CA1111362A

CA1111362A - Automatic locking clutch

Info

Publication number: CA1111362A
Application number: CA319,096A
Authority: CA
Inventors: Mark J. Fogelberg
Original assignee: Borg Warner Corp
Current assignee: Borg Warner Corp
Priority date: 1978-01-11
Filing date: 1979-01-04
Publication date: 1981-10-27
Also published as: GB2012379B; JPS636375B2; JPS54108315A; GB2012379A

Abstract

Abstract A clutch for engaging a driving member (10) with a driven member (20) automatically upon application of torque to rotate the driving member in either direction, for maintaining engagement in either the drive or coast mode of operation and during the transition between drive and coast, for maintaining engagement in either forward or reverse operation and during the transition between forward and reverse, and for disengaging automatically upon interruption of the torque and slight rotation in the opposite direction. The clutch includes a mechanism (42-60-76) for developing high frictional drag upon initial rotation of the driving member to effect clutch engagement, and low frictional drag thereafter to conserve power.

Description

1~11362 AUTOMATIC LOCKING CLUTCH

This invention relates generally to clutches. More particularly, it relates to a clutch for use in effecting locking engagement between a front drive axle and a front wheel of a four-wheel drive vehicle in response to the application of power to thefront drive axle. The clutch automatically effects disengagement upon cessation of the application of power to the front drive axle, together with a direction reversal thereof.
Heretofore, various clutching mechanims have been used for engaging a front drive axle with its associated wheels in a four-wheel drive vehicle. One such mechanism normally is dis-engaged to allow the wheels to rotate independently of the front drive system. This requires that the operator lock each clutch manually to engage the front drive axle and wheels, and to unlock them manually to disengage.
Another such mechanism provides an overrunning clutch which engages automatically when power is applied to the front drive axle and when operation is in the drive mode. However, such an overrunning clutch disengages automatically upon operation in the coast mode. In other words, the overrunning clutch engages when the rotational speed of the axle tends to exceed the rotational ;
speed of the wheel, but disengages when the rotational speed of the wheel tends to exceed that of the axle. Such overrunning clutches generally provide some means by which the operator may override manually to insure locking engagement between the axle and wheels.
Yet another such mechanism provides a clutch which operates in response to the application of torque to the front drive axle to move pins into slots so as to engage the axle ".'' ~

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with its associated wheels. Although a mechanism of this type will effect engagement in either the drive or coast mode of operation, there is the possihility that the pins will slip out of the slots during movement between drive and coast, in which case the clutch would disengage and then re-engage automatically. At normal operating speeds such disengagement and re-engagement could cause severe shocks to the clutch components and, indeed, to the entire front driveline. This would result in a dangerous and possibly destructive condition. Further, in a float condition wherein the axle is rotating but no torque is transferred between the axle and wheels, an inadvertent tendency for movement between the drive and coast modes of operation could develop. This could cause the clutch to disengage and then re-engage, and establish the same dangerous condition.
Canadian Application 302,899 filed May 9, 1978 is directed to an automatic locking clutch which overcomes the deficiencies of the prior devices. As disclosed therein, the clutch will automatically engage a front drive axle and an associated wheel in response to engagement of the front-wheel drive system will maintain engagement positiveiy in the drive and coast modes of operation as well as during the transition hetween drive and coast, will maintain engagement positively in forward and reverse operation as well~
as during the transition between forward and reverse, and will disengage automatically when the front-wheel drive system is disengaged.
The automatic locking clutch includes a ring for developing frictional drag sufficiently high to cause clutch tm/~ -2-~111362 engagement. Thereafter, this high drag continues, although it is not required to maintain engagement. Thus, in order to conserve power, reduce heat, ease the problems of material selection, etc., there remains a need for an automatic locking clutch of this type which will develop relatively high frictional drag initially to effect automatic clutch engagement, and which will develop relatively low frictional drag thereafter.
A primary object of this invention is to provide an improved automatic clutch which will meet the need noted above. The invention is directed to an improved clutch for automatically effecting engagement between driving and driven members in response to rotation of the driving member. The clutch maintains positive engagement between members so long as the driving member rotates, and disengages automatically ~hen rotation of the driving member is discontinued. The clutch of the present invention is adapted for use in four-wheel drive vehicles where it is desirable to provide auto-matic engagement of the front wheels when the operator engages the front-wheel drive system. The clutch is operative when the vehicle is engaged in forward or reverse, and maintains engagement positively until the operator shifts out of four-wheel drive and reverses direction~
The present invention resides in an automatic clutch including first and second rotatable members forming drive and driven members with first and second clutch elements respectively rotatable with the first and second members, the elements being engageable in drive and coast modes, the first element being movable relative to the first member toward and away from engagement with the second element. First means is tm/~

