Work machine

Abstract

To provide a work machine which is mounted with a hydraulic driving device for supplying hydraulic oil to a plurality of hydraulic actuators from a pump for a closed circuit and a pump for an open circuit driven by an engine, and can improve startability of the engine under low temperature environment.SOLUTION: In a state in which start of an engine 110 is instructed through a key switch 80, before driving of a starter motor 70 is started, a controller 90 converts switching valves 2d, 4d, 6d, and 8d for traveling which connect pumps 12, 14, 16, and 18 for an open circuit to travel motors 24 and 25 into open states, among a plurality of switching valves 1a to 1d, 2a to 2d, 3a to 3d, 4a to 4d, 5a to 5d, 6a to 6d, 7a to 7d, and 8a to 8d, in a state in which control valves 60 and 61 for traveling are held at neutral positions.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a working machine such as a hydraulic excavator.

Background Art

[0002] In recent years, energy saving has become an important development item in working machines such as hydraulic excavators and wheel loaders. In this type of working machine, a hydraulic system that hydraulically drives a working unit such as a front working machine is used, and energy saving of the hydraulic system itself is important. Therefore, the application of a hydraulic closed circuit system in which a hydraulic actuator is connected in a closed circuit by a hydraulic pump and the speed of the hydraulic actuator is directly controlled by the hydraulic pump has been studied. This hydraulic closed circuit system has no pressure loss due to a control valve and no flow loss because the hydraulic pump discharges only the required flow rate. In addition, since the potential energy of the hydraulic actuator and the energy during deceleration can be regenerated, a high energy saving effect can be obtained.

[0003] Patent Document 1 proposes a configuration in which an open circuit pump and a closed circuit pump are connected to a plurality of hydraulic actuators via switching valves, respectively, to enable combined operation and high-speed operation of the hydraulic actuators. At the same time, a configuration is proposed in which a discharge valve is provided to discharge the discharge oil of the open circuit pump when the hydraulic actuator is not driven, such as during operation standby.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, in order to surely start the engine even in a low-temperature environment where the outside air temperature is low and the working oil viscosity is high, it is preferable that the starting torque at the time of engine starting is as low as possible. In order to reduce the starting torque, it is conceivable to open the discharge valve connected to the open circuit pump at the time of starting and discharge it to the working oil tank. However, since the opening and closing control of the discharge valve is performed using the discharge oil of the control pump directly connected to the engine, in a state where the working oil viscosity is high in a low-temperature environment, when the discharge valve is closed during cranking at the time of engine starting, the discharge pressure of the open circuit pump rises to the set pressure of the relief valve provided to protect the circuit, and a large amount of power is required to drive the open circuit pump. As a result, the load on the engine increases.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide a work machine equipped with a hydraulic drive device that supplies hydraulic oil from a closed circuit pump and an open circuit pump driven by an engine to a plurality of hydraulic actuators and can improve the startability of the engine in a low-temperature environment.

Means for Solving the Problems

[0007] To achieve the above object, the present invention includes an engine, a closed-circuit pump and an open-circuit pump driven by the engine, a plurality of hydraulic actuators including a traveling motor, an operating device for instructing the operation of the plurality of hydraulic actuators, a plurality of switching valves having an open state and a closed state, and selectively connecting the closed-circuit pump and the open-circuit pump to any one of the plurality of hydraulic actuators in the open state, and among the plurality of switching valves, a traveling switching valve for connecting the open-circuit pump to the traveling motor and an oil passage connecting the traveling switching valve and the traveling motor, a traveling control valve for controlling the flow rate of the hydraulic oil supplied from the open-circuit pump to the traveling motor and discharging the hydraulic oil supplied from the open-circuit pump to the hydraulic oil tank at the neutral position, a starter motor for starting the engine, a key switch for instructing the start of the engine, and an operation signal input from the operating device is input, and a controller for outputting control signals to the plurality of switching valves and the traveling control valve. In the working machine, when the controller is instructed to start the engine via the key switch, before starting the drive of the starter motor, the traveling control valve is held in the neutral position and the traveling switching valve is set to the open state.

