JPH0321762B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive mechanism for a hydraulic motor used in a working machine equipped with a hydraulic motor, and in particular to a drive mechanism for a hydraulic motor suitable for driving a travel motor of a construction machine. Regarding the drive mechanism.

[Prior Art] A construction machine, for example, a hydraulic excavator, has a lower traveling body driven by a hydraulic motor, an upper rotating body rotatably provided on the lower traveling body, and a rotating upper body installed on the upper rotating body to perform work. and a front mechanism that constitutes a section. The hydraulic motor of the lower traveling body is driven by oil discharged from a hydraulic pump installed in the upper rotating body and rotated by a prime mover such as an engine.
A drive circuit for such a hydraulic motor will be explained based on the drawings.

FIG. 1 is a drive circuit diagram of a hydraulic motor of a conventional hydraulic excavator. In the figure, 1 is a variable displacement hydraulic pump (hereinafter simply referred to as a hydraulic pump) that is rotationally driven by a prime mover, and 2 is a fixed displacement hydraulic motor that is driven by oil discharged from the hydraulic pump 1, which is the lower part of the hydraulic excavator. There is one on each side of the vehicle. 3 is a traveling speed reducer interposed between the drive wheels of the undercarriage and the fixed displacement hydraulic motor 2. A control valve 4 is interposed between the hydraulic pump 1 and the fixed displacement hydraulic motor 2, and controls the rotation direction of the fixed displacement hydraulic motor 2. 4a is a rod connected to the spool of the control valve 4, and 5 is a cam of a predetermined shape provided on the rod 4a. 6 is a brake valve of the fixed displacement hydraulic motor 2; 7 is a crossover relief valve that connects both pipelines when a predetermined differential pressure is reached between the pipelines on both sides of the fixed displacement hydraulic motor 2;
8 is a main relief valve, and 9 is a discharge amount control device for the hydraulic pump 1.

The outline of the configuration of the discharge amount control device 9 of the hydraulic pump 1 will be described below. The hydraulic pump 1 has a variable displacement mechanism (hereinafter, this is represented by a swash plate)
1a, and the discharge amount of the hydraulic pump 1 is controlled by changing the amount of tilting thereof. Reference numeral 10 denotes a tilt control cylinder whose piston rod is connected to the swash plate 1a, and by driving this tilt control cylinder 10, the amount of tilt of the swash plate 1a can be changed. 11 is an auxiliary hydraulic pump that supplies pressure oil to the tilt control cylinder 10; 12 is an auxiliary hydraulic pump 11;
It is a relief valve connected to. 13 is a pressure compensation controller that operates according to the discharge pressure of the hydraulic pump 1;
0 is switched according to the discharge pressure, and the tilting control cylinder 10 is driven to control the tilting amount of the swash plate 1a to be optimal. A link mechanism 14 connects the pressure compensation controller 13 and the piston rod of the tilting control cylinder 10, and feeds back the amount of tilting of the swash plate 1a to the pressure compensation controller 13 to maintain an optimum amount of tilting. 15 is an external command controller that switches the oil path between the auxiliary hydraulic pump 11 and the tilting control cylinder 10 like the pressure compensation controller 13;
The external command controller 15 operates in accordance with the drive of the actuator driven by the hydraulic pump 1, and controls the tilting amount of the swash plate 1a to be optimal. The amount of tilting of the swash plate 1a is maintained optimally by being fed back to the external command controller 15 via the link mechanism 14.

Here, a mechanism for giving an external command to the external command controller 15 will be explained. Generally, hydraulic pump 1
serves as a hydraulic power source not only for the fixed displacement hydraulic motor 2 but also for other actuators. Therefore, each of the plurality of actuators driven by the hydraulic pump 1 is provided with a control valve, and these plurality of control valves are collected together to form a control valve group. Like the control valve 4, a rod (same as the rod 4a) is connected to the spool of each control valve, and each rod is provided with a cam having the same shape as the cam 5. Each cam is arranged in the same plane and in the same row. That is, although only the cam 5 is shown in the figure, the other cams are also arranged in the same row in the direction perpendicular to the plane of the paper.
In this configuration, 16 in the figure is a long roller that contacts all of the cams, and 17 is this roller 1.
6 and the external command controller 15.