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provided for movinq the first element toward engagement with the second element upon rotation of the first member in one direction and for maintaining the first and second elements engaged in the drive and coast modes when the first element is subject to rotation. Second means is provided for moving the first element away from engagement with the second element when the first member is not subject to rotation.
The first means includes camming means having a rotatable cam, a cam follower rotatable with the first element and means for developing a force tending to retard rotation of the cam. The camming means is effective sequentially for moving the first element toward engagement with the second element upon relative rotation between the cam and cam follower and for rotating the cam with the cam follower in opposition to the retarding force. The camming means reduces the magnitude of the retarding force upon the rotation of the cam with the cam follower.
In a specific embodiment of this invention, there is included a movable clutching sleeve associated with the driving member and a fixed clutchina sleeve associated with the driven member. The movable clutching sleeve is positively cammed into locking engagement with the fixed clutching sleeve upon rotation of the driving member. A blocking device prevents inadvertent disengagement of the clutching sleeves in the event of a tendency for the driven member to overrun the driving member. As a result, the positive locking relationship is maintained in the drive and coast modes of operation as well as during transition between drive and coast. Furthermore, the arrangement is such that engagement is maintained when the tm/,~ 3a-driving member is rotated in forward or reverse as well as during transition between forward and reverse drive.
The elutch of this invention also includes an improved mechanism for developing a frictional drag force to cause camming of the movable elutehing sleeve. The mechanism incorporates a wrapped spring type of clutch characterized as having relatively high re-tm/J~ 3b--: ....

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sistance to slippage in the spring tightening or wrapp;ng direction, and relatively low resistance to slippage in the spring loosening or unwrapping direction. Upon initial rotation of the driving member, the spring is caused to tighten, thereby causing camming of the movable clutch sleeve. After camming is completed, the spring is caused to loosen, thereby reducing frictional drag to a minimum.
One way of carrying out the invention is described in -;
detail below with reference to drawings which illustrate only one specific embodiment, in which:- :
FIGURE 1 is a sectional view showing details of the improved automatic locking clutch;
FIGURE 2 is a sectional view taken along the line 2-2 of FIGURE 1 showing additional details of the clutch, FIGURE 3 is a developed view taken along the line 3-3 of FIGURE 1 showing the clutch in its disengaged position;
FIGURE 4 is a developed view similar to FIGURE 3 showing the clutch at an initial stage of movement toward its forward drive position, FIGURE 5 is a developed view similar to FIGURE 3 showing the clutch at a later stage of movement toward its forward drive position;
FIGURE 6 is a developed view similar to FIGURE 3 showing the clutch in its forward drive position, FIGURE 7 is a developed view similar to FIGURE 3 showing the clutch in its reverse drive position; and FIGURE 8 is a schematic view showing an associated transfer case for use in conjunction with the clutch.
While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and herein will be described in detail a preferred embodiment. It should be understood that the present disclosure is considered to be an exemplification of the principles of the invention and is not 1~1136Z

