JPH0810028B2 - Hydraulic drive circuit - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

 The present invention relates to a hydraulic drive circuit.

[Prior art]

Most construction machines use hydraulic pressure because they can easily obtain a large operating force from a small power source and can drive a plurality of things from a single power source. Of these, for example, in a wheel loader, a hydraulic pump for driving a wheel and a hydraulic pump for driving a bucket are separately provided, and a driving force is given by one engine. An example of a hydraulic drive circuit used in such a wheel loader is shown in FIG.
This hydraulic drive circuit will be described with reference to FIG. In FIG. 4, this hydraulic drive circuit includes one engine 1, a variable displacement hydraulic pump 2 for driving the traveling driven by the engine 1, a fixed displacement hydraulic pump 3 for bucket work, and a variable displacement hydraulic pump. A hydraulic motor 4 which is rotationally driven by the hydraulic pressure from 2, and a displacement volume changing mechanism (hereinafter referred to as a swash plate) 6 of the variable displacement hydraulic pump 2.
An actuator 7 for operating the actuator 7, a direction switching valve 8 for switching the operating direction of the actuator 7, and an accelerator lever for simultaneously controlling the tilt amount of the swash plate 6 and the rotation speed of the engine 1.
Mainly consists of 17 and. The variable displacement hydraulic pump 2 is a double displacement type variable displacement pump, is connected to a hydraulic motor 4 via main lines 10 and 11, and has a mechanical transmission having a plurality of stages from an output shaft of the hydraulic motor 4. The driving force is transmitted to 12 and the differential gear 13, and further transmitted from the differential gear 13 to the wheel 5 to rotate the wheel 5. An auxiliary device 14 including a crossover release valve, a flushing valve, a charge pump, and the like is provided between the main lines 10 and 11, and together with the variable displacement hydraulic pump 2 and the hydraulic motor 4, constitutes a closed circuit. In the variable displacement hydraulic pump 2, the discharge direction and the discharge flow rate are controlled by a swash plate 6, and the swash plate 6 is a hydraulic source 15
It is operated by the actuator 7 which takes a position corresponding to the pressure of the hydraulic oil supplied from the pressure reducing valve 16 as a pressure control valve and the direction switching valve 8. In addition, the actuator 7
Sets the tilting amount of the swash plate 6 by the pressure of the hydraulic oil supplied from the hydraulic pressure source 15 via the pressure reducing valve 16 and the direction switching valve 8, and is operated by the switching means (not shown) of the direction switching valve 8. The switching direction of the swash plate 6 is controlled. The pressure of the hydraulic oil supplied to the direction switching valve 8 is the pressure reducing valve 16
The set pressure is set according to the operation amount of the accelerator lever 17 that commands the target rotation speed of the engine 1. Now, when the directional control valve 8 is switched to the left side in FIG. 4, when the accelerator lever 17 is tilted in the direction of arrow A, the pressure reducing valve 16 operates via the spring 17a, and the pressure on the secondary side of the pressure reducing valve 16 is activated. To raise. The pressure oil on the secondary side of the pressure reducing valve 16 is supplied to the left side chamber of the actuator 7 in FIG. 4 via the direction switching valve 8, and the right side chamber of the actuator 7 is supplied to the hydraulic tank 18 via the direction switching valve 8. Since it is open,
The swash plate 6 tilts and the variable displacement hydraulic pump 2 sucks the pressure oil on the main line 10 side and discharges it to the main line 11 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 12 and the differential gear 13. At the same time, the hydraulic pump 3 is also driven by the engine 1 and pressure oil is sent to a work device (not shown) to perform a predetermined work. When the accelerator lever 17 is further tilted in the direction of arrow A from the above state, the secondary side pressure of the pressure reducing valve 7 becomes higher, the tilt amount of the swash plate 6 becomes further larger, and the discharge amount of the variable displacement hydraulic pump 2 increases. Will increase. As a result, the rotation speed of the hydraulic motor 4 is further increased, the rotation speed of the engine 1 is also increased, the discharge amount of the hydraulic pump 3 is increased, and the output of the work device is also increased. For example, when the transmission 12 is a gearbox for switching between high speed (H) and low speed (L) two stages, the relationship between the speed of a vehicle equipped with this hydraulic drive circuit and the operation amount of the accelerator lever 17, that is, the stroke amount is shown in FIG. become that way. According to FIG. 5, up to the stroke amount X ₁ , the tilt amount of the swash plate 6 increases and the engine 1
As the number of revolutions increases, the vehicle speed increases by drawing a secondary curve. When the swash plate 6 by X ₁ is a stroke volume is larger than after X ₁ reaches the maximum tilting, the tilting amount of the swash plate 6 is the vehicle speed maintaining maximum value, a function of the rotational speed only the engine 1, engine speed It grows in proportion to the number. The absolute value of the vehicle speed is as indicated by reference sign H or L in the figure depending on the gear ratio of the gearbox.

