Actuator for the frictional engaging device

An actuator for a four wheel drive transfer mechanism which is laid in a power transmission device and is controlled by an electrical signal sent from a controlling unit comprises a torque generating mechanism which converts electrical energy into a torque, and a torque-thrust conversion mechanism which converts the torque generated by the torque generating mechanism into a thrust force. The thrust force generated from the torque-thrust conversion mechanism is applied to the frictional engaging device to control torque distribution between front and rear vehicle wheels.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an actuator to operate a frictional 
engaing device such as a frictional clutch and a frictional brake, etc., 
in particular relates to an actuator which converts revolutionary force 
into thrusting force mechanically. 
2. Description of the Prior Art 
A power transmission device of a motor vehicle in general such as an 
automatic transmission or a four wheeel driving device uses a frictional 
engaging device such as a multiple disc clutch, multiple disc brake (or 
band), and a differential lock clutch (full-time) or a two or four-wheel 
switching clutch (part time) to control each component of a planetary gear 
mechanism. 
Previously the frictional engaging device has employed a hydraulic actuator 
(hydro-thrust conversion mechanism) comprising a piston and a cylinder to 
press or release the discs. 
And as shown in FIG. 2 the mechanism employing the hydraulic actuator works 
an oil pump by the revolution of an engine, regulates an oil pressure 
generated by the pump by a hydraulic control mechanism such as a regulator 
valve, and sends the regulated oil pressure to the hydro-thrust conversion 
mechanism comprising the actuator through a hydraulic switching mechanism 
made up by a control valve, etc. at required moment. 
By the hydro-thrust conversion mechanism hydraulic pressure is converted 
into thrust force, the thrust force is applied to the frictional engaging 
device made up by a multi disc clutch, etc. through a frictional engaging 
pressing mechanism, and the frictional engaging device is engaged. And 
this time a sensor detects throttle pressure, vehicle speed and running 
condition, and sends such signals to a controlling portion (CPU). The 
electrical signals are sent to each solenoid to control the hydraulic 
control mechanism and the hydraulic switching mechanism at the required 
moment. 
Furthermore as shown in FIG. 3, as an another example, a solenoid type 
clutch and brake which converts electric power into thrust force directly 
without using hydraulic pressure is shown. 
Accordingly in the case of hydraulic pressure the problems of oil leakage, 
response delay, difficulty of precise control and complexity of the 
mechanism come out, and reliability is sacrificed because the electric 
signals once are conveted into hydrualic pressure. 
In addition if hydro-system is employed an oil pump is required as a source 
of hydraulic pressure application. The oil pump is directly connected to 
an engine to work, however the engine itself is not provided exclusively 
for the oil pump. And the revolution of the engine varies, so, utilizing 
the engine output to work the oil pump has to have loss and needs extra 
effort to take out the output of the engine. Another case employs an 
electric motor to work the oil pump, however this case requires a space 
for the motor. Consequently such space has to be considered in spite of 
the space in a vehicle being limited, and efficiency is sacrificed because 
electric power which is controlable with ease is converted into hydraulic 
pressure. 
On the other hand the mechanism utilizing solenoid power directly has no 
problems regarding hydraulic pressure mentioned above, however the devices 
become big and heavy to get transmission power and braking power 
tantamount to the mechanism utilizing hydraulic power. 
The present invention is purposed to provide an actuator for frictional 
engagement which enables precise and quick control though a size of the 
device and is comparatively small. 
SUMMARY OF THE INVENTION 
While the invention is believed to be readily understood from the above 
description, a brief summary will now be set forth. 
As shown in FIG. 1, a mechanism comprises a torque generating mechanism 
such as AC or DC motors and ultra sonic motor, which converts electric 
energy to torque; and a torque-thrust conversion mechanism, which converts 
torque obtained from a bolt mechanism (including ball thread mechanism) a 
cam mechanism and so on into thrust force with an increase of force. And 
the thrust force converted by the conversion mechanism is applied to a 
frictional engaging device such as multiple disc clutch, multiple disc 
brake and band brake, etc. by a frictional engaging pressing mechanism 
such as a pressing rod, etc. 
