Hydraulic drive device

Abstract

An object of the present invention is to provide a hydraulic drive system that can accurately estimate a deterioration state of an on / off valve that opens and closes a hydraulic line that connects a hydraulic pump to an actuator. To this end, a controller computes a first valve-opening lag time from output of a first valve opening command signal (valve opening command value) instructing a first on / off valve to open to opening of the first on / off valve, and computes a first valve-closing lag time from output of a first valve closing command signal (valve closing command value) instructing the first on / off valve to close to closing of the first on / off valve. The controller determines a deterioration state of the first on / off valve on the basis of the first valve-opening lag time and the first valve-closing lag time.

Description

Technical Field

[0001] The present invention relates to a hydraulic drive system mounted in a work machine such as a hydraulic excavator.Background Art

[0002] In a system requiring a plurality of hydraulic on / off valves for driving one actuator, if the on / off valve that has failed cannot be identified, increase in the maintenance cost due to replacement of even the on / off valve that is not required to be replaced occurs.

[0003] To address this problem, in a work machine described in Patent Document 1, a command to open or close a valve is input to all mounted on / off valves and whether or not the on / off valve is stuck is determined on the basis of the difference between the inlet port pressure and the outlet port pressure of the on / off valve, and the on / off valve that is stuck is identified.

[0004] However, in a state in which the on / off valve is stuck, a problem arises that driving of the actuator is limited or driving of the actuator is impossible. Thus, it is desired that the lifetime of the on / off valve can be predicted before the on / off valve fails due to being stuck or the like.

[0005] To address this issue, in a hydraulic drive system of a work machine described in Patent Document 2, the lifetime of an on / off valve is predicted from the number of times of opening and closing and the use time concerning the on / off valve, and an estimated load (product of the differential pressure across the on / off valve and an estimated passing flow rate) on the on / off valve.Prior Art DocumentPatent Documents

[0006] Patent Document 1: JP-6616675-B Patent Document 2: JP-6902508-B Summary of the InventionProblem to be Solved by the Invention

[0007] However, in the hydraulic drive system of the work machine described in Patent Document 2, the individual difference of the on / off valve is not considered in predicting the lifetime, and thus the prediction accuracy varies on each on / off valve basis. Therefore, in order to execute replacement before each on / off valve fails in a system including a plurality of on / off valves, the timing of the replacement is required to be set to a timing earlier than the end of the predicted lifetime, and increase in the maintenance cost occurs due to replacement of even the on / off valve that has not reached the lifetime limit.

[0008] The present invention has been made in view of the above-described problem, and an object thereof is to provide a hydraulic drive system that can accurately estimate a deterioration state of an on / off valve that opens and closes a hydraulic line that connects a hydraulic pump to an actuator.Means for Solving the Problem

[0009] In order to achieve the above-described object, the present invention provides a hydraulic drive system including a first hydraulic pump having two input / output ports, an actuator, a first hydraulic line that connects one of the two input / output ports to one input / output port of the actuator, a second hydraulic line that connects another of the two input / output ports to another input / output port of the actuator, a first on / off valve that connects or disconnects the first hydraulic line and the second hydraulic line, an operation device that instructs the actuator to operate, and a controller that controls the first on / off valve in response to an operation signal input from the operation device. The controller is configured to compute a first valve-opening lag time from output of a first valve opening command signal instructing the first on / off valve to open to opening of the first on / off valve, and compute a first valve-closing lag time from output of a first valve closing command signal instructing the first on / off valve to close to closing of the first on / off valve, and determine a deterioration state of the first on / off valve on the basis of the first valve-opening lag time and the first valve-closing lag time.Advantages of the Invention

[0010] According to the present invention, the deterioration state of the on / off valve that opens and closes the hydraulic line that connects the hydraulic pump to the actuator can be accurately estimated. Thus, by replacing, before failure, only the on / off valve with a high probability of failure, downtime of the work machine can be shortened and the maintenance cost of the work machine can be reduced.Brief Description of the Drawings

[0011] [Fig. 1] Fig. 1 is an external view of a hydraulic excavator in a first embodiment of the present invention. [Fig. 2] Fig. 2 is a hydraulic circuit diagram of a hydraulic drive system in the first embodiment of the present invention. [Fig. 3] Fig. 3 is a diagram depicting clock time history data on a solenoid valve command value and an output pressure of a solenoid valve (operation pressure) when an on / off valve is opened. [Fig. 4] Fig. 4 is a diagram depicting processing relating to computation of a valve-opening lag time by a controller in the first embodiment of the present invention. [Fig. 5] Fig. 5 is a diagram depicting clock time history data on the solenoid valve command value and the output pressure of the solenoid valve (operation pressure) when the on / off valve is closed. [Fig. 6] Fig. 6 is a diagram depicting processing relating to computation of a valve-closing lag time by the controller in the first embodiment of the present invention. [Fig. 7] Fig. 7 is a diagram depicting the clock time history data on the solenoid valve command value and the output pressure of the solenoid valve (operation pressure) when the on / off valve is opened with comparison between the data at the time of shipment of the hydraulic excavator or immediately after replacement of a component incorporated in the on / off valve and the data after deterioration over time. [Fig. 8] Fig. 8 is a diagram depicting the clock time history data on the solenoid valve command value and the output pressure of the solenoid valve (operation pressure) when the on / off valve is closed with comparison between the data at the time of shipment of the hydraulic excavator or immediately after replacement of a component incorporated in the on / off valve and the data after deterioration over time. [Fig. 9] Fig. 9 is a flowchart depicting processing executed by the controller in the first embodiment of the present invention. [Fig. 10] Fig. 10 is a hydraulic circuit diagram of the hydraulic drive system in a second embodiment of the present invention. [Fig. 11] Fig. 11 is a diagram depicting an internal configuration of an on / off valve of an open circuit in the second embodiment of the present invention. [Fig. 12] Fig. 12 is a flowchart depicting processing executed by the controller in the second embodiment of the present invention. Modes for Carrying Out the Invention

[0012] Embodiments of the present invention are described below with reference to the drawings. In these embodiments, the present invention is applied to a hydraulic drive system mounted in a hydraulic excavator. However, the present invention can be applied also to a hydraulic drive system mounted in another work machine.[First Embodiment]

[0013] Fig. 1 is an external view of a hydraulic excavator in a first embodiment. A hydraulic excavator 100 includes a track structure 101 and a swing structure 102 attached onto the track structure 101. The machine body of the hydraulic excavator 100 is composed of the track structure 101 and the swing structure 102.

