JPH06469B2 - Four-wheel drive work vehicle - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a front wheel shift structure for a four-wheel drive work vehicle.

[Conventional technology]

In a normal four-wheel drive type work vehicle, the driving speeds of the front wheels and the rear wheels are substantially equal, but in recent years, agricultural tractors have been equipped with front wheel transmissions that shift the power to the front wheels. An example of this structure is disclosed in JP-A-61-150830.

The disclosed front wheel transmission is configured to be switchable between two states: a standard drive state in which a drive speed is substantially equal to the rear wheel drive speed and a speed-up drive state in which a drive speed is higher than the rear wheel drive speed. Therefore, the vehicle runs in the standard drive state when the vehicle goes straight normally. When the front wheel transmission is switched to the speed-increasing drive side during turning, the front part of the machine body is positively pulled in the turning direction, and a sharp turn can be relatively easily performed even on soft ground.

[Problems to be solved by the invention]

The condition of the working ground traveling on the agricultural tractor is
There are a wide variety of things like wetlands, turf, etc.,
The turning radius during work is also not constant. However, in the above-mentioned configuration, since the gear ratio of the front wheels to the rear wheels in the speed-up drive state is constant, the drive speed of the front wheels and the turning speed of the front part of the aircraft do not match well, and the front wheels roughen the work ground. There were times when it ended up.

In view of the above-mentioned problems, the present invention has an object to provide a structure capable of making a sharp turn without particularly roughening the work ground.

[Means for solving problems]

A feature of the present invention is that in a four-wheel drive type work vehicle as described above, a front wheel transmission that continuously increases to a drive speed higher than the drive speed of the rear wheels is used as a transmission system for steerable front wheels. A rotation speed detection sensor for detecting the rotation speed of each of the left and right rear wheels is provided, and the front wheel transmission is increased according to an increase in the rotation speed difference between the left and right rear wheels based on the detection by the rotation speed detection sensor. It is provided with a control device that operates at high speed, and its operation and effect are as follows.

[Work]

When the front wheels are steered from the straight ahead state to start turning and the difference in the rotational speeds of the left and right rear wheels begins to occur, the front wheels are gradually accelerated in accordance with the increase in the rotational speed difference. In this state, the turning radius is larger than the steering angle of the front wheels, but the front part of the aircraft is pulled in the turning direction as the front wheels accelerate, and the driving state of the front wheels corresponds to the steering angle of the front wheels. Reaching a turning condition with a turning radius. After that, the front wheels are driven at a driving speed suitable for the steering angle of the front wheels, that is, the turning speed of the front part of the body.

〔The invention's effect〕

As described above, it becomes possible to increase the front wheels to the drive speed suitable for the turning speed of the front part of the machine body in accordance with the difference in the rotational speeds of the left and right rear wheels, and the sharp turning can be performed without particularly roughening the work ground. I can do it now.

〔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 (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) ) Between the first hydraulic clutch (18) and the second driven gear (17) and the front wheel output shaft (15) between the second hydraulic clutch.
(19) is configured. Then, as shown in FIG.
An electromagnetic control valve (24) for supplying / discharging pressure oil to / from the first and second hydraulic clutches (18), (19) is provided, and a control valve (24) for operating the control valve (24) is provided. Controllers that emit signals (23)
Is provided.

On the other hand, as shown in FIG. 1, rotation speed detection sensors (11a), (11) for detecting the respective rotation speeds of the left and right rear wheels (2).
b) is provided, and signals from the rotation speed detection sensors (11a) and (11b) are input to the control device (23). And
If the difference between the peripheral speeds (VRa), (VRb) of the left and right rear wheels (2) calculated based on the detection values of the rotation speed detection sensors (11a), (11b) is within a set range, control is performed. The device (23) determines that the aircraft is in a straight traveling state and sets the control valve (24) to the first hydraulic clutch.
(18) Operate the pressure oil supply side to put the first hydraulic clutch (18) into the engaged state. In this state, power is applied to the front and rear wheels (1), (2)
Are transmitted to the front wheels (1) in a standard drive state in which the average peripheral velocities of are substantially equal.

Next, detailed description will be given of the state at the time of turning, as shown in the figure, the peripheral speed (VRa) of the left and right rear wheels (2) calculated based on the detection of the rotation speed detection sensors (11a), (11b). , (VRb) has a relation as in the first equation (C ₁ ).

