Coasting device for a vehicle

The present invention is a type of coasting device for a vehicle provided between a half shaft and a drive hub with external threads. A forward running ring and a rearward running ring, each with a truncated conical shaped surface, are mounted on the threaded section of the drive hub. An outer casing is coaxially provided at the outer circumference of the drive hub, the internal tapered surfaces of the casting matching the external truncated conical shaped surfaces of the two rings to form an overrunning clutch and a self-locking device. Thus, the inertial energy of vehicles can be sufficiently utilized, the release of harmful emissions from engines reduced, the wear of machine parts decreased and the driver's labor eased.

BACKGROUND OF THE INVENTION 
The present invention relates to a type of coasting device for a vehicle 
used to accomplish a relative rotating or free running between a driving 
wheel and a half shaft. 
Undoubtedly, it is a much desired way for saving fuel to coast forward by 
inertia when a vehicle travels at a certain speed. However, automotive 
drive is generally a constant-engaging one at present. Therefore, when the 
rotation speed of the half shaft is lower than that of the drive wheel, 
not only is the coasting resistance of the vehicle increased, but also the 
engine is activated inversely to rotate idly with high speed, thus making 
the inertial energy of the vehicle unable to be utilized completely and 
ultimately increasing the wearing of operating parts. 
The applicant filed an application for a patent for utility model entitled 
"A Coasting Device With Double Cone-Surfaces Clutch for Vehicle" on Sep. 
22, 1992, in The People's Republic of China. The application resulted in 
the grant of a patent right on Jun. 26, 1993, (Patent No. ZL92220827.1) 
which patent is cited here as a reference. 
The cited patent disclosed a type of coasting device with a clutch having 
double conical-shaped surfaces for a vehicle, which accomplished 
overrunning clutching by the coasting device, which device comprised a 
forward truncated cone-shaped surface for forward running and a second 
truncated cone-shaped surface for rearward running. 
However, by further experimentation and research, it has been determined 
that the invention of the cited patent has certain defects. For example, 
the reacting speed of the device of the coasting device is slow and its 
internal and external gears, which are used as a locking device, are 
subject to such stress that they can be broken. While overrunning 
clutching, collisions between the conical surface for rearward running and 
its matched rear conicalshaped surface can occur since the double 
conical-shaped surfaces are formed as an integral part. This results in a 
disturbance in the coasting, which has a negative effect to the coasting, 
even to the extent that the vehicle may be unable to travel normally. 
Furthermore, it is a relatively complex structure. 
SUMMARY OF THE INVENTION 
The present invention discloses an improved type of coasting device for a 
vehicle. The object of the present invention is to make the half shaft and 
the drive hub separate automatically to accomplish coasting by means of 
the coasting device when the rotational speed of the vehicle is lower than 
that of the drive hub. The drive hub will be engaged with the outer casing 
automatically by means of the coasting device so as to transmit the power 
from the half shaft to the outer casing through the drive hub when the 
rotational speed of the half shaft is greater than that of the drive hub. 
The vehicle coasting device of the present invention comprises: a half 
shaft; a drive hub with an external thread coaxially provided outside of 
the half shaft; an overrunning clutch having a forward running ring and a 
rearward running ring, both matched with the external thread of the drive 
hub and having a truncated conical, or frustum, shape with tapered 
conical-shaped surfaces, and the tapered conical-shaped surfaces of the 
rings are oppositely disposed, and the rings are threaded onto the 
threaded section of the drive hub; a retainer ring provided between the 
two running rings; an outer casing coaxially provided outside of the drive 
hub with an annular chamber formed inside the casing, the chamber being 
provided with internal conical surfaces to match the conical surfaces of 
the two rings; said device also including a locking device provided 
outside the rearward running ring. 
From the above description, in conjunction with FIG. 3, it will be obvious 
that the opposing running rings of the central cylindrical portion of the 
vehicle coasting device have their outer rims in the shape of a truncated 
cone, or, frustum. Corresponding components of the assembly assume the 
same surface in reverse. In order to simplify the explanation of the 
structure, and not by way of limitation, these surfaces will hereinafter 
be merely referred to as "tapered". 