[0014] The track structure 101 has crawlers disposed on the left and right sides and left and right travelling motors 10a (only the left side is depicted) that are hydraulic actuators and give travelling power to the left and right crawlers. The swing structure 102 is allowed to swing relative to the track structure 101 by a bearing mechanism (not depicted) interposed between the track structure 101 and the swing structure 102 and a swing motor (not depicted) that is a hydraulic actuator.

[0015] The swing structure 102 has a main frame 105 as a support structure. A work device 103 is attached to a front portion of the main frame 105. A counterweight 108 is mounted on a rear portion of the main frame 105. A cab 104 is mounted on a left front portion of the main frame 105. An engine (not depicted) that is a prime mover, a hydraulic pump 1a (depicted in Fig. 2) driven by the engine, and the like are housed on the front side of the counterweight 108.

[0016] In the work device 103, a boom 111, an arm 112, and a bucket 113 are joined by a link mechanism, and each make rotational motion around a link shaft. This allows the work device 103 to execute work such as excavation. The work device 103 includes a boom cylinder 7a, an arm cylinder 7b, and a bucket cylinder 7c as hydraulic actuators that cause the rotational motion of the boom 111, the arm 112, and the bucket 113.

[0017] Fig. 2 is a hydraulic circuit diagram of a hydraulic drive system mounted in the hydraulic excavator 100. A hydraulic drive system 200 includes the hydraulic pump 1a on the double delivery side, an actuator 5ab that is a single-rod hydraulic cylinder, an on / off valve 25a, an operation device 2, pressure sensors 10a1, 10a2, 10a3, and 10a4, a controller 20, and a recording device 5. In Fig. 2, the boom cylinder 7a, the arm cylinder 7b, and the bucket cylinder 7c depicted in Fig. 1 are represented by the actuator 5ab, and depiction of a part relating to driving of the other hydraulic actuators is omitted.

[0018] One input / output port of the hydraulic pump 1a is connected to one input / output port of the actuator 5ab by a hydraulic line 61. The other input port of the hydraulic pump 1a is connected to the other input / output port of the actuator 5ab by a hydraulic line 62. The on / off valve 25a connects or disconnects the hydraulic lines 61 and 62. The hydraulic pump 1a, the actuator 5ab, the hydraulic lines 61 and 62, and the on / off valve 25a form a closed circuit 60.

[0019] The on / off valve 25a has valve elements 53a1 and 53a2, a solenoid valve 25a1, filters 50a1, 50a2, 50a3, and 50a4, check valves 51a1, 51a2, 51a3, and 51a4, and a pressure sensor 52a. The input sides of the check valves 51a1 and 51a2 are connected to the front and the back of the valve element 53a1 through the filters 50a1 and 50a2. The input sides of the check valves 51a3 and 51a4 are connected to the front and the back of the valve element 53a2 through the filters 50a3 and 50a4. The filters 50a1 to 50a4 remove foreign matters in a hydraulic fluid that flows into the check valves 51a1 to 51a4.

[0020] The output sides of the check valves 51a1 to 51a4 are connected to one input port of the solenoid valve 25a1. The other input port of the solenoid valve 25a1 is connected to a tank 4. A highest pressure Pa of the hydraulic lines 61 and 62 is input to the one input port of the solenoid valve 25a1 through the check valve 51a1 to 51a4. A drain pressure Po (pressure of the hydraulic fluid discharged to the tank 4) is input to the other input port of the solenoid valve 25a1. An output port of the solenoid valve 25a1 is connected to spring chambers 55a1 and 55a2 of the valve elements 53a1 and 53a2. Springs 25a21 and 25a22 that apply a force in a pressing-down direction to the valve elements 53a1 and 53a2 are disposed in the spring chambers 55a1 and 55a2.

[0021] The solenoid valve 25a1 can be switched to a position 25a3 to introduce the drain pressure Po to the spring chambers 55a1 and 55a2 and a position 25a4 to introduce the highest pressure Pa to the spring chambers 55a1 and 55a2. The solenoid valve 25a1 is connected to the controller 20 through an electrical wiring line such that an electrical signal from the controller 20 can be input thereto. When a valve opening command signal for the on / off valve 25a is input from the controller 20 to the solenoid valve 25a1, the solenoid valve 25a1 is switched from the position 25a4 to the position 25a3. Due to this, the pressure in the spring chambers 55a1 and 55a2 lowers to the drain pressure Po. Thus, the valve elements 53a1 and 53a2 are pressed up, and the hydraulic lines 61 and 62 are connected.