Now, when the control valve 4 is switched to the left position in the figure in order to run the hydraulic excavator, the oil discharged from the hydraulic pump 1 is supplied to the fixed displacement hydraulic motor 2 via the control valve 4 and the brake valve 6, and The hydraulic motor 2 rotates and the hydraulic excavator travels. At the same time, the cam 5 also moves to the right in the figure, and as is clear from the shape of the cam 5, the roller 16 rides on the high end of the cam and is lifted upward. Therefore, the external command controller 15 is driven by the link mechanism 17 to switch the oil path, and the tilt control cylinder 10 is driven to increase the tilt amount of the swash plate 1a to increase the discharge amount of the hydraulic pump 1. let
The configuration and operation of the discharge amount control device 9 of the hydraulic pump 1 as described above are described in Japanese Patent Publication No. 47-6703 and are well known, so a detailed explanation thereof will be omitted.

Figures 2a to 2c show the swash plate 1 of the hydraulic pump 1 when the fixed displacement hydraulic motor 2 is driven as described above.
FIG. 3 is a characteristic diagram of the tilting angle (that is, the tilting amount) of a, the traveling speed of the fixed displacement hydraulic motor, and the output torque. FIG. 2a is a diagram showing the relationship between the discharge pressure P of the hydraulic pump 1 and the tilt angle θ of the swash plate 1a. When the discharge pressure P is below a certain value _P1 , the tilt angle of the swash plate 1a is controlled to a large tilt angle _θ1 by the discharge amount control device 9 shown in FIG. 1, and the discharge amount from the hydraulic pump 1 becomes large. The fixed displacement hydraulic motor 2 rotates at high speed, and the hydraulic excavator also travels at high speed. On the other hand, when the hydraulic excavator travels in a place with high resistance such as a slope or wetland, the discharge pressure of the hydraulic pump increases and exceeds the pressure _P1 .
As a result, the tilting angle θ of the swash plate 1a decreases, the discharge amount of the hydraulic pump 1 also decreases, and the rotation of the fixed displacement hydraulic motor 2 also decreases, causing the hydraulic excavator to travel at a low speed. Note that point A indicates the state of the hydraulic pump 1 when the hydraulic excavator is running on flat ground. FIG. 2b is a diagram showing the relationship between the rotation speed N and the output torque T with respect to the input pressure P of the fixed displacement hydraulic motor 2. When the input pressure P is below a certain value _P1 , the discharge amount of the hydraulic pump 1 is large. Therefore, the rotational speed N is also the maximum rotational speed _N1 , but on a slope or the like, the input pressure P increases and the rotational speed N decreases. Output torque T
is proportional to pressure P. In other words, when running on flat ground, the input pressure P is small, no large torque T is required, and high speed running is possible at a large rotational speed _N1 ;
On a slope or the like, the torque T is increased and the rotational speed N is lowered, resulting in low-speed running. FIG. 2c shows the tilting angle θ of the fixed displacement hydraulic motor 2, and since it is a fixed displacement type, the tilting angle θ is naturally constant at the value _θ'1 .

In such a conventional traveling device, since a fixed displacement hydraulic motor 2 is used, its maximum rotation speed and maximum output torque are also fixed values. When the fixed displacement hydraulic motor 2 is driven at the maximum rotation speed (when the hydraulic excavator is traveling at the maximum speed), a large flow of discharge oil is supplied from the hydraulic pump 1.

[Problem to be solved by the invention]

By the way, the piping distance between the hydraulic pump 1 and the fixed displacement hydraulic motor 2 is long because the former is installed on the upper revolving structure and the latter is installed on the lower traveling structure, and there is a control panel in between. valve 4,
A center joint (not shown), a brake valve 6, etc. are provided. Therefore, when a large flow of discharge oil is supplied from the hydraulic pump 1 to the fixed displacement hydraulic motor 2, the circuit pressure loss becomes extremely large, and in order to compensate for this loss, it is necessary to The drawback was that it required increased horsepower.

In addition, in large construction machinery, etc., fixed displacement hydraulic motors equipped with swash plates are sometimes used, but in this case, the tilt angle of the swash plate can be manually changed to either large or small. The motor has the same performance as the fixed capacity hydraulic motor 2 when the tilting angle is small, and can run at high speed when driving on flat roads or other normal driving conditions, and when the tilting angle is increased when driving on slopes, etc. The aim is to further increase traction,
This motor has the same drawback as the fixed displacement motor 2 in that the circuit pressure loss is large. Moreover,
The operator must constantly change the tilting angle of the variable displacement hydraulic motor depending on the load on the motor, and it is almost impossible to make an appropriate change. In addition, in order to obtain a large traction force, there is a large difference between the speed when the tilting angle is small and when it is increased, so the speed when the tilting angle is large is forced to be lower than necessary. It also has the disadvantage of not obtaining

