Anti torque shock control device and method engaging torque transmitting clutch between vehicle wheels when transmission is shifted from non drive range to drive range

In a 2WD/4WD transmission system for a vehicle including a central differential device for variably differentiating rotational power between a pair of front wheels and a pair of rear wheels, and a clutch for selectively locking the differential device for positive four wheels driving, an anti torque shock device is incorporated therein, to suppress occurrence of shock due to a backlash in the differential device being abruptly cancelled when the transmission system was shifted from non condition of the transmission system and at least temporarily engaging the clutch to lock the differential device when the transmission system is shifted into the driving engagement.

BACKGROUND OF THE INVENTION 
The present invention relates to an anti torque shock control method and 
device for a power transmission system for a vehicle, and more 
particularly relates to such an anti torque shock control method and 
device, particularly applicable to a vehicle power transmission system in 
which a clutch is provided for selectively engaging two of the vehicle 
wheels together at least partially. 
The present invention has been described in Japanese Patent Applications 
Ser. Nos. Showa 60-194634 (1985) and Showa 61-176468 (1986), both of which 
were filed by an applicant the same as the entity assigned or owed duty of 
assignment of the present patent application; and the present patent 
application hereby incorporates into itself by reference the text of said 
Japanese Patent Applications and the claims and the drawings thereof; 
copies are appended to the present application. 
Nowadays a greatly increasing number of automotive vehicles are being 
constructed with four wheel drive transmission systems, because such four 
wheel drive operation, in which all four wheels of the vehicle are powered 
from its engine via its transmission, is very suitable for driving on poor 
or slippery road surfaces such as in mud or over bad ground, or upon roads 
covered with mud, snow, ice, or rain. One type of such transmission system 
is the so called part time four wheel drive system, in which a 2WD/4WD 
control clutch is included which can switch the transmission operational 
mode between a two wheel drive operational mode and a four wheel drive 
operational mode, i.e. typically which can selectively power the front 
wheels of the vehicle from the engine while the rear wheels of the vehicle 
ae always being powered from said engine. 
Also, there is currently sometimes provided a type of so called full time 
four wheel drive type of transmission which remains always engaged to four 
wheel drive without any episodes of two wheel driving, and this type is 
becoming more and more popular. In such a four wheel drive transmission 
system for an automotive vehicle, it is usual to provide a center 
differential device for distributing rotational power between the front 
wheels of the vehicle and the rear wheels of the vehicle, as well as the 
per se conventional rear differential device that provides differential 
action between the two rear vehicle wheels and the also per se 
conventional front differential device that provides differential action 
between the two front vehicle wheels. Such a central or front-rear 
differential device is provided in order to provide a differential action 
between said front vehicle wheels (considered as a pair) and said rear 
vehicle wheels (also considered as a pair) when the vehicle is turning 
around a curve, in order to eliminate the possibility of the occurrence of 
the so called tight corner braking pnenomenon created by the different in 
the turning radiuses of the front wheels of the vehicle and the rear 
wheels thereof. Also, it has been practiced to provide a device to such a 
front-rear differential device which prevents said front-rear differential 
device from performing differential action, in a selective fashion. When 
such a center differential action inhibition means, which typically may be 
a friction engaging means such as a hydraulic clutch, is actuated, it 
causes the differential action provided by said front-rear differential 
device between the front vehicle wheels and the rear vehicle wheels to be 
at least partially prevented, and instead said front vehicle wheels, 
considered as a pair, are driven from the vehicle engine, and also said 
rear vehicle wheels, considered as a pair, are at least partially 
independently driven from said vehicle engine. Such types of structure are 
at least partly disclosed, for example, in Japanese Patent Application 
Laying Open Publication Ser. No. 50-147027 (1975), Japanese Patent 
Application Laying Open Publication Ser. No. 55-72420 (1980), Japanese 
Patent Application Laying Open Publication Ser. No. 56-138020 (1981), and 
Japanese Utility Model Application Laying Open Publication Ser. No. 
61-73430 (1986), none of which is it intended hereby to admit as prior art 
to the present patent application except to the extent in any case 
required by applicable law. 
Also, there is a per se known type of so called limited slip differential 
device for a vehicle, not necessarily particularly associated with any 
four wheel drive transmission system, in which a differential device is 
provided for driving two vehicle wheels on the same vehicle axle with 
differential effect being provided therebetween, and in which a 
differential control clutch is provided to said differential device for 
selectively at least partially inhibiting said differential effect 
provided thereby. 
Now, when a transmission for a vehicle is being used which has a fluid 
torque converter or a similar type of fluid coupling and also an auxiliary 
speed change mechanism such as an automatic transmission, the problem 
arises that, when the operating range of such a transmission is shifted 
from a non drive range such as "P" range or "N" range to a drive range 
such as "D" or "R" range, at this time drive force starts to be 
transmitted to certain vehicle drive wheels whereas before this was not 
the case, and this engenders a risk of slack in a differential device 
(either a front or a rear differential device, or a front/rear type of 4WD 
differential device) of the vehicle causing shift shock and so called 
"clonking", which not only is disconcerting and uncomfortable for 
passengers in the vehicle, but is liable to shorten the life of the 
transmission and/or the differential device, and to compromise their 
reliability. 
Particularly with a four wheel drive type of vehicle, whether or not said 
be provided with a center differential device (i.e. a front/rear type of 
4WD differential device), since it is typical in such a case for a rear 
differential device to be provided for providing differential effect 
between the two rear vehicle wheels and also for a front differential 
device to be provided for providing differential effect between the two 
front vehicle wheels, in this case when the operating range of the 
transmission is shifted from a non drive range such as "P" range or "N" 
range to a drive range such as "D" or "R" range, at this time one of these 
front and rear differential devices will typically have less slack and 
will take up drive first, whereupon the action of the central differential 
device will speed up the rotational motion of the other one of said front 
and rear differential devices, thus producing a relatively large shift 
shock or so called "clonking". 
Further, in the event that such a front-rear differential device of the 
type described above is of an unequal distribution type which distributes 
drive torque substantially unequally between the front vehicle wheels and 
the rear vehicle wheels, then, when the operating range of the 
transmission is shifted from a non drive range such as "P" range or "N" 
range to a drive range such as "D" or "R" range, at this time the pair of 
vehicle wheels (typically the rear wheels) which receive more torque sink, 
or more properly the portion of the vehicle body above said pair of 
vehicle wheels drops, more than does the portion of the vehicle body above 
the other pair of vehicle wheels (typically the front wheels); and this 
causes the so called vehicle squat problem, which is troublesome and 
disconcerting for the vehicle passengers, and can lead to difficulties 
with vehicle steering and control. This problem further is accentuated in 
the case of a relatively soft vehicle suspension. 
SUMMARY OF THE INVENTION 
The inventors of the present invention have considered the various problems 
detailed above in the aforementioned case of shifting a vehicle 
transmission system from a non drive range operational mode to a drive 
range operational mode, from the point of view of the desirability of 
minimizing the torque shock at such a time. 
Accordingly, it is the primary object of the present invention to provide 
an improved anti torque shock control method for a vehicle, and a 
corresponding device for implementing said method, which avoid the 
problems detailed above. 
It is a further object of the present invention to provide such an anti 
torque shock control method and device, which are effective for a four 
wheel drive type vehicle transmission system. 
It is a further object of the present invention to provide such an anti 
torque shock control method and device, which are effective for a full 
time four wheel drive type vehicle transmission system. 
It is a yet further object of the present invention to provide such an anti 
torque shock control method and device, which are particularly effective, 
in the case that the vehicle front-rear differential device is of an 
unequal distribution type which distributes drive torque substantially 
unequally between the front vehicle wheels and the rear vehicle wheels. 
It is a yet further object of the present invention to provide such an anti 
torque shock control method and device, which are effective for maximizing 
transmission life and reliability. 
It is a yet further object of the present invention to provide such an anti 
torque shock control method and device, which prevent the occurrence of 
the vehicle squat phenomenon. 
It is a yet further object of the present invention to provide such an anti 
torque shock control method and device, which maximize vehicle 
controllability. 
According to the most general device aspect of the present invention, these 
and other objects are attained by, for a power transmission system for a 
vehicle comprising at least two wheels, a transmission mechanism, and a 
selectively engagable clutch for being selectively engaged to at least 
partially rotationally couple together said two vehicle wheels: an anti 
torque shock control device, comprising: (a) a means for detecting whether 
or not shift range of said transmission mechanism is a vehicle non driving 
range or a vehicle driving range; and: (b) a means for controlling said 
cluch to be at least partially engaged, when shift range of said 
transmission mechanism, as detected by said detecting means therefor, 
alters from a vehicle non driving range to a vehicle driving range; and, 
according to the most general method aspect of the present invention, 
these and other objects are attained by, for a four wheel drive power 
transmission system for a vehicle comprising at least two wheels, a 
transmission mechanism, and a selectively engagable clutch for being 
selectively engaged to at least partially rotationally couple together 
said two vehicle wheels: an anti torque shock control method, wherein: (a) 
it is detected whether or not shift range of said transmission mechanism 
is a vehicle non driving range or a vehicle driving range; and: (b) said 
clutch is controlled to be at least partially engaged, when shift range of 
said transmission mechanism, as thus detected, alters from a vehicle non 
driving range to a vehicle driving range. 
The anti torque shock control device and method of the present invention, 
as specified above, are effective because thereby shift shock and so 
called "clonking" of the transmission and of any differentials included in 
the power train are reduced, as will be made clear from the descriptions 
of the preferred embodiments, given hereinafter. 
The clutch may be a switchover clutch for controlling said vehicle between 
two wheel drive operation and four wheel drive operation, selectively 
coupling between front wheels of said vehicle and rear wheels of said 
vehicle; or it may be a central differential control clutch for 
controlling a central differential device of said vehicle between a mode 
of operation in which said central differential device provides central 
differential effect between front wheels of said vehicle and rear wheels 
of said vehicle, and a mode of operation in which said central 
differential device provides no such central differential effect between 
said front wheels of said vehicle and said rear wheels of said vehicle; or 
it may be an axle differential control clutch for controlling a 
differential device of said vehicle between a mode of operation in which 
said axle differential device provides differential effect between a pair 
of left and right wheels of said vehicle on the same axle, and a mode of 
operation in which said axle differential device provides no such 
differential effect between said same axle pair of left and right wheels 
of said vehicle. In either of the first two cases, the effect of the 
present invention is that during the shifting of the range of the 
transmission mechnaism, in front to rear direct connection type four wheel 
drive operation, clonking of only one of the front and the rear 
differential devices of the vehicle is avoided, and there by large shift 
shock and "clonking" are avoided. On the other hand, in the last case, the 
effect of the present invention is that during the shifting of the range 
of the transmission mechanism, since the differential device of the 
vehicle is locked up, thereby large shift shock and "clonking" are 
definitely and positively avoided. 
