JPH0681807A - Hydraulic motor driving circuit - Google Patents

Abstract

PURPOSE:To improve the reliability, safety and the like by supplying oil pressure to a braking mechanism for certainly releasing a brake even if a specific command pressure is not generated by a solenoid switching valve because of failures. CONSTITUTION:A manual switching valve 31 is provided between a solenoid switching valve 20 and a parking brake 21, and the parking brake 21 is selectively connected to the solenoid switching valve 20 or a pilot oil pressure source 9. In any abnormal case where specific command pressure is not generated from the solenoid switching valve 20 because of failures of electric system like a pressure sensor 16 or a control unit 18, the discharge pressure from the pilot oil pressure source 9 is supplied to the parking brake 21, moreover the brake can be released by switching the position of the manual switching valve 31 to an abnormal position B from a normal position A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a hydraulic excavator,
The present invention relates to a hydraulic motor drive circuit for controlling the drive of a traveling hydraulic motor or a turning hydraulic motor provided in a construction machine such as a hydraulic crane, and in particular, a hydraulic pressure provided with a brake mechanism that releases a brake by a command pressure from an electromagnetic switching valve. The present invention relates to a motor drive circuit.

[0002]

2. Description of the Related Art FIGS. 5 and 6 show examples in which a hydraulic motor drive circuit according to the prior art is used in a construction machine such as a hydraulic excavator.

In the drawing, reference numeral 1 denotes a traveling hydraulic motor provided on the sprocket (neither of which is shown) side of a lower traveling body of a hydraulic excavator. The hydraulic motor 1 is, for example, a swash plate type or an oblique shaft type. , A radial piston type hydraulic motor is used, and a variable capacity section 1A including a swash plate, a valve plate, a cam ring, etc. is provided. And the hydraulic motor 1
Is a variable capacity unit 1 via a servo actuator 2 described later.
By operating A, the motor capacity can be variably adjusted.

Reference numeral 2 denotes a servo actuator which is attached to the hydraulic motor 1 and constitutes a tilt control mechanism together with a displacement control valve 12 which will be described later. The servo actuator 2 is slidable in the cylinder 2A and the cylinder 2A. A piston 2B is provided, a piston rod 2C having a proximal end fixed to the piston 2B, a distal end protruding outside the cylinder 2A and connected to the variable capacity portion 1A of the hydraulic motor 1, and a piston 2B defined inside the cylinder 2A. It is composed of a large oil chamber 2D and a small oil chamber 2E, and each oil chamber 2D, 2E is connected to the capacity control valve 12.

Then, the servo actuator 2 is
When the motor self-pressure, which will be described later, is supplied to the oil chambers 2D and 2E, respectively, the piston rod 2C expands in the direction of arrow A due to the difference in pressure receiving area, so that the motor capacity of the hydraulic motor 1 becomes constant. Is. Further, when the displacement control valve 12 is switched and the motor self-pressure is supplied only to the small oil chamber 2E, the piston rod 2C is contracted in the direction of arrow B, so that the displacement of the motor becomes constant. ing.

Reference numeral 3 denotes a hydraulic pump provided on the upper swing body of the hydraulic excavator and driven by an engine (neither of which is shown), 4 denotes a tank, and the hydraulic pump 3 and the tank 4 are connected via pipes 5A and 5B. Is connected to the hydraulic motor 1, and a brake valve (not shown) attached to the hydraulic motor 1 is provided in the middle of each of the pipes 5A and 5B.

Reference numeral 6 denotes a hydraulic pilot type directional control valve provided between the hydraulic motor 1 and the hydraulic pump 3 and the tank 4 and provided in the middle of each of the pipes 5A and 5B. It is composed of a spool switching valve at the position of port 3, and is connected to pilot valves 8B and 8C of a traveling lever device 8 described later via pilot conduits 7A and 7B. Then, the directional control valve 6 is switched from the neutral position (a) to the forward drive position (b) and the reverse drive position (c) when the pilot pressure of not less than the predetermined switching pressure Pc is supplied from the pilot valves 8B and 8C. As a result, the hydraulic oil from the hydraulic pump 3 is supplied to and discharged from the hydraulic motor 1 as the motor drive pressure.

