The Toyota Prius Hybrid - Part 3

In the final part of our special on the Toyota Prius hybrid vehicle, we take a look beyond its complex petrol/electric drive systems...

Multi-Monitor System

One of the key features of the Prius interior is its 5.8-inch electro-multivision touch screen. The screen serves as the controls for the audio system and the optional satellite navigation system.

The touch screen audio control allows adjustment of all sound parameters - volume, bass, treble, etc - as well as the sound source. Standard fitment is a 6-stack CD player, AM/FM tuner and cassette deck.

The navigation system uses a DVD data storage module, which is installed beneath the driver's seat. A single DVD holds all of the road map information for Australia - the equivalent of sixteen street directories. The DVD system gives the benefit of quick recomputation of a route if the driver misses a turn.

A dedicated navigation ECU is used, taking inputs from a vehicle speed and gyro sensor. Satellite inputs are derived from an antenna integrated into the front of the dashboard.

A dual map function provides an overall route overview and close-up details of the next turn. The map scale can be changed, and overall map can be oriented so that North faces 'up' or in the direction of travel. Voice guidance is used in addition to the map display.

There are also a few monitor screens that can be viewed.

The Energy Monitor screen shows the operating status of the hybrid system - like whether it's running directly off the HV battery or it is regenerative braking. It's the screen to watch when you're learning how the hybrid system works. The state of HV battery charge is also shown.

This Consumption screen is useful for examining past driving habits. The average fuel consumption - indicated in litres per 100 kilometres - is shown in 5-minute intervals. The instantaneous fuel consumption rate is also shown. Battery charge recovered is shown with 'stars', each marking 50Wh regenerated. Total fuel consumption (before resetting) and total travel distance are also shown.

The vehicle's service history can also be entered into the Maintenance screen.

Body

The Prius body is amongst the most aerodynamic in its class. Toyota has paid particular attention to the contours of the A-pillar, external mirrors and windscreen glass. The height and shape of the bumper has also been optimised to "rectify" the airflow under the floor and along the body sides.

Undercarriage airflow is further enhanced with specially shaped rear floor, fuel tank and engine undercover. Note also the small fairing placed immediately in front of each wheel - these help to smooth the airflow around the tyres.

From front to rear, the top surfaces of the Prius are shaped to provide attached airflow over its entire length. This - combined with a sharp boot cut-off and rear spoiler - help to achieve a very low co-efficient of drag. Toyota claims the Prius has a wonderful 0.29 Cd - especially good considering the small size of the car.

Structurally, the body has been designed to absorb front and side impact energy, and the occupant cell gives minimum deformation. Many of the panels - such as the doors, bonnet and boot - are made from high-strength steel. Standard safety equipment includes pillar reinforcements, side-impact beams and floor cross-members, reinforced joints, energy absorbing pads in the front door panels and centre pillar garnish and a head impact structure that deforms internally. The HV battery is fully sealed and mounted in the middle of the vehicle, its high power cables are heavily shielded and routed under the cabin floor and are protected from stone damage.

Other safety features built into the Prius are front seatbelt pre-tensioners and force limiters.

Using an electric sensing system, the pre-tensioners minimise occupant movement in the event of an accident by pulling on (ie tensioning) the belt. The seatbelt pre-tensioners activate at the same time the airbags deploy. In a relatively large collision, the tension of the seatbelt applied to the occupant is known to be quite high. The Prius' force limiters restrain this tension to control the amount of force applied to the occupant's chest area. Fitted to the rear seat are ALR (Automatic Locking Retractor)/ELR (Emergency Locking Retractor) seatbelts and a child restraint anchorage behind each seating position.

Noise and vibration is reduced through the use of a 'dash panel silencer', floor silencer, foamed urethane sponge, felt and silencer pads applied to the roof and pillars. The raw material for much of the soundproofing has been recycled.

Suspension

The front of the Prius is suspended by MacPherson-type struts teamed with L-shaped lower arms. The system incorporates anti-dive geometry, 1mm of toe-in, one-degree and two-minutes of castor and twenty-six-minutes of negative camber. Toyota's 'Nachlauf geometry' has also been built in - by locating the king pin axis ahead of the axle centre, this is said to achieve excellent straight-line stability and improved steering feel. A front swaybar is fitted, linked to the shock absorber body. The shock absorber itself is a low-pressure gas sealed type.

The rear suspension uses trailing arms and a curved torsion beam axle with toe control links. The toe control links (integrated into the trailing arms) deform during cornering to reduce toe-out of the outside rear wheel while cornering; this improves stability. Alignment is set at 1mm toe-in and one-degree 30-minutes negative camber. The rear dampers are of the low-pressure gas sealed variety and rear swaybar is also installed.

Double row angular ball bearings are used inside the front and rear axles - these are said to offer low rolling resistance.

Brakes

The Prius is slowed by 255mm ventilated front discs and 269mm solid rears. Because the hydraulic braking system of the Prius cannot always rely on the manifold vacuum of the petrol engine for assistance, its pedal booster assembly incorporates several necessary components - a pump and pump motor, accumulator, pressure switches, relief valve reservoir tank and brake fluid level warning switches.

The pump and pump motor are used to draw the fluid from a reservoir tank and provide high pressure to the accumulator. The accumulator stores the hydraulic pressure generated by the pump; this is needed for normal braking and regenerative brake 'cooperative control'. Pressure switches are used to monitor the pressure inside the accumulator and control the pump motor. If the malfunctioning pump operates continuously, a relief valve returns the fluid to the reservoir tank.

The master cylinder is incorporated into the booster assembly. The master cylinder generates the hydraulic pressure depending on brake pedal effort. The brake booster regulates accumulator pressure in accordance to pedal effort and introduces this pressure to the booster chamber, giving power assistance.

So there you have it - that's the final part to our technical run-down of Toyota's brilliantly engineered Prius hybrid.

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