Lighter Bodyshell with Improved Rigidity
New, laser screw and adhesive body bonding techniques, along with additional spot welding, have substantially increased overall body rigidity. This not only enhances stability and body control, but also allows for a more comfortable ride with no detriment to handling agility.
The comprehensive use of body adhesives is a major factor in the optimisation of the new IS’s handling. Rather than joining panels at points, as in spot welding, the body adhesive technique forms a bond along the entire surface of joined panels, maximising the rigidity of the joints. Over 25 metres of body adhesive has been used in the new IS, with a significant effect on the enhancement of body rigidity and improves the bodyshell’s vibration damping characteristics.
Adopted for the first time on the new LS, the IS also uses laser screw welding which is applied to the door openings and around the upper back panel. This new technique achieves a fine pitch not possible with spot welding, joining a larger panel area than traditional welding to better suppress cross-sectional deformation.
Weight reduction was a second important goal in the development of the new IS bodyshell. The use of hot stamped and high-tensile steel sheets for reinforcements and other critical components combines strength and structural simplification with a reduction in weight. This, allied to the use of aluminium in various locations including the bonnet, has made several key components lighter than in its predecessor.
Revised Front Suspension and New Rear Multilink System
The new IS combines a revised double wishbone front suspension system with a new multilink rear system similar to that of the latest generation Lexus GS. Both systems have been fine tuned to match the driving feel of the new Lexus, combining improved ride comfort with outstanding grip performance and excellent response to steering inputs.
The front suspension system features revisions to the upper support, hub and bearing, stabilizer link, bushing and bar, and the lower arm. The stabiliser layout has been revised and bar rigidity increased by 20% to reduce roll during cornering. Compensating for this increase in stabilizer rigidity, the coil spring rate has been lowered, enhancing ride comfort.
Roll rigidity distribution has been increased to help optimise steering response and stability during emergency manoeuvre. In addition, the front lower arm bushing rigidity has been doubled to enhance yaw response during steering.
The new multilink rear suspension features a separately located coil spring and shock absorber which increases shock absorber efficiency, enhancing ride comfort. This modified layout has increased the pitch between the suspension towers, increasing luggage space.
The multilink system has been substantially revised for installation in the new IS, with revisions to both upper and lower arms, the toe control arm, the upper support, shock absorber, carrier, hub bearing and stabiliser.
The characteristics of the bushing and shock absorber sliding parts have been optimised by adopting a lightweight, resin-free piston with sliding ring, achieving a 53% reduction in suspension friction. And locating the toe control arm at the back increases tyre grip by some 15% when cornering, contributing to excellent stability.
New Electric Power Steering System
Steering feel and feedback is fundamental to an enjoyable driving experience, and the IS’s new Electric Power Steering (EPS) system benefits from a steering gearbox based on that of the new GS, incorporating a variety of tuning implementations.
With particular attention paid to a clear perception of the neutral steering position, the structure and rigidity of each gear box component has been revised to create a lighter, smoother, more accurate steering feel with enhanced response to input and greater feedback to the driver.
The stroke ratio of the power steering gear has been increased by some 8%, changing the rack stroke per pinion turn to 55.6mm. The rigidity of the rack bushing has been increased to four times that of the current model, rack end bushing wear has been reduced, and the use of floating end bushings offers enhanced response to minor steering adjustments. Within the steering gearbox, pinion gear support rigidity has been increased and the ball screw structure has been modified to enhance the smoothness of motor torque transfer.
In conjunction with these comprehensive improvements, the EPS assist characteristics have also been optimised to further enhance the vehicle’s dynamic performance and steering feel.
Enhanced Braking Performance
The IS features a completely new brake system, designed to offer the quick response, smooth, linear effectiveness and controllability appropriate to a Lexus sports sedan.
IS 350 feature 334x30mm ventilated front discs, and 310x18mm ventilated discs to the rear with the lightweight aluminum alloy rear brake calipers derived from the new GS.
The compact, lightweight master cylinder and stroke simulator have been designed using knowledge gleaned from the development of the LFA. Brake booster power has been optimised to enhance brake effectiveness and controllability. And the pedal shape, angle and ratio changed to provide instant response to changes in applied pedal force and greater controllability.
Brake cooling performance has also been improved by the adoption of straighter brake ducts which provide an increase in cooling airflow volume, minimising brake fade even under protracted use.