In FIG. 1 to FIG. 3, the areas enclosed by long and short dash lines have 
similar functions in the respective drawings, dotted lines between 
structures mean electric connection, and double lines between structures 
mean hydraulic connection. 
Based on the above structure, when a control unit generates signals in 
accordance with signals from sensors detecting the throttle opening and 
the vehicle speed electric energy based on the electric signals is 
conveted into torque by the torque generating mechanism. The torque is 
converted into thrust force by the torque-thrust conversion mechanism, and 
the thrust force operates to engage or release the frictional engaging 
device through the frictional engaging pressing mechanism. At this time, 
large thrust force is obtained by a torque amplification mechanism (such 
as a counter gear, worm gear, planetary gear, harmonic drive, 
anti-friction drive and a reduction gear, etc.) situated between the 
torque generating mechanism and the torque-thrust conversion mechanism; a 
power amplification mechanism such as a lever mechanism situated between 
the torque-thrust conversion mechanism and the frictional engaging 
pressing mechanism; or, providing power amplification function to the 
torque-thrust conversion mechanism by itself by employing a small lead 
angle thread.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Explanations are conducted on the present invention along by the drawings. 
A power transmission device 2 in a four wheel drive vehicle of full time 
type as shown in FIG. 4 and FIG. 5 comprises a clutch portion 3 (only case 
is shown), a transmission mechanism 5, a front differential 6, a center 
differential 7 and a transfer portion 9. And these are contained in a 
transaxle housing 10, a transaxle case 11, a transaxle cover 12 and a 
transfer case 13. An actuator 1 for a frictional engaging device to 
regulate or release differential function of the center differential is 
laid in the transfer portion 9. The transmission mechanism 5 comprises a 
multiple speed gear transmission device 16 which is shifted by the 
operation of a lever at the required moment. The revolution of an input 
shaft 15 is changed to respective forward speed and reverse speed through 
the multiple speed gear transmission device 16, and transmitted to an 
output gear 19 fixed on a shaft 17. Furthermore a mount case 22 is 
supported by tapered roller bearings 20, 21 relative to the case 10, 11, 
and an input gear 23 is fixed to the mount case 22. The input gear 23 and 
the output gear 19 mesh each other, and the mount case 22 is rotated due 
to the rotation of the input gear 23. The center differential 7 is laid in 
the mount case 22. A pinion shaft 32a supporting a pinion 32 is vertically 
arranged and is free rotationally supported by the case 22, and right and 
left side gears 33, 35 are also free rotationally supported by the case 
22. The left side gear 33 is made together with a front differential 
carrier 25. A pinion shaft 26a supporting a pinion 26 is vertically 
arranged and is free rotationally supported by the differential carrier 
25, and right and left side gear 27, 29 are laterally long and are also 
free rotationally supported also by the differential carrier 25. And front 
axles 30, 31 are connected to each side gear 27, 29 so that transmission 
is enabled. This structure makes up a front differential 6. A hollow shaft 
36 enclosing the front axle 31 is connected to the left side gear 33 of 
the center differential 7 so that transmission is enabled. A hollow shaft 
37 enclosing the hollow shaft 36 and the front axle 31 are connected to 
the right side gear 35 so that transmission is enabled, and a friction 
clutch 45 which is functioned by the actuator 1 for the frictional 
engaging device is laid between the hollow shaft 37 and the hollow shaft 
36. 
The portion of the actuator 1 is shown in FIG. 6. As shown in FIG. 6, a 
gear mount case 39 is free rotationally supported by a radial roller 
bearing 40, a thrust bearing 41 and a tapered roller bearing 42 in the 
transfer case 13. Outside the gear mount case 39, a transfer output gear 
38 is fixed by bolt, and meshes with a gear 44a of a drive shaft 44. 
