Center differential lock mechanism controlling device

In a four wheel drive vehicle having an anti-lock brake system in combination with a front differential gear, a rear differential gear and a center differential gear, a center differential lock mechanism between the front differential gear and the center differential gear is automatically disengaged when a throttle opening sensor detects a low degree of throttle opening independently of the vehicle speed. The device for automatically disengaging the center differential lock mechanism is operated under the control of an operating unit receiving input signals from a center differential gear operating switch, a vehicle speed sensor, a rear wheel speed sensor, a brake lamp sensor and a throttle opening sensor.

BACKGROUND OF THE INVENTION 
The present invention relates generally to a controlling system for a 
center differential lock mechanism with an anti-lock brake system. More 
particularly, the present invention is concerned with a system for 
controlling a center differential lock mechanism in accordance with the 
operating condition of a throttle valve and an anti-lock brake system. 
An example of a prior art control method for all-wheel driven vehicle is 
disclosed in U.S. Pat. No. 4,753,131 patented on Jun. 7, 1988. The vehicle 
comprises a drive unit, a transmission gear, a front axle-differential, a 
rear-axle differential and an intermediate differential. The torque of the 
drive unit is transmitted by way of the transmission gear to the 
intermediate differential. Driving shafts are operatively connected to the 
intermediate differential. An operating cylinder is arranged between the 
intermediate differential and the rear-axle differential. The intermediate 
differential and the rear-axle differential are provided for differential 
locks. The differential lock which is provided for the intermediate 
differential controls the transmission of the torque for the driving 
shafts. The differential lock which is equipped with the rear-axle 
differential controls the transmission of torque for rear output shafts. 
Two rear wheels are connected to the rear output shafts. The 
slip-controlled brake system includes a pedal actuated three-circuit 
braking pressure generator with a hydraulic energy supply and with a 
hydraulic accumulator. Two front wheels are connected to the front-axle 
shaft by way of semi-axles. The front wheels are in hydraulic 
communication with separate first and second brake circuits, while the 
rear wheels are connected jointly to the third brake circuit. 
The rotational speeds of the wheels will be determined by wheel rotational 
sensors in the form of electric signals which are supplied to a slip 
control unit or to an electric circuit. Upon commencement of brake slip 
control or upon recognition of a locked condition braking is ensured by 
corresponding logic in the electric circuit. 
In this related art, the slip-controlled brake system is operated in 
accordance with the depressing of a brake pedal. The intermediate 
differential is simultaneously controlled at the beginning of the 
depressing of the brake pedal. Based on the above mentioned controlling 
operation, the response time of the intermediate differential is slow. 
This is a problem for the controlling of the intermediate differential 
operation. 
SUMMARY OF THE INVENTION 
It is a primary object of the present invention to produce a four wheel 
drive controlled vehicle which is equipped with a hydraulic controlled 
center differential lock mechanism. 
It is another object of the present invention to produce a control method 
for a four wheel drive vehicle which is equipped with a center 
differential lock mechanism and an anti-lock brake system which prevents a 
locked state of the wheels. 
It is a further object of the present invention to provide a control method 
for a four wheel drive vehicle which prevents the engagement of the center 
differential lock mechanism under braking conditions. 
These objects and advantages are achieved, for example, by providing a 
center differential lock mechanism controlling system and an anti-lock 
brake system for a vehicle with four wheel drive which is equipped with a 
front differential gear, a rear differential gear and a center 
differential gear, a center differential lock mechanism between the front 
differential gear and the center differential gear, an anti-lock brake 
controlling unit for controlling braking of the vehicle upon the 
occurrence of an imminent locked condition, a center differential gear 
operating unit controlling engaging and/or disengaging the differential 
lock mechanism, a throttle opening sensor detecting the opening of a 
throttle valve; the center differential gear operating unit includes means 
for automatically disengaging the center differential lock when the 
throttle opening sensor detects a low degree of throttle opening. 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a four wheel drive vehicle includes an internal 
combustion engine or torque generating drive unit 10, a transmission 11, 
center differential gear 12, a front differential gear 13, a rear 
differential gear 14 and four wheels 15a through 15d. The torque of the 
drive unit 10 is transmitted by way of the transmission gear 11 to the 
center differential gear 12. The torque of the center differential gear 12 
is transmitted by way of driving shafts 16, 17 to the front and rear 
differential gears 13, 14. A front axle-shaft 18 is connected to the front 
differential gear 13, and a rear axle-shaft 19 is connected to the rear 
differential gear 14. 