[0022] When a valve closing command signal for the on / off valve 25a is input from the controller 20 to the solenoid valve 25a1, the solenoid valve 25a1 is switched from the position 25a3 to the position 25a4. Due to this, the pressure in the spring chambers 55a1 and 55a2 rises to the highest pressure Pa. Thus, the valve elements 53a1 and 53a2 are pressed down, and the hydraulic lines 61 and 62 are disconnected. At this time, the hydraulic fluid passes through only the filter disposed on the upstream side of the check valve that allows the hydraulic fluid at the highest pressure Pa to pass therethrough among the check valves 51a1 to 51a4. Thus, if clogging occurs in the filter that allows the hydraulic fluid at the highest pressure Pa to pass therethrough, a lag time from the output of the valve closing command signal to closing of the on / off valve 25a (valve-closing lag time TB) becomes long. On the other hand, when the solenoid valve 25a1 has deteriorated, both the valve-closing lag time and a lag time from the output of the valve opening command signal to opening of the on / off valve 25a (valve-opening lag time TA) become long. Further, the valve-opening lag time TA and the valve-closing lag time TB change also depending on the temperature of the hydraulic fluid that circulates in the closed circuit 60.

[0023] The pressure sensors 10a1 and 10a2 are disposed on the hydraulic line 61 in order to sense the pressure across the valve element 53a1 (pressures Pa1 and Pa2), and are connected to the recording device 5 through an electrical wiring line. The pressure sensors 10a3 and 10a4 are disposed on the hydraulic line 62 in order to sense the pressure across the valve element 53a2 (pressures Pa3 and Pa4), and are connected to the recording device 5 through an electrical wiring line. The pressure sensor 52a is disposed to sense the output pressure of the solenoid valve 25a1 (operation pressure Pi for the valve elements 53a1 and 53a2), and is connected to the recording device 5 through an electrical wiring line. Sensing values of the pressure sensors 10a1 to 10a4 and 52a (pressures Pa1 to Pa4) and a sensing value of the pressure sensor 52a (operation pressure Pi) are recorded in the recording device 5 together with a sensing clock time.

[0024] The operation device 2 has an operation lever 2a that can be operated through inclining and a sensor (not depicted) that senses the inclining amount (lever operation amount) of the operation lever 2a as an electrical signal (lever operation amount signal). The sensor of the operation device 2 is connected to the controller 20 through an electrical wiring line such that the sensor can input the lever operation amount signal to the controller 20. The controller 20 outputs the valve opening command signal or the valve closing command signal for the on / off valve 25a in response to the lever operation amount signal, and controls the flow rate of the hydraulic fluid supplied from the hydraulic pump 1a to the actuator 5ab. This allows an operator of the hydraulic excavator 100 to drive the actuator 5ab by operating the operation lever 2a.

[0025] Fig. 3 is a diagram depicting clock time history data on a solenoid valve command value Sp and the output pressure of the solenoid valve 25a1 (operation pressure Pi) when the on / off valve 25a is opened. The solenoid valve command value Sp is a value indicating the level of the electrical signal output from the controller 20 to the solenoid valve 25a1. A clock time ta0 is a clock time at which the solenoid valve command value Sp has changed from a valve closing command value So indicating an instruction to close the on / off valve 25a to a valve opening command value Sn indicating an instruction to open the on / off valve 25a. A clock time ta1 is a clock time at which the operation pressure Pi has reached the drain pressure Po. The controller 20 computes, as the valve-opening lag time TA, the time (= ta1 - ta0) from a clock time at which the solenoid valve command value Sp has changed to the valve opening command value Sn to a clock time at which the operation pressure Pi has reached the drain pressure Po. Processing by the controller 20 relating to the computation of the valve-opening lag time TA is depicted in Fig. 4. The controller 20 reads out the clock time history data on the operation pressure Pi from the recording device 5, and extracts the clock time ta1 at which the operation pressure Pi has reached the drain pressure Po. The controller 20 reads out the clock time history data on the solenoid valve command value Sp from the recording device 5, and extracts the clock time ta0 at which the solenoid valve command value Sp has been changed to the valve opening command value Sn. The controller 20 computes a value obtained by subtracting the clock time ta0 from the clock time ta1 as the valve-opening lag time TA, and records it in the recording device 5. The controller 20 reads out clock time history data on a hydraulic fluid temperature Tep from the recording device 5, and extracts the hydraulic fluid temperature Tep at the clock time ta0 to store it as a valve-opening-time hydraulic fluid temperature TepA in the recording device 5.

[0026] Fig. 5 is a diagram depicting clock time history data on the solenoid valve command value Sp and the output pressure of the solenoid valve 25a1 (operation pressure Pi) when the on / off valve 25a is closed. A clock time tb0 is a clock time at which the solenoid valve command value Sp has changed from the valve opening command value Sn to the valve closing command value So. A clock time tb1 is a clock time at which the operation pressure Pi has reached the highest pressure Pa. The controller 20 computes, as the valve-closing lag time TB, the time (= tb1 - tb0) from a clock time at which the solenoid valve command value Sp has changed to the valve closing command value So to a clock time at which the operation pressure Pi has reached the highest pressure Pa. Processing by the controller 20 relating to the computation of the valve-closing lag time TB is depicted in Fig. 6. The controller 20 reads out clock time history data on the pressures Pa1 to Pa4 from the recording device 5, and generates clock time history data on the highest pressure Pa. The controller 20 reads out the clock time history data on the operation pressure Pi from the recording device 5, and compares it with the clock time history data on the highest pressure Pa to extract the clock time tb1 at which the operation pressure Pi has reached the highest pressure Pa. The controller 20 reads out the clock time history data on the solenoid valve command value Sp from the recording device 5, and extracts the clock time tb0 at which the solenoid valve command value Sp has been changed to the valve closing command value So. The controller 20 computes a value obtained by subtracting the clock time tb0 from the clock time tb1 as the valve-closing lag time TB, and records it in the recording device 5. The controller 20 reads out the clock time history data on the hydraulic fluid temperature Tep from the recording device 5, and extracts the hydraulic fluid temperature Tep at the clock time tb0 to store it as a valve-closing-time hydraulic fluid temperature TepB in the recording device 5.

