Hydraulic drive arrangement for a construction machine

Abstract

The hydraulic drive device of the construction machine according to the present application includes a control valve (30) provided between a hydraulic pump (10) and a hydraulic actuator (20), an operator (40) that receives an actuator operation and causes the control valve to act, an unloading valve (50), an unloading operation valve (56) that receives an input of an unloading operation instruction and changes a pilot pressure of the unloading valve (50), a target pressure estimation section (73), and an unloading operation instruction section (70). The target pressure estimation section estimates a target pressure that increases as a holding pressure of the hydraulic actuator increases. The unloading operation instruction section inputs an unloading operation instruction for causing a pump pressure of the hydraulic pump (10) to follow the target pressure to the unloading operation valve (56). According to the present application, it is possible to reliably ensure the operation of the hydraulic actuator and to suppress the generation of a shock pressure.

Description

TECHNICAL FIELD

[0001] The present application relates to a device for hydraulically driving a movable element provided in a construction machine. BACKGROUND

[0002] A hydraulic driving device provided in a construction machine, as described in Japanese Patent Laying-Open No. 2004-347040, includes a hydraulic pump for ejecting hydraulic oil, a hydraulic actuator connected to a movable element of the construction machine, a control valve provided between the hydraulic pump and the hydraulic actuator, an operator for operating the control valve, and a relief valve. The hydraulic actuator is operated by the hydraulic oil supplied from the hydraulic pump, and the movable element is moved in a specific direction. The control valve is composed of a hydraulic pilot switching valve, and the direction and flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic actuator are changed according to the pilot pressure input to the control valve. The operator is composed of, for example, an operating lever and a remote control valve. The remote control valve allows the pilot pressure corresponding to the operation applied to the operating lever to be applied to the control valve, and the control valve is operated in accordance with the operation. The relief valve limits the pump pressure, and thus defines the upper limit of the circuit pressure.

[0003] However, in the above-described hydraulic driving device, when the hydraulic actuator is started, the injection pressure of the hydraulic pump, i.e., the pump pressure, sharply increases, and this can greatly affect the operation of the engine. Specifically, when the operating lever is operated in a state where the hydraulic actuator is at rest, and the injection amount of the pump increases and the control valve is opened wide, the state where the function of the relief valve for adjusting the pump pressure cannot catch up with the increased pump pressure in the period before the actual start of the hydraulic actuator is instantaneously generated. This can cause the pump pressure to sharply increase to a pressure corresponding to the load of the hydraulic actuator, i.e., an impact pressure can be generated. The impact pressure can cause the load torque of the engine to sharply increase, and thus the engine speed can sharply decrease. This can cause the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic actuator to decrease, and thus the responsiveness at the time of start can decrease.

[0004] Japanese Patent Laying-Open No. 2004-347040 describes that the hydraulic pump is composed of a variable displacement type hydraulic pump, and the capacity of the hydraulic pump is adjusted so that the flow rate of the hydraulic oil flowing through the relief valve provided between the hydraulic pump and the tank, i.e., the relief flow rate, approaches 0, and thus the energy loss at the relief valve is suppressed. However, such control cannot effectively suppress the generation of the impact pressure. SUMMARY

[0005] An object of the present application is to provide a hydraulic drive device provided in a construction machine including a movable element, which is capable of reliably starting a hydraulic actuator in accordance with opening of a control valve and effectively suppressing generation of a shock pressure at the time of opening of the control valve.

[0006] The hydraulic drive device according to the present application is provided in a construction machine including a movable element, which is driven by hydraulic pressure. The hydraulic drive device includes a hydraulic pump, a hydraulic actuator, a control valve, an operator, a pump pressure detector, an actuator holding pressure detector, an unloading operation valve, a target pressure estimation section, and an unloading operation command section. The hydraulic pump discharges hydraulic oil. The hydraulic actuator is coupled to the movable element and performs work for moving the movable element by receiving supply of the hydraulic oil discharged from the hydraulic pump. The control valve is interposed between the hydraulic pump and the hydraulic actuator and is capable of being opened in a manner that allows supply of the hydraulic oil from the hydraulic pump to the hydraulic actuator. The operator causes the control valve to be opened in accordance with an actuator operation for causing the hydraulic actuator to perform work. The pump pressure detector detects a pump pressure, which is a pressure of the hydraulic oil discharged from the hydraulic pump. The actuator holding pressure detector detects an actuator holding pressure, which is a pressure required for holding the hydraulic actuator in a stopped state against a load applied to the hydraulic actuator. The unloading valve is constituted by a pilot switching valve having a pilot port and is provided in an unloading line to be opened at an opening degree corresponding to a pilot pressure input to the pilot port, thereby causing the hydraulic oil to flow through the unloading line at a flow rate corresponding to the opening degree. The unloading line is configured to allow the hydraulic oil discharged from the hydraulic pump to bypass the control valve and the hydraulic actuator and directly return to a tank. The unloading operation valve is constituted by a solenoid valve capable of receiving input of an unloading operation command to operate in a manner that changes the pilot pressure input to the unloading valve in accordance with the unloading operation command. The target pressure estimation section estimates a target pressure of the pump pressure on the basis of the actuator holding pressure detected by the actuator holding pressure detector. The target pressure estimation section estimates the target pressure in a manner that the target pressure is a pressure equal to or higher than a minimum pressure required for the hydraulic actuator to perform work against the load and equal to or lower than a limit pressure set in advance. The unloading operation command section generates a command for causing the pump pressure detected by the pump pressure detector to follow the target pressure as the unloading operation command and inputs the command to the unloading operation valve. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 is a circuit diagram showing a hydraulic drive device of a construction machine according to an embodiment of the present application.

[0008] Figure 2is a block diagram showing a functional configuration of a controller included in the hydraulic drive device.

[0009] Figure 3 is a flowchart showing an operation control action performed by the controller.

[0010] Figure 4 is a graph showing an example of a time change of a cylinder speed, which is a speed of an action of a hydraulic cylinder in the hydraulic drive device, and an opening of the unloading valve operated by the controller.

[0011] Figure 5 is a graph showing an example of a time change of a pump pressure of the hydraulic drive device.

