JPH068088B2 - Four-wheel drive work vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a standard drive state in which power is transmitted to a steerable front wheel at a drive speed substantially equal to a rear wheel drive speed, and a rear wheel drive speed. The present invention relates to a four-wheel drive type work vehicle including a front wheel transmission that switches to an increased drive state in which transmission is performed at a higher drive speed.

[Conventional technology]

In recent years, models equipped with front wheel transmissions have appeared as described above, and when this front wheel transmission is operated to the speed-increasing drive side at the time of turning, it does not roughen the ground, and even on soft ground it can easily make sharp turns. It can be done.

An example of the configuration of the operation system of the front wheel transmission is disclosed in Japanese Patent Laid-Open No. 59-176121.
It is disclosed in the publication. This is a configuration in which the steering wheel and the front wheel transmission are linked to each other, and when the steering operation is performed from the straight traveling state to the set angle or more, the front wheel transmission is switched from the standard driving state to the speed increasing driving state.

[Problems to be solved by the invention]

When turning in a general four-wheeled vehicle, the turning radius of the front wheels becomes larger than the turning radius of the rear wheels, and so-called a difference between inner and outer wheels occurs. Therefore, in order for the four-wheel drive vehicle to turn smoothly,
It is preferable that the drive speed of the front wheels be increased more than the drive speed of the rear wheels according to the difference between the inner and outer wheels.

However, when turning in the above-described four-wheel drive type work vehicle, since the driving speeds of the front and rear wheels are still equal at the start of turning,
The driving speed of the front wheels becomes slower than the driving speed suitable for the previous turning, and the front wheels are apparently in a state where the front wheels are braked. After that, when the steering angle of the front wheels is operated above the set angle and the front wheels enter the speed-up drive state, the front wheels are braked and the running speed slightly decreases, and the front wheels suddenly become faster than the rear wheels. Since it will be pulled by and a shock will occur due to sudden acceleration at that time, it will be uncomfortable for the operator. Such a phenomenon is often seen in long wheel-based four-wheel drive work vehicles in which the difference between the inner and outer wheels is large.

Here, the present invention focuses on the above-mentioned problems, and an object thereof is to alleviate a shock during a switching operation of a front wheel transmission during turning.

[Means for solving problems]

A feature of the present invention is that in the four-wheel drive type work vehicle described above, when the steering handle for steering the front wheels is operated at a set steering angle or more, the power transmission to the front wheels is turned off only during the set time, The front wheel transmission is configured to be switched to the speed-increasing drive side after the lapse of the set time, and the operation and effect are as follows.

[Work]

With the configuration described above, if the steering wheel is operated to turn by more than the set steering angle, the front wheel transmission is switched to the speed-increasing drive side, but only after the set time immediately before the switching operation. A two-wheel drive state with two wheels is revealed. Since the apparent braking state of the front wheels disappears during the two-wheel drive state, the speed decrease at the start of turning in the standard drive state is alleviated during the two-wheel drive state.

Therefore, the difference between the traveling speed in the two-wheel drive state before the speed-increasing drive state and the traveling speed in the speed-increasing drive state is smaller than that in the conventional configuration, and the front wheels are in the speed-increasing drive state. There is less shock when switching.

〔The invention's effect〕

As described above, shocks can be alleviated when turning by utilizing the speed increasing effect of the front wheel transmission, and the riding comfort of the four-wheel drive work vehicle is improved.

〔Example〕

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

As shown in FIG. 3, an engine (4), a main clutch (5), and a main clutch (5) are mounted on a machine body frame (3) that rotatably supports a pair of left and right steering type front wheels (1) and rear wheels (2). A lift arm that mounts a mission case (6) and a control unit (7), and connects various working devices such as a rotary tiller to the rear of the machine in a vertically movable manner.
(8) and the PTO shaft (9) for transmitting power to the working device constitute a four-wheel drive agricultural tractor.

