Originally Posted By: Ben99GT
Rotational cam torque is what is used to move the oil,
and thus camshaft centerlines, as opposed the strictly hydraulic cam phasers which depend on oil pressure entirely for phasing.
I use the word "backlash" to describe "the reversing torque caused by the slope of the cams". It's important to describe that because it shouldn't be suggested as 'drag' or the force required to move turn the cam (which includes frictional losses) that this principle is based on, else one could not advance the timing. The backlash provides both forward and reverse torque, thus the ability to retard and advance timing. The side of the phaser in which the oil is put allows the backlash effect to degree the phaser as oil is metered (at gallery pressure FYI) by the hydraulic solenoid in the head.
Borg-Warner's solution to harness the backlash for actuation assistance purposes is really all this is. The oil being fed into the chambers is still fed at gallery pressure, so even to say that there is NO work done by hydraulic pressure here is not correct. This is precisely why I called it what it is; backlash-assisted hydraulic cam phasing.
I guess my point before establishing it as a hydraulic unit, is that it retains the pitfalls of a hydraulic device, such as susceptibility to viscosity (temp, grade)) -harnesing backlash energy to the mix simply improves performance, but it's performance will still vary with viscosity. I don't see precision or latency matching that of an electronic servo unit