Technical Innovations
Variable valve timing from Jacobs
As controller area networks (CANs) for vehicles become more commonplace, engine designers are pursing advanced, next-generation variable-valve-actuation (VVA) technologies to achieve the elusive goal of direct, cycle-to-cycle, digitally controlled air management.
Jacobs Vehicle Systems believes that precision control of the last part of the ICE "trinity" (spark, fuel, and air) will bring even more astounding performance.
A partial list of engine benefits resulting from cycle-to-cycle ICE air management includes:
- Reduced fuel consumption
- Lower emissions
- Improved starting and idle
- Faster warm-up
- Increased low-speed torque
- Reduced transient response time (or, in "blown" engines, reduced turbo lag)
- Engine braking (compression release)
- Exhaust-gas-temperature control for aftertreatment systems
- Advanced combustion processes using multiple types of fuel.
The race toward throttleless gasoline engines and "variable displacement" involves a whirlwind of technologies. Tremendous promise is held in the application of increasingly flexible air and fuel systems, according to Jacobs. Most systems released and under study are for gasoline engines, where big benefits are easiest to reap. Some state that even diesel engines could benefit with the right system, especially in terms of emissions control/reduction and driveability. Which valvetrain architecture will be the basis of future engines remains a question.
 Jacobs concept to be used for engine testing and production viability analysis for heavy-duty VVA system. |
Technologies can be divided into two groups: systems using camshafts and camless systems. Technologies may also be classified as primarily mechanical, electrical, or hydraulic (or various combinations of these).
The commercialization of high volume, digitally-controlled, lost motion, electrohydraulic VVA systems for diesel engines of all sizes is part of Jacobs' near-term corporate objective. Why diesel VVA? Because, Jacobs says, the company has more than 40 years of expertise in precision valve actuation for compression-release engine braking in heavy-duty diesel engines. The low-lift secondary exhaust valve opening shortly before TDC compression (Jake Brake technology) turns power-producing diesels into power-dissipating vehicle retarders. Indeed, hydromechanically created compression-release valve events can be seen as an early form of VVA technology.
In pursuit of increased engine retarding power, engineers at Jacobs realized that variable timing of the compression-release event was needed for ultimate performance across the engine-speed range. It also led to the realization that application of the same hydraulic principles used for engine braking could significantly improve positive power engine performance and emissions control as well as enable further increases in retarding power at all engine speeds.
Jacobs is continuing to produce engine-retarding systems while concurrently developing VVA systems. With such inherent efficiencies of the diesel, worthwhile benefits remain a challenge. However, Jacobs has predicted benefits for a high-speed diesel engine that include:
- Reduced fuel consumption (4-5% average in various missions)
- Increased low-speed torque 400 kPa (8333 psi)
- Improved startability
- Improved transient response (20% quicker vs. standard engine at low RPM)
- Braking power (80% of positive power).
Concepts have been initiated at Jacobs for gasoline engines to take advantage of known benefits in fuel economy and emissions reduction. Working within reliability paradigms of heavy-duty engines, the concepts add little in the way of incremental engine parts or expense and can even eliminate some existing engine hardware.
Relying on a conventional camshaft with special profiles enables engine benefits to be achieved reliably without concern for dreaded valve-to-piston contact. Cam-based lost motion systems are capable of the types of valve event flexibility that diesel or petrol engine designers would like to have.
Capabilities of Jacobs VVA systems include control of valve lift within cam profile limits to enable early valve closing (Miller-cycle benefits); secondary valve events (e.g., compression-release braking, internal EGR); valve-lift cancellation (cylinder cut-out/variable displacement); and lift variation for reduced valvetrain power consumption, fuel economy, and breathing.
- Patrick Ponticel
Vicon models motion
 Vicon demonstrated at the SAE 2002 World Congress its motion-capture technology, which employs high-definition cameras and multiple sensors attached to a person's body. |
The U.S. Army Tank-automotive and Armaments Command (TACOM) has recently implemented Vicon's motion-capture technology in its virtual prototyping initiatives. TACOM's Automotive Research Center (ARC) has installed a 16-camera Vicon 8i system, which will be used to perform digital-human simulation and analysis in support of human-interface development for wheeled and tracked military vehicles. The ARC will be working with the University of Michigan for dynamic reach studies.
TACOM's efforts into virtual prototyping began about five years ago when its Research Development & Engineering Center (TARDEC) ceased construction of full-scale mockups of vehicles during the conceptual phase of vehicle development. TACOM then began to employ new digital-human modeling tools such as Vicon's motion capture system to assess human-factors and ergonomic issues, producing more accurate data than obtained from previous electromagnetic motion-capture systems.
The Vicon 8i can perform motion capture at 1-million pixel resolution using the company's Mcam high-definition cameras. According to John Francis, Senior Sales Engineer with Vicon, a human-factors or ergonomics specialist using Vicon's motion capture technology can conduct multiple variable permutations such as tracking head movements/coordination, motor reaction, ingress/egress, and seated-operator studies with immediate feedback.
Vicon is taking its motion-capture technology further through its collaboration with EDS to develop virtual-reality-based product design, manufacturing, and maintenance evaluation. The joint-effort will provide an optimized interface between Vicon's motion-capturing technology and EDS PLM solutions' Jack digital-human modeling software.
EDS's Jack software is used for the creation of physiologically realistic digital humans that can be manipulated in the virtual space. Vicon's technology adds the ability to capture highly accurate real-time human motion data that can be used to drive these digital figures.
- Frank Bokulich
