(Ride & Handling)
Finding the Yin and Yang, Ride Comfort and Easy Handling
It is well known that two important dimensions of vehicle performance—ride and handling—are inversely proportional goals, such that focusing on one dimension unfortunately compromises the other. And so the engineers must strive to find the optimal balance that suits the characteristics of the model in development—a task easier said than done. R&H performance is “felt” at a sensory level that is not easily quantified, and every driver, each with different habits, seems to have divergent criteria for evaluation.
Still, Hyundai Motor Group is striving to find that balance: under the larger premise of designing a “Fun to Drive” car, we are developing various R&H technologies that best suit the driving habits of our most representative groups of consumers.
TECHNOLOGYCore Technologies of R&H
The Optimal Balance Between the Passenger, Vehicle and the Road
An important yardstick for R&H performance is whether the vehicle responds well to the driver’s intention. Sometimes, the vehicle must be able to smoothly cruise the uneven surface, softening the shock delivered to the passenger; other times, such as during high speeds or while cornering, it is also important to maintain firm stability, the compromise to ride comfort notwithstanding.
For those who maintain more than a passing interest in R&H, the terms ‘steering’ and ‘suspension’ should be familiar. It is not an understatement to say that the history of the steering wheel is effectively the history of automotive handling. In the early years, the steering wheels were mechanical. Then came the ‘power steering’ system, whereby the driver’s steering effort was assisted hydraulically. Around the new millennium came the C-MDPS, which added a motor to the steering column, and the R-MDPS, which added an electric motor to the rack between the front wheels; together they gave the drivers options on a system that would best suit their habits and needs.
Meanwhile, the suspension, another important part responsible for ride comfort, was witnessing innovations that allowed it to better deal with various road surfaces and ensure vehicle stability. The mechanical suspension of the early years evolved by employing a variable damping force controller; then, when electronic control mechanisms became the new mainstream, it evolved into the modern-day ECS (Electronic Control Suspension), now able to more rigorously secure ride comfort in all situations.
The modern R&H research seeks the simultaneous development of both the steering and the suspension, zoning in on the ever-coveted optimal balance that maximizes handling and minimizes compromise to ride comfort. In that vein, we are tapping into our accumulated R&H know-how in high-performance vehicles (e.g. WRC race cars), internalizing its lessons into our mass-produced vehicles.
1. Ride ComfortMeticulous in Design: The Suspension
In Search of Simultaneous Improvement of R&H
The suspension system, one large pillar of R&H performance, works to minimize the physical shock delivered to the passengers in the cabin while also maintaining the physical balance of the vehicle. The system is composed of many parts—the shock absorber, coil (or air) spring, stabilizer bar, lower arm, to name a few—that serve critical roles in the system’s functionality. So improving the suspension implies not just a holistic improvement of the system but also optimizing the structure and characteristics of individual parts.
To that end, one recent focus in R&H development has been achieving a more meticulous suspension design—one that can be varied to match different segments and the increasingly divergent needs of modern consumers.
For large rear-wheel-drive cars, the suspension received structural changes prioritizing a luxurious, tranquil ride. The dual-type upper arm on the front wheel was replaced with the single-type, for improvements in not only comfort but also steering; the rear-wheel assist arm was moved backward (with respect to the vehicle’s forward direction), which allowed the rear wheel to stay straight without veering outside while cornering. Lastly, most of these parts were made in aluminum, contributing to the vehicle’s lightweight design and sprightly handling.
Mid-to-large front-wheel-drive cars’ suspensions are characteristically difficult to adjust. Make it too firm, and the car will feel as if it is “jumping” across the road surface; make it too soft, and the rear wheels will often lose their grip during high speeds. To alleviate these problems on both ends, the engineers applied the HRS (Hydraulic Rebound Stopper) and the MVS (Modular Valve System) to the rear suspension, effectively reducing the rebound shock to the rear seats and improving anti-rolling and shock absorbing.
For the sport sedans that embody the brand’s “Fun to Drive” philosophy, the front wheels were equipped with lower arms made of two aluminum links. The strut was inserted directly into the brackets, helping improve the tires’ grip during high speeds and/or cornering. In addition, rebound springs were inserted into the damper’s interior, working to minimize the intensity of the wave-like motion of the car over a speed bump and to prevent the tires from being lifted during fast cornering. The rear wheels also underwent a structural change in the assist arm, again improving cornering stability.
