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A variable force solenoid (VFS) is an electro-hydraulic device that controls pressure proportionally or inversely proportionally to a signal (voltage or current) obtained from the on-board controller of a powertrain. A low flow VFS is used as a signal level devices for transmission line pressure control or application of clutches.
The solenoid can be useful for positioning, stopping mid-stroke, or for low velocity actuation; especially in a closed loop control system. A uni-directional solenoid would actuate against an opposing force or a dual solenoid system would be self cycling. The proportional concept is more fully described in SAE publication 860759 (1986).
A transmission solenoid or cylinoid is an electro-hydraulic valve that controls fluid flow into and throughout an automatic transmission. Solenoids can be normally open or normally closed. They operate via a voltage or current supplied by the transmission computer or controller.
A small solenoid can generate a limited force. An approximate relationship between the required solenoid force F s, the fluid pressure P, and the orifice area A for a direct acting solenoid valve is: [3] = = where d is the orifice diameter. A typical solenoid force might be 15 N (3.4 lb f).
In most solenoids, the solenoid is not immersed in a higher permeability material, but rather some portion of the space around the solenoid has the higher permeability material and some is just air (which behaves much like free space). In that scenario, the full effect of the high permeability material is not seen, but there will be an ...
Reluctance motor subtypes include synchronous, variable, switched and variable stepping. Reluctance motors can deliver high power density at low cost, making them attractive for many applications. Disadvantages include high torque ripple (the difference between maximum and minimum torque during one revolution) when operated at low speed, and ...
For variable valve lift, competing technologies (e.g., Honda's VTEC and BMW's Valvetronic) use electromechanical concepts, achieving valve lift variation via dedicated mechanisms; it can also be combined with camshaft phasers to allow control of both valve lift and phase. In contrast, MultiAir uses managed hydraulic fluid to provide variable ...
The servo valves of the World War II-era were similar to this — using a solenoid to drive a spool valve. Advancement of EHSVs took off in the 1950s, largely due to the adoption of permanent magnet torque motors as the first stage (as opposed to solenoids).