JP2002089506A - Hydraulic system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic system capable of reducing a hydraulic pump load on a starter in engine starting up. SOLUTION: A hydraulic system 1 is provided with an electromagnetic selector valve 19 closing and opening a load sensing circuit 100 reporting required hydraulic fluid flow amount from each system 1A, 1B, 1C, 1D to a variable capacity pump 12 in the load sensing circuit 100. A tube path 57 and a second drain tube path are connected with the electromagnetic selector valve 19 in starting up of an engine 1E to minimize output of the variable capacity pump 12. Accordingly, load on the engine 1E during starting up of the engine 1E can be reduced to lighten load on a starter 1F starting up the engine 1E for a good starting up property of the engine 1E.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic system, and more particularly, to a hydraulic system provided with a pump driven by an engine and supplying hydraulic pressure to parts requiring hydraulic pressure.

[0002]

2. Description of the Related Art Conventionally, a construction machine having a plurality of working machine systems, such as a motor grader, has a hydraulic system for supplying hydraulic pressure to these working machine systems. In a hydraulic system, a large-capacity pump is employed as a hydraulic pump in order to constantly supply an amount of oil to a plurality of working machine systems. The drive shaft of the large-capacity pump is connected to the engine, for example, a crankshaft or a camshaft, via a transmission mechanism including a pulley and a timing belt, and the large-capacity pump is driven by the engine. I have.

[0003] When the engine is started, the engine usually starts to be rotated by a starter. For this reason, in a construction machine or the like having a large capacity pump, if the large capacity pump is connected to the crankshaft of the engine or the like, a load corresponding to the large capacity pump is applied to the starter, and it becomes difficult for the engine speed to increase. . In particular, when it is cold, it becomes even more difficult to start the engine. Also, in a hydraulic system having a pressure accumulating mechanism in the steering system or the brake system, the accumulation of pressure in the accumulator by the large-capacity pump starts when the engine is started, so that a large hydraulic torque is generated when the engine is started, and the burden on the starter is further increased. As the engine becomes larger, the number of revolutions of the engine becomes harder to rise, and the engine becomes harder to start.

In order to solve such a problem, before starting the engine, the large-capacity pump is disconnected from the engine by a manual switching operation, and then the engine is started by a starter. It is conceivable that the large-capacity pump is connected to the engine again, thereby improving the startability of the engine.

[0005]

However, in the structure in which the large-capacity pump is separated from the engine as described above, at the time of starting the engine, the operator needs to perform an operation of disconnecting the large-capacity pump from the engine. After starting, there is a problem that it is necessary to perform an operation of connecting the large capacity pump to the engine again, which is troublesome. Also, if the operator forgets to reconnect the large-capacity pump to the engine after starting the engine, the hydraulic pressure has not risen, so the working machine system cannot be used until the large-capacity pump is connected to the engine and the hydraulic pressure rises. Problems arise.

An object of the present invention is to provide a hydraulic system capable of reducing the load on a hydraulic pump applied to a starter when an engine is started.

[0007]

Means for Solving the Problems In order to achieve the above object, the hydraulic system of the present invention has the following arrangement.
The invention according to claim 1 is a tank that stores oil, a variable displacement pump that is driven by an engine to pump oil from the tank, is provided so as to be connectable to the variable displacement pump, and is connected to the variable displacement pump. A supply hydraulic circuit for supplying oil to the oil pressure required portion, a load sensing circuit for transmitting a required flow rate of oil from the oil pressure required portion to the variable displacement pump, and a load sensing circuit provided in the middle of the load sensing circuit; An electromagnetic switching valve that shuts off and opens a circuit, and shuts off or opens the load sensing circuit at the time of starting the engine to change the output of the variable displacement pump. .

According to the present invention, the required flow rate of the oil from the portion requiring the hydraulic pressure is transmitted to the variable displacement pump through the load sensing circuit, whereby the output of the variable displacement pump is changed. An electromagnetic switching valve that shuts off and opens the load sensing circuit is provided in the middle of such a load sensing circuit, and the output of the variable displacement pump can be changed by linking the electromagnetic switching valve with the start of the engine. did. Therefore, the output of the variable displacement pump can be changed by controlling the opening / closing of the load sensing circuit by the electromagnetic switching valve at the time of engine start. Therefore, when the output of the variable displacement pump is changed at the time of starting the engine, for example, if the output of the variable displacement pump is set to be minimized, the load on the engine is reduced, and the engine is started, for example, the starter is started. Is lightened, and the startability of the engine is improved.