Wheel brake devices 20a through 20d are mounted on wheels 15a through 15d, 
respectively. Hydraulic pressure conduits (not shown) are connected to the 
wheel brake devices 20a through 20d. An antilock brake operating unit 21 
is arranged on the four wheel drive vehicle. The wheel brake devices are 
controlled in accordance with an electric control signal which is 
calculated by the anti-lock brake operating unit 21 to provide the desired 
braking condition. Electric lines are provided between the anti-lock brake 
operating unit 21 and wheel brake devices 20a through 20d. The anti-lock 
brake operating unit 21 produces the most suitable slip rate between the 
wheel and the ground surface. A center differential lock mechanism 30 
(shown in FIG. 2) is arranged between the center differential gear 12 and 
the front differential gear 13. 
FIG. 2 is a diagram of a control system and hydraulic pressure circuit for 
controlling the anti-lock brake system for the four wheel drive vehicle. 
The center differential lock mechanism 30 is controlled in accordance with 
a center differential gear operating unit 31 in the form of a 
microprocessor. A center differential gear operating switch 32, a vehicle 
speed sensor 33, a rear wheel speed sensor 34, a brake lamp switch 35 and 
a throttle opening sensor 36 are connected to the center differential gear 
operating unit 31. The center differential gear operating switch 32 is 
controlled by a manual operation. In this arrangement electric signals are 
fed to the center differential gear operating unit 31 from the center 
differential gear operating switch 32, the vehicle speed sensor 33, the 
rear wheel speed sensor 34, the brake lamp switch 35 and the throttle 
opening sensor 36. The center differential gear operating switch 32 
determines an operating condition or a non-operating condition of the 
center differential lock mechanism 30. The vehicle speed sensor 33 detects 
the present vehicle speed and transforms it into an electric signal. The 
brake lamp switch operates a brake lamp in accordance with the foot brake 
condition which is operated by a driver. When the foot brake is operated, 
the brake lamp turns on and the electric signal is delivered to the center 
differential gear operating unit 31. The throttle opening sensor 36 
measures the opening ratio of the throttle valve and the opening ratio is 
transformed into an electric signal. The center differential gear 
operating unit 31 determines the operating condition of the center 
differential lock mechanism 30 from the input of one or more electric 
signals. 
In the hydraulic pressure circuit for the center differential lock 
mechanism 30, a solenoid valve 37 is operatively connected to the 
hydraulic pressure circuit. A drain port 37a is formed in the solenoid 
valve 37. A plurality of hydraulic pressure conduits 38a, 38b and 38c are 
provided in the hydraulic pressure circuit. When the solenoid valve 37 is 
energized, communication between the drain port 37a and the hydraulic 
pressure conduits is established. On the other hand, when the solenoid 
valve 37 is de-energized, communication between the drain port 37a and the 
hydraulic pressure conduits is interrupted. A normally closed type 
solenoid valve 37 is employed in this embodiment. A shift valve 39 is 
operatively connected to the hydraulic pressure conduits 38a, 38b and 38c. 
The shift valve 39 includes a spool 39a. The spool 39a is operated in 
accordance with the control condition of the solenoid valve 37. 
The differential lock mechanism 30 basically includes a ring gear mounting 
case 30a, a hydraulic clutch 30b, operating means 30c for controlling the 
hydraulic clutch 30b and an outer housing 30d of the front differential 
gear 13. The engagement and disengagement of the hydraulic clutch 30b is 
controlled in accordance with the operation of the operating means 30c. 
