such as traveling of the work machine 1 and swinging of the boom 13 and the like and the possible differential flow rate ΔQ.

The bleed-off flow rate Qb in the equation (1) is obtained by using the flow coefficient Kq, the bleed-off area value B planned according to the use state, and the target discharge pressure SP required according to the use state. It can be expressed by the relational expression of Expression (2).
Qb = Kq × B × √SP (2)
Qb: Bleed-off flow rate Kp: Flow coefficient B: Planed bleed-off area value SP: Target discharge pressure Here, the bleed-off area value B in the equation (2) is prepared in the controller 19 in advance and the control valve V1 A hydraulic oil tank T which is a value calculated by a function having as input an operation amount s of .about.8 (a sum of the operation amounts s when operating a plurality of control valves V1 to 8). The opening area value of the passage (bleed-off oil passage) communicating with the.

If the differential flow rate ΔQ in the equation (1) is almost zero and ignored, the target discharge pressure SP can be obtained statically by the following equation (3).
SP = {(SQ−Qa) / (Kq × B)} ² (3)
SP: Target discharge pressure SQ: Set discharge amount of pump P Qa: Actuator flow rate Kp: Flow rate coefficient B: Plane bleed-off area value In formula (3), when the center bypass oil passage 40 is closed, hydraulic oil is Since oil is not discharged into the tank T, if a slight leak on the circuit is ignored, the discharge amount Q of the pump P (that is, the tilt input signal H1 of the swash plate 20) is expressed by the equations (1) and (3). It can be substituted as a signal representing the actuator flow rate Qa.

SP = {(SQ−Q) / (Kq × B)} ² (4)
SP: Target discharge pressure SQ: Set discharge amount of pump P Q: Actual discharge amount of pump P Kp: Flow coefficient B: Plane bleed-off area value Next, the numerator in the right side in equation (4) is expressed as a flow rate value Xa. (= SQ-Q) and the bleed-off characteristic value Xb (= Kq × B) as the denominator, the control of the hydraulic system will be described with reference to the block diagram of FIG.

As shown in FIG. 5, the controller 19 uses a pump discharge amount conversion unit 52 to convert the gradient input signal H1 from the pump P from the set discharge amount SQ set according to the use state by the set discharge amount calculation unit 51. The flow rate value Xa is calculated by subtracting the discharge amount Q.
Next, the controller 19 calculates a bleed-off characteristic value Xb by multiplying the scheduled bleed-off area value B corresponding to the operation amount s (operation signal H2) of the operating means 18 by the flow coefficient Kp.

The flow rate value Xa described above is divided by the bleed-off characteristic value Xb, and the value is squared to obtain the target discharge pressure SP (see formula (4)).
Then, based on this target discharge pressure SP, closed loop control of the discharge pressure Pp of the pump P is performed. In other words, the discharge pressure Pp (pressure input signal H3) of the pump P is subtracted from the target discharge pressure SP, and the gain (Gc) having a phase compensation function with respect to the deviation between the target discharge pressure SP and the fed back discharge pressure P. The pressure output signal D <b> 1 (command signal) multiplied by is output to the pump pressure control unit 17.

The pump pressure control unit 17 adjusts the pump relief pressure Pr of the electromagnetic relief valve 26 according to the pressure output signal D1 and operates the swash plate 20 via the pump actuator 23, so that the discharge pressure Pp of the pump P becomes the target discharge. Control is performed so as to converge to the pressure SP.
By performing the closed loop control, it is possible to compensate and cancel out the pump pipe volume and the leakage that affect the differential flow rate ΔQ in the equation (1).

When all the control valves V1 to 8 are neutral, 0 is input to the controller 19 as the operation signal H2. In this case, the bleed-off area value B calculated by the controller 19 is the maximum, that is, the bleed-off characteristic value Xb, which is the denominator in the right side of Equation (4), is relatively larger than the numerator flow value Xa. Thus, the value of the target discharge pressure SP becomes small.
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 also almost input as 0, so that the pump P has a minimum required neutral target discharge pressure. It is only necessary to maintain a pressure corresponding to (= (SQ / Kq × B) ² ), and energy waste is reduced.