[0027] Fig. 7 is a diagram depicting the clock time history data on the solenoid valve command value Sp and the output pressure of the solenoid valve 25a1 (operation pressure Pi) when the on / off valve 25a is opened with comparison between the data at the time of shipment of the hydraulic excavator or immediately after replacement of a component incorporated in the on / off valve and the data after deterioration over time. A valve-opening lag time TA1 (= ta3 - ta0) of the on / off valve 25a that has deteriorated over time is longer than a valve-opening lag time TA0 (= ta2 - ta0) of the on / off valve 25a before the deterioration over time. At the time of shipment of the hydraulic excavator or immediately after replacement of a component incorporated in the on / off valve, the controller 20 records, in the recording device 5, the valve-opening lag time TA0 and a valve-opening-time hydraulic fluid temperature TepA0 that is the hydraulic fluid temperature when the solenoid valve command value Sp has been changed to the valve opening command value Sn.

[0028] Fig. 8 is a diagram depicting the clock time history data on the solenoid valve command value Sp and the output pressure of the solenoid valve 25a1 (operation pressure Pi) when the on / off valve 25a is closed with comparison between the data at the time of shipment of the hydraulic excavator or immediately after replacement of a component incorporated in the on / off valve and the data after deterioration over time. A valve-closing lag time TB1 (= tb3 - tb0) of the on / off valve 25a that has deteriorated over time is longer than a valve-closing lag time TB0 (= tb2 - tb0) of the on / off valve 25a before the deterioration over time. At the time of shipment of the hydraulic excavator or immediately after replacement of a component incorporated in the on / off valve, the controller 20 records, in the recording device 5, the valve-closing lag time TB0 and a valve-closing-time hydraulic fluid temperature TepB0 that is the hydraulic fluid temperature when the solenoid valve command value Sp has been changed to the valve closing command value So.

[0029] Fig. 9 is a flowchart depicting processing executed by the controller 20. The controller 20 executes determination concerning clogging of the filters 50a1 to 50a4 and determination concerning deterioration of the solenoid valve 25a1 in accordance with the flowchart depicted in Fig. 9. Each step is described below.

[0030] First, the controller 20 acquires a valve-opening-time hydraulic fluid temperature TepAn and a valve-closing-time hydraulic fluid temperature TepBn at the time of previous determination and the latest valve-opening-time hydraulic fluid temperature TepA and valve-closing-time hydraulic fluid temperature TepB (steps S101 and S102). At the time of first determination, the controller 20 acquires the valve-opening-time hydraulic fluid temperature TepA0 and the valve-closing-time hydraulic fluid temperature TepB0 recorded at the time of shipment of the hydraulic excavator or immediately after replacement of a component incorporated in the on / off valve as the valve-opening-time hydraulic fluid temperature TepAn and the valve-closing-time hydraulic fluid temperature TepBn at the time of the previous determination.

[0031] Subsequent to the steps S101 and S102, the controller 20 determines whether or not the difference between the valve-opening-time hydraulic fluid temperature TepAn at the time of the previous determination and the latest valve-opening-time hydraulic fluid temperature TepA is smaller than one degree and the difference between the valve-closing-time hydraulic fluid temperature TepBn at the time of the previous determination and the latest valve-closing-time hydraulic fluid temperature TepB is smaller than one degree (step S103). When the determination result of the step S103 is NO, this flow is ended. This can prevent erroneous determination due to a difference in the hydraulic fluid temperature from that at the time of the previous determination.

[0032] When the determination result of the step S103 is YES, the controller 20 determines whether or not the operation pressure Pi is equal to the highest pressure Pa (step S104). When the determination result of the step S104 is NO, this flow is ended.

[0033] When the determination result of the step S104 is YES, the controller 20 acquires a valve-opening lag time TAn and a valve-closing lag time TBn at the time of the previous determination and the latest valve-opening lag time TA and valve-closing lag time TB (steps S105 and S106). At the time of the first determination, the controller 20 acquires the valve-opening lag time TA0 and the valve-closing lag time TB0 recorded at the time of shipment of the hydraulic excavator or immediately after replacement of a component incorporated in the on / off valve as the valve-opening lag time TAn and the valve-closing lag time TBn at the time of the previous determination.

[0034] Subsequently to the steps S105 and S106, the controller 20 computes an increase amount ΔTA of the valve-opening lag time TA (= TA - TAn) and an increase amount ΔTB of the valve-closing lag time TB (= TB - TBn) (step S107).

[0035] Subsequent to the step S107, the controller 20 determines whether or not the increase amount ΔTB of the valve-closing lag time TB is equal to or larger than a predetermined threshold Tr (step S108). When the determination result of the step S108 is YES, the controller 20 determines whether or not the increase amount ΔTA of the valve-opening lag time TA is equal to or larger than a predetermined threshold Ts (step S109).

[0036] When the determination result of the step S109 is YES, the controller 20 determines that the solenoid valve 25a1 has deteriorated, and issues an alert to prompt the solenoid valve 25a1 to be replaced (step S110). When the determination result of the step S109 is NO, the controller 20 determines that the filter 50a1 to 50a4 is clogged, and issues an alert to prompt the filter 50a1 to 50a4 to be replaced (step S111). The thresholds Tr and Ts are decided in consideration of how the machine body is used, the frequency of maintenance, and the like.