Furthermore, in the case that such a central differential device is of an 
unequal distribution type which normally distributes drive torque 
substantially unequally between the front vehicle wheels and the rear 
vehicle wheels, then, since such a control clutch is according to the 
present invention engaged during the shifting of the range of the 
transmission mechanism, the drive torque is at this time distributed 
according to the load on the front and rear vehicle axles, thus avoiding 
the occurrence of the so called vehicle squat phenomenon when the range of 
the transmission mechanism is shifted from a non drive range to a drive 
range. 
Further, according to an alternatively expressed device aspect of the 
present invention, the above specified objects and others are attained by, 
for a four wheel drive power transmission system for a vehicle comprising 
a pair of front wheels, a pair of rear wheels, an automatic transmission 
mechanism, and a central differential device comprising a selectively 
engagable central differential control clutch which can be selectively 
either disengaged or engaged respectively to either provide central 
differential effect between said front pair of vehicle wheels and said 
rear pair of vehicle wheels, with the torque distribution proportion then 
being provided to said rear pair of vehicle wheels being substantially 
greater than the torque distribution proportion then being provided to 
said front pair of vehicle wheels, or not to provide any such central 
differential effect between said front pair of vehicle wheels and said 
rear pair of vehicle wheels: an anti torque shock control device, 
comprising: (a) a means for detecting whether or not currently set shift 
range of said automatic transmission mechanism is a vehicle non driving 
range or a vehicle driving range; (b) a means for controlling said central 
differential control clutch to be at least partially engaged, when shift 
range of said transmission mechanism, as detected by said detecting means 
therefor, alters from a vehicle non driving range to a vehicle driving 
range; and: (c) a means for ensuring that, during a rapid vehicle start, 
said central differential control clutch is disengaged; and, according to 
an alternatively expressed method aspect of the present invention, the 
above specified objects and others are attained by, for a four wheel drive 
power transmission system for a vehicle comprising a pair of front wheels, 
a pair of rear wheels, an automatic transmission mechanism, and a central 
differential device comprising a selectively engagable central 
differential control clutch which can be selectively either disengaged or 
engaged respectively to either provide central differential effect between 
said front pair of vehicle wheels and said rear pair of vehicle wheels, 
with the torque distribution proportion then being provided to said rear 
pair of vehicle wheels being substantially greater than the torque 
distribution proportion then being provided to said front pair of vehicle 
wheels, or not to provide any such central differential effect between 
said front pair of vehicle wheels and said rear pair of vehicle wheels: an 
anti torque shock control method, wherein: (a) it is detected whether or 
not currently set shift range of said automatic transmission mechanism is 
a vehicle non driving range or a vehicle driving range; (b) said central 
differential control clutch is controlled to be at least partially 
engaged, when shift range of said transmission mechanism, as detected by 
said detecting means therefor, alters from a vehicle non driving range to 
a vehicle driving range; and: (c) it is ensured that, during a rapid 
vehicle start, said central differential control clutch is disengaged. 
During sudden starting off of the vehicle, because of the sudden vehicle 
acceleration the effective weight imposed upon the rear vehicle axle is 
increased, and thus it is better to provide more torque to the rear 
vehicle wheels even if the vehicle squat phenomenon is thereby produced; 
and thus, according to the above described control device and method, 
although generally during shifting of the range of the transmission 
mechanism from a non drive range to a drive range the central differential 
device cluch should as described above be engaged in order to reduce 
vehicle squat, nevertheless during sudden starting off of the vehicle this 
engagement of said central differential device clutch should be eschewed, 
in order to aid with proper vehicle starting off.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described with reference to the preferred 
embodiments of the method and of the device thereof, and with reference to 
the figures. 
First Exemplary Overall Vehicle Power Train Structure 
FIG. 1 is a schematic longitudinal skeleton view of a vehicle power train 
which incorporates the preferred embodiment of the anti torque shock 
control device of the present invention, said device performing a 
corresponding method embodiment. In this figure, the reference numeral 1 
denotes an internal combustion engine of said vehicle, which is mounted, 
in this first exemplary case, longitudinally in the front engine room (not 
particular shown) of said vehicle. And the reference numeral 2 denotes an 
automatic speed change device (automatic transmission) of a per se known 
type, while 3 denotes a four wheel drive power transfer device of a so 
called part time four wheel drive type, which is selectably operable 
either in four wheel drive mode or in two wheel drive mode, so as 
selectably either to drive both the rear pair of wheels of the vehicle and 
also the front pair of wheels of the vehicle or alternatively to drive 
only said rear pair of wheels of said vehicle but not said front pair of 
wheels of said vehicle, as will be explained in detail hereinafter, said 
four wheel drive power transfer device 3 not having any capability of 
providing any particular front/rear differential action. 
In more detail, the automatic speed change device 2 incorporates a fluid 
torque converter 5 of a per se known construction, and the power input 
shaft of this fluid torque converter 5 is connected to and receives 
rotational power from a crank shaft of the internal combustion engine 1. 
And the fluid torque converter 5 is housed within a torque converter 
housing 4 fitted against and secured to the main body of the internal 
combustion engine 1, while the automatic speed change device 2 comprises a 
gear transmission mechanism 7, which is likewise housed within a speed 
change device housing fitted against and secured to the torque converter 
housing 4. And the input shaft of the gear transmission mechanism 7 is 
connected to and receives rotational power from the power output shaft of 
the fluid torque converter 5; and thereby the gear transmission mechanism 
7 receives rotational power from the internal combustion engine 1, with a 
certain degree of slippage and also torque amplification being provided 
for said rotational power by the fluid torque converter 5 (unless a lock 
up clutch thereof, if provided thereto, is activated) as is per se 
conventional. This gear transmission mechanism 7 may for the purposes of 
this specification be of a per se known type incorporating various 
planetary gear mechanisms and friction engaging mechanisms such as 
clutches and brakes, and, according to selective actuation of friction 
engaging mechanisms provided by an electrically controlled 
electric/hydraulic control mechanism 9 of a per se known sort including 
various speed change solenoids and so on, provides any one of a plurality 
of speed reduction stages between its said power input shaft and its power 
output shaft, its said power output shaft driving the four wheel drive 
power transfer device 3. Particularly accordingly to the appropriate 
setting for the present invention, the combination of this automatic speed 
change device 2 and this electric/hydraulic control mechanism 9 is so 
constituted as to be capable of operating in various transmission 
operational ranges, including one or more drive ranges such as "D" range, 
"S" range, "L" range, and "R" range, and one or more non drive ranges such 
as "P" range and "N" range, according to the behest of the driver of the 
vehicle, who typically sets such as automatic transmission operational 
range upon a manual range setting device, not particularly shown in the 
figures, such as a shift lever or transmission push buttons or the like. 
This four wheel drive power transfer device 3 incorporates a through shaft 
49, which extends clear through said four wheel drive power transfer 
device 3 so that its one end extends out therefrom in the direction to the 
right as seen in FIG. 1, i.e. towards the front of the vehicle in this 
particular exemplary implementation, and is connected to the power output 
shaft of the gear transmission mechanism 7 so as to function as a power 
input shaft for this four wheel drive power transfer device 3; while the 
other end of this through shaft 49 extends out of the four wheel drive 
power transfer device 3 in the opposite direction to the left as seen in 
FIG. 1, i.e. towards the rear of the vehicle to this particular exemplary 
implementation, so as to function also as a power output shaft for the 
rear wheels of the vehicle as will be described shortly. And a hollow 
sleeve shaped intermediate front wheel drive shaft 16 is provided, fitted 
around this through shaft 49 at its portion within the housing of this 
four wheel drive power transfer device 3, and this hollow sleeve shaped 
intermediate front wheel drive shaft 16 functions as another power output 
member for the four wheel drive power transfer device 3 for supply power 
to the front wheels of the vehicle, and is rotationally connected to a 
front wheel power output shaft 17 provided below said sleeve shaped 
intermediate front wheel drive shaft 16 from the point of view of the 
figure and in the actual vehicle body also and with its central axis 
parallel to the central axis of said sleeve shaped intermediate front 
wheel drive shaft 16, via a sprocket wheel 18 fixedly mounted on the 
outside of said intermediate front wheel drive shaft 16, an endless chain 
20 fitted around this sprocket wheel 18, and another sprocket wheel 19 
which is fixedly mounted on said front wheel power output shaft 17. One 
end of the front wheel power output shaft 17 protrudes from the housing of 
this four wheel drive power transfer device 3 in the leftwards direction 
in the figure, i.e. towards the front end of the vehicle in this 
particular exemplary implementation. 
Via a universal joint 23 of a per se known sort, the rear end of the 
through shaft 49 rotationally drives the front end of a rear wheel 
propeller shaft 24. And the rear end of this rear wheel propeller shaft 24 
is connected via another universal joint (not particularly shown) to a 
differential device, (not particularly shown either), for driving the rear 
wheels (also not shown) of the vehicle. 
And, via a universal joint 25 also of a per se known sort, the front end of 
the front wheel power output shaft 17 rotationally drives the rear end of 
a front wheel propeller shaft 26. Thus, this front wheel propeller shaft 
26 extends alongside and generally below the automatic speed change device 
2 including the fluid torque converter 5 therein, roughly parallel to the 
longitudinal axis thereof. The front end of this front wheel propeller 
shaft 26 is rotationally connected, via another universal joint 27 also of 
a per se known sort, to the rear end (relative to the vehicle body, not 
shown) of an intermediate shaft 28, which is supported from the torque 
converter casing 4 by means of a bearing assembly. And this intermediate 
shaft 28 is at its front end (also relative to the vehicle body) engaged 
by a spline construction or the like to the outer end of a input drive 
pinion shaft 31, which constitutes the power input shaft of a front 
differential device 30 which drives the front wheels (not shown) of the 
vehicle, and which is rotatably supported by bearings at its intermediate 
portion from the casing 32 of the front differential device 30; this 
casing 32 is integrally formed with the oil pan 29 of the internal 
combustion engine 1. The inner end of this input drive pinion shaft 31 is 
provided with a drive pinion 33 which is constituted as a bevel gear, with 
said drive pinion 33 being meshingly engaged with a driven ring gear 34 of 
the front differential device 30. 
Further, within the four wheel drive power transfer device 3 there is 
provided a hydraulically operated wet type multi plate type clutch 50, 
which selectively either rotationally connects together, in this first 
exemplary case, the through shaft 49 and the sleeve shaped intermediate 
front wheel drive shaft 16, or alternatively allows said members to rotate 
freely with respect to one another. This wet clutch 50 is selectively 
operated, either to be engaged or to be disengaged, by an electrically 
actuated electric/hydraulic control device 22 to be described shortly. 
