JP6367677B2 - Hydraulic circuit control device and hydraulic circuit control method - Google Patents

Description

  The present invention relates to a hydraulic circuit control device and a hydraulic circuit control method.

  Conventionally, in the field of construction machinery such as hydraulic excavators, a hydraulic circuit in which an actuator is connected to a variable displacement pump driven by an engine and capable of adjusting a discharge flow rate from the outside via a plurality of closed center type directional control valves. Is used. This hydraulic circuit can control a variable displacement pump by calculation of an electronic control unit so that a closed center type directional control valve can be substituted for a center bypass type directional control valve. (Referred to as “virtual bleed-off control”).

  Virtual bleed-off control mathematically replaces the bleed-off characteristics of the bleed-off hydraulic system with a center bypass type directional control valve, that is, the part that controls the pressure supplied to each actuator and the flow rate of control oil. Thus, the discharge pressure of the variable displacement pump is controlled by calculation by the electronic control unit. In the conventional bleed-off control, control is performed while actually returning a part of the control oil pumped by the variable displacement pump to the oil tank, so that the variable displacement pump cannot be effectively used. On the other hand, virtual bleed-off control controls the center bypass from the directional control valve by controlling the discharge pressure of the variable displacement pump as if the hydraulic circuit had a bleed-off characteristic by calculation by an electronic control unit. By omitting the passage, it is possible to discharge only the control oil having the actually required flow rate (see, for example, Patent Document 1).

International Publication WO2013 / 128622

  Here, in a machine used in an industrial field such as a construction machine such as a hydraulic excavator, an engine which is a drive source of a variable displacement pump has a plurality of rotations set to different rotation speeds as engine drive modes. A number mode is provided. The rotation speed mode is set, for example, in 3 to 10 stages, and an appropriate rotation speed mode is selected when the engine is operating. The flow rate of the control oil actually discharged from the variable displacement pump (hereinafter referred to as “actual pump discharge flow rate”) is variable depending on the tilt amount of the swash plate or the tilt shaft of the variable displacement pump detected by the tilt amount sensor. It is a value multiplied by the rotation speed of the capacity pump. That is, if the engine speed is different, the variable displacement pump speed is also different, and the maximum pump discharge flow rate is also changed.

  At this time, when the engine speed is small, the actual pump discharge flow rate may reach the upper limit before the lever stroke becomes maximum in a region where the stroke amount of the operation lever that determines the operation amount of the actuator is large. . Therefore, in the virtual bleed-off hydraulic system, the flow rate of the control oil supplied to the actuator (hereinafter referred to as “actuator flow rate”) may be saturated before the lever stroke becomes maximum. In such a virtual bleed-off hydraulic system, the operation of the actuator has the same speed characteristics regardless of the engine speed mode even during the period until the actuator flow rate is saturated. Therefore, as an operator, there has been a problem that the speed saturation suddenly appears from the state of operating at the same speed characteristic without depending on the rotation speed mode, and the operability is felt abnormal.

  Specifically, FIG. 5 shows a pump corresponding to a lever stroke in a hydraulic excavator that employs a virtual bleed-off hydraulic system that has a three-stage engine speed mode and is optimized for a mode with the maximum set speed. The flow characteristics and pressure characteristics are shown. FIG. 5 shows flow rate characteristics and pressure characteristics when it is assumed that the load pressure on the actuator is always constant. In FIG. 5, the solid line indicates the actual pump discharge flow rate Qreal of the variable displacement pump, and the broken line indicates the pump discharge pressure Preal. In the optimized mode 3, the actual pump discharge flow rate Qreal smoothly and monotonically increases in the entire lever stroke region.

  On the other hand, in the mode 1 and the mode 2, the lever stroke region surrounded by the dotted line has the same flow rate characteristic as the mode 3, and it can be seen that the movement start position of the actuator is constant regardless of the mode. However, even in the lever stroke area after the area surrounded by the dotted line, the same flow rate characteristic is realized regardless of the mode. As a result, in mode 1 and mode 2, the actual pump discharge flow rate Qreal is saturated during the stroke. To do. Therefore, in mode 1 and mode 2, the driver feels abnormal operability.