According to a second aspect of the present invention, there is provided a tank for storing oil, a hydraulic pump driven by an engine to pump oil from the tank, and provided so as to be connectable to the hydraulic pump. A supply hydraulic circuit for supplying oil to the hydraulic pressure required portion, a drain circuit provided so as to be connectable to the hydraulic pump and returning oil from the hydraulic pump to the tank, and a required flow rate of oil from the hydraulic required portion A load sensing circuit that transmits the load sensing circuit to the hydraulic pump, and is provided in the middle of the load sensing circuit, and shuts off and opens the load sensing circuit, and shuts off or opens the load sensing circuit at the time of starting the engine. The electromagnetic switching valve for connecting the hydraulic pump and the drain circuit is provided. Than it is.

According to the present invention, the required flow rate of the oil from the hydraulic pressure required portion is transmitted to the hydraulic pump through the load sensing circuit, whereby the connection between the hydraulic pump and the supply hydraulic circuit, and the connection between the hydraulic pump and the drain The degree of connection with the circuit is adjusted. In the middle of such a load sensing circuit, an electromagnetic switching valve for shutting off and opening the load sensing circuit is provided, and the electromagnetic switching valve is provided so as to be interlocked with the start of the engine.
The opening and closing of the load sensing circuit can be set when the engine is started, and the connection between the hydraulic pump and the supply hydraulic circuit and the connection between the hydraulic pump and the drain circuit can be adjusted with the opening and closing of the load sensing circuit. Therefore, when the electromagnetic switching valve is switched at the time of starting the engine, if the hydraulic pump and the drain circuit are set to be connected, the normal drain circuit is set at a lower pressure than the supply hydraulic circuit. Therefore, the oil pumped by the hydraulic pump is returned to the tank, and the load on the engine is reduced. For this reason, the load on the engine to be started, for example, the starter is reduced, and the startability of the engine is improved.

According to a third aspect of the present invention, in the hydraulic system according to the first or second aspect, the engine is provided with a key switch for starting the engine. It is characterized by being connected to the key switch. According to the present invention, the electromagnetic switching valve is connected to the key switch for starting the engine.
If the electromagnetic switching valve is energized when entering the TART, the start of the engine and the switching operation (cutoff / opening) of the electromagnetic switching valve can be easily linked.

According to a fourth aspect of the present invention, in the hydraulic system according to any one of the first to third aspects, an accumulator is provided in the supply hydraulic circuit, and an accumulator corresponding to the hydraulic pressure in the accumulator is provided. The electromagnetic switching valve is switched over. According to the present invention, the electromagnetic switching valve can be switched in accordance with the oil pressure in the accumulator, so that the accumulator can accumulate the pressure within a range that does not impose a burden on starting the engine.

According to a fifth aspect of the present invention, in the hydraulic system according to any one of the first to fourth aspects, the solenoid-operated directional control valve is connected to the electromagnetic switching valve until a predetermined time has elapsed since the start of the engine. A delay circuit for maintaining the open / closed state of the electromagnetic switching valve switched at the time of starting is provided. According to the invention,
Since the electromagnetic switching valve is provided with the delay circuit, the open / close state of the electromagnetic switching valve can be maintained until the rotation of the engine is stabilized. As a result, a load can be prevented from being applied to the pump immediately after the start of the engine whose rotation is unstable, and the engine stop can be more effectively prevented.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, first and second embodiments of the present invention will be described with reference to the drawings. First Embodiment FIG. 1 shows a hydraulic system 1 according to a first embodiment of the present invention. The hydraulic system 1
It is provided on a construction machine such as a motor grader (not shown), and is provided as a first hydraulic pressure-required part of the construction machine.
It supplies hydraulic pressure to the working machine system 1A, the second working machine system 1B, the steering system 1C, and the brake system 1D. The first working machine system 1A and the second working machine system 1
B, steering system 1C, and brake system 1D
Although not shown, a first working machine mechanism (for example, a mechanism for vertically moving a blade (not shown) or a mechanism for operating a ripper, etc.) provided on a construction machine, a second working machine mechanism (for example, a drawbar (not shown)) And a hydraulic circuit for operating the steering mechanism and the brake mechanism, respectively. Such a hydraulic system 1 includes a tank 11 for storing oil, and a swash plate type variable displacement pump 12 is connected to the tank 11. The variable displacement pump 12 supplies pressure oil to a main pipeline 21. I have.