Reference numeral 8 denotes a traveling lever device as pilot type operating means provided in a driver's cab (not shown) of the hydraulic excavator. The traveling lever device 8 is an operating lever 8A.
And a pressure reducing valve type pilot valve 8B, 8C for generating pilot pressure in response to tilting operation of the operating lever 8A. The pilot valve 8B, 8C serves as a tank 4 and another hydraulic source. Is connected to the pilot hydraulic power source 9. When the driver tilts the operation lever 8A to the forward side or the reverse side, the traveling lever device 8 generates a pilot pressure according to the operation amount and switches the directional control valve 6. .

Reference numeral 10 denotes a motor-side high-pressure selection valve provided between the hydraulic motor 1 and the direction switching valve 6 and provided in the middle of each pipe 5A, 5B. The motor-side high-pressure selection valve 10 is provided for each pipe 5A. , The pressure on the high-pressure side of the motor drive pressure flowing through 5B is derived as the motor self-pressure and supplied to the capacity control valve 12 via the self-pressure pipe 11.

Reference numeral 12 denotes a displacement control valve attached to the hydraulic motor 1 together with the servo actuator 2. The displacement control valve 12 is composed of a hydraulic pilot type 4-port 2-position spool valve. The capacity control valve 12 has one end connected to the motor-side high pressure selection valve 10 and the tank 4, and the other end connected to each oil chamber 2 of the servo actuator 2.
In addition to being selectively connected to D and 2E, the pilot port 12A is connected to an electromagnetic switching valve 20 described later via another pilot conduit 13.

The displacement control valve 12 is normally in the large displacement position (a) to extend the piston rod 2C of the servo actuator 2 in the direction of arrow A, and through the pilot conduit 13 to a predetermined position. When the switching pressure Pm is supplied to the pilot port 12A, the switching position is switched from the large capacity position (a) to the small capacity position (b), and the piston rod 2C of the servo actuator 2 is contracted in the arrow B direction.

Reference numeral 14 denotes a pilot side high pressure selection valve as a pilot pressure derivation means provided between the pilot pipelines 7A and 7B. The pilot side high pressure selection valve 14 flows in the pilot pipelines 7A and 7B. The pressure on the high pressure side of the pilot pressure is derived as the pilot line pressure Pk,
A pressure sensor 1 to be described later via a pilot pressure derivation conduit 15.
6 is to be supplied.

Reference numeral 16 is provided on the upper revolving structure side, and a pilot side high pressure selection valve 14 is provided via a pilot pressure derivation pipe line 15.
The pressure sensor 16 is connected to the pilot pressure derivation pipe 15, and the pressure sensor 16 converts the pressure in the pilot pressure derivation pipe 15 into an electric signal to detect the pressure. Is output to the control unit 18 described later.

Reference numeral 17 denotes a tilting switch provided in the driver's cab. The tilting switch 17 is selectively switched by a driver to output tilting signals of "H" and "L" to the control unit 18. It is designed to output to. Here, when the tilt signal is "H", it means selection of low torque and high speed running state, and when the tilt signal is "L", it means selection of high torque and low speed running state.

Reference numeral 18 denotes a control unit which is provided on the side of the upper revolving structure and serves as a control means composed of a CPU and the like as a microcomputer. The control unit 18 has a pressure sensor 16 and a tilt switch 17 on its input side. The electromagnetic switching valve 20 is connected to the output side thereof.
Are connected. In addition, the control unit 18
6, a command pressure control processing program shown in FIG. 6 and a switching pressure Pc of the directional control valve 6 are stored in a memory circuit including a ROM and a RAM.
Etc. are stored. Then, the control unit 18 controls the pilot line pressure P detected by the pressure sensor 16.
A control signal is output to the electromagnetic switching valve 20 based on k, and a predetermined command pressure P is generated by the electromagnetic switching valve 20.

Reference numeral 19 is a command pressure line provided between a parking brake 21 and a pilot hydraulic power source 9 which will be described later, and 20 is an electromagnetic switching valve provided on the upper swing body side and provided in the middle of the command pressure line 19. The respective electromagnetic switching valve 20 is shown as a proportional electromagnetic switching valve. The electromagnetic switching valve 20 has a pilot hydraulic power source 9 and a tank 4 on the inflow side.
Is selectively connected, and its outflow side is connected to the parking brake 21 via the command pressure line 19 and to the capacity control valve 12 via the pilot line 13. The electromagnetic switching valve 20 generates a predetermined command pressure P between the discharge pressure Pf of the pilot hydraulic pressure source 9 and the tank pressure based on the control signal amount from the control unit 18.