Further, inside the gear mount case 39, a hub 43 is fixed on the hollow 
shaft 36. A multiple disc type frictional clutch 45 is laid between the 
hub 43 and the gear mount case 39, and one end of the clutch 45 is 
supported by the gear mount case 39 and the other end contacts a pressing 
rod 46. And in the vicinity of the transfer case 13, a DC (direct current) 
motor 47 is laid. An output shaft 47b is inserted into the transfer case 
13 by through a seal bearing 49 and is free rotationally supported by a 
bearing 50, and a gear 51 is fixed at the edge of the shaft 47b. At the 
right side of the gear mount case 39, a ball thread mechanism 56 
comprising a torque-thrust conversion mechanism having a hollow male 
thread 52, a hollow-female thread 53 and many steel balls 55 is laid. The 
male thread 52 is restrained in the axial direction by the transfer case 
13. Further, the female thread 53 is free rotationally supported by the 
case 13, and the end of the female thread 53 contacts the pressing rod 46 
through a thrust bearing 57. A coned disc spring 59 is laid between the 
femal thread 53 and the transfer case 13. The coned disc spring 59 gives 
pressure to the friction clutch 45 through the female thread 53 to keep 
proper response. A gear 60 is fixed on the female thread 53 by spline, and 
a reduction gear 61 which decreases the revolution and increase the torque 
is free rotationally supported in the transfer case 13. The reduction gear 
61 comprises a large diameter gear 61a and small diameter gear 61b, the 
former (61a) meshes with the gear 51, and the latter (61b) meshes with the 
gear 60. 
The rotation of wherein the engine is transmitted to the transmission 
mechanism 5 through the clutch portion 3. At the transmission mechanism 5, 
the rotation is shifted to required speed, then, transmitted to the output 
gear 19, and to the mount case 22 through the input gear 23. In normal 
four wheel running, the rotation of the mount case 22 is transmitted to 
the left and right side gear 33, 35 from the pinion 32 of the center 
differential 7. Further the rotation of the left side gear 33 is 
transmitted to the friction clutch 45 through the hollow shaft 36, and to 
the pinion 26 of the front differential 6 through the differential carrier 
25. From the pinion 26, the rotation of the left side gear 33 is further 
transmitted to the left and right gears 27, 29 and the left and right 
front axle 30, 31. On the other hand, the rotation of the right side gear 
35 is transmitted to the mount case 39 through the hollow shaft 37, and 
from the mount case 39, the rotation is transmitted to the drive shaft 44 
through the transfer output gear 39 and the gear 44a. Further, the 
rotation of the right side gear 35 is transmitted to the both right and 
left rear axles through the rear differential (not shown in FIG.). 
In the case of skid due to snow, frozen road surface, etc. or the tire(s) 
being caught by wayside groove, the controlling portion receives the 
signals from each sensor (not shown in FIG.) detecting the opening of the 
throttle, the vehicle speed, etc., or receives the signals from a driver 
through switches, and the controlling portion sends the signals to the DC 
motor 47 to rotate up to the required amount of rotation. The rotation of 
the DC motor 47 is transmitted to the reduction gear 61 from the gear 51; 
by the reduction gear 61, the rotation is decreased and the torque is 
increased; the rotation of the reduction gear 61 is transmitted to the 
gear 60. The rotation of the gear 60 moves the female thread 53 in the 
ball bolt mechanism 56 to the left of the axial direction, and then the 
torque is converted into the thrust force. Furthermore, the female thread 
53 presses the pressing rod 46 through the bearing 57 to engage the 
frictional clutch 45. Under this condition, the center differential 7 does 
not perform the differential motion, so the hollow shaft 36 (front) and 
the hollow shaft 37 (rear) rotate together. And the rotation of the shafts 
36 and 37 is transmitted to the differential carrier 25 and the drive 
shaft 44. Due to this the same rotational speed is transmitted to the 
front and rear wheels, so that the condition which is unable to transmit 
due to skid is prevented. 
