Tech Briefs
Bosch accents diesel technology
 Bosch's high-pressure common-rail system is currently used on several heavy-duty GM pickups, though the company claims it is also "ideal for passenger-car applications." |
To U.S. light-passenger-vehicle owners, diesel is about as commonplace as a car without headlights. The majority of Americans mistakenly believe diesel-fueled vehicles are noisy and performance-lax.
"The main barriers to diesel in the U.S. come from a bad perception of diesel vehicles from the 1970s and the fact that gasoline has been a relatively inexpensive fuel. But much has changed," said Hermann Scholl, Chairman of the Board for Robert Bosch GmbH, during a diesel ride-and-drive media event at the Bosch Proving Grounds in Flat Rock, MI.
The U.S. diesel market is vastly different from Europe, where four of every 10 vehicles sold have a diesel engine. Volkswagen is "the only automaker selling light-duty diesel passenger cars in the U.S.," said Stuart Johnson, Manager of the Technical Group Engineering and Environment Office for Volkswagen of America in Auburn Hills, MI. In 2000, about 20,000 VWs were sold in the U.S. with diesel engines. (The VW Golf, Jetta, and New Beetle are available with a diesel engine in the U.S.; all three models use a Bosch distributor pump.)
 Bosch invests much time and money into the research and development of diesel technologies. Shown is the company's diesel unit injector. |
Recent diesel technologies from Bosch are the Unit Injector System and the Common Rail System (seen in the U.S. via the V8 diesel Duramax/Isuzu engine available on the Chevrolet Silverado and GMC Sierra heavy-duty pickup trucks). "The Common Rail System is ideal for passenger-car applications because of its relatively compact packaging design and its flexible performance," said William Rutecki, Director of Diesel Products for the Robert Bosch Corp.'s Automotive Group in Farmington Hills, MI. "We have the ability to vary rail pressure and injection events across the speed and load range of the engine."
As the U.S. begins to phase in new emissions standards in 2004, automotive players are working to make diesel technology survive. "(U.S.) regulations are still focused on the traditional emissions like oxides of nitrogen and particulate matters," said Scholl. "But we believe a much stronger emphasis should be on carbon dioxide emissions, and diesel technology has already played a lead role in carbon dioxide reduction in Europe."
In recent years, Bosch has invested $1.3 billion for research and development of diesel technologies. The company is presently developing its next generation of common-rail diesel technology, looking for ways to increase injection pressure capabilities up to 180 MPa (26 ksi) as well as improve rate shaping control capabilities (possibly via piezo or advanced solenoid control), according to Rutecki. Those improvements would further reduce emissions and noise as well as provide more low-end torque, "which means more power at low speed and/or low rpm."
- Kami Buchholz
GM hybrid-electric truck technology
 The GMT-800 full-size pickup truck provides ample space for the power controller and its radiator underhood, with the lead-acid battery pack mounting beneath the cargo bed. The integrated starter/alternator fots within the transmission bell housing, so it requires no additional space. Click to enlarge |
While the federal government debates stiffer fuel-economy requirements for trucks and SUVs, General Motors is developing a hybrid-electric drive system for its V8 engines that will enable GM to boost the economy of its GMT-800 full-size trucks by between 10 and 15% without compromising towing and hauling capacity. The hybrid Chevrolet Silverado prototype employs a conventional 5.3-L pushrod GM V8, rated at 213 kW (285 hp). Engineers have replaced the traditional starter and alternator with a 4.8-kW (6.4-hp) electric motor that is integrated into the engine's flywheel. The integrated starter is not used as an assist motor, as on the Honda Insight and Toyota Prius; it provides instant stop/start capability and captures energy during deceleration.
The stop/start function of the system feels similar to that of the Prius; customers will notice little difference other than the quietness while stopped. In other conditions, the prototype drives like a typical Chevrolet truck.
The alternator provides power to a 42-V pack of lead-acid batteries (chosen for both cost and proven durability reasons) that support electrically driven onboard systems, such as the electrohydraulic power-steering system and a pump that maintains fluid pressure in the torque converter when the engine is stopped. GM selected an electrohydraulic power-steering booster instead of purely electric assist—such as the one on the Chevrolet Corvette—because of the high loads common in truck applications, according to Gary Ostby, Program Engineering Manager for the parallel hybrid truck.
An electric motor also circulates coolant to provide heat when the engine is shut off. As more 42-V components become available, the company plans to incorporate them into the design because 42-V subsystems tend to be smaller and lighter, contributing to even better gas mileage. The company chose to drive the air-conditioning compressor off the accessory belt drive, rather than opting for electrical power, and installed a restricted orifice in its system so pressure would not bleed down immediately when the engine is off. This design choice also provides air-conditioning capacity for a period of time that depends on ambient temperature, interior temperature, solar load, and thermostat setting. If refrigerant pressure drops too low, the engine automatically restarts.
GM's approach to hybrid truck design is in contrast to DaimlerChrysler's and its hybrid Durango SUV. DaimlerChrysler opted for a V6 engine assisted by an electric motor for V8 levels of acceleration. GM wanted to improve the economy of its trucks without sacrificing cargo-carrying capacity, so it relied only on the V8 engine for power and used the integrated starter/alternator to boost efficiency.
"That means I can tow boats, haul a full load, climb steep grades—all the situations that I buy a V8 for—and still have improved fuel economy," said Tom Stephens, Vice President, GM Vehicle Integration.
The company won't comment on the likely price of the optional hybrid system, but says that it will be palatable to customers when it goes on sale in model year 2004. "We aren't going to price the thing so people won't buy it," said Ostby.
One of the top attractions of the hybrid truck for many buyers may be its built-in, 110-V power outlets. Contractors can power tools on job sites more quietly, cleanly, and efficiently than with a generator. And unlike a generator left overnight at a job site, the truck is not at great risk of theft. Consumers will appreciate the ability to power critical appliances at home during power outages, making the hybrid truck worth a small premium over the conventional version, according to Ostby.
- Dan Carney