Accordingly the four wheel drive power transfer device 3, which receives 
rotational power input from the gear transmission mechanism 7 and always 
outputs said rotational power via the through shaft 49 to the rear vehicle 
wheels, can be controlled by the selective operation of the wet clutch 50 
either to provide said rotational power also to the front wheel power 
output shaft 17, i.e. to cause the vehicle to be operated in four wheel 
drive mode, or alternatively not to provide any such rotational power to 
said front wheel power output shaft 17 and thus to cause the vehicle to be 
operated in two wheel drive mode. 
Thus, the power distribution ratio (drive torque distribution) between the 
intermediate front wheel drive shaft 16 and the rear wheel propeller shaft 
24, of course when the clutch 50 of this four wheel drive power transfer 
device 3 is engaged, is unity, and therefore this four wheel drive power 
transfer device 3 is of the type which distributes the drive torque 
equally between the rear vehicle wheels and the front vehicle wheels. 
The Hydraulic Clutch 50 
In FIG. 2, there is shown a schematic view of the actuation and control 
system for the clutch 50 of the four wheel drive power transfer device 3 
which thus selectively couples together the through shaft 49 and the 
sleeve shaped intermediate front wheel drive shaft 16. In this figure, the 
reference numeral 51 denotes an actuating hydraulic fluid pressure chamber 
of said clutch 50, said actuating hydraulic fluid pressure chamber 51 
being partly defined by a piston or the like (not particularly shown) of 
said clutch 50, and, when supplied with actuating hydraulic fluid pressure 
greater than a determinate pressure level, pressing together via said 
piston, against the biasing force of a biasing means (not shown either) 
which is overcome, two sandwiched together sets of clutch plates (also not 
particularly shown) of said wet clutch 50, one of said clutch plate sets 
being rotationally mounted to said through shaft 49 and the other of said 
clutch plate sets being rotationally mounted to said sleeve shaped 
intermediate front wheel drive shaft 16. Thus, when this actuating 
pressure chamber 51 is thus supplied with actuating hydraulic fluid 
pressure of a particular sufficiently great line pressure level, it causes 
said two sandwiched together sets of clutch plates to be mutually 
rotationally engaged, thus rotationally coupling together said through 
shaft 49 and said sleeve shaped intermediate front wheel drive shaft 16 
and thus putting the four wheel drive power transfer device 3 into its 
four wheel drive operational mode; while, on the other hand, when said 
actuating pressure chamber 51 is not thus supplied with actuating 
hydraulic fluid pressure of said particular pressure level, it allows said 
two sandwiched together sets of clutch plates to be mutually rotationally 
disengaged by the biasing action of said biasing means, thus rotationally 
decoupling said through shaft 49 and said sleeve shaped intermediate front 
wheel drive shaft 16 from one another, thereby stopping the driving of 
said sleeve shaped intermediate front wheel drive shaft 16 by the engine 1 
and thus putting the four wheel drive power transfer device 3 into its two 
wheel drive operational mode. 
Although no particular use is made of such a concept in the shown first 
preferred embodiments of the anti torque shock control method and device 
of the present invention, in fact, if said actuating pressure chamber 51 
is supplied with actuating pressure of a lower level than said line 
pressure level, it can cause said two sandwiched together sets of clutch 
plates to be mutually rotationally engaged to only a certain degree with a 
certain amount of slippage being available between them, thus rotationally 
coupling together said through shaft 49 and said sleeve shaped 
intermediate front wheel drive shaft 16 with a certain slippage amount 
therebetween, and thus putting the four wheel drive power transfer device 
3 into its four wheel drive operational mode with a certain slippage 
amount. 
Hydraulic fluid pressure is supplied to the pressure chamber 51 by the 
following arrangements, which correspond to the electric/hydraulic control 
device 22 of FIG. 1. A hydraulic fluid pump 52 picks up hydraulic fluid 
from a sump of the transmission system and pressurizes it. This 
pressurized hydraulic fluid is then supplied to a pressure regulator valve 
53 of a per se known sort which regulates its pressure to a determinate 
line pressure value mentioned above. This line pressure is then fed via a 
restricted orifice and a conduit to said actuating pressure chamber 51 of 
said wet clutch 50, and this conduit is further connected to a control 
port 55 of an electromagnetically actuated hydraulic fluid drain valve 54. 
This electromagnetically actuated hydraulic fluid drain valve 54 has a 
solenoid 57 which controls the motion of a valve element 56 thereof. When 
the solenoid 57 is supplied with actuating electrical energy by a 
transmission control device 35 which will be explained hereinafter, then 
against the biasing force exerted by a compression coil spring 58 which is 
overcome said valve element 56 is impelled so that its tip is pushed 
against said control port 55, thus interrupting communication through said 
control port 55 and allowing hydraulic fluid pressure to be supplied into 
said actuating pressure chamber 51. When, on the other hand, said solenoid 
57 is not supplied with any actuating electrical energy by a transmission 
control device 35 which will be explained hereinafter, then by the biasing 
force exerted by said compression coil spring 58 which is not opposed said 
valve element 56 is biased so that its tip is brought away from said 
control port 55, thus permitting communication throug said control port 55 
and thereby communicating the actuating pressure chamber 51 to drain and 
preventing allowing hydraulic fluid pressure from building up inside said 
actuating pressure chamber 51. In these first preferred embodiments of the 
anti torque shock control device of the present invention, therefore, line 
pressure is or is not supplied to said actuating pressure chamber 51 of 
said wet clutch 50, respectively according as to whether or not actuating 
electrical energy is supplied from said transmission control device 35 to 
this electric/hydraulic control device 22, and said wet clutch 50 thereby 
either is engaged, or is left disengaged, respectively. 
However, in an alternative possible implementation, it would be possible 
for this electric/hydraulic control device 22 to be supplied with a pulsed 
electrical signal from the transmission control device 35, and in such a 
case, according to the duty ratio of the pulsed electrical signal, the 
ON/OFF duty factor of the electromagnetically actuated hydraulic fluid 
drain valve 54 would be determined, and this would enable the pressure 
provided in the pressure chamber 51 of the wet clutch 50 to be set to any 
pressure level between zero and line pressure level, and thereby the 
degree of rotational coupling together of the through shaft 49 and the 
sleeve shaped intermediate front wheel drive shaft 16 of the four wheel 
drive power transfer device 3 could be controlled to be any value between 
substantially zero and the substantially full rotational coupling together 
condition; and thereby the action of said four wheel drive power transfer 
device 3 for providing four wheel drive could be controlled to be any 
amount between substantially zero and substantially the fully four wheel 
drive condition. 
Operation of This First Power Train 
This vehicle power train operates as follows. When the clutch 50 of the 
four wheel drive power transfer device 3 is operated by the transmission 
control device 35 so as not to rotationally connect together the through 
shaft 49 and the sleeve shaped intermediate front wheel drive shaft 16, 
then the four wheel drive power transfer device 3 functions so as only to 
drive the rear wheel propeller shaft 24 but not to drive the intermediate 
front wheel drive shaft 17, i.e. so as to receive rotational power 
provided by the engine 1 of the vehicle and transmitted to said four wheel 
drive power transfer device 3 via the automatic speed change device 2, and 
to distribute said rotational power only to the rear wheels of the vehicle 
taken as a combination but not to the front wheels of the vehicle taken as 
a combination. This is the two wheel drive operational mode. On the other 
hand, when the clutch 50 of the four wheel drive power transfer device 3 
is operated by the transmission control device 35 so as to completely 
rotationally connect together the through shaft 49 and the sleeve shaped 
intermediate front wheel drive shaft 16, then the four wheel drive power 
transfer device 3 functions so as to drive the rear wheel propeller shaft 
24 and also to drive the intermediate front wheel drive shaft 17, i.e. so 
as to receive rotational power provided by the engine 1 of the vehicle and 
transmitted to said four wheel drive power transfer device 3 via the 
automatic speed change device 2, and to distribute said rotational power 
both to the rear wheels of the vehicle taken as a combination and also to 
the front wheels of the vehicle taken as a combination. This is the four 
whel drive operational mode. And intermediate modes of operation of the 
four wheel drive power transfer device 3 are available according to 
intermediate degrees of rotational coupling together of the through shaft 
49 and the sleeve shaped intermediate front wheel drive shaft 16, by 
appropriate control thereof exerted by the transmission control device 35 
as explained above. 
The Transmission Control System 
The following detectors and sensors are provided to this system (vide FIG. 
1). A road speed sensor 36 detects a value representative of the road 
speed of the vehicle by measuring the rotational speed of the through 
shaft 49, and outputs an electrical signal representative thereof. A 
throttle position sensor 37 detects a value representative of the current 
load on the internal combustion engine 1 by measuring the opening angle of 
the throttle valve (not particularly shown) of a carburetor (not shown 
either) of said engine 1, and outputs an electrical signal representative 
thereof. (However, in other constructions other forms of load sensor could 
be used in place of this throttle position sensor 37). A set range sensor 
38 detects the set position of the previously mentioned manual range 
setting device such as a range setting valve or the like which is provided 
for the transmission mechanism 2, and outputs an electrical signal 
representative thereof. And a manually operated 2WD/4WD select switch 39 
is provided in the passenger compartment of the vehicle so as to be 
readily accessible to the driver of the vehicle, and can be set to either 
or two positions, a first position for indicating that the vehicle is to 
be operated in two wheel drive mode, i.e. that the four wheel drive power 
transfer device 3 is to be set to provide only rotational power to the 
rear wheel propeller shaft 24 and not to the front wheel power output 
shaft 17, and a second position for indicating that the vehicle is to be 
operated in four wheel drive mode, i.e. that the four wheel drive power 
transfer device 3 is to be set to provide rotational power both to the 
rear wheel propeller shaft 24 and also to the front wheel power output 
shaft 17. The output signals of these four sensors and switches 36, 37, 
38, and 39 are fed to a transmission control device 35, previously 
mentioned. 
