Advanced Automotive Technology: Visions of a Super-Efficient Family Car

lift schedules are realized for the intake valves. (This type of engine

burn to achieve remarkable efficiency in a small car.)^49

Another version of VVT also shuts off individual cylinders by

example, an eight-cylinder engine can operate at light load as

has been combined with

deactivating the valves.

a four-cylinder engine

lean

For
(by
deactivating the valves for four of the cylinders) and as a six-cylinder engine at moderate load.
Such systems have also been tried on four-cylinder engines in Japan with as many as two cylinders
deactivated at light load. At idle, such systems have shown a 40 to 45 percent decrease in fuel
consumption, while composite fuel economy has improved by 16 percent on the Japanese 10-15
mode test since both pumping and fictional losses are reduced by cylinder deactivation.^50 Earlier
systems had problems associated with noise, vibration, and emissions that resulted in reduced
acceptance in the market place, but more recent systems introduced in Japan have solved most of
the problems. OTA had the opportunity to drive Mitsubishi’s MIVEC V-6 which features VVT
and cylinder shutoff, and noise and vibration effects on this vehicle from cylinder shutoff were
barely noticeable.

Total effect
All of the aforementioned technologies can reduce pumping loss, increase volumetric efficiency,
increase specific output, and reduce fuel consumption at part load, but the benefits are not
additive. Most manufacturers provided estimates of benefits for several combinations; for
example, a recent paper by engineers from Porsche forecast a 13 percent reduction in fuel
consumption with no loss in performance for a system featuring variable valve timing and lift,
variable resonance intake, and cylinder cutoff (from a baseline vehicle featuring a four-valve
engine with a two-stage resonance intake and cam phase adjustment) .51 This estimate is more
optimistic than what many manufacturers believed to be possible.

DISC and Two-Stroke Engines.

Direct Injection Stratified Charge (DISC) Engines are considered as the highest level of
technology refinement for SI engines. These engines are almost completely unthrottled, and will
require variable valve timing to reach their maximum potential fuel efficiency. Their high
efficiency is associated with high compression ratio (up to 13), absence of throttling loss, and
favorable characteristics of the products of combustion. Although DISC engines have been
researched for decades (with some versions such as Ford’s PROCO almost entering production)
there is renewed excitement about DISC owing to:

(^49) U.S. Environmental Protection Agency Test Car List, Honda Civic VX Test Result,” 1993.
(^50) K. Matano et al., “Development of a New Multi Mode Variable Valve Timing Engine,”SAE paper 930878, 1993. BMW has tested a similar
system on an eight-cylinder engine, with slightly more modest results--35 percent reduction in fuel consumption at idle, 7 percent overall reduction in
DIN 1/3 test. Karl-Heinz Ziwica, BMW, personal 51 communication May 15, 1995.
C. Brustle, "Lightweight Engines with High , Specific Power,” FISITA Congress, Peking, October 1994.