Volvo opens new £4.5m
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proving ground by Paul Brockington
• A pave track with a computer-designed profile for heavy commercial vehicle tests is included in the facilities of a new Volvo £4.5m proving ground near Boris, Sweden, that was shown to some 250 journalists from 15 countries last week, the main high-speed track of 6km having banked sections that provide for speeds up to 200 kph for cars.
The final stage of the proving ground will be completed in June 1974, but existing facilities include a series of brake-testing tracks with high friction, low friction, mixed and patchy surfaces that enable braking performances to be evaluated under a wide variety of wet and dry conditions.
Apart from the 400-metre pave section a number of "life-time" test trucks with asphalted surfaces is available, notably one with divided undulating surfaces of varying "pitch" that simulate the characteristics of a cross-country route but provide for exact repeats of a particular test.
A 1 in 3 gradient section, a clay track and a salt-water trough are available in addition to forestry areas (that are employed for testing forestry machines and cross-country vehicles), a comfort track for testing shock absorbers, a simulated building construction site for testing contractors' plant and a variety of dirt roads.
Of special importance to the testing of tracks of all types, the 400-metre circular pave track has an irregular computerformulated surface pattern designed to produce resonance in every component of the chassis and bodywork somewhere along the track. The recording van is based on a former military cross-country vehicle and was demonstrated connected by a cable to a G89 32-ton-gvw artic travelling on the pave at 20 kph and 35 kph.
Signals from accelerometers and strain gauges are fed into a 12-channel amplifier and thence to a recording tape for analysis of vibrations and deflection.
The van can also be used for analysis of vehicles running on other types of track.
Prototype cross-country vehicles demonstrated during the press visit, comprised 4x4 and 6x6 types destined for the Swedish armed forces. A 52-ton-gvw double-bottom outfit was seen equipped with a TV rearview set and other safety features. And additional details were given of the controlled exhaust back-pressure system, currently applied to a TD70 turbocharged diesel (CM April 20) to aid low-load operation that will, it is claimed, later provide for operating on compression ratios down to 12 to 1 on full load when used in conjunction with an electrically energized intake heater.
Some 4000 4x4 and 6x6 cross-country vehicles have been ordered by the Swedish armed forces ordnance administration, the payloads of the two types being 900kg and 1500kg respectively. They are powered by a Volvo B30A car-type petrol engine developing 120 bhp and as demonstrated to CM have remarkable cross-country abilities.
Known as the TD7OD or city engine, the turbocharger diesel with controlled exhaust has a compression ratio of 14.5 to,1 which is adequate to create sufficient heat for starting without an intake heater.
While its peak. output is somewhat lower than the 207 bhp DIN produced by the standard TD7OB at 2400 rpm, which is fitted to the F86, its low-speed torque is more favourable and exhaust emission will meet the 1974 American Federal Regulations by a substantial margin.
Applications to bigger engines and units of lower compression ratio (down to 12 to 1) will necessitate the use of an electrically energized preheater for starting, the control valve of the turbocharger being then fully open.
The new system provides for raising the effective compression ratio of a turbocharged engine without the complication and cost of employing variable compression ratio pistons. The valve is pneumatically operated and is controlled by the throttle pedal. Closing the valve dilutes the fuel charge and raises its temperature.