Field of the invention

The invention relates to the field of a clutch with torque limiting function.

Background of the invention

Automotive vehicles use starter motors to crank the engine while starting. In a starter motor, the drive is transmitted via a one-way clutch. The one-way clutch is positioned between the starter motor and the pinion to engage with the engine ring gear. The function of the one-way clutch is to transmit the drive to the pinion when the starter motor is driving the drive shaft, and to disengage the pinion from the drive shaft as soon the pinion starts to rotate at high speeds post engine start up. The central components of a one-way clutch comprise a shell with rollers disposed circumferentially between an inner ring and a pinion, with the rollers being free to move along a constricted space by support of springs. The rollers establish the frictional contact between inner ring and the pinion and hence transmit the drive from the inner ring to the pinion and further to the engine.

Once the engine starts accelerating, the pinion is not able to match the speed of the engine and begins to overrun when starter motor needs to crank abnormal load, during engine back-rock or when the vehicle is started with the gearbox not being in neutral position. As a result the pinion experiences very high torque. This high torque when transmitted back to the starter motor via the inner ring, results in damage to the components starter motor. Moreover the torque experienced by the pinion is high enough to crush the rollers within the constricted space thereby damaging the one-way clutch.
Prior art US 5706700, teaches about an overrunning clutch for starters. The overrunning clutch according to the prior art is designed to absorb the impact torque during overloading of the starter motor. In the case of the prior art a fitting concave portion to fit the rolling element is formed on one of the inner circumference of the outer ring portion and the outer circumference of the inner ring portion.

Hence there is need to protect the components of the one-way clutch from high engine loads as mentioned above. Moreover, there is also a need for a clutch that prevents the starter motor from overloading and protects ring gear in the flywheel by limiting the torque on the starter motor. In conventional clutch prevention of damage to the components of clutch is not possible, leading to reduction in life of components of clutch and the ring gear in the flywheel.

Advantages of the invention

The advantage of this invention as claimed in the independent claim is to enhance the life of rollers used in a clutch by preventing torque transmission from the engine to the starter motor via the clutch. Another advantage of the invention is to protect the starter motor and the ring gear in the flywheel from engine overload during cranking, thereby protecting the components of clutch from damage.

Brief description of the accompanying drawings

Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

Figure 1 illustrates a torque limiting clutch incorporating the embodiments of the present invention;

Figure 2 illustrates a torque limiting clutch under overload condition; and

Figure 3 illustrates a method for limiting the amount of torque by the use of torque limiting clutch in an engine.

Detailed description of the embodiments

Figure 1 illustrates a torque limiting clutch 100 incorporating the embodiments of the present invention. The torque limiting clutch 100 comprises a casing 101, an inner ring 102 and an outer ring 103 and one or more rollers 104. The rollers 104 are disposed circumferentially between the outer ring 103 and the inner ring 102. The inner ring 102 and the outer ring 103 are located within the casing 101. The outer ring 103 is spaced radially apart from the inner ring 102. The inner ring 102 is mounted on a drive shaft.

The drive shaft receives power from a starter motor. The power from the drive shaft is transmitted to the inner ring 102. As the inner ring 102 rotates, the rollers 104 that are in contact with the inner ring 102 also rotate thereby transmitting power to the pinion. The inner ring 102 is designed so as to rotate in only one direction with respect to the outer ring 103.

The outer ring 103 is a pinion. The pinion engages with the ring gear of the engine thereby causing the engine to start. Once the engine accelerates it develops power due to burning of the combustible charge. During acceleration of the engine, the speed of rotation of pinion becomes very high and the starter motor begins to overrun. There is a need to disengage the starter motor from the pinion during overload condition in order to avoid damage to the components of the starter motor. The disengagement is achieved by varying the movement of rollers 104 that are located between the inner ring 102 and the outer ring 103.

The rollers 104 are adapted to slide within a space defined between the inner ring 102 and the outer ring 103. The rollers 104 slide within the space guided by a helical spring 107 connected between each of the rollers 104 and the outer ring 103 of the torque limiting clutch 100. The tension on the helical spring 107 enables contact between the rollers 104, the inner ring 102 and the outer ring 103.