The present invention has been made in view of the above circumstances, and its purpose is to eliminate the above-mentioned conventional drawbacks,
It is an object of the present invention to provide a drive mechanism for a hydraulic motor that can reduce pressure loss in a conduit while causing the hydraulic motor to perform a desired drive.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a hydraulic pump having a variable capacity mechanism, a hydraulic motor and other hydraulic actuator having a variable capacity mechanism driven by the hydraulic pump, and which includes a setting means for setting the displacement volume of the hydraulic pump to a predetermined value when the hydraulic actuator is driven, and setting the displacement volume of the hydraulic pump to a value lower than the predetermined value when only the hydraulic motor is driven; When the high pressure side pressure of the hydraulic motor is below a predetermined pressure, the displacement volume of the hydraulic motor is maintained at a predetermined low value, and when the pressure exceeds the predetermined pressure, the displacement volume of the hydraulic motor is increased in accordance with the pressure. The present invention is characterized in that it is provided with a driving means for driving, and a switching means for setting the driving means in an inactive state and setting the displacement volume of the hydraulic motor to a predetermined value.

[Effect]

The setting means sets the displacement volume of the hydraulic pump to a predetermined value (maximum value or a value close to it) determined by the engine output when another hydraulic actuator or another hydraulic actuator and hydraulic motor are driven simultaneously. However, when only the hydraulic motor is driven, the displacement volume of the hydraulic pump is set to a value smaller than the predetermined value. On the other hand, the drive means maintains the displacement volume at a low value when the high-pressure side output of the hydraulic motor is below a predetermined pressure, and adjusts the displacement volume accordingly when the output exceeds the predetermined pressure (when the load increases). Enlarge. Thereby, it is possible to reduce the discharge flow rate of the hydraulic pump and reduce pipe line loss while obtaining the desired drive of the hydraulic motor. Furthermore, if necessary, the displacement volume of the hydraulic motor is set to a predetermined value by the switching means, regardless of the load pressure.

〔Example〕

The present invention will be explained below based on the embodiment shown in FIG.

FIG. 3 is a hydraulic circuit diagram of a drive mechanism for a hydraulic motor of a hydraulic excavator according to an embodiment of the present invention. In the figure, the same parts as those shown in FIG. 1 are given the same reference numerals. 18 is a variable displacement hydraulic motor (hereinafter simply referred to as a hydraulic motor) provided in the lower running body of the hydraulic excavator, and 18a is a variable displacement displacement mechanism (hereinafter represented by a swash plate) of the hydraulic motor 18. 9a is the swash plate 18a of the hydraulic motor 18
This is a tilting angle control device that controls the tilting angle of the hydraulic pump 1, and has almost the same configuration as the discharge amount control device 9 of the hydraulic pump 1. That is, 10a is a tilting control cylinder, 13a is a pressure compensation controller, 14a is a link mechanism, and 15a is an external command controller. 19 is a manually operated switching valve for external command;
Its input port is connected to the auxiliary hydraulic pump 11, and its output port is connected to the pilot port of the external command controller 15a. A shuttle valve 20 introduces pressure from both ends of the hydraulic motor 18 and selects the high pressure side, and the pressure selected by the shuttle valve 20 is connected to a pilot port of the pressure compensation controller 13a. The pressure compensation controller 13 of the discharge amount control device 9 is driven by the discharge pressure of the hydraulic pump 1, whereas the tilt angle controller 13 is driven by the discharge pressure of the hydraulic pump 1.
When the pressure selected by the shuttle valve 20 is less than a predetermined pressure (pressure P ₂ described later), the tilt angle of the swash plate 18a is changed to a predetermined small tilt angle (tilt angle θ _n2 described later). When the pressure exceeds a predetermined pressure, the swash plate 18a is driven to a larger tilt angle in accordance with the pressure. Further, while the external command controller 15 of the discharge amount control device 9 is driven via the link mechanism 17 by the movement of the cam 5, the external command controller 15a is driven by switching the external command switching valve 19. It is something.
Pressure compensation controller 13a and external command controller 15
Tilt control cylinder 10a when a is driven,
The operation of the link mechanism 14a is the same as that of the discharge amount control device 9. 1 is a cam provided on the rod 4a of the control valve 4. As shown, the cam 21 has both ends cut off and is lower than the cam 5 shown in FIG. That is, both ends thereof are formed lower than cams provided on the rods of control valves of other actuators driven by the hydraulic pump 1.

