JPH0321761B2 - - 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.

[Conventional technology]

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 front rotating body provided on the upper rotating body and constituting a working section. It is equipped with a mechanism. 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. Reference numeral 3 denotes a travel reduction gear 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 the 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. 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 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 tilting angle of the swash plate 1a is controlled to a tilting angle _θ1 larger than that of 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.
Figure 2b shows the input pressure P of the fixed displacement hydraulic motor 2.
It is a diagram showing the relationship between the rotation speed N and the output torque T for a given value. When the input pressure P is below a certain value _P1 , the discharge amount of the hydraulic pump 1 is large, so the rotation speed N also reaches the maximum rotation speed _N1 . Input pressure P on slopes etc.
increases, and the rotational speed N decreases. Output torque T is proportional to pressure P. In other words, when driving on flat ground, the input pressure P
is small and does not require a large torque T and can run at high speed at a large rotational speed _N1 , but on slopes etc., the torque T is increased and the rotational speed N is lowered to run at a low speed. 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., there are examples of using variable displacement hydraulic motors equipped with a swash plate, but in this case, the tilt angle of the swash plate is 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,
Just like the fixed displacement hydraulic motor 2 described above, this motor has the disadvantage of large circuit pressure loss. Moreover, the driver must constantly change the tilt angle according to the load on the variable displacement hydraulic motor, and it is almost impossible to make an appropriate change. In addition, in order to make the operability as easy as possible, the difference between the speed when the tilt angle is small and when it is increased is kept within a certain range, and the thermal efficiency is improved so that the speed difference is not too large. will become worse.

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. It is characterized in that it is provided with a driving means for driving.

[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.

〔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, 18a is a variable displacement displacement mechanism (hereinafter represented by a swash plate) of the hydraulic motor 18, and 19 is a slanted displacement mechanism. A motor tilting cylinder that drives the plate 18 to change its tilting angle; 20 is a hydraulic motor 18;
This is a shuttle valve that introduces pressure from both ends of the valve and selects the high pressure side. The pressure selected by the shuttle valve 20 is directed to the motor tilting cylinder 19. 2
1 is a cam provided on the rod 4a of the control valve 4. The cam 21 is connected to the first
Compared to the cam 5 shown in the figure, both ends thereof are cut off and are lower. 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. When the control valve 4 is switched to one of the positions, for example, to the left side in the figure, in order to run the hydraulic excavator, 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, control valve 4
With the operation of , the cam 21 moves to the right side, and the roller 1
6 rides on the left end of the cam 21, link mechanism 17, external command controller 15, tilting control cylinder 1
0 to increase the tilt angle of the swash plate 1a of the hydraulic pump 1. Now, if the roller 16 rides on the ends of the cam 5 at both ends shown in FIG. 1, the tilting angle of the swash plate 1a is set to θ ₁ as shown in FIG. If the tilting angle of the swash plate 1a when it rides on the end of the low cam 21 is θ ₂ , then both tilting angles θ ₁ and θ ₂ have a relationship of θ ₁ > θ ₂ as shown in FIG. 4a. be. In FIG. 4a, the broken line portion shows the conventional characteristics shown in FIG. 2a, and point A shows the state of the hydraulic pump 1 when traveling on flat ground. In the conventional example, when the discharge pressure of the hydraulic pump 1 is less than pressure _P1 , the swash plate 1a
While the tilting angle of the hydraulic pump 1 is constant at the angle θ ₁ , in this embodiment, the discharge pressure of the hydraulic pump 1 is the pressure P ₁
The tilting angle of the swash plate 1a is constant at an angle θ ₂ when the pressure is less than or equal to the pressure P ₂ . Since the angle θ ₂ 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 motor capacity. Are 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, the input pressure of the hydraulic motor 18 increases, so that the required output is not sufficient. 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, the rotational speed of the hydraulic motor 18 can be increased by reducing the tilt angle of the swash plate 18a. From the above, even if the tilting angle of the swash plate 1a of the hydraulic pump 1 is reduced to reduce its discharge amount, the input pressure can be increased by decreasing the tilt angle of the swash plate 18a of the hydraulic motor 18. This means that it is possible to increase the rotational speed while obtaining sufficient output torque.