When all the control valves V1 to 8 are neutral, the pressure output signal D1 is sent from the controller 19 to the proportional solenoid 28 of the electromagnetic relief valve 26 so that the pump relief pressure Pr becomes equal to the pressure of the adjustment spring 27 of the electromagnetic relief valve 26. Is output. Therefore, the value of the neutral target discharge pressure is mechanically determined to be 35 kgf / cm ² by the spring 29 of the pump control valve 25 and the adjustment spring 27 of the electromagnetic relief valve 26 in consideration of the pressure loss and leakage due to the electromagnetic relief valve 26. It is said.

When the control valves V1 to 8 are moved from the neutral position to the operation position, the bleed-off area value B on the controller 19 is decreased and the target discharge pressure SP is once increased.
However, when the target discharge pressure SP becomes higher than the load pressure applied to the hydraulic actuators M1, M2, C1-5, and the working oil starts to flow into the oil chambers of the hydraulic actuators M1, M2, C1-5, the target discharge pressure SP. The discharge amount Q (actuator flow rate Qa) of the pump P is increased so as to maintain this value, and the operating speeds M1, M2, C1 to 5 of the hydraulic actuator are increased.

An 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 the equation (4), is relatively smaller than the bleed-off characteristic value Xb that is the denominator. On the contrary, the value of the target discharge pressure SP becomes smaller.
In this way, the target discharge pressure SP rises and falls gradually and converges to the discharge pressure Pp of the pump P and the discharge amount Q of the pump P that maintain the actuator speed corresponding to the operation amount s of the operation unit 18, and the operation unit 18. The flow rate of the pump P is controlled so that the target discharge pressure SP is as much as necessary according to the planned bleed-off area value B calculated from the operation amount s.

Therefore, the actual discharge amount Q of the pump P is limited to the amount supplied to the hydraulic actuators M1, M2, and C1-5 if the leakage on the circuit is ignored, and the waste of energy is reduced.
Next, control for preventing a breathing phenomenon when the boom 13 (or the arm 14) is lowered will be described.
In FIG. 3, when the operation means 18 is operated to lower the boom 13 (or the arm 14) from the neutral position so that the boom 13 (or the arm 14) is lowered (or the arm is lowered), the operation signal H 2 corresponding to the operation direction and the operation amount s is obtained from the controller 19. Is input. Based on the operation signal 2, the controller 19 outputs a command signal D2 to the proportional solenoid 37 of the boom control valve V6 (or the arm control valve V5). By this command signal D2, the spool of the boom control valve V6 (or the arm control valve V5) is operated from the neutral position to the lowered position 49A (49B) in proportion to the operation amount s of the operation means 18.

  On the other hand, the controller 19 calculates a target discharge pressure SP corresponding to the operation amount s of the operation means 18, and the pump P discharges the pressure oil so as to reach the target discharge pressure SP. 14), when the load on the rod side of the boom cylinder C3 (the bottom side of the arm cylinder C4) is reduced, the discharge pressure of the pump P does not increase, and the discharge amount of the pump P increases. At this time, if no measures are taken, if the rotational speed of the engine E is low, the flow rate of the pump P will not catch up with the speed of descent of the boom 13 or the like (the arm 14 or the like) before the pressure oil A shortage of supply occurs, and a phenomenon called “breathing” occurs in which the boom 13 (or arm 14) stops instantaneously due to the negative pressure on the pressure oil supply side of the boom cylinder C3 (or arm cylinder C4).

Therefore, in the hydraulic system 16 according to the present embodiment, the boom is detected before the pressure oil supply amount shortage is detected by detecting a sign that the pressure oil supply amount shortage occurs to the boom cylinder C3 (or the arm cylinder C4). The “breathing” phenomenon is prevented by returning the spool of the control valve V6 (or the arm control valve V5).
The action for preventing the “breathing” phenomenon will be described. When a sign that the supply amount of pressure oil is insufficient for the boom cylinder C3 (or the arm cylinder C4) is detected, the boom control valve V6 (or the arm control valve V5) is detected. ) Is returned from the controller 19 to the boom control valve V6 (or the arm control valve V5), the spool is returned, and the boom control valve V6 (or the arm control valve V5) is an actuator. The opening area of the ports 34a and 34b is reduced.

  At this time, in the hydraulic system 16 of the present embodiment, the operation amount s of the operation means 18 does not change, and the expected bleed-off area value B is calculated from the operation signal H2 of the operation means 18, and the pump P Since the set discharge amount SQ is not changed, the flow rate corresponding to the operation amount s of the operation means 18 is discharged from the pump P when pressure oil is supplied to the boom cylinder C3 (or the arm cylinder C4).

