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Two-pedal 10-speed Beaver beats code on brakes
Page 53
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SLi-PER-SIZE brakes feature on a model added by Leyland Motors Ltd. to its Freightline Beaver range. Designated Model BE.TR.1PR it differs from existing chassis mainly in having the semi-automatic gearbox—incorporating an integral two-speed splitter section—shown by Leyland at the NEW SAFETY STANDARDS for motor
recent Frankfurt Show.
Like the original semi-automatic Beaver, the new version has a gross train weight rating of 30/32 tons. Other new features: an improved braking system with load-sensed valve on the driving axle, a new front axle with larger brake drums and a higher-capacity radiator.
The 10-speed gearbox eliminates the need for a two-speed axle, as employed in the original Beaver with this type of transmission. And another feature of the design is that a power take-off can be provided.
The splitter unit is built into the gear casing between the main epicyclic trains and the fluid coupling. It is a two-speed unit giving a direct drive and an overdrive, the step between them being designed to split each main-gearbox ratio by about one-half. Split ratios are obtained by flicking a small switch mounted on the change-speed knob.
The splitter consists of a simple epicyclic gear train. Direct drive is obtained by a spring-loaded multi-plate friction clutch which locks together the sun wheel and carrier in the epicyclic train. Overdrive 0.77 to 1 is obtained by admitting air pressure to an annular diaphragm, and initial movement of this disengages the direct-drive clutch. Further travel engages the overdrive clutch, which locks the sun wheel to the casing to provide the necessary reaction for overdrive.
Maximum torque input limit of the box is 600 lb.ft and the power-take-off is suitable for an output of this figure. It can operate when the vehicle is stationary or in motion.
Wheelbase of the BE.TR.1PR is 9ft 6in. and the Ergomatic tilt cab is retained unchanged—as also is the Leyland 0.680 200 bhp diesel engine. But a change made in the engine cooling system for improved efficiency consists primarily of an increase of 4in. in the depth of the radiator.
Bigger brakes Braking on the new model is designed to go further even than the Code of Practice requirements for braking efficiency. The Code is not a legal document. It has been compiled by a committee consisting of the MoT and members of the SMMT and other interested bodies. It goes deeply into design considerations for commercial vehicles. This Code of Practice is likely to form the basis of "type approval" when such a system is introduced into Britain by the MoT. On design-target braking efficiencies, 60 per cent for the service brake is called for, with a secondary brake efficiency of 30 per cent and a parking brake capable of holding the laden vehicle on a 19 per cent (1 in 5.26 to 1) gradient.
To meet these figures on the new Beaver, Leyland has increased the total braking area to 688 sq.in. This increase of 6.5.3 sq.in. is obtained by the use of 6in.-wide front brake shoes as against 4.5in. on other Beaver tractive units. The rear brakes continue at 7in. wide and the front axle is rated for 5.25 tons.
Brake actuation is by Type 24 multidiaphragm chambers at the front axle and Type 20 single diaphragms at the rear axle. The front diaphragms are pressurized for the secondary system at the same time as the semi-trailer auxiliary connection. A load-sensing device is connected to the driving axle brakes to reduce the effort here under light-laden conditions and included in the brake system is a condenser /ejector unit to prevent moisture entering the air pressure circuits.
An example of the new semi-automatic Beaver will be one of the main exhibits by Leyland at the Scottish Show in Glasgow next week.