In addition to the above, in accordance with the figures, from FIG. 7 to 
FIG. 21, the modified plans of the present invention are explained. The 
portions same as those in FIG. 4 or FIG. 6 are given same numbers and 
explanation is deleted. 
The example shown in FIG. 7 is that the thrust force generated from the 
transfer output gear 38 which is a hypoid gear is sustained by the case 
13a through the tapered roller bearings 40a, 42a; and the thrust force 
generated from the ball bolt mechanism 56 and applied to the frictional 
clutch 45 is sustained by the case 13a through the thrust bearings 41 and 
57a. 
Namely the bearings are respectively allocated for sustaining of the thrust 
force generated from the transfer output gear 38, and the thrust force 
generated from the ball bolt mechanism. Consequently the load which is 
sustained by bearings is reduced and the durability of the bearings is 
expanded. 
The example shown in FIG. 8 is that the female thread 53b in the ball bolt 
mechanism 56b is fixed to the ring 80 which has spline on both outside and 
inside, so that the female thread 53b is movable axially without rotation. 
And the ring 80 is connected to the transfer case 13b, and, the male 
thread 52b and the motor 47 are connected through the redution gear 61c. 
Due to the above, during engagement of the frictional clutch 45 the axial 
force to the right direction is applied to the female thread 53b. This 
axial force is also applied to the right side of the mount case 39b. On 
the other hand, the axial force to the left direction on the male thread 
52b is applied for engaging the frictional clutch 45, and applied to the 
left side of the mount case 39c. Accordingly, the thrust force generated 
from the ball bolt mechanism 56b is sustained by the bolt 81 only. Because 
of this the thrust force is not transmitted to the transfer case 13b, so 
that the weight of the transfer case 13b is reduced. 
The example shown in FIG. 9 is that the cam mechanism 83 is employed for 
the torque thrust conversion mechanism. The cam mechanism 83 comprises; 
the roller 84; the cam 85 which has the cam surfce 85a and the hub 85b 
connected to the transfer case 13c by the ring 80a; the hub 85b axially 
movable without rotation; and the cam 86 having the cam surface 86a and 
the hub 86b free rotationally supported inside the hub 85b. The cam 86 is 
connected to the reduction gear 61c through the hub 86b. 
Consequently, when the roation of the motor 47 is transmitted to the cam 86 
through the reduction gear 61c, the cam mechanism 83 moves axially by the 
relative rotation between the cam 86, and the cam 85 whose rotation is 
restrained by the ring 80a. The thrust force generated by this axial move 
is applied to the frictional clutch 45 and engages the clutch 45. On the 
other hand, the reaction force to the thrust force applied to the clutch 
45 is sustained by the bolt 81 through the thrust bearing 57b and the 
right side mount case 39d. And the thrust force applied to the frictional 
clutch 45 through the thrust bearing 82a is sustained by the bolt 81 
through the left side mount case 39c. Due to the above, the transfer case 
13c is reduced in weight because the thrust force converted by the cam 83 
is sustained by the bolt 81 only and no thrust force is transmitted to the 
case 13c. 
The example shown in FIG. 10 is that the coned disc spring 62 is laid 
between the frictional clutch 45 and the pressing rod 46. Due to the 
spring 62 the vibration from the clutch 45 is absorbed in the spring 62, 
so that such vibration is not transmitted to the torque-thrust conversion 
mechanism 56 including the ball-bolt mechanism 56. Further, instead of the 
spring 62, other elastic materials such as rubber can accomplish the same 
objective. And the spring 62 can be laid in any place between the motor 47 
and the clutch 45. 
The example shown in FIG. 11 is that the actuator for frictional engaging 1 
is laid on the friction clutch 45a for the differential motion located 
between the input pinion 32b for the input of driving force of the center 
differential 7a and the rear output pinion 37. 
The example shown in FIG. 12 is that the actuator 1 for frictional engaging 
is laid in the friction clutch 45b located between the input pinion 32c 
for the input of driving force and the output shaft 36. And the right side 
gear 35 of the center differential 7b directly meshes with the rear 
driving ger 44a. 
