Page 191 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Hybrid vehicle design CHAPTER 7.1

from the batteries during acceleration (so-called motor systems require complex control mechanisms, large
assist) to boost engine performance to the level of capacity batteries, as well as a separate motor and gen-
a 1.5 litre petrol engine as well as acting as a generator erator. Honda chose instead a system in which the motor
during deceleration to recharge the batteries. As a result is linked directly to the engine, assisting it during accel-
engine output is increased from a high 50 to 56 kW with eration for a reduction in consumption and acting as
motor assist, but it is low speed torque that mainly a generator during deceleration. When cruising, there is
benefits, boosting a non-assist 91 Nm at 4800 rpm to no assistance and lean burn keeps fuel consumption to
113 Nm at 1500 rpm. a minimum. A very wide, flat torque curve is achieved
A new type of lightweight aluminium body, (d), offers through the benefits of VTEC technology at high engine
a high level of rigidity and advanced safety performance. speeds and the substantial boost provided by the electric
It is a combination of extruded, stamped and die cast motor at low and mid-range engine speeds. This ap-
aluminium components and body weight is said to be proach allows for superior fuel efficiency and excellent
40% less than a comparable steel body. All outer panels driving performance over a wide range of driving
are aluminium except for the front wings and rear wheel situations.
skirt which are made from recyclable abs/nylon com- The key to the engine operating at exceptionally low
posite. Total kerb weight is 835 kg (850 kg including air air/fuel ratios is rapid combustion of the mixture, since
conditioning). Aerodynamic characteristics include combustion time increases as the mixture becomes
a streamlined nose, a low height and long tapered roof, leaner. By adopting a new swirl port to enhance the tur-
narrow rear track, low drag grille, aluminium aero bulence of the mixture in the cylinder, a compact com-
wheels, rear wheel skirt, a flat underside, and a tail bustion chamber and a high compression ratio are
designed to reduce the area of air separation. Insight also achieved. The design is an evolution of the conventional
uses low-rolling-resistance tyres that have been designed VTEC-E mechanism where swirls are generated by
to provide good handling, ride comfort and road noise almost closing one of the pair of inlet valves. In the new
characteristics. All these features give the Insight an design, the inlet ports are set up in a more vertical
aerodynamic drag coefficient of 0.25. direction to generate more powerful swirls flowing into
Further fuel savings are provided by an auto idle stop the cylinder. This has been made possible with a new
system. In simple terms, the engine cuts out as the car is VTEC mechanism. Rather than inlet and exhaust rocker
brought to a standstill, and restarting is achieved by arms carried on separate rocker shafts, the Insight fea-
dipping the clutch and placing the car in gear. In com- tures just one rocker shaft with the included angle of the

bination, Honda calculates that weight reduction mea- valves narrowed from 46 to 30 , allowing the high swirl
sures, aerodynamics and reduction of rolling resistance port shape and the compact combustion chamber to be
contribute to approximately 35% of the increase in fuel realized. Conventional lean burn engines, with their
efficiency, and the IMA system a further 65% compared oxygen rich exhaust gases, mean reducing NO x emissions
to a 1.5 litre Civic. Further features include ABS, electric is technologically difficult. The Insight’s improvement in
power steering, dual air bags, AM/FM stereo cassette, combustion efficiency goes some way towards solving the
power windows and mirrors, power door locks with problem. However, a newly developed catalytic con-
keyless entry, automatic air conditioning and an anti-theft verter containing additives able to absorb NO x , provides
immobilizer. an elegant solution to the problem. During lean-burn
The battery system is designed to avoid overcharging driving, NO x is directly absorbed; it is later reduced to
or complete emptying and in the unlikely event of motor harmless nitrogen in stoichiometric driving conditions.
failure, the Insight will run on the petrol engine alone. At The system also helps to boost fuel efficiency, since it
the front, the suspension consists of struts, with an alu- allows a widening of the lean burn range and therefore
minium forged knuckle and lower arm, anti-roll bar improved efficiency. Emissions performance is further
linked to the dampers, and light aluminium cast wheels; improved by an exhaust manifold-integrated cylinder
while at the rear, a light and compact suspension features head. Rather than a conventional arrangement of an in-
a twist beam with variable cross-section, and trailing dependent exhaust port for each cylinder, the ports are
arms with bushes having a toe-control function. Electric combined into one in the cylinder head structure. Con-
power steering, optimized for feel and feedback, has siderable weight reduction is the result, but just as
been used to make further fuel savings. It features important, the small radiation area minimizes heat loss,
a centre takeoff and aluminium forged tie-rod. enabling quick activation of the catalytic converter.
The company argue that in conventional petrol/elec- New technologies have reduced the overall friction of
tric hybrid systems, the vehicle is powered by the elec- the engine by 38% compared with a conventional
tric motor alone at low speeds. At higher vehicle speeds, 1.5 litre engine. Among the measures adopted are roller
or when recharging is required, engine torque is directed type rocker arms, adapted to the single cam VTEC
to the driven wheels or used to drive a generator. Such mechanism, providing a 70% reduction in friction losses.

193