[0012] Figure 6 is a graph showing an example of a time change of the pump pressure and the like in a case where the unloading valve is suddenly closed in association with a cylinder operation. DETAILED DESCRIPTION

[0013] Hereinafter, a preferred embodiment of the present application will be described with reference to the accompanying drawings.

[0014] Figure 1 is a circuit diagram showing a hydraulic drive device of a construction machine to which an embodiment of the present application is applied. The hydraulic drive device is provided with a hydraulic pump 10, a hydraulic cylinder 20, a control valve 30, an operator 40, an unloading valve 50, an unloading operation valve 56, a plurality of sensors, and a controller 70.

[0015] The construction machine includes at least one movable element capable of being hydraulically driven. The construction machine is, for example, a hydraulic excavator, a hydraulic crane, a hydraulic dismantling machine. In a case where the construction machine is a hydraulic excavator, the at least one movable element includes a swing arm, a boom, and a bucket that constitute a work attachment, a track included in a lower traveling body to perform a traveling action, an upper swing body included in an upper swing body to swing with respect to the lower traveling body around a longitudinal axis, and the like.

[0016] The hydraulic pump 10 is driven by an engine mounted on the construction machine to eject working oil in a tank. The hydraulic pump 10 of the present embodiment is a variable displacement type hydraulic pump including a pump body whose displacement is variable, and an adjuster 11 for changing the displacement. The adjuster 11 operates the pump body so that the displacement of the pump body reaches a displacement corresponding to a displacement command signal when the adjuster 11 receives an input of the displacement command signal from the controller 70.

[0017] The hydraulic cylinder 20 is an example of the hydraulic actuator of the present application. The hydraulic cylinder 20 is connected to a specific movable element 18, and extends and contracts to cause the specific movable element 18 to move in the direction of extension and contraction when supplied with the working oil discharged from the hydraulic pump 10. The specific movable element 18 is selected from the at least one movable element. In the case where the construction machine is the hydraulic excavator, the hydraulic cylinder 20 is, for example, a boom cylinder that rotates the boom, a stick cylinder that rotates the stick, or a bucket cylinder that rotates the bucket.

[0018] The hydraulic actuator of the present application can also be an actuator other than the hydraulic cylinder, such as a hydraulic motor. In the case where the construction machine is the hydraulic excavator, the hydraulic motor is, for example, a swing motor that causes the upper swing body to swing, or a travel motor that causes the crawler belt to travel.

[0019] The hydraulic cylinder 20 includes a cylinder body 22, a piston 24, and a piston rod 26. The cylinder body 22 is formed in a cylindrical shape so as to enclose a cylinder chamber. The piston 24 is housed in the cylinder body 22 so as to divide the cylinder chamber into a head-side chamber 22h and a rod-side chamber 22r. The piston rod 26 extends from the piston 24 in a direction that penetrates the rod-side chamber 22r in the axial direction, protrudes to the outside of the cylinder body 22, and is connected to the movable element 18 that is a drive target. The hydraulic cylinder 20 discharges working oil from the rod-side chamber 22r and extends when the head-side chamber 22h is supplied with working oil, and discharges working oil from the head-side chamber 22h and contracts when the rod-side chamber 22r is supplied with working oil.

[0020] The control valve 30 is provided between the hydraulic pump 10 and the hydraulic cylinder 20 that is a hydraulic actuator. When the control valve 30 is closed, the supply of working oil from the hydraulic pump 10 to the hydraulic cylinder 20 is blocked. When the control valve 30 is opened with an appropriate opening area, working oil in a flow rate corresponding to the opening area is allowed to be supplied to the hydraulic cylinder 20.

[0021] The control valve 30 of the present embodiment is configured by a three-position directional switching valve of a pilot-operated type. Specifically, the control valve 30 has a first pilot port 32A and a second pilot port 32B that can each receive input of a pilot pressure.

[0022] When no pilot pressure is input to the first pilot port 32A and the second pilot port 32B, the control valve 30 maintains a neutral position 34N. That is, when the control valve 30 is closed, the hydraulic pump 10 and the hydraulic cylinder 20 are blocked from each other, that is, the supply of working oil from the hydraulic pump 10 to the hydraulic cylinder 20 is blocked.

[0023] When the first pilot port 36A is supplied with a pilot pressure, the control valve 30 is displaced from the neutral position 34N to a first drive position 34A by a stroke corresponding to the magnitude of the pilot pressure. That is, the control valve 30 is opened by an opening area corresponding to the stroke. Thus, the control valve 30 forms a first supply oil passage and a first return oil passage. The first supply oil passage allows the working oil ejected from the hydraulic pump 10 to be supplied to the head-side chamber 22h of the hydraulic cylinder 20 at a flow rate corresponding to the opening area. The first return oil passage allows the working oil discharged from the rod-side chamber 22r of the hydraulic cylinder 20 to return to the tank.

[0024] Conversely, when the second pilot port 36B is supplied with working oil, the control valve 30 is displaced from the neutral position 34N to a second drive position 34B by a stroke corresponding to the magnitude of the pilot pressure. That is, the control valve 30 is opened by an opening area corresponding to the stroke. Thus, the control valve 30 forms a second supply oil passage and a second return oil passage. The second supply oil passage allows the working oil ejected from the hydraulic pump 10 to be supplied to the rod-side chamber 22r of the hydraulic cylinder 20 at a flow rate corresponding to the opening area. The second return oil passage allows the working oil discharged from the head-side chamber 22h of the hydraulic cylinder 20 to return to the tank.

[0025] The operator 40 operates in a manner that accepts a cylinder operation to input a pilot pressure corresponding to the cylinder operation to the control valve 30. The cylinder operation is an actuator operation exerted on the operator 40 by an operator to cause the hydraulic cylinder 20 as the hydraulic actuator to act. The operator 40 causes the control valve 30 to open in correspondence to the cylinder operation exerted on the operator 40, so that the hydraulic cylinder 20 connected to the control valve 30 can operate.