  Although it is conceivable to set a virtual bleed-off area for each rotational speed mode, in order to realize this, a large capacity memory is required in the control device. In other words, the actual hydraulic system has different bleed-off characteristics for each actuator. When the number of actuators is n and the number of rotation speed modes is m, n × (m−1) bleed-off characteristics are obtained. A memory capacity to be stored is required, and the feasibility is poor.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to operate an actuator in a virtual bleed-off hydraulic system even when the engine speed mode is changed. It is an object of the present invention to provide a novel and improved hydraulic circuit control apparatus and hydraulic circuit control method capable of maintaining the characteristics and flow characteristics.

  In order to solve the above-described problems, according to one aspect of the present invention, a variable displacement pump driven by an engine whose output rotation speed can be set in a plurality of stages, and each connected to the variable displacement pump via a directional control valve A hydraulic circuit configured to switch the operating direction of the actuator by operating the direction control valve based on an operation amount input to each of the direction control valves. In the control device for the hydraulic circuit, the virtual discharge flow rate setting unit that sets the virtual discharge flow rate of the variable displacement pump to a predetermined value regardless of the actual rotational speed of the variable displacement pump, and the variable displacement pump Regardless of the actual number of revolutions, this is the estimated flow rate to all the actuators, with the number of revolutions of the variable displacement pump as a predetermined value set in advance. An actuator flow rate calculation unit for obtaining an estimated actuator flow rate, a bleed-off flow rate calculation unit for calculating virtual bleed-off flow rates from all the directional control valves based on an operation amount for each of the directional control valves, and the total estimated actuator A pump control unit that obtains a virtual discharge pressure based on a difference obtained by subtracting the flow rate and the virtual bleed-off flow rate from the virtual discharge flow rate, and controls the variable displacement pump based on the virtual discharge pressure. A control device for the hydraulic circuit is provided, which can solve the above-described problems.

  Further, the pump control unit is configured to obtain the virtual discharge pressure by further using a compression coefficient of a pump piping system, a reference value of the engine speed Ne0 (rpm), and an actual engine speed. When Ne_m (rpm) and the reference compression coefficient of the pump piping system is C′p, the piping compression coefficient C′p_m when the actual engine speed is Ne_m (rpm) is expressed as C′p_m = C′p * It is good also as Ne0 / Ne_m.

  The actuator flow rate calculation unit may set a pump discharge flow rate obtained by multiplying a rotation amount of the variable displacement pump by a predetermined value and a tilt amount of the variable displacement pump as the total estimated actuator flow rate.

  In order to solve the above-described problem, according to another aspect of the present invention, a variable displacement pump driven by an engine capable of setting an output rotational speed in a plurality of stages, and the variable displacement via a directional control valve, respectively. A plurality of actuators connected to a pump, and configured to switch the operation direction of the actuator by operating the direction control valve based on an operation amount input to each of the direction control valves. In the control method of the hydraulic circuit for controlling the circuit, the step of setting the virtual discharge flow rate of the variable displacement pump to a predetermined value regardless of the actual rotational speed of the variable displacement pump; Regardless of the number of revolutions, the number of revolutions of the variable displacement pump is set to a predetermined value set in advance, and a total estimated value that is an estimated flow rate to all the actuators. A step of obtaining an actuator flow rate, a step of calculating virtual bleed-off flow rates from all the directional control valves based on an operation amount for each of the directional control valves, a total estimated actuator flow rate and the virtual bleed-off flow rate Providing a virtual discharge pressure based on a difference obtained by subtracting the virtual discharge flow rate from the virtual discharge flow rate, and controlling the variable displacement pump based on the virtual discharge pressure. Is done.

  As described above, according to the present invention, in the virtual bleed-off hydraulic system, the operability and flow rate characteristics of the actuator can be maintained even when the engine speed mode is changed.

It is a circuit diagram which shows the structure of the hydraulic circuit which concerns on embodiment of this invention. It is a block diagram which shows the control processing of the variable displacement pump which concerns on the same embodiment. It is a control block diagram of the control device according to the embodiment. It is a figure which shows the characteristic of the variable displacement pump which concerns on the same embodiment. It is a figure which shows the characteristic of the variable displacement pump of the conventional virtual bleed-off hydraulic system.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

[1. Overall configuration of hydraulic circuit]
First, an example of the configuration of a hydraulic circuit according to an embodiment of the present invention will be described. FIG. 1 shows a hydraulic circuit for controlling a plurality of hydraulic actuators 1a, 1b. This hydraulic circuit is configured as a hydraulic circuit applicable to, for example, a hydraulic excavator operated by a plurality of hydraulic actuators. The actuators 1a, 1b,... Are connected to the discharge circuit 3 of the variable displacement pump 2 driven by the engine E via closed center type directional control valves 4a, 4b, respectively.