This transmission control device 35 outputs control signals for controlling 
the electric/hydraulic control device 22 for the four wheel drive power 
transfer device 3 and the electrical/hydraulic control mechanism 9 for the 
gear transmission mechanism 7, as will now be explained. No concrete 
illustration of the structure of any particular realization of the 
transmission control device 35 will be given herein, since various 
possibilities for the details thereof can be easily supplemented by one of 
ordinary skill in the electronic art based upon the functional disclosures 
set out in this specification. In the various preferred embodiments of the 
anti torque shock control device of the present invention, in each case, 
the transmission control device 35 is typically concretely realized as a 
micro computer and its associated circuitry, said micro computer operating 
at the behest of a control program, various ones of which will be 
partially detailed shortly. However, it should be particularly understood 
that such realizations in the micro computer form, although preferred, are 
not the only ways in which the transmission control device 35 can be 
provided; in other possible embodiments it could be constituted as an 
electrical device not incorporating a micro procssor, or indeed it could 
be a purely hydraulic device. In the preferred case, however, such a micro 
processor will typically comprise: a CPU (central processing unit) which 
obeys said control program to be described shortly and which inputs data, 
performs calculations, and outputs data; a ROM (read only memory) which 
stores said program to be described shortly and initialization data 
therefor and so on; and a RAM (random access memory) which stores the 
results of certain intermediate calculations and data and so on; and these 
devices together will constitute a logical calculation circuit, being 
joined together by a common bus which also links them to an input port and 
an output port which together perform input and output for the system. And 
the system will typically also include buffers for the electrical signals 
outputted from the various sensors and switches 36 through 39 to the input 
port device, and drive circuits through which actuating electrical signals 
are passed from the output port device to a speed change control solenoid 
or solenoids (not particularly shown in the figures) of the 
electrical/hydraulic control mechanism 9 for controlling the automatic 
speed change device 2 and to the control solenoid 57 of the 
electric/hydraulic control device 22 for controlling the four wheel drive 
power transfer device 3. 
The First Preferred Embodiments 
Now, in FIG. 3, a fragmentary flow chart is shown for a portion of the 
aforementioned control program which directs the operation of the 
transmission control device 35, according to the first preferred 
embodiment of the anti torque shock control method of the present 
invention, so as to realize the first preferred embodiment of the anti 
torque shock control device of the present invention. This flow chart will 
now be explained. It should be understood that the transmission control 
device 35 generally functions so as to engage an appropriate one of the 
various speed stages of the gear transmission mechanism 7 of the 
transmission mechanism 2 according to the current values of various 
vehicle operating parameters such as the vehicle road speed as sensed by 
the vehicle road speed sensor 36, the engine load (throttle opening) as 
sensed by the throttle position sensor 37, and the operating range of the 
transmission as manually set by the vehicle driver on the setting means 
therefor as sensed by the set range sensor 38; such a function may be 
performed in a per se conventional way, and no particular program therefor 
is shown or suggested in this specification, since various possibilities 
for the details thereof can be easily supplemented as appropriate by one 
of ordinary skill in the transmission control and the programming arts, 
particularly when based upon the functional disclosures set out in this 
specification. The flow chart of FIG. 3 only shows the portion of the 
control program of the transmission control device 35 which controls the 
clutch 50 of the four wheel drive power transfer device 3, i.e. only shows 
the anti torque shock control routine of the transmission control device 
35, which controls the supply of actuating electrical energy to the 
solenoid 57 of the electric/hydraulic control device 22. This program 
portion is executed at regular intervals of for example a few 
milliseconds, of course after the engine 1 is started as the four wheel 
drive vehicle incorporating it is driven. In summary: when the selected 
range for the operation of the automatic speed change device 2, as 
indicated by the set range sensor 38, is a drive range, i.e. typically is 
the "D" range, the "S" range, the "L" range, or the "R" range, then this 
transmission control device 35 controls the supply of actuating electrical 
energy to the solenoid 57 of the electric/hydraulic control device 22 to 
be ON or OFF, according respectively as to whether or not the manually 
operated 2WD/4WD select switch 39 is switched to its position indicating 
four wheel drive operation; with the added feature, particularly according 
to the concept of the present invention, that said transmission control 
device 35 controls the supply of actuating electrical energy to said 
solenoid 57 of said electric/hydraulic control device 22 to be ON, 
irrespective of the setting of said manually operated 2WD/4WD select 
switch 39, while the selected range for the operation of the automatic 
speed change device 2, as indicated by the set range sensor 38, is a non 
drive range, i.e. typically is the "P" range or the "N" range, and also 
for a certain determinate time period after said selected range for the 
operation of the automatic speed change device 2 has altered from being a 
non drive range such as typically the "P" range or the "N" range, to being 
a drive range such as typically the "D" range, the "S" range, the "L" 
range, or the "R" range. 
Thus, in this anti torque shock control routine, at its beginning in its 
first decision step 50, said micro processor makes a decision as to 
whether or not the currently set range for the automatic speed change 
device 2, as determined from the output signal of the set range sensor 38 
therefor, is a non drive operational range, or not. Typically, as 
mentioned above, such a non drive range will be either the "P" range or 
the "N" range. If the answer to this decision is YES, so that in fact the 
currently engaged operational range for said automatic speed change device 
2 is a non drive operational range, then next the flow of control passes 
to the decision step 51. On the other hand, if the answer to this decision 
is NO, so that in fact the currently engaged operational range for said 
automatic speed change device 2 is not a non drive operational range and 
hence must be a drive operational range such as "D" range, "S" range, "L" 
range, or "R" range, then next the flow of control passes to the decision 
step 54. 
In the decision step 51, the micro processor makes a decision as to whether 
or not the current value of vehicle road speed, as indicated by the road 
speed sensor 36, is less than a determinate road speed value Vset, which 
is set to be a very low value, so that, effectively, this decision step 
tests as to whether or not the vehicle is substantially at rest. If the 
answer to this decision is YES, so that in fact the current value of 
vehicle road speed is less than said determinate road speed value Vset and 
the vehicle is substantially at rest, then next the flow of control passes 
to the step 52. On the other hand, if the answer to this decision is NO, 
so that in fact the current value of vehicle road speed is greater than 
said determinate road speed value Vset and the vehicle is not 
substantially at rest, then next the flow of control passes to the 
decision step 59. 
In the step 52, at which program point it has been established that the 
vehicle is substantially at rest and the automatic speed change device 2 
is being operated in a non drive range, the value of a flag F1 is set to 
unity. And then next the flow of control passes to the step 53. 
In this step 53, the micro processor outputs an appropriate control signal 
to the electric/hydraulic control device 22, i.e. energizes the solenoid 
57, so as to ensure that the wet clutch 50 of the four wheel drive power 
transfer device 3 is engaged by supply of line pressure to the actuating 
pressure chamber 51 thereof. Thus full four wheel drive operation is 
provided, and both the rear wheels of the vehicle and also the front 
wheels of the vehicle are together connected to any output power which may 
be being provided from the automatic speed change device 2. And then next 
the flow of control passes to leave this routine, without doing anything 
further. 
On the other hand, if the currently set range for the automatic speed 
change device 2, as determined in the decision step 50 from the output 
signal of the set range sensor 38 therefor, is not a non drive operational 
range, then next, in the decision step 54, the micro processor makes a 
decision as to whether or not the value of the flag F1 is unity. If the 
answer to this decision is YES, so that in fact F1=1, then next the flow 
of control passes to the decision step 55. On the other hand, if the 
answer to this decision is NO, so that in fact F1=0, then the flow of 
control skips to pass next to the decision step 59, which is also the 
point to which the flow of control was passed in the NO branch from the 
decision step 51. 
In the decision step 55, at which point it is determined that the currently 
set range for the automatic speed change device 2 is a drive operational 
range and also the vehicle speed is below the determinate value Vset 
therefor, the micro processor makes a decision as to whether or not the 
value of a flag F2 is unity. This flag F2 is used for showing whether or 
not a timer has been started. If the answer to this decision is YES, so 
that in fact the value of said flag F2 is unity and said timer has been 
already started, then the flow of control skips to pass next to the 
decision step 57. On the other hand, if the answer to this decision is NO, 
so that in fact the value of said flag F2 is zero and said timer has not 
yet been started, then next the flow of control passes to the step 56. 
In the step 56, the micro processor starts the aforementioned timer, and 
also sets the value of the flag F2 to unity, to indicate that said timer 
has been started. And then next the flow of control passes to the decision 
step 57. 
In this decision step 57, the micro processor makes a decision as to 
whether or not the time interval currently counted by the timer has 
exceeded a certain determinate time interval Tset. If the answer to this 
decision is YES, so that in fact the timed interval has indeed exceeded 
said determinate time interval Tset, then next the flow of control passes 
to the step 58. On the other hand, if the answer to this decision is NO, 
so that in fact the timed interval has not yet exceeded said determinate 
time interval Tset, then next the flow of control passes to the step 53, 
in which, as before, the clutch 50 of the four wheel drive power transfer 
device 3 is engaged by supply of line pressure to the actuating pressure 
chamber 51 thereof, so as to cause full four wheel drive operation to be 
provided, so that both the rear wheels of the vehicle and also the front 
wheels of the vehicle are together connected to the output power provided 
from the automatic speed change device 2. 
On the other hand, in the step 58, at which point it is determined that the 
determinate time interval Tset has been timed by the timer. i.e. that said 
determinate time interval Tset has elapsed since shifting the set 
operational range of the automatic speed change device 2 as detected by 
the set range sensor 38 from a non drive range select position to a drive 
range select position, the micro processor sets the values of the flags F1 
and F2 both to zero, and also resets the timer. And then next the flow of 
control passes to the decision step 59. 
In this decision step 59, the micro processor makes a decision as to 
whether or not the manually operated 2WD/4WD select switch 39 is set to 
its position indicating four wheel drive vehicle operation. If the answer 
to this decision is YES, so that in fact four wheel drive operation is 
currently selected, then next the flow of control passes to the step 53, 
as before, and definitely four wheel drive vehicle operation is performed. 
On the other hand, if the answer to this decision is NO, so that in fact 
two wheel drive operation of the vehicle is currently desired, then next 
the flow of control passes to the step 60. 
In this step 60, the micro processor outputs an appropriate control signal 
to the electric/hydraulic control device 22, i.e. deenergizes the solenoid 
57, so as to ensure that the wet clutch 50 of the four wheel drive power 
transfer device 3 is disengaged according to non supply of line pressure 
to the actuating pressure chamber 51 thereof. Thus two wheel drive 
operation is provided, and only the rear wheels of the vehicle but not the 
front wheels of the vehicle are connected to any output power which may be 
being provided from the automatic speed change device 2. And then next the 
flow of control passes to leave this routine, without doing anything 
further. 
And, by the repetition of the FIG. 3 program in a relatively tight and 
quick cycle with a period of the order of milliseconds, the control of the 
clutch 50 of the four wheel drive power transfer device 3 is maintained. 
Thus, according to this mode of control according to these first preferred 
embodiments of the anti torque shock control method and device of the 
present invention, when the operational range of the automatic speed 
change device 2 is switched from a non drive range such as "P" range or 
"N" range to a drive range such as "D" or "R" range, in fact by the 
vehicle driver manually actuating the manual setting means therefor and 
thereby actuating the set range sensor 38 to provide an indication 
thereof, at this time, for a certain time period Tset and irrespective of 
the current setting of the manually operated 2WD/4WD select switch 39, the 
clutch 50 of the four wheel drive power transfer device 3 is definitely 
engaged, so as at least for this short time period Tset to definitely 
provide four wheel drive operation of the vehicle; and this prevents the 
occurrence of any large drive train torque shock upon this shifting of the 
operational range of the automatic speed change device 2 from a non drive 
range such as "P" range or "N" range to a drive range such as "D" or "R" 
range. Accordingly, the reliability and the life span of the drive train 
as a whole of the vehicle are desirably extended. Furthermore, the 
emission of any unpleasant noise such as "clonking" during this engagement 
of a transmission drive range from a non drive range is positively 
avoided, and further vehicle squat during such an operation, which might 
occur if two wheel drive operational mode of the vehicle were being 
provided at this time due to the powering up of the rear wheels of the 
vehicle while the front vehicle wheels were not powered up, is definitely 
prevented. 
