In truth, there’s also a display on the facia to tell you which of the three power units
(a petrol engine and an electric motor to drive the front wheels, and a second electric motor for the rear wheels) are in use at any time.
Toyota is proud of this vehicle, and justifiably so. It incorporates the lessons learned from the company’s first production hybrid, the Prius, which was launched in December 1997 and has already sold more than 100 000 worldwide. The Estima, of which 7 000 examples have been sold since the launch in June 2001, is the first production hybrid to have four-wheel drive. But it is not an off-road vehicle; the second pair of wheels are driven to improve traction on slippery roads.
To understand the advantages of a hybrid vehicle it’s worth looking at a conventional car. The average saloon needs only between 25 and 30 per cent of its power at normal cruising speeds, with the rest kept in reserve for hills and acceleration. The engine spends a great deal of the time at a fairly small throttle opening, where it is very inefficient, so it uses more fuel than necessary. One answer is to have an extra power source that can be activated when the driver demands more power, and this is where the hybrid enters the picture.
At the front of the Estima is the petrol engine, linked to the first electric motor by a planetary gear set. These two units drive the front wheels via a CVT (continuously variable transmission) and two clutches. The petrol engine displaces 2,4 litres and develops 96 kW at 5 600 r/min and 190 N.m at 4 000 r/min, while the front electric motor develops 13 kW and 110 N.m.
The rear wheels are driven by the second electric motor, which develops 18 kW and 108 N.m. Both electric motors run on 216 volts AC. An inverter changes the propulsion battery’s DC to AC to power the vehicle, or change the 216-volt alternator’s AC to DC to charge this battery as well as the 12-volt lead-acid unit that powers the accessories.
At the front of the Estima is the petrol engine, linked to the first electric motor by a planetary gear set. These two units drive the front wheels via a CVT (continuously variable transmission) and two clutches. The petrol engine displaces 2,4 litres and develops 96 kW at 5 600 r/min and 190 N.m at 4 000 r/min, while the front electric motor develops 13 kW and 110 N.m.
The rear wheels are driven by the second electric motor, which develops 18 kW and 108 N.m. Both electric motors run on 216 volts AC. An inverter changes the propulsion battery’s DC to AC to power the vehicle, or change the 216-volt alternator’s AC to DC to charge this battery as well as the 12-volt lead-acid unit that powers the accessories.
The auxiliary electric power units make it possible to run the petrol engine at fuel mixtures closer to the chemically correct, resulting in a further reduction in emissions. Special attention has been paid to engine internals to reduce frictional losses. For example, the bore centrelines are offset compared to the crankshaft centreline, to reduce the amount of side-thrust on the power stroke.
Driving the hybrid is easy, once you get used to some unusual features.
When you turn the key, the engine does not start immediately, but one or two
seconds later. There are none of the typical starter motor sounds, as the engine is turned over by a watercooled 216-volt AC integrated starter/alternator driven by a belt, which explains why starting is so silent. The engine idles very quietly, and cuts out when you stop for more than a few seconds. If you pull away very slowly, the power comes from the two electric motors, but at about 10 km/h the petrol engine starts and from then on it will supply most of the power. Floor the throttle, and all three units combine.
At a constant cruising speed all the power is supplied by the petrol engine. When you coast or brake, the two electric units change to alternators, to charge the main nickel-metal-hydride battery. The facia displays a clever diagram that shows you which power unit is in use and when charging is taking place.
Initially, you’re so fascinated by the diagram that you fail to pay full
attention to the road. The switchover between power units, the starting of the petrol engine, and the control of the CVT are in the hands of an electronic control unit. The changes are seamless, but the transmission is not as sophisticated as the Multitronic used in the latest Audis.
The engine frequently revs without any extra acceleration becoming apparent, similar to driving a car with a slipping clutch, but the effect can be minimised by not pushing the throttle pedal down fast. One of the advantages of this hybrid became apparent when we used the air-conditioning system on a very hot day with the vehicle and engine stationary. The outlets supplied cold air as if the engine was running, but after some minutes the engine started automatically, ran for a few minutes, stopped again, and continued this cycle as long as the air-con was engaged. Another advantage – but only in Japan – is the provision of two 100-volt AC power sockets, suitable for domestic appliances such as kettles, small fridges or computers.
The rest of the hybrid Estima (Previa in some markets) is similar to the normal petrol version. There are sliding doors on each side, and a number of storage spaces. The braking system features electronic control, which provides for wheel-by-wheel braking, and is combined with a sophisticated stability control system.
The parking brake is unusual, but effective. It is engaged by a foot-operated pedal similar to the unit fitted to most Mercedes-Benz models, but differs in being released by pressing the same pedal again. Assistance for the power steering system is electric, so a constantly-running pump is not necessary, resulting in a claimed three per cent reduction in fuel consumption. However, the steering is very light, and lacks feel. An audio system is hidden behind the screen that shows details of the power flow, but a press of a button will open it up so that a CD can be inserted.
Performance is quite brisk, with 100 km/h coming up in 13,22 seconds, while top speed is limited to an indicated 180 km/h (a real 167 km/h). Acceleration is about the same as that of an average two-litre MPV, with the electric motors and the CVT keeping torque at a high level.
Fuel consumption depends very much on the driving conditions. Hybrids are at their best in town traffic, where the computer can select the best power unit for prevailing conditions. Every closed throttle signals a regenerative charge of the battery, and the engine is cut during long stops.
When cruising at a constant speed, the petrol unit does all the work, which is when fuel consumption is at its worst. Our test route covers freeways and town traffic, and includes a mountain pass, giving a good mix of different conditions, so our overall index of 9,4 litres/100 km is a lot better than the 12-plus that one can expect from a similar petrol-only MPV.