  In the hydraulic circuit of FIG. 1, only two actuators 1a and 1b and two closed center type directional control valves 4a and 4b are shown. As the variable displacement pump 2, a known pump such as an axial piston pump having a pump displacement control mechanism such as a swash plate can be used. Hereinafter, a variable displacement pump capable of controlling the discharge flow rate by adjusting the inclination of the swash plate will be described as an example.

  The hydraulic circuit includes a pump pressure control device 6 for controlling the discharge pressure of the variable displacement pump 2. The pump pressure control device 6 is connected to the discharge circuit 3 of the variable capacity pump 2. The pump pressure control device 6 includes a control valve 6b and a negative electromagnetic proportional valve 6c. The pressure of the discharge circuit 3 (hereinafter referred to as “actual discharge pressure”) Preal acts on one end face of the spool of the control valve 6b. Further, the elastic force of the spring 6d and the control oil pressure P'c controlled by the negative electromagnetic proportional valve 6c act on the other end face of the spool of the control valve 6b. An appropriate area difference is given to both ends of the spool, and the position of the spool of the control valve 6b is controlled by the balance of these forces.

  The negative electromagnetic proportional valve 6c is a valve that functions as a proportional relief valve. A spring force is applied to one end face of the piston of the electromagnetic proportional valve 6c, and control supplied to the other end face based on the control oil pressure P'c and a control signal P'tgt from the control device 12. The force generated by the proportional solenoid 6a that varies in proportion to the current acts. The position of the piston of the electromagnetic proportional valve 6c is controlled by the balance of these forces, and the control oil at a predetermined flow rate is released according to the position of the piston, and the pressure P'c acting on the spool of the control valve 6b is adjusted.

  As described above, the actual pump discharge pressure Preal of the variable displacement pump 2 is input to the pump pressure control device 6, and is output via the control valve 6b when the control device 12 controls the electromagnetic proportional valve 6c. The pressure can be adjusted. A control piston 7 is connected to the output side of the pump pressure control device 6, and the stroke amount of the control piston 7 is changed by changing the pressure output from the pump pressure control device 6. Can be controlled. Therefore, the actual pump discharge pressure Preal of the variable displacement pump 2 can be controlled.

  The closed center type directional control valves 4a and 4b are provided with a proportional solenoid 8 for moving the spool. When the solenoid driving amplifier 13 is operated by the operation lever 9 such as an electric joystick via the control device 12, the proportional solenoid 8 is excited according to the inclination angle of the operation lever 9. As a result, the spools of the closed center type directional control valves 4a and 4b move to desired positions, and the actuator port 10 is controlled to have an opening area corresponding to the movement distance. As a result, control oil having a flow rate corresponding to the opening area is supplied to the actuators 1a and 1b.

  A command amount such as an inclination angle of the operation lever 9 for operating each closed center type direction control valve 4a, 4b or a movement amount of the spool of each closed center type direction control valve 4a, 4b is electrically detected by a sensor. The The detected command amount or movement amount is a parameter indicating the operation amount Sk (k = 1, 2,...) Corresponding to the operation amount of each closed center type directional control valve 4a, 4b. In the example of FIG. 1, a command electric signal transmitted from the operation lever 9 to the solenoid drive amplifier 13 via the control device 12 is used as a parameter indicating the operation amount Sk.

  The variable displacement pump 2 includes a tilt amount sensor 11 for measuring the tilt of the swash plate, and is variable by multiplying the tilt amount detected by the tilt amount sensor 11 by the rotation speed Np of the variable displacement pump 2. The actual pump discharge flow rate Qreal of the displacement pump 2 can be calculated. The closed center type directional control valves 4a and 4b are actually valves without a bleed-off flow path, and if neglecting slight leakage of control oil on the circuit, the actual pump discharge flow rate Qreal and the total actuator of the variable displacement pump 2 It becomes substantially equal to the flow rate Qa. In the hydraulic circuit described in the present embodiment, a plurality of actuators 1a, 1b,... Are connected to one variable displacement pump 2, and the total actuator flow rate Qa is all closed center type directional control. This means the sum of the flow rates of the control oil supplied to the actuators 1a, 1b... Via the actuator ports 10 in the valves 4a and 4b.