Here, the operation of this embodiment will be explained with reference to the characteristic diagrams shown in FIGS. 4a to 4c. First, the operation when the external command switching valve 19 is switched to the lower position and the auxiliary hydraulic pump 11 and the external command controller 15a are cut off will be described. Control valve 4 to run the hydraulic excavator
When either one of them is switched, for example to the left side position in the drawing, the oil discharged from the hydraulic pump 1 is supplied to the hydraulic motor 18 via the control valve 4 and the brake valve 6 to rotate it. On the other hand, by operating the control valve 4, the cam 21 moves to the right side,
The roller 16 rides on the left end of the cam 21 and increases the tilt angle of the swash plate 1a of the hydraulic pump 1 via the link mechanism 17, the external command controller 15, and the tilt control cylinder 10. Now, the tilting angle of the swash plate 1a when the roller 16 rides on the ends of the high cams 5 at both ends shown in FIG. 1 is θ ₁ as shown in FIG. 2a,
Assuming that the tilt angle of the swash plate 1a when riding on the ends of the low cams 21 at both ends in this embodiment is θ ₂ ,
Both tilt angles θ ₁ and θ ₂ are θ ₁ > θ ₂ as shown in Fig. 4a.
There is a relationship between In Figure 4a, the dashed line is in Figure 2a.
The conventional characteristics shown in FIG. In the conventional example, when the discharge pressure of the hydraulic pump 1 is equal to _or less than the pressure P1, the tilt angle of the swash plate _1a is constant at an angle θ1, whereas in this embodiment, the discharge pressure of the hydraulic pump 1 is When the pressure is less than or equal to the pressure _P2 which is greater than the pressure _P1 , the tilt angle of the swash plate 1a is constant at the angle _θ2 . and the angle θ ₂
Since is smaller than the angle θ ₁ , the discharge amount of the hydraulic pump 1 is reduced compared to the discharge amount in the conventional example.

By the way, if the tilting angle of the swash plate 18a of the hydraulic motor 18 is reduced, the input pressure of the hydraulic motor 18 increases, and the output torque of the hydraulic motor 18 is proportional to the product of the input pressure and the tilting angle. It has been known. Therefore, in a certain range where the load on the hydraulic motor 18 is low, such as when a hydraulic excavator is running on flat ground, even if the tilting angle of the swash plate 18a is reduced,
Since the input pressure of the hydraulic motor 18 increases, a sufficient required output torque can be obtained. On the other hand, the rotation speed of the hydraulic motor 18 is proportional to the supplied discharge amount and inversely proportional to the tilt angle of the swash plate 18a. Therefore, when the supplied discharge amount is constant, reducing the tilt angle of the swash plate 18a will cause the hydraulic motor 18 to
The number of rotations can be increased. From the above, even if the tilt angle of the swash plate 1a of the hydraulic pump 1 is reduced to reduce the discharge amount, the hydraulic motor 18
By decreasing the tilt angle of the swash plate 18a and increasing the input pressure, it is possible to obtain sufficient output torque and increase the rotational speed.

Therefore, in this embodiment, the height of both ends of the cam 21 is set such that the tilting angle of the swash plate 1a when the roller 16 rides thereon is a small tilting angle θ ₂ shown in FIG. 4a.
On the other hand, the shuttle valve 2
When the high pressure side pressure selected at 0 is less than the predetermined pressure _P2 shown in FIG.
The characteristics of the pressure compensation controller 13a are set so that the tilt angle θ _n2 is smaller than the tilt angle θ ₁ '. Then, as shown in FIG. 4a, even though the discharge amount of the hydraulic pump 1 is reduced, the rotation speed of the hydraulic motor 18 is changed to the input pressure as shown in FIG. 4b.
The rotation speed N ₁ of the conventional fixed displacement motor 2 can be made equal to P ₂ or less. As a result,
When the hydraulic excavator runs on flat ground, the pressure drop in the circuit is significantly reduced due to the reduction in the discharge amount of the hydraulic pump 1, and the drive speed of the hydraulic motor 18 is made the same as the drive speed of the conventional fixed displacement motor 2. be able to. Note that point B shown in FIG. 4a shows the state of the hydraulic pump 1 when traveling on flat ground.

