JPH03181674A - Hydraulic driving circuit - Google Patents

Abstract

PURPOSE:To obtain an exhaust amount of a variable capacity pump immediately responding to the increase and decrease of the engine rotational frequency by connecting lines branched from the front side and the rear side of the throttle of the exhaust line of a constant capacity hydraulic pump to both end chambers of an actuator. CONSTITUTION:When the rotational frequency of an engine 1 is increased, the exhaust amount per unit time of a constant capacity hydraulic pump 30 linking to the engine 1 is increased, and the pressure difference before and behind a throttle 32 is increased. Since the pressure oil before and behind the throttle 32 is led to both end chambers of the actuator 7, the actuator 7 inclines an oblique plate 6 which is a displacement capacity variable machine of a variable capacity hydraulic pump 2, and increases the exhaust amount per rotation of the variable capacity hydraulic pump 2. On the other hand, when the rotational frequency of the engine 1 is reduced, the pressure difference before and behind the throttle 32 is also reduced, the actuator 7 is restored to the neutral direction responding to the pressure difference, and the exhaust amount of the variable capacity hydraulic pump 2 is reduced.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a hydraulic drive circuit.

[Conventional technology]

Most construction machines use hydraulic power because large operating forces can be easily obtained from a small power source, and multiple items can be driven from one power source. Among these, for example, in a wheel loader, a hydraulic pump that drives the wheels and a hydraulic pump that drives the packets are provided separately, and the driving force is provided by a single engine. An example of a hydraulic drive circuit used in such a wheel loader is shown in FIG.
This hydraulic drive circuit will be explained with reference to the same figure. In FIG. 4, this hydraulic drive circuit includes one engine 1, a variable displacement hydraulic pump 2 for traveling drive driven by this engine 1, a fixed displacement hydraulic pump 3 for packet work, and a variable displacement hydraulic pump. 2, an actuator 7 that operates the variable displacement mechanism (hereinafter referred to as swash plate) 6 of the variable displacement hydraulic pump 2, and a direction switch that switches the operating direction of the actuator 7. An accelerator lever 1 that simultaneously controls the valve 8, the amount of tilting of the swash plate 6, and the rotation speed of the engine 1.
It is mainly composed of 7. The variable displacement hydraulic pump 2 is a double-discharge type variable displacement pump, and is connected to a hydraulic motor 4 via main lines IO and 11.
The driving force is transmitted from the output shaft of the hydraulic motor 4 to a mechanical transmission 12 having multiple stages and a differential gear 13, and further transmitted from the differential gear 13 to the wheel 5. Rotate. Amphibious line 10. +1
A device 14 including a crossover release valve, a flushing valve, a charge pump, etc. is provided between them, and forms a closed circuit together with the variable displacement hydraulic pump 2 and the hydraulic motor 4. The discharge direction and discharge flow rate of this variable displacement hydraulic pump 2 are controlled by a swash plate 6, and this swash plate 6 is connected to a hydraulic power source I5.
It is operated by an actuator 7 that assumes a position according to the pressure of hydraulic oil supplied from a pressure reducing valve 16 as a pressure control valve and a directional switching valve 8. Further, the actuator 7 sets the amount of tilting of the swash plate 6 by the pressure of hydraulic oil supplied from the hydraulic source 15 via the pressure reducing valve 16 and the directional control valve 8, and controls the amount of tilting of the swash plate 6 by the switching means (not shown) of the directional control valve 8. The switching direction of the swash plate 6 is controlled by the operation. The pressure of the hydraulic oil supplied to the directional control valve 8 is controlled by the pressure reducing valve 16.
The set pressure is determined according to the operating amount of the accelerator lever 17 that commands the target rotation speed of the engine l. Now, when the accelerator lever 17 is tilted in the direction of arrow A with the directional control valve 8 being switched to the left side in FIG. to rise. The pressure oil on the secondary side of the pressure reducing valve 16 is
The supply is supplied to the left side chamber of the actuator 7 in FIG. 4 through the directional switching valve 8, and the right side chamber of the actuator 7 is opened to the hydraulic tank 18 via the directional switching valve F8, so that the swash plate 6 can be tilted. Then, the variable displacement hydraulic pump 2 sucks in the pressure oil from the main line II side and discharges it to the main line II side to rotate the hydraulic motor 4 in the direction of arrow B. As a result, the wheel 5 is rotationally driven from the output shaft via the transmission I2 and the differential gear I3. At the same time, the hydraulic pump 3 is also driven by the engine 1, and pressure oil is delivered to a working device (not shown) to carry out a predetermined work. When the accelerator lever 17 is further tilted in the direction of the arrow from the above state, the pressure on the secondary side of the pressure reducing valve 7 becomes higher, the amount of tilting of the swash plate 6 also becomes larger, and the discharge of the variable displacement hydraulic pump 2 is increased. The amount increases. As a result, the rotational speed of the hydraulic motor 4 further increases, the rotational speed of the engine 1 also increases, the discharge amount of the hydraulic pump 3 also increases, and the output of the working device also increases. For example, when the transmission 12 is a gearbox that switches between high speed (H) and low speed (L), the relationship between the speed of a vehicle equipped with this hydraulic drive circuit and the operation amount, that is, the stroke amount of the accelerator lever 17 is the fifth. It will look like the figure. According to Figure 5,
Up to the stroke amount X1, the vehicle speed increases in a quadratic curve due to an increase in the amount of tilting of the swash plate 6 and an increase in the rotational speed of the engine 1. When the stroke amount of the swash plate 6 becomes larger than xI after the swash plate 6 reaches its maximum tilt at becomes proportionally larger. The absolute value of this vehicle speed is as indicated by the symbol H or L in the figure, depending on the gear ratio of the gearbox.

