"Making our vehicles both secure and enjoyable to drive is one of the highest priorities at Lexus," said Lexus Group Vice President and General Manager Denny Clements. "The new GS is already a great handling car, but VDIM allows it to be driven much closer to its limits while maintaining the seamless quality of operation that our customers expect."
VDIM enhances handling and traction control systems that normally react to an already unstable condition by anticipating tire slippage before a skid, slide or wheel spin occurs and make stabilizing corrections that maximize dynamic capability. This coupled with tight integration of all systems makes VDIM feel transparent to the driver, making driving more enjoyable.
To do this, VDIM uses an active control strategy that takes its cues from a comprehensive range of sensors including steering angle, yaw rate, deceleration, brake pressure, brake pedal stroke, wheel speed and others. Their signals are used individually by the various traction control systems and collectively by VDIM. Data is gathered from more sources and processed earlier and faster than previous designs, helping to make VDIM less obtrusive yet highly effective.
These proven systems include Vehicle Stability Control (VSC), Traction Control (TRC), Brake Assist (BA), Anti-Lock Brakes (ABS) and Electronic Throttle Control with intelligence (ETC-i). In addition, three important new technologies are employed that are central to the effectiveness of VDIM: Electric Power Steering (EPS), Variable Gear Ratio Steering (VGRS) and Electronically Controlled Brakes (ECB).
VDIM then integrates all of these elements with powerful proprietary software to help manage the total vehicle dynamic package.
ECB is one of the key new technologies that make VDIM possible. It's a "brake-by-wire" system that translates brake pedal pressure into electric signals that, via computer control, help provide precise and optimized braking control in virtually any traction condition. The ECB system is also backed by conventional hydraulic brake control in the unlikely event of electronic failure. ECB's electronic control provides quick brake response when needed, which helps the VDIM system to anticipate and help correct skids before they happen.
Although new in this application, the VGRS system is a further development of the technology recently introduced on the Lexus LX 470. VGRS provides two benefits that the driver can feel by electronically adjusting the steering ratio according to vehicle speed.
First, it provides a relatively quick steering ratio in very low speed conditions, which notably improves maneuverability for parking and similar situations. From low to medium speeds the steering ratio progressively slows to appropriate levels for driver comfort in city driving. In higher speed conditions such as freeway driving, the steering ratio is reduced (slower) in order to help provide a more secure and comfortable feel for the driver.
Another important function of VGRS is called "differential steering control" which helps the steering system correct for a delay in steering responseï¿½something that occurs in all vehicles. This function helps enhance driving feel in lane changes and other transitional situations.
Perhaps most importantly, in difficult driving conditions VGRS interacts with other systems via VDIM to actively and automatically apply subtle changes in steering angle, ratio and effort in order to assist the driver in maintaining smooth control, even in side winds, all while remaining virtually transparent to the driver.
EPS is yet another important steering development that makes contributions to driving feel and controllability. Rather than using the purely passive hydraulic assist found in conventional power steering systems, EPS uses precise electronic assist via the built in DC motor in the steering gear housing. The assist is computer controlled to help provide comfortable and controllable levels of steering effort in most driving situations. With VDIM interaction, the amount of assist can be instantly varied for the conditions at hand.
By eliminating the engine-driven hydraulic pump, EPS also reduces fuel consumption. And stripped of the usual hydraulic system of pump, hoses, pipes and fluid, the simplified steering gear is lighter and more compact than conventional steering systems.
With all of the traction control technologies working together under the VDIM "umbrella," handling and smoothness is dramatically improved. Whether driving through town or enthusiastically on a winding road, the VDIM system works constantly and seamlessly to maintain comfort and handling balance, without spoiling the fun. This makes VDIM a perfect match for the high performance levels of the 2006 Lexus GS 430 luxury sport sedan.
Credit: Lexus USA