JPH0798456B2 - Hydraulic circuit for switching drive of four-wheel drive type vehicle - Google Patents

Description

TECHNICAL FIELD The present invention relates to a traveling switching hydraulic circuit for a four-wheel drive type traveling vehicle such as a tractor to which a front loader and a rotary cultivator can be mounted.

(Prior Art) For example, in a four-wheel drive agricultural tractor, when a front loader is mounted, a forward / reverse switching device is provided in a traveling power transmission system in order to frequently switch forward / reverse and to request high-speed reverse. In addition, when a rotary cultivator is installed, high work performance in the field is required, and therefore a front wheel speed switching device that increases the peripheral speed of the front wheels more than the rear wheels to reduce the turning radius is provided.

Each of the switching devices is equipped with a wet hydraulic clutch, and forward and backward and high and low speeds can be switched by the operation of the hydraulic clutch.These hydraulic circuits have their own hydraulic pumps or front wheel speed switching. The hydraulic circuit is connected in series to the hydraulic circuit for power steering, or for lifting or lowering the working machine or for posture control.

(Problems to be Solved by the Invention) However, when the former unique pump is provided, it causes a high cost, and the latter does not result in a high cost. However, the front wheel speed switching device can be used at the same time as power steering or working machine operation. Yes, if a shunt valve is installed and oil is shunted, the flow rate on the mainstream side will decrease when the engine is running at low speeds, resulting in insufficient pressure, which may reduce the operating speed or cause inoperability. In addition, because the operating pressure is different, it is necessary to provide a pressure reducing valve, so that the pump pressure may change, heat may be generated, and horsepower may be lost.

By the way, the forward-reverse switching device and the front wheel speed switching device are rarely used at the same time, that is, since it is dangerous to make a sharp turn during the work of the front loader, the front wheel speed switching device is not used and the rotary work device is not used. Since there is almost no need to go backward, the forward / reverse switching device is not used, and
The circuit pressures of both devices are set to be substantially equal.

Therefore, the present invention is a four-wheel drive type traveling system in which the hydraulic circuit of the front wheel speed switching device is connected in parallel to the hydraulic circuit with the relief valve of the forward / reverse switching device to enable cost reduction and normal operation of each device. An object of the present invention is to provide a traveling switching hydraulic circuit for a vehicle.

(Means for Solving the Problem) A specific configuration for solving the problem in the present invention is a traveling power transmission system, in which forward and backward movement is performed by switching forward and reverse between the engine 1 and a transmission such as a main transmission. A switching device 18 and a front wheel speed switching device 14 for switching the drive speed of the front wheels 8 between the transmission and the front wheels 8 are provided, and the forward / reverse switching device 18 is provided with a forward / reverse switching hydraulic clutch AC. The speed switching device 14 is provided with front wheel speed switching hydraulic clutches BC,
The hydraulic circuit A with the relief valve 53 of the forward / reverse switching hydraulic clutch AC and the hydraulic circuit B of the front wheel speed switching hydraulic clutch BC are connected in parallel to one hydraulic pump 52.

(Operation) The hydraulic pressure from the hydraulic pump 52 is sent to the forward / reverse switching device 18 via the switching valve A1 of the forward / backward switching hydraulic circuit A, and the hydraulic clutch AC is operated in the forward / reverse direction so that the traveling power is the forward power or the reverse power. The power is transmitted to the rear. This hydraulic clutch for switching between forward and reverse
When AC is being moved forward, hydraulic pressure flows through the relief valve 53 to the lubricating oil passage 31 to lubricate and cool the hydraulic clutch AC.

At the same time, the pressure oil from the hydraulic pump 52 also builds pressure in the front wheel speed switching hydraulic circuit B, and the on / off valve B2 and the front wheel speed switching valve B1 are operated, whereby the hydraulic clutch BC
Then, the hydraulic clutch BC is operated without time loss to change the front wheel 8 from the peripheral speed substantially the same as that of the rear wheel 6 to about double speed.

This front wheel speed switching hydraulic clutch BC is not operated at the same time as the forward / reverse switching hydraulic clutch AC.
There is no problem even if they are connected in parallel from 52.

(Example) Hereinafter, the Example of this invention is described based on drawing.

FIG. 2 shows a traveling power transmission system of a four-wheel drive type tractor to which a front loader, a rotary tiller and the like can be mounted,
The power of the engine 1 is transmitted to the transmission 3 via the main clutch 2.

The transmission 3 includes a forward / reverse switching device 18, which will be described later, a main transmission,
A rear wheel drive system in which power is transmitted from a bevel pinion shaft 4 which is an output shaft thereof to a rear wheel 6 via a rear wheel differential device 5 , A front wheel drive system in which power is transmitted to the front wheels 8 via the transmission gear 7 is branched.

