A clutch mechanism for a vehicle drive train wherein a drive member and driven member are inter-engaged by pawls. In the preferred embodiment the driven member surrounds the drive member in concentric relationship and provides facing surfaces that are configured to receive pairs of pawls or pawl portions selectively extended from the drive member surface to the driven member surface. A control member is mounted on the drive member with limited rotation relative to the rotation of the drive member. The control member includes a cam slot and the pawls are provided with laterally extended cam follower tabs that extend into the cam slots. The control member is provided with a rotationally retarding means whereby whichever direction the drive member rotates, the control member is shifted to the trailing position within the range of permitted rotation. The pawl pairs carried by the drive member are thus positioned at differing positions relative to the cam slots and the cam slots dictate which pawls are projected into engagement with the driven member.

FIELD OF THE INVENTION 
This invention relates to a clutch mechanism for automatic engagement 
between rotating members in either direction of rotation. 
BACKGROUND OF THE INVENTION 
This invention is primarily applicable to the drive trains of vehicles 
wherein drive power is provided for both front and rear wheels. More 
particularly, it is applicable to vehicles that have one set of wheels 
permanently engaged and the other set of wheels engaged as needed, in 
either direction of travel. 
A vehicle may have the rear wheels permanently engaged and under favorable 
driving conditions the front wheels are not engaged. Should the rear 
wheels start to slip, e.g., when driving on ice or snow or when trying to 
get unstuck from a stuck condition, the front wheels automatically engage. 
Such engagement is provided by a clutch mechanism interposed between a 
component of the vehicles drive train connected to the permanently driven 
wheels (drive component) and a component of the drive train connected to 
the normally passive wheels (driven component). When slipping starts to 
occur, the rear wheels rotate faster than the front (passive) wheels and 
this translates into the drive component rotating faster than the driven 
component. 
The clutch mechanism of the invention reacts to such overrunning rotation 
of the drive component and causes the clutch mechanism to inter-engage the 
drive and driven components thus imparting drive power to the normally 
passive wheels. 
A known clutch mechanism designed for this purpose is disclosed in U.S. 
Pat. No. 5,195,604. Rollers retained in a cage are interposed between a 
drive ring and a driven ring mounted in concentric relation. The annular 
spacing between the two rings (in which the rollers reside) is configured 
so that the radial distance between the rings varies between positions 
where the spacing between the ring is greater than the diameter of the 
rollers and where the distance is smaller than the diameter of the 
rollers. When overrunning occurs, the rollers move to the positions of 
smaller spacing and become wedged between the rings and thereby interlock 
the two rings. This occurs in either forward or reverse direction. 
Roller clutches have some disadvantages, however. The wedgetype of 
interlocking generates radial stresses that require relatively massive 
drive and driven rings. This adds weight and takes up room in areas where 
such characteristics are undesirable. The present invention is directed to 
the replacement of the roller clutch mechanism with a pawl clutch 
mechanism. The use of a pawl clutch mechanism for the purposes described 
above is disclosed in U.S. Pat. No. 4,222,473. The pawl clutch mechanism 
of the '473 patent does not automatically (inherently) shift between front 
and reverse drive and requires the positive shifting (manual activation) 
of a phasing ring, e.g., via a solenoid. An even earlier patent (U.S. Pat. 
No. 2,181,244) discloses a pawl clutch mechanism as applied to 
locomotives. A complex and massive mechanism includes forward and rearward 
directed pawls mounted on trunnions and connected to forward and rearward 
drag members via trunnion arms. The pawls are pivoted by the resistive 
action of drag members, one set of pawls is pivoted into engagement and 
another set out of engagement depending on the direction of rotation. 
It is an objective of the present invention to provide inherent shifting of 
a pawl type clutch mechanism in either direction of rotation produced by a 
more simple and efficient design (as compared to the prior mechanisms) and 
to provide this design in a compact package as required for vehicle 
application. 
BRIEF DESCRIPTION OF THE INVENTION 
The preferred embodiment of the present invention includes an inner drive 
ring (a drive component) and an outer driven ring (a driven component). 
Each ring is configured to have mated shoulders adapted for engagement by 
a first set of pawls when the rings are driven in a forward direction, and 
for engagement by a second set of pawls when the rings are driven in a 
reverse or rearward direction. A spring urges each pawl into engagement. 
