E s sentials of Steering Design Described by R. Pentony, M.I.Mech.E. "
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WHEN a vehicle is difficult to control,' the driver becomes tired and prone to accident, and it is an interesting fact that often he does not correctly diagnose the cause of his fatigue," said Mr. R. Pentony, M.1.Mech.E.' in his address as new chairman of the Automobile Division of the Institution of Mechanical Engineers.
Outlining the qualities to be looked for first in the steering of a vehicle, Mr. Pentony placed them in the order of mechanical safety, ease of steering, sensitivity to touch, directional stability. absence of road shock, self-centring action, long life and adjustability.
'Allowance for Neglect
Enlarging upon these factors, he said that "in no circumstances must any part of the steering mechanism fracture or become detached when the vehicle is in motion." Steering gear should be of sufficient dimensions for the loads tmposed upon it, and allowance should be made to prevent neglect, abuse and wear from leading to serious trouble.
Ease of steering could be obtained by designing a system which had little friction or with a gear reduction of low ratio. Neither of these was permissible to its full extent. Mr. Pentony added. "for a steering of high mechanical efficiency may transmit any road shock to the driver, and he is apt to lose the feel of the Vehicle."
A gear of low ratio was dangerous because of the time required to effect a change of direction. Road shock transmitted to the steering wheel could be unpleasant and tiring, and, if the efficiency were lowered, the gear might be heavy and even more tiring to the driver. He considered that a case could be made for a variable ratio from lock to lock, and that this would be obtained through the steering box, outside linkage or a combination of both.
Directional stability depended upon stiff construction of all parts, rigid attachment between axles, springs and frame, and the construction of tyres and their pressure. The number of working parts should be reduced to a minimum, thereby preventing lost .motion from developing wheir driving straight ahead.
The steering gear," said Mr. Pentony, "should be sufficiently sensitive for the driver to appreciate what is happening at the road wheels, but excessive shock should not exist." Cobble stones should not be felt and deep pot holes only faintly discerned. Anything in the nature of permanent friction was to be deprecated Self centring, he thought, was a desirable feature which was dependent on the design of the front axle or its equivalent. When planning the inclination of the swivel pins for the selfcentring action, care was necessary to ensure that the steering action was not increased.
Longevity and Efficiency
Mr. Pentony considered that constructing a steering gear for longevity was the surest way of obtaining one with the minimum of lost motion. Adjustments for wear should be, as far as possible, .automatic, but the adjustment mechanism should be located in an accessible position, in cases where automatic adjustment was not possible. Automatic lubrication of all the frontaxle and steering bearings, together with larger bearing surfaces, was desirable, so that the lubricant was not immediately" squeezed out, as was often the case to-day.
The speaker continued by describine modern steering mechanisms, and concluded by saying that "it is only by close attention to design features which directly affect refinement and lower cost that we shall be able to maintain our place in the markets of the world against the fierce-competition offered by cars of other nations."