Apparatus for controlling the shift between two and four-wheel drivings

An improved apparatus for controlling the shift between two and four-wheel drivings comprises sensors for detecting the revolution velocities of a propeller and axle shafts, and a calculation unit for calculating a predetermined time duration during which the difference of the revolution velocities is less than a predetermined value after a shift member of the propeller shaft is shifted. A shift member of the axle shaft is shifted at a time during the predetermined time duration to be calculated by the calculation unit so that the shift is smoothly performed from two to four-wheel drivings without producing any gear sound or noise even in a high speed running.

FIELD OF THE INVENTION 
The invention relates to an apparatus for controlling the shift between two 
and four-wheel drivings, and more particularly to an apparatus for 
controlling the shift between two and four-wheel drivings in which the 
shift is smoothly performed without producing any gear sound or noise even 
in a high speed running thereby improving the durability of a gear shift 
system of a four-wheel driving car. 
BACKGROUND OF THE INVENTION 
One of conventional apparatuses for controlling the shift between two and 
four-wheel drivings is described in Japanese Patent laid open No. 
61-119425 (119425/1986). The apparatus for controlling the shift between 
two and four-wheel drivings comprises a first sensor for detecting a shift 
member of a transfer means to be shifted, and a second sensor for 
detecting a revolution velocity of a propeller shaft wherein a shift 
member of an axle shaft is shifted when the second sensor detects the 
revolution velocity of the propeller shaft to be increased up to a 
transient building-up level whereby the shift is finished from two to 
four-wheel drivings. 
In the conventional apparatus for controlling the shift between two and 
four-wheel drivings, however, the shift is not performed from two to 
four-wheel drivings as smoothly as expected because the shift member of 
the axle shaft is delayed to be actuated, for instance, by 0.07 to 0.1 
sec. so that the difference of revolution velocities is occured between 
the propeller and axle shafts for the reason why such a delaying time can 
not be actually avoided in actuating any mechanical means. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the invention to provide an apparatus for 
controlling the shift between two and four-wheel drivings in which a shift 
member of an axle shaft is shifted at a precise timing to result in 
four-wheel driving. 
It is a further object of the invention to provide an apparatus for 
controlling the shift between two and four-wheel drivings in which a shift 
is performed smoothly from two to four-wheel drivings without producing 
any gear sound or noise even in a high speed running. 
According to the invention, an apparatus for controlling the shift between 
two and four-wheel drivings comprises, 
first means for detecting a revolution velocity of a propeller shaft for 
wheels to which driving torque is interrupted to be conveyed under 
two-wheel driving condition, 
second means for detecting a revolution velocity of an axle shaft for said 
wheels, 
means for calculating a predetermined time duration during which the 
difference of the revolution velocities is less than a predetermined value 
between said propeller and axle shafts in accordance with the revolution 
velocities thereof detected by said first and second means when a shift 
member of a transfer means is shifted from two to four-wheel driving 
conditions, and 
means for controlling a shift member of said axle shaft to be shifted 
during said predetermined time duration whereby the shaft is finished from 
two to four-wheel drivings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
In FIGS. 1 and 2, there is shown an apparatus for controlling the shift 
between two and four-wheel drivings which comprises a clutch means C/L, a 
transmission means T/M including an over-drive means OD, and a transfer 
means T/F including a center brake means C/B and high/low shifting means 
HI/LO. In the transfer means T/F, an output shaft 1 is provided with a 
clutch gear 2 and freely with a sprocket drive 4 having a hub 3. The hub 3 
is provided in spline connection with a sleeve 5 which is shifted by a 
shift fork (not shown). For the shift of the sleeve 5, or first shift 
member, as shown in FIG. 2, there are provided a vacuum means 6 which 
comprises a diaphragm 10 being composed of a rubber sheet 8 fixed to a 
cylinder 7 and metal plates 9 layered on the both surfaces of the rubber 
sheet 8, and pipes 11a and 11b for supplying negative pressure to cylinder 
chambers 7a and 7b separated by the diaphragm 10. The vacuum means 6 is 
connnected to a shift rod 34 which actuates a switch 35 for detecting the 
shift of the sleeve 5 from two to four-wheel drivings. The sprocket drive 
4 is connected to a corresponding sprocket driven 13 by a chain 12 thereby 
rotating propeller shaft 14. The propeller shaft 14 is connected through a 
bevel gear 15 to a differential means 16 which distributes driving torque 
to axle shafts 17a and 17b for front wheels. The axle shaft 17a is 
provided with a hub 19 having a sleeve 18 fixed in spline connection 
thereto, while an axle shaft 17c which is to be connected to the axle 
shaft 17a or second shift member, as shown in FIG. 1, is provided with a 
clutch gear 20. The sleeve 18 is shifted by a shift fork (not shown) fixed 
to a shift rod 21 to be moved in the direction of an arrow by a vacuum 
means (not shown). A revolution velocity of the aforementioned propeller 
shaft 14 is detected by a sensor 22, while that of the axle shaft 17c is 
detected by a sensor 23. 
