JPS591606B2 - Hydrostatic power transmission equipment for hydraulic vehicles, etc. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydrostatic power transmission system mainly designed to improve the maneuverability of a hydraulically driven vehicle.

In general, this kind of conventional hydrostatic power transmission device has a main pipe 3 connecting a variable displacement pump 1 and a hydraulic motor 2, as shown in FIG.
, 4, the pressure oil of the boost auxiliary pump 6, which is maintained at a constant pressure Pb by the boost relief valve 5, is checked by the check valve 7,
A boost circuit for replenishing the amount of leakage from pumps, motors, etc., a bypass valve 9, and high-pressure relief valves 10 and 11 are installed in parallel in the low-pressure side main line via 8.

The reason why the bypass valve 9 is provided in the illustrated circuit is that if it were absent, the vehicle would be There is only one point in the neutral zone where the speed is zero, and when the tilting lever 12 is operated manually, the slight deviation of the neutral position of the tilting lever 12 causes the vehicle to fluctuate slightly (hereinafter referred to as creep), making it difficult to control the vehicle. The performance will deteriorate significantly, so
This is to ensure the neutral zone ±α as shown in FIG.

To explain this, let us assume that the pressures in the main pipes 3 and 4 are PA and PB. For example, in the case of PA<PB, if the amount of oil discharged from the pump 1 is very small, it will become PB--PB, and the pump pressure liquid will flow from the main pipe 3 to the bypass valve. Since the hydraulic motor 2 is bypassed to the main pipe 4 side through the orifice 13 of 9, the hydraulic motor 2 does not rotate, and therefore the vehicle does not run. That is, the neutral zone can have a certain width, and even if the neutral point of the pump 1 is slightly out of alignment, the creep phenomenon of the vehicle can be prevented. However, the orifice opening degree of the bypass valve 9 is determined by the pressure difference PA-PB before and after the orifice that occurs when the pressure oil passes through the orifice 13, and the bypass valve 9.
The difference in pressure before and after the orifice in the neutral zone is determined by the balance between the spring forces of springs 14 and 15.
, 15, the orifice 13 begins to be constricted, and the differential pressure further increases accordingly. It's narrowing down rapidly.
For this reason, the vehicle speed starts in stages as shown in FIG. 13, and a large shock is generated, resulting in extremely poor starting performance. Therefore, the present applicant has proposed a hydrostatic power transmission device (Japanese Patent Application No. 51-87525 (Japanese Unexamined Patent Publication No. 53-87) that eliminates the above-mentioned drawbacks.
-20231)) was proposed.

