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
New Saab and Citroen technology at Geneva



Saab's prototype variable-compression 1.6-L supercharged engine.


Lower part of monohead for Saab's variable compression (SVC) engine with tilting mechanism.


Saab's SVC design.


Citroen's latest Hydractive suspension system.

Designing and successfully developing a production-practical, variable-compression-ratio (CR) engine has long been a challenge to the automotive industry, but now Saab regards it as being within sight. At the Geneva Motor Show, Saab revealed its SVC (Saab Variable Compression) prototype power unit that it believes could lead the way to a production application.

"It has always been known that variable compression, or, more correctly, variable expansion ratio, has a significant contribution to thermodynamic efficiency, and the dream of coming up with a design suitable for production has lingered over the horizon for many years," said Kjell ac Bergstrom, Saab Automobile's Vice President-Powertrain. "With our new engine that dream is closer to reality than ever before. And the SVC can be focused on fuel economy, high performance, or a combination of both."

A fixed CR is always a compromise, which is why Saab has been working on variable-compression systems for almost 20 years. But it was the advent of advanced electronic engine control that really allowed the SVC to develop. The engine shown at Geneva was a supercharged five-cylinder, 1.6-L unit producing a very high output for its volume of 168 kW (225 hp) and maximum torque of 305 N•m (225 lb•ft). Bergstrom made the point that variable compression on its own is not enough to bring very significant benefits—but it is when operating with a supercharger.

The Saab SVC is an innovative design, with the upper section of the engine physically moving to vary the CR. According to Saab, the SVC engine consists of an upper part comprising a cylinder head with integrated cylinders (monohead) and a lower part consisting of the engine block, crankshaft, and pistons. The compression ratio is varied by adjusting the slope of the upper part of the engine in relation to the lower part. This alters the volume of the combustion chamber with the piston at top dead center. To achieve this, the monohead is pivoted at the crankcase via a hydraulic actuator moving through a maximum 4°. The CR can be varied between 8:1 and 14:1 automatically. To increase the CR, the slope of the monohead is reduced. The volume of the combustion chamber will then decrease and the CR will increase.

The monohead is sealed at the crankcase by a rubber bellows. The optimum CR is selected by the engine-management system based on information regarding engine speed, load, and fuel quality. The system gives wide fuel flexibility, with CO2 emissions reduced proportionately to fuel consumption. The joint face between the upper and lower parts of the engine is about 20 cm (7.9 in) lower than normal. One objective in the development work on the SVC concept was to retain as many of the basic elements of a conventional engine as possible. Bergstrom sees the SVC concept as suitable for two-, four-, or six-stroke engines.

The compressor is linked to an intercooler and delivers a maximum boost pressure of 280 kPa (41 psi), considerably higher than Saab's turbocharger system used on its conventional production engines. Despite Saab's experience with turbochargers (it first used them on production cars in the mid to late 1970s) it opted for a supercharger for the SVC because none of the turbochargers available today would meet the company's criteria for high boost pressure and have the fast response required.

Saab states that many patents exist for variable CR engines. Its own work started in 1981, but it was not until the end of that decade that the work gathered pace. Its first patent application was filed in 1990. An early 2.0-L engine using SVC delivered higher power and torque than would have been practically usable, says the company. Next came a 1.4-L six-cylinder in-line engine in the mid-1990s. The objective was that an SVC engine of that design would have the performance and power output of a naturally aspirated 3.0-L V6, but at 30% lower fuel consumption.

Saab went to the German engine-development company FEV Motorentechnik at Aachen for an independent assessment of the SVC engine. Saab says the company submitted an evaluation "to confirm that the engine attained targets set up, and that it was also possible to make further advances by continued development work." However, the 1.4-L engine was abandoned in favor of the five-cylinder 1.6-L that offered better packaging.

The company believes that the SVC would have been "impossible" to develop without an advanced engine-management system. The addition of variable compression as a further control parameter in the already complex control system of today's modern car engines makes very strict demands on the system. The engine-management system for the SVC engine is a special version of the Saab Trionic system—developed in-house by Saab and in use on the company's turbocharged engines since 1991.


Citroen Xsara Dynactive.

Citroen also showcased some interesting technology at Geneva. Making its debut was the Xsara Dynactive station wagon, which uses parallel hybrid technology. It is equipped with a 56-kW (75-hp) gasoline engine and a 25-kW (34-hp) electric motor coupled to the same shaft upstream of an automatic gearbox. According to the company, the electronic supervisor optimizes the use of each powertrain component to reduce fuel consumption, limit CO2 emissions, and enhance driving pleasure. It can be operated in zero-emissions mode. The gasoline engine is used only when it offers a higher level of efficiency than the electric motor, cutting out automatically when not needed. The car features regenerative braking. A multifunction screen in the car shows the flow of energy between the wheels, power units, and battery.

Traction is provided by both the gasoline engine and electric motor; by the gasoline engine alone, with the electric motor switched off; by the gasoline engine, with the electric motor in generator mode to recharge the battery; by the electric motor alone, with the gasoline engine off; and by deceleration/descent, when energy is recovered by the electric motor in generator mode. Citroen says that by combining the automatic gearbox with the hybrid power system it has made new progress toward optimum driving comfort. The information on driving style detected by the gearbox affects not only the gearshifts, but also the operating variants of the hybrid powertrain.

Citroen also revealed its third-generation Hydractive hydropneumatic suspension system at Geneva. It allows the height of a vehicle to vary according to speed. The center of gravity shifts by about 15 mm (0.6 in) for improvements in drag. Over very poor surfaces ride height may increase by 20 mm (0.8 in). The suspension system offers normal or sport settings.

Stuart Birch

AEI May 2000

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.