Quote:
Originally Posted by SPL
...
...More likely in my view is the fact that the transaxle's primary lubrication comes from the oil pump driven from the ICE's output shaft [pages 39 & 40]. If the ICE was not spun (in order to operate the transaxle oil pump) while coasting at speed, there would probably be insufficient lubrication of the transaxle's gears and bearings. The oil pump drive cannot simply be moved to the MG2 output shaft instead, since then there would be no lubrication if the ICE were running with the car stationary — for example when the ICE is charging the battery, warming up, or providing heat for the cabin. So, the oil pump is driven by the appropriate shaft. [It now appears that I was mistaken when I said in another thread that the transaxle oil pump was driven by the MG2 output shaft. I shall correct that error....]
Stan
|
I don't think the limitation in neutral is related to lubrication. An analysis of the lubrication system reveals that the oil slinging arrangment is quite a bit more sophisticated that might be initially evident. The gear systems contain machined areas to accomodate oil transport by slinging and the housing contains a number of reserviors that receive oil in this manner that are actually supplly containers for gravity fed lubrication points. Besides, at speeds above 42 miles per hour, the ICE
is turning (in fuel cutoff) to protect MG1. Neutral does not prevent the ICE from turning, it just shuts down fuel injection and ignition.
So what is neutral for? The primary thing is probably to let the car be moved on the ground over short distances without the danger of an engine start. This can't be done in park, and in any other gear, an engine start is a possibility, even in reverse (in fact, probably). The electrics are probably kept up for the power steering motor to permit the car to be controlled while rolling, but dynamic braking is disabled to prevent the artificial "drag" used to simulate the coast of a conventionally powered car.
Is it useful as an easier way to "stealth" the TCH? That's a matter of pure opion and personal preference. My take is that, yes, it does essentially the same thing as an accelerator position in the drive gears that results in no battery charge or discharge, and that that accelerator position is harder to hold in the TCH than the Prius. BUT, the benefit is very slight because it requires a very precise grade wherein the coast requires neither power or braking to maintain (you don't have access to power, and braking costs you energy becasue only friction brakes are available), and the coast must be long enough that you cannot hold it with the accelerator, and you accept the extra complication and risk that comes with an extra action (shift lever) for a sudden power demand or hard braking. All of this is for a very small efficiency gain of about 10% at idle or speeds below 42MPH (above that the ICE is turning so you are not in "stealth" anyway) for a very limited time period. SO, I don't do it as I simply don't think there is enough gain for the effort and risk increase.