In the shown type of normal operation of the four wheel drive power 
transfer device 3, in this exemplary application of the anti torque shock 
control device of the present invention, said four wheel drive power 
transfer device 3 was manually switched by the vehicle operator between 
its two wheel drive operational mode and its four wheel drive operational 
mode, according to control by the manually operated 2WD/4WD select switch 
39. However, in an alternative application, it might be possible for said 
selection between two wheel drive operation and four wheel drive 
operation, in other words for the control of the wet clutch 50 of the four 
wheel drive power transfer device 3, to be performed automatically 
according to a control method and device therefor, for example according 
to the difference between the rotational speed of the front vehicle wheels 
and the rotational speed of the rear vehicle wheels, and/or according to 
the load on the internal combustion engine 1, and/or according to the 
steering angle of the steering system (not particularly shown) of the 
vehicle, and/or according to the braking situation of the vehicle, and/or 
the like. In such a case, according to the present invention, similarly to 
the above described operation, when the operational range of the automatic 
speed change device 2 is switched from a non drive range such as "P" range 
or "N" range to a drive range such as "D" or "R" range, at this time for a 
certain time period Tset and irrespective of any such otherwise determined 
current control state for selecting between two wheel drive and four wheel 
drive transmission operation, the clutch 50 of the four wheel drive power 
transfer device 3 should be definitely engaged, so as at least for this 
short time period Tset to definiately provide four wheel drive operation 
of the vehicle. The same benefits and advantages would be available, in 
such a case, as detailed above with regard to the first preferred 
embodiment of the anti torque shock control device of the present 
invention as shown in FIGS. 1 through 3; accordingly, intimate details 
thereof will not be particularly descanted upon. 
The Second Power Train and the Second Preferred Embodiments 
It should be noted that the merit of the present invention with regard to 
anti torque shock control relates generally to the rotational coupling 
together of two at least of the wheels of the vehicle to which said 
present invention is provided, and is not to be considered as being 
specifically limited to the selective operation of such a four wheel drive 
power transfer device as the four wheel drive power transfer device 3 of 
the shown application of the first preferred embodiments of the anti 
torque shock control method and device of the present invention as 
described above, in order to swtich said four wheel drive power transfer 
device between the two wheel drive operational mode and the four wheel 
drive operational mode; such an application is merely a specialized use of 
the principle of the present invention. In the next preferred embodiments 
of the anti torque shock control method and device of the present 
invention, there is exemplarily shown the control of a differential 
control clutch which controls a central differential device of a full time 
four wheel drive transmission system either to provide, or not to provide, 
its differential action. This is another application of the principle of 
the present invention. 
In detail then, in FIG. 4 which is similar to FIG. 1 relating to the first 
preferred embodiments there is shown a schematic longitudinal skeleton 
view of a vehicle power train and of a control system therefor, which 
incorporates the second preferred embodiment of the anti torque shock 
control device of the present invention, for practicing the second 
preferred method embodiment. In this figure, parts which are like to parts 
shown in FIG. 1 are denoted by the same reference numerals. In this second 
preferred embodiment, the difference with regard to the power train of the 
vehicle is that the four wheel drive power transfer device 3, rather than 
being a simple device incorporating substantially only a clutch as was the 
four wheel drive power transfer device 3 of the application of the first 
preferred embodiments described above, instead incorporates a center 
differential device 10 of a planetary gear wheel type for providing full 
time differential action between the front wheels of the vehicle and the 
rear wheels of the vehicle during the full time four wheel drive operation 
thereof. And the difference relating to the control system is that the 
switch 39, rather than being a manually operated 2WD/4WD select switch 39 
as in the case of the FIG. 1 construction, is now a center differential 
lock/unlock switch. Now the detailed construction of this center 
differential device 10 will be explained; in this connection, the through 
shaft 49, which was provided in the FIG. 1 construction, here on the other 
hand is no longer provided. The center differential device 10 comprises a 
sun gear 13, a ring gear 14, a carrier 11, and a plurality of planetary 
pinions 12 rotatably mounted to said carrier 11 and meshed between the sun 
gear 13 and the ring gear 14 and performing planetary movement between 
them in a per se known manner. The carrier 11 functions as an input member 
for this center differential device 10, and is rotationally connected to 
the output shaft of the gear transmission mechanism 7 via a shaft which 
passes through the central axis of the hollow sun gear 13. The ring gear 
14 functions as one power output member for the center differential device 
10 for supplying power to the rear wheels of the vehicle, and is 
rotationally connected to a rear wheel power output shaft 15 which extends 
out of the four wheel drive power transfer device 3 in the direction to 
the left as seen in FIG. 1, i.e. towards the rear of the vehicle in this 
particular exemplary implementation. The rear end of this rear wheel power 
output shaft 15 is connected via the universal joint 23 to the rear wheels 
propeller shaft 24 to drive the rear vehicle wheels. And the sun gear 13 
functions as another power output member for the center differential 
device 10 for supplying power to the front wheels of the vehicle, and is 
rotationally connected to a sleeve shaped intermediate front wheel drive 
shaft 16, which corresponds to the front wheel drive shaft 16 of the FIG. 
1 application for the first preferred embodiments, via a drum member 
fitted around the center differential device 10 as a whole. 
Thus, the power distribution ratio (drive torque distribution) between the 
intermediate front wheel drive shaft 16 and the rear wheel power output 
shaft 15, when this four wheel drive power transfer device 3 is operating, 
is determined by the relative tooth counts of the sun gear 13 and the rear 
gear 14 in the following manner: 
EQU Rr=1/(1+Rg) 
EQU Rf=Rg(1+Rg) 
where: 
Rr is the rear wheel distribution ratio; 
Rf is the front wheel distribution ratio: 
and Rg is the ratio of the number of teeth on the sun gear 13 to the number 
of teeth on the ring gear 14. 
Because the number of teeth on the sun gear 13 is naturally greater than 
the number of teeth on the ring gear 14, thus, providing that the number 
of teeth on the sprocket wheel 18 and the number of teeth on the sprocket 
wheel 20 are the same, this four wheel drive power tranfer device 3 is of 
the type which distributes a larger amount of torque to the rear vehicle 
wheels than to the front vehicle wheels. 
Further, within the four wheel drive power transfer device 3 there is 
provided a hydraulically operated wet type multi plate type clutch 21, 
which selectively either rotationally connects together the sun gear 13 
and the ring gear 14 (actually the ring gear 14 is selectively 
rotationally connected by the clutch 21 to the drum member enclosing the 
whole planetary gear apparatus, which is rotationally connected to said 
sun gear 13), or alternatively allows said members to rotate freely with 
respect to one another. This wet clutch 21 is selectively operated by an 
electrically actuated electric/hydraulic control device 22, corresponding 
to the electric/hydraulic control device 22 of the FIG. 1 application of 
the first preferred embodiments. Accordingly, the four wheel drive power 
transfer device 3, which receives rotational power input from the gear 
transmission mechanism 7 and outputs said rotational power to the rear 
wheel power output shaft 15 and to the front wheel power output shaft 17, 
can be caused either to provide differential action for distributing said 
rotational power between said rear wheel power output shaft 15 and said 
front wheel power output shaft 17, or not to provide any such differential 
action and just to drive said shafts 15 and 17 independently, by selective 
engagement or non engagement of said clutch 21, which may be operated by a 
system like the FIG. 2 clutch operating system. In detail, when hydraulic 
pressure of at least a determinate pressure level is supplied to the 
pressure chamber of the clutch 21, said 21 is engaged, thereby 
rotationally coupling together the sun gear 13 and the ring gear 14, and 
thereby stopping the differential action of the central differential 
device 10 of the four wheel drive power transfer device 3. In this case, 
the center differential device 10 functions so as to provide no 
differential effect between the rear wheel power output shaft 15 and the 
intermediate front wheel drive shaft 17, i.e. so as to distribute the 
rotational power provided from the engine 1 via the automatic speed change 
device 2 directly to the rear wheels of the vehicle taken as a combination 
and also to the front wheels of the vehicle taken as a combination in an 
even fashion without any provision of any differential effect. On the 
other hand, when no such hydraulic pressure is supplied to the pressure 
chamber of said clutch 21, said clutch 21 is disengaged, thereby 
rotationally decoupling the sun gear 13 and the ring gear 14 and allowing 
them to rotate substantially independently, and thereby the central 
differential device 10 of the four wheel drive power transfer device 3 is 
allowed to perform differential action without substantial impediment 
thereof. In this case, the center differential device 10 functions so as 
to provide its differential effect between the rear wheel power output 
shaft 15 and the intermediate front wheel drive shaft 17, i.e. so as to 
receive rotational power provided by the engine 1 of the vehicle and 
transmitted to said four wheel drive power transfer device 3 via the 
automatic speed change device 2, and to distribute said rotational power 
between the rear wheels of the vehicle taken as a combination and the 
front wheels of the vehicle taken as a combination. Accordingly, in this 
case, the power distribution (torque distribution) ratio between the front 
wheels of the vehicle and the rear wheels of the vehicle is determined, 
when the four wheel drive power transfer device 3 is operating in the 
above mode, by the ratio of the tooth counts of the sun gear 13 and the 
ring gear 14, as explained above. 
This vehicle power train may be operated, according to the second preferred 
embodiments of the anti torque shock control method and device of the 
present invention, according to the FIG. 3 flow chart (with mutatis 
mutandis in a per se obvious fashion regarding the center differential 
lock/unlock switch 39). In this case, when the clutch 21 of the four wheel 
drive power transfer device 3 is operated by the transmission control 
device 35 so as not to rotationally connect together the sun gear 13 and 
the ring gear 14, then, when the operational range of the automatic speed 
change device 2 comes to be switched from a non drive range such as "P" 
range or "N" range to a drive range such as "D" or "R" range by the 
vehicle driver manually actuating the manual setting means therefor and 
thereby actuaing the set range sensor 38 to provide an indication thereof, 
then, starting at this time and for a certain time period Tset thereafter, 
and irrespective of the current setting of the center differential 
lock/unlock switch 39, the clutch 50 of the four wheel drive power 
transfer device 3 is definitely engaged, so as at least during this 
relatively short time period Tset to definitely prevent central 
differential device operation during the four wheel drive operation of the 
vehicle; and this prevents the occurrence of any large drive train torque 
shock upon this shifting of the operational range of the automatic speed 
change device 2 from a non drive range such as "P" range or "N" range to a 
drive range such as "D" or "R" range, and prevents the shift shock being 
preferentially suffered by one of the front and rear differential devices 
of the vehicle (in this shown exemplary case it would be the rear 
differential device that would suffer more than the front differential 
device). Further, the ill effects that might occur due to slack in one 
only of the differential devices of the vehicle are mitigated. 