[0037] When the determination result of the step S108 is NO or subsequent to the step S110 or S111, the controller 20 updates the valve-opening lag time TAn and the valve-closing lag time TBn at the time of the previous determination by the latest valve-opening lag time TA and valve-closing lag time TB, and updates the valve-opening-time hydraulic fluid temperature TepAn and the valve-closing-time hydraulic fluid temperature TepBn at the time of the previous determination by the latest valve-opening-time hydraulic fluid temperature TepA and valve-closing-time hydraulic fluid temperature TepB (steps S112 and S113), to end this flow.(Summarization)

[0038] In the first embodiment, in the hydraulic drive system 200 including the first hydraulic pump 1a having two input / output ports, the actuator 5ab, the first hydraulic line 61 that connects one of the two input / output ports to one input / output port of the actuator 5ab, the second hydraulic line 62 that connects the other of the two input / output ports to the other input / output port of the actuator 5ab, the first on / off valve 25a that connects or disconnects the first hydraulic line 61 and the second hydraulic line 62, the operation device 2 that makes an instruction to operate the actuator 5ab, and the controller 20 that controls the first on / off valve 25a in response to an operation signal input from the operation device 2, the controller 20 computes the first valve-opening lag time TA from output of the first valve opening command signal (valve opening command value Sn) instructing the first on / off valve 25a to open to opening of the first on / off valve 25a, and computes the first valve-closing lag time TB from output of the first valve closing command signal (valve closing command value So) instructing the first on / off valve 25a to close to closing of the first on / off valve 25a. The controller 20 determines the deterioration state of the first on / off valve 25a on the basis of the first valve-opening lag time TA and the first valve-closing lag time TB.

[0039] According to the first embodiment configured as described above, the deterioration state of the on / off valve 25a of the closed circuit 60 can be accurately estimated. Thus, by replacing, before failure, only the on / off valve 25a of the closed circuit 60 with a high probability of failure, downtime of the hydraulic excavator 100 can be shortened and the maintenance cost of the hydraulic excavator 100 can be reduced.

[0040] Further, the first on / off valve 25a in the first embodiment has the first valve element 53a1 that connects or disconnects the first hydraulic line 61, the second valve element 53a2 that connects or disconnects the second hydraulic line 62, the first check valves 51a1 to 51a4 that output the highest pressure Pa of the first hydraulic line 61 and the second hydraulic line 62, the first filters 50a1 to 50a4 disposed on the upstream side of the first check valves 51a1 to 51a4, and the first solenoid valve 25a1 that outputs the drain pressure Po, as the operation pressure Pi for the first valve element 53a1 and the second valve element 53a2, in response to the first valve opening command signal (valve opening command value Sn) and outputs the highest pressure Pa, as the operation pressure Pi for the first valve element 53a1 and the second valve element 53a2, in response to the first valve closing command signal (valve closing command value So). The controller 20 computes, as the first valve-opening lag time TA1, the time taken from the output of the first valve opening command signal (valve opening command value Sn) to the drain pressure Po being reached by the output pressure of the first solenoid valve 25a1, and computes, as the first valve-closing lag time TB, the time taken from the output of the first valve closing command signal (valve closing command value So) to the output pressure of the first check valve 51a1 to 51a4 (highest pressure Pa) being reached by the output pressure of the first solenoid valve 25a1. The controller 20 determines that the first solenoid valve 25a1 has deteriorated when the increase amount ΔTB of the first valve-closing lag time TB is equal to or larger than the predetermined first threshold Tr and the increase amount ΔTA of the first valve-opening lag time TA is equal to or larger than the predetermined second threshold Ts. The controller 20 determines that the first filter 50a1 to 50a4 is clogged when the increase amount ΔTB of the first valve-closing lag time TB is equal to or larger than the first threshold Tr and the increase amount ΔTA of the first valve-opening lag time TA is smaller than the second threshold Ts. Due to this, solenoid valve deterioration and filter clogging of the on / off valve 25a of the closed circuit 60 can be sensed. Thus, it becomes possible to eliminate the deterioration state of the on / off valve 25a by replacing only the solenoid valve 25a1 or the filter 50a1 to 50a4.[Second Embodiment]

[0041] A second embodiment of the present invention is described with focus on a difference from the first embodiment. Fig. 10 is a diagram depicting a circuit configuration of the hydraulic drive system in a second embodiment. The hydraulic drive system 200 in the present embodiment includes an open circuit 70 in addition to the closed circuit 60. The open circuit 70 includes a hydraulic pump 1b of a single delivery type, a hydraulic line 71 that connects a delivery port of the hydraulic pump 1b to one input / output port of the actuator 5ab, an on / off valve 25b that connects or disconnects the hydraulic line 71, a meter-out valve 30, a bleed-off valve 31, and pressure sensors 10b1 and 10b2.

[0042] A suction port of the hydraulic pump 1b is connected to the tank 4. The meter-out valve 30 is disposed on a hydraulic line 72 that connects the actuator 5ab to the tank 4. The bleed-off valve 31 is disposed on a hydraulic line 73 that connects the delivery port of the hydraulic pump 1b to the tank 4, and discharges, to the tank 4, a fluid with the minimum flow rate delivered from the hydraulic pump 1b. The pressure sensors 10b1 and 10b2 are disposed on the hydraulic line 71 in order to sense the pressure across the on / off valve 25b (pressures Pb1 and Pb2), and are connected to the recording device 5 through an electrical wiring line. Sensing values of the pressure sensors 10b1 and 10b2 (pressures Pb1 and Pb2) are recorded in the recording device 5 together with a sensing clock time.

[0043] Fig. 11 is a diagram depicting an internal configuration of the on / off valve 25b of the open circuit 70. The on / off valve 25b has a valve element 53b1, a solenoid valve 25b1, filters 50b1 and 50b2, check valves 51b1 and 51b2, and a pressure sensor 52b. The input sides of the check valves 51b1 and 51b2 are connected to the front and the back of the valve element 53b1 through the filters 50b1 and 50b2. The filters 50b1 and 50b2 remove foreign matters in a hydraulic fluid that flows into the check valves 51b1 and 51b2.