The operation of this embodiment will now be described by referring to 
FIGS. 2 and 3. FIG. 3 is a flow chart showing the operation of the center 
differential lock mechanism. 
When the solenoid 37 is in the energized condition as shown in FIG. 2, the 
pressure conduit 38a communicates with the drain port 37a of the solenoid 
valve 37. In accordance with the foregoing condition, the spool 39a is 
located in the upper position as shown. In this operating condition, the 
pressure conduit 38b and the pressure conduit 38c communicate with each 
other. Since these conduits 38b and 38c communicate with each other 
hydraulic pressure is introduced into the operating means 30c. The 
hydraulic clutch 30b then operates in the engaged condition. The torque is 
directly transmitted between the ring gear mounting case 30a and the outer 
housing 30d. 
When the solenoid 37 is in the de-energized condition, the communication 
between the pressure conduit 38a and the drain port 37a is interrupted. In 
accordance with the foregoing condition, the spool 39a is shifted to a 
downward position. In this operating condition, the communication between 
the pressure conduit 38b and the pressure conduit 38c is interrupted. 
Since these conduits 38b and 38c do not communicate, hydraulic pressure is 
not introduced into the operating means 30c. The hydraulic clutch 30b is 
then in the disengaged condition. The torque from the ring gear mounting 
case 30a is then transmitted to the front differential gear 13 by way of 
the center differential gear 12. 
The center differential gear operating unit is controlled in accordance 
with the flow chart of FIG. 3 which includes the following steps. 
S1 - The state of the output port of the operating unit 31 is set at the 
initial level. 
S2 - The data indicating the state of the center differential gear 
operating switch 32, the vehicle speed sensor 33, the rear wheel speed 
sensor 34, the brake lamp switch 35 and the throttle opening sensor 36 are 
input to the unit 31 to be processed and arranged in accordance with the 
predetermined function. 
S3 - The data from step S2 is processed and the operating condition of the 
center differential lock mechanism is determined. 
S4 - At the moment an inoperative condition or a low degree throttle valve 
condition of the throttle valve is detected, an "energized" operating 
signal is supplied to the solenoid valve 37. When the operating condition 
of the throttle valve is detected, the de-energizing operating signal is 
supplied to the solenoid valve 37. 
S5 - Based on step S4, an "energized" signal is supplied to the solenoid 
valve. 
FIG. 4 illustrates a partial cross-sectional perspective view of the center 
drive train of the center differential gear and the front differential 
gear. A ring gear 50 connects with an output portion of the transmission 
(not shown). The ring rear 50 is rigidly connected to the ring gear 
mounting case 30a. The ring gear mounting case 30a is operatively 
connected to an outer casing 12a of the center differential gear 12. A 
transfer mounting case 51 and a ring shaped transfer drive gear 52 are 
rigidly connected to the outer casing 12a by means of bolts. The driving 
shaft 17 is operatively connected to the transfer drive gear 52 to 
transmit torque to the rear differential gear 14 (not shown in FIG. 4). 
The outer housing 30d of the front differential gear 13 is operatively 
connected to the front pinion gears 53. 
Under the disengaged condition of the hydraulic clutch 30b the drive force 
from the transmission is transmitted to the front differential gear 13 by 
way of the center differential gear 12. 
Under the engaged condition of the hydraulic clutch 30b the drive force 
from the transmission is transmitted to the front differential gear 
directly. The hydraulic clutch 30b includes a plurality of clutch discs 
30e and clutch discs 30f. The clutch discs 30e are splined to the ring 
gear mounting case 30a. The clutch discs 30f are splined to the outer 
housing 30d of the front differential gear 13. The engagement and 
disengagement of the hydraulic clutch 30b are controlled in accordance 
with the hydraulic pressure supplied to the operating means 30c. 
While the invention has been particularly shown and described with 
reference to preferred embodiments thereof, it will be understood by those 
in the art that the foregoing and other changes in form and details may be 
made therein without departing from the spirit and scope of the invention.