T VEHICLE DYNAMICS he relationship between a driver and their vehicle is often very special. Whether it’s the tactile nature of a sports car or the cosseting ride of a luxury sedan, every model has its own unique feel. Crafting the ride and handling characteristics of a vehicle is a true art form but still involves a considerable amount of subjective evaluation and hands-on tuning. In terms of elements such as steering feel, ride comfort and quality, and handling – the usual vehicle dynamics areas of interest – the general expectation is very high. This is particularly true in the US and European markets and is likely to be so for some time. As Dr Flavio Friesen, senior chief engineer for vehicle systems and integration at British car maker Lotus, comments, subjective measurements alone are not enough and must be complemented by numerical data from the virtual and real worlds: “Although much of the initial target-setting is driven by objective results, the process of fine-tuning the vehicle attributes will always be done subjectively. In doing so, we can better deliver on our core brand attributes.” The job of the dynamicist is tough. The process starts by defining the product and its individual qualities, including targets for steering, handling, ride comfort and performance. These can then be broken down into sub-targets for attributes, such as cornering stability, transitional stability, primary and secondary ride, with objective and subjective targets for each. Steer in the right direction Vehicle dynamics was once an exclusively analog domain, defined by the behavior of passive springs and dampers, fixed-rate steering racks and mechanical differentials. Now, however, active chassis systems have brought an element of software tuning to all these areas. “The use of electronic stability control (ESC) systems is probably one of the biggest differences in philosophy between manufacturers when it comes to vehicle dynamics development,” observes Cayman Dynamics’ John Heider. “Some manufacturers will do all their base vehicle development around the fundamental hardware, with no help from ESC at that stage. Others are far more reliant on active systems to shape the vehicle’s behavior.” This decision is very specific to the individual manufacturer, and contrary to what one might expect, it doesn’t necessarily correlate with the segment or the vehicle’s performance level. The proliferation and complexity of these systems is likely to increase as electrification becomes the norm – introducing even more control options. However, Heider believes that the fundamentals will remain the same. “There’s certainly more software development involved, whether it’s electric power steering systems or adaptive suspension systems or active roll bars,” he explains. “These are technologies that didn’t exist 20 years ago. But fundamentally they’re still doing the same job. The first step in tuning active dampers, for instance, is always to establish the passive valve codes.” On the subject of software tuning, Nandakumar Puspanathan, principal engineer for vehicle dynamics at Premcar and Prodrive China, says that the final week of a project is usually spent testing to ensure everything works together, and tuning the electric power-assisted steering (EPAS) to client requirements. “Steering feedback and effort buildup are sometimes confused with one another, especially with the ability to create an artificial feel with today’s EPAS systems. As a result, there are a number of cars with insufficient change in steering effort when there is a loss of grip – and these vehicles often have poor feedback and [do not instil] driver confidence.” It is an intricate, integrated process. Specialists develop and assess each of the chassis elements independently, then come together to test as one. Friesen says, “The role of the vehicle dynamics lead engineer is pivotal here as they function like an orchestra’s conductor, working together with the numerous chassis specialists to deliver a vehicle that is in tune with the ride and handling DNA.” For objective studies, Lotus uses a standardized assessment procedure, comprising offline simulation, test bench analysis and proving ground measurement. Subjective aspects are scrutinized, harnessing a mixture of DIL, proving ground and public road testing. “Early in the development process, we focus on base suspension setup, tire development and initial steering tuning,” explains Friesen. “We then proceed with the tuning and integration of mechatronic systems, such as rear-wheel steering, active anti-roll bars and integrated chassis controls. Here we focus on attributes such as the transition from linear to non-linear driving conditions. Toward the end of the project, the steering tuning always goes through one final confirmatory check.” Expert opinion Manufacturers frequently lean on external consultancies in their vehicle dynamics programs. According to industry www.AutomotiveTestingTechnologyInternational.com 38 MARCH 2024