JPH0717201B2 - Hydraulic circuit of work vehicle - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hydraulic circuit used for a work vehicle such as an agricultural tractor, and more specifically, a hydraulic piston for operating a friction clutch for switching a traveling transmission. Is provided so that the clutch can be operated by refueling,
The present invention relates to a hydraulic circuit of a work vehicle in which the hydraulic piston and the power steering cylinder are connected in parallel to a hydraulic pump.

[Conventional technology]

In the above-mentioned work vehicle, conventionally, when a hydraulic pressure drop occurs on the clutch side, the hydraulic pressure on the steering side is released to the clutch side and is reduced accordingly.

[Problems to be solved by the invention]

When the steering operation of the power steering cylinder and the clutch engagement / disengagement change of the clutch hydraulic piston occur at the same time, such as when performing downshift operation while turning the vehicle by driving the wheels to the limit on the shore, especially the clutch When the clutch is switched to off, the hydraulic pressure in the clutch side circuit is lower than when the clutch is engaged, and the hydraulic pressure in the steering side circuit is decreased due to the release to the clutch side circuit. Due to the fact that the hydraulic pressure is restored to the original high pressure and the hydraulic pressure in the steering side circuit is also restored to the original high pressure, and because the hydraulic oil acts on the power steering cylinder to extend and contract, A shock was applied to the power steering cylinder, and this shock was transmitted to the steering wheel, causing the driver to feel discomfort.

An object of the present invention is to make sure that the power steering function is exerted, prevent pressure fluctuations in the steering side circuit due to changes in the on / off state of the shifting hydraulic clutch, and realize smooth shock-free shifting. Is to

[Means for solving problems]

A characteristic configuration of the present invention is, in the hydraulic circuit of a work vehicle described above, wherein an oil supply path from the hydraulic pump is provided at a branch point to a first oil supply path toward the power steering cylinder and a second oil supply path toward the hydraulic piston. And a pressure compensating sequence valve for branching and opening to the first oil supply passage when the hydraulic pressure on the hydraulic pump side becomes equal to or higher than a first set pressure to supply the pressure oil equal to or higher than the first set pressure to the power steering cylinder. , A check valve for blocking only oil flow from the power steering cylinder side to the hydraulic pump side is arranged in series, and the second oil supply passage is provided with a second hydraulic pressure on the hydraulic piston side.
A pressure reducing valve is provided which closes when the pressure becomes equal to or higher than a set pressure and prevents the hydraulic oil from being supplied to the hydraulic piston at a pressure equal to or higher than the second set pressure. The action and effect thereof are as follows.

[Work]

High pressure oil above the first set pressure can be constantly supplied to the power steering cylinder via the pressure compensating sequence valve, and the check valve will operate even if the pressure drop occurs in the clutch side circuit due to clutch disengagement. The oil supply passage is closed so that the pressure on the steering side does not escape to the clutch side, and the pressure on the power steering side is prevented from decreasing.

Also, to the hydraulic piston side that operates the friction clutch,
As it prevents the supply of pressure oil at a higher pressure than necessary,
When hydraulic oil is supplied to operate the friction clutch to engage the clutch, it is possible to prevent a shift shock from occurring due to the sudden engagement of the clutch.

〔The invention's effect〕

Therefore, according to the present invention, by introducing the pressure compensating sequence valve and the check valve into the power steering side circuit, the steering side circuit can be maintained at a necessary high pressure regardless of the hydraulic pressure fluctuation of the clutch side circuit, It is now possible to operate reliably and comfortably without generating shocks due to hydraulic pressure fluctuations.

In addition, the introduction of a pressure reducing valve into the clutch side circuit has made it possible to achieve smooth gear shifting without shock.

〔Example〕

As shown in FIG. 3, various works such as a rotary tiller are provided at the rear portion of the traveling machine body having front wheels (1) steerable and drivable and rear wheels (2) drivable. Attaching a lift arm (3) that connects the device so that it can be moved up and down, and a power take-off shaft (4) that transmits power to the connecting work device,
It constitutes an agricultural tractor.