The power of the front wheel drive system is transmitted from the transmission gear 7 to the first transmission shaft 10 via the gear 9, and is transmitted from the first transmission shaft 10 to the second transmission shaft 12 via the two-wheel / four-wheel switching clutch 11. It A front wheel propulsion shaft 13 is provided in parallel with the second transmission shaft 12, and a front wheel speed switching device 14 is provided between the shafts 12 and 13.

The front wheel propulsion shaft 13 drives a front wheel differential device 16 via a bevel pinion 15, and a front wheel 8 via a front wheel final reduction mechanism 17.
Transmit power to.

1 and 2, the forward / reverse switching device 18, the front wheel speed switching device 14 and their hydraulic circuits A and B are shown.

The forward / reverse switching device 18 is housed in a transmission case 22, and a forward drive pinion 24 and a reverse drive pinion 25 are fixed to a cylindrical propulsion shaft 23 to which power is transmitted from the main clutch 2, and a forward drive on a counter shaft 26. The gear 27 and the reverse gear 28 are loosely fitted, and power can be transmitted to the reverse pinion 25 and the gear 28 via a back idler gear (not shown). Therefore, the transmissions such as the main transmission, the sub transmission, and the super speed reducer are located rearward of the forward-reverse switching device 18 in the traveling power transmission direction, and the forward-reverse switching device 18 is provided between the engine 1 and the main transmission. It is provided in.

Forward / reverse gears 27 and 28 are alternatively provided on the counter shaft 26 as the shaft 2
A forward / reverse switching hydraulic clutch AC fixed to 6 is provided, and the counter shaft 26 is provided with a forward oil passage 29, a reverse oil passage 30 and a lubricating oil passage 31 for supplying pressure oil to the hydraulic clutch AC. There is.

The front wheel speed switching device 14 is arranged in the lower front portion of the mission case 22 and can be retrofitted from the outside. The front wheel 12a of the second transmission shaft 12 is divided into two parts and the front wheel propulsion shaft 13 is also divided into two parts. It has a rear shaft 13a.

A transmission case 33 is detachably attached to the front lower abdomen of the transmission case 22. The transmission case 33 supports the rear shaft 13a so as to project forward, and a bearing portion 34 projecting into the transmission case 22 is integrally formed. The front shaft 12a is rotatably supported by 34.

Large and small pinions 36 and 37 are fixed to the front shaft 12a, and constant and constant gears 38 and double speed gear 39 that are normally meshed with the large and small pinions 36 and 37 are attached to the rear shaft 13a.
Is loosely fitted, and a wet front wheel speed switching hydraulic clutch BC is provided between the gears 38, 39.

The hydraulic clutch BC is connected to the piston 41 that presses the clutch plate 40 with the shift gear 43 via the connecting rod 42, and the rear shaft 13
When there is no pressure in the oil supply passage 44 formed in a,
The shift gear 43 meshes with the constant speed gear 38, connects the constant speed gear 38 to the rear shaft 13a, transmits rotation to the front wheels 8 to be substantially the same peripheral speed as the rear wheels 6, and pressure is applied to the oil supply passage 44. Then, the piston 41 is moved against the spring 45 and presses the clutch plate 40 to connect the double speed gear 39 to the rear shaft 13a, so that the front wheel 8 and the rear wheel 6 are substantially separated from each other.
It transmits the rotation which becomes the double or the high peripheral speed of the front and back.

The front wheel speed switching device 14 is assembled in advance so that it can be installed as an option, and is inserted into the cassette case from below the mission case 22, and a hand is put through an inspection window of the mission case 22 to set the second transmission shaft 12 The coupling 46 is moved to connect the front wheel 12a so as to be integrally rotatable.

This front wheel speed switching device 14 is unitized like the conventional front wheel drive transmission device having only one set of gears,
It can be adopted selectively and can be adopted as a Dera option.

However, the mission case 22 can be divided into front and rear, and after the change device is installed in each, the mission case
Before assembling 22, the front wheel speed switching device 14 may be mounted and the front and rear of the second transmission shaft 12 may be connected by the coupling 46.

The hydraulic circuit A of the forward / reverse switching hydraulic clutch AC and the hydraulic circuit B of the front wheel speed switching hydraulic clutch BC are connected in parallel.

The two hydraulic pumps 51, 52 are driven by the engine 1, the main pump 51 is connected to a working machine lifting hydraulic system, a working machine attitude control hydraulic cylinder, a power steering cylinder, etc., and the sub-pump 52 is connected to the hydraulic circuit A. It is connected to the.

A forward / reverse switching circuit A1, an inching valve A2, a modulating valve mechanism A3, etc. are incorporated in the forward / reverse switching hydraulic circuit A. By manually switching the forward / reverse switching valve A1, pressure oil passes through the inching valve A2. Then, the oil is supplied to the forward oil passage 29 or the reverse oil passage 30 and the inching valve A2 is stepped on to rapidly interrupt the oil fed to the oil passages 29 and 30.