Effect of the Invention

[0008] According to the present invention, when the engine is started, the discharged oil of the open-circuit pump is discharged to the hydraulic oil tank through the traveling switching valve and the center bypass oil passage of the traveling control valve, so that the increase in the discharge pressure of the open-circuit pump is suppressed. As a result, the driving load of the open-circuit pump at the time of engine start becomes small, so that it is possible to improve the startability of the engine in a low-temperature environment where the viscosity of the hydraulic oil becomes high.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

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Figure 11

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each figure, the same reference numerals are given to equivalent parts, and duplicate descriptions will be omitted as appropriate.

[0011] FIG. 1 is a side view of a hydraulic excavator in this embodiment, FIG. 2 is a view seen from the direction of arrow A in FIG. 1, FIG. 3 is a view seen from the direction of arrow B in FIG. 1, and FIG. 4 is a view seen from the direction of arrow C in FIG. 2. Note that the present invention is also applicable to other working machines such as cranes and wheel loaders.

[0012] The hydraulic excavator 100 includes a crawler-type lower traveling body 101 and an upper revolving body 102 rotatably mounted on the lower traveling body 101. The lower traveling body 101 is driven by left and right traveling motors 24 and 25, and the upper revolving body 102 is driven by a swing motor 23.

[0013] A front working machine 103 for performing excavation work or the like is attached to the front side of the upper swing body 102. The front working machine 103 includes a boom 104 rotatably attached in the vertical direction to the front side of the upper swing body 102, an arm 105 rotatably attached to the tip of the boom 104 in the vertical or front-rear direction, and a bucket 106 rotatably attached to the tip of the arm 105 in the vertical or front-rear direction. The boom 104 is driven by a boom cylinder 20, the arm 105 is driven by an arm cylinder 21, and the bucket 106 is driven by a bucket cylinder 22.

[0014] The upper swing body 102 is equipped with an engine 110, a pump assembly 111, a valve assembly 112, a center joint 113, a hydraulic oil tank 50 (shown in FIG. 5), and the like.

[0015] Travel control valves 60, 61 for controlling the flow rate of the hydraulic oil supplied to the travel motors 24, 25 are arranged at positions facing the travel motors 24, 25 of the lower travel body 101. The travel motors 24, 25 are supplied with the hydraulic oil sucked up from the hydraulic oil tank 50 by the open circuit pumps 12, 14, 16, 18 (shown in FIG. 5) included in the pump assembly 111 through the travel switching valves 2d, 4d, 6d, 8d (shown in FIG. 5) included in the valve assembly 112, the center joint 113, and the travel control valves 60, 61. The hydraulic oil discharged from the travel motors 24, 25 returns to the hydraulic oil tank 50 via the travel control valves 60, 61 and the center joint 113. Since the travel control valves 60, 61 are installed on the lower travel body 101 with less heat sources, they are easily affected by the outside air. Therefore, when the travel operation is started after the vehicle body has stopped for a long time in a cold region, there is a concern about heat shock caused by warm oil flowing into the cold travel control valves 60, 61. This countermeasure will be described later.

[0016] FIG. 5 is a hydraulic circuit diagram of a hydraulic drive device mounted on a hydraulic excavator 100. The hydraulic drive device 200 includes an engine 110, a hydraulic oil tank 50, a plurality of hydraulic pumps 10 to 18 included in a pump assembly 111 (shown in FIG. 1), a plurality of hydraulic actuators 20 to 25, and a plurality of switching valves 1a to 1d, 2a to 2d, 3a to 3d, 4a to 4d, 5a to 5d, 6a to 6d, 7a to 7d, 8a to 8d, relief valves 30 to 33, and discharge valves 40 to 43 included in a valve assembly 112 (shown in FIG. 1), and traveling control valves 60, 61.

