Hydraulics is used extensively in mobile equipment for its high power density — a combination of small size, light weight, and high power output. To squeeze a little more power density into its KVA-7VO series of variable-displacement axial-piston pumps, Bosch Rexroth, Hoffman Estates, Ill., constructs pump housings with aluminum alloy — but more importantly, the pump also features an unconventional bearing arrangement that requires less space.
In conventional bearing arrangements, a tapered roller bearing accommodates thrust load, and a cylindrical roller bearing (close to the drive-end of the shaft) carries radial load. However, analysis showed that the cylindrical roller bearing can be exposed to misalignment, which could shorten bearing service life.
To achieve full service life using a cylindrical roller bearing, the housing would had to have been made stronger and heavier, which would have made the pump more expensive and lowered its power density.
To overcome this problem, SKF engineers replaced the cylindrical roller bearing with a type C 2207 TN9/C3 CARB toroidal roller bearing. This bearing combines the selfaligning capability of a spherical roller bearing with the unconstrained axial displacement ability of a cylindrical roller bearing without any reduction in bearing service life. It is lubricated by complete oil immersion and is capable of speeds to 2500 rpm.