[0044] The output sides of the check valves 51b1 and 51b2 are connected to one input port of the solenoid valve 25b1. The other input port of the solenoid valve 25b1 is connected to the tank 4. A highest pressure Pb of the hydraulic line 71 is input to the one input port of the solenoid valve 25b1 through the check valve 51b1 or 51b2. The drain pressure Po (pressure of the hydraulic fluid discharged to the tank 4) is input to the other input port of the solenoid valve 25b1. An output port of the solenoid valve 25b1 is connected to a spring chamber 55b1 of the valve element 53b1. A spring 25b21 that applies a force in a pressing-down direction to the valve element 53b1 is disposed in the spring chamber 55b1.

[0045] The solenoid valve 25b1 can be switched to a position 25b3 to introduce the drain pressure Po to the spring chamber 55b1 and a position 25b4 to introduce the highest pressure Pb to the spring chamber 55b1. The solenoid valve 25b1 is connected to the controller 20 through an electrical wiring line such that an electrical signal from the controller 20 can be input thereto. When a valve opening command signal for the on / off valve 25b is input from the controller 20 to the solenoid valve 25b1, the solenoid valve 25b1 is switched from the position 25b4 to the position 25b3. Due to this, the pressure in the spring chamber 55b1 lowers to the drain pressure Po. Thus, the valve element 53b1 is pressed up, and the hydraulic line 71 is connected.

[0046] When a valve closing command signal for the on / off valve 25b is input from the controller 20 to the solenoid valve 25b1, the solenoid valve 25b1 is switched from the position 25b3 to the position 25b4. Due to this, the pressure in the spring chamber 55b1 rises to the highest pressure Pb. Thus, the valve element 53b1 is pressed down, and the hydraulic line 71 is disconnected. At this time, the hydraulic fluid passes through only the filter disposed on the upstream side of the check valve that allows the hydraulic fluid at the highest pressure Pb to pass therethrough out of the check valves 51b1 and 51b2. Thus, if clogging occurs in the filter that allows the hydraulic fluid at the highest pressure Pb to pass therethrough, a lag time from the output of the valve closing command signal to closing of the on / off valve 25b (valve-closing lag time TD) becomes long. On the other hand, when the solenoid valve 25b1 has deteriorated, both the valve-closing lag time TD and a lag time from the output of the valve opening command signal to opening of the on / off valve 25b (valve-opening lag time TC) become long. Further, the valve-opening lag time TC and the valve-closing lag time TD change also depending on the temperature of the hydraulic fluid that circulates in the closed circuit 60.

[0047] The pressure sensor 52b is disposed to sense the output pressure of the solenoid valve 25b1 (operation pressure for the valve element 53b1), and is connected to the recording device 5 through an electrical wiring line. A sensing value of the pressure sensor 52b (operation pressure for the valve element 53b1) is recorded in the recording device 5 together with a sensing clock time.

[0048] Referring back to Fig. 10, because the actuator 5ab is a single-rod hydraulic cylinder, the volume of the hydraulic fluid that can be supplied differs between the rod side and the bottom side. In order to compensate for the volume difference (volume difference corresponding to entry of the rod), when operation of extending the cylinder is executed, the on / off valve 25b is opened to supply the hydraulic fluid to the bottom side of the actuator 5ab. On the other hand, when operation of retracting the cylinder is executed, the responsiveness of the retraction is improved by opening the meter-out valve 30 to discharge the hydraulic fluid on the bottom side to the tank 4. As described above, the open circuit 70 has such a configuration as to be capable of giving or receiving the hydraulic fluid corresponding to the excess or deficiency of the hydraulic fluid in the closed circuit 60.

[0049] The controller 20 in the present embodiment executes determination concerning solenoid valve deterioration and determination concerning filter clogging for the on / off valve 25a of the closed circuit 60 in accordance with the flow depicted in Fig. 9, and executes determination concerning solenoid valve deterioration and determination concerning filter clogging for the on / off valve 25b of the open circuit 70.

[0050] In the hydraulic drive system 200 in the present embodiment, whereas the hydraulic fluid in the open circuit 70 circulates between the open circuit 70 and the tank 4, most part of the hydraulic fluid in the closed circuit 60 remains in the closed circuit 60 without circulating between the closed circuit 60 and the tank 4. Thus, progress of deterioration is fast in the hydraulic fluid in the closed circuit 60 compared with the hydraulic fluid in the open circuit 70. The present embodiment is characterized by informing a replacement timing of the hydraulic fluid in the closed circuit 60 by comparing the deterioration state of the on / off valve 25a of the closed circuit 60 with the deterioration state of the on / off valve 25b of the open circuit 70.

[0051] Fig. 12 is a flowchart depicting processing executed by the controller 20 in the second embodiment. Before starting the processing of this flow, the controller 20 computes, in accordance with the flow depicted in Fig. 9, the increase amount ΔTA of the valve-opening lag time TA and the increase amount ΔTB of the valve-closing lag time TB concerning the on / off valve 25a of the closed circuit 60, and an increase amount ΔTC of the valve-opening lag time TC and an increase amount ΔTD of the valve-closing lag time TD concerning the on / off valve 25a of the closed circuit 60. Each step in Fig. 12 is described below.

[0052] First, the controller 20 determines whether or not the increase amount ΔTB of the valve-closing lag time TB concerning the on / off valve 25a of the closed circuit 60 is equal to or larger than the predetermined threshold Tr (step S201). When the determination result of the step S201 is NO, this flow is ended.

[0053] When the determination result of the step S201 is YES, the controller 20 determines whether or not the increase amount ΔTA of the valve-opening lag time TA concerning the on / off valve 25a of the closed circuit 60 is equal to or larger than the predetermined threshold Ts (step S202). When the determination result of the step S202 is YES, the solenoid valve 25a1 of the on / off valve 25a of the closed circuit 60 has deteriorated, and comparison with the open circuit 70 is impossible. Thus, this flow is ended. When the determination result of the step S202 is NO, the controller 20 advances the processing to a step S205 to be described later.

