I had a little time today so I analyzed some real time data on my C-Max that I recorded several months ago. I recorded speed data of the various components of the Hybrid transmission using ForScan to calculate certain fixed ratios so that one can compare the 2013 ratios with newer MY ratios as Ford said that they made “hardware” changes to the transmission for MY 2014.
“The upgrades build on powertrain software updates Ford announced last month for the 2013 C-MAX Hybrid. The 2014 C-MAX also will benefit from several hardware changes, including: Gearing changes that result in a more efficient transmission drive ratio” - FORD
Of course now we need someone to do the same for MY 2014+ so that my 2013 data can be compared with MY 2014+ data.
The attached chart shows the relationship of the motor, generator, and ICE speeds and calculated speed ratios.
1) Vehicle speed averages 72.2 mph as recorded. “The hybrid vehicle uses three methods to calculate vehicle speed. The PCM uses the ABS signal if available, and will substitute the motor speed if the ABS signal is missing. The PCM will use the engine and generator speed calculation if both the ABS and motor speeds are unavailable.”
2) Tire speed is calculated based on changing the tire revolutions per mile to yield the 2.51 axle ratio. The tire revs per mile needed to get a 2.51 ratio was 811. The spec tire ratio is 803. This is a difference of 1%. However, “a tire transitions from an unloaded to loaded state as it rolls, continuously flattening where the tread footprint comes into contact with the road. These continuous transitions result in some tread slippage, again increasing the tire revolutions per mile beyond what simple math would indicate.”
3) (Motor speed / Tire speed) ratio is calculated to be 9.0
4) (Motor speed + Generator speed) / ICE speed) ratio averages 3.55. The variances from the 3.55 are attributed to variances in scanning frequency when there are large, quick changes in the variables (for example ICE ramping up / down). The ForScan scan rate averages 83 milliseconds with a standard deviation of 20 milliseconds. Thus, the time from the first data point scanned to the last data point scanned during the large, quick changes will likely affect the calculated ratio since I'm not using the time stamp associated with each variable but rather the time stamp for the first variable scanned (too difficult to try to sync the time stamps for each variable scanned).
Below are observations from the chart.
1) When ICE speed is 0 rpm, the Motor speed and Generator speed are equal but of opposite sign.
2) When Generator speed is zero, the overall ICE / Wheel ratio is 2.51 – the axle ratio.
3) The Generator effectively controls the overall ratio in this case from a numerically high ratio of 3.3 (ICE RPM about 3000) to a low ratio of 1.7 (ICE RPM about 1660).
Edited by Plus 3 Golfer, 04 October 2016 - 02:02 PM.