[Problems to be Solved by the Invention]

However, in the above conventional hydraulic drive circuit, the accelerator lever 17 is used to operate the spring 17a of the pressure reducing valve 16,
The actuator 7 is controlled by the secondary pressure corresponding to the force of the spring 17a. Therefore, the response of the pressure on the secondary side of the pressure reducing valve 16, particularly the accelerator lever 17 is returned in the direction of arrow c, and the force of the spring 17a of the pressure reducing valve 16 is weakened to reduce the pressure on the secondary side.
When the swash plate 6 is returned to the neutral direction by the spring force in the actuator 7, it is necessary to discharge the fluid in the actuator. However, since the discharge is performed by the leakage from the pressure reducing valve or the like, the secondary side pressure is reduced. There is a problem that the response becomes slow, and the discharge amount of the variable displacement hydraulic pump 2 that responds to the decrease in the engine speed cannot be obtained. Also, the accelerator lever
Since the engine 1 and the pressure reducing valve 16 must be operated by the valve 17, not only the structure becomes complicated, but also the positional adjustment between them is difficult. Therefore, an object of the present invention is a simple structure that does not require a pressure reducing valve, and a displacement volume changing mechanism of a variable displacement pump is made to respond in response to an increase or decrease in the engine speed, so that the discharge amount can be increased or decreased. It is to provide a driving circuit.

[Means for Solving the Problems]

To achieve the above object, a hydraulic drive circuit according to the present invention includes a variable displacement hydraulic pump and a fixed displacement hydraulic pump driven by one engine, an actuator for operating a displacement volume variable mechanism of the variable displacement hydraulic pump, and A fixed capacity hydraulic pump is provided with a throttle provided in a discharge line, and the actuator has a first working chamber at both ends thereof for tilting the volume varying mechanism, and a side for returning the volume varying mechanism to a neutral position. Second action chambers are formed respectively, and a first line branched from the upstream side of the throttle is used as a first action chamber of the actuator, and a second line branched from the downstream side of the throttle is used as a second action of the actuator. It is characterized by being connected to each room.

[Action]

When the number of rotations of the engine is increased, the discharge amount per unit time of the fixed displacement hydraulic pump that works in conjunction with this increases, so that the pressure difference before and after the throttle increases. The pressure oil on the upstream side of the throttle is guided to the first working chamber of the actuator via the first line, and the pressure oil on the second working chamber is discharged to the downstream side of the throttle via the second line. Therefore, due to the pressure difference, the actuator tilts the displacement volume variable mechanism of the variable displacement hydraulic pump to increase the discharge amount per one rotation of the variable displacement hydraulic pump. On the other hand, when the engine speed decreases, the discharge amount of the fixed displacement hydraulic pump also decreases, and the pressure difference before and after the throttle also decreases. According to this pressure difference, the actuator is returned to the neutral direction, and the discharge amount of the variable displacement hydraulic pump is reduced. In this way, the actuator is controlled by the pressure difference between the front and rear of the throttle, which is caused by the change in the discharge amount of the fixed displacement hydraulic pump that works in conjunction with the engine, so that the discharge amount of the variable displacement hydraulic pump that responds quickly to the increase or decrease in the engine speed can be obtained. .