When the hydraulic excavator travels on a place with high resistance such as a slope, the input pressure of the hydraulic motor 18 is
Exceeds _P2 . This pressure is guided to the pressure compensation controller 13a by the shuttle valve 20, the pressure compensation controller 13a moves by an amount corresponding to the introduced pressure, and the tilting control cylinder 10a is driven in accordance with this movement. That is, the tilting control cylinder 10a adjusts the tilting angle of the swash plate 18a to the minimum tilting angle θ _n2 as shown in FIG. 4c according to the pressure selected by the shuttle valve 20.
to the maximum tilt angle θ _n1 . Now, when the tilt angle of the swash plate 18a is the angle θ _n2 , the point on the rotation speed characteristic curve at the input pressure P ₂ is α ₁ , and if the tilt angle of the swash plate 18a is fixed at the angle θ _n1 The dot-dashed line shows the rotational speed characteristic curve of input pressure.
If the point on the rotation speed characteristic curve at P ₃ is α ₂ , the hydraulic motor 1 when the input pressure exceeds P ₂
8 is on the straight line connecting point α ₁ and point α ₂ .
Also, when the tilting angle of the swash plate 18a is the angle θ _n2 , the point on the output torque characteristic line at the input pressure P ₂ is β ₁ , and the output torque when the tilt angle of the swash plate 18a is fixed at the angle θ _n1 Input pressure P ₃ where the characteristic straight line is shown by a two-dot chain line
If the point on the straight line is β ₂ , then the input pressure is
The output torque of the hydraulic motor 18 when P ₂ is exceeded is on the straight line connecting the point β ₁ and the point β ₂ . That is, when the load on the hydraulic pump 18 increases due to running on a slope, etc., and its input pressure exceeds a predetermined pressure _P2 , the rotation speed of the hydraulic pump 18 rapidly decreases, while the output torque of the hydraulic pump 18 rapidly decreases. increases to When a hydraulic excavator is running on a slope or escaping from a wetland, it is not necessary to run at high speed, and it is sufficient to secure sufficient output torque.
This can be said to be an extremely desirable characteristic. Note that the actuator of the motor 18 and the control device 13
Of the links 14a connected to a, the control device 13
If a structure is adopted in which only the connection part a with the link 14a is cut to perform only on/off control of the pressure, the tilting of the swash plate _18a can be controlled as the load torque of the motor 18 increases under a constant set pressure P2. The amount of oil in the cylinder 10a can be gradually increased so that the amount of oil can be increased. As a result, the output torque and tilt angle of the motor 18 can be controlled as shown in FIGS. 5a and 5b, and the same functions as described above can be obtained.

Next, the operation when the external command switching valve 19 is manually switched to the upper position will be described. Now, let us consider a case where a hydraulic excavator is climbing an extremely steep slope, or a case where the hydraulic excavator is placed on the loading platform of a trailer truck by passing through a plate that is passed between the ground and the loading platform of the trailer truck. In such a case, it is necessary to gradually move the hydraulic excavator straight. However, the loads on the left and right hydraulic motors may become unbalanced depending on the road surface, the condition of the plate placed on the loading platform, etc. In this case, depending on the automatic control by the pressure compensation controller 13a, there will be a difference in the rotational speed of the left and right hydraulic motors, causing the hydraulic excavator to curve or meander, making it difficult to operate and, in some cases, causing a dangerous situation. condition may occur. The external command switching valve 19 is provided to avoid this. When the external command switching valve 19 is switched to the upper position, the external command controller 15a is driven by the hydraulic pressure of the auxiliary hydraulic pump 11, and the swash plate 18a also changes its tilt angle accordingly. In this embodiment, the tilt angle in this case is set to be the tilt angle θ _n1 shown in FIG. 4c. In this way, when the external command switching valve 19 is switched, the high-pressure side pressure of the hydraulic motor 18 is not involved in driving the swash plate 18a, and the automatic control is locked. On the other hand, the tilting of the swash plate 1a of the hydraulic pump 1 when the control valve 4 is operated is as described above. Therefore, when climbing steep slopes, etc., the swash plate 18
Since the tilt angle a is large, the speed decreases as shown in FIG. 4b, but the output torque becomes extremely large, making it suitable for running on steep slopes.
Furthermore, since the automatic control is locked, the hydraulic excavator can be operated according to the driver's will, and the above-mentioned danger can be avoided.