[0017] The hydraulic pumps 10 to 17 are driven by the engine 110. The hydraulic pump 10 is a control pump composed of a fixed displacement pump. The hydraulic pumps 11, 13, 15, 16 are closed circuit pumps composed of double tilt pumps. The hydraulic pumps 12, 14, 16, 18 are open circuit pumps composed of single tilt pumps. The discharge ports of the open circuit pumps 12, 14, 16, 18 are connected to the hydraulic oil tank 50 via the relief valves 300 to 33 and the discharge valves 40 to 43. The relief valves 30 to 33 are provided to protect the circuit and open when the discharge pressure of the open circuit pumps 12, 14, 16, 18 becomes equal to or higher than the set pressure. The discharge valves 40 to 43 open when the open circuit pumps 12, 14, 16, 18 are not in use and discharge the minimum flow rate of hydraulic oil discharged from the open circuit pumps 12, 14, 16, 18 to the hydraulic oil tank 50. The opening and closing control of the discharge valves 40 to 43 is performed hydraulically using the discharge oil of the control pump 10.

[0018] The switching valves 1a to 1d have an open state and a closed state. Further, the switching valves 1a to 1d selectively connect the closed-circuit pump 11 to any one of the hydraulic actuators 20 to 23 in the open state. The switching valves 3a to 3d have an open state and a closed state. Further, the switching valves 3a to 3d selectively connect the closed-circuit pump 13 to any one of the hydraulic actuators 20 to 23 in the open state. The switching valves 5a to 5d have an open state and a closed state. Further, the switching valves 5a to 5d selectively connect the closed-circuit pump 15 to any one of the hydraulic actuators 20 to 23 in the open state. The switching valves 7a to 7d have an open state and a closed state. Further, the switching valves 7a to 7d selectively connect the closed-circuit pump 17 to any one of the hydraulic actuators 20 to 23 in the open state.

[0019] The switching valves 2a to 2d have an open state and a closed state. Further, the switching valves 2a to 2d selectively connect the open-circuit pump 12 to any one of the hydraulic actuators 20 to 22 or the traveling motors 24, 25 in the open state. The switching valves 4a to 4d have an open state and a closed state. Further, the switching valves 4a to 4d selectively connect the open-circuit pump 14 to any one of the hydraulic actuators 20 to 22 or the traveling motors 24, 25 in the open state. The switching valves 6a to 6d have an open state and a closed state. Further, the switching valves 6a to 6d selectively connect the open-circuit pump 16 to any one of the hydraulic actuators 20 to 22 or either of the traveling motors 24, 25 in the open state. The switching valves 8a to 8d have an open state and a closed state. Further, the switching valves 8a to 8d selectively connect the open-circuit pump 18 to any one of the hydraulic actuators 20 to 22 or the traveling motors 24, 25 in the open state. The opening and closing control of the switching valves 1a to 1d, 2a to 2d, 3a to 3d, 4a to 4d, 5a to 5d, 6a to 6d, 7a to 7d, 8a to 8d is performed electromagnetically by opening and closing the solenoid valves built in each switching valve with a control signal from the controller 90 without using the discharge oil of the control pump 10. Therefore, it is possible to open and close the switching valves 1a to 1d, 2a to 2d, 3a to 3d, 4a to 4d, 5a to 5d, 6a to 6d, 7a to 7d, 8a to 8d even in the key-ON state before the engine 110 starts.

[0020] In the oil passages connecting the switching valves 2d, 4d, 6d, 8d (hereinafter referred to as traveling switching valves) that connect the open - circuit pumps 12, 14, 16, 18 to the traveling motors 24, 25 and the traveling motors 24, 25, center - bypass type traveling control valves 60, 61 are arranged. In the neutral position, the traveling control valves 60, 61 discharge the hydraulic oil supplied from the open - circuit pumps 12, 14, 16, 18 to the hydraulic oil tank 50 via the center - bypass oil passages 62, 63. In the left - and - right switching positions, the traveling control valves 60, 61 supply the hydraulic oil supplied from the open - circuit pumps 12, 14, 16, 18 to the traveling motors 24, 25 and discharge the hydraulic oil discharged from the traveling motors 24, 25 to the hydraulic oil tank 50. The switching control of the traveling control valves 60, 61 is performed using the discharged oil of the control pump 10.