[0026] Specifically, the operator 40 of the present embodiment has an operation lever 42 and a pilot valve 44. The operation lever 42 is selectively subjected to an operation to tilt the operation lever 42 in a first direction and an operation to tilt the operation lever 42 in a second direction opposite to the first direction as the cylinder operation. The pilot valve 44 has an inlet port and a pair of outlet ports. The inlet port is connected to a pilot pressure hydraulic source, for example Figure 1The pilot pump 15 is shown. The pair of outlet ports are connected to the first and second pilot ports 32A, 32B via first and second pilot lines 36A, 36B, respectively. The pilot valve 44 is linked to the operation lever 42 so as to perform an opening operation in conjunction with the movement of the operation lever 42. The pilot valve 44 opens in correspondence with the cylinder operation applied to the operation lever 42 to allow the pilot pressure to be input from the pilot pressure supply source to either of the first and second pilot ports 32A, 32B. The pilot pressure has a magnitude corresponding to that of the cylinder operation.

[0027] The unloading valve 50 is provided midway through an unloading line 51. The unloading line 51 is a line that allows the working oil ejected from the hydraulic pump 10 to bypass the control valve 30 and the hydraulic cylinder 20 to return directly to the tank.

[0028] The unloading valve 50 is a pilot-operated switching valve, i.e., a pilot switching valve, and has a flow rate adjustment function. Specifically, the unloading valve 50 has a single pilot port 52 connected to the pilot pump 15 and opens with an opening area corresponding to the magnitude of the pilot pressure input from the pilot pump 15 to the pilot port 52, so that the working oil ejected from the hydraulic pump 10 can be released to the tank through the unloading line 51 at a flow rate corresponding to the opening area. The unloading valve 50 of the present embodiment remains in a closed position 53 when no pilot pressure is input to the pilot port 52, completely blocking the unloading line 51. The unloading valve 50 displaces from the closed position 53 to an open position 54 with a stroke corresponding to the magnitude of the pilot pressure input to the pilot port 52 when the pilot pressure is input to the pilot port 52, and opens with an opening area corresponding to the stroke.

[0029] The unloading operation valve 56 is provided between the pilot pump 15 and the pilot port 52 and performs an opening and closing operation to change the pilot pressure input from the pilot pump 15 to the pilot port 52. The unloading operation valve 56 is constituted by a solenoid valve having a solenoid, and opens with an opening degree corresponding to an unloading operation command applied to the solenoid by the controller 70, thereby allowing a corresponding input corresponding to the unloading operation command to be input to the pilot port 52. The unloading operation command specifically refers to the exciting current flowing through the solenoid. The solenoid valve can be a solenoid proportional valve that opens with an opening degree proportional to the exciting current, or a solenoid inverse proportional valve that opens with a smaller opening degree as the exciting current increases.

[0030] The plurality of sensors detect information required for the controller 70 to perform operation control, generate electric signals (detection signals) containing the information, and input the signals to the controller 70. The plurality of sensors of the present embodiment include a pump pressure sensor 60, a head pressure sensor 63H, a rod pressure sensor 63R, a cylinder speed sensor 66, a first pilot pressure sensor 62A, and a second pilot pressure sensor 62B.

[0031] The pump pressure sensor 60 is a pump pressure detector that detects the pump pressure Pd of the hydraulic pump 10, that is, the pressure of the working oil discharged from the hydraulic pump 10.

[0032] The head pressure sensor 63H and the rod pressure sensor 63R detect the head pressure Ph and the rod pressure Pr of the hydraulic cylinder 20, respectively. The head pressure sensor 63H and the rod pressure sensor 63R can function as an actuator holding pressure detector that detects the actuator holding pressure Pah. The actuator holding pressure Pah is, in the present embodiment, a pressure for holding the hydraulic cylinder 20 in a stopped state against a load applied thereto, that is, a cylinder holding pressure.

[0033] The head pressure Ph is the pressure of the working oil in the head side chamber 22h, and is a pressure for holding the hydraulic cylinder 20 in a stopped state against a load applied in a direction in which the hydraulic cylinder 20 is contracted. The rod pressure Pr is the pressure of the working oil in the rod side chamber 22r, and is a pressure for holding the hydraulic cylinder 20 in a stopped state against a load applied in a direction in which the hydraulic cylinder 20 is extended. Therefore, when a load is applied to the hydraulic cylinder 20 in a direction in which the hydraulic cylinder 20 is driven to be extended, the rod pressure sensor 63R functions as the actuator holding pressure detector, and when a load is applied to the hydraulic cylinder 20 in a direction in which the hydraulic cylinder 20 is driven to be contracted, the head pressure sensor 63H functions as the actuator holding pressure detector.

[0034] The cylinder speed sensor 66 detects the cylinder speed Sc. The cylinder speed Sc is the speed at which the hydraulic cylinder 20 is extended and contracted, in other words, the relative movement speed of the piston rod 26 with respect to the cylinder body 22 in the axial direction. Therefore, the cylinder speed sensor 66 can function as an actuator operation detector for detecting whether or not the hydraulic cylinder 20, which corresponds to the hydraulic actuator in the present application, is operating.

[0035] The actuator operation detector of the present application is not limited to the above-described speed sensor. The actuator operation detector can be, for example, a combination of a position sensor that detects the axial position of the piston rod 26 with respect to the cylinder 22 and a differentiator that time-differentiates the axial position, or a combination of the acceleration of the piston rod 26 and an integrator that integrates the acceleration. In addition, in the case where the hydraulic actuator of the present application is a hydraulic motor, the actuator operation detector can be constituted by, for example, a combination of a rotary encoder that detects the rotational angle of the hydraulic motor and a differentiator that time-differentiates the detected rotational angle.

[0036] The first pilot pressure sensor 62A and the second pilot pressure sensor 62B correspond to the pilot pressures input from the operator 40 to the control valve 30 in association with the cylinder operation (actuator operation) detection, and function as actuator operation detectors. Specifically, the first pilot pressure sensor 62A detects an extension drive pilot pressure. This extension drive pilot pressure is the pilot pressure input from the operator 40 to the first pilot port 32A via the first pilot line 36A. The second pilot pressure sensor 62B detects a contraction drive pilot pressure. This contraction drive pilot pressure is the pilot pressure input from the operator 40 to the second pilot port 32B via the second pilot line 36B.

