JPH0681809A - Hydraulic motor driving circuit - Google Patents

Abstract

PURPOSE:To improve the reliability by automatically supplying oil pressure to a brake mechanism for releasing a brake when a specific command pressure is not generated by a solenoid switching valve because of failures. CONSTITUTION:An oil pressure pilot-type switching valve 31 whose switching position is determined by command pressure from a solenoid switching valve 20 is provided between the solenoid switching valve 20 and a parking brake 21. The oil pressure pilot type switch valve 31 is so constituted as switching and connecting the parking brake 21 to a pilot side high pressure selector valve 14 by means of a return spring 31c when a command pressure is below a switching pressure as a specific pressure. Therefore, in any abnormal case where a specific command pressure is not generated from the solenoid switching valve 20 because of failures of electric system like a pressure sensor 16 or the solenoid switching valve 20, the oil pressure pilot type switching valve 31 is automatically returned to an abnormal position B from a normal position A, thereby pilot line pressure from the pilot side high pressure selector valve 14 is supplied to the parking brake 21 through a pilot pressure efferent line 15, a bypass line 32 and a command pressure line 19.

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. 3 and 4 show an example in which a conventional hydraulic motor drive circuit 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. . Further, when the operation amount of the operation lever 8A is in a substantially neutral position where the operation lever 8A is equal to or less than a predetermined amount, the traveling lever device 8 sets the pilot pressure to the tank pressure
That is, it is set to zero.

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. Here, when the traveling lever device 8 is in the neutral position, the hydraulic excavator is stopped and the pilot line pressure Pk is the tank pressure, that is, zero.

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
In the memory circuit composed of ROM, RAM, etc., the command pressure control processing program shown in FIG.
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 structure. 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 automatically supplied to the brake mechanism to reliably brake. Another object of the present invention is to provide a drive circuit for a hydraulic motor that can be released from the above and that can improve reliability and safety.

[0032]

In order to solve the above-mentioned problems, the feature of the structure adopted by the present invention is that the electromagnetic switching valve and the brake mechanism are switched by a command pressure from the electromagnetic switching valve. A hydraulic pilot type switching valve whose position is determined is provided, and the hydraulic pilot type switching valve is configured to switch the brake mechanism from the electromagnetic switching valve side to another hydraulic power source side when the command pressure falls below a predetermined pressure. Especially.

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 switched between a brake mechanism and a hydraulic pilot type. It is preferably connected to a line between the valve and the valve.

[0034]

When the electromagnetic switching valve is operating normally, the brake mechanism and the electromagnetic switching valve are connected via the hydraulic pilot type switching valve, and the brake of the brake mechanism is activated by the command pressure from the electromagnetic switching valve. It will be canceled. On the other hand, when the electromagnetic switch valve does not generate a predetermined command pressure due to an electric system failure or the like, the command pressure falls below the predetermined pressure, the hydraulic pilot type switching valve switches, and the brake mechanism switches to another hydraulic power source. The brake of the brake mechanism is released by the hydraulic pressure from the hydraulic pressure source.

Further, a variable displacement type 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 a brake mechanism and a hydraulic pilot type switching valve. If it is connected to the pipe line between, when the electromagnetic switching valve is operating normally,
The command pressure from the electromagnetic switching valve controls the brake mechanism and the motor displacement of the hydraulic motor. On the other hand, when 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 hydraulic pilot type switching valve. .

[0036]

Embodiments of the present invention will be described below with reference to FIGS. In the embodiment, the same components as those of the prior art shown in FIGS. 3 and 4 described above are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, reference numeral 31 denotes a hydraulic pilot type 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, and the hydraulic pilot type switching valve 31 is 3 in number. It is configured as a spring return type hydraulic pilot type switching valve at the position of port 2, and an inflow side thereof is connected to an electromagnetic switching valve 20 via a command pressure pipeline 19, and a bypass pipeline 32 and a pilot pressure derivation pipeline 15 are provided.
The pilot-side high pressure selection valve 14 is selectively connected via the command line 19 and the pilot line 1 on the outflow side.
A parking brake 21 and a capacity control valve 12 are connected via the switch 3.

Further, the hydraulic pilot type switching valve 31
Indicates that one pilot port 31A is the pilot conduit 3
3 is located on the outlet side of the electromagnetic switching valve 20 and is connected in the middle of the command pressure line 19, and the other pilot port 31
By connecting B to the tank 4, the electromagnetic switching valve 20
The switching position is determined by the balance between the command pressure P from P and the spring force of the return spring 31C.