The change in ride quality is most visible while traveling a curved road. One problem common to old car platforms was that while cornering a curve, the front wheels were prone to understeer (tires slip in the direction you’re traveling, thus increasing the turning radius of the vehicle), compounded by the issue of the rear wheels not responding in time.
To address this issue, changes were made to the caster trail and angle in the front wheel. The caster sets the degree by which the kingpin (steer) axis slants toward the inside/rear of the vehicle, and its angle and trail both influence the steering: caster tends to add damping, while trail tends to add ‘feel.’ Both the caster angle and trail were enlarged, improving stability in high speeds. In the rear wheel, the mounting angle of the shock absorber was adjusted. Previously mounted in a slight forward slant, it now stands nearly straight, better absorbing the shock from traveling protruding surfaces.
Beyond these structural changes, the ECS is another particularly noteworthy evolution to the suspension. The vertical acceleration sensors mounted on the front and the rear of the vehicle measures the car’s movement and sends the measurements to the ECU (Engine Control Unit). The ECU analyzes this data and determines the optimal damping force, and exerts this force to the vehicle via the electronically controlled shock absorber. The rebound spring inside the damper also serves a big role in this process; it limits the intensity of the wave-like motion of the car over a speed bump and prevents the car body roll during corners from lifting the tires.
The Evolution of the Suspension
Preview Air Suspension — Automatic Adjustment of Car Body Height
A technology that uses the forward-facing camera and the navigation info to “preview” the road conditions ahead and pre-adjusts to the optimal damping force.
2. HandlingMore Intricate, More Delicate: Handling
In Search of Nimbleness in Steering
The rationale behind the evolution of the steering wheel to the MDPS (Motor-Driven Power Steering) was simple: better fuel economy. Hydraulic steering was superb in reducing the driver’s steering efforts and in securing stabler handling, but because it used the power from the engine to operate the associated parts, it worsened the fuel economy.
Power Steering was born to address this issue; depending on the mounting position of the motor, it was called either C-MDPS (Column) or R-MDPS (Rack), and was selectively applied to vehicles with the capacity, cost, and weight in mind.
The C-MDPS has the motor mounted on the steering column, and its main advantage is its ease of access. For normal drivers using their vehicles for everyday use, the C-MDPS should more than suffice their handling needs. On the other hand, the R-MDPS has the motor mounted on the rack gear, and its advantage is in superior handling ability guaranteed by having the motor directly control the steering gear. More recently, the motor and the ECU of the R-MDPS have become more intricate enough to potentially serve as the foundation for autonomous driving systems.
The ‘key tech’ in handling development would be the VGR (Variable Gear Ratio) technology, a marked improvement over the fixed gear ratio found in previous steering systems. The VGR, as the name suggests, varies the gear ratio (the proportion of the wheel movement against the movement of the steering rack bar) depending on the situation. At high speeds, the VGR reduces the gear ratio to realize more sensitive handling, and during curves that require large steering movement, the system increases the gear ratio for added nimbleness. Together with other mechanisms like the R-MDPS, DTVC (Dynamic Torque Vectoring Control), and M-LSD (Mechanical-Limited Slip Differential), the VGR contributes to more nimble and stable handling of today.
Another technology that serves to improve the intricacy of steering is the DTVC. The DTVC is the next-gen evolution of the torque vectoring technology, which applies brakes to the inner wheel to smoothen the cornering process. Unlike torque vectoring, which only activates while exiting corners, the DTVC is active throughout the cornering process, delicately applying the needed brake pressure to the inner wheel even when the vehicle is accelerating or maintaining its speed. This helps prevent understeers, not to mention cutting the lap time. The technology is all the more impressive in that it is functional under all road conditions—even in snowy terrain with little friction.