In order to drive the front and rear wheels (1) and (2) and the power take-off shaft (4), the output of the engine (5) is transmitted through the main clutch (6) as shown in FIG. (7) and the power take-off transmission (8) are branched and transmitted, and the output of the traveling transmission (7) is transmitted to the rear wheel differential mechanism (10) via the bevel gear (9).
Further, the power transmission (8) is configured to be transmitted to the front wheel differential mechanism (13) via the clutch gear (11) and the transmission shaft (12) respectively, and the power take-off transmission (8) can be transmitted only in one rotation direction. It is linked to the power take-off shaft (4) via the clutch mechanism (14).

In the travel transmission (7), as shown in FIG. 2, a main transmission unit (7a) capable of switching between four gears,
It is equipped with a forward / reverse switching unit (7b) and a sub-transmission unit (7c) that can be switched between two stages, and introduces the engine output to the main transmission unit (7a) so that the output of the main transmission unit (7a) is a friction type The shift clutch (15) and the forward / reverse switching unit (7b) are used for transmission to the sub-transmission unit (7c), which enables switching between eight forward speeds and eight reverse speeds.

As shown in FIG. 2, the main transmission portion (7a) includes a first hydraulic piston (16) and a second hydraulic piston (17), and
The forward / reverse switching portion (7b) is operated by the forward / reverse lever (18), and the auxiliary transmission portion (7c) is operated by the third hydraulic piston (1).
9), the shift clutch (15) is operated by a fourth hydraulic piston (20), and the first to fourth hydraulic pistons (16), (17) ), (19) and (20) are configured to be operated based on the hydraulic circuit shown in FIG.

That is, the first to third hydraulic pistons (16),
(17) and (19) are connected to one rotary type speed change valve (21), and when the speed change valve (21) is operated to the neutral position (N), the first to third hydraulic pistons (16) , (17), (19) are all in the transmission off position,
When the speed change valve (21) is operated to any one of eight transmission positions (I) to (VIII) of the first speed to the eighth speed, the first hydraulic piston (16) and the second hydraulic piston (17).
One of them and the third hydraulic piston (19) are set to the transmission position. The control valve (22) of the fourth hydraulic piston (20) is connected to the first to third hydraulic pistons (16), (17), (19) via a pressure adjusting mechanism (23) and a pressure reducing valve (24). It is connected to a hydraulic pump (25) that drives the. The first to third hydraulic pistons (1
Each of 6), (17), (19) and the interlocking member (27) of the forward / reverse switching gear (26) is configured as a pilot type operation valve for the control valve (22), and the shift valve (21) is switched. The control valve (22) is automatically switched according to the operation and the switching operation of the forward / reverse lever (18), and the fourth hydraulic piston (20) is operated so that the shift clutch (15) is engaged. The oil supply to the fourth hydraulic piston (20) is released so that oil is supplied or the shift clutch (15) is disengaged.
In short, the operation of switching the traveling transmission (7) is performed by switching the shift valve (21) and the forward / reverse lever (18), and the on / off operation of the clutch (15) for this shift is automatically performed. It will be done in.

In order to enable the steering operation of the front wheels (1), as shown in FIG. 1, a knuckle arm (28) of one of the left and right wheels (1), (1) has a power steering cylinder (29) with a center spring. ), And the power steering cylinder (29) is connected to the fourth hydraulic piston (20).
Is connected in parallel to the hydraulic pump (25), and is connected to the control valve section (31) of the power steering cylinder (29) in the pitman arm (32).
The steering handle (34) is interlocked via the steering gear mechanism (33) and the like. That is, when the steering handle (34) is rotated, the power steering cylinder (29) is expanded and contracted by the pressure oil from the hydraulic pump (25) to swing the knuckle arm (28).