Reference numeral 21 denotes a parking brake as a brake mechanism attached to the hydraulic motor 1, and the parking brake 21
Is configured as a negative brake that constantly prevents the output shaft of the hydraulic motor 1 from rotating.
Connected to. Then, the parking brake 21 is
The hydraulic motor 1 is normally prevented from rotating, and when the command pressure P supplied from the electromagnetic switching valve 20 via the command pressure line 19 exceeds a predetermined brake release pressure Pb, the brake is released to rotate the hydraulic motor 1. Is allowed.

In the figure, reference numeral 22 shown by a chain line indicates a center joint provided in a turning device (not shown), through which oil liquid or the like from the hydraulic pump 3 passes through the center joint 22. Etc.

The drive circuit for the hydraulic motor according to the prior art has the above-mentioned configuration. Next, the command pressure control process by the control unit 18 will be described with reference to FIG.

First, in step 1, the detection signal from the pressure sensor 16 is read, and in step 2, the pilot line pressure Pk detected by the pressure sensor 16 and the switching pressure Pc required to switch the direction switching valve 6 are set. And the pilot line pressure Pk exceeds the switching pressure Pc.
If it is determined to be "NO" in this step 2, the pilot line pressure Pk is lower than the switching pressure Pc and the direction switching valve 6 does not switch, that is, the operating lever 8A of the traveling lever device 8 moves in the forward direction. Since the vehicle is not operated in either the reverse direction, the process moves to step 3 and the command pressure P is set to 0 (tank pressure), so that in step 4, the parking brake 21 remains activated. deep.

At this time, the command pressure P from the electromagnetic switching valve 20 is also supplied to the capacity control valve 12 via the pilot line 13, but the command pressure P is necessary for switching the capacity control valve 12. The switching pressure Pm is lower than that (Pm> P =
0), since the motor self pressure derived by the motor side high pressure selection valve 10 is also the tank pressure, the capacity control valve 12
Maintains the large capacity position (a) and maintains the motor capacity of the hydraulic motor 1 at a large constant capacity.

On the other hand, if "YES" is determined in step 2, the pilot line pressure Pk exceeds the switching pressure Pc of the directional control valve 6, and the directional control valve 6 moves from the neutral position (a) to the forward position (ro). ), When it is switched to any of the reverse positions (c), that is, because the operating lever 8A of the travel lever device 8 is in the traveling state in which the operation lever 8A is tilted in either the forward direction or the reverse direction, the following step Move on to.

Then, in step 5, the tilt switch 1
The tilt signal from the tilt switch 7 is read, and in step 6, it is determined whether or not the tilt signal output from the tilt switch 17 is "H". When it is determined to be "YES" in this step 6, since the tilt signal from the tilt switch 17 is "H" and the driver wants to drive at high speed, the process proceeds to the next step 7 and the electromagnetic A control signal is output to the switching valve 20, and the command pressure P from the electromagnetic switching valve 20 is applied to the parking brake 2
The maximum command pressure PH that exceeds the brake release pressure Pb of 1 and the switching pressure Pm of the displacement control valve 12 is set (PH>Pm>
Pb).

As a result, the parking brake 21 is released and the rotation of the hydraulic motor 1 is permitted.
The displacement control valve 12 is switched from the large displacement position (a) to the small displacement position (b), the piston rod 2C of the servo actuator 2 is contracted in the direction of arrow B, the motor displacement of the hydraulic motor 1 is reduced, and the hydraulic excavator is reduced. Runs at low torque and high speed.

On the other hand, if "NO" is determined in step 6, it means that the tilt signal from the tilt switch 17 is "L" and the driver wants to run at a low speed such as when climbing a slope. , The control signal is output to the electromagnetic switching valve 20, and the command pressure P is set to the minimum command pressure PL which is larger than the brake release pressure Pb of the parking brake 21 and smaller than the switching pressure Pm of the displacement control valve 12. (Pb <PL <Pm <
PH).

As a result, although the brake of the parking brake 21 is released, the displacement control valve 12 maintains the large displacement position (a), so that the hydraulic excavator travels at a high torque and at a low speed.

[0027]

By the way, in the hydraulic motor drive circuit of the hydraulic excavator according to the above-mentioned prior art,
Since the electromagnetic switching valve 20 and the parking brake 21 are connected via the command pressure conduit 19 and the electromagnetic switching valve 20 and the capacity control valve 12 are connected via the pilot conduit 13, the electromagnetic switching valve 20 is connected. By adjusting the command pressure P by the parking brake 21 according to the operation of the traveling lever device 8.
And the capacity control valve 12 can be controlled almost simultaneously.