Accordingly, the reliability and the life span of the drive train as a 
whole of the vehicle are desirably extended. Furthermore, the emission of 
any unpleasant noise such as "clonking" during this engagement of a 
transmission drive range from a non drive range is positively avoided, and 
further vehicle squat during such an operation, which might occur if the 
central differential device effective operarational mode of the vehicle 
were being provided at this time due to the differential powering up of 
the rear wheels of the vehicle as opposed to the front vehicle wheels, is 
definitely prevented. 
Again, in a possible alternative application, it might be possible for said 
selection between central differential device operation and non operation, 
in other words for the usual method of control of the wet clutch 50 of the 
four wheel drive power transfer device 3, to be performed automatically 
according to a control method and device therefor, rather than by the 
manually controlled operation of the center differential lock/unlock 
switch 39 as suggested above. In such a case, according to the present 
invention, similarly to the above described operation, when the 
operational range of the automatic speed change device 2 is switched from 
a non drive range such as "P" range or "N" range to a drive range such as 
"D" or "R" range, at this time for a certain time period Tset and 
irrespective of any such otherwise determined current control state for 
selecting between central differential device operation and non operation, 
the clutch 50 of the four wheel drive power transfer device 3 should be 
definitely engaged, so as at least for this short time period Tset to 
definitely provide no central differential device operation of the 
vehicle. The same benefits and advantages would be available, in such a 
case, as detailed above with regard to the second preferred embodiment of 
the anti torque shock control device of the present invention as shown in 
FIGS. 1 through 3 and discussed above; accordingly, the details thereof 
will not be particularly discussed herein, in view of the desirability of 
conciseness of disclosure. 
Third Exemplary Overall Vehicle Power Train Structure 
FIG. 5 is a schematic longitudinal skeleton view of a vehicle power train 
which incorporates the third preferred embodiment of the anti torque shock 
control device of the present invention, said device performing the third 
method embodiment. In this figure, the reference numeral 60 denotes an 
internal combustion engine of said vehicle, which is mounted, in this 
third exemplary case, transversely in the front engine room (not 
particularly shown) of said vehicle. And the reference numeral 61 denotes 
an automatic speed change device (automatic transmission) of a per se 
known type, while 62 denotes a four wheel drive power transfer device 
which is always operating in so called full time four wheel drive mode, so 
as always to drive both the rear pair of wheels of the vehicle and also 
the front pair of wheels of the vehicle, albeit with the differential 
action provided by this four wheel drive power transfer device 62 being 
selectably either provided or not provided as will be explained in detail 
hereinafter. And the reference numeral 91 denotes a front differential 
device, the differential action provided by which between the two front 
vehicle wheels being also selectably either provided or not provided as 
will be explained in detail hereinafter. 
In more detail, the automatic speed change device 61 incorporates a fluid 
torque converter 63 ofa per se known construction, and the power input 
shaft 60a of this fluid torque converter 63 is connected to and receives 
rotational power from a crank shaft of the internal combustion engine 60. 
And the fluid torque converter 63 comprises a pump impeller member 63a and 
a turbine member 63b, as is per se conventional, while the automatic speed 
change device 61 may, in this case, be a per se conventional type of 
planetary wheel speed change device which incorporates various planetary 
gear mechanisms and which according to selective supply of actuating 
hydraulic fluid pressures to various friction engaging mechanisms 
incorporated in it provides one of various different gearing ratios 
including several forward speed stages and at least one reverse speed 
stage between its power input shaft and its power output shaft. And an 
input shaft of the automatic speed change device 61 is connected to and 
receives rotational power from the power output shaft of the fluid torque 
converter 63; and thereby the automatic speed change device 61 receives 
rotational power from the internal combustion engine 60, with a certain 
degree of slippage and also torque amplification being provided for said 
rotational power by the fluid torque converter 63 (unless a lock up clutch 
thereof, if provided thereto, is activated) as is per se conventional. 
This switching over of speed stages of the automatic speed change device 
61 is controlled by a per se known type of electrically controlled 
electric/hydraulic control mechanism 70. And the automatic speed change 
device 61 has a power output gear pinion 65 to which it supplies output 
rotational power. 
The four wheel drive power transfer device 62 incorporates a center 
differential device 80 of a bevel gear wheel type for providing full time 
differential action between the front wheels of the vehicle and the rear 
wheels of the vehicle during the full time four wheel drive operation 
thereof. Now the detailed construction of this center differential device 
80 will be explained. It comprises a differential case 82 which is 
provided integrally with a power input gear wheel 81 which is meshed with 
the aforementioned output gear pinion 65, and to this differential case 82 
there are rotatably mounted by two pinion shafts 83 two differential 
pinions 84 which directly oppose one another. On the right as seen in the 
figure there is provided a rear wheel power output gear wheel 85 which is 
meshed with both of these differential pinions 84, and similarly on the 
left as seen in the figure there is provided a front wheel power output 
gear wheel 86 which is likewise meshed with both of the differential 
pinions 84. 
To the rear wheel power output gear wheel 85 there is connected a rear 
wheel output side gear wheel 78, and a rear wheel drive gear wheel 89 is 
meshed with this rear wheel output side gear wheel 87 and drives a rear 
wheel drive shaft 88. This rear wheel drive shaft 88 rotationally drives 
the front end of the rear wheel propeller shaft (not particularly shown) 
the rear end of which rotationally drives a power input shaft of a rear 
wheels differential device (not particularly shown either) for driving the 
rear wheels (also not shown) of the vehicle. 
Further, to the front wheel power output gear wheel 86 there is connected 
the end of a tubular front wheel drive shaft 90 which rotationally drives 
the differential case 92 of a front wheels differential device 91 of a 
bevel gear wheel type for providing differential action between the front 
wheels of the vehicle. Now the detailed construction of this front wheels 
differential device 91 will be explained. It comprises said differential 
case 92, and to this differential case 92 there are rotatably mounted by 
two pinions shafts 93 two differential pinions 94 which directly oppose 
one another. On the left as seen in the figure there is provided a left 
front wheel power output gear wheel 96 which is meshed with both of these 
differential pinions 94, and similarly on the right as seen in the figure 
there is provided a right front wheel power output gear wheel 95 which is 
likewise meshed with both of the differential pinions 94. The left front 
wheel power output gear wheel 96 rotationally drives a left front wheel 
drive shaft 98 which leads to the left front wheel of the vehicle (not 
particularly shown) to drive it, and similarly the right front wheel power 
output gear wheel 95 rotationally drives a right front wheel drive shaft 
97 which passes through the center of the center differential device 80 
and then leads to the right front wheel of the vehicle (not particularly 
shown either) to drive it. 
Further, within the four wheel drive power transfer device 62 there is 
provided a hydraulically operated wet type multi plate type clutch 100, 
which selectively either rotationally connects together, in this second 
exemplary case, the differential casing 82 which is the rotational power 
input member of the center differential device 80 and the tubular front 
wheel drive shaft 90, or alternatively allows said members to rotate 
freely with respect to one another. This wet clutch 100 is selectively 
operated by an electrically actuated electric/ hydraulic control device 
120, and, according to this operation, said four wheel drive power 
transfer device 62, which receives rotational power input from the 
automatic speed change device 64 and outputs said rotational power to the 
rear wheel power output shaft 88 and to the front wheel power output shaft 
90, can be caused either to provide differential action for distributing 
said rotational power between said rear wheel power output shaft 88 and 
said front wheel power output shaft 90, or not to provide any such 
differential action and just to drive said shafts 88 and 90 independently, 
or to function in an intermediate mode of providing a certain degree of 
said differential action albeit somewhat impeded. 
The Hydraulic Clutch 100 
Now, this clutch 100 of the central differential device 80 of the four 
wheel drive power transfer device 62 and its actuation and control system 
120 will be explained, with reference to FIG. 6 which is a schematic 
partial sectional view of said clutch 100; and in this figure there is 
further shown in block diagram form the actuation and control system for 
said clutch 100. In this figure, the reference numerals 21a and 21b denote 
two sets of clutch plates of said clutch 100, said clutch plate sets 21a 
and 21b being sandwiched together with the one 21a of said clutch plate 
sets being rotationally coupled to one of said differential casing 82 and 
said shaft 90 while the other 21b of said clutch plate sets is 
rotationally coupled to the other of said differential casing 82 and said 
shaft 90. Each of these clutch plates is in fact formed as a circularly 
symmetric flat annulus of which only a half section can be seen in FIG. 6. 
Similarly, a generally symmetric actuator is designated as 110, and this 
actuator 110 comprises an outer cylinder bore 110a and an inner cylinder 
bore 110b which cooperate to define a toroidal cylindrical space between 
them; these outer and inner cylinder bores 110a and 110b are formed in 
some member which rotates with one of the differential casing 92 and the 
shaft 90. And an annular piston member 112 is fitted in said toroidal 
space, with its outer cylinder surface sliding in the outer cylinder bore 
110a with a sealing ring 110a interposed therebetween, and with its inner 
cylindrical surface sliding in the inner cylinder bore 110b with a sealing 
ring 110b interposed therebetween. Thereby, a hydraulic pressure chamber 
111 is defined to the left of the piston member 112 in FIG. 6, between it 
and an end of the toroidal cylindrical space between the outer cylinder 
bore 110a and the inner cylinder bore 110b, with a surface designated as 
112c of the piston member 112 serving to partly define said pressure 
chamber 111. The opposite side of the piston member 112 from the surface 
112c thereof is formed with a pair of longitudinally raised circular ribs 
112d, and these ribs 112d are positioned so as to confront the superposed 
sandwich of the clutch plate sets 21a and 21b. And the piston member 112 
is biased in the leftwards direction as seen in the figure, so as to 
reduce the volume of the pressure chamber 111, by an annular compression 
spring 113 which bears against an annular member 114 fitted to the inner 
cylinder bore 110 b. 
