JPS5937389Y2 - work vehicle - Google Patents

Description

[Detailed description of the invention] The present invention relates to work vehicles equipped with a hydraulic system such as tractors and blue dozers, and is particularly concerned with preventing cavitation caused by the hydraulic pump when the oil temperature in the hydraulic system is low, and with the load applied when starting the starter. The aim is to reduce the number of

2. Description of the Related Art Tractors and bulldozers are equipped with a hydraulic system that drives a hydraulic pump by an engine and supplies pressurized oil to a lifter or the like using the hydraulic pump.

By the way, such a hydraulic system is installed near the driver's seat or can be controlled as appropriate using a lid operating lever, but when operating a work vehicle such as a tractor or bulldozer in cold weather, the hydraulic system is When the device is operated under control, the oil in the hydraulic device is at a low temperature, causing cavidation (foaming phenomenon) by the hydraulic pump.

Therefore, when pressure oil that has caused cavitation is supplied to a hydraulic cylinder that drives a lifter or the like, the oil contains bubbles and cannot apply appropriate hydraulic pressure, making it impossible to properly drive the lifter.

In addition, if the oil temperature in the hydraulic system is low, the viscosity of the oil is rising, and when the engine is started, the hydraulic pump is driven, causing problems such as an increase in the load on the starter. .

In order to deal with such a situation, the present invention detects the oil temperature in the hydraulic system using an oil temperature sensor, and when the oil temperature falls below a predetermined value, the driving force of the engine is transferred to the hydraulic pump based on the detection signal of the oil temperature sensor. This is to prevent cavitation and reduce the load on the starter by disabling the electromagnetic clutch that transmits the signal.

The present invention will be described in detail below with reference to drawings showing an embodiment using a tractor.

In FIG. 1, reference numeral 1 denotes a tractor that heaps front wheels 2 and rear wheels 3, which are provided at a predetermined distance on the left and right sides of the machine body, respectively, and is powered by a power unit (not shown) mounted on the front of the tractor 1. The tractor 1 is configured to transmit power to the rear wheels 3 via an appropriate transmission mechanism within the transmission case 4, and drive the rear wheels 3 to cause the tractor 1 to travel.

A suitable agricultural machine (not shown) is connected to this tractor 1 via a swingable top link 5 and a lower link 6 provided on the left and right sides of the rear part of the machine, and this agricultural machine is connected to a lift arm 7. The lift arm 7 is configured to be driven by a hydraulic cylinder 8 (see FIG. 2) placed and fixed on the transmission case 4. be done.

FIG. 2 schematically shows a hydraulic circuit of a working vehicle according to the present invention.

9 is an engine, 10 is an electromagnetic clutch, and 11 is a hydraulic pump. By driving the engine 9 and exciting the electromagnetic clutch 10, the driving force of the engine 9 is transferred to the hydraulic pump 1.
1 and can be driven.

12 is a relief valve, 13 is an oil tank, 14 is a 3-point 3
It is a position switching type control valve, and by operating the operating lever 14a of the 3-point/3-position switching type control valve 14, the lift arm 7 can be moved up and down, and when the lift arm 7 is not allowed to move up and down. It is in the neutral position shown.

A hydraulic cylinder 8 for driving the lift arm 7 up and down is connected to a hydraulic pump 11 via a control valve 14.

Furthermore, an oil temperature sensor 17 and a heater 18 are arranged in the oil in the oil tank 13.

FIG. 3 is an electrical circuit diagram of the main parts of the work vehicle according to the present invention, in which 15 is a battery and 16 is a key switch for the engine.

Reference numeral 17 indicates an oil tank 1 disposed within the oil tank 13.
An oil temperature sensor such as a temperature sensing element or a temperature relay that detects the oil temperature in 3, and a normally closed contact 17b that opens when the oil temperature reaches a predetermined value or more and when the oil temperature reaches a predetermined value or less. It has a normally open contact 17a that closes the circuit.

18 is a heater disposed in the oil tank 13; 19L;
10a is a solenoid for the electromagnetic clutch 10. By energizing the solenoid 10a, the input shaft and output shaft of the electromagnetic clutch 10 are connected.

The negative electrode of the battery 15 is grounded to the aircraft body, and a key switch 16 is connected between the positive and negative electrodes of the battery 15.
Both ends of the series circuit of the normally closed contact 17b and the heater 18 are connected.

Further, a heating indicator lamp 19L is connected in parallel to the heater 18.

A series circuit of the normally open contact 17a and the solenoid 10a of the electromagnetic clutch 10 is connected in parallel to both ends of the series circuit of the normally closed contact 17b and the heater 18.