[0037] The controller 70 controls the pump pressure Pd of the hydraulic pump 10 by the operation of the unloading valve 50, and also controls the pump capacity of the hydraulic pump 10. Specifically, the control valve 70 has Figure 2 The target pressure estimation section 73, the unloading operation command section 76, and the pump capacity command section 78 shown in the drawing function as means for executing the above-described control.

[0038] The target pressure estimation section 73 estimates the target pressure Pdo of the pump pressure Pd. This target pressure Pdo is estimated on the basis of the actuator holding pressure Pah as described in detail later. Specifically, the greater the actuator holding pressure Pah, the greater the estimated target pressure Pdo.

[0039] The unloading operation command section 76 generates an unloading operation command on the basis of the target pressure Pdo, the actual pump pressure Pd detected by the pump pressure sensor 60, and the cylinder speed Sc detected by the cylinder speed sensor 66, and inputs the unloading operation command to the solenoid of the unloading operation valve 56. As a result, the pilot pressure input to the unloading valve 50 is changed in accordance with the unloading operation command, and the opening degree of the unloading valve 50 is adjusted to an opening degree corresponding to the magnitude of the pilot pressure.

[0040] The pump capacity command unit 78 generates a pump capacity command based on the pump pressure Pd and the pilot pressure detected by the first pilot pressure sensor 62A and the second pilot pressure sensor 26B, and inputs the pump capacity command to the regulator 11 of the hydraulic pump 10, thereby controlling the pump capacity of the hydraulic pump 10. In this embodiment, the pump capacity command unit 78 generates a pump capacity command for performing positive control and horsepower control as the pump capacity control. The positive control is a control that increases the capacity of the hydraulic pump 10 based on an increase in the pilot pressure detected by the first pilot pressure sensor 62A and the second pilot pressure sensor 62B, i.e., an increase in cylinder operation (actuator operation). The horsepower control is a control based on the engine's horsepower curve limit, which is the pump horsepower estimated based on the pump pressure Pd and the pump capacity. The pump horsepower is the horsepower required to drive the hydraulic pump 10.

[0041] Next, refer to Figure 3 Flowcharts and Figure 4 The graph illustrates the actual operational control actions performed by the controller 70 and the function of the devices accompanying these actions.

[0042] The controller 70 reads the detection signals generated by each of the plurality of sensors (step S10) and performs the following calculation control based on these detection signals.

[0043] (1) Determine the actuator holding pressure Pah (step S11)

[0044] When no cylinder operation (actuator operation) is performed, the pilot pressure detected by the first pilot pressure sensor 62A and the second pilot pressure sensor 62B is essentially 0, and the hydraulic cylinder 20 remains in a stopped state. At this time, the head pressure Ph and rod pressure Pr of the hydraulic cylinder 20 are detected by the head pressure sensor 63H and the rod pressure sensor 63R. The target pressure estimation unit 73 of the controller 70 determines the larger of the detected head pressure Ph and rod pressure Pr as the actuator holding pressure (cylinder holding pressure) Pah.

[0045] Specifically, in the case of the boom cylinder (hydraulic cylinder 20), the boom, stick, and bucket constituting the working attachment, as well as the object held by the bucket, are subjected to gravity. The head pressure Ph of the boom cylinder, which overcomes this neutrality and keeps the boom cylinder stationary, is greater than the rod pressure Pr of the boom cylinder. Therefore, in this case, the target pressure estimation unit 73 determines the head pressure Ph of the boom cylinder as the actuator holding pressure.

[0046] (2) Determine whether cylinder operation (actuator operation) has been performed (step S12)

[0047] The unloading operation command section 76 of the controller 70 determines whether or not the cylinder operation (actuator operation) is performed. This determination is performed based on whether or not the first pilot pressure sensor 62A and the second pilot pressure sensor 62B detect a pilot pressure. In a case where either of the first pilot pressure sensor 62A and the second pilot pressure sensor 62B detects a pilot pressure, i.e., detects the cylinder operation (step S12: YES), the processing of step S13 described later is performed. In a case where neither of the first pilot pressure sensor 62A and the second pilot pressure sensor 62B detects a pilot pressure (step S12: NO), the unloading operation command section 76 performs the processing of next step S18.

[0048] (3) Control in standby (step S18, step S20)

[0049] In a case where the cylinder operation (actuator operation) is not detected (step S12: NO), the control valve 30 is held in the neutral position 34N, i.e., is fully closed. In this neutral position 34N, the control valve 30 blocks the oil passage between the hydraulic pump 10 and the hydraulic cylinder 20 and the oil passage between the tank and the hydraulic cylinder 20, respectively, and holds the hydraulic cylinder 20 in a stopped state. The pump capacity command section 78 of the controller 70 inputs a capacity signal command for minimizing the pump capacity of the hydraulic pump 10 to the regulator 11. On the other hand, the unloading operation command section 76 of this controller 70 generates an unloading operation command for inputting a pilot pressure for fully opening or nearly fully opening the unloading valve 50 to the unloading valve 50 and inputs it to the unloading operation valve 56 (step S18, step S20). The opening operation of the unloading valve 50 described above suppresses the circuit pressure to the standby pressure Pwt that is nearly the minimum pressure, so that the load on the engine is minimized.

[0050] (4) Estimation of target pressure (step S13: YES, step S14)

[0051] In a case where the cylinder operation (actuator operation) is detected (step S12: YES), the target pressure estimation section determines whether or not the actual cylinder speed Sc detected by the cylinder speed sensor 66 is less than a predetermined operation determination speed Sco (step S13). The operation determination speed Sco is a speed set for the cylinder speed Sc for determining whether or not the hydraulic cylinder 20 has actually started to operate (perform work), and is a very small value as shown in the following expression. Figure 4

[0052] The target pressure estimation section 73 estimates the target pressure Pdo of the pump pressure Pd in a case where the cylinder speed Sc is less than the operation determination speed Sco (step S13: YES), i.e., in a case where it is considered that the hydraulic cylinder 20 has not performed work (step S14).

