Overrunning alternator decoupler pulley with bare wire spring and grease lubrication

Field of the Invention

The invention relates to a belt drive assembly for driving belt driven accessories in an engine of an automotive vehicle, and more particularly, to a decoupling mechanism for allowing the belt drive accessories to operate temporarily at a speed other than the belt drive assembly.

Description of the Prior Art

It is widely know in an automotive vehicle engine to transfer a portion of the engine output to a plurality of belt driven accessories utilizing an endless serpentine belt. Typically, each component includes an input drive shaft and a pulley coupled to a distal end of the drive shaft for driving engagement with the bolt. An example of such a belt driven accessory is an alternator.

It is also know to provide a decoupler operatively coupled between the pulley and the alternator to allow the alternator drive shaft to "overrun" or rotate at a faster speed than the pulley and to allow the speed of the pulley to oscillate with respect to the alternator drive shaft due to oscillations in the engine speed.

Examples of decouplers are disclosed in the <patcit id="pcit0001" dnum="US6083130A"><text>United States Patent 6,083,130, issued to Mevissen et al. on July 4, 2000</text></patcit> and the <patcit id="pcit0002" dnum="US5139463A"><text>United States Patent 5,139,463, issued to Bytzek et al. on August 18, 1992</text></patcit>.

<patcit id="pcit0003" dnum="US6083130A"><text>US 6,083,130</text></patcit> relates to a decoupler comprising a coated wrap spring clutch structure, in which the spring steel material is coated with friction material for engagement with an interior surface of a pulley. The friction material is a rubber friction enhancing material wherein preferably a so-called "T-701" rubber-based material is used. The decoupler comprises a coil spring, positioned between an annular flange portion and a ring structure. The annular flange portion is integrally formed with a hub, and the ring structure is positioned within an annular end cap fixedly attached to the hub structure.

<patcit id="pcit0004" dnum="WO0192746A"><text>WO 01/92746</text></patcit> discloses a clutch spring directly coupling a hub member with a pulley. It remains desirable, i.e. it is the object of the present invention, to provide a decoupler that is easy to manufacture and has good durability.

SUMMARY OF THE INVENTION

According to the present invention, the object is solved by a decoupler assembly comprising the features of independent claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: <ul id="ul0001" list-style="none" compact="compact"><li>Figure 1 is a front view of an engine of an automotive vehicle incorporating a decoupler assembly according to one aspect of the invention;</li><li>Figure 2 is an enlarged fragmentary sectional view of the decoupler assembly;</li><li>Figure 3 is a perspective view of a clutch spring in the decoupler assembly;</li><li>Figure 4 is a perspective view of a carrier for carrying one end of the clutch spring in the decoupler assembly;</li><li>Figure 5 is a perspective view of the clutch spring assembled to the carrier.</li></ul>

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the figures, an engine for an automotive vehicle is generally indicated at 10 in Figure 1. The engine 10 includes a crankshaft 12 driving an endless serpentine belt 14, as commonly known by those having ordinary skill in the art. The engine 10 also includes a belt driven accessory 16 driven by the belt 14. Described in greater detail below, a decoupler assembly 20 is operatively assembled between the belt 14 and the belt driven accessory 16 for automatically decoupling the belt driven accessory 16 from the belt 14 when the belt 14 decelerates relative to the belt driven accessory 16 and allowing the speed of the belt 14 to oscillate relative to the belt driven accessory 16. Additionally, a detailed description of the structure and function of a decoupler assembly can be found in applicant's <patcit id="pcit0005" dnum="US6083130A"><text>United States Patent 6,083,130, which issued on July 4, 2000</text></patcit>.

Referring to Figure 2, the decoupler assembly 20 includes a hub 22 having opposite first 24 and second 26 ends and a generally cylindrical body 28 extending axially therebetween. The body 28 includes opposite inner 30 and outer 32 surfaces extending between the first 24 and second 26 ends of the hub 22. The inner surface 30 includes a plurality of inner threads 33 adjacent the first end 24 for fixedly securing the hub 22 to a drive shaft 15 from the belt driven accessory 16. A reduced diameter portion 34 is formed in the first end 24. The reduced diameter portion 34 includes an outer mounting surface 36 having a smaller outer diameter than the body 28. An abutment surface 38 opposite the second end 26 extends generally radially between the outer mounting surface 36 and the body 28. An annular thrust washer 39 is seated on the outer mounting surface 36 adjacent the abutment surface 38.

A socket 40 is formed in the second end 26 for receiving a suitable tool therein for rotatably threading the hub 22 onto the drive shaft 15. An annular first flange 41 extends radially outwardly from the body 28 adjacent the second end 26. The first flange 41 includes an outer flange surface 42 having a larger outer diameter than the body 28. An annular surface 44 extends generally radially between the body 28 and the outer flange surface 42 opposite the second end 26. A generally helical first slot 46 is formed in the annular surface 44 defining a first locating surface 48 therein.

A generally cylindrical pulley 50 is rotatably journaled to the hub 22. More specifically, the pulley 50 extends between opposite first 52 and second 54 ends. The pulley 50 includes an inner surface 56 extending between the first 52 and second 54 ends. A ball bearing member 57 is coupled between the pulley 50 and the hub 22. The bearing member 57 includes an inner race 58 fixedly secured to a portion of the outer mounting surface 36 and an outer race 59 fixedly secured to a portion of the inner surface 56 adjacent the first end 52 of the pulley 50. A plurality of ball bearings 55 is rollingly engaged between the inner 58 and outer 59 races of the bearing member 57. A cylindrical bushing 60 is journal mounted between the pulley 50 and the first flange 41. The bushing 60 includes a sleeve wall 62 extending between a portion of the inner surface 56 adjacent the second end 54 and the outer flange surface 42 of the first flange 41. A bushing bushing flange 64 extends radially inwardly from the sleeve wall 62 and abuts the annular surface 44 in the first flange 41.