  In the present embodiment, the control device 12 includes an A / D converter 12a, a computing unit (CPU) 12b, a D / A converter 12c, and a storage unit 14. The memory | storage part 14 is a memory | storage element illustrated by RAM, ROM, etc., and memorize | stores the program and various information which are performed by CPU12b. In the control device 12, arithmetic processing is performed based on various electric signals input to the control device 12. In the present embodiment, the control device 12 functions as a virtual discharge flow rate setting unit, an actuator flow rate calculation unit, a bleed-off flow rate calculation unit, and a pump control unit.

2. Hydraulic Circuit Control Method Next, the hydraulic circuit control processing executed by the arithmetic processing by the control device 12 according to the present embodiment will be specifically described. FIG. 2 is a block diagram showing control of the pump discharge pressure by the control device 12 of the hydraulic circuit according to the present embodiment. The CPU 12b of the control device 12 executes arithmetic processing shown by a block diagram within a dotted line B in FIG.

  The control device 12 obtains the first virtual discharge obtained based on the maximum discharge pressure Pmax of the variable displacement pump 2 as the system pressure and the characteristic curve defining the relationship between the discharge pressure P of the variable displacement pump 2 and the discharge flow rate Q. The pressure Pidea1 is compared with the second virtual discharge pressure Pidea2 obtained based on the operation amount Sk, and the variable displacement pump 2 is controlled using the obtained minimum value as the pump discharge pressure command value Ptgt. In the present embodiment, the maximum discharge pressure Pmax of the variable displacement pump 2 is included in the comparison target. The reason why the maximum discharge pressure Pmax is included is to prevent a discharge pressure equal to or higher than the maximum discharge pressure Pmax of the variable displacement pump 2 from being indicated as the pump discharge pressure instruction value Ptgt of the variable displacement pump 2. However, the maximum discharge pressure Pmax is not always necessary as long as the present invention is implemented.

(Calculation of first virtual discharge pressure)
The first virtual discharge pressure Pidea 1 is obtained from the horsepower calculation of the engine based on the actual pump discharge flow rate Qreal of the variable displacement pump 2. Specifically, as described above, the actual pump discharge flow rate Qreal can be obtained by multiplying the tilt amount detected by the tilt amount sensor 11 by the rotation speed Np of the variable displacement pump 2. The actual pump discharge flow rate Qreal is converted to a first virtual discharge pressure Pideal 1 based on a characteristic curve that defines the relationship between the discharge pressure P and the discharge flow rate Q of the variable displacement pump 2. The product of the discharge pressure P and the discharge flow rate Q of the variable displacement pump 2 represents the horsepower of the engine, and the first virtual discharge pressure Pidea1 is the value of the discharge flow rate Q of the variable displacement pump 2 from the viewpoint of the horsepower of the engine. Try to set an upper limit. The characteristic curve is, for example, a constant discharge flow rate Q regardless of the discharge pressure P up to a predetermined pressure P1, and the product of the discharge pressure P and the discharge flow rate Q is constant in a region exceeding the pressure P1. It is preferable that

(Calculation of second virtual discharge pressure)
The second virtual discharge pressure Pidea2 is based on the operation amount Sk of the closed center type directional control valves 4a and 4b by a process different from the process of obtaining the first virtual discharge pressure Pidea1 based on the characteristic curve. It is obtained by the arithmetic processing shown in the alternate long and short dash line A. An example of the arithmetic processing within the one-dot chain line A in FIG. 2 will be specifically described with reference to the control block diagram in FIG.

  First, the control device 12 sets a virtual discharge flow rate (hereinafter referred to as “virtual pump discharge flow rate”) Qidea of the variable displacement pump 2 to a predetermined value. That is, the control device 12 executes processing as a virtual discharge flow rate setting unit. As will be described later, the second virtual discharge pressure Pidea2 is calculated in a closed loop based on a flow rate value ΔQ obtained by subtracting the total estimated actuator flow rate Qai and the virtual bleed-off flow rate Qb from the virtual pump discharge flow rate Qidea. Therefore, the virtual pump discharge flow rate Qidea may be different from the actual pump discharge flow rate Qreal.