Next, the operation of the hydraulic circuit of the working vehicle according to the present invention will be explained with reference to FIGS. 2 and 3.

In the work vehicle of the present invention, the engine (not shown) is started by turning on the engine key switch 16, and the oil tank 1 is started.
If the oil temperature in the oil temperature sensor 17 is above a predetermined value, the normally open contact 17a of the oil temperature sensor 17 is closed, the normally closed contact 17b is open, and the solenoid 10a of the electromagnetic clutch 10 is energized.

The driving force of the engine is transmitted to the hydraulic pump 11 via the electromagnetic clutch 10 by the excitation of the solenoid 10a, and the hydraulic pump 11 pumps out the oil in the oil tank 13, and when the control valve 14 is switched to the neutral position, The oil sent out returns to the oil tank 13.

If the operating lever 14a of the 3-point/3-position switching type control valve 14 is operated in the direction of the arrow to switch to the P side, the pressure oil sent out from the hydraulic pump 11 will be transferred to the control valve 14.
As a result, the rod 8a of the hydraulic cylinder 8 moves forward and lifts the lift arm 7.

On the other hand, when the control lever 14a of the control valve 14 is operated to switch to the Q side, the pressure oil sent out from the hydraulic pump 11 flows back into the oil tank 13, and the oil in the hydraulic cylinder 8 also flows through the control valve 14. The oil flows back into the oil tank 13 through the oil tank 13, and the weight of the lift arm 7 causes the rod 8a to retreat, causing the lift arm 7 to gradually descend.

By the way, if the oil temperature in the oil tank 13 has fallen below a predetermined value when the key switch 16 is turned on to start the engine, the normally open contact 17a of the oil temperature sensor 17
is open, and the normally closed contact 17b is closed.

Therefore, the solenoid 10a of the electromagnetic clutch 10 is not excited.

Therefore, the driving force from the engine is not transmitted to the hydraulic pump 11, and the hydraulic pump 11 is not driven.

On the other hand, by closing the normally closed contact 17b, the heater 1.8 and the heating indicator light 19L are energized, raising the temperature of the oil in the oil tank 13 and at the same time displaying the heating state of the oil.

When the oil temperature reaches a predetermined temperature or higher, the oil temperature sensor 17 operates to close the normally open contact 17a, and the normally closed contact 1
7b is opened and pressure oil is supplied by the hydraulic pump 11 as described above.

That is, if the temperature of the oil sent out by the hydraulic pump 11 is above a predetermined value and there is no risk of cavitation occurring, the hydraulic pump 11 can be driven at the same time as the engine is started.

On the other hand, if the oil temperature is below a predetermined value and there is a risk that cavitation will occur, the hydraulic pump 11 will not be driven.

As detailed above, according to the work vehicle of the present invention, the oil temperature in the hydraulic system is detected by the oil temperature sensor, and when the oil temperature is lower than a predetermined value, the hydraulic pump 11 driven by the engine is not driven. This makes it possible to prevent cavitation that is likely to occur due to the drive of the hydraulic pump 11 when the oil is at a low temperature, and prevents unsuitable pressure oil containing bubbles from being supplied to the hydraulic cylinder 8. operation can be ensured at all times.

In addition, since the hydraulic pump 11 is not driven when the oil temperature is low, that is, when the oil viscosity is high, there is no excessive load on the starter that starts the engine, and the load at the time of engine starting can be kept approximately constant. There are advantages.

[Brief explanation of the drawing]

Fig. 1 is a left side view of a tractor which is an embodiment of a working vehicle according to the present invention, Fig. 2 is a schematic hydraulic circuit diagram of the hydraulic system of the tractor, and Fig. 3 is a schematic diagram of the hydraulic system for controlling the hydraulic system. It is an electrical circuit diagram. 2...Front wheel, 3...Rear wheel, 5...
...Top link, 6...Lower link, 7.
...Lift arm, 8...Hydraulic cylinder, 9...Engine, 10...Electromagnetic clutch, 10a...Solenoid, 11...・・・
・Hydraulic pump, 13...Oil tank, 14...
...3-point/3-position switching type control valve, 17...
Sensor, 17a... Normally open contact, 17b...
...Normally closed contact, 18...Heater.

Claims (1)

[Scope of utility model registration request] A work vehicle equipped with a hydraulic system, comprising an electromagnetic clutch interposed between a hydraulic pump of the hydraulic system and an engine that drives the hydraulic pump, and an oil temperature sensor that detects the temperature inside the hydraulic system, A work vehicle characterized in that the electromagnetic clutch is configured to be disengaged when the oil temperature detected by the oil temperature sensor is lower than a predetermined value.