[Problem to be solved by the invention]

However, in the above conventional hydraulic drive circuit, the spring 17a of the pressure reducing valve 16 is operated by the accelerator <-17, and the actuator 7 is controlled with the secondary pressure corresponding to the force of the spring 17a. There is. Therefore, the response of the pressure on the secondary side of the pressure reducing valve 16, especially the accelerator lever 17, is returned in the direction of arrow C, and the spring 17 of the pressure reducing valve 16 is
When the force a is weakened to reduce the secondary pressure and the swash plate 6 is returned to the neutral direction by the spring force inside the actuator 7, it is necessary to discharge the fluid inside the actuator, but this can be done from a pressure reducing valve, etc. Because this is done by leaking
There is a problem in that the decreasing response of the secondary side pressure becomes slow, and the displacement amount of the variable displacement hydraulic pump 2 cannot be obtained in response to the decrease in engine speed. Further, since the engine 1 and the pressure reducing valve I6 must be operated by the accelerator lever 17, there are problems such as not only a complicated structure but also difficulty in adjusting their relative positions. SUMMARY OF THE INVENTION An object of the present invention is to provide a hydraulic drive circuit that has a simple structure that does not require a pressure reducing valve and is capable of operating a variable displacement mechanism of a variable displacement pump in immediate response to increases and decreases in engine speed. It is in.

[Means to solve the problem]

In order to achieve the above object, the hydraulic drive circuit of the present invention includes:
A variable displacement hydraulic pump and a fixed displacement hydraulic pump driven by one engine, and an actuator that operates a variable displacement mechanism of the variable displacement hydraulic pump, a restriction is provided in the discharge line of the fixed displacement hydraulic pump, and the It is characterized in that a pair of lines branching from the front and rear of the throttle are connected to both end chambers of the actuator.

[Effect]

When the rotational speed of the engine is increased, the discharge amount per unit time of the fixed capacity hydraulic pump that is linked to this increases, and therefore the pressure difference before and after the throttle increases. The pressure oil before and after this restriction is guided to the chambers at both ends of the actuator, so the actuator tilts the variable displacement mechanism of the variable displacement hydraulic pump due to the pressure difference, thereby increasing the discharge per rotation of the variable displacement hydraulic pump. This will increase the amount. On the other hand, if the engine speed decreases, the discharge amount of the fixed displacement hydraulic pump also decreases, and the pressure difference across the throttle also decreases. In response to this pressure difference, the actuator is returned to the neutral direction, reducing the displacement of the variable displacement hydraulic pump. In this way, the actuator is controlled by the pressure difference before and after the throttle, which occurs due to fluctuations in the discharge volume of the fixed displacement hydraulic pump that is linked to the engine, so the discharge volume of the variable displacement hydraulic pump can be obtained that immediately responds to increases and decreases in engine speed. .