The pawls have axially extended cam follower tabs that are projected into 
configured cam slots of a control ring. The control ring surrounds a fixed 
bearing surface and spring biased drag or brake shoes permit but resist 
rotation of the control ring. With the rings rotated in one direction, 
(e.g., to drive the vehicle in a forward direction), the control ring 
resists rotation until the cam follower tabs of the pawls are located at 
one rotative position of the cam slot. In this position, one set of pawl 
portions is cammed in opposition to the urging of the spring and 
centrifugal force to a disengaged position, and the other set of pawls is 
spring biased (aided by centrifugal force) into an engaged position. When 
the direction of the vehicle is reversed, i.e., with the drive and driven 
rings being rotated in the opposite direction, the control ring resists 
rotation until the pawls are positioned at the opposite side of the cam 
slot. In this position the pawl positions are reversed. 
It will be apparent that the objective of the drag shoes is to provide the 
control ring with resistance to the rotation induced by the drive ring. 
This is most readily accomplished by frictional engagement with a fixed 
bearing surface. However, frictional engagement with a bearing surface 
that simply rotates more slowly than the drive and driven rings would also 
suffice and is encompassed by the fixed bearing surface reference. Such 
braking is alternatively referenced herein as having frictional engagement 
to ground, ground engagement meaning any frictional engagement that urges 
the control ring to a trailing position. It is further contemplated, 
however, that other forms of rotational retarding features may be provided 
to retard rotation of the control ring or member. 
The cam slots are preferably configured with an overlying (radially 
outward)resistive detent applied to the disengaged pawls. The detent 
prevents undesired movement of the control ring which may otherwise occur 
at high speed rotation as centrifugal force acting on the drag shoes of 
the control ring urges the drag shoes to lift away from the fixed bearing 
surface. Because the centrifugal force increases as speed of rotation 
increases, the detent, and therefore the control ring, is increasingly 
resistive to rotational movement relative to the drive member and thereby 
counters the reduced drag force which correspondingly decreases due to the 
same centrifugal force acting on the drag shoes. 
There are conditions when it is desirable to have both sets of pawls in the 
engagement position. For example, such full pawl engagement may be 
desirable for providing engine braking as applied to all four wheels when 
descending a steep grade. The configuration of the cam slot can allow such 
simultaneous engagement with the control ring in a mid-position and as 
will be described, such a mid-position can be achieved with a supplemental 
clutch member connecting the control ring to the driven ring. This same 
mid-position of the cam slot can be used to force disengagement of both 
pawls for uninterrupted two-wheel drive mode as will also be explained. 
These additional features and other features and advantages will be more 
fully appreciated upon reference to the following detailed description 
having reference to the accompanying drawings. Further, whereas the 
preferred embodiment is briefly described above, the broad concept of the 
invention is considered to encompass the use of pawls in both rotative 
directions controlled by a single control member that inherently shifts 
the pawls between forward and rearward operational positions i.e., without 
driver involvement, and to provide such feature in a compact package for 
vehicle drive train application.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 illustrates an application for the present invention and represents 
a vehicle chassis. Wheels 10 represent the rear wheels of a vehicle and 
wheels 12 represent the front wheels. An engine 14 provides rotative power 
to a transmission 16 which transmits the rotative power to a propeller 
shaft 18 which interconnects with axles 20 though differential 22 for 
driving rear wheels 10. 
In this example the rear wheels are permanently connected to the engine 14 
and it is desirable to have the front wheels 12 also engaged with the 
engine when needed. Should the rear wheels be unable to provide sufficient 
drive power for propelling the vehicle i.e. when the rear wheels are 
unable to establish sufficient gripping with the underlying surface and 
start to slip, it is desirable to also engage the front wheels and thereby 
provide the additional gripping of the front wheels with the underlying 
surface. 
Accordingly the vehicle of FIG. 1 is provided with a transfer case 24 that 
is connectable to the transmission 16. A front propeller shaft 26 extends 
from the transfer case to front wheel axles 28 through front end 
differential 30 and thus to the front wheels 12. 