In FIGS. 3A and 3B, there is shown the sensor 22 which comprises a wheel 24 
fixed on the outer surface of the propeller shaft 14 to be rotated 
together, a light emitting diode 25, and a phototransistor 26. The wheel 
24 is formed at the outer periphery to have concave portions 24a and 
convex portions 24b so that light from the diode 25 is passed through the 
concave portions 24a to be received by the transistor 26, and is 
interrupted by the convex portions 24b. 
FIG. 4B shows control system in the embodiment according to the invention 
which are started to be operated by a two to four-wheel drive shifting 
button 39 which is to be turned on by a driver in a car so that a transfer 
means shift system and front axle shift system are actuated separately. 
The transfer means shift system comprises a circuit 40 for producing a 
signal by which the vacuum means 6 is to be shifted from two to four-wheel 
driving conditions, a driving circuit 50 for shifting a shift member of 
the transfer means in accordance with the signal from the circuit 40, and 
a circuit 52 for producing a signal which is input to an input interface 
41 to inform a control unit that the shift member is shifted in the 
transfer means. The front axle shift system comprises a circuit 53 for 
producing a signal by which a system indicated by a reference numeral 100 
is actuated to control the front axle shift member to be shifted from two 
to fourwheel drivings at a predetermined timing to be calculated therein 
in accordance with the turning on of the button 39 by the driver. In the 
system 100, the sensors 22 and 23 are actuated to output signals of the 
revolution velocities of the propeller and front axle shafts 14 and 17c to 
a control unit 42. The control unit 42 controls a calculation unit 44 to 
conduct predetermined calculations in accordance with programs stored in 
ROM 43, and RAM 45 to memorize data and results of the calculations 
temporarily during the calculation process. As a result, control signals 
are output from an output interface 46 to which a shift driving circuit 47 
for shifting the shift member including the sleeve 18 connecting the axle 
shafts 17a and 17c to each other is connected, and to which a display 
driving circuit 49 for actuating a display means 48 to be described later 
is connected. The shift driving circuit 47 actuates a front axle shift 
means 51 comprising the sleeve 18, shift rod 21 and so on. 
FIGS. 4B and 4C show the display means 48 comprising a pair of light 
emitting diodes 48a and 48b in which only the light emitting diode 48a is 
turned on to indicate that the sleeve 5 is shifted, but the shift is not 
completely finished from two to four-wheel drivings because the sleeve 18 
is not shifted, while both the light emitting diodes 48a and 48b are 
turned on by the actuation of an axle shift switch (not shown) to indicate 
that the shift is finished completely when the sleeve 18 is shifted. 