The outer casing comprises a first and a second cylinder, both having 
internal tapered surfaces, and being rigidly connected with a middle 
cylinder, forming an internal chamber with a cylindrical shape in the 
middle, tapered (as explained above) at both ends. When the half shaft is 
rotated by the engine, the drive hub rigidly connected with the half shaft 
will be rotated; the forward running ring, which matches the external 
thread on the drive hub, will approach the internal tapered surface of the 
second cylinder until it locks up with such internal tapered surface so as 
to transfer the power to the outer casing; and the vehicle wheels attached 
to the outer casing will be rotated together. When the rotational speed of 
the engine is decelerated, that of the half shaft will also be 
decelerated, but the vehicle wheels will continue to run forward by the 
force of inertia. The forward running ring will be rotated back to 
approach the retainer ring along the thread to accomplish separation from 
the internal tapered surface of the second cylinder of the outer casing 
and thereby achieve a coasting condition. 
The locking device comprises a pair of brake shoes provided with externally 
mounted compression springs. The locking device is provided outside the 
rearward running ring to make the brake shoes grasp the rearward running 
ring. Provided at the shoe tip of one brake shoe is a cam mechanism, in 
which the cam can be rotated by an electro-magnetic device to release or 
lockup the brake shoe. Provided at the shoe tip of the other brake shoe is 
another, different, cam mechanism, in which the cam can be rotated by a 
centrifugal weight device to release or lockup the other brake shoe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment is not intended to be exhaustive or to limit the 
invention to the precise form disclosed. For purposes of illustration, and 
not of limitation, the embodiment of the invention depicted in the 
drawings and described hereafter is placed in a Dong Feng series 
automobile. This is an automobile which is manufactured in the People's 
Republic of China. It has been chosen and is herein described in order to 
best explain the invention and its practical use to enable others skilled 
in the art to best utilize the invention. The coasting device may be 
applied to any vehicle or series of vehicles without departing from the 
scope of the invention and with minor modification by one who is skilled 
in the art. 
Referring now to FIG. 1, drive hub 2 and half shaft 1 are rigidly connected 
by bolts 5 through flange 4. Provided between drive hub 2 and half shaft 1 
is a shaft bushing 6, and provided between drive hub 2 and shaft bushing 6 
are bearings 7 and 8. Bearing 7 is locked to shaft bushing 6 by nuts 9 and 
10. External thread 3 is provided on the outside of drive hub 2, a 
rearward running ring 11 and a forward running ring 12 match with external 
thread 3 on drive hub 2, and the two rings 11 and 12 are spaced apart by 
retainer ring 13. 
Provided on the outer circumference of rearward running ring 11 is a pair 
of brake shoes 14. Outer casing 16 is coaxially provided to surround the 
drive hub; provided on outer casing 16 are adjustable springs 15, which 
act against brake shoes 14. Spring 15 is provided inside a spring seat. A 
screw 34 is threaded onto the seat and contacts spring 15. The spring 
pressure is increased when screw 34 is turned in a clockwise direction, 
i.e., toward the inside, and is decreased when screw 34 is turned in a 
counter-clockwise direction, i.e., outwardly. By means of the pressure 
from springs 15, the brake shoes will grasp rearward running ring 11 
(lockup state). 
Outer casing 16 is assembled by a first cylinder 17, having an internal 
tapered surface corresponding to the tapered surface of rearward running 
ring 11, a second cylinder 18 having an internal tapered surface 
corresponding to the tapered surface of forward running ring 12, and a 
middle cylinder 19. The three cylinders are rigidly connected by bolts 20. 
Outer casing 16 is connected with the wheel rib and the brake hub (not 
shown) of the vehicle by bolts through holes 33. 
Referring to FIGS. 2, 3 and 4, brake shoes 14 are mounted on the outer 
surface of rearward running ring 11 and will grasp rearward running ring 
11 (lockup state) under the pressure from springs 15. The pressure from 
springs 15 is adjustable. Provided at the shoe tip of one brake shoe 14 is 
cam 25, which is mounted on one end of cam shaft 26; a pinion 27, engaged 
with a rack 28, is mounted on the other end of the cam shaft. 