It will be appreciated that to achieve the engagement/disengagement of the 
front wheels to the engine, the front wheel drive train represented by the 
transmission, transfer case, front propeller shaft, front wheel 
differential and front wheel axles, requires at least one point of 
separation which defines a drive component and a driven component. These 
components are in adjacent relationship and a clutch member is actuated to 
interconnect the components (for engine driving also of the front wheels) 
or disconnect the components (for engine driving of the rear wheels only). 
As previously indicated and hereby repeated, the arrangement as between 
the front and rear wheels discussed above may be reversed, i.e., with the 
front wheels permanently engaged and the rear wheels in part-time 
engagement. 
FIG. 2 is an exploded, perspective view and FIGS. 3 and 4 are sectional 
views of the drive and driver components and the clutch mechanism for 
engagement/disengagement of these components. Item 32 is the drive 
component and item 34 is the driven component. The clutch mechanism 
encompasses features of the drive and driven components as well as 
numerous other features illustrated in the drawings as will now be 
described. 
For clarification purposes it will be appreciated that each of the drive 
and driven components are permanently connected into the drive train. In 
the illustrated embodiment, drive component 32 has splines 36 connected to 
a splined shaft (not shown) of the drive portion of the drive train and 
driven component 34 has splines 38 connected to a splined shaft (not 
shown) of a driven portion of the drive train. There are however other 
connection mechanisms and those skilled in the art will be well versed on 
such other connecting mechanisms and will readily adapt the concepts 
herein to such mechanisms. 
The driven component 34 of the illustrated embodiment includes a cam ring 
40 that is rotatably connected to a carrier 41 by key 42 engaging keyway 
44 of the carrier 41. The features of the cam ring 40 may be integrally 
embodied in the driven component depending on the perceived benefits in 
manufacturing and assembly of the different parts, a criteria that governs 
the illustrated design in a number of respects. 
The cam ring 40 of driven component 34 is provided with an inner 
configuration 46 that forms cavities and the drive component 32 is 
provided with an exterior configuration 48 that is also provided with 
cavities of a different shape but nevertheless mated as will become 
apparent. From FIG. 3 it will be seen that inner configuration 46 and 
exterior configuration 48 are in concentric, spaced apart , face to face 
relation when assembled. 
Seated in the cavities of exterior configuration 48, are configured leaf 
springs 50. From FIG. 2, it will be noted that each leaf spring includes a 
base portion 52 and a pair of wing portions 54. Interposed between each 
wing portion 54 and the interior configuration 46 of cam ring 40 is a pawl 
56 (see FIG. 4). As will be apparent there are a pair of pawls 56 for each 
spring 50. One of the pawls of each pair of pawls is for engagement in 
forward direction and the other of the pawls is for engagement in reverse 
direction as will be hereafter explained. 
The engagement of the pawls as generally explained above is controlled by a 
control member 58. An enlarged view of the control member is illustrated 
in FIG. 5. The control member is ring shaped including a circumferential 
flange 60 and a radial flange 62. As noted in FIGS. 2 and 3 the radial 
flange is adjacent the spacing between configurations 46,48 and adjacent 
the springs 50. As will also be noted, the circumferential flange 58 of 
the control member extends axially away from this spacing. 
Returning to FIG. 5, the radial flange 62 of the control member 58 is 
provided with cam slots 64. The configuration of the cam slots 64 is best 
illustrated in FIG. 4. As illustrated the cam slots 64 is shaped to have 
narrow sides 66 and a widened center 68. Now return to FIG. 2 and note 
that each of the pawls 56 are provided with a guide or cam follower tab 
70. These guide or cam follower tabs are extended into cam slots 64 as 
seen in FIGS. 3 and 4. As will be further noted, each slot accommodates 
two tabs 70, one being contained in a configured side portion 66 and the 
other in the widened center portion 68 of the slot. The orientation of the 
tabs 70 (one being confined in a side portion and the other in a center 
portion of the slot) is produced by movement of the control member 58 
relative to the drive component 32 as will now be explained. 
