Error 404--Not Found

From RFC 2068 Hypertext Transfer Protocol -- HTTP/1.1:

10.4.5 404 Not Found

The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent.

If the server does not wish to make this information available to the client, the status code 403 (Forbidden) can be used instead. The 410 (Gone) status code SHOULD be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address.

Error 404--Not Found

Error 404--Not Found

From RFC 2068 Hypertext Transfer Protocol -- HTTP/1.1:

10.4.5 404 Not Found

The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent.

If the server does not wish to make this information available to the client, the status code 403 (Forbidden) can be used instead. The 410 (Gone) status code SHOULD be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address.

Tech Briefs

May 2002
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GM shows versatility with Versatrak


The rear-differential module contains a twin gerotor, which consists of two gerotor hydraulic fluid pumps, two seven-plate wet clutch packs, and five hydraulic pressure valves.
Click to enlarge

General Motors has developed an all-wheel-drive system that it claims is quiet, efficient, and effective in low-traction situations. Called Versatrak, its design is "so light and compact that it fits under a flat rear load door," said Anna Kretz, Vehicle Line Executive for GM's minivans and crossover vehicles. "This enables GM to make this system available in vehicles such as the Pontiac Aztec and Buick Rendezvous, as well as our trio of minivans." The GM minivans include the Pontiac Montana, Chevrolet Venture, and Oldsmobile Silhouette.

A team of engineers from GM and Austrian driveline specialist Steyr-Daimler-Puch Fahzeugtechnik developed originally for the Aztec the on-demand all-wheel-drive system, which uses front-wheel drive for ordinary road conditions and automatically adds rear-wheel drive as necessary while the vehicle is operated under slippery road conditions. This change in drive is done without perceptible influence on vehicle handling or driving comfort, according to GM, without buttons to press or levers to throw.

"Versatrak is a mechanical system that transfers torque directly when front-wheel slippage occurs and can direct as much as 44% of the engine's power to each rear wheel either individually or simultaneously as needed," said Charles Kingsley, Vehicle Chief Engineer for GM's crossover vehicles.

The short- and long-arm independent rear suspension of the Buick Rendezvous employs a rear crossmember, upper and lower control arms, and knuckle assemblies.

GM describes the Versatrak system as beginning with a power take-off (PTO) unit bolted to the right end of a vehicle's front-mounted transaxle, a propeller shaft from the PTO to a rear-differential module, and halfshafts from the rear-drive module to each rear wheel. An aluminum driveshaft links the PTO unit with the rear-drive module. Inside the rear module, sensors in the twin Geromatic gerotor pumps react to differences in the rotational speed of the front and rear wheels. The gerotor is a "non-conventional assembly," according to GM, of two gerotor hydraulic fluid pumps, two seven-plate wet clutch packs, and five hydraulic pressure valves. The twin gerotor is licensed from Santa Barbara, CA-based ASHA Technologies.

All power is directed to the front wheels as long as no speed difference is sensed. If one of the front wheels begins to slip, the rear-mounted gerotor units pressurize fluid to engage the clutches that redirect torque to one—or both—rear wheels, enabling the rear wheels to provide traction that allows the vehicle to keep moving forward despite muddy, snowy, or slippery road surfaces. Hydraulic pressure forces a disc-shaped piston to engage the seven-plate clutch and apply torque through the halfshaft to each rear wheel. If the rear wheel is also on a slick surface, it will match the speed of the front wheels, reducing hydraulic pressure and disengaging the halfshaft and wheel. Torque from the propeller shaft is then re-routed to the other rear wheel. The propeller shaft uses a rear sliding constant velocity joint, which allows the driveshaft to vary in length to compensate for rocking motions of the transverse engine and transaxle.

The PTO unit has a three-piece housing with a helical geartrain consisting of three helical gears and a 90° hypoid gearset. An input helical gear welded to the right side of the differential carrier transfers torque through the other two helical gears and a hypoid gearset that turns 90° to route the torque to the propeller shaft. Four stamped, steel stiffening braces secure the PTO to the transaxle case, engine block, and oil pan.

Sensors in the twin gerotor pumps react to differences in the rotational speed of the front and rear wheels.
Click to enlarge

According to GM, the system performs the functions of a four-wheel-drive system that has both center and rear differentials—performed by the twin gerotor—with limited slip capabilities. This feature enables performance equivalent to a four-wheel-drive vehicle with torque-sensing center (between the front and rear axles) and rear (between the rear wheels) differentials, which have been available generally on only luxury and high-performance cars with four-wheel drive. Some other on-demand four-wheel-drive systems allow one front and one rear wheel to slip since they have open differentials in both front and rear axles.

The Versatrak system is mechanically and functionally identical on all the vehicles. However, the torque tube bolted between the rear-drive module and the propeller shaft is about 102 mm (4 in) longer on the Rendezvous to accommodate its longer wheelbase. The minivans, with wheelbases of about 200 mm (8 in) more than the Rendezvous and 305 mm (12 in) more than the Aztec, use a longer driveshaft to accommodate the extra length.

- Jean L. Broge


Diesel: The fuel of the future


A worker assembles the HDi engine block at PSA's Trémery factory. PSA has a collaborative agreement with Ford for diesel-engine development.