[0021] The engine 110 is provided with a starter motor 70 for starting the engine 110, an engine oil pre - circulation motor 71 for circulating engine oil in the engine 110, an engine oil pressure switch 72 that turns off when the pressure of the engine oil circulating in the engine 110 is below a predetermined threshold value and turns on when the pressure of the engine oil circulating in the engine 110 exceeds the predetermined threshold value, and an engine speed sensor 73 for detecting the engine speed. The starter motor 70 and the engine oil pre - circulation motor 71 are controlled by a controller 90. The controller 90 is connected to a key switch 80 for energizing the electronic devices and an engine start switch 81 for starting the engine 110.

[0022] Based on the signals input from the operating device 82 (operation signals) and the signals input from various sensors (not shown) (sensor information), the controller 90 performs opening / closing control of the switching valves 1a - 1d, 2a - 2d, 3a - 3d, 4a - 4d, 5a - 5d, 6a - 6d, 7a - 7d, 8a - 8d, the discharge valves 40 - 43, and the travel control valves 60, 61, and also performs flow control of the hydraulic pumps 11 - 18. Further, the controller 90 starts the engine 110 based on the respective signals input from the key switch 80, the engine start switch 81, the engine oil pressure switch 72, and the engine speed sensor 73. The controller 90 includes an arithmetic device such as a CPU, a storage device such as a ROM and a RAM, an input / output interface for performing signal input / output with external devices, etc., and realizes various functions by executing the programs stored in the ROM, etc.

[0023] Figure 6 is a diagram showing the classification of the body states of the hydraulic excavator 100. The engine rotation state is set to ON when the engine speed is equal to or higher than a certain value, and OFF when it is less than the certain value. The body state when the key switch 80 is ON, the engine rotation state is OFF, the engine start switch 81 is ON, and the travel switching valves 2d, 4d, 6d, 8d are open is defined as the engine start state. The body state when the key switch 80 is ON, the engine rotation state is OFF, and the engine start switch 81 is OFF is defined as the key ON state. The body state when the key switch 80 is ON and the engine rotation state is ON is defined as the operation standby state. The body state when the key switch 80 is OFF is defined as the key OFF state. Note that the operation standby state is a state in which no operation signal (front operation signal, swing operation signal, or travel operation signal) is input from the operating device 82. The state in which an operation signal is input while in the operation standby state is defined as the operation state, and the state in which the operation standby state continues for a certain period of time or more is defined as the auto - idle state.

[0024] FIG. 7 is a flowchart showing the processing of the controller 90 related to the transition of the vehicle body state. Note that the processing related to the transition to the operation state and the auto-idle state is omitted. The controller 90 first determines whether the key switch 80 is OFF (step S101). If the determination result in step S101 is YES, it transitions to the key-off state (step S102).

[0025] If the determination result in step S101 is NO, it determines whether the engine rotation state is ON (step S103). If the determination result in step S102 is YES, it transitions to the operation standby state (step S104).

[0026] If the determination result in step S103 is NO, it determines whether the engine start switch 81 is OFF (step S105). If the determination result in step S105 is YES, it transitions to the key-ON state (step S106). If the determination result in step S105 is NO, it transitions to the engine start state (step S107).

[0027] FIG. 8 is a flowchart showing the processing of the controller 90 when it transitions to the engine start state. The controller 90 first opens the travel switching valves 2d, 4d, 6d, 8d and turns on the engine oil pre-circulation motor 71 (step S201). By opening the travel switching valves 2d, 4d, 6d, 8d, the discharge oil of the open circuit pumps 12, 14, 16, 18 is discharged to the hydraulic oil tank 50 through the center bypass oil passages 62, 62 of the travel control valves 60, 61 held in the neutral position. Thereby, even when the discharge valves 40 to 43 are not open at the time of engine start, it is possible to prevent the increase in the discharge pressure of the open circuit pumps 12, 14, 16, 18. Note that as long as the travel control valves 60, 61 are in the neutral position, no hydraulic oil is supplied to the travel motors 24, 25, so the lower traveling body 101 does not operate against the operator's intention.