With reference to FIG. 2, recall that the springs 50 and pawls 56 are 
seated in the cavities of outer configuration 48. The cavities have 
shoulders 72 against which one edge of the pawl is abutted. (One pawl of 
each pair of pawls being directed against one of the shoulders 72 and the 
other pawl directed against the other of the shoulders 72). Now note that 
the control member 58 is free to rotate relative to drive component 32 a 
limited amount i.e. a boss 74 on the control member 58 projects into a 
depression 76 in the drive component 32. As best seen in FIG. 4., the 
depression 76 is wider than the boss 74 and thus the control member 58 can 
rotate relative to the control member by a limited degree of rotation 78. 
In FIG. 4, the control member 58 is rotated to the extreme clockwise 
position relative to the drive component 32, i.e., the drive component 
being driven counter clockwise indicated by arrow 92. In this position the 
pawls 56 are positioned at the left side of the cam slot 64. Note the dash 
line in FIG. 4 indicating the position of shoulders 72 of configuration 48 
relative to the cam slot 64. Also note that the guide tab 70 of the right 
pawl (of the pair of pawls in cam slot 64) is projected radially outward 
and in this position the pawl is projected into a cavity of driven 
component 34. The left pawl is cammed by the configuration of the slot to 
a retracted position. Upon relative rotation of the control member in the 
opposite direction, i.e. to the extreme counterclockwise position (by 
distance 78) the pawls are shifted to the right side of the cam slot, and 
then the left pawl is extended into engagement with the driven component 
and the right pawl is retracted out of engagement due to the restrictive 
configuration of the right side of the cam slot. The clockwise and 
counterclockwise rotation of the control member relative to the drive 
component is produced by a drag mechanism which will now be explained. 
The circumferential flange portion 60 of control member 58 (see FIG. 5) is 
provided with openings 80 (eight openings 80 illustrated in FIG. 2). Now 
refer to FIGS. 2 and 3 and note that drag shoe segments 82 project 
outwardly from within flange portion 60 and through the openings 80 and, 
accordingly, are rotatively fixed to the control member 58. The drag shoe 
segments are urged inwardly toward bearing surface 86 by a garter spring 
84 whereby the braking of the shoes is transmitted to the control member. 
The control member 58 with drag shoe segments 82 mounted thereon is 
positioned around a fixed bearing surface 86 of a friction ground member 
88. The ground member 88 is attached to a fixed portion of a vehicle 
chassis as indicated by mounting ears 90. 
OPERATION 
As previously explained the present invention is primarily directed to 
drive trains of vehicles and particularly to vehicles having two wheel and 
four wheel drive capability with four wheel drive capability engaged only 
as needed. Thus when the vehicle is traveling on a dry road, the standard 
two wheel drive provides sufficient gripping of the road surface so that 
four wheel drive is not needed. Under such conditions the clutch mechanism 
operates substantially in a passive state although some torque is being 
transmitted to the front axle under most driving conditions. FIG. 4 
represents a counterclockwise drive direction as indicated by arrow 92. 
The drive power is accordingly applied to drive component 32. The control 
member 58 resists rotation in this counter clockwise direction by reason 
of the connection of the drag shoe segments 82 with the circumferential 
flange 60 of control member 58, and because the drag shoe segments 82 are 
biased against the bearing surface 86 by garter spring 84. 
The resistance to rotation of the control member 58 causes the control 
member to fall behind the rotation of the drive component 32 until the 
bosses 74 on the control member 58 become abutted against the trailing 
shoulder 94 of the depression 76 of the drive component. Because the drive 
component carries the pawls 56, the shift of the cam slots 64 is to the 
extreme clockwise position relative to the pawls, thereby positioning the 
leading pawl of each pair of pawls at the confined side of the cam slot 
(and thereby retraction of the leading pawl ) and positioning the trailing 
pawl in the widened center 68 of the slot. The trailing pawl thus is 
biased by a wing portion 54 of spring 50 outwardly toward the driven 
component 34 and more specifically into a cavity of inner configuration 
46. 
It will be appreciated that on a dry road surface and assuming that the 
four wheels are appropriately matched(and further assuming for description 
purposes only, that the rear wheels are the drive wheels), the rear wheels 
being driven will provide the primary propulsion to the vehicle and the 
front wheels will provide only that small portion of propulsion afforded 
through slippage of the rear tires. To the extent that the front wheels 
want to travel faster than the rear wheels, a situation that typically 
occurs during cornering or deceleration, because the trailing pawls are 
angularly projected outward from the drive component 32 to the driven 
component 34 in the drive direction 92 (see FIG. 4), the interior 
configuration 46 of driven member 42 functions in the manner of a cam to 
simply ride over the pawls (forcing the pawls inward) and thereby avoid 
engagement. 