VRa: VRb = (R ₁ −B): (R ₁ + B) ………… (C ₁ ) R ₁ : The average turning radius of the left and right rear wheels B: 1/2 of the tread The average turning radius (R ₁₎ of the average turning radius (R ₂₎ and a wheel base of the front wheel (1) (A) and the rear wheel (2) has a relationship as follows (C _3).

R ₂ ² = A ² + R ₁ ² …………………… (C ₃ Therefore, the speed increase ratio (α) of the front wheel (1) to the rear wheel (2) during turning is calculated by the following equation (C ₄ ).

Substituting the previous expression (C ₂ ) into this expression (C ₄ ) The speed increasing ratio (α) is obtained by the above equation (C ₅ ).

Next, the structure for continuously increasing the speed of the front wheel (1) will be described. As shown in Fig. 4 (a), the second hydraulic clutch (19) is operated to the pressure oil supply side with respect to the control valve (24). Signal to control device (2
If it continues to oscillate from 3), the second hydraulic clutch (19) will be completely in the engaged state, and the power from the rear wheel differential drive shaft (12) will be the second drive / driven gears (14), (17) and Second hydraulic clutch (19)
The first hydraulic clutch (18) is transmitted to the front wheels (1) in a speed-up drive state in which the speed is higher than the standard drive state in which the first hydraulic clutch (18) is turned on and operated. The speed increasing ratio in this speed increasing drive state is uniquely determined by the gear ratio.

On the other hand, as shown in FIGS. 4B and 4C, a signal for operating the control valve (24) to the pressure oil supply side of the second hydraulic clutch (19) is intermittently oscillated, and the control valve (24 ) Is intermittently opened and closed, the pressure sufficient to keep the second hydraulic clutch (19) completely in the closed state does not act on the second hydraulic clutch (19). In such a state, slippage occurs in the second hydraulic clutch (19) and the second hydraulic clutch (19) is decelerated more than the speed-up drive state in the fully entered state. Power is transmitted by. Therefore, the degree of slippage of the second hydraulic clutch (19) can be changed by changing the total sum of the oscillation times to the entry side of the second hydraulic clutch (19) within the set time (t). The front wheels (1) can be continuously operated to change gears during the speed-up drive state.

Then, as shown in FIG. 1, rotation speed detection sensors (20), (21) are attached to the front wheel output shaft (15) and the rear wheel differential drive shaft (12) on the lower side from the front wheel transmission (10), It is connected to the control unit (23). And the rotation speed detection sensor (20),
Average peripheral speed of front wheel (1) calculated based on detection of (21)
The control device (23) controls the control valve (24) so that (V _F ) and the average peripheral velocity (V _R ) of the rear wheels (2) are such that V _F = αV _R α = gear increase ratio during turning. Is operated intermittently as described above.

[Another embodiment]

In the above-described embodiment, the speed increasing system of the front wheel transmission is hydraulically operated, but a structure of a friction type continuously variable transmission such as a belt type may be adopted.

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 four-wheel drive type working vehicle according to the present invention,
FIG. 1 is a schematic plan view showing a control system of a front wheel transmission, FIG. 2 is a side view of the front wheel transmission, FIG. 3 is an overall side view of an agricultural tractor, and FIGS. 4 (a), (b), ( (C) is a diagram showing an oscillating state of a signal from the control device to the second hydraulic clutch pressure oil supply side to the control valve. (1) …… Front wheel, (2) …… Rear wheel, (10) …… Front wheel transmission, (1
1a), (11b) ... Rotation speed detection sensor, (23) ... Control device.

Claims (1)

[Claims] 1. A front wheel capable of steering a front wheel transmission (10) which continuously increases to a driving speed higher than that of the rear wheel (2).
Provided with a transmission system to (1), provided with a rotation speed detection sensor (11a), (11b) for detecting the rotation speed of each of the left and right rear wheels (2), the rotation speed detection sensor (11a), ( A four-wheel drive work vehicle provided with a control device (23) for increasing the speed of the front wheel transmission (10) according to an increase in the rotational speed difference between the left and right rear wheels (2) based on the detection from 11b).