|2014 Cadillac ELR Click to enlarge.|
Cadillac unveiled the anticipated 2014 ELR extended range electric (EREV) vehicle (based on the Converj concept, earlier post) at the North American International Auto Show. (Earlier post.) ELR production begins in the US in late 2013 in limited numbers, said Bob Ferguson, Cadillac global vice president. Sales start early in 2014 in North America, expanding to global markets including China and Europe.
The EREV technology, proven in the Chevrolet Volt, is uniquely tuned for Cadillac in the ELR; the powertrain delivers 295 lb-ft of torque (400 N·m)—about 12% more than the 3.6L V-6 in the SRX. (The 2012 Chevrolet Volt produces 273 lb-ft/370 N·m.)
Powertrain. The ELR EREV powertrain combines a drive motor (117-135 kW); a generator motor (55 kW) and a 1.4L gasoline-powered range-extender generator. GM is expressing traction motor power as a range because it hasn’t yet finalized the number, and is still working on optimizing performance vs. how rapidly the battery pack is drained. The electric machine itself is essentially the same as in the Volt, but tweaked—mainly via software—based on the experience over the past few years.
Total system power out of the battery is 154 kW (not just to the wheels).
The ELR’s battery is a T-shaped, 16.5 kWh lithium-ion battery pack (The Volt’s is 16 kWh) comprising 288 prismatic Li-ion cells, located along the centerline of the vehicle, between the front and rear wheels for optimal weight distribution. The 5.5-foot-long (1.6 m), 435-pound (198 kg) pack with liquid active thermal control delivers a GM-estimated range of about 35 miles (56 km) of pure electric driving, depending on terrain, driving techniques and temperature. The full driving range exceeds 300 miles (480 km). (By comparison, the Volt offers 38 miles of electric driving, and a full range of 382 miles (615 km).
Charging the ELR’s battery can be done with a 120V electrical outlet or a dedicated 240V charging station. The vehicle can be completely recharged in about 4.5 hours using a 240V outlet, depending on the outside temperature.
Once the vehicle is plugged in, owners can schedule either immediate or delayed charges, even coordinating charging according to departure time or when electricity rates are lower. Owners also can manage and monitor the ELR online or with their smartphone and RemoteLink, a mobile app powered by OnStar.
The ELR’s battery is covered by an eight-year/100,000-mile warranty.
Regenerative braking and Regen on Demand. The ELR is equipped with a fully blended electro-hydraulic brake system that enables seamless blending of regenerative braking and traditional disc braking based on the brake pressure applied by the driver.
During regenerative braking, the system converts the vehicle’s momentum to electrical power and stores the energy in the battery pack. If the battery is fully charged, the brake controller directs the system to conduct traditional friction braking. The system uses a high-pressure hydraulic pressure accumulator to provide boosted braking.
ELR’s exclusive Regen on Demand feature allows the driver to temporarily regenerate energy from the vehicle’s momentum via steering-wheel paddles adapted from traditional performance cars. The electricity is stored in the vehicle's high-voltage propulsion battery for later use. When engaged, Regen on Demand also provides vehicle deceleration that is slightly more than what a typical vehicle experiences while coasting, providing control and dynamic performance characteristics typical to downshifting in a manual-transmission vehicle.
To engage Regen on Demand the driver simply takes his or her foot off the accelerator and pulls back on either the left or right steering-wheel paddle to begin regenerating electricity. Releasing the paddle disengages Regen on Demand, allowing the vehicle to coast normally. The driver can engage and disengage Regen on Demand as desired and as traffic conditions allow.
A four-channel anti-lock braking system is standard and includes electronic Brake Force Distribution, which uses independent rear control for improved stability and braking during cornering, as well as more effective use of the rear brakes as vehicle loading occurs. Also, the disc brake system features large, vented front and solid rear Duralife rotors with Ferritic Nitro-Carburizing (FNC) finishing technology to reduce corrosion and deliver longer life.
Drive modes. The ELR offers four user-selectable drive modes:
Sport mode automatically reconfigures the accelerator pedal response to provide quicker torque application and more sensitive feedback to driver inputs through altered suspension and steering settings.
Tour mode. This is the default setting on the ELR and is expected to be used most often and provides the greatest driving comfort and efficiency.
Mountain mode automatically adjusts the system to provide needed power in mountainous environments when vehicle performance could otherwise be compromised. Mountain mode allows ELR to sustain a sufficient state of charge so supplemental power is available from the battery if needed.
Hold mode allows owners to direct when the ELR uses its gas-powered electric generator, reserving the remaining battery charge for later use. This feature helps enhance efficiency because owners who mix city and highway driving can save the battery charge for city travel, where the ELR EV mode operates most efficiently.