Thus, when hydraulic pressure of a particular pressure level is supplied to 
the pressure chamber 111, the piston member 112 is driven in the 
rightwards direction as seen in the figure against the biasing action of 
the compression spring 113 which is overcome, so that the raised circular 
ribs 112d press against the superposed sandwich of the clutch plate sets 
21a and 21b, and this causes said clutch plate sets 21a and 21b to be 
rotationally coupled together, thereby rotationally coupling together the 
differential casing 82 and the shaft 90. Further, the degree of rotational 
coupling together of said differential casing 82 and said shaft 90 is 
determined by the magnitude of the pressure level supplied to said 
pressure chamber 111, with a roughly linear proportionality obtaining 
therebetween; and thereby the differential action of the central 
differential device 80 of the four wheel drive power transfer device 62 is 
impeded by an amount corresponding to the pressure level supplied to said 
pressure chamber 111. On the other hand, when no such hydraulic pressure 
is supplied to the pressure chamber 111, the piston member 112 is biased 
by the biasing action of the compression spring 113 in the leftwards 
direction as seen in the figure, so that the raised circular ribs 112d 
release the superposed sandwich of the clutch plate sets 21a and 21b, and 
this causes said clutch plate sets 21a and 21b to be rotationally 
decoupled from one another, thereby rotationally decoupling the 
differential casing 82 and the shaft 90 from one another and allowing them 
to rotate substantially independently; and thereby the central 
differential device 80 of the four wheel drive power transfer device 62 is 
allowed to perform differential action without substantial impediment 
thereof. 
Hydraulic fluid pressure of any desired pressure level within a certain 
range is supplied to the pressure chamber 111 of this hydraulic actuator 
110 by the following arrangements. A hydraulic fluid pump 71 picks up 
hydraulic fluid from a sump of the transmission system and pressurizes it. 
This pressurized hydraulic fluid is then supplied to a pressure regulator 
valve 121 of a per se known sort which regulates its pressure to a 
determinate line pressure value. This line pressure is then fed to a port 
designated as "b" of an electromagnetically actuated hydraulic fluid 
switching valve 122. This electromagnetically actuated hydraulic fluid 
switching valve 122 is of a per set known type, and has in all three 
ports, designated as "a", "b", and "c": when actuating electrical energy 
is supplied to a solenoid or the like (not particularly shown) of said 
electromagnetically actuated hydraulic fluid switching valve 122, then the 
port "a" thereof is communicated to the port "b" thereof while the port 
"c" thereof is communicated to no other port; while, on the other hand, 
when no such actuating electrical energy is supplied to said solenoid or 
the like of said electromagnetically actuated hydraulic fluid switching 
valve 122, then the port "a" thereof is communicated to the port "c" 
thereof while the port "b" thereof is communicated to no other port. The 
port "a" of this electromagnetically actuated hydraulic fluid switching 
valve 122 is communicated to the pressure chamber 111 of the hydraulic 
actuator 110, while on the other hand the port "c" of said 
electromagnetically actuated hydraulic fluid switching valve 122 is 
communicated to a hydraulic fluid drain. 
The electromagnetically actuated hydraulic fluid switching valve 122 is 
supplied, from a transmission control device 130 which will be discussed 
shortly, with a pulsed electrical signal. According to the duty ratio of 
this pulsed electrical signal, the ON/OFF duty factor of the 
electromagnetically actuated hydraulic fluid switching valve 122 is 
determined. when the pulsed electrical signal is in the ON state, then the 
port "a" of the electromagnetically actuated hdyraulic fluid switching 
valve 122 is communicated to the port "b" thereof and is thus supplied 
with hydraulic fluid pressurized to line pressure level, while, on the 
other hand, when the pulsed electrical signal is in the OFF state, then 
the port "a" of the electromagnetically actuated hydraulic fluid switching 
valve 122 is communicated to the port "c" thereof and is thus drained. 
Therefore, according to the duty ratio of the pulsed electrical signal 
supplied by the transmission control device 130, the pressure provided in 
the pressure chamber 111 of the hydraulic actuator 110 can be set to any 
pressure level between zero and line pressure level, and thereby the 
degree of rotational coupling together of the differential casing 82 and 
the shaft 90 of the central differential device 80 of the four wheel drive 
power transfer device 62 can be controlled to be any value between 
substantially zero and the substantially full rotational coupling together 
condition; and thereby the differential action of said central 
differential device 80 of said four wheel drive power transfer device 62 
can be impeded by any amount between substantially zero and substantially 
the fully impeded condition. 
The Hydraulic Clutch 105 
There is also provided a front differential control clutch 105, which is a 
similar type of device to the clutch 100 just described and may be 
structured similarly and controlled by a similar form of control system: 
as far as FIG. 5 is concerned, the block symbolizing the 
electric/hydraulic control device 120 is to be understood as embracing the 
control systems for both these clutches 100 and 105. This front 
differential control clutch 105 is provided between the differential 
casing 92 of the front differential device 91 and the right side front 
wheel power output shaft 97 thereof, and according to its selective 
operation by selective supply of actuating hydraulic fluid pressure 
selectively either locks said members together with regard to mutual 
rotation thereof, or allows said members to rotate substantially freely 
with respect to one another. Thus, this front differential control clutch 
105 either allows, or inhibits, the operation of the front differential 
device 91, according to its control by the electric/hydraulic control 
device 120. 
This vehicle power train operates in a manner which will be clear to one of 
ordinary skill in the art, based upon the discussions in this 
specification, and hence will not be further explained in view of the 
desirability of conciseness of explanation. 
The Transmission Control System and the Third Preferred Embodiments 
The following detectors and sensors are provided to this system (vide FIG. 
5). A road speed sensor 131 detects a value representative of the road 
speed of the vehicle by measuring the rotational speed of the rear wheel 
power output shaft 88 or of some other rotating member, and outputs an 
electrical signal representative thereof. A throttle position sensor 132 
detects a value representative of the current load on the internal 
combustion engine 10 by measuring the opening angle of the throttle valve 
(not particularly shown) of a carburetor (not shown either) of said engine 
60, and outputs and electrical signal representative thereof. A set range 
sensor 133 detects the set position of a manual range setting device such 
as a range setting valve or the like which is provided for the automatic 
speed change device 61, and outputs an electircal signal representative 
thereof. A 4WD transfer device input torque sensor 134 senses the torque 
that is being supplied as input torque to the four wheel drive power 
transfer device 62, and outputs an electrical signal representative 
thereof. And a manually operated 4WD transfer device lock select switch 
135 is provided in the passenger compartment of the vehicle so as to be 
readily accessible to the driver of the vehicle, and can be set to either 
or two positions, a first position for indicating that the vehicle is to 
be operated with the four wheel drive power transfer device 62 set to be 
locked up and not to provide any differential action, and a second 
position for indicating that the vehicle is to be operated with the four 
wheel drive power transfer device 62 set to be providing its differential 
action; this lock select switch 135 outputs an electircal signal 
representative of its setting. The output signals of these five sensors 
and switches 131, 132, 133, 134, and 135 are fed to the transmission 
control device 130. 
This transmission control device 130 outputs control signals for 
controlling the electric/hydraulic control device 120 for the four wheel 
drive power transfer device 14 and the front differential device 91, and 
the electrical/hydraulic control mechanism 70 for the automatic speed 
change device 64. No concrete illustration of the structure of any 
particular realization of this transmission control device 130 will be 
given herein, since various possibilities for the details thereof can be 
easily supplemented by one of ordinary skill in the electronic art based 
upon the functional disclosures set out in this specification; typically, 
said transmission control device 130 is again concretely realized as a 
micro computer and its associated circuitry, said micro computer operating 
at the behest of a control program. Functionally, this transmission 
control device 130 controls the switch over of the automatic speed change 
device 64 according to preset and prestored patterns, depending upon the 
setting of the aforementioned manually actuated range setting device for 
the vehicle, upon the current value of vehicle road speed as detected by 
the vehicle road speed sensor 131, and upon the current value of engine 
throttle opening as detected by the throttle position sensor 132. Further, 
according to the concept of the third preferred embodiments of the anti 
torque shock control device and method of the present invention, said 
transmission control device 130, when the set range sensor 133 detects 
that said aforementioned manually actuated range setting device for the 
vehicle is manually shifted from a non drive operational mode such as "P" 
range or "N" range to a drive operational mode such as "D" range, "S" 
range, "L" range, or "R" range, regardless of the current value of the 
torque that is being supplied as input torque to the four wheel drive 
power transfer device 62 as detected by the sensor 134 therefor, and 
regardless of the current position of the manually operated 4WD transfer 
device lock select switch 135, sends control signals to the 
electric/hydraulic control device 120 so as to lock up the clutch 100 for 
the four wheel drive power transfer device 62 and so as to lock up the 
front differential control clutch 105. Thereby, the same advantages as 
described above with regard to the first and second preferred embodiments 
of the anti torque shock control device and method of the present 
invention are obtained. And this locking up the clutches 100 and 105 is 
maintained over a certain time interval. After this switching over period, 
i.e. when said transmission control device 130 decides that the manually 
actuated range setting device for the vehicle has been left manually 
shifted to a drive operational mode such as "D" range, "S" range, "L" 
range, or "R" range for at least a determinate time period, then said 
transmission control device 130 controls the front differential control 
clutch 105 to be released, and further controls the electric/hydraulic 
control device 120 so as to control the torque transmission capacity of 
the clutch 100 for the four wheel drive power transfer device 62 according 
to the value of the torque that is being supplied as input torque to the 
four wheel drive power transfer device 62, and according to the setting of 
the lock select switch 135: but these matters are not strictly related to 
the present invention. 
Thus, also according to this mode of control according to these third 
preferred embodiments of the anti torque shock control method and device 
of the present invention, when the operational range of the automatic 
speed change device 64 is switched from a non drive range such as "P" 
range or "N" range to a drive range such as "D" or "R" range by the 
vehicle driver manually actuating the manual setting means therefor and 
thereby actuating the set range sensor 133 to provide an indication 
thereof, at this time, for a certain time period and irrespective of the 
current setting of the manually operated lock select switch 135, the 
clutches 100 and 105 of the four wheel drive power transfer device 62 and 
the front differential device 91 are definitely engaged, so as at least 
for this short time period to definitely provide, in particular, no 
differential action between the two front wheels of the vehicle, as well 
as no differential action between the front wheels of the vehicle and the 
rear wheels of the vehicle; and both of these actions help with preventing 
the occurrence of any large drive train torque shock upon this shifting of 
the operational range of the automatic speed change device 2 from a non 
drive range such as "P" range or "N" range to a drive range such as "D" or 
"R" range. Accordingly, as before, the reliability and the life span of 
the drive train as a whole of the vehicle are desirably extended, and 
furthermore the emission of any unpleasant noise such as "clonking", from 
either of the four wheel drive power transfer device 62 and the front 
differential device 91, during this engagement of a transmission drive 
range from a non drive range, is positively avoided. 
