Patent ID: 7635668

Claim:
A method for lubricating a vehicle hydraulic system capable of transferring rotational energy into a stored energy reservoir and later reconverting the stored energy to rotational energy to aid propulsion, the method employing a composition comprising: (a) about 0.2 wt % to about 1 wt % of a substantially nitrogen free dispersant derived from the reaction product of: (i) a polyalkenyl-substituted acylating agent, wherein the polyalkenyl-substituted acylating agent is polyisobutenyl succinic anhydride; and (ii) a polyol, wherein the polyol is pentaerythritol; (b) an oil of lubricating viscosity; and (c) about 0.4 wt % to about 2 wt % of a zinc hydrocarbyl dithiophosphate wherein component (c) consists essentially of primary zinc hydrocarbyl dithiophosphates.