【Example】

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are for explaining a hydraulic drive circuit according to an embodiment of the present invention. FIG. 1 is a circuit diagram of the hydraulic drive circuit, and FIG. 2 is a vehicle speed and a stroke amount of an accelerator lever. It is a characteristic view showing the relationship of. Hereinafter, constituent elements that are the same as or can be regarded as the same as those of the conventional example shown in FIG. 4 are denoted by the same reference numerals, and the description of the 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 1, and lines 31 and 33 for supplying pressure oil from the fixed displacement hydraulic pump 30 to the directional control valve 8 and a line for discharging the pressure oil. A sequence valve 22 is provided in a bypass line 25 connecting with 34, and an opening / closing valve 24 is provided from the line 33 to a pilot line 23 of the sequence valve 22. Further, the sequence valve 22 can set the cracking pressure by the spring 22a. Further, a diaphragm 32 is provided in the line 31, the upstream side of the diaphragm 32 is connected to the line 33, and the downstream line is connected to the line 34. The pressure on the upstream side of the throttle 32 increases or decreases in accordance with the discharge amount corresponding to the number of rotations of the fixed displacement hydraulic pump 30 that operates in conjunction with the engine per unit time. That is, when the rotational speed of the engine 1 is increased, the discharge amount per unit time of the fixed displacement hydraulic pump 30 that works in conjunction with this increases, and therefore the pressure difference around the throttle 32 increases. The pressure oil on the upstream side of the throttle 32 is, when the direction switching valve 8 is on the right side symbol,
The pressure oil in the second working chamber 7b, which is the left end chamber of the actuator 7, is guided from the first line 33 to the first working chamber 7a, which is the left end chamber of the actuator 7, through the direction switching valve 8 and the second working chamber 7b. Since it is discharged to the downstream side of the throttle 32 via the line 34, the actuator 7 tilts the swash plate 6 of the variable displacement hydraulic pump 2 due to the pressure difference, and discharges per rotation of the variable displacement hydraulic pump 2. Increase the amount. On the other hand, when the rotation speed of the engine 1 decreases, the discharge amount of the fixed displacement hydraulic pump 30 also decreases, and the pressure difference before and after the throttle 32 also sharply decreases. In response to this pressure difference, the actuator 7 is rapidly returned to the neutral direction, the swash plate 6 is rapidly returned to the neutral direction, and the discharge amount of the variable displacement oil pump 2 is rapidly reduced. Engine 1
Actuator 7 with the pressure difference around throttle 32 caused by the fluctuation of the discharge amount of fixed displacement hydraulic pump 30
Is controlled, it is possible to obtain the discharge amount of the variable displacement hydraulic pump 2 that responds quickly to the increase / decrease in the rotation speed of the engine 1. Therefore, the tilting amount of the swash plate 6, that is, the discharge amount per one rotation of the variable displacement hydraulic pump 2, is the rotational speed of the engine 1 until the tilting amount of the swash plate 6 becomes maximum (see the second X ₁ ). Increase accordingly. On the contrary, according to the decrease in the rotation speed of the engine 1,
The discharge amount per one rotation of the variable displacement hydraulic pump 2 sharply decreases. Here, when the on-off valve 24 is switched to the opening direction when working in the low speed L range, the pilot valve of the sequence valve 22 is changed.
23 is connected to connect the lines 33 and 34 when the differential pressure across the pilot spool reaches a preset cracking pressure by the spring 22a of the sequence valve 22. Then, the stroke amount X ₂ of the accelerator lever 17 which becomes the cracking pressure is set to the accelerator lever 17 at which the secondary increase in vehicle speed ends.
By setting the lower value than the stroke amount X ₁ (second reference curves LL in the figure), the discharge amount of the variable displacement hydraulic pump 2 in accordance with the stroke amount in a range lower than the stroke length X ₂ and the engine The rotation speed increases, and the vehicle speed increases according to the quadratic curve on the low speed L side similar to the conventional one. When the stroke amount reaches X ₂ , the sequence valve 22 operates to connect the lines 33 and 34 by the bypass line 25. As a result, the directional control valve 8