[0028] Following step S201, it is determined whether the engine oil pressure switch has turned ON (step S202). While the engine oil pressure switch is OFF, the determination in step S202 is repeatedly made.

[0029] If the determination result in step S202 is YES, the engine oil pre-circulation motor 71 is turned OFF and the starter motor 70 is turned ON (step S203).

[0030] Following step S203, it is determined whether the engine rotation state has turned ON (step S204). While the engine rotation state is OFF, the determination in step S204 is repeatedly made.

[0031] If the determination result in step S204 is YES, the starter motor 70 is turned OFF, the discharge valves 40 - 43 are opened, and the traveling changeover valves 2d, 4d, 6d, 8d are closed (step S203), and this flow ends.

[0032] Figure 9 is a time chart showing the transition of the vehicle body state. Until time t0, since the key switch 80 is OFF, it is in the key OFF state. When the key switch 80 turns ON at time t1, it shifts to the key ON state. When the engine start switch 81 turns ON at time t2, the engine oil pre-circulation motor 71 turns ON and the traveling changeover valves 2d, 4d, 6d, 8d are in the open state (shifts to the engine start state). When the engine oil pressure switch 72 turns ON at time t3, the engine oil pre-circulation motor 71 turns OFF, the discharge valves 40 - 43 open, and the traveling changeover valves 2d, 4d, 6d, 8d close (shifts to the operation standby state). When a traveling operation signal is input at time t4, the discharge valves 40 - 43 close and the traveling changeover valves 2d, 4d, 6d, 8d are in the open state (shifts to the operation state). When the traveling operation signal stops being input at time t5, the traveling changeover valves 2d, 4d, 6d, 8d are in the closed state and the discharge valves 40 - 43 open (shifts to the operation standby state). When the key switch 80 turns OFF at time t5, the engine rotation state becomes OFF, the engine oil pressure switch 72 becomes OFF, and the discharge valves 40 - 43 close (shifts to the key off state).

[0033] FIG. 10 is a flowchart showing the processing of the controller 90 when shifting to the auto idle state. First, the controller 90 reduces the engine speed to the auto idle speed (step S301). Following step S301, the exhaust valves 40 to 43 are closed and the traveling switching valves 2d, 4d, 6d, 8d are opened (step S302), and the flow ends. As a result, in the auto idle state, the discharge oil of the open circuit pumps 12, 14, 16, 18 returns to the hydraulic oil tank 50 via the center bypass oil passages 62, 63 of the traveling control valves 60, 61 held at the neutral position. As a result, even when the vehicle body has stopped for a long time in a cold region, by flowing hydraulic oil through the center bypass oil passages 62, 63 of the traveling control valves 60, 61 installed in the lower traveling body 101 with few heat sources, the traveling control valves 60, 61 can be warmed up, so it is possible to prevent heat shock caused by warm hydraulic oil flowing into the cooled traveling control valves 60, 61.

[0034] FIG. 11 is a time chart showing the transition of the vehicle body state from the operation state to the auto idle state. Until time t7, since the front operation signal or the turning operation signal among the front operation signal, turning operation signal, and traveling operation signal is input, the operation state continues. When none of the front operation signal, turning operation signal, and traveling operation signal are input at time t7, the exhaust valves 40 to 43 open and the operation standby state is entered. At the timing (time t8) when the operation standby state continues for a certain period of time, the vehicle shifts to the auto idle state, the engine speed decreases from the rated speed to the auto idle speed, the exhaust valves 40 to 43 close, and the traveling switching valves 2d, 4d, 6d, 8d become open.