At this time, the switching valve 43 is switched to the closed position 43b, and the discharge oil of the pump P is not bleed from the center bypass oil passage 40 to the tank T.
In other words, the pressure oil supply flow rate to the boom cylinder C3 (or the arm cylinder C4) is substantially preserved by returning the spool when a sign of insufficient pressure oil supply to the boom cylinder C3 (or the arm cylinder C4) is detected. In addition, since the discharge amount of the pressure oil from the boom cylinder C3 (or the arm cylinder C4) is reduced, there is no shortage of supply of the pressure oil to the boom cylinder C3 (or the arm cylinder C4), and the engine E during idling is low. The “breathing” phenomenon that occurs during rotation can be prevented.

As a result, even when a heavy object is mounted, it is possible to prevent the occurrence of an overrun of the lowering speed of the boom 13 or the lowering speed of the arm (arm squeezing speed).
Further, in the hydraulic system 16 in the present embodiment, the “breathing” phenomenon can be prevented by controlling the spool by the controller 19, so that the boom cylinder C 3 (or arm cylinder) during the lowering operation of the boom 13 (or arm 14). It is not necessary to provide a throttle for preventing breathing in the circuit on the return side of the pressure oil from C4), or from the boom cylinder C3 (or arm cylinder C4) when the boom 13 (or arm 14) is lowered. Even when a throttle is provided in the circuit on the return side of the pressure oil, the opening area of the throttle can be increased, so that the boom 13 (or arm 14) can be operated efficiently when the engine E is rotating at high speed. Can do.

  As in this embodiment, the controller 19 obtains the target discharge pressure SP by the equation (4), and the command signal D1 calculated based on the deviation between the target discharge pressure SP and the actual discharge pressure Pp of the pump P. In the hydraulic system 16 configured to control the discharge amount Q of P, when the boom 13 or the like is lowered, if the pressure on the pressure oil supply side of the boom cylinder C3 is reduced due to the weight drop of the boom 13 or the like, the pump P discharge pressure does not increase.

If the discharge pressure of the pump P does not rise indefinitely, the discharge amount of the pump P increases, so the value of (SQ-Q) decreases and the target discharge pressure SP decreases.
When all the control valves V1 to 8 are neutral, the minimum discharge pressure of the pump P is mechanically set to 35 kgf / cm ² by the spring of the pump control valve 25 of the pump pressure control unit 17 and the adjustment spring 27 of the electromagnetic relief valve 26. Therefore, even if the target discharge pressure SP becomes 0, the pump P discharges exceeding the set discharge amount SQ in an attempt to ensure 35 kgf / cm ² .

Therefore, the precursor of the shortage of the pressure oil supply amount can be understood by looking at the change in the value of the target discharge pressure SP or the value of (SQ-Q).
Therefore, in this embodiment, the controller 19 is provided with the pressure oil supply shortage detection unit 53, and the pressure oil supply shortage detection unit 53 detects a precursor of the pressure oil supply shortage, and detects a precursor that the pressure oil supply amount shortage occurs. Then, the controller 19 outputs a command signal D2 ′ for returning the spool to the boom control valve V6 (or the arm control valve V5) to return the spool.

  Specifically, as a first detection method for detecting a sign that an insufficient pressure oil supply amount occurs, the pressure applied to the boom cylinder C3 (or the arm cylinder C4) when the value of the target discharge pressure SP falls below a predetermined value. A method of detecting a precursor of oil supply shortage is employed, and by returning the spool of the boom control valve V6 (or the arm control valve V5), the value of the target discharge pressure SP does not fall below a predetermined value. I have control.

As the predetermined value, in this embodiment, the discharge pressure of the pump P at the neutral time of all the control valves V1 to 8 is set to 35 Kgf / cm ^2. For example, the discharge pressure of the pump P at the neutral time is 35 Kgf. Set to 50 kgf / cm ² near / cm ² .
In addition, as a second detection method for detecting a sign that a shortage of pressure oil supply occurs, the boom cylinder C3 ((QQ) in equation (4) has been lowered because the value of (SQ-Q) has fallen below a predetermined value close to zero. Alternatively, a method of detecting a sign of insufficient pressure oil supply to the arm cylinder C4) is adopted, and the value of (SQ-Q) is obtained by returning the spool of the boom control valve V6 (or the arm control valve V5). Is controlled to be less than the predetermined value (for example, 0.05 × SQ or less).

