Finite element modeling and analysis is common in vehicle and component development. Toyota engineers and their colleagues at the Toyota Central R&D Labs have taken the method to another aspect of vehicles: the people who drive and are transported in them. Seigo Kuzumaki, project general manager, Vehicle Safety, Toyota Motor Corp. (TMC), says, "We have found that data derived from crash test dummies has been useful—but limited." So they devised what's called "THUMS" for Total Human Modeling for Safety. This FEM model is of the entire human body—that's "entire" as in the skeletal structure, internal organs, and muscles. And there is actually a THUMS family, consisting of a typical-sized male, a small-build female, a six-year old, and because they're out there, two different-sized pedestrians.
Because an increasing amount of vehicle development is being done in the virtual world, Kuzumaki notes, THUMS is designed to be used during the virtual crash test phase.
The Toyota Way. Like other vehicle manufacturers, Toyota is increasing its safety engineering efforts. And they do it in a manner that can be described as "The Toyota Way." Kuzumaki explains that there is a "corporate agenda" at TMC "aimed at reducing accidents, death, and injuries on a global basis." He continues, "To do this, we need to understand why accidents occur and what causes injuries. First, we collect and analyze data of accidents that took place in the real world. Then, through analysis and virtual modeling, we develop countermeasures based on this data. Finally, before commercializing these countermeasures, we use actual vehicles to verify them. We believe that using this cycle from the marketplace, to the research office, to the test course, then back to the marketplace, is the key to creating safe vehicles." (Note the word "countermeasures," which is often heard in relation to the Toyota Production System.)
While passive safety is a continuing pursuit, it is the area of active safety—or the means by which accidents can be, ideally, avoided—that's of increasing concern. This area is where a panoply of acronyms can be found, from the now familiar ABS, to TRAC (traction control), EBD (electronic brakeforce distribution) to BA (brake assist). In the steering arena, there is ESP, or electric power steering and VGRS, or variable gear-ratio steering.
Putting It Together. There is an omnibus Toyota development, VDIM or Vehicle Dynamics Integrated Management. This involves the integration of the control of the brakes, steering, and engine control in a more active manner than is ordinarily the case because, according to Paul Williamsen of the University of Toyota, there is a single algorithm for orchestrating all of these aspects so that "the vehicle is more controllable and stable." For example, a VDIM-equipped vehicle has an array of sensors that provide input to the VDIM system. So by making comparisons of things like the yaw rate, individual wheel speeds, and steering angle, the system is able to determine whether adjustments need to be made via the brakes, steering, and/or throttle. Says Williamsen, "The sooner the detection, the more subtle the adjustment." In other words, VDIM works before the driver may be aware that he's losing it.*
The ability for VDIM to do its job is predicated on having things like VGRS, which varies the ratio between the pinion and the rack, and controls the turning angle of the wheels based on vehicle driving speed. VGRS features an actuator that has a reduction mechanism with strain wave gearing that adjusts the actual gear ratio between the steering pinion and rack. Because of the intelligence in that system—as well as that in the braking, powertrain, and chassis systems—VDIM is able to provide a better-driving vehicle, even for less-than-best drivers.
Chuck Gulash, vice president, Toyota Technical Center USA (Ann Arbor), notes, "When a consumer purchases a new vehicle, he or she naturally assumes that it will provide a requisite level of passenger safety. No one manufacturer owns safety, although there are many of us who continue to make it an important attribute of our products. Our goal is to continue the pursuit in developing vehicles, systems and components that make it easier for drivers to avoid accidents." Like VDIM.
*In driving the '06 Lexus GS 430s at the Toyota Arizona Proving Grounds in Wittman, Arizona, on both slick and split-mu surfaces through slaloms, I had the opportunity to experience first hand the capabilities of VDIM—and the limited capabilities of the driver. VDIM was transparent. When the VDIM was deactivated for purposes of showing the effects of VDIM—in keeping with the Toyota approach of genchi genbutsu (go see for your self the actual situation)—I managed to spin the car with a certain amount of unanticipated gusto. Fortunately for me and the test engineer who had to endure the ride, these conditions were open and safe.