intended to limit the invention to this embodiment.
Referring to the drawings now in greater detail, and with particular reference to FIGURE l, 2, and 3, there is shown a driving member or shaft lO, which in one preferred form of the invention is the front axle of a four-wheel drive vehicle. Axle lO
is rotatably supported in a conventional manner within an axle housing 12. Axle 10 extends outwardly beyond the spindle of housing 12, and a spring retainer 14 is secured to the outer end thereof by a bolt 16 or the like. A collar 18 is secured to axle lO for rotation therewith, and is located between the spindle of housing 12 and spring retainer 14.
A driven member 20, which in one preferred form of the invention is the front wheel hub of a four-wheel drive vehicle, is supported by a conventional bearing, not shown, for rotation about housing 12. Lock nuts 22 secure this bearing in the usual manner. An end nut 24 is fastened to the spindle of housing 12 and defines a smooth cylindrical surface 26.
A hub extension sleeve 28 is secured to wheel hub 20 for rotation therewith. Hub extension 28 extends outwardly beyond spring retainer 14 and bolt 16, and a suitable cap 30 closes its outer end. Hub extension 28 defines a plurality of clutch teeth 32.
An axle clutch sleeve 34 is splined to collar 18 for rotation therewith and sliding movement relative thereto. Sleeve 34 defines a plurality of clutch teeth 36 adapted for meshing engagement with teeth 32 of hub extension 28. Sleeve 34 also defines a plurality of cam followers in the form of outwardly radially extending pins 38. A suitable spring 40 reacts against spring retainer 14 and biases sleeve 34 inwardly such that teeth 36 normally are out of meshing engagement with teeth 32.
An annular cam 42 is spaced from the spindle of housing 12 and from sleeve 34 so as to be rotatable relative thereto. Cam . ~ ~

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42 defines a plurality of pairs of outwardly diyerging ramp surface portions 44 and 46, each pair being connected by a flat surface portion 48. A pin 38 is cooperable with each pair of ramp .
surface portions 44 and 46. Cam 42 also defines a pair of spaced slots 49 and 50 in alignment with cylindrical surface 26 of nut 24. Slot 49 is partially defined by surfaces 52 and 54, and slot 50 by surfaces 56 and 58 of cam 42.
An annular stop member 60 is concentric with cam 42.
Member 60 defines a plurality of pairs of outwardly diverging surfaces 62 and 64 parallel to but spaced farther apart than surfaces 44 and 46 of cam 42. Surfaces 62 and 64 terminate in outwardly extending projections 66 and 68. Projection 66 and 68 respectively extend outwardly beyond flat surface 48 of cam 42 adjacent the junction with ramp surfaces 44 and 46. Member 60 also defines a notch 70 in alignment with slots 49-50 of cam 42, and with surface 26 of nut 24. Notch 70 is partially defined by surfaces 72 and 74 of member 60 such that notch 70 extends beyond slots 49-50 with surfaces 72 and 74 spaced farther apart than surfaces 52 and 58 of cam 42.
A friction drag mechanism of the wrapped spring clutch type includes a multi-turn drag spring 76 wrapped around cylindrical surface 26 of nut 24 with a slight interference fit so that some residual frictional drag force is developed therebetween. Spring 76 has ends 78 and 80 respectively extending radially through slots 49 and 50 of cam 42 and into notch 70 of member 60. In the disengaged position shown in FIGURE 3, spring ends 78 and 80 are spaced from surfaces 54 and 56, respectively. With pins 38 and ramp surfaces 44-46 in the position shown in FIGURE 3, sleeve 34 is in the position shown in FIGURE 1. Teeth 32 and 36 are out of mesh, and wheel hub 20 rotates freely about axle 10, which is stationary when the associated vehicle is in two-wheel drive.