However, in the prior art, the command pressure P is automatically adjusted by outputting a control signal from the control unit 18 to the electromagnetic switching valve 20, so that the pressure sensor 16 and the control unit 1 are controlled.
8. If electrical equipment such as the electromagnetic switching valve 20 fails or the electrical wiring connecting them is broken, the command pressure P can be generated by the electromagnetic switching valve 20 even if the traveling lever device 8 is operated. No, the parking brake 21 cannot be released.

Therefore, according to the above-mentioned conventional technique, when the traveling lever device 8 is operated when the electric system such as the electromagnetic switching valve 20 fails, the pilot valves 8B and 8C of the traveling lever device 8 generate the same. The directional switching valve 6 is switched by the pilot pressure, the drive pressure from the hydraulic pump 3 is supplied to the hydraulic motor 1 and the hydraulic motor 1 tries to rotate, but the command pressure P remains the tank pressure, so the parking brake. The phenomenon that 21 is not released occurs.

As a result, the hydraulic motor 1 rotates without releasing the parking brake 21, the motor oil temperature rises, and the brake portion of the parking brake 21 is worn and damaged.
There is a problem that reliability and safety are significantly reduced. In addition, when the electric system such as the electromagnetic switching valve 20 fails while the hydraulic excavator is running, the braking force of the parking brake 21 suddenly acts on the rotating hydraulic motor 1 to increase the motor oil temperature and the parking speed. There is a problem that the brake 21 is damaged and the life, traveling safety, reliability, etc. are significantly reduced.

The present invention has been made in view of the above-mentioned problems of the prior art. Even when a predetermined command pressure is not generated from the electromagnetic switching valve due to a failure or the like, the hydraulic pressure is supplied to the brake mechanism to reliably release the brake. Another object of the present invention is to provide a drive circuit for a hydraulic motor, which is capable of improving reliability and safety.

[0032]

In order to solve the above-mentioned problems, the feature of the configuration adopted by the present invention is that the brake mechanism is provided between the electromagnetic switching valve and the brake mechanism. A manual switching valve for selectively switching to the hydraulic power source is provided.

The hydraulic motor is a variable displacement type hydraulic motor having a displacement control valve for adjusting the motor displacement according to the pilot pressure, and the pilot port of the displacement control valve is a brake mechanism and a manual switching valve. Preferably, it is connected to a line between

[0034]

When the electromagnetic switching valve is operating normally, the brake mechanism and the electromagnetic switching valve are connected by the manual switching valve, and the brake of the brake mechanism is released by the command pressure from the electromagnetic switching valve. On the other hand, if the specified command pressure is not generated from the electromagnetic switching valve due to an electric system failure, etc., the manual switching valve is switched to connect the brake mechanism to another hydraulic source, Supply the hydraulic pressure to release the brake of the brake mechanism.

Further, a variable displacement hydraulic motor having a displacement control valve for adjusting the displacement of the hydraulic motor according to the pilot pressure is used, and the pilot port of the displacement control valve is provided with a brake mechanism and a manual switching valve. If the electromagnetic switching valve is operating normally, the brake mechanism and the motor capacity of the hydraulic motor can be controlled by connecting to the pipeline between them when the electromagnetic switching valve is operating normally. On the other hand, when it is abnormal that the command pressure is not generated from the electromagnetic switching valve, the brake mechanism and the motor capacity of the hydraulic motor are controlled by the hydraulic pressure from another hydraulic source supplied via the manual switching valve.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS. In the embodiment, the same components as those of the conventional technique shown in FIGS. 5 and 6 described above are designated by the same reference numerals, and the description thereof will be omitted.

First, FIG. 1 shows a first embodiment of the present invention.

In the figure, reference numeral 31 denotes a manual switching valve provided between the electromagnetic switching valve 20 and the parking brake 21 and provided in the middle of the command pressure line 19. The manual switching valve 31 is a 3-port 2-port type. It is configured as a position switching valve, and an inflow side thereof is connected with an electromagnetic switching valve 20 via a command pressure line 19, and a pilot hydraulic power source 9 is selectively connected via a bypass line 32, and its outflow side. A parking brake 21 and a capacity control valve 12 are connected to the side via a command pressure line 19 and a pilot line 13.

The manual switching valve 31 is normally in the normal position (a), and the parking brake 21 and the capacity control valve 12 are connected to the electromagnetic switching valve 20.
When the driver performs switching operation, the normal position (a) is switched to the abnormal position (b), and the parking brake 21 and the capacity control valve 12 are piloted via the bypass conduit 32. It is connected to the hydraulic pressure source 9 and supplies a discharge pressure Pf (Pf> Pb) larger than the brake release pressure Pb of the parking brake 21 from the pilot hydraulic pressure source 9.

