Click Image to Enlarge
The 2014 Cadillac ELR. It is manufactured at General Motors' Detroit-Hamtramck Assembly Plant along with its extended-range electric vehicle sibling, the Chevrolet Volt.
The production version of the 2014 ELR (above) and the 2009 Converj concept (below). According to Chris Thomason, ELR chief engineer, by working to achieve the Converj from the start of product development, they were able to accelerate the program.
While achieving good aerodynamics is essential for any modern vehicle, it is absolutely critical for a car like the ELR, which operates as a full electric car for approximately 35 miles. So in the front of the car, the grille is largely sealed to minimize turbulence in the engine compartment, and at the back of the car, the vertical tail lamps have a sharp, crisp form, so air breaks off cleanly.
The ELR power architecture. At the front is a 1.4-liter, gasoline-powered electric generator. Running down the center is a T-shaped 16.5-kWh lithium-ion battery pack. The front wheels are powered by a permanent magnet traction motor that produces 117 kW (note: the Chevrolet Volt’s motor is less powerful, producing 111 kW, which is one of the many fundamental differences between the two cars). There is a second permanent magnet motor/generator that produces 55 kW of power.
Pam Fletcher, executive chief engineer, Electrified Vehicles, GM, says of the ELR: “In the end, it provides the ultimate luxury experience: electric drive.” Then provides examples of why that is the case. “There is quick, liquid acceleration of the electric drive. It provides instantaneous torque. And it does so smoothly and quietly.”
The propulsion system used for the ELR is that used for the Chevrolet Volt, as well. It is a front drive car. It is powered by an electric motor that provides from 117 to 135-kW of drive power (there is a second 55-kW generator motor). There is an “onboard, gas-powered electric generator,” a.k.a., an 84-hp, 1.4-liter gasoline engine. It runs premium fuel. Chris Thomason, ELR chief engineer, points out that one of the reasons why premium is preferred is because the ELR offers an estimated electric-only range of 35 miles, which means that if you drive fewer than 35 miles and then plug the car in, you’re not going to be burning any gasoline to propel you, so there is a concern with the longevity of the fuel; there is software that initiates generator/engine start to burn some of the fuel should there be too long a period when the car is driven purely as an electric vehicle. It is worth noting that the GM nomenclature for the system is “EREV,” or “extended-range electric vehicle,” with the extended range—projected to be >345 miles—being facilitated by the generator that is used to charge the lithium-ion batteries housed in a 5.5-ft long T-shaped container that runs down the center of the ELR, consequently making the two-door coupe a four-passenger vehicle.
The “instantaneous torque” that Fletcher mentions is on the order of 295 lb-ft. Which propels the 4,050 lb. car forward with some alacrity. Top speed: 106 mph.
The Volt underpinnings notwith-standing, this isn’t simply a top hat placed on a Chevy structure. Rather, there are some fundamental changes made to make the ELR a true Cadillac.
The suspension, for example. The Volt front suspension is an independent MacPherson strut-type with side-loaded strut modules, specially tuned coil springs, direct-acting hollow stabilizer bar and hydraulic ride bushings. The ELR uses what is called a HiPer strut—for “high performance” with continuously variable real-time damping, and the other elements common to the Volt. HiPer strut is based on the MacPherson strut design. But it has dual-path top mounting to separate the transfer of spring and damper loads to the body structure. The rear suspension setup for the Volt is a torsion beam with a double-walled, U-shaped profile at the rear, and specially tuned coil spring and hydraulic bushings. The ELR has a compound crank with Watts link, a double-walled U-shaped profile at the rear, specially tuned coil springs, hydraulic bushings, and Sachs shocks with continuous damping.
The ELR front suspension is like that in the Cadillac XTS. The rear suspension is like that of the SRX.