Should the vehicle encounter slippery road conditions, it can happen that 
the rear wheels (the drive wheels) will lose gripping power and start to 
slip i.e. rotate faster than what is transmitted to the movement of the 
vehicle. The front wheels being passive will rotate only relative to the 
movement of the vehicle and thus the drive component 32 starts to rotate 
faster than the driven component 34. Now the trailing pawls 56 engage a 
cavity of interior configuration 46 of the driven component 32 and the 
front wheels are converted from passive rotating wheels to drive rotating 
wheels. 
The operation of the control member 58 and pawls 56 in reverse direction 
i.e. opposite to drive direction 92, will not be described in detail in 
that the operation is the same as just described but with the other pawl 
of the pair of pawls becoming the trailing pawl. The same but opposite 
effect is produced by the drag shoes i.e. the control ring 58 resists 
rotation and shifts to the opposite side of depression 76 whereby the 
trailing pawls are centered in cam slots 64 and angularly projected (by 
spring 50) outwardly toward the interior configuration of the driven 
component. 
Whereas the above describes the desired operation of the clutch mechanism 
in most typical types of road conditions, there are other conditions to 
consider. When the vehicle is driven at high speeds, the control member 
will substantially lose its resistance to rotation by reason of the drag 
shoe segments lifting off the bearing surface 86 due to centrifugal force. 
It may even be desirable for this to occur as wearing of the shoe segment 
is thereby reduced. When the drag resistance applied to control member 58 
is abated, there is opportunity for the control member to drift forward 
relative to the drive component. In the preferred embodiment of the 
invention such drifting is avoided by providing a detent 96 in the 
configuration of the cam slot 64 (see FIG. 4). The detent at slow speeds 
provides very little resistance to the sliding of guide tab 70 (of pawl 
56) from a configured side slot portion toward the widened center portion 
of slot 64. However, at high speeds the same centrifugal force that 
produces lifting of the drag shoe segments also induces lifting of the 
pawls and the detent then becomes a significant deterrent to rotational 
movement of the control plate. It will be appreciated that the two 
resistive forces are inversely related so that the garter spring force as 
compared to the detent force is sufficiently greater at a slow speed to 
insure shifting of the control member 58 to a trailing position when the 
direction of drive is reversed. 
The present invention contemplates also a need for selectively eliminating 
the clutch operation. For example, a vehicle descending a steep grade will 
desirably provide engine braking, i.e., whereby the engine provides a drag 
on the driven wheels as the vehicle attempts to travel by gravity 
influence faster than the engine speed. It is desirable under such 
circumstances that all four wheels are rotatably fixed to the engine in 
both directions of rotation. This can occur if both pawls 56 of each pawl 
set are projected into the cavity configuration 46 of the driven component 
34 thereby providing engagement whenever either component overruns the 
other. The control member will provide such projection of both pawls if 
the center position 68 of cam slot 64 is sufficiently long so that a 
center position of pawls will allow both pawls to project outwardly, e.g., 
as illustrated in FIG. 9. An alternative version of desired clutch 
elimination is achieved when the center portion 68 is shortened. In this 
case, both pawls will be depressed as illustrated in FIG. 10 and then the 
vehicle will function in two-wheel drive only. In either version, the pawl 
positions are centered relative to the cam slot 64 by center positioning 
and affixing the position of the control member 58 relative to the drive 
component 32. Such mechanism is described with reference to FIGS. 6-8. 
The components that interact to neutralize the clutch mechanism are shown 
in FIG. 6. Drive component 32' is essentially unchanged from that shown in 
FIG. 2 as is the brake shoe segment 82' and garter spring 84'. The control 
member of FIG. 6 (performing the function of control member 58 of FIG. 2) 
is in two portions identified as portions 98, 100. The control member 
portion 98 includes the cam slot 64' and boss portions 74' having 
functions similar to cam slot 64 and boss 74 of control member 58 in FIG. 