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When the operator desires to establish four-wheel drive, he directs power to axle 10. Collar 18 and sleeve 34 rotate with axle 10. Assuming that forward rotation of axle 10 results in downward movement of sleeve 34, as shown in FIGURE 3, pins 38 will abut ramp surfaces 46 and drive cam 42 downwardly, as shown in FIGURE 4. Surface 56 will abut spring end 80 and carry spring 76 around surface 26 of nut 24. As spring 76 tightens, or tends to wrap around surface 26, the frictional drag force tending to retard downward movement of cam 42 is increased, lC and a relatively high frictional drag results. Pins 38 move up ramp surfaces 46 to the position shown in FIGURE 5, thereby sliding sleeve 34 outwardly until teeth 36 are in alignment with teeth 32. Pins 38 abut projections 68 and drive member 60 downwardly as they move along flat surface 48 to the position shown in FIGURE 6. Oam 42 no longer is driven by pins 38. However, surface 72 of member 60 abuts spring end 78, moving it downwardly into abutment with surface 54 of cam 42. Spring end 80 is moved downwardly away from surface 56, and spring 76 loosens, or tends to unwrap around surface 26. The frictional drag force tending to retard downward movement of member 60 is decreased, and a relatively low frictional drag results. Cam 42 also is carried downwardly with very little energy loss, heat buildup, etc.
Sleeve 34 is moved outwardly against the biasing force of spring 40 from the position shown in FIGURE 3 to the position shown in FIGURE 6. Teeth 36 are moved outwardly into alignment with teeth 32, and positive engagement is established between axle 10 and wheel hub 20 in the drive mode. Teeth 32 and 36 are constructed such that the backlash therebetween is smaller than the distance between pins 38 and the top of ramp surfaces 46 along flat surface 48.
When the vehicle shifts from drive to coast, as for example when the operator lifts his foot off of the accelerator, :. ~

~1111362 hub 20 tends to overrun axle 10. In this condition teeth 32 shift from the full-line position shown in FIGURE 6 to the dotted-line position of FIGURE 6. In effect, an engine braking condition is established, and hub 20 drives axle 10. Pins 38 continue to abut projections 68, and member 60 continues to carry cam 42 through spring end 78. Spring 76 continues to loosen, and frictional drag remains relatively low. The vehicle may shift back and forth between drive and coast, but teeth 32 and 36 will remain in meshing alignment, thus ensuring that four-wheel drive operation lo is maintained.
When the operator desires to move in reverse, he stops the vehicle, shifts the transmission into reverse, and then starts the vehicle once again, all the while remaining in four-wheel drive. Because the backlash between teeth 32 and 36 is smaller than the distance between pins 38 and the top of ramp surfaces 46, tooth contact is established before pins 38 start to ride down ramps 46. Sufficient pressure is established between teeth 32 and 36 such that sleeve 34 is held against the biasing force of spring 40. Pins 38 move directly from the position shown in FIGURE 6 to the position shown in FIGURE 7, in which they abut projections 66.
Pins 38 do not ride down ramps 46 and up rams 44, due to the windup in teeth 32 and 36. Four-wheel drive operation is maintained.
When in reverse, the vehicle may shift between the drive and coast modes while remaining positively engaged for four-wheel drive operation.
An important advantage of the arrangement disclosed herein is that a positive drive condition is maintained in both the drive and the coast modes, either in forward or reverse. This positive drive is established automatically, thereby eliminating any need for manually locking the wheel hubs.

