Pulley with controlled surface irregularity for an internal combustion engine

Abstract: An accessory drive system for an internal combustion engine includes a multi-ribbed belt (14) and pulley system (10,12). Shear generators (30) are machined, formed or moulded and extend axially from the driving pulley's faces (28) such that the shear generators expand the drive belt (14) in a plurality of regions. The shear generators are formed as either spheroids (30) projecting into the V of the V-pulley such that the spheroids (30) extend from two faces of adjacent grooves at approximately the midpoint (32) between the root (34) and apex (36) of the V, or as shifted circumferential grooves (44) of a multi-ribbed pulley (10) having a continuous wave pattern. These shear generators cause a plurality of localised high tension regions at the highest pressure zone of the belt/pulley friction interface, improving circumferential friction, and therefore torque capacity, with minimal effect on belt wear due to their smoothness.

Description: This invention relates to a drive pulley system for an internal combustion engine. More particularly, the present invention relates to an improved pulley system which produces enhanced traction between the pulley and a drive belt in wet operating conditions. Pulley drive systems for powering the accessories of internal combustion engines are used to transmit power through a belt, with the belt making frictional contact with the face of the pulleys. The use of pulley systems to accomplish the transfer of power has been proven to have certain deficiencies inasmuch as pulleys rely upon friction for their motive force. Once the friction is lost between the pulley and the belt, as may be the case with an accumulation of water on the surface of the pulley system, slip occurs. Water on the surface of the pulley system causes the coefficient of friction between the belt and the pulley faces to decrease, causing either an objectionable squealing noise which will be audible to the driver as the belt slips or a change in speed of the driven accessory. Currently, conventional multi-ribbed belts and pulleys are used on several drive systems with automobile engines. The pulley's circumferential grooves for receiving friction belts such as multi-rib belts have grooved surfaces which are very smooth; therefore, the coefficient of friction between the surfaces of the grooves relative to the friction belt is very low. Prior work has focused on improving friction within different belt systems or has focused on modifying the belt itself. Due to the different flexural properties of the belts, a solution that corrects for the loss of friction with one belt system cannot be readily applied to solving the same problem with another belt system. U.S. Patent 1,601,662 describes transferring power to a laterally flexible belt with a steel laminate, used with either a variable effective diameter or a fixed diameter pulley. This belt is very different from a multi-ribbed belt, which is laterally fixed and rigid. Also the tensions associated with a variable speed gear are higher than those associated with a constant speed gear. U.S. Patent 4,781,660 describes transferring power to a chain belt operating at high speed at a small wrap angle. A V-pulley described in the '660 patent comprises a pair of conical pulley faces that the chain belt contacts, with each being provided with a rough surface. The smaller wrap angle taught would also lower the total torque capacity between a belt and the pulley. In addition, the frequency of the roughness defined and shown in this is too high to be effective with a multi-ribbed belt, because the multi-ribbed belt would lift out of the fixed multi-ribbed belt pulley. U.S. Patent 4,898,567 describes a V-block belt system aimed at reducing noise levels during operation. The system relies on the assistance of a special belt with intermittently spaced V blocks. The type of belt taught differs significantly from a smooth multi-ribbed belt. U.S. Patent 4,905,361 describes a conventional multi-ribbed pulley, designed to work with a multi-ribbed belt. The invention teaches the addition of axial grooves which extend in an axial direction over a surface of the pulley in which the circumferential groove is formed, and a higher friction surface which is formed by roughening the surface. However, with this invention, combined with the characteristic hardness of the rib stock rubber of at least 65 shore durometer of all known K section V-ribbed belts, the belt would simply be elevated out of the grooves and would ride across the top of the bumps with less effective wrap surface. Hence, there would be lower friction and subsequently lower belt/pulley torque capacity than a pulley without the roughness as described in this patent. It is known that modified multi-ribbed belts having smaller V angles perform slightly better under wet-slip conditions than conventional multi-ribbed belts. This could be because the tips of the pulley dig into the belt rib valleys and create a local pressure wedging in this area. The sharper, longer V of the belt provides full rubber to steel contact during the wet slip situation, which prevents hydroplaning as the belt digs into the bottom of the pulley. However, this technique causes undue wear to the belts because the tip loads will wear out the rib section of the belt, eliminating future point contacts. UK Patent No 1441054 which contains