In the hydraulic circuit shown in FIG. 2, the control valves V1 to V8 may be configured by closed center type direct acting spool type directional switching valves without providing the center bypass oil passage 40, the low pressure relief valve 42 and the switching valve 43. .
Further, as a method of detecting a sign of insufficient pressure oil supply, a flow rate sensor for detecting the pressure oil flow amount on the rod side and bottom side of the boom cylinder C3 (or arm cylinder C4) is provided, and the boom 13 (or arm 14) is provided. During the lowering operation, the flow rates of the boom cylinder C3 on the pressure oil entering side and the pressure oil exit side are detected, and the value of (pressure oil entering side flow rate−pressure oil exit side flow rate) approaches 0, indicating that the pressure oil supply is insufficient. A precursor may be detected.

As another method, a pressure sensor detects the pressure on the pressure oil entering side when the boom cylinder C3 (or the arm cylinder C4) is lowered, and when the pressure approaches 0, an indication of insufficient pressure oil supply is given. You may make it detect.
The above-described detection method for detecting a precursor of insufficient pressure oil supply amount from the value of the target discharge pressure SP and the value of (SQ-Q) does not require a separate sensor and can be simply configured.

In the present embodiment, the boom 13 or the arm 14 is taken as an example, but the driven member is not limited to the boom 13 or the arm 14.
Further, in the hydraulic system 16 of the present embodiment, when the driver turns the engine key (engine starting means) to start the engine E, the engine starting means is configured so that the battery Ba rises and starts the controller 19. A start input signal H 4 is input from 56 to the controller 19.

In the conventional hydraulic system 16, when the engine is started, the discharge oil from the pump P does not escape to the tank T, the circuit becomes high pressure, and the load is applied to the cell motor and battery for starting the engine. In the system 16, when the engine E is started, for example, the discharge amount Q of the pump P is maximum, and the maximum relief pressure (for example, 250 kgf / cm ² ) of the negative electromagnetic relief valve 26 in the pump pressure control unit 17 is high. However, since the relief pressure of the low pressure relief valve 42 is 40 kgf / cm ² , hydraulic oil escapes from the center bypass oil passage 40 and the engine can be started with a small force.

Therefore, since the load applied to the cell motor can be reduced, it is not necessary to increase the voltage capacity of the battery Ba or to provide another battery Ba for starting the engine, and the battery Ba can be reduced in size.
Further, after starting the engine, when the neutral of all control valves V1~8 is neutral target discharge pressure, a 35 kgf / cm ^2, for less than 40 Kgf / cm ² of the relief pressure of the low-pressure relief valve 42, hydraulic oil waste No oil is discharged into the tank T.

When the control valves V1 to 8 are operated, before the oil passage from the pump P to the hydraulic actuators M1, M2, C1 to 6 and the oil passage from the actuator to the tank T are opened, the switching valve 43 causes the center bypass oil passage 40 to be opened. If is closed, the target discharge pressure SP can be controlled in the same manner as the control described above.
Further, in the hydraulic system 16 of the present embodiment, a temperature sensor 57 that electrically detects the temperature of the hydraulic oil is provided, and the temperature of the hydraulic oil detected by the temperature sensor 57 is the temperature input signal H6. Is input to the controller 19.

Then, when all the control valves V1 to 8 are neutral and the temperature of the hydraulic oil is equal to or lower than a predetermined temperature (for example, 0 ° C. to 20 ° C.), the discharge pressure Pp of the pump P is set higher than the set pressure of the low pressure relief valve 42. By performing control to increase (for example, 50 kgf / cm ² ), the hydraulic oil is bleed into the tank T via the center bypass oil passage 40.
Therefore, even when the control valve V1 to 8 is at a low temperature, such as when using a work machine in a cold region, etc., by operating the control oil V1-8 by flowing hydraulic oil inside before operating the spool. The influence of the control valves V1 to V8 on the spool operation can be reduced.

  Further, as shown in FIG. 4, the hydraulic system 16 is provided with a variable throttle 60 in a communication oil path 59 that communicates an oil path 58 that feeds hydraulic oil to the pump actuator 23 and the tank T. The throttle amount can be adjusted by the controller 19, and the flow rate of the hydraulic oil discharged from the communication oil path 59 to the tank T can be controlled by the delay output signal D4 from the controller 19.