The hydraulic pilot type switching valve 31 is provided.
When a predetermined command pressure P is supplied from the electromagnetic switching valve 20 and exceeds the switching pressure Pa (P> Pa), the state shown in the figure is switched to the normal position (a), the parking brake 21 and the capacity control valve 12 are switched. Is connected to the electromagnetic switching valve 20, and the electromagnetic switching valve 2
The command pressure P from 0 is supplied.

On the other hand, when the vehicle is stopped or the electric system is broken,
When the command pressure P from the electromagnetic switching valve 20 becomes the tank pressure and falls below the switching pressure Pa (Pa> P = 0), the hydraulic pilot type switching valve 31 is moved from the normal position (a) to the abnormal position by the spring force of the return spring 31C. Return to (B) and park the brake 21
The capacity control valve 12 is connected to the pilot side high pressure selection valve 14 via the bypass line 32 and the pilot pressure derivation line 15, and the pilot side high pressure selection valve 14 is connected to the pilot side high pressure selection valve 14 according to the tilting operation amount of the traveling lever device 8. The pilot line pressure Pk (Pk, which is greater than the brake release pressure Pb of the parking brake 21)
> Pb) is supplied.

However, even if the hydraulic pilot type switching valve 31 is switched to the abnormal position (b) when the vehicle is normally stopped, since the traveling lever device 8 is in the neutral position, the pilot line pressure Pk is also zero and the parking brake 21. Is not released.

Here, the hydraulic pilot type switching valve 31
The relationship between the switching pressure Pa and the command pressure P is expressed by the following formula 1.

[0043]

[Equation 1] Pa <PL <PH

That is, regardless of whether the command pressure P from the electromagnetic switching valve 20 is the highest command pressure PH or the lowest command pressure PL, the command pressure P exceeds the switching pressure Pa of the hydraulic pilot type switching valve 31, During normal traveling, the hydraulic pilot type switching valve 31 is switched to the normal position (a), while the command pressure P becomes the tank pressure and the switching pressure Pa is changed due to a failure of the electric system such as the electromagnetic switching valve 20 while the vehicle is stopped. When it falls below, the hydraulic pilot type switching valve 31 is automatically returned from the normal position (a) to the abnormal position (b) by the spring force of the return spring 31C.

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, a hydraulic pilot type switching valve 31 is provided which is located between the electromagnetic switching valve 20 and the parking brake 21 and whose switching position is determined by the command pressure P from the electromagnetic switching valve 20. When the command pressure P falls below the predetermined switching pressure Pa, the pilot type switching valve 31
Since the parking brake 21 is switched and connected to the pilot side high pressure selection valve 14 which derives the pilot line pressure Pk according to the operation amount of the traveling lever device 8, the pressure sensor 1
6, when there is an abnormality in which the predetermined command pressure P does not occur from the electromagnetic switching valve 20 due to a failure in the electrical system of the control unit 18, the electromagnetic switching valve 20, etc., the hydraulic pilot type switching valve 3
1 is automatically returned from the normal position (a) to the abnormal position (b) by the return spring 31C, and the pilot line pressure Pk from the pilot side high pressure selection valve 14 is converted into the pilot pressure derivation line 15 and the bypass line 32. , Can be reliably supplied to the parking brake 21 via the command pressure line 19.

As a result, even if an abnormality occurs in the electromagnetic switching valve 20 or the like, the parking brake 21 can be reliably and automatically released according to the operation amount of the traveling lever device 8, and the parking brake 21 is released. It is possible to effectively prevent the hydraulic motor 1 from rotating without being operated, prevent an increase in motor oil temperature and prevent the parking brake 21 from being damaged, and greatly improve the life, reliability, safety, and the like. Even if the hydraulic pilot type switching valve 31 is switched to the abnormal position (b),
If the travel lever device 8 is at an operation amount less than a predetermined amount, that is, substantially in the neutral position and the pilot line pressure Pk is the tank pressure, that is, zero, the parking brake 21 is not released and safety is improved.

Further, the pilot port 12A of the capacity control valve 12 is connected to the command pressure line 19 between the hydraulic pilot type switching valve 31 and the parking brake 21 via the pilot line 13.
Since the connection is made in the middle of the operation, the capacity control valve 12 is switched by the pilot line pressure Pk from the pilot side high pressure selection valve 14 in the abnormal case where the predetermined command pressure P is not generated from the electromagnetic switching valve 20. You can also

That is, the pilot line pressure Pk from the pilot side high pressure selection valve 14 is the same as the above-mentioned minimum command pressure PL,
If it 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 <P
k <Pm), and the pilot line pressure Pk allows the parking brake 21 to be released and the vehicle to run at a low speed while the motor capacity of the hydraulic motor 1 is kept large.