The variable displacement pump 12 is driven by an engine 1E provided in a construction machine. The drive shaft of the variable displacement pump 12 is constituted by a pulley, a timing belt, and the like, for example, a crankshaft and a camshaft of the engine 1E. It is connected via a transmission mechanism. Engine 1E
Is connected to the starter 1F.
When the key switch 1G connected to
The starter 1F operates to start.

A filter 13 is provided in the main line 21, and a first pilot switching valve 14 for three-port two-position switching is provided at a tip of the filter 13. A main pipe 21 is connected to a P port which is an inlet of the first pilot switching valve 14, and an A port and a B which are outlets are provided.
A first supply pipe 22 and a second supply pipe 23 are connected to the ports, respectively. When the first pilot switching valve 14 is at the position (A), the main line 21 and the first supply line 22 are connected, and the second supply line 23 is connected.
Is shut off and at the position (b), the main pipeline 21 and the second
The supply line 23 is connected, and the first supply line 22 is shut off.

The leading end of the first supply pipe 22 is branched into two, and one of the branched first work equipment pipes 24 is connected to the first work equipment system 1A, and the other second work equipment pipe 24 is connected to the second work equipment system 1A. The working machine pipeline 25 is connected to the second working machine system 1B. First
A first check valve 15 for preventing a flow from each working machine system 1A, 1B to the first pilot switching valve 14 is provided in the middle of the supply pipeline 22. Second supply line 23
Has one end branched into two, one of the branched steering lines 26 is connected to the steering system 1C, and the other brake line 27 is connected to the braking system 1D.
It is connected to the. The second check valve 20 and the accumulator 16 are provided in series in the brake line 27 in this order. The second check valve 20 prevents a flow from the brake system 1D to the first pilot switching valve 14.

The first pilot switching valve 14 has the first
A first pilot line 14A and a second pilot line 14 for guiding pilot pressure to the pilot switching valve 14, respectively.
B is connected. The first pilot pipe 14 </ b> A is connected to a pipe 54 connected to the brake pipe 27 upstream of the second check valve 20. The second pilot line 14 </ b> B is connected in the middle of the second supply line 23. When the pilot pressure is not applied, the first pilot switching valve 14 is always at the position (B) by the spring pressure, and the pilot pressure from the second pilot line 14B is
When the pressure exceeds the combined pressure of the spring pressure and the pilot pressure from the first pilot line 14A, the position is switched to the position (a).

The variable displacement pump 12 is of a swash plate type as described above, and has a hydraulic cylinder 12 for changing the swash plate angle.
1 and a piston 122 are provided. Piston 1
When 22 moves to the left side in the figure, the swash plate angle increases, the output of the variable displacement pump 12 increases, and the piston 122
Moves to the right side in the figure, the swash plate angle decreases, and the output of the variable displacement pump 12 decreases. The diameter of the piston 122 is large on the left side in the figure and small on the right side in the figure, and the hydraulic cylinder 121 is also formed corresponding to the shape of the piston 122. Large diameter side 121A of hydraulic cylinder 121
When substantially the same hydraulic pressure is supplied to the left side (in the figure) and the small diameter side 121B (the right side in the figure), the pressure receiving area of the large diameter side (left side in the figure) of the piston 122 is larger than that of the small diameter side (right side in the figure). Is larger, the piston 122 moves to the right in the figure.

The hydraulic system 1 is provided with a load sensing circuit 100 for transmitting a required flow rate of oil from each of the working machine systems 1A and 1B, the steering system 1C, and the brake system 1D to the variable displacement pump 12. .
The load sensing circuit 100 changes the output of the variable displacement pump 12. The load sensing circuit 100 includes a pump discharge pressure pipe 41 connected to the main pipe 21 of the variable displacement pump 12. The pump discharge pressure pipe 41 is connected to the large-diameter side 121A and the small-diameter side 121B of the hydraulic cylinder 121. , The discharge pressure of the variable displacement pump 12 is supplied.

The distal end of the pump discharge pressure pipe 41 is branched into two pipes 42 and 43. One of the branched small-diameter pipes 42 is connected to the small-diameter side 121B of the hydraulic cylinder 121, and the other pipe is used. The passage 43 is connected to the C port of the second pilot switching valve 17 that switches between three ports and two positions. Second
The D port and the E port of the pilot switching valve 17 include:
The first drain pipe 44 and the large-diameter pipe 45 are connected to each other. The first drain pipe 44 has a tip connected to the tank 11, and the large diameter pipe 45 has a tip connected to the large diameter side 121 </ b> A of the hydraulic cylinder 121. When the second pilot switching valve 17 is at the position (C), the large-diameter side pipe 45 and the first drain pipe 44 are connected,
At the position (d), the other pipeline 43 is shut off, and the large-diameter side pipeline 45 is connected to the other pipeline 43, and the first drain pipeline 44 is shut off. . The second pilot switching valve 17 supplies the discharge pressure of the variable displacement pump to the large-diameter side 121A of the hydraulic cylinder 121 via the pipelines 41, 43, and 45.