[0053] ​As a feature of the present embodiment, the target pressure estimating section 73 estimates the target pressure Pdo based on the holding pressure of the hydraulic cylinder 20, i.e., the actuator holding pressure Pah. When a load in the direction of contraction of the hydraulic cylinder 20 acts on the hydraulic cylinder 20, the actuator holding pressure Pah is the pressure for overcoming the load and holding the hydraulic cylinder 20 in a stopped state, i.e., the head pressure Ph detected by the head pressure sensor 63H. When a load in the direction of elongation of the hydraulic cylinder 20 acts on the hydraulic cylinder 20, the actuator holding pressure Pah is the pressure for overcoming the load and holding the hydraulic cylinder 20 in a stopped state, i.e., the rod pressure Pr detected by the rod pressure sensor 63R.

[0054] Specifically, the target pressure estimating section 73 adds the operation pressure ΔPop corresponding to the size of the pilot pressure detected by the first pilot pressure sensor 62A and the addition pressure ΔPad corresponding to the loss of working oil pressure from the hydraulic pump 10 to the hydraulic cylinder 20 to the actuator holding pressure Pah determined in step Sll, i.e., the holding pressure required for overcoming the load applied to the hydraulic cylinder 20 in the direction of elongation or contraction and holding the hydraulic cylinder 20 in a stopped state, thereby estimating the target pressure Pdo.

[0055] The actuator holding pressure Pah is included in the target pressure Pdo in order to raise the pump pressure Pd to the actuator holding pressure Pah. The operation pressure ΔPop is included in the target pressure Pdo in order to cause the pump pressure Pd to vary in correspondence with the size of the pilot pressure detected by the first pilot pressure sensor 62A. The addition pressure ΔPad includes the pressure loss at the control valve 30 and the pressure loss at each pipe, and is included in the target pressure Pdo in order to achieve a pump pressure Pd for overcoming the above pressure losses and reliably operating the hydraulic cylinder 20.

[0056] Specifically, as an example of the operation for setting the target pressure Pdo, an operation based on the following formula (1) is cited, for example.

[0057] Pdo = Pah + ΔPop + ΔPad... (1)

[0058] When a load in the direction in which the hydraulic cylinder 20 is contracted is applied to the hydraulic cylinder 20, the actuator holding pressure Pah corresponds to a pressure against which the load is overcome and by which the hydraulic cylinder 20 is held in a stopped state, i.e., the head pressure Ph detected by the head pressure sensor 63H. When a load in the direction in which the hydraulic cylinder 20 is elongated is applied to the hydraulic cylinder 20, the actuator holding pressure Pah corresponds to a pressure against which the load is overcome and by which the hydraulic cylinder 20 is held in a stopped state, i.e., the rod pressure Pr detected by the rod pressure sensor 63R. The operation pressure ΔPop corresponds to the magnitude of the pilot pressure detected by the first pilot pressure sensor 62A. The added pressure ΔPad is set based on the pressure loss. The added pressure ΔPad has a value greater than the pressure loss and is set to a value such that the target pressure Pdo including the added pressure ΔPad is below the limit pressure Pdr set in advance.

[0059] The added pressure ΔPad is preferably set to a value that takes into account variation in the pressure loss. The pressure loss varies depending on the state of the working oil, such as temperature that affects the viscosity of the working oil, the kind of working oil, and the flow rate. The added pressure ΔPad can be set to a fixed value, such as a value slightly greater than the maximum value estimated for the pressure loss, or can be set to a variable that varies depending on the temperature of the working oil (or the air temperature) or the flow rate.

[0060] The limit pressure Pdr is an upper limit pressure of the target pressure Pdo set to be able to suppress the impact pressure. The limit pressure Pdr is preferably set taking into account the momentary increase in the pump pressure.

[0061] The operation of the target pressure Pdo is not limited to the case where it is performed based on the above-described equation (1). The operation can also be performed based on another mathematical equation. Specifically, the operation method can be appropriately set within a range where the target pressure Pdo is a pressure above a minimum required pressure and satisfies the condition of being below the limit pressure Pdr. The minimum required pressure is a minimum pressure required for the hydraulic cylinder 20 to act against the load.

[0062] (5) Generation and input of unloading operation command (steps S16, S20)

[0063] The unloading operation command section 76 generates the following unloading operation command depending on whether or not the hydraulic cylinder 20 is operating, i.e., depending on the magnitude relationship between the cylinder speed Sc and the operation determination speed Sco in the present embodiment.

[0064] In a stage where the cylinder speed Sc is smaller than the operation determination speed Sco (step S13: YES), that is, in a stage where it is considered that the hydraulic cylinder 20 has not substantially started to operate, the unloading operation command section 76 generates an unloading operation command for causing the actual pump pressure Pd detected by the pump pressure sensor 60 to follow the target pressure Pdo (step S16). Specifically, the unloading operation command section 76 of the present embodiment calculates a deviation δPd (= Pd - Pdo) of the pump pressure Pd from the target pressure Pdo, and generates an unloading operation command for performing feedback control (for example, PID control) of the pump pressure Pd based on the deviation δPd.

[0065] The unloading operation command section 76 inputs the above-mentioned generated unloading operation command to the unloading operation valve 56 (step S20), whereby a pilot pressure corresponding to the unloading operation command is input to the pilot port 52 of the unloading valve 50. The unloading valve 50 opens with an opening area corresponding to the pilot pressure, whereby the working oil ejected from the hydraulic pump 10 is allowed to be directly released to the tank in a flow rate corresponding to the opening area.

[0066] Figure 5 is an example of a temporal change of the pump pressure Pd under the above-mentioned control. In this example, the cylinder operation (actuator operation) is not detected before time t1 (step S12: NO), whereby the pump pressure Pd is maintained at the standby pressure Pwt. The cylinder operation (actuator operation) is detected after time t1 (step S12: YES), and the controller 70 starts to perform control for causing the pump pressure Pd to follow the target pressure Pdo.