2. Control member portion 100 has openings 80' which receive brake shoe 
segments 82', again like the control member 58 of FIG. 2. The two control 
member portions 98 and 100 are keyed together by lugs 102 of control 
member portion 98 fitting the mouth of V groove 104. 
The functional difference is provided by a centering ring 106 interposed 
between the two control member portions 98 and 100. Boss portions 108 of 
centering ring 106 snugly fit the depressions of exterior configuration 
48' of drive component 32' and thus the centering ring 106 is fixed 
rotatably but not axially relative to drive component 32'. The 
circumferential wall segments 110 of control member portion 100 fit 
through annular slots 112 of centering ring 106 with web segments 114 
positioned in V grooves 104. As will be noted, the web segments 114 have 
substantial clearance when positioned near the mouths of V grooves 104 and 
when positioned inwardly toward the apex of the grooves, they are confined 
to the center of the groove. 
The interfit between the control member portions 98, 100 (including the 
brake shoes 82' and garter ring 84') and the centering ring 106 will be 
observed in FIG. 8. It will be appreciated from FIGS. 6 and 8 that the 
centering ring when positioned at the mouth of the V groove 104 does not 
interfere with the clutch mechanism. The control member 98, 100 (in 
combination) has limited rotative movement relative to drive component 32' 
by reason of boss portion 74' being undersized relative to depression 48'. 
Whereas boss 108 of centering ring 106 fills the depression 48' and 
therefore locks the centering ring 106 rotatably to the drive component 
32', the centering ring 106 is free to rotate relative to the control ring 
as long as web 114 of the centering ring is located at the mouth of the V 
groove 104. 
Upon axial movement of the centering ring 106 toward the apex of V groove 
104, the web 114 contacts one of the sides of the groove 104 (like a cam 
action) and forces the relative rotation of the centering ring and control 
member 98, 100 until the web 114 is located in the apex. At this position 
the centering ring 106 and the control member 98, 100 are interlocked 
rotatably. Accordingly, the drive component and the control ring are 
interlocked rotatably. By designing this interlock position to provide for 
centering of the pawls 56 in the cam slot 64' as illustrated in FIG. 9 and 
10, the pawls are thereby locked in the center position to either lock the 
drive and driven components against overrunning by either component for 
full-time four-wheel drive (as viewed in FIG. 9) or unlock the drive and 
driven components and thus provide two-wheel drive (as viewed in FIG. 10). 
Movement of the centering ring as between the mouth and apex of the V 
groove 104 is controlled by an actuator 116 mounted on housing 118 as 
viewed in FIG. 7. The actuator moves a piston 120 back and forth (left and 
right as seen in FIG. 7). A saddle ring 122 is fixed to the piston 120 and 
the centering ring 106 is held in the saddle ring 122 as shown. The 
centering ring is shown in solid lines at the clutch operating position, 
i.e., with the web segments 114 positioned in the mouth of V groove 104, 
and in dash lines in the clutch neutralized position, i.e., with the web 
segment 114 in the apex of the V groove 104. Actuator 116 is selectively 
actuated manually by the vehicle operator or by a computer which are 
schematically illustrated collectively in FIG. 1 by reference 120. No new 
disclosure is added by this amendment as the disclosure is contained in 
original claims 10 and 11. 
An alternative to the actuator and centering ring of FIGS. 6-8 is a 
centering spring illustrated in FIG. 10. The centering spring 124 is 
further disclosed in the commonly owned parent application identified 
above. The centering ring is anchored to the drive component (not shown in 
FIG. 10 but shown in the parent application) and the ends 124E of the 
spring 124 bias the control member 58 (98) to the center position. In this 
alternative design, it is desirable to remove the urging force of the 
friction shoes which can be accomplished by providing the ground member 88 
of FIG. 2 to be selectively rotatable, i.e., with the ground member being 
releasably lockable to the housing. The ground member is normally locked 
except when the clutch mechanism is to be neutralized. A rotatable but 
lockable ground member is illustrated in commonly owned U.S. patent 
application Ser. No. 08/721,822. 
The above described embodiments are set forth herein as preferred examples 
of the invention and those skilled in the art will conceive of numerous 
variations without departing from the true intent and scope of the 
invention. Accordingly, the invention is not limited to these preferred 
embodiments and instead is encompassed by the definition of the claims 
appended hereto.