[0035] (Summary) In this embodiment, a hydraulic excavator 100 includes an engine 110, closed-circuit pumps 11, 13, 15, 17 and open-circuit pumps 12, 14, 16, 18 driven by the engine 110, a plurality of hydraulic actuators 20 to 25 including travel motors 24, 25, an operation device 82 for instructing the operation of the plurality of hydraulic actuators 20 to 25, a plurality of switching valves 1a to 1d, 2a to 2d, 3a to 3d, 4a to 4d, 5a to 5d, 6a to 6d, 7a to 7d, 8a to 8d having open and closed states and selectively connecting the closed-circuit pumps 11, 13, 15, 17 and the open-circuit pumps 12, 14, 16, 18 to any of the plurality of hydraulic actuators 20 to 25, among the plurality of switching valves 1a to 1d, 2a to 2d, 3a to 3d, 4a to 4d, 5a to 5d, 6a to 6d, 7a to 7d, 8a to 8d, travel switching valves 2d, 4d, 6d, 8d for connecting the open-circuit pumps 12, 14, 16, 18 to the travel motors 24, 25, travel control valves 60, 61 disposed in an oil passage connecting the travel motors 24, 25 and controlling the flow rate of the hydraulic oil supplied from the open-circuit pumps 12, 14, 16, 18 to the travel motors 24, 25 and discharging the hydraulic oil supplied from the open-circuit pumps 12, 14, 16, 18 to the hydraulic oil tank at the neutral position, a starter motor 70 for starting the engine 110, a key switch 80 for instructing the start of the engine 110, and a controller 90 to which an operation signal input from the operation device 82 is input and which outputs control signals to the plurality of switching valves 1a to 1d, 2a to 2d, 3a to 3d, 4a to 4d, 5a to 5d, 6a to 6d, 7a to 7d, 8a to 8d and the travel control valves 60, 61. When the controller 90 is instructed to start the engine 110 via the key switch 80, before starting the drive of the starter motor 70, the travel control valves 60, 61 are held in the neutral position and the travel switching valves 2d, 4d, 6d, 8d are set to the open state.

[0036] According to the present embodiment configured as described above, when the engine is started, the discharged oil of the open circuit pumps 12, 14, 16, 18 is discharged to the hydraulic oil tank 50 through the travel switching valves 2d, 4d, 6d, 8d and the center bypass oil passages 62, 63 of the travel control valves 60, 61. Therefore, an increase in the discharge pressure of the open circuit pumps 12, 14, 16, 18 is suppressed. As a result, since the driving load of the open circuit pumps 12, 14, 16, 18 at the time of engine start becomes small, it is possible to improve the starting performance of the engine 110 in a low temperature environment where the viscosity of the hydraulic oil becomes high.

[0037] Further, in the present embodiment, the hydraulic excavator 100 includes an engine oil pre-circulation motor 71 that circulates engine oil in the engine 110, and an engine oil pressure switch 72 that is in an OFF state when the pressure of the engine oil circulating in the engine 110 is equal to or lower than a predetermined threshold value and is in an ON state when the pressure of the engine oil exceeds the predetermined threshold value. When the controller 90 is instructed to start the engine 110 via the key switch 80, the travel switching valves 2d, 4d, 6d, 8d are opened while the travel control valves 60, 61 are held in the neutral position, and the driving of the engine oil pre-circulation motor 71 is started. After the engine oil pressure switch 72 is switched to the ON state, the driving of the engine oil pre-circulation motor 71 is stopped and the driving of the starter motor 70 is started. Thereby, it is possible to prevent damage or injury to the engine 110.

[0038] In addition, in the present embodiment, the hydraulic excavator 100 includes a lower traveling body 101 driven by traveling motors 24 and 25, and an upper slewing body 102 rotatably mounted on the lower traveling body 101. The traveling control valves 60 and 61 are disposed on the lower traveling body 101. When a state in which no operation signal is input from the operation device 82 continues for a certain period of time, the controller 90 opens the traveling changeover valve while holding the traveling control valves 60 and 61 in the neutral position. As a result, even when the vehicle body has stopped for a long time in a cold region, the traveling control valves 60 and 61 disposed on the lower traveling body 101 with less heat sources can be warmed up by flowing hydraulic oil through the center bypass oil passages 62 and 63 of the traveling control valves 60 and 61, so that it is possible to prevent heat shock caused by warm hydraulic oil flowing into the traveling control valves 60 and 61 in a low temperature state.