  However, since it is necessary to make the value larger than the discharge flow rate assumed when the actual hydraulic circuit is used, in this embodiment, the maximum discharge flow rate Qmax of the variable displacement pump 2 is used as the virtual pump discharge flow rate Qidea. ing. Thereby, the virtual pump discharge flow rate Qidea becomes the same value regardless of the engine speed mode, that is, irrespective of the actual speed of the variable displacement pump 2.

  Moreover, the control apparatus 12 calculates | requires the total estimated actuator flow volume Qai used as the sum total of the flow volume of the control oil supplied to all the actuators 1a, 1b .... That is, the control device 12 executes processing as an actuator flow rate calculation unit. In a hydraulic system that does not actually have a bleed-off flow path, the actual pump discharge flow rate Qreal (the rotational speed Np of the variable displacement pump 2 × the tilting amount) and the total actuator flow rate Qa are equal. However, the control device 12 of the present embodiment sets the calculated rotational speed to a predetermined value Np0 that is determined in advance regardless of the engine speed mode, that is, regardless of the actual speed Np of the variable displacement pump 2. The total estimated actuator flow rate Qai is obtained by multiplying this by the tilt amount.

  Thus, the total estimated actuator flow rate Qai has the same value regardless of the engine speed mode, that is, regardless of the actual speed of the variable displacement pump 2 if the tilt amount is the same. That is, the calculation by the control device 12 is apparently flow rate control, but actually, the tilt amount control is executed because the engine speed is constant. By executing the tilt amount control in this way, control independent of the engine speed mode can be executed. Further, by executing the tilt amount control in this way, even when the engine is driven in a drive mode other than the mode in which the engine is driven at a preset rotational speed, the virtual pump discharge flow rate and the virtual Since the bleed-off flow rate is already determined, it can be easily controlled.

  Note that the rotational speed Np0 of the variable displacement pump 2 in the calculation may be the maximum value of the rotational speed of the variable displacement pump 2 that can be realized on the basis of the maximum output of the engine, or on the basis of the energy-saving operation of the engine. The rotational speed of the variable displacement pump 2 during energy saving operation may be used.

  Further, the control device 12 determines the total of the virtual bleed-off flow paths of the closed center type directional control valves 4a, 4b,... According to the total manipulated variable S based on the virtual bleed-off characteristics stored in advance. The opening area Ab is obtained. The calculated virtual total opening area Ab is multiplied by the m-th root of the second virtual discharge pressure Pidea2 calculated at this time, and further multiplied by the flow coefficient Kq of the center bypass directional control valve. Obtain the bleed-off flow rate Qb. That is, the control device 12 executes processing as a bleed-off flow rate calculation unit. The m-th root may be a square root, for example.

  Of course, the actual closed center type directional control valves 4a, 4b,... Are of the closed center type without the bleed-off flow path, and the total opening area Ab of the virtual bleed-off flow path is a calculated value. . This virtual bleed-off characteristic indicates the relationship between the virtual total opening area Ab and the total manipulated variable S in the closed center type directional control valves 4a, 4b... Used, the center bypass type direction in the conventional bleed-off hydraulic system. It can be set by obtaining in advance using a design method similar to the bleed-off characteristic of the control valve.

  Then, the controller 12 subtracts the total estimated actuator flow rate Qai and the virtual bleed-off flow rate Qb from the virtual pump discharge flow rate Qidea to obtain a flow rate value ΔQ (ΔQ = Qidea−Qai−Qb). The second virtual discharge pressure Pidea2 can be calculated by dividing and integrating the obtained flow rate value ΔQ by the reference compression coefficient C′p of the pump piping system using a digital filter or the like. At this time, the control device 12 of the present embodiment corrects the reference compression coefficient C′p in the rotational speed mode so that the dynamic characteristics of the variable displacement pump 2 become similar in all engine rotational speed modes.

  Specifically, when the engine is operating in a certain rotation speed mode m, the flow rate value ΔQm (s) calculated according to the operation amount S is the value of the variable displacement pump 2 set in the calculation of the total estimated actuator flow rate Qai. When the engine speed in the case of the engine speed Np0 is the reference value Ne0 and the actual engine speed is the actual engine speed Ne_m, it can be expressed by the following equation (1).

