Vehicle Stability• Essential on Motorways
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Three-wheel Braking of Light Vehicles Advocated to Prevent Sliding
ONLY one speaker disagreed with the forecast made by Mr. G. Grime, of the Road Research Laboratory, at a meeting of the Automobile Division of the Institution of Mechanical Engineers in London, last week, that commercial-vehicle speeds on the motorways would not exceed about 55 m.p.h. The dissenter envisaged coach
speeds around 70 m.p.h. .
The two speakers were taking part in a discussion on "The Effect of Motorways on Vehicle Design and Durability," after the presentation, of a prepared contribution by Dr. D. J. K. Stuart, of the British Motor Corporation.
Quoting speeds on Continental and American highways, Mr. Grime said 53-54 m.p.h. was the normal average in most countries. This corresponded with speeds on Preston by-pass. In America, typical operators of heavy commercial vehicles did not favour a speed as high as 50 m.p.h., but it was normally exceeded slightly.
Tyres a Problem
There would be few mechanical breakdowns at these moderate speeds, but heat generation in tyres would create a special problem. Vehicle stability would assume great importance with regard to both safety and economic running.
Anti-skid brakes should be employed, and in the case of lighter vehicles the braking effort should be applied to one of the two rear wheels (as well as the front wheels). This would reduce maximum braking efficiency by 20 per cent., but would provide sideways stability in the event of a skid. Dispelling doubts about this claim, Mr. Grime said he was "perfectly serious," and added that he would favour a device providing differential braking at the rear.
Mr. F. G. Parnell (Automotive Products Co., Ltd.) confirmed that locking the front wheels was less dangerous than locking the rear wheels, because it did not cause deflection from the line of travel. He asked whether a "limited antiskid" device could be evolved.
The need for brakes giving improved efficiency was emphasized by a number of members. One of them—a fleet operator—complained that the efficiencies of the foot and hand brakes of a new eight-wheeler were 50 per cent. and 18 per cent. respectively. Mr. Parnell replied that an efficiency of 50 per cent. was the maximum required by many commercialvehicle makers, because greater braking effort could injure the passengers and cause the loads of goods to shift forward. All wheels on an eight-wheeler should be braked.
Mr. Grime pointed out that a good braking system was often inefficient when the vehicle was overloaded. A great deal of research work would be necessary to raise the standard of commercial-vehicle braking to the average represented by private cars. When produced in quantity.
al 0 disc brakes should be as economic to manufacture as drum brakes. Improved brakes would be essential on the motorways. One of the main problems was to Eliminate lag between application and operation of brakes.
Application lag was mentioned by Mr. Parnell in connection with hand brakes. Although the multi-pull brake provided a favourable efficiency, its performance was, he said, inadequate in an emergency because of delay. He advocated that independently operated servo hand brakes should be legalized.
The relation between braking efficiency and tyre design was briefly discussed by another member, who referred to the possibilities of the low-profile cover. This might, he claimed, enable single tyres to be employed at the rear in place of twin wheels and might give improved braking.
Further observations on safety factors included a statement that wheel-hub fractures and tyre fires were frequent on the German autobahn.
A member emphasized the importance of a good view to the rear, and another speaker, citing Continental practice, said the duplication of traffic indicators should be compulsory because of the danger that could result from failure. This was supported by a member who advocated the compulsory duplication of brakelight systems. Both suggestions were commended by the chairman, Mr. R. A. Wilson-Jones.
Dealing with members' views on head-. lights, Mr. Grime stated that the reduced dazzle of yellow headlamps was derived mainly from sharper cut-off of the beam. Yellow light had slightly lower intensity than a white beam. In the main, dazzle could be attributed directly to mis-aiming the headlights. The use of full headlight power on the motorways should be prevented by law until an anti-dazzle screen had been erected in the centre.
Cabs Under Fire
Severe criticisms of cab appointments were made. A fleet operator emphasized that a "complete re-think" on driving comfdrt would he necessary. The "appalling noise of the engine" in a forward-control vehicle—the major cause of driver fatigue—would have to be isolated. Mr. Grime pointed out that a forward-control cab provided an increase in load-carrying length of 1 ft. 2 in.—a small gain for the sacrifices involved.
He claimed that there was not enough collaboration between vehicle designers and users. Higher powers would be essential for the speed increases envisaged, and it would probably be necessary to pay £100 more for the engine, as well as £100 extra for an improved cab. Engine lubrication was a prominent topic. Commenting on statements made in Dr. Stuart's contribution, Mr. F. Lawrence (Shell) said additives were available which effectively inhibited oxidation at high lubricant temperatures and prevented the formation of hot sludge and so on.
Dr. Stuart replied that most engines of motorway vehicles would operate at a high oil temperature, and large oil pumps and improved cooling characteristics might be required. In the region of 130-140° C. an additive-treated oil might be unstable when lubricating parts subject to high rates of shear.
After agreeing that finality in lubricant developments had not been attained Mr. Lawrence said some engine makers failed to ensure that the most suitable oil was used. The relatively high cost of polymer additives was an important factor to the user. Anti-scuff additives were available.
Mr. Wilson-Jones said that no statement had been published regarding the lubricating properties of viscosity improvers, the proportion of which might be as high as 5 per cent. Referring to large oil pumps, he asked why a highpressure system was necessary. Dr. Stuart replied that high pressures were not necessary for efficient engine operation, but that, with the assistance of a relief valve, they enabled a gauge reading to be obtained which afforded a reliable indica, tion whether oil was being circulated.
Criticizing typical British vehicles on account of their low oil capacity, a member claimed that adequate capacity, combined with a finned sump, would obviate the need for oil additives. An oil cooler might upset the balance of cooling. A high oil temperature could increase consumption from a normal rate of 2,000-3,000 m.p.g. to about 700 m.p.g. Experience in Germany had shown that safety at high speeds largely depended upon "the sustained reliability of small parts."
High Top Gear Needed
The necessity to employ a high top gear for motorway operations was emphasized by a number of speakers. One said that the use of an overdrive gear could reduce the oil temperature by as much as 20 per cent.
Referring to the suspension of public service vehicles, a member claimed that the application of air-hydraulic units might enable the suspension and braking systems to be interconnected in such a way that the braking effort was proportioned between the front and rear axles according to weight distribution.
On the possible use of gas turbines, Dr. Stuart said their application to heavy commercial vehicles was more feasible than to lighter types. The petrol engine had reached almost its limit of power output and consumption.
In the case of oil engines, development was concentrated on supercharging. There was no foreseeable limit to the development of the gas turbine. It should be possible to produce a unit equipped with an efficient heat exchanger which would operate as economically as an oil engine