Page 192 - Automotive Engineering Powertrain Chassis System and Vehicle Body

CH AP TER 7 .1 Hybrid vehicle design

A special ‘micro dimple’ surface treatment of the piston of freedom in design, and a reduction in the number of
skirt improves the retention of the oil film between the parts required has been adopted, for example to produce
piston and the cylinder reducing friction by approxi- the roof side rails. Widely different sections and the need
mately 30%, in conjunction with offset cylinders and low for high rigidity called for the special jointing method
tensile piston rings. By using case hardening for signifi- involving die cast aluminium, which permits a high
cantly increased strength, slimmer connecting rods have degree of shaping and flexibility in joining different
been adopted, achieving a reduction in weight of 30%. shaped sections. However, in the case of the rear out-
A newly developed magnesium alloy, with a high degree rigger, where structural frames meet from three di-
of heat resistance, has been used for the engine sump in rections and which serves as the installation area for the
place of aluminium alloy, giving a 35% weight reduction. suspension frame, an alternative was required. Its deep
Other weight saving technology includes: a thin sleeve box-like shape means that if it were formed with the
block, the new VTEC cylinder head, bracketless ancillary conventional die cast method its wall thickness would
equipment, a magnesium PCU case, and an increase in become too thick and too heavy. So the thixo-cast
plastic parts (intake manifold, cylinder head cover, water method was used, said to be a first in body frame con-
pump pulley). struction. This involves pouring aluminium in a half
The ultra-thin brushless motor of 10 kW output solidified rather than molten state to create a uniform
sandwiched between the engine and transmission has and fine metal structure allowing a 22% thinner wall
a central rotor manufactured using the lost wax thickness, 20% higher strength, and a 20% weight re-
method, to give a precise shape and high strength, duction. In comparison with the NSX, the Insight uses
which achieves a 20% weight reduction. For the rotor 15% fewer body parts and 24% fewer welding spots to
magnet, improvements to the neodymium sintered give weight and productivity savings.
magnet used in the Honda EV Plus mean an improve-
ment in the magnetic flux density or torque ratio by
8%, while improved heat resistance has made a cooling 7.1.5 Hybrid passenger and goods
system unnecessary. In order to create a thin motor,
a split stator with compact salient-pole field winding vehicles
and centralized bus ring forms a very simple structure
allowing a width of 60 mm, 40% thinner than if con- 7.5.1 Hybrid-drive buses
ventional technologies were used. The Ni–MH battery
pack installed at the rear of the car is held in a compact Passenger service vehicles have been the first to use
cylindrical pack. A series connection of 120 cells each hybrid drives on a commercial scale, usually employing
with 1.2 V provides a voltage of 144 V. Ni–MH bat- a series layout. In a series hybrid configuration, part of
teries are said by the company to offer stable output the traction energy is converted into electrical energy,
characteristics regardless of the charging condition, as and then into mechanical energy, and part flows to the
well as excellent durability. The PCU, mounted along- wheels directly via a mechanical transmission. It is argued
side the battery pack, provides precision control of the that this configuration can potentially offer higher overall
motor assist and battery regeneration functions, as well efficiency. In a series layout, all the IC engine energy is
as the supply of electricity to the standard 12 V battery converted into electrical energy and then into mechanical
through a DC/DC converter. The inverter which drives energy. Such a configuration could offer advantages
the motor, and is the most important element in the where the electric motor is designed as a very high effi-
PCU, consists of a compact 3 phase integrated type ciency unit regardless of the load upon it. Furthermore,
switching module. the ability to use pure electrical transmission allows for
The weight target was a body-in-white of 150 kg, or flexibility, in system management, in optimizing engine
half that of the Civic 3 door, the closest comparable sized operating conditions and reducing noise output. It also
Honda model; compared with the Civic it was reduced to allows greater freedom in mechanical packaging, including
47%, yet torsional rigidity is up by 38%, and bending electric motors direct driving the wheels, and for the
rigidity up by 13%. Hexagonal extruded aluminium incorporation of future fuel-cell technology.
cross-sections are used for the front side frame, bringing This was the thinking behind the choice of a series
a weight saving of 37% while also attaining high energy system by Fiat in their pioneering hybrid bus, Fig. 7.1-17,
absorbing characteristics compared to a conventional a flow diagram for the system being shown at (a). The
steel frame. The side sill and roof side rail which con- DC compound motor used, with separately excited field,
tribute considerably to the overall body rigidity, although had interpoles and compensating windings to expand the
simpler in cross-section, achieve 47% and 53% weight load range of maximum efficiency operation both as
reductions respectively. A new manufacturing technique, a motor and generator. Armature current was varied, by
‘three-dimensional bending forming’, provides a degree means of a thyristor chopper, from zero to base speed,

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