The pressure of the hydraulic oil supplied to the actuator 7 is constant, and the discharge amount per one rotation of the variable displacement hydraulic pump 2 is also constant. Therefore, even if the stroke amount becomes larger than X ₂ , the discharge amount of the variable displacement hydraulic pump 2 remains a small value corresponding to the stroke amount X _2, and therefore the vehicle speed is proportional to only the rotation speed of the engine 1. , That is, as indicated by LL. All other operations are the same as in the conventional example. As a result, the output of the engine 1 can be increased to the maximum limit and the work device can be driven by the maximum output of the second fixed displacement hydraulic pump 3 while keeping the vehicle speed lower than the conventional one. As described above, according to the above embodiment, the following effects can be obtained. The discharge line 31 of the fixed displacement hydraulic pump 30 is provided with a throttle 32, and the first line 33 branched from the upstream side of the throttle 32 is
A second line 34 branched from the downstream side of the throttle 32 is connected to the first working chamber 7a of the actuator 7 and is connected to the second working chamber 7b of the actuator 7 to discharge the fixed displacement hydraulic pump that works in conjunction with the engine. Since the actuator is controlled by the pressure difference between the front and rear of the throttle caused by the fluctuation of the amount, it is possible to obtain the discharge amount of the variable displacement hydraulic pump that immediately responds to the increase and decrease of the engine speed. Moreover, since it is not necessary to connect the accelerator lever 17 and the pressure reducing valve, the hydraulic piping becomes simple. By providing the sequence valve 22, the operating pressure supplied to the actuator 7 can be limited when the pressure becomes higher than the preset pressure, so that the discharge amount of the variable displacement hydraulic pump 1 can be suppressed. It is possible, which makes it possible to increase the number of gear stages without changing the mechanical transmission. In the above-described embodiment, the fixed displacement hydraulic pump 30 generates the operating pressure of the actuator 7. However, FIG. 3 shows that the flow rate of the fixed displacement hydraulic pump 30 is effectively used. The fixed displacement hydraulic pump 30 shown in FIG. 3 has a function of generating an operating pressure of the actuator 7 and charging the main pipelines 10 and 11 of the closed circuit for driving the hydraulic motor 4 with pressurized oil. In the above embodiment, the actual operating speed of the engine 1 is detected from the pressure difference generated before and after the throttle 32, and the sequence valve 22
By switching the valve by setting the cracking pressure of, the 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, and these are performed by mechanical means. It is conceivable to configure it by means of a physical means. An example of this is shown in FIG. In FIG. 3, constituent elements that are the same as or can be regarded as the same as those of the embodiment and the conventional example are given the same reference numerals. In FIG. 3, the engine 1 is provided with a tachometer 40 for detecting the number of revolutions, and the tachometer 40 is
The number of revolutions detected by the tachometer 40 is electrically processed, and the detected number of revolutions is used as a parameter to arbitrarily select a switching set value of the electromagnetically operated on-off valve 41 described later, and the on-off valve is switched to the switch device 42. A processing device 43 capable of outputting the switching signal of 41 is connected. Further, the on-off valve 41 is inserted in the bypass line 25 connecting the lines 33 and 34 between the lines 33 and 34 in the same manner as in the above-mentioned embodiment, and by the switching output of the switching device 42 operated by the output from the processing device 43. , The open position and the closed position are selected electromagnetically. Other parts, which are not particularly described, are configured the same as those shown in FIG. With the configuration described above, the engine 1 can be operated by the tachometer 40.
When the number of rotations of the switch reaches a switching set value set in advance in accordance with work conditions and the like, the open / close valve 41 is operated via the switch device 42 to supply the high pressure side line to the actuator 7.
The pressure oil flowing through 33 can be led out to the low pressure side line 34 to make the pressure applied to the actuator 7 constant. In this embodiment, since the switching set value is set by electrical means, it is extremely easy to select or change the set value as compared with the above embodiment, and a control start instruction for performing this type of control is given. Can also be processed in the processing device 43,
This has the effect of simplifying the configuration.

