|A cutaway view of the VUE hybrid. Click to enlarge.|
GM used the North American International Auto Show to debut its mild hybrid 2007 Saturn Vue Green Line (earlier post) and the 2008 Chevrolet Tahoe Two-mode Hybrid (earlier post), featuring the first application of a two-mode full hybrid system in an SUV. GM also announced that it would apply the two-mode system in an upcoming hybrid version of the Cadillac Escalade.
The 2007 Saturn Vue Green Line Hybrid Belt Alternator Starter (BAS) system features a electric motor/generator mated to a 2.4-liter VVT four-cylinder engine and 4T45-E four-speed transmission powertrain that delivers an estimated 27 mpg city and 32 mpg highway (29 mpg combined)—a 20% improvement in combined fuel economy compared to the conventional VUE with a smaller and less powerful 2.2-liter engine.
The Vue Green Line’s hybrid system provides engine shut-off at idle, fuel cut-off during deceleration, electric motor/generator assist during acceleration and the capability to capture electrical energy through regenerative braking. The system consists of six elements:
The electric motor/generator unit that replaces the alternator, and is capable of 156 Nm of auto-start torque;
Engine-coolant cooled power electronics that control the motor/generator unit and provide 12-volt vehicle accessory power;
A Cobasys NiMHax 36-Volt NiMH hybrid battery pack capable of delivering and receiving more than 10 kW of peak power;
An engine control module;
An engine accessory drive with new, dual-tensioner assembly and cord belt that enables transfer of motoring and generating torque;
Hybrid-enabled Hydra-Matic 4T45-E electronically controlled four-speed automatic transaxle that includes an auxiliary oil pump and unique hybrid controls.
In motoring mode, the hybrid system quickly restarts the gasoline engine upon brake pedal release and provides momentary acceleration assistance as needed. The vehicle’s 12-volt accessory power also is generated in this mode.
In the generating mode, the hybrid system is used to provide both 12-volt accessory power and power to charge the battery pack. To perform these functions, the engine is used to power the motor/generator unit, which then provides a three-phase electrical output. In this mode, the energy required to drive the engine may come from either gasoline when accelerating, or the kinetic energy of the moving vehicle when decelerating with the fuel cut off.
The Vue’s hybrid system will cost less than $2,000 and the full vehicle price will start at less than $23,000.
For the 2008 Chevrolet Tahoe Two-mode Hybrid, GM paired the two-mode hybrid system with a 5.3-liter Vortec V8 that also features GM’s cylinder deactivation system, Active Fuel Management (earlier post).
|Layout of the two-mode hybrid system in the Tahoe. Click to enlarge.|
GM expects the two-mode hybrid to deliver a 25% improvement in combined fuel economy over the 20 mpg expected from the non-hybrid counterpart (i.e., an estimated 25 mpg US for the full-size SUV). The Tahoe Two-mode Hybrid will go on sale in 2007 as a 2008 model, along with the GMC Yukon Two-mode Hybrid. Pricing and production volumes have not been announced.
The two-mode hybrid system (earlier post) derives from the technology GM applies in its heavy-duty hybrid systems for transit buses, and is being co-developed by BMW and DaimlerChrysler for application in light-duty vehicles.
The two-mode system uses two 60kW motors coupled to two gearsets and is designed to provide a more flexible range of operating power, control and efficiency in both city and highway driving than obtained with a single-motor implementation.
In the first mode, at low speed and light loads, the vehicle can operate in three ways: electric power only, engine power only or in any combination of engine and electric power. In this mode, one motor acts as a generator, while the other provides drive (motor) power.
The second mode is used primarily at highway speeds. In addition to electric assist, the second mode provides full eight-cylinder engine power when conditions demand it, such as when passing, pulling a trailer or climbing a steep grade. In this mode, In the second, both motors selectively operate in motoring or generating modes depending upon the vehicle speed.
The second mode also integrates Active Fuel Management, cam phasing, and late-intake valve closure for more efficient engine operation in addition to the electric support.
The two-mode system is designed to fit within the approximate space of a conventional automatic transmission—a form-factor advantage compared to single-mode systems that rely on larger electric motors.
The controller determines when the vehicle should operate in either mode of the two-mode drive system. Input from the controller determines the necessary torque for the driving conditions and sends a corresponding command to the engine and electric motors.
A 300-volt battery pack provides electric power for the system.
One of the intended design advantages of the two-mode system is the ability to package it in a variety of form factors for application in a range of vehicles.
Our hybrid strategy will not be confined to small cars or a limited number of vehicle architectures. Rather, we will offer sophisticated hybrid technology in a wide range of vehicles, and give customers what they’ve always wanted... choice.
In addition to the technologies themselves, the ability to haul large numbers of people in hybrid vehicles is going to be a competitive advantage for GM as we enter the hybrid segment in earnest.
We’ve focused our early efforts on large vehicles—“people haulers” like transit buses...and utility vehicles such as the Chevy Tahoe and Saturn Vue. Why? Because that’s where the most volume is, that’s where the most fuel is consumed...so that’s where our hybrid technologies are able to do the most good for the greatest number of customers.—Mark LaNeve, Vice President of Vehicle Sales, Service and Marketing for GM North America
The full-size SUV sector is also facing erosion in the market, partly due to concerns over fuel economy, and that erosion is adding to GM North America’s financial pain. Bolstering the sector is of stated strategic importance to GM, which is also emphasizing its E85 capability, as well as its diesel potential.
Missing from the presentations in Detroit, however, was mention of the company’s hydrogen fuel-cell work—even in Tom Stephens’ (GM Group Vice President of GM Powertrain) introductory remarks about GM’s quest to “reinvent the automobile and to remove our vehicles from the environmental debate.” The current-generation Sequel fuel cell concept, announced last year at the Detroit show (earlier post), was absent from the floor.