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1~1136Z
077159-WG g When the operator desires to establish two-wheel drive, he stops the vehicle, discontinues the transfer of power to axle 10, and moves the vehicle in the opposite direction slightly to relieve the windup in teeth 32 and 36, and to bring pins 38 into contact with either ramps 44 or 46. Spring 40 biases sleeve 34 inwardly to the position shown in FIGURES 1 and 3. The operator may then proceed in either direction in two-wheel drive.
In one preferred form of the invention, direct drive may be established from an engine to a rear drive axle, for example, with offset drive being established to a front drive axle, for example. As shown in FIGURE 8, such an arrangement includes a transfer case having an input 82 adapted to receive power from the transmission of a four-wheel drive vehicle. A rear output 84 is connected directly to input 82, and is connected through a rear propeller shaft to the rear axle. A sprocket 86 is journalled for rotation relative to input 82, and a complimentary sprocket 88 is secured to a front output 90 which is connected through a front propeller shaft to front axle 10. A suitable chain 92 couples sprokets 86 and 88 for power transfer therebetween. A clutch 94 is controllable by the vehicle operator through a suitable actuating mechanism 96. In one position, clutch 94 disengages sprocket 86 from input 82 such that power is transferred from input 82 to output 84, but not to output 90. Two-wheel drive is established.
In another position, clutch 94 engages sprocket 86 with input 82 such that power is transferred from input 82 to both outputs 84 and 90. With clutch 94 engaged and power transferred to output 90, front axle 10 rotates and four-wheel drive is established automatically.
Thus it will be seen that positive drive is established automatically in both the drive and coast modes of operation when four-wheel drive is engaged. The automatic feature eliminates any necessity for manual lock-up in order to insure positive drive.

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077159-WG - lO -The automatic feature maintains four-wheel drive in either the drive or coast modes, and during the transition between drive and coast. Similarly, four-wheel drive is maintained in either forward or reverse operation, and during the shift between forward and reverse.
A friction clutch incorporating a drag spring is arranged to develop a relatively high frictional drag force which is used to cam the automatic locking clutch into engagement. The drag spring is arranged to develop a relatively low frictional drag force after automatic clutch engagement.
It should be apparent that although the invention provides a novel arrangement for clutching the front drive axle and its associated wheels in a four-wheel drive vehicle, it is readily available for use in any environment where automatic clutching between driving and driven members is desired.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In an automatic clutch including first and second rotatable members forming drive and driven members, first and second clutch elements respectively rotatable with said first and second members, said elements being engageable in drive and coast modes, said first element being movable relative to said first member toward and away from engagement with said second element, first means for moving said first element toward engagement with said second element upon rotation of said first member in one direction and for maintaining said first and second elements engaged in the drive and coast modes when said first member is subject to rotation, and second means for moving said first element away from engagement with said second element when said first member is not subject to rotation; the improvement wherein said first means comprises camming means having a rotatable cam, a cam follower rotatable with said first element, and means for developing a force tending to retard rotation of said cam, said camming means being effective sequentially for moving said first element toward engagement with-said second element upon relative rotation between said cam and cam follower and for rotating said cam with said cam follower in opposition to said retarding force, said camming means reducing the magnitude of said retarding force upon said rotation of said cam with said cam follower.

2. The invention of Claim 1, said camming means having rotatable stop means, said cam defining ramp and flat surfaces, and said force developing means including a spring wrapped relative to a stationary member, said spring being engageable by said cam and rotatable thereby in a wrapping direction to develop a relatively high friction drag force, said spring being engageable by said stop means and rotatable thereby in an unwrapping direction to develop a relatively low friction drag force, rotation of said first member in said one direction driving said cam into engagement with said spring for rotation thereof in said wrapping direction thereby establishing said relative rotation between said cam and cam follower, said relative rotation causing said cam follower to ride up said ramp surface onto said flat surface thereby moving said first element toward engagement with said second element, continued rotation of said first member in said one direction driving said stop means into engagement with said spring for rotation thereof in said unwrapping direction, said cam being drivable with said stop means upon rotation of said spring in said unwrapping direction for establishing said rotation of said cam with said cam follower, said first and second elements being engageable in said drive and coast modes when said cam follower is on said flat surface.

3. The invention of Claim 2, rotation of said first member in another direction developing sufficient force in said first and second elements when engaged in said drive and coast modes to overcome the effect of said second means.

