At Lexus and Toyota we have opened a window to the future of advanced handling and stability technology with the new vehicle dynamics integrated management system (VDIM). Through the intelligent use of the latest technology, VDIM operates quicker, sooner and less overt than conventional stability control systems; anticipating, rather than reacting to loss of vehicle control. It is programmed to allow the driver to approach the vehicle's handling limits before it employs subtle adjustments to the electronically controlled throttle, brakes and steering systems to ensure that stability is not lost.
VDIM is standard on the 2006 Lexus RX 400h luxury hybrid SUV, the all-new GS 430 mid-size luxury sport sedan and, due out this October, the IS 350 entry-luxury sport sedan. VDIM is also standard on the 2006 Toyota Highlander hybrid SUV.
VDIM uses an active control strategy that takes its cues from a comprehensive range of sensors that include steering angle, yaw rate, deceleration, brake pressure, brake pedal stroke, wheel speed among others. The data is used individually by various traction control systems and collectively by the VDIM system. Vehicle data is gathered from more sources on board the vehicle than ever before, and it's processed much more rapidly, helping to make VDIM less obtrusive yet highly effective.
It includes 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), electronically controlled brakes (ECB), and in the GS 430, variable gear ratio steering (VGRS). VDIM then integrates all of these elements with powerful proprietary software to help seamlessly manage the total vehicle driving dynamics.
Our ECB system 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 that was first introduced on the Lexus GS 430 and recently introduced on the Lexus LX 470. VGRS provides several benefits, including active steering, that enhance driving pleasure and control in a seamless manner.
First, it provides a relatively quick steering ratio in low speed conditions, which notably improves maneuverability for parking and similar situations. From low to medium speeds the steering ratio progressively slows to levels more appropriate for driver comfort in city driving. In higher speed conditions such as freeway driving, the steering ratio is reduced even further 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 slight delay in steering response — something that occurs in all vehicles. This function helps enhance driver feel in lane changes and other transition maneuvers.
Perhaps most important, in difficult driving conditions VGRS interacts with other systems via VDIM to actively and automatically apply subtle changes in steering angle ratio and steering effort in order to assist the driver in maintaining smooth control, even in side-winds, all while remaining virtually transparent to the driver.
The EPS system is yet another important steering development that makes contributions to driver feel and controllability by using 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 all of the traction control technologies working together under the VDIM “umbrella,” handling smoothness is dramatically enhanced. Whether driving through town or enthusiastically on a winding road, the VDIM system works constantly and seamlessly to maintain comfort and driving balance, without spoiling the fun.
ABOUT THE AUTHOR
Robert S. Carter is vice president and general manager of the Lexus division, Toyota Motor Sales USA, Inc.