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 motor tilt cylinder 19 are set so that the tilt angle θ _n2 is smaller than the tilt angle θ ₁ '. Then, as shown in FIG. 4a, the hydraulic pump 1
Despite reducing the discharge amount of
Input the rotation speed of the hydraulic motor 18 as shown in
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 . In this case, if it starts moving from the pressure just before the spring pressure _P2 in the cylinder 19, the swash plate 18a will move as the load torque increases.
The tilt angle increases and reaches its maximum immediately after pressure P ₂ . This pressure _P2 is guided from the shuttle valve 20 to the motor tilting cylinder 19, and the motor tilting cylinder 1
9 automatically changes the tilt angle of the swash plate 18a between the minimum tilt angle θ _n2 and the maximum tilt angle θ _n1 as shown in FIG. 4c in accordance with the introduced pressure. In addition,
The reason why the pressure increases linearly from the tilt angle θ _n2 to _the tilt angle θ _n1 at the pressure P ₂ shown in FIG.
As a result of the increase in tilting, the pressure immediately decreases, so this is due to the operation in which the tilting increases while the pressure remains constant. Now, when the tilt angle of the swash plate 18a is θ _n2 , the point on the rotational speed characteristic curve immediately before the input pressure P ₂ is α ₁ , and the point immediately after that when the tilt angle becomes large is α ₂ . , In addition, if the rotation speed characteristic curve when the tilting angle of the swash plate 18a is fixed at the angle θ _n1 is indicated by a dashed line, and the point on the rotation speed characteristic curve at input pressure P ₃ is α ₃ , the input pressure P When the rotation speed of the hydraulic motor 18 exceeds ₂ , the rotation speed of the hydraulic motor 18 is at point α ₁ and point α ₂
It is on a straight line passing through and connecting point _α3 . Also, the swash plate 18a
When the tilt angle of the swash plate 18a is fixed at the angle θ _n1 , the point β ₁ on the output torque characteristic line immediately before the input pressure P ₂ is β 2 , the point immediately after is β ₂ , and the tilt angle of the swash plate 18a is fixed at the angle θ _n1 If the point on the straight line at the input pressure P ₃ where the output torque characteristic straight line is indicated by a two-dot chain line is β ₃ , the output torque of the hydraulic motor 18 when the input pressure P ₂ is exceeded is between the points β ₁ and the point β. It lies on the straight line passing through ₂ and connecting β ₃ .
That is, when the load on the hydraulic motor 18 increases due to running on a slope, etc., and its input pressure exceeds a predetermined pressure _P2 , the rotation speed of the hydraulic motor 18 rapidly decreases, while the output torque of the hydraulic motor 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 ensure sufficient output torque, so the above characteristics can be said to be extremely desirable for the hydraulic motor 18.

In this way, in this embodiment, when the hydraulic motor is driven, only the cam provided on the control valve rod 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. can greatly reduce the burden on

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.

〔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.
When the flow rate is low and the pressure on the high pressure side of the hydraulic motor is below a predetermined pressure, the tilting angle of the variable displacement mechanism of the hydraulic motor is made small, and when the predetermined pressure is exceeded, the tilting angle is adjusted according to the pressure. By making the pressure change greatly, it is possible to make the hydraulic motor perform the desired drive while also significantly reducing the pressure loss in the pipeline, which in turn suppresses the increase in horsepower of the prime mover and contributes to energy savings. 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.

[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. Hydraulic circuit diagrams of the drive mechanism of the hydraulic motor of the hydraulic excavator, FIGS. 4a, b, and c are characteristic diagrams of the hydraulic pump and hydraulic motor shown in FIG. 3. 1... Hydraulic pump, 1a, 18a... Swash plate, 4
...Control valve, 4a... Rod, 9...
...Discharge rate control device, 16...Roller, 18...Hydraulic motor, 19...Motor tilting cylinder, 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 is provided for driving the hydraulic motor to maintain the 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. Hydraulic motor drive mechanism.