Chasing Chassis

A look at what’s being used for a sports coupe, a premium sedan and a crossover utility, three state-of-the-market vehicles.

The Coupe.
Cadillac is pressing forward with technology, not simply in the world of interfaces and infotainment, but when it comes to the way its vehicles ride and handle.

And while it is doing this across the board, it is nowhere more evident than in the V-Series line of cars that it is putting on the road (and, yes, track).

The latest case in point is the 2016 ATS-V which has a 464-hp, 444-lb-ft of torque twin-turbocharged V6 (0 to 60 mph, 3.8 seconds), so even if you’re using it to go get groceries, you’re going to need a chassis up to the task. So Cadillac engineers redesigned the chassis and suspension (and drivetrain) for the vehicle.

Structurally, the car features unique shock tower-to-plenum braces; a strengthened rocker bulkhead; stronger rear cradle-to-rocker braces; an aluminum shear panel at the front of the chassis; and V-braces for the engine compartment, all of which result in 25% greater structural stiffness for the ATS-V vs. the non-V version.

Speaking of stiffness, there is a multi-link, double-pivot MacPherson-strut front suspension with ride and handling links that use zero-compliance cross-axis ball joints instead of the conventional elastomeric bushings, higher-rate springs, and a stiffer stabilizer bar, which results in 50% greater roll stiffness.

The rear suspension is a five-link setup that features reduced roll center migration, stronger lateral control, and effective anti-squat geometry. Elements used are stiffer bushings, new cradle mounts, higher-rate springs, and a stiffer stabilizer bar.

Cadillac has long used the magnetor-heological fluid-based Magnetic Ride Control system. Sensors “read” the road and then signal the shocks to make the appropriate adjustments. (There is an electromagnetic coil in the piston that generates a flux; orientation of the magnetic particles in the fluid is predicated on whether the coil is active and how strong a magnetic field is generated.) This third-gen system is said to provide 40% faster response than its predecessor; if the car is going 60 mph, it can calculate and adjust for every inch of the road. (Given that there are 63,360 inches in a mile, this means there are that many adjustments every minute traveled at 60 mph.)

Chassis control includes Performance Traction Management which allows the driver to select from five different settings (including “Competition”) for stability and traction control.

The ATS-V is also equipped with a Servotronic II variable-ratio electric power steering system from ZF Steering Systems. There are Brembo brakes; the system includes 14.5-in. front rotors with staggered six piston calipers and 13.3-in. rear rotors with four piston calipers.

The Sedan.

The all-new Jaguar XF is, of course, an aluminum-intensive vehicle (OK: there is some steel used, such as hot-formed boron steel B-pillars and a trunk lid consisting of two laser-brazed steel stampings).

But the intensity of the aluminum can’t be overlooked nor overstated.

Listen to Mike Cross, Jaguar chief engineer, Vehicle Integrity: “The all-new XF has to deliver driver reward through agility and immediacy of response when it’s called for, and yet great ride composure and comfort too. The all-new XF’s light and rigid aluminum-intensive architecture is a key enabler for us delivering those attributes, as it provides an optimal basis for finely tuning the ride and handling characteristics of the car.”

Not surprisingly, the chassis is aluminum-intensive, as well.                

Like the double-wishbone front sus-pension, which is entirely aluminum. The front suspension features high camber stiffness so that the tires can quickly generate lateral force so that there is sharp, immediate turn-in for cornering. In addition to which, a high roll camber gain facilitates maintaining the tires’ contact patch, so there is good grip.

The rear suspension setup is what Jaguar calls “Integral Link.” Rather than having a multi-link rear suspension, they were looking for a means to achieve a separation between the tuning of the lateral and longitudinal stiffness. So, for example, the bushings are setup so that the wheels can move rearwards and upwards when hitting a bump while, at the same time, the camber stiffness can be increased for responsiveness.

Steering for the XF is with electric power-assisted steering (EPAS). Not only does this system include filters that dampen inputs from irregular road surfaces and algorithms that compensate for changes in the ambient temperature, but because the motor works only when necessary, they’ve found that it provides a fuel savings of up to 3%, based on the European combined cycle.

The XF can be fitted with new passive dampers that provide frequency-dependent damping. That is, the damping force is varied based on both the velocity that the damper piston moves and the frequency. There is an extra valve in the piston that provides an additional bypass so that when driving, say, on surface streets, the valve is open so that some fluid flows through it rather than through the main valve in the piston, thereby providing a smooth ride. However, as speeds increase, the valve closes and the fluid is forced through the piston, thereby increasing the damping force and resulting in a firmer ride.

Jaguar also has its “Adaptive Dynamics” system for the XF, which monitors body movement 100 times per second and the wheel movement 500 times per second, with algorithms making the adjustments of the shocks.

And for those who really want to tune in their ride, there is “Configurable Dynamics,” which allows adjustments of the throttle, shift points, steering feel, and Adaptive Dynamics through a touchscreen interface.

The Crossover

Among the new vehicles that’s furthest away from an ATS-V or a Jaguar XF is the 2016 Honda Pilot. While it is a crossover that is unlikely to have to do much in the way of going off road, the engineers did consider that possibility in developing the chassis for the vehicle (e.g., the approach and departure angles—18° and 19.7°, respectively—are appropriate; there is an AWD system with computer-controlled traction capability, so going off road is not outside the conceivable), but they really looked at on-road ride comfort and handling.

The Pilot features four-wheel independent suspension. In the front is a strut-type setup with forged-aluminum lower control arms, hydraulic bushings, coil springs, and a solid stabilizer bar. The upper front damper mounts have what’s called a “triple path” load-bearing system to absorb road vibration and harshness.

The rear suspension is a multi-link design with a tubular stabilizer bar. The control arms in the back are all steel. The upper damper mounts are located on the body side rails for greater rigidity; notably, the setup transmits suspension loads to the rigid body side frame, rather than to the rear wheelhouse, thereby allowing the tuning of the bushings to accommodate both ride comfort and precise handling. The forward trailing arm that had been used on the rear suspension of the previous-generation Pilot has been eliminated; consequently, the floor of the new vehicle is 1.4-in. lower than the previous one, helping ingress and egress.

The Pilot features “amplitude reactive” dampers, which are mechanically based (unlike the electronically based Magnetic Ride Control previously mentioned). There are two separate pistons, a primary and secondary. During normal driving conditions, when there are just small road inputs, the main piston works alone. However, when there are rough roads or large steering and braking inputs, the second piston supplements the main piston to provide additional damping force.

While the dampers are mechanical, the steering is electric. It is called a “Motion-Adaptive” electric power steering system; it works with the Vehicle Stability Assist such that during cornering and in slippery road conditions, there are inputs that “prompt” the driver to steer in the right direction.

As for brakes, there are discs all around and a four-channel ABS system. The front brakes feature 12.6-in. diameter ventilated discs and two-piston calipers; the solid rear discs are 13-in. in diameter and use single-piston calipers.