Then, when the working machine 1 performs continuous punching or continuous bucket soiling, when the boom control valve V6 or the bucket control valve V4 is continuously reciprocated, the neutral position of the spool is reached. Control is performed to adjust the opening degree of the variable throttle 60 so as to reduce the discharge amount Q of the pump P with a delay from the return of.
According to this, for example, when the operating lever 18a of the operating means 18 is raised 100% → neutral position 0% → lowered 100%, the controller 197 (delayed output signal D4) returns the spool 15 to the neutral position. The pump discharge amount Q of the pump P is reduced with a delay, and the discharge amount Q of the pump P becomes 100% → 50% → 100%.

That is, if the operation amount s of the control valves V1 to 8 is 0% in the neutral position, the discharge amount Q of the pump P corresponding to this is originally 0, but the discharge amount Q of the pump P is controlled by the above control. This means that 50% of the maximum discharge amount Qmax of the pump P is discharged even when the control valves V1 to 8 are in the neutral state without being completely reduced to 0.
As a result, when the spool of the control valve V6 (V4) is continuously reciprocated by continuous punching operation or the like, the pump discharge amount Q does not become 0 even when the spool returns to the neutral position. Improves.

  Further, at this time, hydraulic oil exceeding the discharge amount Q of the pump P corresponding to the operation amount s of the control valves V1 to 8 is discharged from the pump P. By opening the center bypass oil passage 40, the control valves V1 to V1 are discharged. Even if the hydraulic oil exceeding the discharge amount Q of the pump P corresponding to the operation amount s of 8 is discharged, the hydraulic oil can be released to the tank T and the pressure increase in the circuit of the hydraulic system 16 can be suppressed. .

In addition, this invention is not limited to embodiment mentioned above. Each configuration of the hydraulic system 16 of the working machine 16 or the entire structure, shape, dimensions, and the like can be appropriately changed in accordance with the spirit of the present invention.
For example, in the hydraulic system 16, as shown in FIG. 6A, the switching valve 43 is urged in the direction of switching to the closed position 43 b by the urging spring 44 and the solenoid 45 is activated by the excitation signal D 3 from the controller 19. It may be configured to be switched to the open position 43a when excited.

In this case, when the engine is started, an opening output signal (current that excites the ON / OFF solenoid 45) is sent to the switching valve 43 by a starting input signal H4 input from the engine starting means 56 to the controller 19, and the switching valve 43 The spool is set to the open position 43a.
Further, when the pressure oil is bleed through the center bypass oil passage at the time of heat-up control of the control valves V1 to 8 or at the time of control such as continuous hammering or continuous bucket landslide, the spool of the switching valve 43 is opened to the open position 43a. To.

When the center bypass oil passage 40 is closed, it is only necessary to interrupt the output of the excitation signal D3 sent to the solenoid 45 of the switching valve 43. After the interruption, the switching valve 43 is biased by the biasing spring 44. Moves to the closed position 43b, and the center bypass oil passage 40 is closed.
Moreover, as shown in FIG.6 (b), the switching valve 43 can also be abbreviate | omitted. In this case, as shown in FIG. 7, the control valves V1 to 8 are connected to the tank T from the oil passage PC and the hydraulic actuators M1, M2, C1-5 from the pump P to the hydraulic actuators M1, M2, C1-5. The center bypass oil passage 40 is closed before the reaching oil passage CT opens.

Therefore, the controller 19 operates the center bypass oil passage before the oil passage PC from the pump P to the hydraulic actuators M1, M2, C1-5 and the oil passage CT from the hydraulic actuators M1, M2, C1-5 to the tank T are opened. It is not necessary to perform control to close 40, and the control system can be simplified.
Further, as shown in FIG. 6C, the low pressure relief valve 42 is omitted, and an electromagnetic proportional valve capable of adjusting the opening degree of the center bypass oil passage 40 by the controller 19 on the oil passage end side of the center bypass oil passage 40. 61 may be provided.

The electromagnetic proportional valve 61 opens the center bypass oil passage 40 by an open signal when the engine E is started, during the heat-up control of the control valves V1 to 8, and during neutral control during control such as continuous hammering or continuous bucket landslide.
Similarly to the above case, before the oil passage PC from the pump P to the hydraulic actuators M1, M2, C1-5 and the oil passage CT from the hydraulic actuators M1, M2, C1-5 to the tank T are opened, or the engine After the start of E, the center bypass oil passage 40 is closed by a closing signal.