The modulating valve mechanism A3 is a relief valve provided in the lubricating oil passage 31 that is connected in parallel to the switching valve A1.
53, a cylinder 54 that adjusts the operating pressure of the relief valve 53, and a throttle portion 56 and a check portion 57 that are provided in an operation oil passage 55 that connects the cylinder 54 and the switching valve A1. .

When the switching valve A1 is in the neutral position, the modulating valve mechanism A3 supplies the pressure oil from the sub-pump 52 with low oil pressure to the hydraulic clutch AC as lubricating oil, and the switching valve A1 is switched to the forward position or the reverse position. When the relief valve
The operating pressure of 53 is gradually increased from a low pressure to a high pressure to increase the oil pressure of the oil supplied to the hydraulic clutch AC to smoothly shift from the half-clutch state to the full-clutch state, and the traveling vehicle moves forward or backward. Relief valve
53 is maintained at high pressure to prevent hydraulic clutch AC from disengaging.

The front wheel speed hydraulic circuit B is connected to the relief valve 53 in parallel with the protruding side of the sub-pump 52, and an on / off valve B2 and a front wheel speed switching valve B1 are arranged in series. The on / off valve B2 is manually operated, while the switching valve B1 is automatically operated by the steering operation member 59.

That is, the cam member 60 is attached to the steering operation member 59, for example, the pitman arm, and when the pitman arm is swung to steer the front wheels 8 to the left and right by about 35 °, the cam member 60 operates the switching valve B1. Then, the pressure oil is supplied to the hydraulic clutch BC.

Since this front wheel speed switching hydraulic circuit B is in parallel with the relief valve 53, if the hydraulic pressure set by the relief valve 53 stands up and the on / off switching valve B2 is turned on, the hydraulic clutch BC will not lose time during a sudden turn. When operating and operating the forward / reverse switching valve A1, since the front wheel speed switching valve B1 is not used, the hydraulic circuit A is supplied with the total amount of oil of the sub-pump 52.

When the switching valve A1 is in the neutral position, no pressure is built up in the front wheel speed switching hydraulic circuit B, but since the traveling vehicle is stopped at this time, the hydraulic clutch BC is not activated. Further, the hydraulic circuits A and B have the following characteristics when the switching valve B1 is operated.
Since the amount of oil to the hydraulic circuit A may decrease, it is preferable to provide the check valve 61 and / or the accumulator 62 in order to prevent the hydraulic clutch AC from loosening. Further, the hydraulic circuit A may be provided with only the relief valve 53 instead of the modulating valve mechanism A3.

(Effects of the Invention) According to the present invention described in detail above, in a four-wheel drive traveling vehicle in which forward and backward travel is switched on the front side in the power transmission direction with respect to the main transmission, and the driving speed of the front wheels can be switched, the forward and backward switching device.
Since the hydraulic clutch AC of 18 and the hydraulic clutch BC of the front wheel speed switching device 14 are hardly switched at the same time, the hydraulic circuits A and B for supplying pressure oil to them are connected to one hydraulic pump 52. Even if they are connected in parallel, there is no load fluctuation in the parallel circuit, each circuit can be operated normally and selectively, a shunt valve is not required, and both circuits A and B can use approximately the same hydraulic pressure. Therefore, the hydraulic circuit B for switching the front wheel speed does not require a relief valve and a pressure reducing valve, and there is no generation of heat or loss of horsepower, and the manufacturing is simple and inexpensive.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention, and FIG. 2 is a diagram showing a traveling transmission system of a four-wheel drive type traveling vehicle. 14 …… front wheel speed switching device, 18 …… forward / reverse switching device, 29…
… Forward oil passage, 30 …… Reverse oil passage, 31 …… Lubricating oil passage, 38 ……
Constant speed gear, 39 …… Double speed gear, 52 …… Sub hydraulic pump, 53
...... Relief valve, A ...... Forward / backward switching hydraulic circuit, B
...... Front wheel speed switching hydraulic circuit, AC ...... Hydraulic clutch, BC
...... Hydraulic clutch, A1 …… forward / reverse switching valve, B1 …… front wheel speed switching valve.

Claims (1)

[Claims] 1. A traveling power transmission system, a forward / reverse switching device (18) for switching between forward and reverse between the engine (1) and a transmission such as a main transmission, and the transmission and front wheels (8). And a front wheel speed switching device (14) for switching the driving speed of the front wheels (8) between the front wheel and the rear wheel, and a forward / reverse switching hydraulic clutch (AC) and a front wheel speed switching device. A front wheel speed switching hydraulic clutch (BC) is provided in each of (14), a hydraulic circuit (A) with a relief valve (53) of the forward / reverse switching hydraulic clutch (AC), and a front wheel speed switching hydraulic clutch (BC). The hydraulic circuit (B) of (1) is connected to one hydraulic pump (52) in parallel, and the hydraulic circuit for switching travel of a four-wheel drive type traveling vehicle is characterized.