【The invention's effect】

As is clear from the above, the hydraulic drive circuit of the present invention includes a variable displacement hydraulic pump and a fixed displacement hydraulic pump driven by one engine, an actuator for operating the displacement volume changing mechanism of the variable displacement hydraulic pump, and A fixed capacity hydraulic pump is provided with a throttle interposed in a discharge line, and the actuator has a first working chamber at both ends thereof on a side for tilting the volume variable mechanism and a second working chamber on a side for neutrally returning the variable mechanism. Two working chambers are formed, and a first line branched from the upstream side of the throttle is a first working chamber of the actuator, and a second line branched from the downstream side of the throttle is a second line of the actuator.
Since the actuator is controlled by the pressure difference before and after the throttle that is connected to the working chambers and changes in the discharge amount of the fixed displacement hydraulic pump that works in conjunction with the engine, the discharge amount of the variable displacement hydraulic pump responds quickly to the increase or decrease in the engine speed. Is obtained. In particular, when the engine speed decreases, the pressure difference before and after the throttling sharply decreases, so that the actuation response of the actuator becomes quick, and the discharge amount of the variable displacement hydraulic pump that responds to the decrease in the engine speed quickly is obtained. Further, even if the operation amount of the accelerator lever does not correspond to the engine speed, the discharge amount of the variable displacement hydraulic pump has an advantage that it corresponds to the engine speed. Further, since it is not necessary to connect the accelerator lever and the pressure reducing valve as in the conventional case, the structure is simplified and the positional adjustment between them is not necessary.

[Brief description 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 the vehicle speed and the stroke of an accelerator lever in the above embodiment, and FIG. 3 is related to another embodiment. FIG. 4 is a circuit diagram showing a main part of a hydraulic drive circuit, FIG. 4 is a circuit diagram of a hydraulic drive circuit according to a conventional example, and FIG. 5 is a characteristic diagram showing a relationship between a vehicle speed and a stroke of an accelerator lever. 1 ... Engine, 2 ... Variable displacement hydraulic pump, 3 ... Hydraulic pump, 4 ... Hydraulic motor, 6 ... Swash plate, 7 ... Actuator, 8 ... Direction switching valve, 10,11 ... Main line , 1
2 ... transmission, 16 ... pressure reducing valve, 17 ... accelerator lever, 2
2 …… Sequence valve, 23 …… Pilot line, 24 ……
On-off valve, 25 …… bypass line, 32 …… throttle, 33,34…
Line, 40 Tachometer, 41 Open / close valve, 42 Switch device, 43 Processing unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page Judgment panel Judge General Toru Sakai Judge Judge Funaki Susumu Jitsuba Shiba (56) References JP-B-45-33149 (JP, B1)

Claims (1)

[Claims] 1. A variable displacement hydraulic pump (2) and a fixed displacement hydraulic pump (30) driven by one engine (1) and a displacement volume variable mechanism (6) of the variable displacement hydraulic pump (2). Actuator (7)
And the fixed capacity hydraulic pump (30) discharge line (31)
The actuator (7) has a first working chamber (7a) on both sides of which the volume varying mechanism (6) is tilted, and the volume varying mechanism (6). )
The second working chamber (7b) is formed on the side for returning the neutral state, and the first line (33) branched from the upstream side of the throttle (32) is connected to the first working chamber (7a) of the actuator (7). ), The second line (34) branched from the downstream side of the throttle (32) is connected to the second working chamber (7b) of the actuator (7), respectively.