History of the Camless Engine
History shows that the idea of a camless internal combustion engine has its origins as early as 1899, when designs of variable valve timing surfaced. It was suggested that independent control of valve actuation could result in increased engine power (1). More recently, however, the focus of increased power has broadened to include energy savings, pollution reduction, and reliability.
To provide the benefits listed above, researchers throughout the previous decade have been proposing, prototyping, and testing new versions of valve actuation for the internal combustion engine. Their designs have taken on a variety of forms, from electro-pneumatic (1) to electro-hydraulic (2), (3). These designs are based on electric solenoids opening and closing either pneumatic or hydraulic valves. The controlled fluid then actuates the engine valves.
Much of the available documentation deals with the either the control of the solenoids or the computer modeling of such control systems (2), (3), (4), (5), and (6). The research on the control of the solenoids is crucial since their precision and response is a limiting factor to developing a reliable camless valve actuator.
A comprehensive project using solenoid control of pneumatic actuators was completed in 1991 (1). This research included the development of the actuators, a 16 bit microprocessor for control, and comparative testing between a standard Ford 1.9 liter, spark ignition, port fuel injected four cylinder engine and the same engine modified for camless actuation. Testing compared the unmodified engine to that of the same engine, altered to include eight pneumatic actuators in place of the standard camshaft. As Gould et al states, their work cannot be considered feasible for implementation due to the high power requirements of the actuator. Furthermore, concerns related to the lack of research for the gas flow dynamics in variable valve timing designs were raised by the authors. The altered flow dynamics may have contributed to inconsistently favorable results.
Since the new research proposed by the University of South Carolina utilizes the emerging field of piezoelectric devices to replace solenoids in previous designs, a literature review of piezoelectric – hydraulic actuators was completed. Through this search, it was found that the combination of accuracy, force, and displacement were the greatest challenges facing such actuators.
Recent research completed by Mauck et al (7) indicates that the need for “smart wing” technology is centered around the ability of a hybrid piezo-hydraulic pump to produce large displacements (0.1 to 10 mm) with high forces (10 to 2000 N). This is inline with this proposal; however, the actuation frequency of (1) is limited to low or intermediate frequencies (0.1 to 200 Hz). This is not compatible with the high frequency requirements of a camless engine.
Earlier work by Yokota and Akutu (8) results in an on-off poppet-type valve that operates at higher speeds. However, actuation is limited to 2 kHz and simple binary function – open or closed. This is also not compatible with the requirements of variable timing and lift needed for the camless engine.
Another, more recent, advance in high operating frequency piezoelectrically-driven hydraulic actuators was completed by Roberts et al (9). Their system provides actuation at frequencies up to 24 kHz, but valve stroke is limited to 40 mm.
(1) Gould, L; Richeson, W; and Erickson, F., 1991, “Performance Evaluation of a Camless Engine Using Valve Actuation with Programmable Timing,” SAE Paper No. 910450.
(2) Dobson, N. and Muddell, G., 1993, “Active Valve Train System Promises to Eliminate Camshafts,” Automotive Engineer February / March 1993.
(3) Anderson, M; Tsao, T-C; and Levin, M., 1998, “Adaptive Lift Control for a Camless Electrohydraulic Valvetrain,” SAE Paper No. 981029
(4) Kim, D; Anderson, M; Tsao, T-C; and Levin, M., 1997, “Dynamic Model of a Springless Electrohydraulic Valvetrain,” SAE Paper No. 970248
(5) Ashhab, M-S; and Stefanopoulou, A., 2000, “Control-Oriented Model for Camless Intake Process – Part 1,” Transactions of the ASME Vol 122, March 2000
(6) Ashhab, M-S; and Stefanopoulou, A., 2000, “Control of a Camless Intake Process – Part II,” ASME Journal of Dynamic Systems, Measurement, and Control – March 2000
(7) Mauck, L; Menchaca, J; and Lynch, C., 2000, “Piezoelectric Hydraulic Pump Development,” Proceedings of SPIE – The International Society for Optical Engineering 3985 Mar 6-9, 2000
(8) Yokoat, S; and Akutu, K., 1991, “Fast-acting Electro-hydraulic Digital Transducer. (A Poppet-type On-off Valve Using a Multilayered Piezoelectric Device),” JSME International Journal, Series 2: Fluids Engineering, Heat Transfer, Power, Combustion, Thermophysical Properties Vol. 34 No. 4, Nov. 1991
(9) Roberts, D; Hagood, N; Su, Y-H; Li, H; Carretero, J., 2000, “Design of a Piezoelectrically-driven Hydraulic Amplification Microvalve for High Pressure, High Frequency Applications,” Proceedings of SPIE – The International Society for Optical Engineering 3985 Mar 6-9, 2000
University of South Carolina
Department of Mechanical Engineering