The second pilot switching valve 17 has the second
Third pilot line 17A and fourth pilot line 17 for guiding pilot pressure to pilot switching valve 17, respectively.
B is connected. When the pilot pressure is not applied, the second pilot switching valve 17 is always at the position (C) due to the spring pressure, and the pilot pressure from the third pilot line 17A is changed to the spring pressure and the fourth pilot line 17B from the fourth pilot line 17B. If the combined pressure with the pilot pressure is exceeded, the position (d)
Switch to.

The lines connected to the respective pilot lines 17A and 17B of the second pilot switching valve 17 will be described in detail below. Each of the first working machine system 1A, the second working machine system 1B, and the steering system 1C includes
First to derive inlet pressures at A, 1B and 1C respectively
Inlet pressure line 31, second inlet pressure line 32, and third line
The inlet pressure pipelines 33 are respectively connected. The inlet pressure is the inlet pressure of an operation valve (not shown) provided in each of the systems 1A, 1B, and 1C. These pipelines 31 to 3
3 is joined to the third pilot line 17A at its tip, and this third pilot line 17A
The inlet pressures of A, 1B, and 1C are used as pilot pressure, and are led to the second pilot switching valve 17. That is, the third pilot line 17A guides the load sensing (LS) pump pressure to the second pilot switching valve 17.

On the other hand, a first outlet pressure pipeline 51 and a second outlet pressure pipeline 52 are respectively connected to the first working machine system 1A and the second working machine system 1B to guide the outlet pressure in each of the systems 1A and 1B. Have been. The outlet pressure is the outlet pressure of an operation valve (not shown) provided in each of the systems 1A and 1B. These pipes 51 and 52 are joined at the tip thereof, and the tip of the joined pipe 53 is connected to the third pipe.
It is connected to the upstream side of the check valve 18. The distal end of the pipeline 54 connected to the brake pipeline 27 is branched into two, one of which is the first pilot pipeline 14A described above, and the other of which is the distal end of the pipeline 55. Branch into two conduits 56 and 57. The pipe 56 is connected to the upstream side of the third check valve (flow path selection valve) 18 to which the above-described pipe 53 is connected, and the pipe 57 is one of the two-port two-position switching electromagnetic switching valves 19. Connected to the port. A second drain pipe 58 is connected to the other port of the electromagnetic switching valve 19, and the tip of the second drain pipe 58 is connected to the tank 11.

When the electromagnetic switching valve 19 is at the position (e), the line 57 and the second drain line 58 are shut off, and the position (f)
At this time, the pipeline 57 and the second drain pipeline 58 are connected. The electromagnetic switching valve 19 is connected to the key switch 1G of the engine 1E, and is connected to the key switch 1G.
The position is switched by an input signal sent from the switch, and is usually at the position (e) by spring pressure.
When G enters START, an input signal is sent to switch to position (F). Further, a timer 19A as a delay circuit is provided between the key switch 1G and the electromagnetic switching valve 19. When the input signal from the key switch 1G is given to the timer 19A, the timer contact is closed and the input signal is sent to the electromagnetic switching valve 19,
When the input signal from the key switch 1G is interrupted, the timer contact of the timer 19A opens after a predetermined time, and the electromagnetic switching valve 1
Since the input signal is not sent to 9, the electromagnetic switching valve 19 switches to the position (e).

The above-mentioned fourth pilot pipeline 17B is connected downstream of the third check valve 18 to which both the pipeline 53 and the pipeline 56 are connected.
Of the two pipelines 53 and 56, the oil in the pipeline with the higher hydraulic pressure is supplied to the downstream fourth pilot pipeline 17B as pilot pressure oil. That is, the fourth pilot line 1
7B guides a load sensing (LS) pressure to the second pilot switching valve 17.

The supply hydraulic circuit of the present invention comprises a main line 21, first and second supply lines 22, 23, and a first line.
Not only the pipelines 24 and 25 for the second working machine, the pipeline 26 for the steering, and the pipeline 27 for the brake, but also the pipelines (not shown) provided in the respective systems 1A to 1D. I have. The load sensing circuit 100 includes a second pilot switching valve 17, third and fourth pilot lines 17A and 17B, a third check valve 18, first to third inlet pressure lines 31 to 33, and a pump discharge pressure. Pipe 41, small-diameter and large-diameter pipes 42, 45, first and second outlet pressure pipes 51, 52, respective pipes 43, 53 to 57,
The first and second drain pipes 44 and 58 are included.

