Atkinson Build "0 " Bus
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Atkinson Passenger Chassis with Direct Air-operated Epicyclic Gearbox has No Clutch or Gear-engaging Pedal : Other New Atkinson Models Comprise a Tractor with Scanunell Coupling Gear and Two Light Six-wheelers for 10-ton Loads TNE latest addition to the Atkinson range of passenger vehicles has no clutch or gear-engaging pedal, all 'gear changes being made from a small lever in the cab which has direct air control to Cylinders: operating the topgear clutch and brake bands of an epiCyclie gearbox. Because. of its airpressure control, the new gearbox unit will be available at present only in the Alpha chassis equipped with the Gardner six7cylindered oil engine, which has a unit-mounted compressor.
The direct-air-control four-speed epicyclic -gearbox, made by Self Changing Gears, Ltd:, Coventry; is used in railcars, but Atkinson Lorries (1933); Ltd., Walton-Ie-Dale, near Preston, are the first to offer it in a road vehicle. An Alpha chassis equipped with this transmission arrangement will be M the demonstration park at the Scottish Show and another new Atkinson model, also in the demonstration park, will be a 10-ton articulated tractor built for the Scammell coupling gear. In addition to these vehicles, Atkinson are also building two light six-wheelers for 10-ton payloads.
The Atkinson Alpha at the Scottish Show will be the 16-ft. 6-in.-wheelbase chassis with the Gardner 6HLW engine mounted horizontally amidships, and the Clayton twin-cylinder 10-cu. ft. compressor attached directly to the forward end of the engine. This compressor has.a,triple belt drive from .a crankshaft pulley and suppliesair to two reservoirs, onefor brake operation and the second for the gearbox and door gear.
In . place of the conventional clutch there is an 18-in. hydraulic coupling which is connected to the air-operated gearbox by a short shaft having a Layrub Type 36 coupling. The gearbox is attached in unison with the engine, an extended bell housing being interposed to accommodate the coupling. Access is provided to the hydraulic-coupling filler plug and to the gland packing adjuster.
Because the air-operated epicyclic gearbox weighs about the same as the normal gearbox, no alteration is required to the engine mounting units. The standard Hardy Spicer propeller shaft links the output coupling of the gearbox to the hypoid final drive, which for this chassis has a ratio of 4.78 to I.
At the front the normal gear lever is replaced by a turret carrying a Westing! house five-way valve controlled by a short lever which, if lifted and times through .90°, is locked in the neutra position. -This lever operates in a gab and through two trunnions at its basi to rock a selector plate which opens on of five air valves, depending on tin position of the control lever.
To ensure that the braking systen operates at all times, the air-cornpresso! supply is fed first to the brake reservoii which operates at a maximum pressure of 90 p.s.i., but the gearbox ai. reservoir is set to 55-60 p.s.i. workint pressure, This second reservoir i! piped direct to the driver's control valvc and each of the four forward anc reverse valves is in turn connected by .1 pipe from the relay valve to the appro. priate air cylinder at the gearbox:
The top-gear air operating cylinder i! mounted outside the gearbox, but the other four areinside. These cylinder! are of different sizes and the'diametca of. the pistons is proportional to tht torque reaction ' which each brake. ha!
to sustain. .
There is . no bus-bar to the direc! air-operated gearbox, eaCh' brake beirq applied directly by its own piston. The rate at which the brake is applied .01 released is controlled by restrietor built into the unions contained in tht gearbox. This timing device give )ntinuity of drive while the gear kange is being made.
The epicyclie gearbox, with direct airnration, is in its basic -principles the me as the conventional " self-change " ;arbox, the direct-drive top being a 1116 pie-plate clutch unit and the direct ratios carried through planetary pnstant-mesh gearing in compound ains.
Its case is designed for unit attachent with the engine, as shown by"the tkinson Alpha chassis, but it is drilled• id tapped to take brackets for remote ounting. The standard ratios of 4.07, 42, 1.6 to 1 and direct drive forward -ovide a speed range of 10.4 m.p.h. to m.p.h. in the Alpha chassis, which Ls 10.00-20-in. tyres at both axles, Another Atkinson passenger model at e Scottish Show will be the P.L.745.1-1 re-cylinder under-floor engined chassis. us chassis, which is now being made T bus or coach operation, is available ith a frame tapering at the near-side ont and rear overhang to reduce the ;ight of the loading 'platform of a oritor rear-entrance body.
The fourand five-cylinder horiintal-engined passenger chassis have Layton Dewandre triple-servo braking :ar, a recent modification being. to wer the position of the master servo afford a more convenient floor line. use two chassis are equipped with re-speed gearboxes and hypoid-drive :les.
The new Atkinson articulated tractor, ith Scam mell coupling gear, is built ith an 8-ft. 9-in.-wheelbase to afford 35-ft, turning circle. It is a forwardIntro] model employing the Gardner
four-cylindered oil engine developing 75 b.h.p. at 1,700 r.p.m. and 236 lb.-ft. torque.
This unit is installed with a David Brown five-speed direct-drive-top gearbox having indirect ratios of 6.52, 3,91, 2.48 and 139 to L This gear spread, in conjunction With an Eaton two-speed axle, affords a Maximum speed of 37 [m.p.h. and enables a 1-in-51 gradient to be climbed with full load in the lowest gear. Vacuum operation is pa:elided for the control of the two-speed axle, which has ratios of 4.89 and 6.80 to 1.
The . frame of the tractor unit is shaped to accept the Scammell coupling gear and neatness is shown in employing the spare-wheel carrier amidships to carry the semi-trailer brake and coupling release cross-shafts, The semitrailer hand brake lever has a ring at the top and is pulled up from floor level.
. To obtain a direct linkage between the brake pedal and servo the Clayton Dewandre unit is dropped below frame level and flange-mounted to its support. Special rear springs have been developed for the Scammell type tractor, and the vacuum reservoir, reaction valve and semi-trailer brakeoperating cylinder are accessibly placed.
The two new light six-wheelers have been . developed from the Atkinson 12-tonner with double-drive bogie and, apart from their single axle drives, they are similar in specification to the larger model. Both thern 10-ton six-wheelers are available with Gardner fiveor sixcylindered engines and five-speed directdrive top or overdrive gearboxes.
One of the new models has a trailing axle at the rear and the other is a four
wheel-steered chassis. Both have a wheelbase of 15 ft. 1 in. and a lighter
chassis frame than the 12-tonner. A 2Q-ft. body cart be fitted.