Qidea_m：回転数モードｍのときの実ポンプ吐出流量
Qb_m(s)：回転数モードｍ、操作量Ｓのときのブリードオフ流量
Qai_m：回転数モードｍのときの総推定アクチュエータ流量
Qb(s)：エンジン回転数の基準値Ｎｅ０、操作量Ｓのときのブリードオフ流量

Qidea_m: Actual pump discharge flow rate when the speed mode is m
Qb_m (s): Bleed-off flow rate when speed mode is m and manipulated variable S
Qai_m: Total estimated actuator flow rate when the speed mode is m
Qb (s): Bleed-off flow rate when the engine speed reference value Ne0 and manipulated variable S

  Here, the second virtual discharge pressure Pidea2_m in the case of the rotation speed mode m can be expressed by the following equation (2).

  Therefore, the pipe compression coefficient C′p_m in the rotation speed mode m is C′p_m = Ne0 / Ne_m * C′p, and the reference compression coefficient C′p is corrected according to the engine rotation speed mode to C By setting 'p_m', it can be seen that if the static characteristics of the variable displacement pump 2 are the same, the dynamic characteristics of the variable displacement pump 2 show similar characteristics.

  In the control device 12 of the present embodiment, the second virtual discharge pressure Pidea2 when the virtual pump discharge flow rate Qidea is a constant value and the total estimated actuator flow rate Qai is 0 is constant regardless of the rotation speed mode. . Therefore, since only the bleed-off flow rate Qb changes according to the operation amount S, the movement start position of the actuator is constant regardless of the rotation speed mode. Even when the total estimated actuator flow rate Qai is not 0 but is sufficiently small, Qide >> Qai and Qai = 0 are considered, so that the fine operation region has the same characteristics regardless of the rotation speed mode. doing. Therefore, the static characteristics of the variable displacement pump 2 are the same. That is, the dynamic characteristics of the variable displacement pump 2 show similar characteristics.

  FIG. 4 shows the flow rate characteristic and pressure characteristic of the variable displacement pump 2 obtained under the same conditions as in FIG. 5 in the hydraulic excavator adopting the virtual bleed-off hydraulic system. In FIG. 4, the solid line indicates the actual pump discharge flow rate Qreal, and the broken line indicates the pump discharge pressure Preal. As shown in FIG. 4, in the hydraulic circuit according to the present embodiment, the start position of the actuator is the same regardless of the engine speed mode, and the engine speed mode is changed in the fine operation region surrounded by the dotted line. Even in this case, the flow rate characteristic of the variable displacement pump 2 is stable. It can also be seen that the engine speed mode can be changed smoothly without saturation of the flow rate characteristic regardless of the engine speed mode.

(Indication of pump discharge pressure)
Returning to FIG. 2, the control device 12 compares the obtained first virtual discharge pressure Pidea 1 and second virtual discharge pressure Pidea 2, and further the maximum discharge pressure Pmax of the variable displacement pump 2, and determines the minimum value of them. The pump discharge pressure command value Ptgt is set. Then, the control device 12 controls the discharge pressure of the variable displacement pump 2 in a closed loop based on the control signal P′tgt that is inverted by subtracting the pump discharge pressure command value Ptgt from the maximum discharge pressure Pmax of the pump. . That is, the control device 12 executes processing as a pump control unit.

  As a result, the solenoid drive amplifier 5 receives the control signal P′tgt of the control device 12 and strengthens the excitation of the proportional solenoid 6a of the negative electromagnetic proportional valve 6c. As a result, in inverse proportion to the magnitude of the excitation, in other words, the pressure P′c of the negative electromagnetic proportional valve 6c is proportionally controlled according to the pump discharge pressure instruction value Ptgt, whereby the control valve 6b is Operated. As a result, the control piston 7 moves the pump capacity control mechanism to control the pump capacity, that is, the pump discharge flow rate. As a result, the discharge pressure of the variable displacement pump 2 is controlled, and the control valve 6b is operated against the pressure P'c of the negative electromagnetic proportional valve 6c. As described above, since the pump discharge pressure is controlled in a closed loop, the actual pump discharge pressure Preal is substantially equal to the pump discharge pressure instruction value Ptgt.

  In the present embodiment, the negative electromagnetic proportional valve 6c is used, and the variable displacement pump 2 can be driven with the maximum pressure when the control signal P'tgt is not output. However, a positive electromagnetic proportional valve may be used instead of the negative electromagnetic proportional valve. In this case, the process of inverting the pump discharge pressure command value Ptgt is omitted, and the pump discharge pressure command value Ptgt and the control signal P′tgt are treated as equal.

