TITLE OF INVENTION

A BEARING ASSEMBLY

FIELD OF INVENTION

This invention relates to bearing assemblies which dampen impact and noise in various applications. Such bearing assemblies may be used in internal combustion engine applications.

RACKGROUND OF THE PRESENT INVENTION

Roller element bearings are a common form of bearing often used in engine applications. One such application relates to bearing of a crankshaft in an engine.

The crankshaft assembled with associated connecting rod(s) is employed in internal combustion engines to convert reciprocating motion of the piston(s) of the engine to unidirectional rotary motion about the axis of the crankshaft. The crankshaft assembly is housed in two structural components called crankcases. The crankcases are normally split into two parts, described as crankcase LH and crankcase RH in the description below, in a convenient fashion, for assembly of the crankshaft and the other engine components to be housed within the crankcase.

The piston assembly of an internal combustion engine reciprocates in the cylinder and is joined to the crankshaft by a connecting rod which is free to articulate at the piston end about the piston pin and at the crankshaft end about the crank pin. There is provided a bearing at the crank pin side of the connecting rod called the "big end bearing". The crankshaft is supported on bearings located in the crankcase LH and crankcase RH. These bearings are of the "rolling element" type, normally of the ball bearing or roller bearing type.

The inner race of these roller element bearing typically has a tight fit on the crankshaft and outer races are located in circular portions formed in crankcase RH and LH. In typical engines, the bearings may have a clearance fit in the crankcase RH and crankcase LH essentially for ease of assembly. The crankcase assembly is provided with an oil gallery to facilitate supply of pressurized oil by an oil pump from an oil sump to different moving parts of engine for lubrication purposes. When the crankcases are manufactured from light alloy

_

2 such as aluminum alloy, inserts made of a suitable grade of grey cast iron are provided on main bearing seating area.

The cylinder head assembly is fixed on the top of the cylinder block by fastening means to facilitate induction of combustible fuel air mixture and to facilitate exhaust of combustion products following combustion. Clamping of the cylinder head to the cylinder creates a closed space bounded by the top of the piston, inner diameter of the cylinder block and combustion chamber of the cylinder head.

During the power stroke of a four stroke engine, the pressure created in the combustion chamber generates forces acting on the piston which in turn act on the crankshaft assembly. This forces the crankshaft to rotate on bearings and the outer races of bearings transfer the forces to the crankcases LH and RH. As the ignition rate increases, the frequency of impact of the crankshaft on the LH and RH crankcases increases. Furthermore, as the combustion burn- rate increases (due to, for example, dual spark plug ignition), the harshness of impact of the crankcase on the LH and RH crankcases increases. In each case, this generates noise.

In the phase from end of the exhaust (TDC) to the end of induction stroke (BDC), inertial force pulls the crankshaft against the crankcases towards the cylinder head thus reversing the direction of the force.

This cycle repeats itself a number of times equal to rotational speed of engine during engine operation and the crankshaft is cyclically forced or pulled to one side of the crankcases (cylinder head side, due to piston assembly inertia force) and forced or pounded to the other side (opposite to cylinder head, due to combustion pressure). This causes impact of bearing outer races on the crankcase resulting in transfer of energy from the crankshaft assembly to the crankcases. The resulting vibration of the crankshaft assembly in the crankcases excites the crankcases in certain ways resulting in a characteristic noise from the engine (combustion roughness).

The above phenomenon of impact, noise and vibration transmittal is exacerbated when one or more of the following is present, viz:

1) the bearing used as crankshaft bearings are roller element bearings and not shell (or also known as hydrodynamic) bearings. The roller element bearing has poor dampening characteristics particularly when its outer race has a clearance fit in the crankcase, which may

be present at working temperature of the engine, that is, there is a clearance between the outer race and a bearing surface of the crankcase

2) The crankcases are manufactured from light alloy, for example aluminum alloy and are designed with lower wall thickness nominally in the range of say 3 mm to 6 mm from cost and weight considerations.

3) engines have rapid combustion characteristics, for example dual spark plugs, swirl port, high compression ratio and so on.

4)

Analogous applications to bearing of crankshafts may be envisaged where impact, noise and vibration may be caused duringjhe service life of a roller element bearing _s

It is therefore an object of the present invention to provide a bearing assembly comprising a roller element bearing which generally lessens the impact, noise and vibration particularly in the operation of the engine.

SUMMARY OF THE INVENTION

With this object in view, the present invention provides a dampened bearing assembly comprising a roller element bearing having a raceway confining at least one roller element and a race with a bearing surface for bearing against a bearing surface of an adjacent component; and means for supplying a pressurised fluid to said bearing surface of said race for dampening transmission of impact of said roller element bearing to said adjacent component in use.

A bearing surface may comprise a distribution means for distributing pressurized fluid, such as a lubricating oil, around the outer race of the bearing by a distribution means. This groove may be circumferential. If the adjacent component is a crankcase and the bearing assembly supports a crankshaft within the crankcase, a crankshaft assembly, the distribution means includes a groove in the bearing surface of the crankcase. The race may be an outer race clearance fitted within the adjacent component at adjacent component operating temperatures, for example at crankcase or engine operating temperatures. The race may be press-fitted within the adjacent component at assembly temperatures. In such case, the distribution means assists in formation of an oil film in the clearance between outer race and crankcase bearing surface while confining the oil film to the clearance. There is no outlet provided for oil from the clearance.