For example, as shown in FIG. 2, the bypass pipe 161f-, the first
Instead of the bypass valve 9 shown in the figure, pressure control valves 18 and 19 are provided before and after the orifice 17, and the pressure control valves 18,
19 is kept open at all times by a spring 20, and a positive differential pressure before and after the orifice 17 is applied to the pressure control valve on the tenth flow side in the direction of the valve opening force.
A positive differential pressure across the orifice 17 is applied to the downstream pressure leg valve in the valve closing direction. Assuming that the pressure oil from the pump 1 starts to be discharged into the main pipe 3,
Since the pressure control valves 18 and 19 are kept open by the spring 20, the pressure oil bypasses the main pipes 3 to 4 through the pressure control valve 18, orifice 17, and pressure control valve 19, and the pump discharge amount is minute. The vehicle will be stopped for a while. In this case, since PA>PB, the pressure control valve 18 is a free flow, and the opening degree of the pressure control valve 19 is adjusted so that the differential pressure PA - PB before and after the orifice is constant. It is automatically controlled by Nohane 20. The fact that the differential pressure before and after the orifice 17 is constant means that the flow rate passing through the orifice is constant, and moreover, it is pressure compensated. This orifice 17 differs from the orifice 13 in FIG. 1 in that the differential pressure before and after the orifice is constant, and the bypass flow rate is constant regardless of the magnitude of the vehicle's running resistance (approximately equal to the pump discharge pressure), so the running speed The amount of oil flowing into the hydraulic motor 2, which determines the amount of oil flowing into the hydraulic motor 2, does not change suddenly. Therefore, the vehicle can be started smoothly and the starting performance is improved. However, this method has the disadvantage that the width of the neutral zone changes as the rotational speed of the pump drive source changes. That is, since the J orifice 17 is fixed, the amount of oil passing through the orifice is constant, and the width α of the neutral zone is α=Q/, where Q1 is the amount of oil passing through the orifice, and n is the rotation speed of the pump 1.
Since it is given by n, if the pump rotation speed changes, the width of the neutral zone will also change. In particular, these four types of vehicles are often driven by the engine, and the transmission range is wide, for example, 500 to 3000 rpm, so the width of the neutral zone is extremely wide when the engine is idling, but the bypass Since the loss is constant, the efficiency decreases greatly, and when the engine rotates at high speeds, the efficiency decrease is small, but it becomes extremely narrow and prone to creep, making it difficult to maneuver during startup. Also,
In this case, even if the tilting lever 12 of the pump 1 is set to the maximum, a certain amount bypasses through the orifice, so the maximum vehicle speed is slightly lowered and efficiency is also lowered. In view of the above points, the present invention has developed a system in which the discharge pressure of the auxiliary boost pump, which is driven by a variable speed drive source common to the variable displacement pump for driving the hydraulic motor, is set to the pilot pressure in the bypass pipe connecting the main pipes on both sides of the hydraulic motor. A switching valve with an orifice and a pressure control valve having the same function as the pressure control valves 18 and 19 explained in FIG. 2 are installed before and after this switching valve with an orifice. The spool of the switching valve with an orifice and the tilting shaft of the variable displacement pump are connected by a rotation interlocking mechanism so that the pressure is proportional to the discharge pressure of the auxiliary boost pump and inversely proportional to the tilting angle of the variable displacement pump. This eliminates the above-mentioned drawbacks.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 3, the variable displacement pump 1 and the auxiliary boost pump 6 are connected to one engine (not shown). Main pipe line 3 connecting variable displacement pump 1 and hydraulic motor 2
, 4 is a boost valve for replenishing the pressure oil of the boost auxiliary pump 6 set by the boost relief valve 5 into the low-pressure side main pipe via check valves 7 and 8 in an amount equivalent to the amount of leakage from the pump, motor, and valves. High pressure relief valves 10 and 11 are installed in parallel, and a switching valve 21 with an orifice is installed in the bypass pipe 16 connecting the main pipes 3 and 4, and the orifice of the switching valve 21 with an orifice is always open by a spring 20 in front and behind it. Pressure control valves 23 and 24 are installed to take the pressure around 22 as the pilot pressure, and the upstream pressure control valve has a positive differential pressure across the orifice in the direction of the valve opening force, and the downstream pressure control valve has A positive differential pressure across the orifice is applied in the valve closing direction, and the pressure chamber 25 of the orifice-equipped switching valve 21 is communicated with the discharge side pipe 27 of the auxiliary pump 6 for the foist via a pipe 26. Another embodiment shown in FIG. 4 is one in which the pressure control valves 23 and 24 shown in FIG. 3 are replaced with one pressure control valve 28, and the other configuration is the same as that shown in FIG. Yes, there is no difference in terms of functionality.

As shown in FIGS. 5 and 6, the orifice-equipped switching valve 21 communicates the oil passages 31 and 32 with a large diameter portion larger than the diameter of the oil passages 31 and 32 through the valve hole 30 of the valve body 29. A spool 33 having an orifice 22 drilled therein is inserted, and the elastic force of a spring 36 interposed between the step 34 of the spool 33 and the valve hole closing cover 35 and the end 37 of the spool 33 and the valve body 29 The spool 33 is clamped by the set pressure of the auxiliary boost pump 6 that leads to the pressure chamber 25 formed by the spool 33, and the opening degree of the orifice 22 is made proportional to the set pressure of the auxiliary pump 6. A pulley 40 is attached to the part protruding from the cover 35 as shown in FIGS.
The opening degree of the orifice 22 is made inversely proportional to the tilting angle of the tilting shaft 43. Although the connection structure between the small diameter portion 39 and the pulley 40 in this embodiment is not shown, a well-known connection structure using a spline or a key is employed. In the figure, 44 is a valve casing to which the variable displacement pump 1, hydraulic motor 2, and orifice-equipped switching valve 21 are mounted. Next, the operation according to the present invention will be explained.

