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).
Article from 'Automotive Industries' detailing the design and features of a new Mack gas-electric bus.
| Identifier | ExFiles\Box 4\6\ 06-page36 | |
| Date | 22th April 1926 | |
| Automotive Industries April 22, 1926 Mack Departs from Usual Practice in Gas-Electric Design Uses single motor drive and retains standard rear axle and differential gear. Two chassis sizes in production, designed for 25 and 29-passenger city-type bodies. G.{Mr Griffiths - Chief Accountant / Mr Gnapp} E.{Mr Elliott - Chief Engineer} electric units. INTERNATIONAL Motor Company, as announced in our news columns last week, has brought out a gas-electric bus made up of the standard Mack city-type bus chassis with General Electric electric equipment. This new bus is different from other gas-electrics of American design in that it uses but one electric motor, thus retaining the standard Mack double reduction rear axle and differential gear. At present, production is confined to two sizes of 196 in. and 225 in. wheelbase designed for 25 and 29-passenger city-type bodies respectively. Additional weight made necessary by the substitution of electrical units for the usual transmission system is 1400 lb., making the total empty weight of the 25-passenger bus 11,200 lb. and that of the larger job 12,150 lb. The generator—DT-1105—is rated at 125 volts and 200 amp. at 1200 r.p.m. It has triple excitation through a shunt winding, a small series winding connected so that as load increases field strength is automatically kept up and by a small field winding on a separate circuit from the main windings which is fed from the 12-volt starting battery, and is designed to provide small initial excitation so that the generator will respond instantly when the throttle is opened. The single motor is a G.{Mr Griffiths - Chief Accountant / Mr Gnapp} E.{Mr Elliott - Chief Engineer}-1101 rated at 125 volts and 140 amp. at 1100 r.p.m. and is of the series type, fan ventilated. Rubber Shock Insulators The front end of the generator is bolted to the engine fly-wheel housing, while the rear end is supported on a drop-forged cross member. The engine and the generator are supported as a single unit by five rubber shock insulators to absorb vibration. The motor is mounted on three rubber shock insulators. The usual controller for giving proper connections for forward and reverse motion and for emergency braking is used, while ordinary operation of the bus is controlled by the accelerator pedal. Emergency electric braking is provided for on the controller by a position in reverse which, with a limiting grid resistance in series, will hold the speed of the bus to about 10 miles per hour. Further braking effort can be supplied by accelerating the engine while the controller is in the reverse position to bring the vehicle to a full stop. A forward braking position is also provided so that even with the engine stopped and other brakes failing, the bus will not roll backwards down grade at a dangerous speed. Vacuum Booster Brake There is no hand brake lever, but the emergency brake, which consists of a drum 11 in. in diameter and 6 in. wide, operating on the propeller shaft, is controlled by the right hand pedal. The service brake on the rear wheels is controlled by the left pedal and the operator’s effort is augmented by the application of a Bragg-Kliesrath vacuum booster brake. The motor of the Mack bus does not protrude above the floor level although the clearance beneath the bus has been maintained at 9½ in., the same as that of the company’s mechanical drive jobs. The engine which furnishes primary power is a standard Mack bus engine of four cylinders with demountable heads cast in pairs and with 4½ in. bore and 5 in. stroke. Horsepower rating is 28.9. Features of design are aluminum alloy pistons; counter-balanced and case hardened crankshaft and timing gears; offset combustion chambers; tubular steel connecting rods, and force feed and splash lubrication. [Diagram Caption] Plan view of new Mack gas-electric bus [Diagram Labels] EMERGENCY BRAKE SERVICE BRAKE ACCELERATOR CONTROLLER TORSION INSULATOR CURRENT RELAY, REVERSE POWER RELAY, SEQUENCE RELAY, & FIELD RESISTOR ELECTRIC BRAKE RESISTANCE IN A SEPARATE HOUSING | ||