The engine employing the dampened bearing assembly or crankcase assembly may employ a rapid combustion system, for example including dual spark ignition means, this kind of engine having a crankshaft subject to a particularly high frequency of impact,

Preferably, the crankcase is of a light aluminum alloy designed with lower wall thickness.

Preferably the pressurized fluid or lubricating oil flow rate to the dampened bearing assembly is neglible in comparison with other oil flow rates in the engine. Application of the invention will therefore not require any increased oil pump capacity or the need for other modification to the engine lubrication system.

Impact or vibration may occur on a continuous or cyclic basis.

In a further aspect of the invention, there is provided a method of dampening transmission of impact in a bearing assembly comprising a roller element bearing having a raceway confining at least one roller element and a race with a bearing surface for bearing against a bearing surface of an adjacent component; wherein a pressurised fluid is supplied to said bearing surface of said race for dampening transmission of impact of said roller element bearing to said adjacent component.

The dampened bearing assembly may be used in crankshaft assemblies and engine applications, each embodiment of which forms a further aspect of the present invention. In a crankshaft assembly, the roller element bearing may be clearance of press fitted within a crankcase. The bearing race, typically the outer race, may be press fitted within the crankcase at assembly temperatures and clearance fitted within the crankcase at crankcase or engine operating temperatures, the clearance being filled with pressurized fluid such as lubricating oil, allowing better cushioning of impact.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The invention may be more fully understood from the following description of a preferred embodiment made with reference to the following figures in which:

Figure 1 illustrates sectional view of a typical four-stroke engine according to the prior art.

Figure 2 illustrates the sectional view of a typical four-stroke engine according to the

invention.

Figure 3 illustrates enlarged view of the portion of a typical four-stroke engine indicating the invention.

Figure 1 illustrates an engine 20 having a crankshaft assembly 1 supported on bearing

10 and bearing 11 both of roller element type, for example ball bearing type. Bearings 10 and

11 are rigidly fitted on each side of crankshaft 22. Crankshaft assembly 1 is connected to one end of a connecting rod 6 by means of a crank pin 8. The other end of the connecting rod 6 is connected to piston 7 which is housed in a cylinder block 5. Crankshaft assembly 1 is housed in the crankcase assembly comprising of crankcase RH 2 and crankcase LH 3. Crankcase RH 2 is provided with an oil gallery 17 to supply pressurized oil from an oil sump (not shown) by oil pump (not shown), to moving parts in the engine 20. Cast iron insert 12 and cast iron insert 13 are integrally manufactured with crankcase LH 3 and crankcase RH 2 to accommodate light aluminum alloy as a material of construction of the crankcases LH 3 and RH 2. Bearings 10 and 11 are assembled in the crankcase RH 2 and crankcase LH 3 respectively. The outer races 10a and 11a of bearings 10 and 11 have a clearance fit in cast iron insert 13 and cast iron insert

12 respectively during operating condition and impact or vibrate against these in operation, such vibration being cyclical in nature, there being no provision to cushion such impacts. Noise is a significant problem.

Referring to Figures 2 and 3, dampening of such impact in the same engine 20 is achieved by providing a bearing assembly including a roller element bearing as before but including means for supply of pressurized lubricating oil to the clearance formed by the outer race HOa of said bearing 110 with a bearing surface of crankcase 102. This is in addition to supply of oil to other parts of the engine. In particular, oil is supplied to the clearance between the bearing of outer race HOa of bearing 110 and its bearing surface bearing against a bearing surface of cast iron insert 113. Cast iron insert 113 is provided with a circumferential groove 115. This groove 115 is connected to an oil gallery 117 through a communicating passage 118 and port 116. The pressurized oil thus flows from the said oil gallery 117 through said communicating passage 118 to groove 115 which distributes oil, spreading oil on the entire annular surface between the outer race HOa of bearing 110 and the inner bearing surface of insert 113 forming a film of oil. This oil film is maintained continuously in the clearance even if the oil is squeezed away from the annular surface. There is no path for the oil film to exit the clearance. The oil film being viscous in nature, cushions bearing impact on the crankcase and reduces the transfer of energy of crankshaft assembly 101 to crankcase 102 that, in turn,

reduces vibration and noise significantly over the engine of Figure 1. Further, as outer race HOa of bearing 110 has clearance in cast iron insert 113, hydraulic lock caused by oil incompressibility is avoided because there is a space into which oil can flow for the purpose of cushioning impact and reducing vibration. Maintenance of this working clearance is demonstrated by the tolerance data below:

The present invention is described and illustrated with reference to the right hand side of crankcase RH 102. The connection of an oil gallery to the bearing 111 on crankcase LH 103 can be made in an identical manner through necessary modifications in the crankcase LH 103 and provision of a communicating passage for supply of pressurized oil from the oil sump by an oil pump to circumferential groove 115 for distributing pressurized oil to the bearing

surface of the outer race I l ia.

Modifications and variations of the bearing assembly of the present invention may be envisaged by the skilled reader of this disclosure. Such modifications and variations are deemed to fall within the scope of the invention. For example, the present invention has been described and illustrated with reference to a single cylinder four-stroke petrol engine. However, the same bearing assembly may be used on all engines wherein the crankshaft bearings have rolling elements and the outer race of bearings have working clearance with crankcases, such as light aluminium alloy crankcases designed with lower wall thickness.