the features of the preamble of claim 1, describes a pulley for a single belt in which the flanges have protuberances on their inner faces to improve grip with a V belt. US Patent No 1792921 describes a power transmitting mechanism including a pulley having a plurality of V grooves, each adapted to receive a respective V belt. Enhanced grip is obtained by forming corrugations in the opposed faces of conical faces forming the V grooves which engage pads on the sides of the V belts. The current invention applies the concept of creating localised high pressure areas through the pulley's geometric characteristics. The system modifies the amount of space between adjacent conical faces of the pulley, thereby creating high pressure areas between the pulley and the belt at the belt/pulley interface. Clearly, it is desirable to be able to have an improved multi-ribbed belt pulley system that will compensate for wet conditions and prevent the belt from slipping on the pulley, thereby preventing a squealing sound as the belt loses traction. According to the present invention an accessory drive system for an internal combustion engine comprises a plurality of driven pulleys, with at least one of the driven pulleys being operatively connected with a rotating accessory. The drive system further comprises a multi-ribbed belt. A driving pulley is attached to a driving shaft of the engine such as a crankshaft. The drive pulley comprises at least one pair of conical pulley faces defining a circumferential groove in the driving pulley and a plurality of spheroids projecting from internally opposing faces of the pulley, with at least some of the spheroids extending from two faces of adjacent grooves. The spheroids expand the drive belt in a plurality of regions as the belt comes into contact with the driving pulley. The spheroids extend from the pulley faces into adjacent pulley grooves such that the spheroids cause a plurality of localised high tension regions at the highest pressure zone of the belt/pulley friction interface. Preferably, the grooves are V-shaped, with each V having at least one spheroid at approximately the midpoint between the root and the apex of the V. It is an advantage of the present system that a high tension area is created in a belt at the highest pressure zone of the belt/pulley friction interface. It is another advantage of the present invention that smooth surfaces of spheroids according to this invention create tension within the belt that is within the belt's elastic range and which does not cause undue wear to the belt. It is another advantage of the present invention that circumferential friction is increased by the spheroids, thereby increasing torque capacity. It is another advantage of the present invention that the accessory drive system will work well under wet slip conditions by smoothly allowing for improved friction between the belt and pulley, thereby maintaining speed of driven items. It is yet another advantage of the present invention that a squealing noise will not be audible. The invention will now be described, by way of example, with reference to the accompanying drawings, in which: FIG. 1 is a schematic representation of an accessory drive system for an internal combustion engine according to the present invention; FIG. 2 is a schematic of a multi-ribbed belt and pulley according to the present invention; FIG. 3a is a side view detail of a driving pulley according to one aspect of the present invention showing spheroid locations at approximately 20° intervals along the circumference of the pulley; FIG. 3b is a sectional view of the driving pulley of FIG. 3a; FIG. 3c is a close-up of FIG. 3b, showing the placement of spheroids within the conical pulley faces; FIG. 4 is an illustration of a driving pulley including spheroids according to the present invention; and FIG. 5 is a plot of results from a friction test stand showing a comparative analysis of a pulley according to the present invention and a conventional prior art pulley. As shown in FIG. 1, an accessory drive system according to the present invention, includes driving pulley 10, which is connected with driven pulley 12 by multi-ribbed belt 14. Driving pulley 10 is attached to driving shaft 16 (such as a crankshaft) of an engine. The present system is used to transmit power from an internal combustion engine to accessories (not shown) within the engine's accessory drive system. Such accessories frequently include an alternator, a power steering pump, an air conditioning compressor, a secondary air pump for emission controls, and other rotating devices known to those skilled in the art. Flexible multi-rib belt 14 is trained over pulleys 10 and 12. As shown in FIG. 2, the working face of multi-rib belt 14 carries a plurality of adjacent V-section ribs 18 with grooves 20 extending therebetween. Belt 14 has a top portion 22 which is flat. Ribs 18 and grooves 20 are parallel to each other and extend over the continuous tractive face of multi-ribbed belt 14. Belt 14 may be made of conventional elastomeric materials, such as neoprene, and may include cords for strengthening. Pulleys 10 and 12 have a plurality of grooves 24 and ribs 26. Grooves 24 are shaped and dimensioned so as to receive belt ribs 18 with little clearance space when belt 14 is in contact with either pulley 10 or pulley 12. Pulley ribs 26 are defined by conical pulley faces 28 of pulley 10. It should be noted that the cross sectional