[3. Example of hydraulic circuit operation]
In the control of the hydraulic circuit executed as described above, the second virtual discharge pressure Pidea2 is smaller than the first virtual discharge pressure Pidea1 in most operating regions, that is, in a situation where there is no fear of engine stall. Thus, the second virtual discharge pressure Pidea2 becomes the pump discharge pressure instruction value Ptgt, and control is performed. Control of the variable displacement pump 2 with the second virtual discharge pressure Pidea2 as the pump discharge pressure command value Ptgt is performed as follows.

  For example, when the operation lever 9 is not operated, the closed center type directional control valves 4a, 4b... Are in the neutral position, and zero is input to the control device 12 as the total operation amount S. In this case, since the total opening area Ab of the virtual bleed-off flow path calculated by the control device 12 is maximized, the second virtual discharge pressure Pidea2, that is, the pump discharge pressure command value Ptgt is a small value. The variable displacement pump 2 discharges control oil based on the pump discharge pressure command value Ptgt. After the actual pump discharge pressure Preal of the discharge circuit 3 of the pump piping system is compressed to the pump discharge pressure command value Ptgt and increased, The actual pump discharge flow rate Qreal requires only a slight leakage of the circuit.

  On the other hand, when the operation lever 9 is operated and the closed center type directional control valves 4a, 4b,... Are operated in the switching position direction, the total opening area Ab of the virtual bleed-off flow path calculated by the control device 12 is Get smaller. Then, since the virtual bleed-off flow rate Qb decreases, the flow rate value ΔQ increases, and as a result of integration, the pump discharge pressure command value Ptgt increases. As a result, the virtual bleed-off flow rate Qb is increased at a certain total operation amount and the flow rate value ΔQ converges to zero. Therefore, the pump discharge pressure instruction value in which the virtual pump discharge flow rate Qidea and the virtual bleed-off flow rate Qb are balanced. It converges to Ptgt and equilibrates.

  Even when the closed center type directional control valves 4a, 4b... Are operated in the switching position direction, the variable displacement pump 2 discharges control oil based on the pump discharge pressure instruction value Ptgt, but the operation lever 9 is operated. As is the case with the actual pump discharge flow rate Qreal, only a slight leakage of the circuit is required.

  If the actual pump discharge pressure Preal is higher than the load pressure of the actuators 1a, 1b,..., The actuators 1a, 1b,. Then, the actual pump discharge flow rate Qreal increases to maintain the actual pump discharge pressure Preal at the pump discharge pressure command value Ptgt, and the moving speed of the actuators 1a, 1b. The estimated actuator flow rate Qai increases, and the flow rate value ΔQ becomes a negative value and decreases. Therefore, the pump discharge pressure command value Ptgt decreases and the virtual bleed-off flow rate Qb decreases.

  Then, the pump discharge pressure command value Ptgt and, as a result, the actual pump discharge pressure Preal decreases, the acceleration of the actuator decreases, and gradually converges to the actual pump discharge flow rate Qreal and the actual pump discharge pressure Preal that maintain the actuator speed corresponding to the operation amount. And equilibrate. During this time, the bleed-off operation is performed only by calculation in the control device 12, and the actual pump discharge flow rate Qreal is limited to the amount supplied to the actuators 1a, 1b,.

  Therefore, the bleed-off flow rate does not actually flow and the pump efficiency is not wasted. Further, since the bleed-off flow path is not required for the closed center type directional control valves 4a, 4b,..., The configuration is simple and inexpensive, and the operability is improved. Furthermore, since the pump discharge flow rate is not limited by the horsepower characteristics of the engine, the pump efficiency is further improved.

  On the other hand, when the control is performed with the second virtual discharge pressure Pidea2 as the pump discharge pressure command value Ptgt, if the discharge flow rate of the variable displacement pump 2 is continuously increased despite the heavy engine load, the engine stall is increased. May occur. However, in such a case, the second virtual discharge pressure Pidea2 calculated based on the operation amount S of the closed center type directional control valves 4a and 4b is calculated based on the horsepower characteristics of the engine. The virtual discharge pressure Pidea1 is exceeded, and control is performed using the first virtual discharge pressure Pidea1 as the pump discharge pressure command Ptgt. Therefore, in the control process of the variable displacement pump 2 according to the present embodiment, if there is a possibility of an engine stall, the pump discharge pressure command value Ptgt is switched to the first virtual discharge pressure Pidea1, so that the engine stall is avoided. be able to.