Chassis and suspension systems. Advanced suspension and damping systems, including Continuous Damping Control—which adjusts damping every two milliseconds—maintain optimal vehicle ride control over varying road surfaces and profiles. The ELR rolls on 20-inch wheels wrapped in tires designed to balance excellent control and cornering capability with efficiency.
ELR is built with a body-frame-integral structure with main underbody rails running continuously from front to rear. Advanced, high-strength steels add strength and conserve weight. Additional contributors to the ELR’s driving experience include:
Wide front and rear tracks—62.1 inches (1,578 mm) in front and 62.4 inches (1,585 mm) in the rear—along with a long wheelbase (106.1 inches / 2,695 mm) and a low center of gravity.
HiPer Strut front suspension featuring lightweight forged aluminum components for reduced weight and more nimble, responsive action.
Dual-pinion, rack-mounted electric power steering system with premium ZF steering gear designed to provide excellent feedback while helping to save fuel.
A semi-independent rear compound-crank suspension with Watts link that incorporates weight-optimized trailing arms to absorb lateral forces, allowing the suspension to be tuned to handle vertical, forward and rearward motions.
Hydraulic ride bushings in the front and rear suspensions.
An electro-hydraulic regenerative brake system that captures energy and sends it to the battery pack.
Standard chassis control systems include antilock brakes, traction control and StabiliTrak electronic stability control.
An isolated four-mount front cradle contributes to the ELR’s overall quietness, noise and vibration performance, and ride and handling dynamics. This is achieved by mounting the engine to the cradle, and then the cradle to the frame. Specifically tuned mounts are tailored to the engine’s inherent torque axis (when running), effectively damping transfer of vibration and noise.
The ELR’s structure also features an exclusive cross-vehicle brace that contributes to a firmer, more precise steering feel.
HiPer Strut front suspension. The HiPer Strut (derived from High Performance Strut) front suspension design helps reduce torque steer and provide more linear and communicative steering through improved camber control. That improves ultimate grip levels in dry and wet conditions, as well as improving the direct feel of the road, while isolating undesirable feedback.
HiPer Strut is based on the MacPherson strut front suspension design and features dual-path top mountings that separate the transfer of spring and damper loads to the body structure, for greater impact isolation on bumps and rough surfaces. Reduced torque steer helps maintain acceleration linearity with a powertrain that delivers 400 N·m.
Hydraulic ride bushings in the front control arms result in a higher degree of ride isolation, quieter performance, and more controlled transfer of road input loads. The control arms and knuckles are constructed of aluminum for more nimble handling and weight reduction. A hollow, direct-acting front stabilizer bar is routed for minimum mass with maximum stiffness designed to result in better performance. The bar is mounted to the rear portion of the cradle with each end of the bar connected to the front strut via a direct-acting link.
Electric power steering. The rack-mounted electric power steering system is designed to provide excellent feedback and make the most of efficiency by requiring energy only when the wheels are turned. It is a dual-pinion system—one for steering and one for power assist—with variable assist. A combined electric motor and sensing unit monitors steering angle and delivers appropriate assist to the steering gear in all scenarios.
A premium ZF steering gear is used with the electric steering system and is designed for torsional stiffness with less operating friction for linear response, smooth, predictable transitions and enhanced connection between the driver, vehicle and road at steering inputs.
Compound-crank rear suspension with Watts link. The ELR’s semi-independent rear suspension features a specifically adapted compound crank (torsion beam) with double-walled, U-shaped profile at the rear and a Watts link. The design combines the advantages of a conventional torsion beam axle with low weight and consistent camber control giving the vehicle excellent stability and enhancing interior space.
|Rendering of the Z-link as applied in the Verano. Click to enlarge.|
(The Watt’s Z-link is based on the Watt’s linkage, a device invented by James Watt in 1784 to drive a steam engine piston in a straight up-and-down motion. Automotive engineers have since used Watt’s linkage to prevent sideways motion between the axle and body of a vehicle. General Motors’ exclusive Z-link design is a refinement of that technology, and is applied on a number of vehicles, including the Buick Verano and the Chevrolet Cruze.)
The Watts Z-link helps center the rear axle during cornering, helping keep the ELR’s handling responses symmetrical on both left-hand and right-hand turns. The linkage’s capability to center the axle during cornering delivers a more balanced driving experience as the rear suspension better follows the lead of the front suspension.
The space-saving layout of the rear axle also helped the engineers achieve a low center of gravity for improved agility. It also allows the fuel tank to fit between the rear wheels, enabling lower positioning of the rear seats.
Cast iron control arms are attached to the steel cross-car beam with a patented “magnetic-arc” welding process, which uses magnetic forces to drive the components together and weld them. The trailing arms on the ELR’s rear suspension incorporate an advanced, thin-wall structure of only 3.3 mm, for a mass savings of about 3.9 lbs. (1.75 kg).