Prius+ 2012 DPL: A flat ride combined with smooth handling

The Prius+'s bodyshell combines the high torsional rigidity fundamental to greater ride comfort with the light weight essential to maximising the efficiency of its Hybrid Synergy Drive^® Powertrain.

The use of high tensile steel in components such as the B-pillar and rocker reinforcement, and the use of hot press materials in the roof reinforcement and front door impact beams offers significant weight savings. The use of an aluminium bonnet and front bumper reinforcement brings further weight reductions.

Particular attention has been paid to torsional rigidity, with reinforcement and bracing optimally positioned throughout the bodyshell.

Improving frontal body rigidity, the front suspension spring supports are coupled with a straight shaped cowl front. Lateral rigidity is improved by the adoption of a cross section which couples the left and right inner wheel housings. To the rear, the cross section member surrounding the back door opening incorporates circular reinforcement to optimise rigidity.

Driving stability is enhanced by the reinforcement of the front suspension tower through the coupling, with a brace, of the front spring support, cowl and front pillar.

In combination, these measures have increased torsional rigidity of the Prius+ bodyshell by 15% over that of a standard Prius. This enhanced body rigidity allows for the adoption of a softer spring setting to improve ride quality with no detriment to handling stability.

Revised Suspension

The Prius+ features the MacPherson strut front and torsion beam rear suspension systems of the standard Prius. However, both front and rear systems have been revised to combine greater agility with increased ride comfort.

To the front, a high caster angle of 6.5 degrees and an optimised stabiliser layout offer excellent stability and steering feel. The shock absorber features a specially designed piston valve with expanding oil paths. This allows for reduced damping force at high piston velocities, thereby reducing impact shock to maintain excellent handling.

The characteristics of the multipass upper support structure have also been optimised for the Prius+. The structure separates coil spring and shock absorber inputs into two pathways, allowing the spring input to be transmitted to the body without going through the upper support. This allows the rubber section to be designed specifically to manage shock absorber input, making it more efficient, and contributing to an ideal balance of handling and ride comfort.

In the case of the Prius+, a reduction of dynamic spring rate in the radial direction of the upper support has reduced road noise, while a 25% increase in the vertical damping coefficient helps realise an even more supple ride for greater comfort.

To the rear, the torsion beam suspension also benefits from an expanding oil path shock absorber. Shock absorber and coil spring mounting location shave been separated to widen the loadspace, and the shock absorber upper mounting has been set 42 mm lower than that of the Prius to further maximise luggage volume. Angled carrier bushings allow for neutral handling, with an understeer tendency to help enhance steering precision.

Improved Electric Power Steering (EPS)

The Prius+ shares the speed-sensitive Electric Power Steering (EPS) of the standard Prius, but it has been tailored to the specific handling characteristics of Toyota's new 7-seat full hybrid.

The system incorporates a high rigidity intermediate shaft design, and the steering gearbox is attached directly to the front suspension member for optimum system rigidity and steering response.

Specific to Prius+, a new control logic and a revised steering gear ratio of 18.1 further enhances the smooth, natural feel of the EPS system.

New Pitch and Bounce Control

The Prius+ introduces the world's first application of a new Pitch and Bounce Control system in a hybrid model. By automatically adjusting electric motor torque in direct response to road surface conditions, the system is able to reduce the pitching motion of the body, improving both ride and handling.

The system uses wheel speed sensor information to establish when the nose of the vehicle is either lifted or lowered. When the nose is lifted, the HSD system's ECU momentarily reduces motor torque to compensate. When the vehicle nose dips, the system adds torque to compensate in a similar manner.

Though system adjustment of electric motor torque is measured in extremely small quantities, it has a noticeable effect on ride and handling. Ride comfort is improved through the perception of a flatter ride due to reduced body movement. And steering feel around the centre line is improved through better ground holding of the tyres.

Enhanced NVH for Uniquely Quiet Driving

Reinforcing the extensive Noise Vibration and Harshness (NVH) suppression measures inherent in the Prius+'s aerodynamic styling and ultra-quiet Hybrid Synergy Drive^® system, particular attention has been paid to noise and vibration reduction.

As with the standard Prius, road and engine noise have been rigorously suppressed through the comprehensive use of high-performance sound proofing materials throughout the engine and passenger compartments. Full thickness glazing and an acoustic windscreen design further reduce wind noise for improved quietness at cruising speeds.

The dashboard inner silencer has been redesigned to improve acoustic separation from the engine bay, and layers of thinsulate up to 23 mm thick have been applied to the back of the instrument panel and the undercovers.

In addition, reducing the spring rate of the upper front suspension mount rubber bushings and adopting newly developed tyres has reduced the amount of road noise, making the cabin even quieter.

As a result, the new Toyota full hybrid sets the highest standards in Noise, Vibration and Harshness (NVH) reduction, sound absorption and vibration damping. This ensures customers enjoy a cabin environment of unequalled calm and quietness at all vehicle speeds.