[0067] The target pressure Pdo is estimated by adding an operation pressure ΔPop and an addition pressure ΔPad to the actuator holding pressure Pah. The actuator holding pressure Pah is the head pressure Ph detected by the head pressure sensor 63H for overcoming a load acting on the hydraulic cylinder 20 in a direction in which the hydraulic cylinder 20 is contracted and for holding the hydraulic cylinder 20 in a stopped state when the load in the direction in which the hydraulic cylinder 20 is contracted acts on the hydraulic cylinder 20, and is the rod pressure Pr detected by the rod pressure sensor 63R for overcoming a load acting on the hydraulic cylinder 20 in a direction in which the hydraulic cylinder 20 is elongated and for holding the hydraulic cylinder 20 in a stopped state when the load in the direction in which the hydraulic cylinder 20 is elongated acts on the hydraulic cylinder 20. The operation pressure ΔPop corresponds to the magnitude of the pilot pressure detected by the first pilot pressure sensor 62A. The addition pressure ΔPad is a pressure corresponding to the pressure loss, and is set in consideration of the limit pressure Pdr. Control based on the target pressure Pdo thus estimated enables the pump pressure Pd to be higher than the actuator holding pressure Pah.

[0068] There is a time lag from when the control valve 30 is opened to when the hydraulic cylinder 20 actually starts to operate, and therefore, the hydraulic cylinder 20 will be kept in a state of being stationary while the pump pressure Pd rises.

[0069] The unloading operation command unit 76 generates an unloading operation command to make the actual pump pressure Pd follow the target pressure Pdo estimated by the target pressure estimation unit 73 of the controller 70, and inputs it to the unloading operation valve 56. The setting of the summed pressure ΔPad prevents the pump pressure Pd from exceeding the limiting pressure Pdr, thereby suppressing the generation of shock pressure. The limiting pressure Pdr is set to prevent the requested torque increase rate from exceeding the output torque increase rate. The output torque increase rate is the increase rate of the torque that the engine can output, and the requested torque increase rate is the increase rate of the engine torque requested to momentarily increase the pump pressure Pd. This limiting pressure Pdr setting effectively suppresses the sudden and rapid opening of the control valve 30 when the hydraulic pump 20 is stationary, which would cause a sharp rise in the pump pressure Pd, thus effectively suppressing the generation of shock pressure.

[0070] When the hydraulic pump 20 starts to operate, the pump pressure Pd decreases, further reducing the possibility of generating impact pressure.

[0071] The hydraulic cylinder 20 actually begins to move and its cylinder speed Sc reaches... Figure 4 The time T1 at which the working speed Sco is determined is the start-up time (step S13: no). Regardless of the actual pump pressure Pd, the unloading operation command unit 76 generates an unloading operation command to fully close the unloading valve 50 and inputs it to the unloading operation valve 56 (steps S17, S20). Therefore, the working oil ejected from the hydraulic pump 10 is not released through the unloading pipeline 51, but is supplied to the hydraulic cylinder 20. This increases the flow rate of the working oil supplied from the hydraulic pump 10 to the hydraulic cylinder 20 and ensures a higher cylinder speed Sco.

[0072] The effects described above are achieved through comparison with Figure 6 The control performed in the comparative example is illustrated by comparison. The control performed in this comparative example involves immediately closing the unloading valve at the actuator operation time T2 to ensure the flow rate of working oil supplied to the hydraulic actuator. The actuator operation time T2 is the moment when the actuator operation is applied. Thus, after the actuator operation is applied but before the hydraulic actuator begins to move, the unloading valve changes from being fully open to being fully closed, i.e., the opening of the unloading valve decreases sharply and significantly, thereby generating a large impact pressure Psg in the pump. Specifically, the impact pressure Psg is expressed by the following equation (2).

[0073] Psg=ρ×c×ΔV…(2)

[0074] In equation (2) above, ρ is the density of the working oil, c is the wave propagation speed, and v is the change in the flow rate of the working oil.

[0075] likeFigure 6 As shown, the aforementioned surge in pressure is accompanied by a sharp increase in pump flow and torque, which can temporarily and significantly reduce pump speed. Reducing the pump capacity of a variable-capacity hydraulic pump as the pump pressure rises is not necessarily effective as a method to suppress this surge in pump torque. This is because there is a significant delay between the controller changing the output to the hydraulic pump's capacity command signal and the actual reduction in pump capacity and torque.

[0076] And through Figure 3 and Figure 4 The control shown can directly and effectively suppress the generation of the shock pressure, i.e., the surge in pump pressure Pd. This is because, in this control, the opening area of ​​the unloading valve 50 is operated during the period from when the control valve 30 is opened until the hydraulic pump 20 actually starts to operate, so that the actual pump pressure Pd follows the target pressure Pdo estimated based on the actuator holding pressure Pah (head pressure Ph or rod pressure Pr), the operating pressure, and the pressure loss.

[0077] Furthermore, according to the operation described above, the unloading valve 50 is fully closed at the moment T1 when it is believed that the hydraulic cylinder 20 has actually started, thereby ensuring that the hydraulic cylinder 20 has a high driving speed. In addition, the unloading valve 50 is fully closed at the starting moment T1, unlike the comparative example described above where the unloading valve 50 is fully closed at the moment the control valve 30 is opened, thus reducing the likelihood of generating impact pressure. This is because, as... Figure 6 As shown, operating the lever increases the pump's output and opens the control valve, causing the pump pressure Pd to increase. The opening of the unloading valve 50 prevents the pump pressure Pd from rising above the limit pressure.

[0078] Furthermore, the pump pressure Pd rises at least to the actuator holding pressure during the phase when the operating lever is operated, thus enabling it to quickly follow the pressure used to start the hydraulic cylinder 20, thereby improving responsiveness.

[0079] In addition, in the case where the hydraulic pump is configured by a variable displacement hydraulic pump so as to be able to control the pump displacement, as in the hydraulic pump 10, the control is performed by a combination of the unloading valve 50 configured by a pilot switching valve having the pilot port 52, the unloading operation valve 56 configured by a solenoid valve that changes the pilot pressure input to the pilot port 52, and has the advantage of having a higher degree of freedom of pump displacement control that can be applied compared to, for example, a device that performs load sensing control. This is because the load sensing control is premised on inputting a load sensing pressure to the unloading valve as a pilot pressure. In the device of the embodiment, the pump pressure control that effectively suppresses the impact pressure is performed by operating the unloading valve 50 by the unloading operation valve 56, and the positive control based on the pilot pressure detected by the first pilot pressure sensor 6A and the second pilot pressure sensor 62B (i.e., based on the size of the cylinder operation) and the horsepower control based on the pump pressure Pd are performed.