[0039] Note that the present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments are shown for explaining the present invention in an easy-to-understand manner and are not necessarily limited to those having all the configurations described.

Description of Reference Numerals

[0040] 1a~1d... switching valves, 2a~2c... switching valves, 2d... traveling switching valve, 3a~3d... switching valves, 4a~4c... switching valves, 4d... traveling switching valve, 5a~5d... switching valves, 6a~6c... switching valves, 6d... traveling switching valve, 7a~7d... switching valves, 8a~8c... switching valves, 8d... traveling switching valve, 10... control pump, 11, 13, 15, 17... closed-circuit pumps, 12, 14, 16, 18... open-circuit pumps, 20... boom cylinder (hydraulic actuator), 21... arm cylinder (hydraulic actuator), 22... bucket cylinder (hydraulic actuator), 23... slewing motor (hydraulic actuator), 24, 25... traveling motors (hydraulic actuators), 30~33... relief valves, 40~43... discharge valves, 50... hydraulic oil tank, 60, 61... traveling control valves, 62, 63... center bypass oil passages, 70... starter motor, 71... engine oil pressure circulation motor, 72... engine oil pressure switch, 73... engine speed sensor, 80... key switch, 81... engine start switch, 82... operating device, 90... controller, 100... hydraulic excavator, 101... lower traveling body, 102... upper slewing body, 103... front working machine, 104... boom, 105... arm, 106... bucket, 110... engine, 111... pump assembly, 112... valve assembly, 113... center joint, 200... hydraulic drive device.

Claims

1. An engine, a closed-circuit pump and an open-circuit pump driven by the engine, a plurality of hydraulic actuators including a travel motor, an operating device for instructing the operation of the plurality of hydraulic actuators, a plurality of switching valves having an open state and a closed state, and selectively connecting the closed-circuit pump and the open-circuit pump to any one of the plurality of hydraulic actuators in the open state, Among the plurality of switching valves, a travel control valve that is disposed in an oil passage connecting the travel switching valve that connects the open-circuit pump to the travel motor and the travel motor, controls the flow rate of the hydraulic oil supplied from the open-circuit pump to the travel motor, and discharges the hydraulic oil supplied from the open-circuit pump to the hydraulic oil tank at the neutral position, a starter motor for starting the engine, a key switch for instructing the start of the engine, In a work machine including a controller that receives an operation signal input from the operation device and outputs a control signal to the plurality of switching valves and the travel control valve, When the controller is instructed to start the engine via the key switch, before starting the drive of the starter motor, the travel control valve is held in the neutral position and the travel switching valve is set to the open state A hydraulic drive device characterized by the above.

2. In the hydraulic drive device according to claim 1, an engine oil pre-circulation motor for circulating engine oil in the engine, an engine oil pressure switch that is in an OFF state when the pressure of the engine oil circulating in the engine is equal to or lower than a predetermined threshold value, and is in an ON state when the pressure of the engine oil exceeds the predetermined threshold value, When the controller is instructed to start the engine via the key switch, it sets the travel switching valve to the open state while holding the travel control valve in the neutral position and starts driving the engine oil pressure circulation motor. After the engine oil pressure switch switches to the ON state, it stops driving the engine oil pressure circulation motor and starts driving the starter motor. A hydraulic drive device characterized by the above.

3. In the hydraulic drive device according to Claim 1, a lower traveling body driven by the travel motor, and an upper revolving body rotatably mounted on the lower traveling body. The travel control valve is arranged on the lower traveling body. When a state where no operation signal is input from the operation device continues for a certain period of time, the controller sets the travel switching valve to the open state while holding the travel control valve in the neutral position. A hydraulic drive device characterized by the above.

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