The ELR offers four selectable driving modes. The default is “Tour.” Two others are fairly EREV-oriented. One is “Mountain,” which adjusts the system so that in the case of, say, climbing a mountain, the battery isn’t exhausted during the climb. There is “Hold,” which allows the driver to reserve the battery charge for when desired (e.g., say when starting out, rather than starting out on electric power from the battery, initial driving would be powered by the generator).
The final mode, “Sport,” is more responsive. Fletcher: “With Sport mode, we amp things up a little—no pun intended. There is a little more feedback from the round through the handling and steering calibration steering and a more progressive throttle.” (The steering system, incidentally, is rack-mounted electric power steering from ZF.)
As many vehicles are beginning to have steering wheel-mounted paddle shifters, the ELR has a slight spin on that. There is a “Regen on Demand” feature that has steering wheel paddles on both sides of the rear of the steering wheel. When the driver lifts from the accelerator and pulls back on a paddle, the regenerative braking system is engaged, slowing the car in a way analogous to downshifting. It will not bring the vehicle to a complete stop.
Back in 2009, Cadillac revealed the Converj concept at the North American International Auto Show (NAIAS). A few months later, GM filed for bankruptcy. One would imagine that the Converj would have ended up as part of the collection of the GM Heritage Cen-ter in Sterling Heights, Michigan.
Instead, it ended up in the Cadillac design studio, as the stylists, designers, and modelers set to work at crafting what would become the production vehicle.
Thomason makes an interesting point about an advantage of using the Converj as a template for the ELR: it helped accelerate the development time. “We often spend a lot of time iterating through design themes, going from many to a few to a select one.” Here they started with one.
Speaking of the design of the ELR, Bob Boniface, director, Cadillac Exterior Design, cites another concept car, the Evoq concept, which was also revealed in Detroit at NAIAS. That was the public reveal of the “Art & Science” approach to its vehicles. “It was mathematically derived,” Boniface says. “The surfaces were shear, with a lot of crisp lines. It was a new aesthetic for automotive design. Today, it is less of a language and more of a philosophy.”
Echoing Thomason, Boniface says of the ELR, “When design team kicked this off, our task was to as accurately as possible interpret the Converj concept as a production vehicle. Concept vehicles are developed very quickly. You don’t spend a lot of time in the wind tunnel. You don’t spend any time in the wind tunnel. When you build a production version of a vehicle, especially an electric vehicle, aerodynamics are very important. Even though this car for all the world looks just like the Converj, there were a lot of things that we had to do to ensure that the car delivered on the promise of 35 miles of petroleum free driving.”
One of the changes within the approach to Art & Science that Boniface notes is the sections of sheet metal between the crisp lines. There is more of a flow, or liquidity,
in place of the previous shear surfaces. Arguably, it is a more sophisticated form and less angularly aggressive.
Then, there are the things that needed to be done to achieve a 0.305 coefficient of drag.
Boniface points to the grille. It’s largely sealed. There is some open space, to distribute some cooling on the inside. Most of the air comes in from under the car through active shutters. “The reason we seal the grille is because we don’t want to send air into the engine compartment where it is unmanaged and becomes turbulent. It creates a lot of drag.”
And drag is something they focused on. The goal is to keep the air attached to the body as much as possible—which explains the slope of the A-pillar, for example—and the back of the car. “At some point,” Boniface says, “the wind has to leave the car. A car with a rounded tail creates large vortices of air—like an anchor. When air leaves the car, you want it to leave quickly.” Which explains the rear spoiler and the shear, crisp, vertical tail lamps. (Vertical lamps have been part of the Cadillac design language since 1948. The ELR offers all-LED exterior lighting.)
Just as the exterior is an expression of Art & Science, form and func-tion, Boniface notes that the interior is, as well. He points out that there’s all hand stitching on the instrument panel and French seams along the sides of the seats. There is authentic material: real wood, real carbon fiber. And there is the serious science of the CUE infotainment system accessed through an eight-inch LCD screen.
“We’re very proud of the car—the way it looks and functions—the entire message of the car,” Boniface says.
And with good reason.