3 and 5, when the engine stops or breaks down, or when the auxiliary boost pump 6 breaks down, the discharge pressure of the auxiliary pump 6 does not increase, so the spool 33 is pushed upward by the spring 36. Orifice 2
2 in the valve hole 30 to cut off communication between the oil passages 31 and 32. This means that the hydraulic brake function, which is one of the greatest features of the closed hydraulic circuit, can be achieved with the amount of bypass oil being zero. When the engine starts and the set pressure of the auxiliary pump 6 increases, the spool 33 is pushed downward against the spring 36, and the oil passages 31 and 32 communicate with each other through the orifice 22. On the other hand, since the pressure control valves 23 and 24 are opened by the spring 20, the pressure oil that has begun to be discharged from the variable displacement pump 1 passes through the pressure control valve 23, the orifice 22, and the pressure control valve 24, and then passes through the main pipe 3. The vehicle is bypassed from 4 to 4, and while the pump discharge amount is very small, the vehicle stops and has a neutral zone of a certain width. In this case, the pressure control valve 23 and the orifice 2
Since the oil pressure Pc between the orifice 22 and the pressure control valve 24 is larger than the oil pressure Pd between the orifice 22 and the pressure control valve 24, the pressure control valve 23 on the upstream side
is a free flow, and the pressure control valve 24 on the downstream side controls the amount of passing oil according to the opening degree of the orifice by the balance between the differential pressure (Pc-Pd) before and after the orifice 22 and the spring 20, and the pressure (vehicle's The pressure is determined by the running resistance and is controlled regardless of the pump discharge pressure (approximately equal to the pump discharge pressure). Further, the amount of oil passing through the orifice 22 is generally not affected by changes in the viscosity of the hydraulic oil due to temperature changes, so it can be said that the amount of oil passing through the orifice 22 is compensated for pressure and temperature. Incidentally, the capacity of the boost auxiliary pump 6, which is a fixed capacity type, increases or decreases in proportion to the engine speed, and the boost relief valve 5 generally has a characteristic that the relief set pressure increases approximately linearly with the relief oil amount ( (overall characteristic) (Fig. 9), the set pressure of the boost relief valve 5 depends on the engine speed, and the opening degree of the orifice 22 is a relief valve that increases or decreases depending on the engine speed. It is determined by the balance between the set pressure and the elastic force of the spring 36.

5 and 6 show the orifice opening state at medium engine speed, and FIGS. 7 and 8 show the orifice opening state at the maximum engine speed. That is, according to the present invention,
Since the amount of oil passing through the orifice Ql/Min is proportional to the rotational speed Nrev/Min of the engine and pump, it can be expressed as follows. Here, ql/Rev is constant and becomes the displacement volume.

As is well known, the displacement q is proportional to the pump tilting angle α, which means that the pump tilting angle α is constant. This means that during a certain pump tilt angle α, the amount of oil passing through the orifice bypasses the oil flow regardless of the engine and pump rotation speeds, and the vehicle stops reliably without any creep phenomenon. A constant center width is obtained at the point. Next, in FIG. 11, when the tilting lever 12 is rotated by a certain angle in one direction from the neutral position, the spool 33 integrated with the small diameter portion 39 rotates by an angle corresponding to the rotation angle of the tilting shaft 43, and the fifth When the orifice 22 is half open at medium speed as shown in Figures 1 and 6, the opening of the orifice 22 begins to decrease as soon as the tilting lever operation is started, and at a certain rotation angle or more, the opening becomes zero, that is, the orifice passes through. The oil amount becomes zero. On the other hand, when the orifice is fully open at the maximum engine speed as shown in FIGS. 7 and 8, the spool 33
The opening degree of the orifice decreases only after it is rotated by a certain angle.
Expressing the above in terms of the relationship between the rotation angle of the operating lever 12 and the vehicle speed, at medium engine speed, the orifice is narrowed when the tilting lever angle is between O and ±α, as shown in Figure 15. It is fully closed and the first position is reached at the maximum engine speed.
As shown in Figure 4, when the tilting lever tilt angle is between O and α2, the orifice is fully open, and when it exceeds ±α2, the orifice opening starts to narrow and becomes fully closed at the maximum tilt angle.The engine will stop due to engine failure. When moving the vehicle, if the spool 33 is pulled against the force of the spring 36 and the oil passages 31 and 32 are communicated, the hydraulic motor 2 rotates freely when the vehicle is being towed, making it easy to move the vehicle. As explained above, in the present invention, the opening of the orifice of the switching valve with an orifice provided in the bypass pipe connecting the main pipes on both sides of the hydraulic motor is boosted by a variable speed drive source common to the variable displacement hydraulic pump. Since the amount of oil passing through the orifice is proportional to the discharge pressure of the auxiliary pump, the amount of oil passing through the orifice is proportional to the rotation speed of the variable speed drive source, and its proportionality constant is the displacement and is proportional to the pump tilting angle. In between, the vehicle stops without any creep phenomenon regardless of the rotational speed of the Z drive source, and a constant neutral zone width is obtained.