Next, the operation of the present embodiment will be described. When the driver turns on the key switch 1G to START, an input signal is given to switch the electromagnetic switching valve 19 to the position (F), and the starter 1F is operated to start the engine 1
The camshaft and crankshaft (not shown) of E start to rotate. Then, the variable displacement pump 12 connected to the engine 1E is driven to pump up the oil in the tank 11. When the pilot pressure is not applied, the first pilot switching valve 14 is always at the position (b) by the spring pressure, so the pumped oil is supplied to the second supply line 23,
It is supplied to a steering system 1C and a brake system 1D through a steering pipeline 26 and a brake pipeline 27, respectively. At this time, the accumulator 16 provided in the middle of the brake line 27 stores pressure.

For the oil flowing through the pipe 54 through the brake pipe 27, the pipe 57 is connected to the second drain pipe 58 via the electromagnetic switching valve 19, so that the pressure in the pipe 55 is low. Therefore, it is easier to flow into the pipeline 55 than the first pilot pipeline 14A. For this reason, the first pilot line 14
The oil pressure of A becomes lower than the oil pressure of the second pilot line 14B connected to the second supply line 23, and the combined pressure of the spring pressure and the pilot pressure from the first pilot line 14A becomes When the pressure becomes lower than the pilot pressure from the second pilot line 14B, the first pilot switching valve 14 switches to the position (a).

Then, the oil pumped up by the variable displacement pump 12 is supplied to the first supply pipe 22 and the first work equipment pipe 2.
4 and the second working machine line 25, and are supplied to the first working machine system 1A and the second working machine system 1B, respectively. As a result, the accumulation of pressure in the accumulator 16 provided in the brake line 27 is stopped. When the driver is turning the key switch 1G to start the engine 1E, normally, the first working machine (not shown) and the second working machine (not shown) are used.
The operation of the work machine has stopped. That is, the operating valves (not shown) of the first working machine system 1A and the second working machine system 1B are in a closed state. Therefore, the first working machine system 1
In A and the second working machine system 1B, the inlet pressure is higher than the outlet pressure, and the second pilot switching valve 17 operates the pilot pressure (inlet pressure) from the third pilot line 17A.
When the pressure exceeds the combined pressure of the spring pressure and the pilot pressure (outlet pressure) from the fourth pilot line 17B, the position is switched to the position (d). When the second pilot switching valve 17 is in the position (d), the discharge pressure of the variable displacement pump 12 passes through the pipelines 41, 43, and 45 and the hydraulic cylinder 121.
, The piston 122 moves rightward in the drawing, the swash plate angle of the variable displacement pump 12 decreases, and the pump output decreases. Thereby, the output of the variable displacement pump 12 at the time of starting the engine 1E is
For example, the variable displacement pump 1 can be minimized (the swash plate angle of the variable displacement pump 12 can be set to zero or a value close to zero).
The load on the engine 1E that drives the engine 2 and the starter 1F can be reduced, and the startability of the engine 1E is improved.

When the engine 1E is started, the driver releases his / her hand from the key switch 1G, so that the key switch 1G is switched from START to ON by, for example, a spring pressure. Since a timer 19A is provided between the key switch 1G and the electromagnetic switching valve 19, the key switch 1G is
After switching to N, the electromagnetic switching valve 19
Is at position (f). That is, as described above, the output of the variable displacement pump 12 remains small.

After a certain period of time has elapsed since the key switch 1G was turned on, the signal from the timer 19A disappears, and the electromagnetic switching valve 19 is switched to the position (e). Then, since the line 57 and the second drain line 58 are shut off, the hydraulic pressure in the lines 57, 56, 55, and 14A increases.
When the oil pressure in the line 56 becomes higher than the oil pressure in the line 53, the oil in the line 56 is supplied to the fourth pilot line 17B via the third check valve 18. Second pilot switching valve 1
Reference numeral 7 switches to the position (c) when the combined pressure of the spring pressure and the pilot pressure of the fourth pilot line 17B exceeds the pilot pressure of the third pilot line 17A.