The example shown in FIG. 13 is that the actuator 1 for frictional engaging 
is laid in the friction clutch 45c to transmit the driving force generated 
from the input shaft 36a of the four wheel driving vehicle (part time 
system) without having the center differential (FF based) to the output 
shaft 65a. 
The example shown in FIG. 14 is that the actuator 1 for frictional engaging 
is laid in the friction clutch 45d to transmit the driving force generated 
from the input shaft 65b of the four wheel drive vehicle without having 
the center differential (FR based) to the output shaft 63d. 
The example shown in FIG. 15 is that the actuator 1 for frictional engaging 
is laid in the friction clutch 45e, as the differential lock mechanism for 
the rear differential 66, which is located between the input shaft 67 and 
the left rear wheel 69. Not limited to this, it is possible to locate the 
acutator 1 for frictional engaging in the friction clutch which is laid 
between the input shaft 67 and the right rear wheel 70, or the left rear 
wheel 69 and the right rear wheel 70. 
The example shown in FIG. 16 and FIG. 17 are that as a torque generator the 
servo motor 47a, wherein rotational number or angle of rotation can be 
controlled, is used, and the long stroked coil spring 71a or the coned 
disc spring 71b is laid between the friction clutch 45 and the ball bolt 
mechanism 56. Consequently, the friction clutch 45 is engaged in 
proportion to the amount of shrinking of the spring 71a or 71b. And the 
amount of shrinking is proportional to the revolution of the motor 47a, so 
by controlling the revolution of the motor 47a the engaging force for the 
friction clutch is also controlled. Further, not to limit to the above 
springs, the same effects are obtained by employing long stroked elastic 
elements. 
In the example shown in FIG. 18, in place of the ball thread mechanism, 
normal thread mechanism is employed. For example the square thread 56a is 
used. The length in diametral direction is reduced because no balls are 
employed in the mechanism. And the DC motor 47 works only when the 
engaging force of the clutch 45 is changed because since friction of the 
mechanism is large accordingly, the thread does not regress while the DC 
motor 47 is off. Still further the thrust force is amplified by making the 
lead angle of the square thread mechanism 56a small. 
The example shown in FIG. 19 is that the cam 72 and the cam follower 74 are 
employed as a torque-thrust conversion mechanism. And to amplify the 
torque the worm gear 73 is employed, and the lever 75 is employed to 
transmit the force to the pressing rod 46 and to amplify the force. Due to 
the above, the stroke of the pressing rod 46 is determined by the rotation 
angle of the cam 72, and moreover the cam 72 is controlled by the 
revolution or the rotative angle of the servo motor 47a. 
The example shown in FIG. 20 is that the planetary gear mechanism 76 
comprising the sun gear 76a, the pinion 76b and the ring gear 76c is 
employed, and the lever 75a is employed to convey the thrust force 
generated from the ball bolt mechanism 56 to the friction clutch 45 and to 
amplify the force. 
The example shown in FIG. 21 is that to amplify the torque the "harmonic 
drive" 77 comprising the inner spline 77a, the outer spline 77b, the 
bearing 77c and the elliptical cam 77d, and the lever 75c is employed to 
convey the thrust force generated from the ball bolt mechanism 56 to the 
pressing rod 46 and to amplify the force. 
The explanations stated here are for the embodiments applied to the clutch 
in the transfer device of the four wheel drive motor vehicle. Not limited 
to this, the present invention is also applicable to the clutches and 
brakes employed in the automatic transmission, and moreover is applicable 
to other clutches and brakes. 
As explained, according to the present invention, the torque which is 
generated from a torque generator such as the motor, etc. is directly 
converted into the thrust force by the torque-thrust conversion mechanism 
along with the amplification of force. Because of the above, the engaging 
force of the frictional engaging device is electrically and directly 
controlled, so the control is easy, the better response is obtained and 
the mechanism itself is structured simply. Furthermore effective control 
is obtained by eliminating the loss caused by the energy conversion.