[0080] The present application is not limited to the above-described embodiments and modifications thereof. The present application includes, for example, the following modes.

[0081] (A) Control Valve

[0082] The control valve of the present application is only required to perform the opening operation in accordance with the actuator operation applied to the operator, and is not limited to Figure 1 The control valve 30 illustrated in FIG. 1 is a three-way pilot switching valve. The control valve of the present application can also be, for example, a two-way switching valve, and can also be a solenoid switching valve.

[0083] (B) Operator

[0084] The operator of the present application is only required to receive the actuator operation by the operator and cause the control valve to perform the opening operation in accordance with the actuator operation. The operator of the present application can also be, for example, a combination of an electric level device, a solenoid valve, and a pilot pressure command section. The electric level device converts the actuator operation applied to the electric level device into an operation signal as an electric signal. The solenoid valve performs the opening and closing operation to change the pilot pressure input to the control valve. The pilot pressure command section inputs the pilot pressure command corresponding to the operation signal to the solenoid valve, and causes the control valve to perform the opening operation corresponding to the operation signal.

[0085] (C) Unloading Operation Command Section

[0086] The unloading operation command section of the present application only needs to generate an unloading operation command for causing the actual pump pressure to follow the target pressure, and the specific generation method is not limited. That is, the unloading operation command section of the present application is not limited to the method of calculating the unloading operation command for feedback control based on the deviation δPd of the pump pressure Pd from the target pressure Pd as in the unloading operation command section 76. For example, the unloading operation command section of the present application can also store a chart prepared for determining the relationship between the input pump pressure and actuator holding pressure and the unloading operation command that should be output, and determine the unloading operation command using the chart. That is, sequential control can also be performed.

[0087] In the present application, the actuator operation detector for detecting the operation of the actuator and the control for fully closing the unloading valve based on the detection thereof are not necessary. For example, the unloading operation command section of the present application can also continue to generate an unloading operation command for causing the actual pump pressure to follow the actuator holding pressure after the actuator is operated.

[0088] (D) Regarding Pump Capacity Control

[0089] In the present application, the pump capacity control is not necessary. Therefore, the hydraulic pump of the present application is not limited to the variable capacity type hydraulic pump as in the hydraulic pump 10, and can also be a fixed capacity type hydraulic pump.

[0090] As described above, the present application provides a hydraulic drive device provided in a construction machine, which can reliably start a hydraulic actuator according to the opening of a control valve, and can effectively suppress the generation of impact pressure when the control valve is opened.

[0091] The hydraulic drive device according to the present application is provided in a construction machine including a movable element, and drives the movable element using hydraulic pressure. The hydraulic drive device includes a hydraulic pump, a hydraulic actuator, a control valve, an operator, a pump pressure detector, an actuator holding pressure detector, an unloading operation valve, a target pressure estimation section, and an unloading operation command section. The hydraulic pump ejects hydraulic oil. The hydraulic actuator is coupled to the movable element, and performs work for moving the movable element by receiving supply of the hydraulic oil ejected from the hydraulic pump. The control valve is interposed between the hydraulic pump and the hydraulic actuator, and is capable of being opened in a manner that allows supply of the hydraulic oil from the hydraulic pump to the hydraulic actuator. The operator causes the control valve to be opened in accordance with an actuator operation for causing the hydraulic actuator to perform work by receiving the actuator operation. The pump pressure detector detects a pressure of the hydraulic oil ejected from the hydraulic pump, i.e., a pump pressure. The actuator holding pressure detector detects an actuator holding pressure, which is a pressure required for holding the hydraulic actuator in a stopped state against a load applied to the hydraulic actuator. The unloading valve is constituted by a pilot switching valve having a pilot port, and is provided in an unloading line to be opened at an opening degree corresponding to a pilot pressure input to the pilot port, thereby causing the hydraulic oil to flow through the unloading line at a flow rate corresponding to the opening degree. The unloading line is configured to allow the hydraulic oil ejected from the hydraulic pump to bypass the control valve and the hydraulic actuator and directly return to a tank. The unloading operation valve is constituted by a solenoid valve capable of receiving input of an unloading operation command, and operates in a manner that changes the pilot pressure input to the unloading valve in accordance with the unloading operation command. The target pressure estimation section estimates a target pressure of the pump pressure based on the actuator holding pressure detected by the actuator holding pressure detector. The target pressure estimation section estimates the target pressure in a manner that the target pressure is a pressure equal to or higher than a minimum pressure required for the hydraulic actuator to perform work against the load and lower than a limit pressure set in advance. The unloading operation command section generates a command for causing the pump pressure detected by the pump pressure detector to follow the target pressure as the unloading operation command, and inputs the command to the unloading operation valve.

[0092] According to the device, the estimation of the target pressure and the control of the pump pressure based on the target pressure can reliably ensure the operation of the hydraulic actuator and can suppress the generation of the impact pressure. That is, the pump pressure is suppressed from sharply rising in conjunction with the sharp opening of the control valve. This is because the target pressure is estimated based on the actuator holding pressure in a manner that the target pressure is above the minimum pressure required for the hydraulic actuator to operate against the load and is below a predetermined limit pressure, and the pump pressure is controlled by the operation of the unloading valve in a manner that the pump pressure follows the target pressure thus estimated. Specifically, in the device, the target pressure estimation section estimates the target pressure based on the actuator holding pressure, and the unloading operation command section generates an unloading operation command for causing the pump pressure to follow the target pressure and inputs the unloading operation command to the unloading operation valve. Thus, the pump pressure required for the hydraulic actuator to reliably operate at the time of opening of the control valve can be ensured, and even if the control valve is suddenly and sharply opened in a state where the hydraulic actuator is at rest, the sharp rise of the pump pressure can be suppressed, and the generation of the impact pressure can be suppressed.

