New, improved Sigma

Press, 22 September 1983, Page 25

New, improved Sigma

Front-wheel drive, extensive use of electronics and turbo power for two of the four versions sold in Japan are the major ingredients in Mitsubishi’s new Sigma range. In spite of the introduction of three completely new models within the last year or so, Mitsubishi sales slipped 4.2 per cent last year. The Japanese corporation evidently decided that the Sigma, a car that has been around for quite a while and looks much the same as it did when first launched although the current version is a secondgeneration model, was the cause of the decline. The new Sigma has similar exterior dimensions to the old one but, with a longer wheelbase and wider track. In appearance it is said to be not unlike West Germany’s Audi 100. Front-end treatment is similar to that of the smaller Mitsubishi Tredia, the flush-fitting headlights and integral front bumper, louvred to channel cooling air to the radiator, being notable features. The waistline is bowed slightly in the cabin area and sweeps up in the luggage boot area to create a restrained wedge shape. The designers have obviously devoted time and effort to produce a good aerodynamic shape, for the Sigma is said to have a drag coefficient of 0.36. The drive train is the now traditional transverse arrangment with the gearbox at the end of the engine and unequal-length, drive shafts. There are four engines in two capacity sizes, with and without turbocharging. The base engine is a normally aspirated 1.8 litre unit which, in effect, is a bored-out version of the Tredia engine, but with an increased compression ratio and enlarged valves. A feature is its electronically controlled carburetter that

senses the engine’s coolant temperature, throttle opening, engine speed and oxygen content in the exhaust gas to control jet mixture, enrichment and slow-cut solenoid valves in accordance with patterns reflecting engine load and temperature. The 1.8-litre turbocharged version develops about lOlkW. This, like the 2-litre turbo engine, comes equipped with Mitsubishi’s electric fuel-injection system, which is manufactured under licence from the West German Bosch firm. The normally aspirated 2litre engine is fitted with the new electro-carburetter and develops 82kW, while the turbocharged version develops 108 kW. Both engines are the same as that used in the older 2-litre Sigma, the only modification being one to eliminate tappet adjustment and at the same time reduce engine noise. Four and five-speed gearboxes, plus a 2 x 4 speed economy and power Supershift arrangement of the 1.8litre models, are offered along with a couple of electronically controlled, lockup clutch automatic gearboxes. One of these is a four-speed, having an overdrive top, and the other is a three-speed. The suspension system comprises struts in front and a torsional beam axle at the rear. The top models come with electronic suspension control. The system comprises sensors for vehicle speed, height and acceleration, a computer and a compressor that pumps air into auxiliary air-springs mounted on top of the dampers. This systems gives the suspension automatic levelling ability to compensate for loads while at more than 90km/h the car’s over-all height is lowered by 20mm for greater stability and lower drag. Additionally the dampers contain rotatable shafts that

open and close valves in the air springs and dampers to raise or lower the spring rate and the'damping force. This part of the system incorporates hard and soft settings that are selected automatically in response to lateral, longitudinal and vertical rates of acceleration. The hard setting comes into effect during cornering, acceleration and braking when the G-forces are high. It also functions when the car is travelling at more than 120km/h. The steering is also electronically controlled, the amount of assistance decreasing with rising vehicle speed rather than rising engine speed. There is also an electronically controlled rear engine mount. This supresses engine vibrations that can occur during hard acceleration and during automatic gear-shifts. The softer damping is retained for normal driving and when the engine is idling. Other and more mundane features are the eight-way adjustable front seats and a rake-adjustable rear seat backrest. The degree of thigh support afforded by the rear seat can be adjusted also. Apparently the next model in the Mitsubishi range to be updated will be the Mirage. In all probability the new

Sigma will not appear in New Zealand assembled form until late next year and it could be 1985 before the revised version of the Mirage reaches these shores