Referring to the power transmission system of the agricultural tractor, as shown in FIGS. 3 and 2, the power from the engine (4) is transmitted through the main clutch (5) to the main transmission and the sub transmission in the transmission case (6). The power transmitted to the transmission (above, not shown) is transmitted from the rear wheel differential drive shaft (12) to the rear wheel differential drive mechanism (2a), and the power branched from the rear wheel differential drive shaft (12) is applied to the front wheels. It is transmitted to the transmission device (10) and is transmitted to the front wheel differential mechanism (1a) via the front wheel output shaft (15).

As shown in FIG. 2, in the front wheel transmission (10), a front wheel output shaft (15) is arranged in parallel with the rear wheel differential drive shaft (12), and the rear wheel differential drive shaft (12) is provided with the first and second. The second drive gears (13), (14) are fixed. Then, the first and second drive gears (13), (1
The first and second driven gears (16), (17) that engage with each of (4) are fitted onto the front wheel output shaft (15) by idling, and the first driven gear (16) and the front wheel output shaft (15) ) And a second hydraulic clutch (19) between the second driven gear (17) and the front wheel output shaft (15)
Is configured.

When the first hydraulic clutch (18) is engaged, the front wheels
When the drive speeds of (1) and the rear wheels (2) are almost equal, and the second hydraulic clutch (19) is in the engaged state, the front wheels are
When the driving speed of (1) becomes higher than that of the rear wheel (2) and the first and second hydraulic clutches (18) and (19) are disengaged, the rear wheel (2) Only two wheels are driven.

Next, the operation system of the front wheel transmission (10) will be described in detail.
As shown in FIG. 1, a potentiometer type steering angle detection sensor (22) is provided at the base of the knuckle arm (21) of the front wheel (1) which is steered by the steering handle (20), and steering angle detection is performed. The signal from the sensor (22) is input to the control device (23). When the steering angle of the front wheel (1) is between the straight-ahead position (θ ₀ ) and the set steering angle (θ ₁ ), the first and second hydraulic clutches (18) of the front wheel transmission (10) The control valve (24) for (19) is operated to the pressure oil supply side for the first hydraulic clutch (18) to be in the standard drive state (4WD-I).

The control valve (24) includes a first hydraulic clutch (18) pressure oil supply side, a second hydraulic clutch (19) pressure oil supply side and both hydraulic clutches (1
It is composed of three positions, the neutral position where oil is drained from 8) and (19). It is an electromagnetic type and is a neutral return type.

Then, when the steering wheel (20) is operated to make a sharp turn and the steering angle of the front wheel (1) exceeds the set steering angle (θ ₁ ), a signal from the operation angle detection sensor (22) is sent. Based on this, the control device (23) cuts off the operation signal to the control valve (24) for a set time. Therefore, within this set time, both hydraulic clutches (18), (19) of the front wheel transmission (10) are disengaged, and the two-wheel drive state of only the rear wheel (2) is revealed. Then, after the set time has elapsed, an operation signal is issued from the control device (23) to the control valve (24), and the control valve (24) is operated to the pressure oil supply side of the second hydraulic clutch (19) to increase the speed. The driving state (4WD-II) is revealed.

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 THE DRAWINGS The drawings show an embodiment of a four-wheel drive work vehicle according to the present invention,
FIG. 1 is a view showing a linked state between a front wheel steering system and a front wheel transmission, FIG. 2 is a side view of the front wheel transmission, and FIG. 3 is an overall side view of an agricultural tractor. (1) …… front wheel, (10) …… front wheel transmission, (20) …… steering handle, (θ ₁ ) …… set steering angle.

Claims (1)

[Claims] 1. A standard drive state in which power is transmitted to a steerable front wheel (1) at a drive speed substantially equal to a rear wheel drive speed,
A four-wheel drive work vehicle equipped with a front wheel transmission (10) for switching to an increased drive state in which transmission is performed at a drive speed higher than the rear wheel drive speed, the front wheel (1) steering handle (20) for steering. Is operated at a set steering angle (θ ₁ ) or more, power transmission to the front wheels (1) is cut off for a set time, and after the set time elapses, the front wheel transmission (10) is driven by the speed increasing drive side. A four-wheel drive work vehicle configured to be switched to.