JPH0651449B2 - Front wheel shift structure of work vehicle - Google Patents

Description

TECHNICAL FIELD The present invention relates to a front wheel shift structure for a four-wheel drive type work vehicle represented by an agricultural tractor.

[Conventional technology]

In an agricultural tractor, which is an example of a four-wheel drive type work vehicle, as disclosed in, for example, Japanese Patent Laid-Open No. 60-4470, a standard drive state in which transmission is performed at a drive speed substantially equal to the rear wheel drive speed, There is a vehicle equipped with a front wheel transmission capable of switching between an amplification drive state in which transmission is performed at a drive speed higher than the rear wheel drive speed.

In this disclosed structure, when the steering handle is steered over the set angle, the front wheel transmission is configured to be switched from the standard drive side to the speed-increasing drive side. Can make small turns.

[Problems to be Solved by the Invention]

The conditions of the work ground on which the agricultural tractor travels are various, such as upland fields, wetlands, and grass fields.

On the other hand, in the conventional configuration, the speed increasing ratio of the front wheels to the rear wheels in the speed increasing drive state is constant, so the driving state of the front wheels and the turning state of the front part of the machine body do not match well during turning, and work with the front wheels There were cases where the ground was damaged.

Also, if the front wheel transmission is switched to the speed-increasing drive side when the front wheels are steered while traveling at a relatively high speed, a small turn is made at a high speed, so the operator is forced to move outward. It may be shaken and difficult to control.

It is an object of the present invention to provide a work vehicle equipped with the above-mentioned front wheel transmission so that a small turn can be made with good maneuverability without particularly roughening the work ground.

[Means for Solving the Problems]

The feature of the present invention resides in the following structure in the front wheel shift structure of the work vehicle as described above.

When the traveling transmission is operated at a higher speed than the predetermined gearshift position, the traction means for preventing the operation of switching the front wheel transmission to the speed-increasing drive side, and the predetermined gearshift position in the traveling transmission In the lower speed range, the control means is provided to change the speed increasing ratio of the front wheels to the rear wheels in the speed increasing drive state of the front wheel transmission according to the shift position of the traveling transmission.

[Work]

(I) Generally, in a work vehicle, a transmission for traveling is operated on the road to a high speed side above a predetermined shift position, and at a work site, a transmission for traveling is operated to a low speed side below a predetermined shift position. I often run.

In the case of traveling on a work site, on a relatively flat work site such as lawn grass, operate the transmission for traveling to the high speed side in the low speed range below the predetermined shift position described above. In a work place where the vehicle travels and is highly uneven, it is often the case that the transmission for traveling is operated to the low speed side in the low speed side shift range below the predetermined shift position to travel.

(Ii) Therefore, according to the configuration of the present invention, the speed increasing ratio (rear speed) in the speed increasing drive state is set in accordance with the speed changing position of the transmission for traveling in the low speed side speed changing range below the predetermined speed changing position. The ratio of the driving speed of the front wheels to the wheels) may be set smaller (for example, twice) on the high speed side of the low speed side shift range below the predetermined shift position, or conversely, on the low speed side shift range below the predetermined shift position. On the low speed side of, set a large speed increasing ratio (3 times etc.)
It becomes possible to do.

In this case, if the speed increasing ratio in the speed increasing drive state is set to a large value, a small turning turn can be smoothly performed even in a work place with severe unevenness. On the contrary, if the speed increasing ratio in the speed increasing state is set to be small, the small turning performance may be slightly lowered, but the front wheels will not cause roughening of the work ground.

When traveling on the work site as described above, the speed increasing ratio in the speed increasing drive state should be automatically changed to a large or small value depending on the gear position of the traveling transmission set according to the state of the work site. become.

(Iii) When traveling by operating the transmission for traveling on the high speed side above a predetermined shift position, such as on the road, the front wheel transmission is not switched to the speed increasing drive side during turning. Instead, the standard drive state in which the front wheels and the rear wheels are driven at substantially equal speeds is maintained.

〔The invention's effect〕

As described above, it is possible to change the speed increasing ratio in the speed increasing drive state during turning to a value suitable for the work site, and it is possible to smoothly make a small turning turn without roughening the work ground. Was able to improve the turning performance.

Further, when the vehicle is traveling at a relatively high speed, the front wheel transmission is configured so as not to be switched to the speed-increasing drive side so that the worker is prevented from being swung outward when the vehicle is traveling. It was possible to improve the sex.

Further, both the setting change of the speed increasing ratio in the speed increasing drive state and the setting of the state in which the switching operation is not performed to the speed increasing drive side during turning are automatically performed by the shift position of the traveling transmission, so that the work vehicle The operability of can also be improved.

〔Example〕

Hereinafter, a four-wheel drive agricultural tractor, which is one of the embodiments of the present invention, will be described with reference to the drawings.

As shown in FIG. 3 and FIG. 1, the power from the engine (1) is transmitted through the main clutch (2) to the main transmission (not shown) in the transmission case (3) and the auxiliary transmission (see FIG. (Not shown)
It is transmitted to (corresponding to a transmission for traveling) and is operated to change gears and transmitted to the rear wheels (4). Then, the power branched from immediately before the rear wheel differential mechanism (15) is transmitted from the front wheel output shaft (6) to the front wheel (7), which can be steered, through the front wheel transmission (5).