4. The invention of Claim 1, said first and second clutch elements respectively defining first and second sets of clutch teeth adapted for meshing engagement in drive and coast modes when said first and second clutch elements are in alignment, said cam being annular and disposed concentric with said drive member, said cam defining a plurality of ramp surfaces and a flat surface, said cam also defining first and second slots, annular stop means concentric with said cam, said stop means defining a plurality of projections extending beyond said flat surface of said cam, said stop means also defining a notch, said cam follower disposed to ride said ramp and flat surfaces of said cam for movement of said first clutch element toward and away from alignment with said second clutch element, said second means for moving said first clutch element being a first spring means biasing said first clutch element away from alignment with said second clutch element, and said means for developing a force being a second spring means wrapped around a stationary member, said second spring means having first and second end portions extending respectively through said first and second slots and into said notch.

5. The invention of Claim 4, said first slot being at least partially defined by a first slot surface of said cam, said second slot being at least partially defined by a second slot surface of said cam, and said notch being at least partially defined by first and second notch surfaces of said stop means, rotation of said first clutch means in one direction causing said cam follower to rotate said cam in said one direction, said second spring means being wrapped around said stationary member such that rotation of said cam in said one direction causes said first slot surface to abut said first end portion and rotate said second spring means in said one direction to thereby tighten said wrapping thereof and develop a relatively high friction drag tending to retard continued rotation of said cam, retarded rotation of said cam causing said cam follower to ride up one of said ramp surfaces and onto said flat surface such that said first clutch means is cammed toward alignment with said second clutch means and such that said cam follower ceases to rotate said cam and abuts one of said projections so as to rotate said stop means in said one direction, rotation of said stop means in said one direction causing said first notch surface to abut said second end portion and rotate said second spring means in said one direction to thereby loosen said wrapping thereof and develop a relatively low friction drag tending to retard continued rotation of said stop means, said rotation of said second spring means by said first notch surface causing said second end portion to abut said second slot surface and rotate said cam in said one direction, said first and second clutch means being rotatable relatively between said drive and coast modes when said cam follower is on said flat surface of said cam, rotation of said first clutch means in the opposite direction when said first and second clutch means are in alignment developing sufficient windup in said first and second sets of clutch teeth to nullify the biasing force of said first spring means.

6. The invention of Claim 1, said second means for moving said first clutch element away from engagement including a resilient means biasing said first clutch element for movement away from alignment with said second clutch element, said rotatable cam defining rise and dwell surfaces, a rotatable stop member, said means for developing a force being spring means wrapped relative to a stationary member for developing frictional drag, said spring means being engageable by said cam and rotatable thereby in a wrapping direction tending to tighten said spring means and thereby develop a relatively high frictional drag force tending to retard rotation of said cam, said spring means being engageable by said stop member and rotatable thereby in an unwrapping direction tending to loosen said spring means and thereby develop a relatively low frictional drag force tending to retard rotation of said stop member, said cam follower being disposed for rotation with and movement relative to the drive member, rotation of the drive member causing said cam follower to engage said cam and drive said cam into engagement with said spring means for rotation thereof in said wrapping direction, retarded rotation of said cam causing said cam follower to ride up said rise surface onto said dwell surface and out of rotatable engagement with said cam member thereby moving said first clutch element into alignment with said second clutch element, said cam follower being engageable with said stop member when on said dwell surface for driving said stop member into engagement with said spring means for rotation thereof in said unwrapping direction, said cam being rotatable with said stop member upon rotation of said spring means in said unwrapping direction for maintaining said cam follower on said dwell surface.

7. The invention of Claim 6, said first and second clutch members respectively defining first and second sets of clutch teeth adapted for meshing en-gagement when said clutch members are in alignment, said clutch teeth having a backlash when said clutch members are in alignment such that said cam follower is maintained on said dwell surface, said clutch teeth developing sufficient windup when in meshing engagement to negate the biasing force of said resilient means.