In this way, in this embodiment, when the hydraulic motor is driven, only the cam provided on the rod of the control valve of the hydraulic motor is made lower than the cams of the control valves of other actuators, thereby lowering the capacity of the hydraulic pump. High discharge pressure and low flow rate, and the tilting angle of the hydraulic motor swash plate by the motor tilting cylinder is set to a small constant tilting angle when the hydraulic motor input pressure is below a predetermined pressure, and exceeds a predetermined pressure. Since the pressure changes greatly depending on the pressure at the time, it is possible to make the hydraulic motor perform the desired drive while significantly reducing the pressure drop in the pipeline, which in turn suppresses the increase in horsepower of the prime mover and saves energy. You can also contribute. Furthermore, when the load on the hydraulic motor increases, a large output torque can be obtained. Furthermore, since the pressure on the high pressure side of the hydraulic motor is guided to the motor tilting cylinder by the shuttle valve, the tilting angle of the hydraulic motor's swash plate can be automatically and continuously optimized, allowing the driver to This can greatly reduce the burden on Furthermore, since the automatic control is locked by the switching valve for external command, it is possible to maintain straight running when traveling on steep slopes, perform stable operation, and avoid danger.

In the above embodiments, the traveling hydraulic motor of a hydraulic excavator was described, but the present invention is not limited to this, and can be applied to various hydraulic motors of various other working machines. Also, the switching valve for external command is linked with the control valve,
If the tilting angle of the hydraulic motor swash plate becomes larger when the control valve is operated to the half-lever position, and if the tilting angle is smaller when the control valve is operated to the full-lever position than when it is at the half-lever position, then Automatic shifting is possible while satisfying the characteristics.

〔Effect of the invention〕

As described above, in the present invention, when the hydraulic motor is driven, the capacity of the hydraulic pump is lowered to achieve high discharge pressure and low flow rate, and when the high pressure side pressure of the hydraulic motor is below a predetermined pressure, the displacement volume of the hydraulic motor is The tilting angle of the variable mechanism is made small, and when the predetermined pressure is exceeded, the tilting angle changes greatly depending on the pressure, so that the hydraulic motor can perform the desired drive, and the pipe line It is possible to significantly reduce the pressure loss of the engine, which in turn suppresses the increase in horsepower of the prime mover and contributes to energy saving. Further, it is also possible to obtain an output torque that can sufficiently cope with the large load of the hydraulic motor. Furthermore, since the tilting angle is changed according to the input pressure of the hydraulic motor, the driving speed of the hydraulic motor can be controlled automatically and smoothly. Furthermore, since a switching means is provided to put the means in an inactive state, any operation can be performed when necessary.

[Brief explanation of the drawing]

Fig. 1 is a drive circuit diagram of a hydraulic motor of a conventional hydraulic excavator, Fig. 2 a, b, and c are characteristic diagrams of the hydraulic pump and hydraulic motor shown in Fig. 1, and Fig. 3 is a diagram according to an embodiment of the present invention. A hydraulic circuit diagram of the drive mechanism of the hydraulic motor of the hydraulic excavator, Figures 4a, b, and c are characteristic diagrams of the hydraulic pump and hydraulic motor shown in Figure 3, and Figures 5a and b are the tilting diagrams shown in Figure 3. FIG. 7 is a characteristic diagram of the output torque and tilt angle of the hydraulic motor when the angle control device is configured to perform only on/off control of pressure. 1... Hydraulic pump, 1a, 18a... Swash plate, 4
...Control valve, 4a... Rod, 9...
...Discharge amount control device, 9a...Tilt angle control device, 1
0a...Tilt control cylinder, 13a...Pressure compensation controller, 15a...External command controller, 16...Roller, 18...Hydraulic motor, 19...External command switching valve, 20...Shuttle valve, 21...cam.

Claims (1)

[Claims] 1. In a hydraulic pump having a variable capacity mechanism, a hydraulic motor having a variable capacity mechanism driven by the hydraulic pump, and another hydraulic actuator, the displacement volume of the hydraulic pump when the other hydraulic actuator is driven is setting means for setting the displacement of the hydraulic pump to a predetermined value and setting the displacement volume of the hydraulic pump to a value lower than the predetermined value when only the hydraulic motor is driven; and when the high pressure side pressure of the hydraulic motor is below the predetermined pressure. A driving means for driving the hydraulic motor to maintain a displacement volume of the hydraulic motor at a predetermined low value and to increase the displacement volume of the hydraulic motor in accordance with the pressure when the predetermined pressure is exceeded; A drive mechanism for a hydraulic motor, comprising a switching means for setting the displacement volume of the hydraulic motor to a predetermined value when the hydraulic motor is in an operating state.