The pulley 50 includes an outer periphery 66 with a plurality of V-shaped grooves 68 formed therein for rollingly engaging and guiding the belt 14.

Referring to Figures 2-5, a one-way clutch assembly 70 is operatively coupled between the hub 22 and the pulley 50. The clutch assembly 70 includes a clutch spring 71 and a carrier 75. The clutch spring 71 includes a plurality of helical coils 72 extending between a bent or hooked proximal end 73 and an opposite distal end 74. Preferably, the clutch spring 71 is formed from an uncoated, spring steel material and has a non-circular cross-section to improve frictional contact. Most preferably, the cross-section of clutch spring 71 is rectangular or square. The clutch spring 71 is press fitted into frictional engagement with the inner surface 56 of the pulley 50. Preferably, a lubricant similar or compatible with grease used in the ball bearing member 57 is applied to minimize wear between the clutch spring 71 and the inner surface 56 of the pulley 50.

The carrier 75 is rotatably mounted on the hub 22. The carrier 75 is generally ring shaped and extends axially between opposite first and second sides 76, 78. A hooked slot 84 is formed in the second side 78 of the carrier 75 and is configured to retain the hooked proximal end 73 of the clutch spring 71. A generally helical second slot 86 is formed in the second side 78 of the carrier 75 defining a second locating surface 88 generally opposing the first locating surface 48 formed in the annular surface 44.

Referring to Figure 2, a helical torsion spring 90 extends between hub 92 and carrier 94 ends. The torsion spring 90 is axially compressed between the first 48 and second 88 locating surfaces for transferring torque between the hub 22 and the carrier 75. More specifically, the hub end 92 of the torsion spring 90 is retained in the first slot 46 of the hub 22. Similarly, the carrier end 94 of the torsion spring 90 is retained in the second slot 86 in the second side 78 of the carrier 75. Axial forces due to the compression of the torsion spring 90 retains the first side 76 of the carrier 75 in abutting engagement with the thrust washer 39. The torsion spring 90 also allows relative movement between the carrier 75 and the hub 22 to accommodate changes in the speed of the pulley 50 due to generally oscillating changes in the operating speed of the engine. The torsion spring 90 and the clutch spring 71 are coiled in opposite directions.

A cap 100 is fixedly assembled to a flange 102 formed in the pulley 50 for preventing contaminants from entering the decoupler assembly 20 and for retaining the lubricant within the decoupler assembly 20.

In operation, the engine 10 is started and the pulley 50 is accelerated and rotated in a driven direction by the belt 14 driven by the engine 10. Acceleration and rotation of the pulley 50 in the driven direction relative to the hub 22 creates friction between the inner surface 56 of the pulley 50 and preferably all of the coils 72 of the clutch spring 71. It should be appreciated that the clutch spring 71 will function even where at the onset at least one of the coils 72 of the clutch spring 71 is frictionally engaged with the inner surface 56 of the pulley 50. The clutch spring 71 is helically coiled such that the friction between the inner surface 56 of the pulley 50 and at least one of the coils 72 would cause the clutch spring 71 to expand radially outwardly toward and grip the inner surface 56 of the pulley 50. Continued rotation of the pulley 50 in the driven direction relative to the hub 22 would cause a generally exponential increase in the outwardly radial force applied by the coils 72 against the inner surface 56 until all of the coils 72 of the clutch spring 71 become fully brakingly engaged with the pulley 50. When the clutch spring 71 is fully engaged with the inner surface 56, the rotation of the pulley 50 is fully directed toward rotation of the drive shaft 15 of the belt driven accessory 16. Additionally, centrifugal forces help to retain the clutch spring 71 in braking engagement with the inner surface 56 of the pulley 50.

The rotational movement of the carrier 75 in the driven direction is transferred to the hub 22 by the torsional spring 90 such that generally the carrier 75, thrust washer 39, hub 22, and the drive shaft 15 from the belt driven accessory 16 rotate together with the pulley 50. Additionally, the torsional spring 90 resiliently allows relative movement between the carrier 75 and the hub 22 to accommodate oscillations in the speed of the pulley 50 due to corresponding oscillations in the operating speed of the engine 10.

When the pulley 50 decelerates, the hub 22 driven by the inertia associated with the rotating drive shaft 15 and the rotating mass within the belt driven accessory 16 will initially "overrun" or continue to rotate in the driven direction at a higher speed than the pulley 50. More specifically, the higher rotational speed of the hub 22 relative to the pulley 50 causes the clutch spring 71 to contract radially relative to the inner surface 56 of the pulley 50. The braking engagement between the clutch spring 71 and the pulley 50 is relieved, thereby allowing overruning of the hub 22 and drive shaft 15 from the belt driven accessory 16 relative to the pulley 50. The coils 72 may remain frictionally engaged with the inner surface 56 while the pulley 50 decelerates relative to the clutch assembly 70 and the hub 22. The coils 72 of the clutch spring 71 begin to brakingly reengage the inner surface 56 as the pulley 50 accelerates beyond the speed of the hub 22.

The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modification and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.