Then, the discharge pressure of the variable displacement pump 12 is supplied only to the small-diameter side 121B of the hydraulic cylinder 121, and the line 45 and the first drain line 44 are connected. The oil on the large-diameter side 121A of the hydraulic cylinder 121 is moved in the
And returns to the tank 11. As a result, the swash plate angle of the variable displacement pump 12 increases, and the pump output increases. When the oil pressure in the pipe 55 increases, the pilot pressure in the first pilot pipe 14A also increases, and the first pilot switching valve 14 generates a pressure equal to the sum of the spring pressure and the pilot pressure in the first pilot pipe 14A. When the pressure exceeds the pilot pressure of the second pilot line 14B, the position is switched to the position (b). Thus, after a predetermined time has elapsed after the start of the engine 1E, the accumulation of pressure in the accumulator 16 is restarted.

According to the above-described embodiment, the following effects can be obtained. (1) The required flow rate of the oil from each system 1A to 1D is transmitted to the variable displacement pump 12 through the load sensing circuit 100, whereby the output of the variable displacement pump 12 is changed. An electromagnetic switching valve 19 for shutting off and opening the load sensing circuit 100 is provided in the middle of the load sensing circuit 100, and the electromagnetic switching valve 19 is provided so as to be linked with the start of the engine 1E. Sometimes load sensing circuit 100
Of the variable displacement pump 12 can be changed as the load sensing circuit 100 opens and closes. Therefore, when the engine is started, the output of the variable displacement pump 12 is changed so that the output of the variable displacement pump 12 is minimized, so that the load on the engine 1E can be reduced, and the starter 1F that starts the engine 1E can be reduced. Can be lightened, and the startability of the engine 1E can be improved.

(2) Set the electromagnetic switching valve 19 to the key switch 1G
And when the key switch 1G enters START, the electromagnetic switching valve 19 is energized, so that the start of the engine 1E and the switching operation of the electromagnetic switching valve 19 can be easily linked. .

(3) Since the electromagnetic switching valve 19 is provided with the timer 19A, the open / close state of the electromagnetic switching valve 19 can be maintained until the rotation of the engine 1E is stabilized. As a result, it is possible to prevent a load from being applied to the variable displacement pump 12 immediately after the start of the engine 1E whose rotation is unstable, thereby preventing an engine stop.

(4) Since the electromagnetic switching valve 19 is provided in the middle of the load sensing circuit 100 through which the pilot pressure oil flows, for example, the main line 21, the first supply line 22, and the second supply line As compared with the case where an electromagnetic switching valve is installed in the main pipeline such as the pipeline 23 or the brake pipeline 27, a small electromagnetic switching valve can be adopted and the cost can be reduced.

[Second Embodiment] FIG. 2 shows a second embodiment of the present invention.
1 shows a hydraulic system 2 according to an embodiment. Here, the present embodiment is different from the above-described first embodiment only in the type of pump for pumping oil from the tank and the load sensing circuit, and the other configurations and operations are the same. Their description is omitted or simplified. In FIG. 2, the hydraulic system 2 includes a tank 11, for example, a gear-type hydraulic pump 61 is connected to the tank 11, and the hydraulic pump 61 supplies pressure oil to the main pipeline 21. In the above-described first embodiment, the first pilot switching valve 14 is provided at the tip of the main pipeline 21. However, in the present embodiment, the first pilot switching valve is not provided, and the main pipeline 21 is not provided. The tip of 21 is branched into a first supply line 22 and a second supply line 23.

The load sensing circuit 200 provided in such a hydraulic system 2 uses a hydraulic pump to determine the required flow rate of oil from the first working machine system 1A, the second working machine system 1B, the steering system 1C, and the brake system 1D. I tell 61. The load sensing circuit 200 includes a third drain line 71 as a drain circuit of the present invention connected in the middle of the main line 21 of the variable displacement pump 12, and a tip of the third drain line 71 is connected to the tank 11. It is connected to the. A third pilot switching valve 62 is provided in the middle of the third drain pipe 71, and the third pilot switching valve 62
Thereby, the third drain pipe 71 can be opened and shut off. The third pilot switching valve 62 is provided with a fifth pilot line 62A for guiding pilot pressure oil to the third pilot switching valve 62. Third pilot switching valve 62
Is usually located at a position where the third drain line 71 is shut off,
When the pilot pressure from the fifth pilot line 62A exceeds a predetermined pressure set in advance, the position is switched to a position where the third drain line 71 is opened.