The hydraulic motor drive circuit according to the present embodiment has the above-mentioned structure, and its basic operation is not different from that of the prior art.

However, in this embodiment, the manual switching valve 31 is provided between the electromagnetic switching valve 20 and the parking brake 21, and the parking brake 21 is connected to the electromagnetic switching valve 20 and the pilot by the manual switching valve 31. Since it is configured to be selectively connected to the hydraulic power source 9, a predetermined command pressure P is not generated from the electromagnetic switching valve 20 due to a failure of the electric system such as the pressure sensor 16, the control unit 18, the electromagnetic switching valve 20 and the like. In this case, the manual switching valve 31 is switched from the normal position (a) to the abnormal position (b) so that the discharge pressure Pf from the pilot hydraulic power source 9 is passed through the bypass pipeline 32 and the command pressure pipeline 19 to the parking brake. 21 can be supplied.

As a result, even if the electromagnetic switching valve 20 or the like is abnormal, the parking brake 21 can be reliably released manually, and the hydraulic motor 1 can effectively rotate without releasing the parking brake 21. To prevent the motor oil temperature from rising and the parking brake 21 from being damaged,
The reliability and safety can be greatly improved.

Further, the pilot port 12A of the capacity control valve 12 is connected to the manual switching valve 31 via the pilot line 13.
Since it is configured to be connected in the middle of the command pressure line 19 between the parking brake 21 and the parking brake 21, the discharge pressure Pf from the pilot hydraulic pressure source 9 is used in the abnormal case where the predetermined command pressure P is not generated from the electromagnetic switching valve 20. The capacity control valve 12 can also be switched.

That is, the discharge pressure Pf of the pilot hydraulic power source 9 is larger than the brake release pressure Pb of the parking brake 21 as well as the minimum command pressure PL, and the switching pressure P of the displacement control valve 12 is increased.
If it is set to be smaller than m (Pb <Pf
<Pm), the discharge pressure Pf causes the parking brake 21 to keep the motor capacity of the hydraulic motor 1 large.
Can be released and the vehicle can run at low speed.

On the other hand, the discharge pressure Pf from the pilot hydraulic pressure source
Is set to be larger than the brake release pressure Pb of the parking brake 21 and the switching pressure Pm of the displacement control valve 12 in the same manner as the maximum command pressure PH (Pb <Pm <P
f) While the brake of the parking brake 21 is released, the motor capacity of the hydraulic motor 1 can be switched to a constant small capacity for high speed traveling.

Next, FIG. 2 shows a second embodiment of the present invention. The feature of this embodiment is that two manual on-off valves are used as the manual switching valves. In this embodiment, the same components as those in the first embodiment described above are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, reference numeral 41 denotes a manual switching valve applied to this embodiment in place of the manual switching valve 31 described in the first embodiment, and the manual switching valve 41 is the first switching valve. Almost the same as the manual switching valve 31 described in the embodiment, the electromagnetic switching valve 20
Is located between the parking brake 21 and the parking brake 21. However, the manual switching valve 41 according to the present embodiment is one manual opening / closing valve 41A provided on the downstream side of the electromagnetic switching valve 20 and provided in the middle of the command pressure line 19.
And another manual on-off valve 41B provided in the middle of the bypass pipe 32, and each of the on-off valves 41A and 41B.
Is connected in the middle of the command pressure line 19.

When the electromagnetic switching valve 20 operates normally, the manual switching valve 41 is one manual switching valve 4
By opening 1A and closing the other manual open / close valve 41B, the command pressure P from the electromagnetic switching valve 20 is supplied to the parking brake 21 and the capacity control valve 12 via the single manual open / close valve 41A. If the electromagnetic switch valve 20 does not generate the predetermined command pressure P and is abnormal, the one manual open / close valve 41A is closed and the other manual open / close valve 41B is opened, so that the pilot Discharge pressure P from hydraulic pressure source 9
f through the other manual opening / closing valve 41B to the parking brake 21
And to the capacity control valve 12.

Thus, in this embodiment having such a configuration, it is possible to obtain substantially the same operational effects as those of the first embodiment described above. However, in this embodiment, since the manual switching valve 41 is composed of the two manual opening / closing valves 41A and 41B, the reliability and the like can be easily reduced at a lower cost as compared with the first embodiment. Can be improved.