As PSA Peugeot Citroën is fond of saying, its factory at Trémery, near Metz in northeast France, is the biggest high-speed diesel-engine plant in the world. Diesel engines account for about 83% of production at the plant. Last year annual diesel output reached 1.45 million units, with a diesel engine completed every 10 s. With the diesel passenger-car market penetration in western Europe having risen from 13.9% in 1990 to 35.8% in 2001 and showing no signs of slackening, output is likely to increase further. According to PSA, diesel is the fuel of the future in the short and medium term. The reason for this rapid increase in popularity is due to three parallel factors: advancing technology, economic necessity, and low levels of CO2 emissions. PSA credits the growth of its own diesel-engine market share with the availability of common-rail technology (since 1998), the development of that technology to include multiple injections, the use of its Diesel Particulate Filter System (DPFS), and the inclusion of diesel engines across its car ranges.

The controlled environment room for HDi assembly in the Trémery plant.

PSA's HDi range of diesel engines is now well established, and the company has formed a liaison with Ford that has seen the successful installation of the French-designed 1.4-L turbocharged unit in the new Fiesta. In general terms, Ford will be responsible for the design and development of diesel engines above 2.0-L for the two companies, with PSA responsible for smaller units.

While a typical diesel engine can provide improvements in both fuel consumption and CO2 emissions of up to 30% compared to a gasoline unit, PSA claims its HDi engines can improve these figures by an additional 20% while maintaining driveability, including low-end torque and the sort of low NVH levels demanded by an ever more discerning customer base. PSA quotes 168 g/km (270 g/mi) as average CO2 emissions from internal-combustion engines in Europe, while the figure for the U.S. is put at 225 g/km (362 g/mi). PSA's diesel engine average is 149 g/km (240 g/mi). The European Automobile Manufacturers Association has entered into a voluntary agreement to reach 140 g/km (225 g/mi) by 2008. In 2001, 48.9% of PSA's world sales were diesel-powered passenger cars and light commercial vehicles. At Trémery, HDi production has risen from 380,000 units in 1999 through 1.04 million units in 2001.

Details of the direct-injection system and combustion chamber of PSA's common rail HDi engine. According to PSA, injection pressures are set to rise.

Although gasoline engines are also produced at the plant, it is diesels that form the major part of output. The four-cylinder engines PSA manufactures at the plant include the 1.8-L eight-valve, 2.0-L in eight-valve and 16-valve versions, and a 2.2-L 16-valve. A new engine range designated DV consists of a 1.4-L in eight- and 16-valve forms plus a 1.6-L.

Patrice Marez, Head of Diesel Engine Control Unit technology for PSA, puts the common-rail (CR) system in the lead on the pathway to development of modern diesel engines—together with improved injector spray (higher-injection pressures, smaller diameter injector nozzle orifices, more orifices, and more uniform combustion) and improved control of heat release (multiple injection, reduced emissions, and noise). Bosch, Siemens, and Delphi supply PSA with technology. Bosch's first-generation CR system that achieved 135 MPa (19 ksi) has been fitted to series production models since 1998 and has been used on the 1.4-L engine since June 2001. Siemens' second-generation CR system that reached 150 MPa (22 ksi) has been used in production since December 2000 and is also used on the 1.4-L engine, while Delphi's first-generation CR system rated at 140 to 160 MPa (20 to 23 ksi) was used on 1.4-L engines starting late last year. Even higher pressures are in prospect, said Marez, rising from 160 to 180 MPa (23 to 26 ksi) initially and then on to 200 MPa (29 ksi). Piezoelectric injector holders will be used "very widely" and will be "indispensable for variable injection rate." Multiple injections will also play a significant role in enhancing efficiency. At present there are three: pilot, to help reduce noise; principal; and post, to aid the DPFS regeneration. "Tomorrow there will be five," said Marez. Those five will be pilot, pre-principal, principal, after-principal (the three reducing temperature and NOx emissions), and post.

Both the Citroën Xsara Picasso (top) and Peugeot 307 use the 2.0-L HDi engine built at Trémery.

As well as these advances in CR technology, other significant contributors to improved performance include an optimized combustion chamber and optimized air system control with variable geometry nozzle turbocharger and EGR (exhaust gas recirculation) solenoid valves, which also contribute to reducing emissions at source. As a result of its HDi development, next year PSA will be producing a "wide range" of Euro IV emissions-compliant vehicles with "a number" being equipped with the company's DPFS.

The Trémery plant runs four shifts for machining, three shifts for diesel-engine assembly, and two shifts for gasoline-engine assembly. Employees at the site total 4100 including 3263 operatives. Machining tasks include crankcases (aluminum and cast iron), crankshafts (steel and cast iron), connecting rods, cylinder heads, and camshafts. Engine assembly involves some 250-350 parts per unit. A "zero-defect" quality policy is in place, with the plant ISO 14001 certified in support of the company's "clean engine, clean plant" philosophy.

- Stuart Birch


More 1 2 3

Error 404--Not Found

Error 404--Not Found

From RFC 2068 Hypertext Transfer Protocol -- HTTP/1.1:

10.4.5 404 Not Found

The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent.

If the server does not wish to make this information available to the client, the status code 403 (Forbidden) can be used instead. The 410 (Gone) status code SHOULD be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address.