[0054] Concurrently with the step S201, the controller 20 determines whether or not the increase amount ΔTD of the valve-closing lag time TD concerning the on / off valve 25b of the open circuit 70 is equal to or larger than the predetermined threshold Tr (step S203). When the determination result of the step S203 is NO, this flow is ended.

[0055] When the determination result of the step S203 is YES, the controller 20 determines whether or not the increase amount ΔTC of the valve-opening lag time TC concerning the on / off valve 25b of the open circuit 70 is equal to or larger than the predetermined threshold Ts (step S204). When the determination result of the step S204 is YES, the solenoid valve 25b1 of the on / off valve 25b of the open circuit 70 has deteriorated, and comparison with the closed circuit 60 is impossible. Thus, this flow is ended.

[0056] When the determination result of the step S204 is NO, the controller 20 determines whether or not a difference obtained by subtracting the valve-opening lag time TC of the open circuit 70 from the valve-opening lag time TA of the closed circuit 60 is equal to or larger than a predetermined threshold Tq (step S205). When the determination result of the step S205 is NO, the hydraulic fluid in the closed circuit 60 has not deteriorated relative to the hydraulic fluid in the open circuit 70. Thus, this flow is ended.

[0057] When the determination result of the step S205 is YES, the hydraulic fluid in the closed circuit 60 has deteriorated relative to the hydraulic fluid in the open circuit 70. Thus, the controller 20 issues an alert to prompt the hydraulic fluid in the closed circuit 60 to be replaced (step S206), and ends this flow. The threshold Tq is decided in consideration of how the machine body is used, the frequency of maintenance, and the like.

[0058] According to the above-described flow, the alert to prompt the hydraulic fluid in the closed circuit 60 to be replaced is issued when the valve-closing lag time TB of the on / off valve 25a of the closed circuit 60 has become significantly longer than the valve-opening lag time TC of the on / off valve 25b of the open circuit 70 in a state in which the filters 50a1 to 50a4 in the on / off valve 25a of the closed circuit 60 and the filters 50b1 and 50b2 in the on / off valve 25b of the open circuit 70 are not clogged.(Summarization)

[0059] The hydraulic drive system 200 in the second embodiment includes the second hydraulic pump 1b having the suction port and the delivery port, the third hydraulic line 71 that connects the delivery port to one input / output port of the actuator 5ab, and the second on / off valve 25b that connects or disconnects the third hydraulic line 71. The controller 20 computes the second valve-opening lag time TC from output of the second valve opening command signal instructing the second on / off valve 25b to open to opening of the second on / off valve 25b, and computes the second valve-closing lag time TD from output of the second valve closing command signal instructing the second on / off valve 25b to close to closing of the second on / off valve 25b. The controller 20 determines the deterioration state of the second on / off valve 25b on the basis of the second valve-opening lag time TC and the second valve-closing lag time TB.

[0060] According to the second embodiment configured as described above, the deterioration state of the on / off valve 25b of the open circuit 70 can be accurately estimated. Thus, by replacing, before failure, only the on / off valve 25b of the open circuit 70 with a high probability of failure, downtime of the hydraulic excavator 100 can be shortened and the maintenance cost of the hydraulic excavator 100 can be reduced.

[0061] Further, the second on / off valve 25b in the second embodiment has the third valve element 53b1 that connects or disconnects the third hydraulic line 71, the second check valves 51b1 and 51b2 that output the highest pressure Pb of the third hydraulic line 71, the second filters 50b1 and 50b2 disposed on the upstream side of the second check valves 51b1 and 51b2, and the second solenoid valve 25b1 that outputs the drain pressure Po as the operation pressure for the third valve element 53b1 in response to the second valve opening command signal and outputs the output pressure of the second check valve 51b1 or 51b2 as the operation pressure for the third valve element 53b1 in response to the second valve closing command signal. The controller 20 computes, as the second valve-opening lag time TC, the time taken from the output of the second valve opening command signal to the drain pressure Po being reached by the output pressure of the second solenoid valve 25b1, and computes, as the second valve-closing lag time TD, the time taken from the output of the second valve closing command signal to the output pressure of the second check valve 51b1 or 51b2 (highest pressure Pb) being reached by the output pressure of the second solenoid valve 25b1. The controller 20 determines that the second solenoid valve 25b1 has deteriorated when the increase amount ΔTD of the second valve-closing lag time TD is equal to or larger than the first threshold Tr and the increase amount ΔTD of the second valve-opening lag time TC is equal to or larger than the second threshold Ts. The controller 20 determines that the second filter is clogged when the increase amount ΔTD of the second valve-closing lag time TD is equal to or larger than the first threshold Tr and the second valve-opening lag time TC is less than the second threshold Ts. Due to this, solenoid valve deterioration and filter clogging of the on / off valve 25b of the open circuit 70 can be sensed. Thus, it becomes possible to eliminate the deterioration state of the on / off valve 25b by replacing only the solenoid valve 25b1 or the filter 50b1 or 50b2.

[0062] Moreover, the controller 20 in the second embodiment determines that the hydraulic fluid flowing in the first hydraulic line 61 and the second hydraulic line 62 has deteriorated when the controller 20 has determined that the first solenoid valve 25a1 and the second solenoid valve 25b1 have not deteriorated and the difference obtained by subtracting the second valve-closing lag time TC from the first valve-opening lag time TA exceeds the predetermined third threshold Tq. This makes it possible to replace the hydraulic fluid in the closed circuit 60 at a proper timing.