On the other hand, the pilot line pressure Pk from the pilot side high pressure selection valve 14 is the same as the maximum command pressure PH,
If it is larger than the brake release pressure Pb of the parking brake 21 and the switching pressure Pm of the displacement control valve 12 (Pb <Pm <P
k), while releasing the brake of the parking brake 21, the motor capacity of the hydraulic motor 1 can be switched to a constant small capacity to perform high speed traveling.

In the above embodiment, the pilot line pressure P from the pilot side high pressure selection valve 14 is used as another hydraulic pressure source.
Although the case of using k has been described as an example, the present invention is not limited to this, and the inflow side of the bypass line 32 ′ is connected to the motor side via the self-pressure pipe 11 as in the modification shown in FIG. By connecting to the high-pressure selection valve 10, the pressure from the motor-side high-pressure selection valve 10 corresponds to the operation amount of the traveling lever device 8, that is, when the operation amount is equal to or less than a predetermined amount, the pressure is zero (tank pressure). It may be used as another hydraulic power source.

Further, the directional control valve 6 and the center joint 2
2 may be provided with another high pressure selection valve, and the pressure from the high pressure selection valve may be used as another hydraulic pressure source according to the operation amount of the traveling lever device 8. In this case, the structure of the center joint 22 is simplified. Can be converted.

Furthermore, in the above-mentioned embodiment, 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.

[0054]

As described in detail above, according to the present invention, a hydraulic pilot type switching valve whose switching position is determined by the command pressure from the electromagnetic switching valve is provided between the electromagnetic switching valve and the brake mechanism. Since the hydraulic pilot type switching valve is configured so that the brake mechanism is switched from the electromagnetic switching valve side to another hydraulic pressure source side when the command pressure becomes equal to or lower than a predetermined pressure, the electromagnetic switching valve is operated to a predetermined level due to an electric system failure or the like. In the abnormal case where the command pressure is not generated, the hydraulic pilot type switching valve can be automatically switched to connect the brake mechanism to another hydraulic power source. As a result, even when the electromagnetic switching valve or the like fails, the hydraulic pressure from another hydraulic source can be supplied to the brake mechanism via the hydraulic pilot type switching valve, and the brake of the brake mechanism can be automatically released. Effectively prevent the hydraulic motor from rotating without releasing the brake of the mechanism,
The rise in motor oil temperature and damage to the brake mechanism can be prevented, and the life, reliability and safety can be improved.

Further, a variable displacement type hydraulic motor having a displacement control valve for adjusting the motor displacement according to the pilot pressure is used as the hydraulic motor, and the pilot port of the displacement control valve is switched between a brake mechanism and a hydraulic pilot type. Since it is configured to be connected to the pipe between the valve and the valve, even if there is an abnormal situation where the command pressure is not generated from the electromagnetic switching valve, the hydraulic pressure from another hydraulic source supplied via the hydraulic pilot type switching valve
It is possible to control the brake mechanism and the motor capacity of the hydraulic motor.

[Brief description of drawings]

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

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

FIG. 3 is a circuit configuration diagram showing a hydraulic motor drive circuit according to a conventional technique.

4 is a flowchart showing a command pressure control process performed by a control unit 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 hydraulic pilot type switching valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomohiko Yasuoka 650 Jinrachicho, Tsuchiura City, Ibaraki Prefecture Hitachi Construction Machinery Co., Ltd. Tsuchiura Factory

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, a hydraulic pilot type switching valve whose switching position is determined by a command pressure from the electromagnetic switching valve is provided between the electromagnetic switching valve and the brake mechanism. The hydraulic pilot type switching valve switches the brake mechanism from the electromagnetic switching valve side to another hydraulic power source side when the command pressure becomes equal to or lower than a predetermined pressure. Hydraulic motor drive circuit, characterized in that the obtaining configuration. 2. A variable displacement hydraulic motor having a displacement control valve for adjusting the motor displacement according to pilot pressure is used as the hydraulic motor, and the pilot port of the displacement control valve is provided with the brake mechanism and the hydraulic pilot. The hydraulic motor drive circuit according to claim 1, wherein the hydraulic motor drive circuit is connected to a pipe line between the hydraulic switching valve and the switch valve.