The fifth pilot line 62A has
A first pipeline 81, a second pipeline 82, a third pipeline 83, and a fourth pipeline 84 connected to A to 1D respectively are merged. These first, second, third, and fourth conduits 81-
84 guides the hydraulic pressure of each system 1A to 1D to the fifth pilot pipeline 62A. In the present embodiment, each pipe 8
1 to 84 are assumed to guide the inlet pressures of the operation valves (not shown) of the respective systems 1A to 1D to the fifth pilot line 62A. A fourth drain pipe 85 is connected in the middle of the fifth pilot pipe 62 </ b> A, and the electromagnetic switching valve 19 is provided in the middle of the fourth drain pipe 85.
Here, the electromagnetic switching valve 19 of the present embodiment is different from the electromagnetic switching valve 19 of the first embodiment described above in that it is at the normal position (f) by spring pressure and opens the fourth drain pipe 85. When the power is supplied, the position is switched to the position (e) and the fourth drain line 85 is shut off.

The load sensing circuit 200 includes the third pilot switching valve 62 and the fifth pilot line 6
2A, the first to fourth conduits 81 to 84, and the third and fourth drain conduits 71 and 85.

Next, the operation of the present embodiment will be described. The description of the same portions as those of the first embodiment will be omitted or simplified. When the driver turns on the key switch 1G to START, an input signal is given to switch the electromagnetic switching valve 19 to the position (e), and the starter 1F is operated to operate a camshaft, crankshaft, or the like (not shown) of the engine 1E. Starts to rotate. Then, the hydraulic pump 61 connected to the engine 1E
Is driven to pump up the oil in the tank 11. The pumped oil is supplied to each of the systems 1A to 1D through the first supply pipe 22 and the second supply pipe 23 and the like. At this time, the accumulator 16 provided in the middle of the brake line 27 stores pressure.

When the hydraulic pressure starts to be supplied to each of the systems 1A to 1D, the inlet pressure of each of the systems 1A to 1D is derived from each of the pipes 81 to 84 and supplied to the fifth pilot pipe 62A. When the pilot pressure in the fifth pilot line 62A exceeds a predetermined value, the third pilot switching valve 62 is switched to
The drain line 71 is opened. As a result, the pressure in the third drain pipe 71 becomes low, so that the oil pumped up by the hydraulic pump 61 does not flow into the first and second supply pipes 22 and 23, and most of the oil is pumped into the third drain pipe. It flows into the road 71. Since most of the oil pumped by the hydraulic pump 61 is not supplied to each system 1A to 1D but returned to the tank 11, the load applied to the hydraulic pump 61 itself can be reduced. Therefore, the engine 1E that drives the hydraulic pump 61 Thus, the load on the starter 1F can be reduced, and the engine 1E
Startability is improved.

When the engine 1E is started, the driver releases his / her hand from the key switch 1G, so that the key switch 1G is switched from START to ON by, for example, a spring pressure. Since a timer 19A is provided between the key switch 1G and the electromagnetic switching valve 19, the key switch 1G is
After switching to N, the electromagnetic switching valve 19
Is at position (e). That is, as described above, most of the oil pumped by the hydraulic pump 61 returns to the tank 11 through the third drain pipe 71.

After a certain period of time has elapsed since the key switch 1G was turned ON, the solenoid-operated directional control valve 19 is switched to the position (F) by the action of the timer 19A. Then, since the fourth drain pipe 85 is opened, the oil from each of the pipes 81 to 84 flows into the fourth drain pipe 85 and returns to the tank 11. For this reason, the pressure in the fifth pilot line becomes low, and the third pilot switching valve is switched to the third drain line 71.
Is shut off. Then, the oil pumped by the hydraulic pump is supplied again to each of the systems 1A to 1D through the first supply pipe 22 and the second supply pipe 23 and the like. On this occasion,
The accumulation of pressure in the accumulator 16 is started again.

According to the present embodiment as described above, the following effects are obtained in addition to the effects (2) to (4) of the first embodiment. (5) Load sensing circuit 200 (drain line 85)
And a third drain pipe 71 connected to the hydraulic pump 61 is connected to the engine 1E by the electromagnetic switching valve 19 in conjunction with the start of the engine 1E. Opened when starting. Accordingly, at the time of starting the engine 1E, most of the oil pumped by the hydraulic pump 61 returns to the tank 11 through the low-pressure third drain pipe 71,
The load on the hydraulic pump 61 itself can be reduced. Therefore, the load on the engine 1E that drives the hydraulic pump 61 and, consequently, the load on the starter 1F can be reduced.
Can have good startability.

The present invention is not limited to the above embodiments, but includes modifications and improvements as long as the object of the present invention can be achieved. For example,
In the first embodiment, the swash plate type variable displacement pump 12 is used, but the variable displacement pump according to the present invention is not limited to this, and may be, for example, an oblique axis type variable displacement pump.

