Hydrodynamic bearingvs hydrostaticbearing

The graphs in Fig.9 show that the oil grade E produces more stable hydrodynamic lubrication in wide ranges of the oil clearance and rotation speeds.

Hydrodynamic bearingmanufacturers

AFR, LS1,LS2, Cathedral Port, Aluminum Heads, 245cc Intake Runner, 73cc Combustion Chamber, 2.165 Intake Valve 1.600 Exhaust Valve, Designed for 4.000+ Bore, Complete w/Parts

However, the energy losses in hydrodynamic friction with the oil grade E are greater by approx. 60 % than those with the oil grade E (Fig.10).

The oil pressure creates a Lift Force separating the journal from the bearing surface. The Lift force counteracts the external force F. The lubricant enforced to squeeze through the gap between the bearing and journal surfaces produces the hydrodynamic friction.

Hydrodynamic bearingapplication

Founder and owner of Smooth Sliding - an engineering consulting company providing services that help to solve related issues. VP R&D at King Engine Bearings. World leading expert (30 years of experience) in design, technology and materials for and in applications such as automotive, energy, aviation, racing, industrial, heavy duty, and others. Founder and owner of SubsTech (Substances & Technologies) – a leading professional website on Materials Science and Engineering. Author of numerous scientific and engineering publications and patents.

Low rotation speeds (100-200 RPM) result in reduction of the values of minimum oil film thickness to the critical level below 0.5 µm / 0.02 thou (Fig.7).

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Fig.12 depict the effect of the loading on stability of hydrodynamic lubrication within a range of oil clearance value.

Hydrodynamic bearingdesign

Hydrodynamic bearingworking principle

The Reynolds equation is used for calculating hydrodynamic conditions of bearing operation: minimum oil film thickness, oil temperature rise, coefficient of friction, power friction loss, oil flow rate.

Hydrodynamic bearingtypes

The most stable hydrodynamic regime of lubrication is established at the maximum value of minimum oil film thickness (MOFT).

Reaction of water on the moving ski produces the hydrodynamic force, which can be presented as a combination of the horizontal vector Fd (drug force) and vertical vector Fl (lift force).

The external force F displaces the journal from the bearing center. The journal surface is getting closer to the bearing surface forming a converging gap (wedge) α between the bearing and the journal surfaces. The presence of this oil wedge is indispensable to the normal operation of a hydrodynamic bearing.

Hydrodynamic bearingvs ballbearing

When a bearing is being designed, theoretical simulation of hydrodynamic lubrication is performed to optimize the bearing dimensions and lubrication conditions.

The equation is solved with the assumption that there is no lubricant flow in the axial direction (infinitely long bearing assumption).

Ocvirk solution for infinitely short bearing assumption neglects circumferential pressure gradients (first term of Reynolds equation).

The balance between the forces determines the final position of the journal: the value of minimum oil film thickness (MOFT) and the distance between the bearing and journal centers (eccentricity e).

Hydrodynamic bearingvs journalbearing

The Fd-to-Fl ratio and their absolute values are determined by the skier speed, his weight and the wedge angle α (angle of attack).

Basics of hydrodynamic force are explained by the example of a water skier. Work of , conditions and principal parameters of hydrodynamic lubrication are considered. Theoretical foundation of (Reynolds Equation) is described. Practical examples are given on application of Reynolds equation for calculating hydrodynamic conditions of bearing operation: minimum oil film thickness, oil temperature rise, power friction loss. It is shown, how theoretical simulations of hydrodynamic lubrication help to optimize the bearing design and lubrication conditions.

When the skier is skimming on the water surface, the forces are balanced: Fd counteracts Ft in the horizontal direction, whereas Fl counteracts Fg in the vertical direction.

Lubricant pressure distribution as a function of journal speed, bearing geometry, oil clearance and lubricant viscosity is described by the Reynolds equation that is a basis for designing hydrodynamic bearings:

Hydrodynamic bearing is a bearing operating with hydrodynamic lubrication, in which the bearing surface is separated from the journal surface by the lubricant film generated by the journal rotation.

Too low towing speed and too little wedge α produce the lift force that is incapable to balance the gravity force and cause the skier to sink.