GM, DC and BMW break new hybrid ground
BY MARTON PETTENDY | 2nd May 2006
As a result of the auto giants’ unprecedented Global Hybrid Co-operation, which is charged with developing a full petrol-electric hybrid power system to enter production next year, the car-making trio claims it is the first to produce a fully integrated combination of electric motors with a fixed-gear transmission.
Claimed to break new ground in terms of fuel consumption, performance and towing capacity for a wide variety of vehicle applications, the trio’s hybrid system combines a two-mode (low and high-speed) electric continuously variable transmission (ECVT) with four fixed gear ratios for the first time.
The hybrid system can use its electric motors for both boosting output and regenerative braking in both ECVT modes and in its four fixed gears, providing a total of six operating functions.
In the first fixed-gear ratio, both electric motors are available to boost the engine or to capture and store energy from regenerative braking, deceleration and coasting.
In the second and fourth fixed-gear ratios one electric motor is available for boost/braking, while both electric motors are available for boost/braking in the third fixed-gear ratio.
GM, DC and BMW say the full hybrid transmission system has an overall mechanical content and size that’s similar to a conventional automatic transmission.
They also claim it can operate in infinitely variable gear ratios or in one of the four fixed-gear ratios, although "a sophisticated electronic control module constantly optimizes the entire hybrid powertrain system to select the most efficient operation point for the power level demanded by the driver".
The joint-venture operation claims several key advantages over other traditional petrol-electric powertrains currently in production, which typically have no fixed mechanical ratios and just one torque-splitting mechanism.
According to the GM-DC-BMW alliance, these "one-mode" hybrid systems need to transmit a significant amount of power through an electrical path that is 20 percent less efficient than a mechanical path.
"This requires usually substantial compromise in vehicle capability or reliance on larger electrical motors, which can create cost, weight and packaging issues." The new system’s reduced power transmission through an electrical path allows the electric motors to be more compact and less dependent on engine size.
More importantly, says the Troy, Michigan-based GM, DaimlerChrysler and BMW Hybrid Development Center, the system allows for efficient operation throughout a vehicle’s operating range, at both low and high speeds.
It’s also claimed to be compatible with application across a broader variety of vehicles, and is "particularly beneficial in demanding applications that require larger engines, such as towing, hill climbing or carrying heavy loads.
"Existing internal combustion engines can be used with relatively minimal alteration because the full hybrid system imposes no significant limitation on the size or type of engine.
"It enables the three auto-makers to package internal combustion engines with the full hybrid transmissions more cost-effectively and offer the fuel-saving technology across a wider range of vehicles." The new hybrid system is currently applicable only to front-engined rear-drive and all-wheel drive vehicles, but has the flexibility to be used in front-engined, front-wheel drive architectures as well.
The Global Hybrid Cooperation was announced last year as an alliance of equals to produce a next-generation hybrid powertrain, with all three partners jointly pooling expertise and resources and each company to individually integrate the hybrid system into vehicles in accordance with brand-specific requirements.
GM has stated its first two-mode hybrid-equipped production models will be the Chevy Tahoe and GMC Yukon large SUVs in 2007. But the world’s largest car-maker says these vehicles will remain very much a "near-term" alternative fuel solution and that fuel cell vehicles remain its ultimate long-term goal.
Meantime, BMW’s 7 Series flagship is the most likely candidate to be the first two-mode hybrid-powered BMW model.
While it’s unclear exactly when the first similarly-powered DaimlerChrysler model will appear, Mercedes-Benz Australia has expressed interest in the two hybrid-powered S-class concepts that appeared at last year’s Frankfurt motor show.
Not powered by the new joint-venture "next-generation" two-mode hybrid system, they comprise V6 petrol and diesel engines mated to a single electric motor.
The S350 hybrid is powered by a 3.5-litre petrol V6 which, combined with an electric motor, produces 221kW and 395Nm of torque, while the S320 hybrid mates a 3.0-litre turbo-diesel V6 with electric power to produce 179kW and 575Nm.
Claimed combined average fuel consumption is 8.3 and 7.7L/100km respectively (about 25 per cent less than their petrol and diesel V6 equivalents) and both hybrid S-class variants could be here as early as late 2007.
Nissan hybrid soon too
SPEAKING at a press conference to announce Nissan’s latest fiscal year earnings early last week, CEO Carlos Ghosn said the company’s purchase of hybrid technology from Toyota is just a short-term measure.In a deal announced in September 2002, Nissan will buy Toyota hybrid components to produce a hybrid Altima, to be built and sold over five years in the US from late this year.
But Mr Ghosn, who has been critical of hybrid vehicles because they are sold at a loss, says Nissan will soon develop its own hybrid systems.
"I don't think this agreement will go for a very long time," he was reported as saying in Automotive News last Tuesday. "We have other projects and are developing our own technology.
"You have to be prudent when all competitors are cutting production or offering incentives (on hybrid vehicles).
"Developing a technology and mass-marketing a technology is something very different," he said.