In the second embodiment, the third pilot switching valve 62 for shutting off and opening the drain line 71 is provided.
For example, a throttle valve that gradually narrows or gradually opens the drain pipe 71 may be provided. Even when such a throttle valve is provided, it is possible to reduce the load applied to the hydraulic pump when the engine is started. .

In each of the above embodiments, the delay circuit is constituted by using the timer 19A. However, as the delay circuit according to the present invention, for example, a timer provided in an engine control computer (not shown) for controlling the engine 1E is used. May be used. In such a case, the same effect as when the timer 19A is used can be obtained.

In each of the above embodiments, the electromagnetic switching valve 19 is
When the starter 1F enters START, the position is set to be switched. For example, the position is set to be switched in accordance with the internal pressure of the accumulator 16 provided in the middle of the brake line 27. May be.
In this way, the pressure can be stored in the accumulator within a range that does not impose a burden on starting the engine.

In each of the above embodiments, the timer 19A is provided in the electromagnetic switching valve 19. However, the timer is not necessarily provided, and the case where the timer is not provided is also included in the present invention. However, if a timer is provided, the load on the pump will be applied to the engine after the rotation has stabilized after the engine starts,
Engine stop can be more reliably prevented.

[0052]

According to the hydraulic system of the present invention, there is an effect that the load on the hydraulic pump applied to the starter can be reduced when the engine is started.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing a hydraulic system according to a first embodiment of the present invention.

FIG. 2 is a hydraulic circuit diagram showing a hydraulic system according to a second embodiment of the present invention.

[Explanation of symbols]

 1, 2 Hydraulic system 1A 1st working machine system which is a required part of hydraulic pressure 1B 2nd working machine system which is a required part of hydraulic pressure 1C Steering system which is a necessary part of hydraulic pressure 1D Brake system which is a necessary part of hydraulic pressure 1E Engine 1G Key switch 11 Tank DESCRIPTION OF SYMBOLS 12 Variable displacement pump 16 Accumulator 19 Solenoid switching valve 19A Timer which is a delay circuit 62 Hydraulic pump 71 Third drain line as drain circuit 100, 200 Load sensing circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3H089 AA07 AA16 AA27 BB01 BB15 BB30 DA03 DA04 DA13 DB16 DB33 DB44 DB45 DB48 DC02 EE32 FF07 FF16 GG02 JJ01 JJ14 JJ15

Claims (5)

[Claims] 1. A tank for storing oil, a variable displacement pump driven by an engine to pump oil from the tank, and provided to be connectable to the variable displacement pump.
A supply hydraulic circuit for supplying oil from the variable displacement pump to a portion requiring hydraulic pressure, a load sensing circuit for transmitting a required flow rate of oil from the portion requiring hydraulic pressure to the variable displacement pump, provided in the middle of the load sensing circuit An electromagnetic switching valve that shuts off and opens the load sensing circuit, and shuts off or opens the load sensing circuit at the time of starting the engine to change the output of the variable displacement pump. Features hydraulic system. 2. A tank for storing oil, a hydraulic pump driven by an engine to pump oil from the tank, and provided so as to be connectable to the hydraulic pump, and supplies oil from the hydraulic pump to a portion requiring hydraulic pressure. A supply hydraulic circuit, a drain circuit that is provided so as to be connectable to the hydraulic pump, and returns oil from the hydraulic pump to the tank; and a load that transmits a required flow rate of oil from the hydraulic pressure required portion to the hydraulic pump. A sensing circuit, provided in the middle of the load sensing circuit, for shutting off and opening the load sensing circuit, and for shutting off or opening the load sensing circuit at the time of starting the engine, the hydraulic pump and the drain circuit. And the electromagnetic switching valve for connecting the solenoid valve. 3. The hydraulic system according to claim 1, wherein the engine is provided with a key switch for starting the engine, and the electromagnetic switching valve is connected to the key switch. A hydraulic system characterized by: 4. The hydraulic system according to claim 1, wherein the supply hydraulic circuit is provided with an accumulator,
A hydraulic system, wherein the electromagnetic switching valve is switched according to the hydraulic pressure in the accumulator. 5. The hydraulic system according to claim 1, wherein the electromagnetic switching valve is configured to switch the electromagnetic switching valve at the time of starting the engine until a predetermined time passes after the engine is started. A hydraulic system comprising a delay circuit for maintaining an open / close state of a switching valve.