In operation (FIG. 6), it is assumed that a car is running under two-wheel 
driving on a highway. Driving torque is conveyed through the clutch means 
C/L and transmission means T/M from an engine to the output shaft 1 of the 
transfer means T/F, and further therefrom to rear wheels. During the 
running of the car, the driver turns on the four-wheel drive button 39 
because rain or wind is heavier. As a result, the two to four-shift signal 
producing circuit 40 and front axle shift actuating circuit 53 are 
actuated. Consequently, negative pressure is supplied to the cylinder 
chamber 7a of the vacuum means 6 by a signal from the circuit 40 so that 
the sleeve 5 is moved in the right direction in FIG. 2 to result in the 
connection between the clutch gear 2 and hub 3 whereby the revolution of 
the output shaft 1 is conveyed through the clutch gear 2 and hub 3 to the 
sprocket drive 4, and further through the chain 12 and sprocket driven 13 
to the propeller shaft 14. The shift rod 34 is also moved by the actuation 
of the vacuum means 6 to actuate the two to four-shift finishing switch 
35. The driver in the car can know by the display 48 in which only the 
light emitting diode 48a is turned on as shown in FIG. 4B that the shift 
of the sleeve 5 in the transfer means T/F is finished, but the shift 
member of the front axle is not shifted. At this time, the sensors 22 and 
23 are actuated in accordance with a signal from the front axle shift 
actuating circuit 53. As shown in FIG. 5, the sensor 22 detects the 
revolution velocity V.sub.P1 of the propeller shaft 14 at the time 
t.sub.1, while the sensor 23 detects the revolution velocity V.sub.A1 of 
the axle shaft 17c which is driven from the road. Further, the revolution 
velocities (V.sub.P1 +.DELTA.V.sub.P1) and (V.sub.A1 +.DELTA.V.sub.A1) are 
detected at the time (t1 +.DELTA.t1), where .DELTA. is a minute value. The 
control unit 42 controls the calculation unit 44 to conduct predetermined 
calculations based upon the signals of the revolutions velocities. In the 
calculation therein, the velocity-inclinations are calculated in 
accordance with the differential values .DELTA.V.sub.P1 /.DELTA.t and 
.DELTA.V.sub.A1 /.DELTA.t, and the time duration t.sub.2 to t.sub.3 during 
which the velocity difference is less than a predetermined value 
.vertline..DELTA.V.vertline. between the propeller shaft 14 and axle shaft 
17c is also calculated in accordance with the velocities V.sub.P1 and 
V.sub.A1 and velocity-inclinations thus calculated. When a time is at 
t.sub.2, that is, when the time t.sub.2 -t.sub.1) is counted from the time 
t.sub.1, the control unit 42 controls the shift driving circuit 47 to move 
the shift rod 21 in the upper direction of an arrow in FIG. 1 so that the 
hub 19 and clutch 20 are connected by the sleeve 18. At this moment, the 
front axle shift finishing switch (not shown) is actuated so that both the 
light emitting diodes 48a and 48b are turned on in the display means 48 as 
shown in FIG. 4C. Consequently, the shift is smoothly performed from two 
to four-wheel drivings without producing any sound or noise even in a high 
speed running because the velocity difference is less than predetermined 
value between the propeller shaft and front axle shaft. 
Although photosensors are used as the sensors 22 and 23 in the embodiment 
described above, magnet sensor, tacho-generator, high frequency 
oscillating proximity switch etc. may be employed, and the position 
thereof is not limited to one illustrated in FIGS. 1 and 2. Further, the 
shift member for the front axle shaft may be provided on the both sides of 
the differential means, although only one is provided on the one side 
thereof. 
On the contrary, the shift member of the transfer means is disconnected 
after that of the front axle means is disconnected, when the shift is to 
be performed from four to two-wheel drivings. 
Although the invention has been described with respect to specific 
embodiment for complete and clear disclosure, the appended claims are not 
to thus limited but are to be construed as embodying all modification and 
alternative constructions that may occur to one skilled in the art which 
fairly fall within the basic teaching herein set forth.