[4. Summary]
As described above, according to the hydraulic circuit according to the present embodiment, the virtual pump discharge flow rate Qidea used for calculating the second virtual discharge pressure Pidea2 is set to a constant value regardless of the engine speed mode, and The pump rotational speed Np for obtaining the total estimated actuator flow rate Qai is a constant value regardless of the engine rotational speed mode. Further, the reference compression coefficient C′p used for the calculation of the second virtual discharge pressure Pidea2 is corrected by the engine speed mode. Therefore, regardless of the engine speed mode, the variable displacement pump 2 has the same static characteristics and similar dynamic characteristics. Therefore, the movement start position of the actuator becomes the same, and no abnormality is felt in the subsequent operation, so that the operability can be improved.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1a, 1b Actuator 2 Variable displacement pump 4a, 4b Closed center type directional control valve 6 Pump pressure control device 6b Control valve 6c Electromagnetic proportional valve 7 Control piston 12 Control device

Claims (4)

A variable displacement pump driven by an engine whose output rotation speed can be set in a plurality of stages, and a plurality of actuators connected to the variable displacement pump via directional control valves, respectively. In a control apparatus for a hydraulic circuit for controlling a hydraulic circuit configured to switch an operation direction of the actuator by operating the directional control valve based on an input operation amount,
A virtual discharge flow rate setting unit that sets the virtual discharge flow rate of the variable displacement pump to a predetermined value regardless of the actual rotational speed of the variable displacement pump;
Regardless of the actual rotational speed of the variable displacement pump, the rotational speed of the variable displacement pump is set to a predetermined value, and the predetermined value is multiplied by the tilt amount of the variable displacement pump . An actuator flow rate calculation unit for obtaining a total estimated actuator flow rate that is an estimated flow rate of
A bleed-off flow rate calculation unit that calculates virtual bleed-off flow rates from all the directional control valves based on the operation amount for each of the directional control valves;
A pump control unit for obtaining a virtual discharge pressure based on a difference obtained by subtracting the total estimated actuator flow rate and the virtual bleed-off flow rate from the virtual discharge flow rate, and controlling the variable displacement pump based on the virtual discharge pressure;
An apparatus for controlling a hydraulic circuit, comprising: The pump control unit is configured to obtain the virtual discharge pressure by further using a compression coefficient of a pump piping system,
When the reference value of the engine speed is Ne0 (rpm), the actual engine speed is Ne_m (rpm), and the reference compression coefficient of the pump piping system is C′p, the actual engine speed is Ne_m. 2. The hydraulic circuit control device according to claim 1, wherein the pipe compression coefficient C′p_m at (rpm) is C′p_m = C′p × Ne0 / Ne_m.   The actuator flow rate calculation unit sets a rotational speed of the variable displacement pump as a predetermined value and uses a pump discharge flow rate obtained by multiplying a tilt amount of the variable displacement pump as the total estimated actuator flow rate. The control apparatus of the hydraulic circuit of 1 or 2. A variable displacement pump driven by an engine whose output rotation speed can be set in a plurality of stages, and a plurality of actuators connected to the variable displacement pump via directional control valves, respectively. In a hydraulic circuit control method for controlling a hydraulic circuit configured to switch an operation direction of the actuator by operating the directional control valve based on an input operation amount,
Setting a virtual discharge flow rate of the variable displacement pump to a predetermined value regardless of the actual rotational speed of the variable displacement pump;
Regardless of the actual rotational speed of the variable displacement pump, the rotational speed of the variable displacement pump is set to a predetermined value, and the predetermined value is multiplied by the tilt amount of the variable displacement pump . Obtaining a total estimated actuator flow rate that is an estimated flow rate of
Calculating virtual bleed-off flow rates from all the directional control valves based on the operation amount for each of the directional control valves;
Obtaining a virtual discharge pressure based on a difference obtained by subtracting the total estimated actuator flow rate and the virtual bleed-off flow rate from the virtual discharge flow rate, and controlling the variable displacement pump based on the virtual discharge pressure;
A method of controlling a hydraulic circuit, comprising:

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