[0093] Specifically, it is desirable that the target pressure estimation section estimate the target pressure in a manner that the target pressure includes the actuator holding pressure and an operation pressure corresponding to the size of the actuator operation. The target pressure including the actuator holding pressure can cause the pump pressure to promptly follow a pressure above the minimum pressure required for the hydraulic actuator to reliably operate at the time of opening of the control valve. Further, the target pressure includes the operation pressure in addition to the actuator holding pressure, and thus the responsiveness of the operation of the actuator corresponding to the actuator operation can be ensured.

[0094] It is desirable that the target pressure estimation section estimate the target pressure in a manner that the target pressure includes the actuator holding pressure and an added pressure set to a value above the pressure loss from the hydraulic pump to the hydraulic actuator. The target pressure estimation section causes the target pressure to include not only the actuator holding pressure but also the added pressure, and thus the control for improving the responsiveness taking into account the pressure loss as a cause of deterioration of the responsiveness can be performed by a simple calculation.

[0095] It is desirable that the hydraulic drive device further includes an actuator operation detector that detects operation of the hydraulic actuator, and the unloading operation command section inputs, as the unloading operation command to the unloading operation valve, a command to make the unloading valve fully closed at the timing at which operation of the hydraulic actuator is detected regardless of the pump pressure. Thus, the working oil released through the unloading line before the hydraulic actuator starts to operate is supplied to the hydraulic actuator, so that the speed of operation of the hydraulic actuator is increased. Also, at the timing at which actual operation of the hydraulic actuator is detected, even if the unloading valve is made fully closed, a sudden rise in the impact pressure, i.e., the pump pressure, is unlikely to occur. This is because, before the start timing Tl, the opening area of the unloading valve is reduced to some extent, and actual operation of the hydraulic actuator (compared with when the hydraulic actuator is at rest) can moderate compression of the working oil in the hydraulic actuator.

[0096] The pump pressure control in the hydraulic drive device is performed based on a combination of the unloading valve composed of a pilot switching valve and a pilot operation valve that changes the pilot pressure input to the unloading valve, so that even if the unloading valve is used, the degree of freedom of pump capacity control is high. Specifically, when the hydraulic pump is a variable capacity type hydraulic pump configured so that the capacity of the hydraulic pump, i.e., the pump capacity, is changed according to a capacity command signal input to the hydraulic pump, i.e., when the pump capacity can be controlled, unloading control and pump capacity control can be performed independently of each other. In this regard, the hydraulic drive device is different from a device that performs so-called load sensing control premised on inputting a load-induced pressure as a pilot pressure to an unloading valve. For example, it is desirable that the hydraulic drive device further includes an actuator operation detector that detects the magnitude of the actuator operation applied to the operator, and a pump capacity command section that generates and inputs a pump capacity command that increases the pump capacity of the hydraulic pump as the actuator operation increases, so that both the unloading control that suppresses a sudden rise in the pump pressure as described above and pump capacity control based on the actuator operation, i.e., so-called positive control, can be performed.

Claims

1. A hydraulic drive device for engineering machinery, installed in engineering machinery including movable elements, wherein the movable elements are driven by hydraulic pressure, characterized in that... include: The hydraulic pump sprays out working oil; A hydraulic actuator, connected to the movable element, performs the work of actuating the movable element by receiving a supply of working oil injected from the hydraulic pump. A control valve, located between the hydraulic pump and the hydraulic actuator, is capable of opening in a manner that allows working oil to be supplied from the hydraulic pump to the hydraulic actuator; The actuator, by receiving actuator operation for actuating the hydraulic actuator, causes the control valve to open according to the actuator operation. Pump pressure detector, which detects the pressure of the working oil ejected from the hydraulic pump, i.e., the pump pressure; An actuator holding pressure detector detects the actuator holding pressure, which is the pressure required to keep the hydraulic actuator in a stopped state against the load applied to it. The unloading valve is composed of a pilot switching valve with a pilot port, which is set in the unloading pipeline that allows the working oil injected from the hydraulic pump to bypass the control valve and the hydraulic actuator and return directly to the housing. The valve is opened with an opening degree corresponding to the pilot pressure input to the pilot port, so that the working oil flows through the unloading pipeline at a flow rate corresponding to the opening degree. The unloading operating valve is composed of a solenoid valve capable of accepting an unloading operation command input, and operates in such a way that the pilot pressure input to the unloading valve changes according to the unloading operation command; The target pressure estimation unit estimates the target pressure of the pump based on the actuator holding pressure detected by the actuator holding pressure detector, such that the target pressure is above the minimum pressure required for the hydraulic actuator to overcome the load and below a preset limit pressure; and... The unloading operation command unit generates an instruction to make the pump pressure detected by the pump pressure detector follow the target pressure as the unloading operation command, and inputs it to the unloading operation valve.

2. The hydraulic drive device for engineering machinery as described in claim 1, characterized in that, The target pressure estimation unit estimates the target pressure in a manner that includes the actuator holding pressure and the operating pressure, the operating pressure corresponding to the magnitude of the actuator operation.

3. The hydraulic drive device for engineering machinery as described in claim 1, characterized in that, The target pressure estimation unit estimates the target pressure in such a way that the target pressure includes the actuator holding pressure and the added pressure, the added pressure corresponding to the pressure loss from the hydraulic pump to the hydraulic actuator.

4. The hydraulic drive device for engineering machinery as described in any one of claims 1 to 3, characterized in that... Also includes: Actuator operation detector, which detects the operation of the hydraulic actuator. When the unloading operation command unit detects the operation of the hydraulic actuator, regardless of the pump pressure, it inputs a command to fully close the unloading valve as the unloading operation command into the unloading operation valve.

5. The hydraulic drive device for engineering machinery as described in any one of claims 1 to 3, characterized in that, The hydraulic pump is a variable capacity hydraulic pump, configured such that its capacity, or pump volume, varies according to the capacity command signal input to the hydraulic pump. The hydraulic drive device also includes: An actuator operation detector detects the magnitude of the actuator operation applied to the actuator; and... The pump capacity command unit generates a pump capacity command that increases the pump capacity of the hydraulic pump as the operation of the actuator increases, and inputs it into the hydraulic pump.

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