At the branch point (P) of the oil supply passage (35) from the hydraulic pump (25), the first oil supply passage (35a) toward the power steering cylinder (29) and the fourth hydraulic piston (2).
It branches to the second oil supply passage (35b) toward the 0) side,
The power supply cylinder (29) opens in the oil supply passage (35a) when the hydraulic pressure on the hydraulic pump side exceeds the first set pressure.
A pressure compensating sequence valve (30) for supplying high-pressure oil above the first set pressure to the valve, and a check valve (3) for blocking only oil flow from the power steering cylinder side to the hydraulic pump side.
6) and the pressure compensation sequence valve (30) is connected to the check valve (3
6) Provided in series in a position well positioned, and closed in the second oil supply passage (35b) when the downstream hydraulic pressure becomes equal to or higher than a second set pressure, the third hydraulic piston (16), ( 17),
A pressure reducing valve (24) for preventing application of a high pressure equal to or higher than the second set pressure to the (19) and the fourth hydraulic piston (20) is provided.

The check valve (36) blocks only the oil flow from the power steering cylinder side to the hydraulic cylinder side, and the steering wheel is operated even if a pressure drop occurs due to the disengagement of the shift clutch (15) in the shift side oil passage. The pressure in the side oil passage is prevented from escaping toward the shift side oil passage.

The pressure reducing valve (24) has a function of suppressing the occurrence of a shift shock or the like due to a sudden clutch engagement operation when driven at a high pressure by driving the friction clutch (15) with a relatively low hydraulic pressure.

Incidentally, (37) shown in FIG. 1 is an accumulator.

The present invention can be applied to various work vehicles such as rice transplanters and trucks as well as agricultural tractors.

It should be noted that reference numerals are added to the claims for convenience of comparison with the drawings, but the present invention is not limited to the structures of the accompanying drawings by the entry.

[Brief description of drawings]

The drawings show an embodiment of a hydraulic circuit of a work vehicle according to the present invention,
FIG. 1 is a hydraulic circuit diagram, FIG. 2 is a transmission system diagram, and FIG. 3 is a side view of the entire agricultural tractor. (7) …… Traveling transmission, (15) …… Friction clutch, (20) …… Hydraulic piston, (24) …… Reducing valve, (25) …… Hydraulic pump, (29) …… Power steering cylinder, (30) …… Sequence valve for pressure compensation,
(35) ... Oil supply passage, (35a) ... First oil supply passage, (35b) ...
… Second oil passage, (36) …… Check valve, (P) …… Branch point.

(72) Inventor Ken Machida 64, Ishizukitamachi, Sakai City, Osaka Prefecture Kubota Iron Works Co., Ltd.Sakai Factory (72) Inventor, Hisakatsu Anmiya 64, Ishizukitamachi, Sakai City, Osaka Prefecture In-house (56) Reference JP-A-57-159406 (JP, A) Actually opened 59-92065 (JP, U) Actually opened 58-28064 (JP, U) Actually opened 56-54661 (JP, U)

Claims (1)

[Claims] 1. A hydraulic piston (20) for operating a friction clutch (15) for switching of a transmission (7) for traveling is provided in a state of being supplied with oil and operated, and the hydraulic piston (20) and power are also provided. A hydraulic circuit of a working vehicle in which a steering cylinder (29) is connected in parallel to a hydraulic pump (25), wherein an oil supply passage (35) from the hydraulic pump (25) is connected to the power steering cylinder (at a branch point (P). 29)
First oil supply passage (35a) heading for and the hydraulic piston (20)
To the second oil supply passage (35b), which opens toward the first oil supply passage (35a) when the hydraulic pressure on the hydraulic pump side becomes equal to or higher than a first set pressure, and the first oil supply passage (35a) is provided to the power steering cylinder (29). A sequence valve (30) for pressure compensation for supplying pressure oil above the set pressure and a check valve (36) for preventing only oil flow from the power steering cylinder side to the hydraulic pump side are arranged in series. The hydraulic piston (20) is installed in the second oil supply passage (35b).
A work vehicle provided with a pressure reducing valve (24) which closes when the hydraulic pressure on the side becomes equal to or higher than a second set pressure and prevents the hydraulic oil (20) from being supplied with pressure oil equal to or higher than the second set pressure. Hydraulic circuit.