Finally, the M-LSD cannot be omitted in a discussion of steering improvements. During sharp corners, where strong lateral acceleration is inevitable, the outer wheels receive most of the load and therefore achieve stronger grip, but the inner wheels conversely shed the load and lose their grip to the road surface. The DTVC, as discussed above, would only apply the brakes to the inner wheels to restore the grip and return the car to its course. The M-LSD, on the other hand, manages to deliver the torque used to limit the inner wheels’ slippage directly to the outer wheels, allowing stable acceleration during corners—but without losing any power.
3. Control SystemHighly Stable, Regardless of the Road Conditions
HTRAC’s Power Control and Distribution
For the safety-minded driver, the ‘4WD’ logo on the back of the car should be eye-catching. The logo may even be a chilling reminder: ‘Remember how anxious you were, sitting behind the wheel on a snowy winding road?’ Four-wheel-drive (4WD), indeed, was developed to soothe such driver anxieties. Electronically sensing the vehicle speed and road conditions, the 4WD system accordingly distributes the power from the engine as well as the brake force across the four wheels, securing stability on slippery roads or during sharp curves.
But with more parts added to the system, the 4WD system suffers from the added noise and vibration and the diminished handling ability and fuel economy. However, HTRAC, Hyundai Motor Group’s cutting-edge 4WD system, has capably addressed these issues. Coined by combining Hyundai’s ‘H’ with traction’s ‘Trac,’ the HTRAC can deliver the engine’s power to the wheels in a variety of modes that correspond to road conditions.
Mounted on the Genesis line for the first time, the HTRAC boosted the traction performance in snowy, icy, rainy roads, while contributing to the vehicle’s fuel economy, NVH performance, and on-road handling.
At the Normal Mode, turning sharp corners enters the vehicle into full 4WD mode; during the Sports Mode, however, more power is delivered to the rear wheels in an arrangement similar to RWD. As long as the vehicle remains relatively stable, the ATCC (Advanced Traction Cornering Control; a mechanism for torque vectoring) works in tandem with the HTRAC to make for more nimble handling.
In legitimately unstable situations, though, the ESC (Electronic Stability Control) intervenes to hold the vehicle in a stable course. The system senses the vehicle speed, steering angle, lateral acceleration, and yaw rate to calculate the vehicle’s intended course. If the current course deviates only a little from the intended course, the system simply adjusts the power delivery ratio to the wheels, depending on the driving mode; if the current course deviates a lot, the system controls the slippage and/or the yaw rate to restore the vehicle back to its intended course.
The HTRAC is also installed on SUVs such as Santa Fe and Tucson, assisting their driving mode features with variable power delivery to the rear wheels. These SUVs, particularly, come with the three ‘Terrain Modes’ for traversing harsh terrains, namely SNOW, MUD, and SAND modes. Each mode functions by setting the power distribution, gear ratio, and acceleration/deceleration levels optimal to the terrain, for which the HTRAC’s role is essential.
The HTRAC was tested in Germany’s Nurburgring circuit, for its endurance under extreme rigor; in Arjeplog, Sweden, for its durability in extreme cold; and in Grossglockner, Austria, for its braking performance. All in all, the tests affirmed the HTRAC’s high marks in driving performance and durability.
Performance Variations Per Driving Mode
The HTRAC optimizes the power distribution to the front/rear wheels to the current driving mode. Under the ECO mode, the system distributes most of the power to the main driving wheels (the front), minimizing the power loss in the supporting rear wheels and thereby maximizing fuel economy. Under the COMFORT mode, the system distributes a greater share of the power to the rear wheels, prioritizing ride comfort. Under the SPORT mode, the system gives a still larger share to the rear wheels, maximizing the dynamism of handling. The power distribution scheme that follows the driving mode, as illustrated below, can also be seen at the cluster.
Driving Performance, Optimized for Terrain
In order to better optimize their driving performance to various terrains (SNOW, MUD, and SAND), the mid-SUV segment and above now comes with the Terrain Mode, which comprehensively controls the vehicle’s AWD status, engine, transmission, and brakes to match the need of the specific terrain.
AWD (All-Wheel-Drive) reacts to the slippage on the front/rear wheels by aggressively adjusting the power distribution to help the vehicle escape. The powertrain optimizes the engine torque and shifting pattern to match the terrain. The ESC applies brakes to the wheels left and right to suppress tire slippages and enable the vehicle to escape from a standstill.