The Fourth Preferred Embodiments 
Next, in FIG. 7, a fragmentary flow chart is shown for a portion of the 
aforementioned control program which directs the operation of the 
transmission control device 35 of the second exemplary power train shown 
in FIG. 4, according to the fourth preferred embodiment of the anti torque 
shock control method of the present invention, so as to realize the fourth 
preferred embodiment of the anti torque shock control device of the 
present invention. This flow chart will now be explained. Again, it should 
be understood that the transmission control device 35 generally functions 
so as to engage an appropriate one of the various speed stages of the gear 
transmission mechanism 7 of the transmission mechanism 2 according to the 
current values of various vehicle operating parameters such as the vehicle 
road speed as sensed by the vehicle road speed sensor 36, the engine load 
(throttle opening) as sensed by the throttle position sensor 37, and the 
operating range of the transmission as manually set by the vehicle driver 
on the setting means therefor as sensed by the set range sensor 38, 
typically in a per se conventional way. Thus, again, the flow chart of 
FIG. 7 only shows the portion of the control program of the transmission 
control device 35 which controls the clutch 50 of the four wheel drive 
power transfer device 3. This program portion is again executed at regular 
intervals of for example a few milliseconds, of course after the engine 1 
is started as the four wheel drive vehicle incorporating it is driven. In 
summary: when the selected range for the operation of the automatic speed 
change device 2, as indicated by the set range sensor 38, is a drive 
range, i.e. typically is the "D" range, the "S" range, the "L" range, or 
the "R" range, then this transmission control device 35 controls the 
supply of actuating electrical energy to the electric/hydraulic control 
device 22 to be ON or OFF, so as to control the clutch 21 to be engaged or 
disengaged, according respectively as to whether or not the manually 
operated center differential device lock/unlock switch 39 is switched to 
its position indicating four wheel drive operation without central 
differential effect, or to its position indicating four wheel drive 
operation with central differential effect; with the added feature, 
particularly according to the concept of the present invention, that said 
transmission control device 35 controls the supply of actuating electrical 
energy to said electric/hydraulic control device 22 to be ON, so as 
definitely to lock up said clutch 21, irrespective of the setting of said 
manually operated center differential device lock/unlock switch 39, while 
the selected range for the operation of the automatic speed change device 
2, as indicated by the set range sensor 38, is a non drive range, i.e. 
typically is the "P" range or the "N" range, and also for a certain 
determinate time period after said selected range for the operation of the 
automatic speed change device 2 has altered from being a non drive range 
such as typically the "P" range or the "N" range, to being a drive range 
such as typically the "D" range, the "S" range, the "L" range, or the "R" 
range; but, if the vehicle is being suddenly started, immediately releases 
said central differential device clutch 21. 
Thus, in this anti torque shock control routine, at its beginning in its 
first decision step 100, said micro processor makes a decision as to 
whether or not the current value of vehicle road speed, as indicated by 
the road speed sensor 36, is less than a determinate road speed value 
Vset, which is set to be a very low value, so that, effectively, this 
decision step 100 tests as to whether or not the vehicle is substantially 
at rest. If the answer to this decision is YES, so that in face the 
current value of vehicle road speed is less than said determinate road 
speed value Vset and the vehicle is substantially at rest, then next the 
flow of control passes to the decision step 101. On the other hand, if the 
answer to this decision is NO, so that in fact the current value of 
vehicle road speed is greater than said determinate road speed value Vset 
and thus the vehicle is not substantially at rest, then next the flow of 
control passes to leave this program portion, without doing anything 
further; and the control steps according to the present invention are not 
applied. 
In this next decision step 101, a decision is made as to whether or not the 
currently set range for the automatic speed change device 2, as determined 
from the output signal of the set range sensor 38 therefor, is a non drive 
operational range, or not. Typically, as mentioned above, such a non drive 
range will be either the "P" range or the "N" range. If the answer to this 
decision is YES, so that in fact the currently engaged operational range 
for said automatic speed change device 2 is a non drive operational range, 
then next the flow of control passes to the decision step 102. On the 
other hand, if the answer to this decision is NO, so that in fact the 
currently engaged operational range for said automatic speed change device 
2 is not a non drive operational range and hence must be a drive 
operational range such as "D" range, "S" range, "L" range, or "R" range 
(for example), then next the flow of control passes to the decision step 
104. 
In the decision step 102, at which program point it has been established 
that the vehicle is substantially at rest and the automatic speed change 
device 2 is being operated in a non drive range, a test is made as to 
whether or not the current value of a flag F is unity. If the answer to 
this decision is YES, so that currently F=1, then the flow of control 
skips to pass next out of this program portion, without doing anything 
further; but, if the answer to this decision is NO, so that the value of F 
is not currently 1, then next the flow of control passes to the step 103. 
In this step 103, the micro processor outputs an appropriate control signal 
to the electric/hydraulic control device 22 to ensure that the clutch 21 
of the four wheel drive power transfer device 3 is engaged. Thus four 
wheel drive operation without any central differential effect is provided, 
and both the rear wheels of the vehicle and also the front wheels of the 
vehicle are independently connected to any output power which may be being 
provided from the automatic speed change device 2, with the torque being 
distributed between the front vehicle wheels and the rear vehicle wheels 
according to the current values of the loads on the front and rear vehicle 
axles, so that the torque distribution ratio is substantially equal or 
50:50. And then the value of the flag F is set to unity, and next the flow 
of control passes to leave this routine, without doing anything further. 
On the other hand, if the currently set range for the automatic speed 
change device 2, as determined in the decision step 101 from the output 
signal of the set range sensor 38 therefor, is not a non drive operational 
range, then next, in the decision step 104, the micro processor makes a 
decision as to whether or not the time interval currently counted by a 
timer since executing this step 104 has exceeded a certain determinate 
time interval Tset, for example about two seconds or so. If the answer to 
this decision is YES, so that in fact the elapsed timed interval has 
indeed exceeded said determinate time interval Tset, then next the flow of 
control passes to the decision step 105. On the other hand, if the answer 
to the dcision is NO, so that in fact the elapsed timed interval has not 
yet exceeded said determinate time interval Tset, then next the flow of 
control passes to leave this program fragment, without doing anything 
further. 
Next, in this decision step 105, at which point it is determined that the 
determine time interval Tset has in fact been timed by the timer, a test 
is made as to whether or not the vehicle is performing a sudden start off 
from rest. This rest may be performed by considering, for example, the 
rate of change of the throttle opening of the vehicle engine. If a sudden 
start is not being performed, then the flow of control passes next to 
leave this program fragment without doing anything further, and the 
engagement of the clutch 21 is continued. On the other hand, if a sudden 
start is being performed, bearing in mind the extra load on the rear 
vehicle wheels, in the step 106 the micro processor outputs an appropriate 
control signal to the electric/hydraulic control device 22 to ensure that 
the clutch 21 of the four wheel drive power transfer device 3 is 
immediately disengaged. Thus operation with central differential device 
differential effect in force is provided. Also the value of the flag F is 
set to zero. And then next the flow of control passes to leave this 
program fragment, without doing anything further. 
And, by the repetition of the FIG. 7 program in a relatively tight and 
quick cycle with a period of the order of milliseconds, the control of the 
clutch 21 of the four wheel drive power transfer device 3 is maintained. 
Thus, according to this mode of control according to these fourth preferred 
embodiments of the anti torque shock control method and device of the 
present inventio, when the operational range of the automatic speed change 
device 2 is switched from a non drive range such as "P" range or "N" range 
to a drive range such as "D" or "R" range by the vehicle driver manually 
actuating the manual setting means therefor and thereby actuating the set 
range sensor 38 to provide an indication thereof, at this time, for the 
certain time period Tset and irrespective of the current setting of the 
center differential lock/unlock switch 39, the clutch 21 of the four wheel 
drive power transfer device 3 is definately engaged, so as at least for 
this short time period Tset to definitely provide operation of the vehicle 
without any central differential action; and this prevents the occurrence 
of any large drive train torque shock upon this shifting of the 
operational range of the automatic speed change device 2 from a non drive 
range such a "P" range or "N" range to a drive range such as "D" or "R" 
range. Accordingly, the reliability and the life spacn of the drive train 
as a whole of the vehicle are desirably extended. Furthermore, the 
emission of any unpleasant noise such as "clonking" during this engagement 
of a transmission drive range from a non drive range is positively 
avoided, and further vehicle squat during such an operation, which might 
occur if two wheel drive operational mode of the vehicle were being 
provided at this time due to the powering up of the rear wheels of the 
vehicle while the front vehicle wheels were not powered up, is definately 
prevented. However, during sudden starting off of the vehicle, this 
central differential clutch 21 is released immediately, whereby the 
differential action of the central differential device 3 is resumed, and 
the front to rear torque distribution provided thereby is determined 
according to the distribution ratio provided by the central differential 
device 10, and this action is appropriate for sudden starting off, because 
typically the rear vehicle wheels will receive more torque than the front 
vehicle wheels. 
The Fifth Preferred Embodiments 
It might happen that the sudden starting off of the vehicle from 
substantial rest might occur at the same time as the shifting of the 
operational range of the automatic speed change device 2 from a non drive 
range to a drive range. In such a case, when it is necessary to 
concentrate upon the starting off characteristics and to release the 
differential clutch immediately, then the step 104 shown in the FIG. 7 
flow chart may be omitted, and the engagement and disengagement of the 
clutch 21 may be performed as shown in the FIG. 8 flow chart, which 
illustrates the operation of the fifth preferred embodiments of the anti 
torque shock control device and method of the present invention. Full 
details of this flow chart and of these fifth preferred embodiments will 
be omitted, since they will be clear to one of ordinary skill in the art 
based upon the above disclosure. 
Conclusion 
In order to reduce the vehicle squat phenomenon, it is optimal for the 
engagement of the differential control clutch 21 to be substanially 
complete, as in the last two embodiments detailed above, so that the front 
vehicle wheels and the rear vehicle wheels should be directly connected 
together; but, if the clutch 21 is not completely engaged but is only 
partially engaged, so that some slippage thereof still occurs, then even 
so the differential effect of the central differential device 10 will be 
impeded although its will not be completely prevented, and thus the torque 
distribution between the front vehicle wheels and the rear vehicle wheels 
will approach equality, so that the vehicle squat reduction effect will 
still be present. Therefore, when the operation range of the automatic 
speed change device 2 is switched from a non drive range to a drive range, 
it is sufficient for the clutch 21 to be only partially engaged, and it is 
not necessary for said clutch 21 to be fully engaged. 
Although the present invention has been shown and described in terms of the 
preferred embodiments thereof, and with reference to the appended 
drawings, it should not be considered as being particularly limited 
thereby, since the details of any particular embodiment, or of the 
drawings, could be varied without, in many cases, departing from the ambit 
of the present invention. Accordingly, the scope of the present invention 
is to be considered as being delimited, not by any particular perhaps 
entirely fortuitous details of the disclosed preferred embodiments, or of 
the drawings, but solely by the scope of the accompanying claims, which 
follow.