From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Investigation into the failure of a Bentley oil pump and proposed dimensional changes.
| Identifier | ExFiles\Box 149\2\ scan0138 | |
| Date | 9th February 1937 | |
| By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} RHC.{R. H. Coverley - Production Engineer} c. to Hs.{Lord Ernest Hives - Chair} c. to E.{Mr Elliott - Chief Engineer} BENTLEY OIL PUMP. Investigations have been carried out as to why the helical gear oil pump LeC.4288 fails so badly with regard to its priming ability after braking. This failure has been found to be due to the assembly of the alum. case and not the 22° helix angle gears. In a bronze case the 22° gears were as good as the straight gears with regard to priming and vice versa, the straight gears were as bad as the 22° gears in the aluminium case LeC.4288. The reason for the failure is an air leak which occurs between the pressure and the suction side of the pump via the clearance which exists between the diameter of the driving bush flange and the diameter of the recess in the case, which houses the flange. The position of this clearance comes at the roots of the teeth, whereas on the driven gear, the bush flange is smaller and is sealed by the plain face of the gears. Existing dimensions and limits (E.60060) driving pinion bush, has a flange dia. of .945" - .950 and the case recess (EB.2131) a dia. of .975" - .985" which results in a leak clearance of .015" - .0175". Will you please incorporate the following dimensional limits and Production can go straight ahead with this pump (LeC.4288.) Leaving the case recess at .975" dia. reduce the limit to +1. Increase the bush flange diameter (E.60060) to .975" with a limit of -½. It will possibly be pointed out that if we were to reduce the flange and recess diameter to that of the driven gear this would cut out the necessity of any fine clearance. Due to the end thrust created by the 22° angle gear, any reduction in diameter of the bush flange would increase the rate of wear and this we wish to avoid as being detrimental to the efficiency of the pump. continued | ||