Electro-magnetic device 29 controls rack 8 to make it move reciprocally, 
thus rotating the cam to release or lock the brake shoes. Provided at the 
shoe tip of the other brake shoe is a cam 30, which is mounted on cam 
shaft 31. A centrifugal weight 32 is mounted on the other end of cam shaft 
31. Under the action of the rotation of outer casing 16, the centrifugal 
weight moves outwardly; the movement of centrifugal weight 32 brings cam 
shaft 31 into rotation, thus making the other brake shoe release or close 
(lockup or free running). That is, only the other brake shoe 14 will be 
released or closed with the movement of centrifugal weight 32 under action 
of the rotation of outer casing 16. 
When the power for forward running is transfered to drive hub 2 through 
half shaft 1, drive hub 2 rotates to bring forward running ring 12 into 
motion toward the internal tapered surface of second cylinder 18 along the 
thread until the tapered surface of ring 12 locks on the internal tapered 
surface of second cylinder 18. This action transfers the rotation to outer 
casing 16, thus making the wheels turn and causing the vehicle to run 
forward. 
When the operator decreases or stops the supply of fuel (decelerates), the 
rotational speed of half shaft 1 is lower than that of outer casing 16. By 
virtue of the rotational inertia of outer casing 16, forward running ring 
12 will retract back (that is, in the direction toward retainer ring 13) 
along the thread, thus drive hub 2 will start running free to fulfill the 
overrunning function of the overrunning clutch. When the speed of half 
shaft 1 increases once again, forward running ring 12 will be brought into 
motion toward the internal tapered surface of second cylinder 18 to repeat 
the afore-mentioned locking process. 
While running in a rearward direction (backing) one brake shoe 14 will be 
closed through rack 28, pinion 27 and cam mechanism 25-26, under the 
activation of electromagnetic device 29, which will keep brake shoe 14 
closed as long as the vehicle is running in the rearward direction. Half 
shaft 1 oppositely rotates to bring rearward running ring 11 into motion 
toward the internal tapered surface of first cylinder 17 until the tapered 
surface of ring 11 locks on the internal tapered surface to force outer 
casing 16 to rotate oppositely, thus accomplishing running in a rearward 
direction. There is no coasting in a rearward direction, because device 29 
will keep brake shoe 14 locked while the vehicle is running in a rearward 
direction so as to bring the rearward running ring into a locking position 
on the internal tapered surface. 
When it is desired to coast while forward running, brake shoes 14 at the 
outer circumference of rearward running ring 11 must be completely 
released. At this time, one brake shoe will be released through rack 28, 
pinion 27 and cam mechanism 25 and 26, under the activation of 
electro-magnetic device 29. The movement of electro-magnetic device 29 is 
controlled by the operator of the vehicle. The other brake shoe will be 
released under the action of centrifugal weight 32. In this way, the 
interference that outer casing 16 actuates on rearward running ring 11, 
causing movement of ring 11 toward the internal tapered surface of first 
cylinder 17, is prevented, and locking between the tapered surfaces will 
be avoided. 
When coasting is not desired, because of rainy or snowy weather, or in 
hilly country, the pressure of springs 15 can be adjusted to cause the 
centrifugal force of centrifugal weight 32 to be lower than the pressure 
of springs 15, thus making brake shoes 14 tightly grasp rearward running 
ring 11. In this case, it is the same as if the coasting device had not 
been mounted, because the half shaft is locked into the forward running 
position (the tapered surface of forward running ring 12 presses against 
the corresponding tapered surface of cylinder 18) and travel safety is 
guaranteed. 
When vehicles are provided with the coasting device of the present 
invention, the inertial energy, or, momentum, of the vehicles will be 
sufficiently utilized. Experimental data have shown that fuel can be saved 
by more than 25%, carbon monoxide emissions greatly reduced, mechanical 
wear significantly decreased and driver's labor eased. 
From the preceding description of the preferred embodiment, it is evident 
that the objects of the invention are attained. Although the invention has 
been described and illustrated in detail, it is to be clearly understood 
that the same is intended by way of illustration and example only and is 
not to be taken by way of limitation. It is to be understood that various 
modifications may be adopted, and the spirit and scope of the invention 
are to be limited only by the terms of the appended claims.