In each of the above embodiments, the case where the pilot hydraulic pressure source 9 is used as another hydraulic pressure source has been described as an example, but the present invention is not limited to this, and for example, the first modification shown in FIG. As in the example, the inflow side of the bypass line 32 ′ is connected to the pilot pressure derivation line 15, and the pilot side high pressure selection valve 1
The pilot line pressure Pk from 4 may be used. In this case, since the traveling lever device 8 and the parking brake 21 are interlocked with each other, the manual switching valve 31 is operated when the electric system fails.
When the vehicle is switched to the abnormal position (b), if the traveling lever device 8 is in the neutral position, the parking brake 21 is not released and the safety can be further improved.

Further, as in the second modification shown in FIG. 4, a hydraulic pressure source 51 separate from the pilot hydraulic pressure source 9 may be used.

Further, in each of the above-described embodiments, the case where the drive of the traveling motor of the hydraulic excavator is controlled has been described as an example, but the present invention is not limited to this, and other hydraulic motors for turning, hydraulic cranes, etc. It can also be widely applied to hydraulic motors for construction machinery.

[0053]

As described in detail above, according to the present invention, between the electromagnetic switching valve and the brake mechanism, the manual switching for selectively switching the braking mechanism between the electromagnetic switching valve and another hydraulic source. Since the valve is provided, if the specified command pressure is not generated from the electromagnetic switching valve due to an electric system failure, etc., the manual switching valve is switched to connect the brake mechanism to another hydraulic pressure source. It is possible to release the brake of the brake mechanism manually by reliably supplying the oil pressure from the source, effectively preventing the hydraulic motor from rotating without releasing the brake of the brake mechanism, and increasing the motor oil temperature. It is possible to prevent damage to the brake mechanism and improve the life, reliability and safety.

A variable displacement type hydraulic motor having a displacement control valve for adjusting the displacement of the motor according to the pilot pressure is used as the hydraulic motor, and the pilot port of the displacement control valve is a brake mechanism and a manual switching valve. Since it is configured to be connected to the pipeline between and, even if the command pressure is not generated from the electromagnetic switching valve, even if there is an abnormality, the hydraulic pressure from the other hydraulic source supplied via the manual switching valve causes the brake mechanism to operate. The motor capacity of the hydraulic motor can be controlled.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a hydraulic motor drive circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram showing a hydraulic motor drive circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit configuration diagram showing a hydraulic motor drive circuit according to a first modification of the present invention.

FIG. 4 is a circuit configuration diagram showing a hydraulic motor drive circuit according to a second modification of the present invention.

FIG. 5 is a circuit configuration diagram showing a hydraulic motor drive circuit according to a conventional technique.

6 is a flowchart showing a command pressure control process performed by the control unit shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 hydraulic motor 3 hydraulic pump 6 directional switching valve 8 traveling lever device (operating means) 9 pilot hydraulic pressure source (other hydraulic pressure source) 12 capacity control valve 14 pilot side high pressure selection valve (pilot pressure derivation means) 18 control unit (control means) ) 20 electromagnetic switching valve 21 parking brake (brake mechanism) 31, 41 manual switching valve 51 hydraulic source (other hydraulic source)

Claims (2)

[Claims] 1. A hydraulic motor, and a pilot-type directional control valve for supplying and discharging pressure oil from a hydraulic pump to the hydraulic motor,
Pilot-type operating means for generating a pilot pressure according to an operation amount and supplying it to the directional control valve, pilot pressure deriving means for deriving a pilot pressure according to the operation amount by the operating means, and the pilot pressure deriving means. Control means for outputting a control signal in accordance with the pilot pressure from the control means, an electromagnetic switching valve for generating a command pressure based on the control signal from the control means, and a command from the electromagnetic switching valve provided in the hydraulic motor. In a hydraulic motor drive circuit including a brake mechanism that releases a brake by pressure, between the electromagnetic switching valve and the brake mechanism, the braking mechanism is selectively switched between the electromagnetic switching valve and another hydraulic source. A hydraulic motor drive circuit having a manual switching valve. 2. A variable displacement type hydraulic motor having a displacement control valve for adjusting a motor displacement according to pilot pressure is used as the hydraulic motor, and a pilot port of the displacement control valve is provided with the brake mechanism and the manual type. The hydraulic motor drive circuit according to claim 1, wherein the hydraulic motor drive circuit is connected to a line between the switching valve and the switching valve.