Therefore, it is possible to significantly improve the maneuverability at the time of starting a hydraulic vehicle driven by an engine or other single-speed variable drive source. In addition, the spool of the J-type switching valve with orifice and the tilting shaft of the variable displacement hydraulic pump are connected by a rotation interlocking mechanism to make the orifice opening degree inversely proportional to the pump tilting angle, so that when the pump is at maximum output, The amount of bypass becomes zero, eliminating the reduction in maximum vehicle speed and efficiency caused by bypass.
It is possible to obtain the same effect as in the case of a circuit configuration shown in FIG. 1, for example, which does not have this type of control valve device. In addition, emergency evacuation of stopped vehicles due to engine trouble can be easily carried out by pulling the spool of the orifice-equipped switching valve to communicate the oil path.

[Brief explanation of drawings]

Figures 1 and 2 are hydraulic system diagrams of conventional equipment, respectively.
Figures 3 and 4 are hydraulic system diagrams showing embodiments of the present invention, Figure 5 is a vertical sectional view of the switching valve with orifice when the orifice is half open, Figure 6 is a side view of the same, and Figure 7 is the orifice. FIG. 8 is a side view of the switching valve with an orifice when fully opened; FIG. 9 is a diagram showing the relationship between the relief amount and relief pressure of the boost relief valve; FIG. 10 is a front view of the hydraulic unit; Figure 11 is a side view of the same side, and Figure 12 is a chart showing the relationship between vehicle speed and pump tilting lever angle when the bypass valve is missing in the hydraulic circuit of Figure 1.
Figure 3 is a chart showing the relationship between vehicle speed and pump tilting lever tilting angle in the hydraulic circuit of Figure 1, and Figures 14 and 15 respectively show vehicle speed and pump tilting lever tilting angle according to the present invention. This is a chart showing the relationship between 1... Variable displacement hydraulic pump, 2...
Hydraulic motor, 3, 4... Main pipe line, 5...
・Boost relief valve, 6... Boost auxiliary pump, 10, 11... High pressure relief valve, 1
2...Tilt lever 16...Bypass pipe, 20...Spring, 21...Switching valve with orifice, 22...Orifice ,23,
24, 28...pressure control valve, 29...
Valve body, 31, 32... Oil passage, 33...
・Spool, 36... Spring, 40, 42...
...Pulley, 41... Endless belt, 43...
...Tilt axis, 44...Valve casing.

Claims (1)

[Claims] 1 In a hydrostatic power transmission system that includes a variable displacement hydraulic pump driven by a common variable speed drive source, a boost auxiliary pump, a boost relief valve, and a hydraulic motor driven by the variable displacement hydraulic pump, the main pipes on both sides of the hydraulic motor A switching valve with an orifice that uses the discharge pressure of the auxiliary boost pump as pilot pressure and makes the opening of the orifice proportional to the pilot pressure is installed in the bypass pipe connecting the channels, and the switching valve with the orifice is always open by spring force before and after the switching valve. On the upstream side of the switching valve with an orifice, this pressure control valve causes the differential pressure before and after the orifice to act in the valve opening direction.
The downstream side of the switching valve with an orifice is equipped with a pilot circuit that applies positive differential pressure before and after the orifice in the valve closing direction.
Furthermore, the spool of the orifice-equipped switching valve and the tilting shaft of the variable displacement hydraulic pump are connected by a rotation interlocking mechanism so that the orifice opening degree of the orifice-equipped switching valve is inversely proportional to the tilting angle of the variable displacement hydraulic pump. A hydrostatic power transmission device for a hydraulic vehicle, etc., characterized by the following.