Note that when the center bypass oil passage 40 is closed, the electromagnetic proportional valve 61 is gradually closed to prevent surge pressure from being generated in the hydraulic system 16.
Further, instead of the electromagnetic proportional valve 61, a proportional valve based on pilot pressure or the switching valve 43 described above may be used. In the case of the switching valve 43, the timing of receiving the opening output signal and the closing output signal is the same as that of the electromagnetic proportional valve 61 described above.

The hydraulic circuit of the hydraulic system 16 is a parallel type, but a tandem type in which the pump ports of the downstream control valves V1 to 8 are sequentially branched from the center port output of the upstream control valves V1 to 8. It may be.
Such as neutral target discharge pressure was set to 35 kgf / cm ^2, although the predetermined relief pressure of the relief valve 11 had a 40 Kgf / cm ^2, and 35 kgf / cm ² the relief pressure to the neutral target discharge pressure 30 kgf / cm ^2, The relief pressure only needs to be set higher than the neutral target discharge pressure SP ′.

13 Boom (driven member)
14 Arm (driven member)
18 Operating means 19 Controller E Drive source (engine)
P pump C3 boom cylinder (hydraulic actuator)
C4 arm cylinder (hydraulic actuator)
V6 Control valve for boom V7 Control valve for arm s Operation amount of operating means H2 Operation signal D1 Command signal D2 Command signal D2 'command signal T Tank SQ Set discharge amount that is the assumed discharge amount of the pump Q Actual discharge amount of the pump B Bleed-off area value to be calculated from operation signal of operation means Kq Flow coefficient SP Target discharge pressure SP of pump
Pp Actual discharge pressure

Claims (3)

A pump (P) constituted by a variable displacement hydraulic pump driven by a drive source (E), hydraulic actuators (C3, C4) driven by pressure oil from the pump (P), and this hydraulic actuator ( The driven members (13, 14) driven to swing up and down by C3, C4), the operating means (18) for operating the driven members (13, 14), and the hydraulic actuators (C3, C4) are controlled. A spool type control valve (V6, V5) and a controller (19) for controlling the spool of the control valve (V6, V5) and the pump (P),
When the operation means (18) is operated, an operation signal (H2) corresponding to the operation amount (s) of the operation means (18) is input to the controller (19) and based on the operation signal (H2). The spool of the control valve (V6, V5) is controlled in proportion to the operation amount (s) of the operation means (18) by the command signal (D2) output from the controller (19) to the control valve (V6, V5). Configured to be
In order to send the discharge oil to the hydraulic actuators (C3, C4) without returning a part of the discharge oil of the pump (P) to the tank (T), in the controller (19), the assumed discharge of the pump (P) From the set discharge amount SQ, which is the amount, the actual discharge amount Q of the pump (P), the bleed-off area value B calculated from the operation signal (H2) of the operation means (18), and the flow coefficient Kq The target discharge pressure SP of the pump (P) is obtained by the following calculation formula,
SP = {(SQ−Q) / (Kq × B)} ²
The working machine in which the discharge amount Q of the pump (P) is controlled by the command signal (D1) calculated based on the deviation between the target discharge pressure SP and the actual discharge pressure (Pp) of the pump (P). In the hydraulic system,
When the operating means (18) is operated so as to lower the driven members (13, 14), a sign that the hydraulic oil supply amount (C3, C4) is insufficient is detected. The controller (19) is configured to output a command signal (D2 ′) for returning the spool of the control valve (V6, V5) from the controller (19) to the control valve (V6, V5) when a sign of insufficient pressure oil supply is detected. A hydraulic system for a work machine characterized by   When the operating means (18) is operated so as to lower the driven members (13, 14), the value of the target discharge pressure SP decreases and the value of the target discharge pressure SP falls below a predetermined value. 2. The hydraulic system for a working machine according to claim 1, wherein a precursor of a shortage of pressure oil supply to the hydraulic actuators (C 3, C 4) is detected, and control is performed to return the spool in this case.   When the operating means (18) is operated so as to lower the driven members (13, 14), the value of (SQ-Q) in the calculation formula decreases and the value of (SQ-Q) becomes zero. 2. The hydraulic system for a working machine according to claim 1, wherein a precursor of a shortage of pressure oil supply is detected when the pressure falls below a predetermined value nearby, and in this case, control is performed to return the spool.

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