Occupants are provided with a spacious and comfortable cabin with ample leg room. Controls are designed to fall easily to hand, and the Insight driver is provided with a wealth of information by the advanced, yet logical, digital display. The central numeric speedometer is flanked on the left by a circular representation of a tachometer and on the right by a fuel gauge, battery gauge and IMA assist/charge indicator. Beneath the speedometer is a display providing average and instant fuel economy, trip mileage and odometer. Behind the two front seats and beneath the three-dimensional glass tailgate is a flat rear storage area, while lifting the rear floor section reveals further storage space.
The Insight is also practical in everyday use. The engine runs on 95 Ron unleaded petrol, servicing costs will be conventional, while the body structure will be easy to repair in the event of accident damage. The battery system is designed to avoid overcharging or complete emptying. In the unlikely event of motor failure, the Insight will run on the petrol engine alone.
The chassis is designed to offer good handling and stability characteristics in keeping with the sporty ethos of the Insight. 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. The light and compact rear suspension features a twist beam with variable cross section with trailing arms. The trailing arm bushes have a toe control function and dampers and springs are separately mounted for low floor height. Electric power steering, optimised for feel and feedback has been used to make further fuel savings. It features a centre take-off and aluminium forged tierod.
As the most advanced Honda to date, development of the Insight has been a complex process indicated by the fact that over 300 patents have been registered: 60 plus on the engine/IMA structure, 120 plus on the engine/IMA control and 120 plus on the body as a whole. The Insight is aimed at the �light green� customer who is interested in environmental considerations but who will enjoy its 'sporty' element. Production for the European market commences in January 2000 and two months later in March it will become the first mass-produced petrol-electric hybrid to be available in Europe.
Why a hybrid system?
So-called hybrid systems combine two different power sources, such as an internal combustion engine and an electric motor, in such a way that their operation is complementary. Each is designed to operate within its most efficient range, to the overall benefit of performance and fuel efficiency. 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 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 IMA system in detail
The 1.0 litre lean burn VTEC engine has been developed from scratch with the aim of ultra-low fuel consumption and reduced exhaust emissions using many of Honda�s state-of-the-art technologies. Main strategies were advanced lean-burn technology, cleaner exhaust emissions, friction reduction, and weight reduction.
Lean burn
An advantage of using efficient lean burn VTEC technology is that a considerable improvement is achieved in fuel efficiency at mid and high speed ranges as well as in city driving. At these higher speed ranges, the effect of a conventional hybrid system is negligible.
The key to operating at exceptionally low air-fuel ratios is rapid combustion of the mixture, since combustion time increases as the mixture becomes leaner. Honda has managed to overcome the problem, bringing substantial improvements in fuel economy, 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. 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 by 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 degrees, allowing the high swirl port shape and the compact combustion chamber to be realised.
Exhaust emissions
The very nature of conventional lean burn engines, with their oxygen rich exhaust gases, means reducing NOx 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 NOx, provides an elegant solution to the problem. During lean-burn driving, NOx 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 a world first, 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 minimises heat loss, enabling quick activation of the catalytic converter.
Friction reduction
The less energy lost through friction, the more that can be recovered by regeneration, and new technologies have reduced the overall friction of the engine by 38 per cent compared with a conventional 1.5 litre engine.
Among the measures adopted are roller type rocker arms, first seen in the Honda S2000 and adapted to the single cam VTEC mechanism, providing a 70 per cent reduction in friction losses; a special �micro dimple� surface treatment of the piston skirt that improves the retention of the oil film between the piston and the cylinder reducing friction by approximately 30 per cent; and offset cylinders and low tensile piston rings.
Weight reduction
A review of the whole engine structure was carried out to create the lightest one-litre engine in the world. Connecting rods, for example, are not only forged steel, but also case-hardened for significantly increased strength. Slimmer connecting rods can thus be adopted, just as they have in the Honda S2000, achieving a reduction in weight of 30 per cent.
A new Honda-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 per cent weight reduction.
Other weight saving technology includes: a thin sleeve block, the new VTEC cylinder head, bracketless ancillary equipment, a magnesium PCU case, and an increase in plastic parts (intake manifold, cylinder head cover, water pump pulley).
The IMA electric motor
The ultra-thin brushless motor of 10 kW output sandwiched between the engine and transmission is highly efficient, light and compact. The central rotor is manufactured using the lost wax method to give a precise shape and high strength, which achieves a 20 per cent weight reduction. For the rotor magnet, improvements to the neodymium sintered magnet used in the Honda EV Plus means an improvement in the magnetic flux density or torque ratio by 8 per cent, while improved heat resistance has made a cooling system unnecessary.
In order to create a thin motor, a split stator with compact salient-pole field winding and centralised bus ring forms a very simple structure allowing a width of 60 mm, 40 per cent thinner than if conventional technologies were used.
The battery pack and control system
The Ni-MH battery pack installed at the rear of the car stores generated electric energy and in turn provides the power for motor assistance. The batteries are held in a compact cylindrical pack. A series connection of 120 cells each with
1.2 V provides a voltage of 144 V. Ni-MH batteries offer stable output characteristics regardless of the charging condition, as well as excellent durability.
The power control unit (PCU), mounted alongside the battery pack, provides precision control of the motor assist and battery regeneration functions, as well as the supply of electricity to the standard 12 V battery through a DC-DC converter. The inverter, which drives the motor and the most important element in the PCU, consists of a compact three phase integrated type switching module.
New Lightweight Aluminium Body Structure
In creating the Insight�s body structure Honda has incorporated expertise gained during the development of the all-aluminium body of the NSX introduced in 1990. The target was a body offering world leading rigidity, collision safety, and recyclability, at the lowest possible weight. The weight target was a body-in-white of 150 kg, or half that of the Civic 3-door, the closest comparable sized Honda model. In actual fact the weight reduction has been 47 per cent, yet torsional rigidity is up by 38 per cent, and bending rigidity up by 13 per cent. The structure makes extensive use of extruded aluminium, which can provide a variety of cross sections and wall thicknesses to cater for the varying requirements of different body elements, to form a very rigid structure.
Thus hexagonal cross sections are used for the front side frame bringing a weight saving of 37 per cent, while also attaining high energy absorbing characteristics compared to a conventional steel frame. The side sill and roof side rail which contribute considerably to the overall body rigidity, although simpler in cross section achieve 47 per cent and 53 per cent weight reductions respectively. A new and technically demanding manufacturing technique, �three-dimensional bending forming� provides a degree of freedom in design and a reduction in the number of parts required and has been adopted, for example, to produce the roof side rails.
Widely different sections and the need for high rigidity called for a special jointing method and die cast aluminium which permits a high degree of shaping and flexibility in joining different shaped sections is used. However, in the case of the rear outrigger, where structural frames meet from three directions and which serves as the installation area for the suspension frame, an alternative was required. Its deep box-like shape means that if it were formed with the conventional die-cast method its wall thickness would become too thick and too heavy. So the thixo-cast method was used, a world first in body frame construction. This involves pouring aluminium in a half solidified, rather than molten state to create a uniform and fine metal structure allowing a 22 per cent thinner wall thickness, 20 per cent higher strength, and a 20 per cent weight reduction.
In comparison with the NSX, the Insight uses 15 per cent fewer body parts and 24 per cent fewer welding spots to give weight and productivity savings.
