Lightweight Electric/Hybrid Vehicle Design

Hybrid vehicle design 163
The battery system is designed to avoid overcharging or complete emptying and in the unlikely
event of motor failure, the Insight will run on the petrol engine alone. At the front, the suspension
consists of struts, with an aluminium forged knuckle and lower arm, anti-roll bar linked to the
dampers, and light aluminium cast wheels; while at the rear, a light and compact suspension
features a twist beam with variable cross-section, and trailing arms with bushes having a toecontrol
function. Electric power steering, optimized for feel and feedback, has been used to make
further fuel savings. It features a centre takeoff and aluminium forged tie-rod.
The company argue that in conventional petrol/electric hybrid systems, the vehicle is powered
by the electric motor alone at low speeds. At higher vehicle speeds, or when recharging is required,
engine torque is directed to the driven wheels or used to drive a generator. Such systems require
complex control mechanisms, large capacity batteries, as well as a separate motor and generator.
Honda chose instead a system in which the motor is linked directly to the engine, assisting it
during acceleration for a reduction in consumption and acting as a generator during deceleration.
When cruising, there is no assistance and lean burn keeps fuel consumption to a minimum. A very
wide, flat torque curve is achieved through the benefits of VTEC technology at high engine speeds
and the substantial boost provided by the electric motor at low and mid-range engine speeds. This
approach allows for superior fuel efficiency and excellent driving performance over a wide range
of driving situations.
The key to the engine operating at exceptionally low air/fuel ratios is rapid combustion of the
mixture, since combustion time increases as the mixture becomes leaner. By adopting a new swirl
port to enhance the turbulence of the mixture in the cylinder, a compact combustion chamber and
a high compression ratio are achieved. The design is an evolution of the conventional VTEC-E
mechanism where swirls are generated by almost closing one of the pair of inlet valves. In the new
design, the inlet ports are set up in a more vertical direction to generate more powerful swirls
flowing into the cylinder. This has been made possible with a new VTEC mechanism. Rather than
inlet and exhaust rocker arms carried on separate rocker shafts, the Insight features just one rocker
shaft with the included angle of the valves narrowed from 46 to 30°, allowing the high swirl port
shape and the compact combustion chamber to be realized. Conventional lean burn engines, with
their oxygen rich exhaust gases, mean reducing NO x emissions is technologically difficult. The
Insight’s improvement in combustion efficiency goes some way towards solving the problem.
However, a newly developed catalytic converter containing additives able to absorb NO x , provides
an elegant solution to the problem. During lean-burn driving, NO x is directly absorbed; it is later
reduced to harmless nitrogen in stoichiometric driving conditions. The system also helps to boost
fuel efficiency, since it allows a widening of the lean burn range and therefore improved efficiency.
Emissions performance is further improved by an exhaust manifold-integrated cylinder head. Rather
than a conventional arrangement of an independent exhaust port for each cylinder, the ports are
combined into one in the cylinder head structure. Considerable weight reduction is the result, but
just as important, the small radiation area minimizes heat loss, enabling quick activation of the
catalytic converter.
New technologies have reduced the overall friction of the engine by 38% compared with a
conventional 1.5 litre engine. Among the measures adopted are roller type rocker arms, adapted to
the single cam VTEC mechanism, providing a 70% reduction in friction losses. A special ‘micro
dimple’ surface treatment of the piston skirt improves the retention of the oil film between the
piston and the cylinder reducing friction by approximately 30%, in conjunction with offset cylinders
and low tensile piston rings. By using case hardening for significantly increased strength, slimmer
connecting rods have been adopted, achieving a reduction in weight of 30%. A newly developed
magnesium alloy, with a high degree of heat resistance, has been used for the engine sump in place
of aluminium alloy, giving a 35% weight reduction. Other weight saving technology includes: a