Next, the front wheel transmission (5) will be described. As shown in Fig. 1, a transmission shaft (8) that receives power from immediately before the rear wheel differential mechanism (15) is installed in parallel with the front wheel output shaft (6), and the transmission shaft (8) has a standard drive gear. (9), first speed-up drive gear (10), second
The speed-up drive gear (11) is fixed. The front wheel output shaft (6) has a multi-plate type first hydraulic clutch (12) and a second hydraulic clutch (1
3), the third hydraulic clutch (14) is attached, and the first, second, third
Hydraulic clutch (12), (13), (14) gear (12a), (13a), (1
4a) is the standard drive gear (9), the first speed-up drive gear (10) and the second
It meshes with the speed-up drive gear (11).

With the above structure, when the first hydraulic clutch (12) is engaged and operated, power is transmitted so that the driving speeds of the front wheels (7) and the rear wheels (4) become substantially equal. When the second hydraulic clutch (13) is engaged and operated, power is transmitted so that the front wheels (7) are driven at a speed approximately twice that of the rear wheels (4), and when the third hydraulic clutch (14) is engaged and operated. The power is transmitted so that the front wheels (7) are driven at a speed approximately three times that of the rear wheels (4).

Next, the hydraulic oil supply system for the first, second, third hydraulic clutches (12), (13), (14) will be described. As shown in FIG. 1, the electromagnetically operated first and second hydraulic oils from the pump (16) are supplied to the first, second, third hydraulic clutches (12), (13) and (14).
2, 3 control valves (17), (18), (19) are provided, and the first, second,
The three control valves (17), (18), and (19) are urged toward the oil discharge side, that is, the clutch disengagement side. 1st, 2nd, 3rd control valves (17), (1
8), Limit switches (21a), (21b) for detecting the operating position of the auxiliary transmission lever (not shown) of the auxiliary transmission capable of shifting four speeds in the control device (20) which issues an operation signal to (19) ， (21c) ，
Signals are input from (21d), a potentiometer (23) for detecting a steering operation angle of the steering handle (22), and a four-wheel drive drive switch (24).

Next, a control flow in the control device (20) will be described.
As shown in FIGS. 1 and 2, the four-wheel drive switch (24)
Is OFF, the first, second, third control valves (17), (18), (1
No operation signal is issued to 9), and the first, second, third hydraulic clutches (12), (13), (14) are disengaged, and the rear two-wheel drive condition is established. If the four-wheel drive switch (24) is ON, the first
An operation signal is issued to the control valve (17) and the first hydraulic clutch (1
2) enters the on state, and in this state the front wheels (7) and the rear wheels (4) are driven at substantially equal speeds.

Then, when the steering handle (22) is steered by the set angle or more and the aircraft starts to turn, the following operation is performed.

When the auxiliary transmission lever is operated to the low speed position of the first speed or the second speed (corresponding to the low speed side shift range below the predetermined shift position of the traveling transmission device), the third control valve (19) is set. An operation signal is emitted and the third hydraulic clutch (14) is in the on state,
The front wheels (7) are driven at about three times the speed of the rear wheels (4) (above,
Equivalent to control means).

When the auxiliary shift lever is operated to the middle speed position of the third speed (corresponding to the shift range on the low speed side below the predetermined shift position of the traveling transmission), the operation signal is sent to the second control valve (18). The second hydraulic clutch (13) is engaged and the front wheels (7)
Are driven at approximately twice the speed of the rear wheel (4) (the above corresponds to the control means).

On the other hand, when the sub-transmission lever is operated to the high speed position of the 4th speed (corresponding to the high speed side above the predetermined speed position of the transmission for traveling), the steering handle (22) cannot be operated. Regardless of this, the state in which the operation signal is issued to the first control valve (17) continues as it is (the above corresponds to the restraint means).

In the claims of the patent claims, reference numerals are given 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 front wheel speed change structure for a work vehicle according to the present invention. FIG. 1 is a view showing a linked state of a front wheel speed change device, a control device and a steering wheel, and FIG. 2 is a control flow in the control device. The flow chart shown in FIG. 3 is an overall side view of the agricultural tractor. (4) …… Rear wheel, (5) …… Front wheel transmission, (7) …… Front wheel, (22) …… Steering wheel.

Claims (1)

[Claims] 1. A standard drive state in which power is transmitted at a speed substantially equal to a rear wheel drive speed to a power transmission system to a front wheel (7) which can be steerably operated,
A front wheel transmission (5) is provided that can be switched to a speed-up drive state in which transmission is performed at a drive speed that is higher than the rear wheel drive speed, and the front wheel transmission (5) is operated by a steering operation over a set angle of the steering wheel (22). ) Are linked to each other so as to be switched to the speed-increasing drive side, and when the traveling transmission is operated to a high speed side above a predetermined gear shift position, the front wheels are moved. Checking means for preventing a switching operation of the transmission (5) to the speed-increasing drive side, and a shift of the traveling transmission in a low-speed shift range below the predetermined shift position in the traveling transmission. A front wheel speed change structure for a work vehicle, comprising control means for changing a speed increase ratio of a front wheel (7) to a rear wheel (4) in a speed-up driving state of the front wheel speed change device (5) according to a position.