shape of multi-rib belt 14 may vary and the shape of the ribs in cross section may also be varied according to this invention. As shown in FIGS. 3a, 3b and 3c driving pulley faces 28 are modified by means of forming, moulding or machining with spheroids 30, which act as shear generators according to one aspect of the invention by extending axially into pulley grooves 24. As shown in FIG. 3a, spheroids 30 are located periodically around the circumference of driving pulley 10. As shown more specifically in FIG. 4, spheroids 30 are optimally located approximately at midpoint 32 between root 34 and apex 36 of the V of pulley rib 26, which is defined by adjacent pulley faces 28. As shown in FIG. 4, spheroids 30 reduce the area within the grooves 20 by extending axially from two pulley faces 28 into adjacent pulley grooves 24. Preferably, spheroids 30 are smooth. FIG. 5 compares the coefficient of friction of a conventional multi-ribbed pulley with a pulley according to the present invention. The test equipment arid methods for determining the friction behaviours of various friction materials will be briefly discussed. A new dynamic belt pulley friction stand was developed, which tests drive belts under more realistic conditions, and which overcomes limitations with previous equipment, including: 1) a single length of belt exposed to the rotating pulley deteriorated quickly and unrealistically, as the pulley rotated; 2) an unrealistic temperature build-up occurred if the pulley speed approached realistic slip speeds; 3) incomplete data were generated because there is variation in the coefficient of friction at different spots on the same belt, but only one is measured; and 4) slow speeds required to preserve the belt obscured certain phenomenon such as wet slip. The previously mentioned friction stand is a dynamic stand which captures the belt speed and pulley rotation characteristics of an actual engine. According to the test procedure, a steady state torque is applied to the driven pulley. Then, the machine slowly unwraps the belt from the driven pulley. As the belt unwraps, eventually there will be slip between the belt and the pulley. As the belt unwraps, a data point is taken at every .2° of unwrapping angle. The approach of unwrapping the pulley, versus increasing the torque until slip occurs has the advantage of minimising the heat build-up at the friction surface that occurs as a slip condition is approached. Because the coefficient of friction is known to increase with temperature, this approach minimises the increase in temperature and makes the process more benign to the belt. The data gathered in Fig. 5 were acquired on the previously described friction test stand using a 169 mm crankshaft pulley. The test pulley was tested at a 45° wrap angle under 180 N of slack side tension. To simulate wet-slip conditions water was run over the system at 300ml/minute. A 20% increase in the coefficient of friction and 45.3% more torque capacity was achieved under a wet slip condition over a conventional multi-ribbed pulley without shear generators. It can be seen that the coefficient of friction between the multi-ribbed belt 14 and driving pulley 10 is increased with the inclusion of spheroids 30. Without wishing to be bound by the theory, it is believed that the spheroids 30 create a localised high pressure area at the belt/pulley interface according to FIG. 4. Localised tension is created in belt 14 as it is stretched within its elastic range over spheroids 30. Thus, the spheroids increase the circumferential friction while causing no undue wear to the belt. With spheroids 30 in driving pulley 10, should the surface of pulley 10 become wet, the increased coefficient of friction will keep belt 14 from slipping along the faces of pulley 10 causing either an audible squealing noise as the belt slips or a change in speed of the driven item.

Claims: An accessory drive system for an internal combustion engine, comprising: a plurality of driven pulleys (12), with at least one of said driven pulleys being operatively connected with a rotating accessory; and a driving pulley (10) attached to a driving shaft (16) of the engine, with said driving pulley comprising; a plurality of conical pulley faces (28) defining a plurality of circumferential grooves (24) in said driving pulley (10), characterised by : a multi-ribbed belt (14); and a plurality of spheroids (30) projecting from internally opposing faces of said pulley (10), with at least some of said spheroids (30) extending from two faces of adjacent grooves (24) such that the spheroids (30) cause a plurality of localised high tension regions at the highest pressure zone of the belt/pulley friction interface. An accessory drive system according to claim 1, wherein said grooves (24) are V-shaped, with each V having at least one spheroid (30) at approximately the midpoint (32) between the root (34) and the apex (36) of the V. An accessory drive system according to claim 2, with each groove (24) having a spheroid (30) at approximately 20° along the circumference of the pulley (10). An accessory drive system according to claim 2, with each groove (24) of a multi-ribbed pulley (10) having a spheroid (30) every 20° along the circumference of the pulley (10).

Inventors: MECKSTROTH RICHARD JOHN, MECKSTROTH, RICHARD JOHN
Applicants: FORD GLOBAL TECH INC, FORD GLOBAL TECHNOLOGIES, INC.
Application year: 1999
Main classification: F16H55
IPC codes: F16H55