[0063] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments and various modifications are included therein. For example, the above-described embodiments have been explained in detail in order to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to that including all configurations explained. Further, it is also possible to add part of a configuration of a certain embodiment to a configuration of another embodiment. It is also possible to delete part of a configuration of a certain embodiment or replace the part by part of another embodiment.Description of Reference Characters

[0064] 1: hydraulic excavator 1a: hydraulic pump (first hydraulic pump) 1b: hydraulic pump (second hydraulic pump) 2: operation device 2a: operation lever 4: tank 5: recording device 5ab: actuator 7a: boom cylinder 7b: arm cylinder 7c: bucket cylinder 10a: travelling motor 10a1 to 10a4, 10b1, 10b2: pressure sensor 20: controller 25a: on / off valve (first on / off valve) 25a1: solenoid valve (first solenoid valve) 25a2, 25a21, 25a22: spring 25a3, 25a4: position 25b: on / off valve (second on / off valve) 25b1: solenoid valve (second solenoid valve) 25b2, 25b21: spring 30: meter-out valve 31: bleed-off valve 50a1 to 50a4: filter (first filter) 50b1, 50b2: filter (second filter) 51a1 to 51a4: check valve (first check valve) 51b1, 51b2: check valve (second check valve) 52a, 52b: pressure sensor 53a1: valve element (first valve element) 53a2: valve element (second valve element) 53b1: valve element (third valve element) 55a1, 55a2, 55b1: spring chamber 60: closed circuit 61: hydraulic line (first hydraulic line) 62: hydraulic line (second hydraulic line) 70: open circuit 71: hydraulic line (third hydraulic line) 72, 73: hydraulic line 100: hydraulic excavator 101: track structure 102: swing structure 103: work device 104: cab 105: main frame 108: counterweight 111: boom 112: arm 113: bucket 200: hydraulic drive system

Claims

1. A hydraulic drive system comprising: a first hydraulic pump having two input / output ports; an actuator; a first hydraulic line that connects one of the two input / output ports to one input / output port of the actuator; a second hydraulic line that connects another of the two input / output ports to another input / output port of the actuator; a first on / off valve that connects or disconnects the first hydraulic line and the second hydraulic line; an operation device that instructs the actuator to operate; and a controller that controls the first on / off valve in response to an operation signal input from the operation device, wherein the controller is configured to compute a first valve-opening lag time from output of a first valve opening command signal instructing the first on / off valve to open to opening of the first on / off valve, compute a first valve-closing lag time from output of a first valve closing command signal instructing the first on / off valve to close to closing of the first on / off valve, and determine a deterioration state of the first on / off valve on a basis of the first valve-opening lag time and the first valve-closing lag time.

2. The hydraulic drive system according to claim 1, wherein the first on / off valve has a first valve element that connects or disconnects the first hydraulic line, a second valve element that connects or disconnects the second hydraulic line, a first check valve that outputs a highest pressure of the first hydraulic line and the second hydraulic line, a first filter disposed upstream of the first check valve, and a first solenoid valve that outputs a drain pressure, as an operation pressure for the first valve element and the second valve element, in response to the first valve opening command signal and outputs an output pressure of the first check valve, as the operation pressure for the first valve element and the second valve element, in response to the first valve closing command signal, and the controller is configured to compute, as the first valve-opening lag time, a time taken from the output of the first valve opening command signal to the drain pressure being reached by an output pressure of the first solenoid valve, compute, as the first valve-closing lag time, a time taken from the output of the first valve closing command signal to the output pressure of the first check valve being reached by the output pressure of the first solenoid valve, determine that the first solenoid valve has deteriorated when an increase amount of the first valve-closing lag time is equal to or larger than a predetermined first threshold and an increase amount of the first valve-closing lag time is equal to or larger than a predetermined second threshold, and determine that the first filter is clogged when the first valve-closing lag time is equal to or greater than the first threshold and the first valve-opening lag time is less than the second threshold.

3. The hydraulic drive system according to claim 2, wherein the hydraulic drive system includes a second hydraulic pump having a suction port and a delivery port, a third hydraulic line that connects the delivery port to one input / output port of the actuator, and a second on / off valve that connects or disconnects the third hydraulic line, and the controller is configured to compute a second valve-opening lag time from output of a second valve opening command signal instructing the second on / off valve to open to opening of the second on / off valve, compute a second valve-closing lag time from output of a second valve closing command signal instructing the second on / off valve to close to closing of the second on / off valve, and determine a deterioration state of the second on / off valve on a basis of the second valve-opening lag time and the second valve-closing lag time.

4. The hydraulic drive system according to claim 3, wherein the second on / off valve has a third valve element that connects or disconnects the third hydraulic line, a second check valve that outputs a highest pressure of the third hydraulic line, a second filter disposed upstream of the second check valve, and a second solenoid valve that outputs the drain pressure, as an operation pressure for the third valve element, in response to the second valve opening command signal and outputs an output pressure of the second check valve, as the operation pressure for the third valve element, in response to the second valve closing command signal, and the controller is configured to compute, as the second valve-opening lag time, a time taken from the output of the second valve opening command signal to the drain pressure being reached by an output pressure of the second solenoid valve, compute, as the second valve-closing lag time, a time taken from the output of the second valve closing command signal to the output pressure of the second check valve being reached by the output pressure of the second solenoid valve, determine that the second solenoid valve has deteriorated when an increase amount of the second valve-closing lag time is equal to or larger than the first threshold and an increase amount of the second valve-opening lag time is equal to or larger than the second threshold, and determine that the second filter is clogged when the increase amount of the second valve-closing lag time is equal to or larger than the first threshold and the second valve-opening lag time is less than the second threshold.

5. The hydraulic drive system according to claim 4, wherein the controller is configured to determine that a hydraulic fluid flowing in the first hydraulic line and the second hydraulic line has deteriorated when the controller has determined that the first solenoid valve and the second solenoid valve have not deteriorated and a difference obtained by subtracting the second valve-opening lag time from the first valve-opening lag time exceeds a predetermined third threshold.

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