The torque limiting clutch 100 is has a plate 105 located on an inner periphery of the outer ring 103, that compresses and/ or expands a compression spring 106 in response to the movement of each of the rollers 104 in contact with the plate 105 along the space.
The plate 105 helps in establishing frictional contact between the pinion and the rollers 104. The load on the pinion along with the frictional contact between the plate 105 and the roller 104, causes the roller 104 to move into wider part of the space. The contact between the inner ring 102 and rollers 104 is thus lost and the inner ring 102 begins to freewheel, Moreover, when a vehicle is started in gear and the vehicle is cranked there is a possibility of damage to the starter motor. This is done when the vehicle runs out of fuel and the vehicle needs to be started via the starter motor. This condition is generally known as start-stop.

Figure 2 illustrates a torque limiting clutch 100 under overload condition. The function of the rollers 104 is to disengage the pinion from the drive shaft when the engine begins to overrun and the pinion experiences a high degree of torque due to overload. The friction between the pinion and the plate 105 causes the compression spring 106 to compress and the rollers 104 slide into the space created by the compression of the spring 106. The contact between the rollers 104 and the inner ring 102 is lost. The inner ring 102 is thus free to rotate without receiving torque from the pinion. The movement of the rollers 104 into the cavity ensures that the rollers 104 are isolated from the load of the pinion and thereby crushing of rollers 104 is avoided.

Figure 3 illustrates a method for limiting the amount of torque by the use of torque limiting clutch 100 in an engine. The compression spring 106 is compressed 301 by the plate 105 in response to an overload on the torque limiting clutch 100. The rollers 104 that are in contact with the plate 105 are slided 302 along the space to cause each of the rollers 104 to slide within a cavity created by the compression spring 106. The space is defined between the inner ring 102 and the outer ring 103 within a casing 101 of the limiting clutch 100. In response to the overload on the pinion the plate 105 compresses the compression spring 106 thereby creating a cavity into which the roller 104 moves and further the roller 104 disconnects the inner ring 102 from the pinion. The distance between each of the rollers 104 and the inner ring 102 is increased 303. The inner ring 102 is rotated 304 without receiving torque from the outer ring 103 when torque on the outer ring 103 matches the engine torque.

It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.

1 WE CLAIM:

1. A torque limiting clutch (100), comprising:

a casing (101);

an inner ring (102) and an outer ring (103) located within said casing (101), said outer ring (103) spaced radially apart from said inner ring (102);

one or more rollers (104) adapted to slide within a space defined between said inner ring (102) and said outer ring (103) , each of said rollers guided by a helical spring (107) connected between each of the rollers 104 and the outer ring 103 of the torque limiting clutch (100);

characterized in that, a plate (105) located on an inner periphery of said outer ring (103), said plate (105) compresses and/ or expands a compression spring (106) that is positioned between said plate (105) and said outer ring (103) in response to the movement of each of said one or more rollers (104) in contact with said plate (105) along said space.

2. The torque limiting clutch (100) of claim 1, wherein said inner ring (102) is mounted on a drive shaft.

3. The torque limiting clutch (100) of claim 1, wherein said outer ring (103) is a
pinion driving a ring gear of an engine.

4. The torque limiting clutch (100) of claim 1, wherein said plate (105) is supported between one of said roller (104) and said outer ring (103).

5. A method for limiting the amount of torque by the use of a torque limiting clutch (100) in an engine , comprising:

compressing a compression spring (106) by a plate (105) in response to an overload on said torque limiting clutch (100).

sliding each of one or more rollers (104) in contact with said plate (105) along a space to cause each of said rollers (104) to slide within a cavity created by said compression spring (106), wherein said space is defined between an inner ring (102) and an outer ring (103) within a casing (101) of said torque limiting clutch (100).

increasing the distance between each of said one or more rollers (104) and said inner ring (102); and

rotating said inner ring (102) without receiving torque from said outer ring (103), when torque on said outer ring (103) matches the engine torque.