【Example】

Embodiments of the present invention will be described below based on the drawings. Figures 1 and 2 are for explaining a hydraulic drive circuit according to an embodiment of the present invention. Figure 1 is a circuit diagram of the hydraulic drive circuit, and Figure 2 is a diagram showing vehicle speed and stroke amount of the accelerator lever. FIG. Hereinafter, components that are the same as or can be considered to be the same as those of the conventional example shown in FIG. 4 will be given the same reference numerals, and explanations of overlapping parts will be omitted as appropriate. In FIG. 1, the variable displacement hydraulic pump 2 and the fixed displacement hydraulic pump 30 are driven by the same engine l, and lines 31 and 33 supply pressure oil from the fixed displacement hydraulic pump 30 to the directional control valve 8, and lines 31 and 33 discharge it. The sequence valve 22 is provided in a bypass line 25 connecting the sequence valve 34 to the pilot line 23 of the sequence valve 22, and the on-off valve 24 is provided in the pilot line 23 of the sequence valve 22 from the line 33. Further, this sequence valve 22 is configured such that a cracking pressure can be set by a spring 22a. Further, a diaphragm 32 is provided on the line 31, and this diaphragm 32
The upstream side of the line is connected to line 33, and the downstream side line is connected to line 34. The pressure on the upstream side of this throttle 32 increases or decreases depending on the discharge amount corresponding to the number of rotations per unit time of the fixed capacity hydraulic pump 30 that is linked to the engine. That is,
When the rotational speed of the engine 1 is increased, the discharge amount per unit time of the fixed capacity hydraulic pump 30 that operates in conjunction with the engine 1 increases, and therefore the pressure difference before and after the throttle 32 increases. Since the pressure oil before and after this throttle 32 is guided to both end chambers of the actuator 7, the actuator 7 tilts the swash plate 6 of the variable displacement hydraulic pump 2 due to the pressure difference, and the pressure oil is guided to both end chambers of the actuator 7. Increase the discharge amount per revolution. On the other hand, if the rotational speed of the engine 1 decreases, the discharge amount of the fixed capacity hydraulic pump 30 also decreases, and the pressure difference before and after the throttle 32 also decreases rapidly. In response to this pressure difference, the actuator 7 is suddenly returned to the neutral direction, the swash plate 6 is rapidly returned to the neutral direction, and the discharge amount of the variable displacement hydraulic pump 2 is rapidly reduced. In this way, the actuator 7 is controlled by the pressure difference before and after the throttle 32 caused by fluctuations in the discharge amount of the fixed capacity hydraulic pump 30 that is linked to the engine I, so the variable capacity hydraulic pump 2 can immediately respond to increases and decreases in the rotational speed of the engine I.
The discharge amount is obtained. Therefore, the amount of tilting of the swash plate 6, that is, the discharge amount per revolution of the variable displacement hydraulic pump 2, will continue to change at the rotational speed of the engine l until the amount of tilting of the swash plate 6 reaches its maximum (see second X). Increase accordingly. Conversely, as the rotational speed of the engine 1 decreases, the discharge amount per rotation of the variable displacement hydraulic pump 2 rapidly decreases. Here, when working in a low speed range, when the on-off valve 24 is switched to the open direction, the pilot line 23 of the sequence valve 22 is connected, and the differential pressure before and after the pilot spool is set in advance by the spring 22a of the sequence valve 22. When the club king pressure is reached, the lines 33 and 34 are communicated. Then, the accelerator lever that produces this cracking pressure
If the stroke amount Xt of the accelerator lever 17 is set to a value lower than the stroke amount X1 of the accelerator lever 17 at which the secondary increase in vehicle speed ends (see curve LLff1 in Fig. 2), the stroke amount will be lower than X. In the range where the stroke amount is low, the discharge amount of the variable displacement hydraulic pump 2 and the engine speed increase in accordance with this stroke amount, and the vehicle speed increases according to a quadratic curve on the low speed side as in the conventional case. When the stroke amount reaches X, the sequence valve 22 is activated and the lines 33 and 34 are bypassed to the bypass line
It is connected by 5. As a result, the pressure of the hydraulic oil supplied to the actuator 7 via the directional control valve 8 becomes constant.
The discharge amount per rotation of the variable displacement hydraulic pump 2 is also constant. Therefore, even if the stroke amount becomes larger than X, the discharge amount of the variable displacement hydraulic pump 2 will be the stroke amount
, remains a small value corresponding to , so that the vehicle speed is proportional only to the rotational speed of the engine 1, that is, expressed as LL. All other operations are the same as in the conventional example. Thereby, the output of the engine 1 can be increased to the maximum limit while the vehicle speed is maintained at a lower speed than before, and the working device can be driven with the maximum output of the second fixed capacity hydraulic pump 3. As described above, the above embodiment has the following effects. ■ Throttle 3 on the discharge line 31 of the fixed capacity hydraulic pump 30
2 is provided, and a pair of lines 33 and 34 branched from before and after this throttle 32 are connected to both end chambers of the actuator 7, and the pressure difference between before and after the throttle caused by fluctuations in the discharge amount of a fixed capacity hydraulic pump linked to the engine is used. Since the actuator is controlled, the discharge amount of the variable displacement hydraulic pump can be obtained in response to increases and decreases in engine speed. Further, since there is no need to connect the accelerator lever 17 and the pressure reducing valve, the hydraulic piping becomes simple. ■ By providing the sequence valve 22, when the pressure becomes higher than a preset pressure, the operating pressure supplied to the actuator 7 can be restricted, so the discharge amount of the variable displacement hydraulic pump I can be suppressed. This makes it possible to increase the number of gears without changing the mechanical transmission. In the above embodiment, the fixed capacity hydraulic pump 30 generates the operating pressure for the actuator 7, but FIG. 3 shows an example in which the flow rate of the fixed capacity hydraulic pump 30 is effectively utilized. The fixed displacement hydraulic pump 30 shown in FIG. It has the function of charging pressure oil to II. In addition, in the above embodiment, the actual operating rotation speed of the engine 1 is detected from the pressure difference generated before and after the throttle 32, and the sequence valve 2
By setting the cracking pressure in step 2, the valve is switched and pressure oil is led from the high pressure side line 33 to the low pressure side line 34 which corresponds to the low pressure circuit.These are done by mechanical means, but these are It is conceivable to construct it by electrical means. An example of this is shown in FIG. In FIG. 3, components that are the same or can be considered to be the same as those of the embodiment and the conventional example are given the same reference numerals. In FIG. 3, an engine 1 is equipped with a tachometer 40 that detects the number of revolutions, and the tachometer 40 electrically processes the number of revolutions detected by the tachometer 40 and processes the detected revolutions. A processing device 43 is connected to the switch device 42 and can output a switching signal for the on-off valve 41 by arbitrarily selecting a switching setting value for opening/closing the electromagnetically operated on-off valve 41 (described later) using the number as a parameter. Further, the on-off valve 41 is inserted between the lines 33 and 34 in the bypass line 25 that connects them as in the above embodiment, and is operated by the switching output of the switch device 42 which is operated by the output from the processing device 43. , an open position and a closed position are respectively selected electromagnetically. Other parts that are not particularly explained have the same structure as shown in FIG. With the above configuration, the engine 1 is detected by the tachometer 40.
When the rotation speed of the on-off valve 41 reaches a switching setting value set in advance according to work conditions, etc., the on-off valve 41 is activated via the switch device 42.
The pressure oil flowing through the high-pressure side line 33 supplied to the actuator 7 can be led out to the low-pressure lul+ line 34, thereby making it possible to keep the pressure applied to the actuator 7 constant. In this embodiment, since the switching set values are set by electrical means, it is much easier to select and change the set values than in the above embodiments, and it is also possible to set the switching set values by electrical means. This can also be processed within the processing device 43, which has the effect of simplifying the configuration.

【Effect of the invention】

As is clear from the above, the hydraulic drive circuit of the present invention is
It is equipped with a variable displacement hydraulic pump and a fixed displacement hydraulic pump driven by one engine, and an actuator that operates a variable displacement mechanism of the variable displacement hydraulic pump, and a throttle is provided in the discharge line of the fixed customer ffi All pressure pump. A pair of lines branching from before and after this throttle are connected to both end chambers of the actuator, and the actuator is controlled by the pressure difference before and after the throttle, which is generated by fluctuations in the discharge amount of a fixed capacity hydraulic pump that works with the engine. It is possible to obtain the discharge amount of a variable capacity heavy hydraulic pump that responds immediately to increases and decreases in rotational speed. In particular, when the engine speed decreases, the pressure difference before and after the throttle rapidly decreases, so the actuator's operational response becomes quick, and the variable displacement hydraulic pump can provide a discharge amount that quickly responds to the decrease in engine speed. Furthermore, even when the operating amount of the accelerator lever does not correspond to the engine speed, the discharge amount of the variable displacement hydraulic pump has the advantage of corresponding to the engine speed. Furthermore, since there is no need to connect the accelerator lever and the pressure reducing valve as in the prior art, the structure is simplified and there is no need to adjust their relative positions.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a hydraulic drive circuit according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between vehicle speed and accelerator lever stroke of the above embodiment, and Fig. 3 is a diagram of another embodiment. FIG. 4 is a circuit diagram showing the main parts of such a hydraulic drive circuit, FIG. 4 is a circuit diagram of a conventional hydraulic drive circuit, and FIG. 5 is a characteristic diagram showing the relationship between vehicle speed and the stroke of the accelerator lever. 1... Engine, 2... Variable displacement hydraulic pump, 3... Hydraulic pump, 4... Hydraulic motor, 6... Swash plate, 7... Actuator, 8... Directional switching valve, 10, II...
...Main line, 12...Transmission, 16...
··Pressure reducing valve,! 7...Accelerator lever-122...
・Sequence valve, 23...Pilot line, 24・
...Opening/closing valve, 25...Bypass line, 32
...Aperture, 33.34...Line, 4
0...Tachometer, 4I...Opening/closing valve, 42...
...Switch device, 43...Processing Fig. 1 Fig. 2 Fig. 5 Stroke Fig. 3

Claims (1)

[Claims] (1) A variable displacement hydraulic pump and a fixed displacement hydraulic pump driven by one engine, and an actuator that operates a variable displacement mechanism of the variable displacement hydraulic pump, and a restriction is installed in the discharge line of the fixed displacement hydraulic pump. A hydraulic drive circuit characterized in that a pair of lines branched from before and after the throttle are connected to both end chambers of the actuator.