Does cruise control affect charging speed?

It's probably due to a combination of the PSD and software algorithms.

Generally speaking, your gas pedal still determines throttle and not speed. When you're using the pedal, you're probably coarse varying the throttle input (moving your foot due to discomfort, natural muscle tremors, etc), leading to extra energy in the system.

The prius uses the M2 motor as a generator to provide counter-force so more ICE energy goes to the wheels (remember M2 is connected to the PSD, M1 is connected to the wheels). The varying throttle means extra energy. At high speeds, I think M1 is also used to add a small amount of energy from M2 to the output (which would otherwise be wasted when the battery is full).

At very high speeds, I think the opposite happens, the car drives the 10kW M2 to increase the planetary PSD speed (effectively varying the gear ratio), and the 50kW M1 is the generator to power this varying gear ratio.

Generally, the software tries to balance M2 and M1 so that the battery is used as little as possible to extend its life. Extra energy from this variation goes into the battery. Energy not available that is needed comes from the battery (such as sudden acceleration requirement).

In very high throttle (RED mode), both the ICE, M2, and M1 are powered, which only takes from the battery. This is unsustainable (hence the RED indicator).


In cruise control this variability would decrease, since the engine can precisely control the ICE throttle and system energy. Hence what may seem like trickle charging, there's less variability in the energy M2 produces and M1 uses, since the software can very finely tune the ICE throttle.

But yeah, I wouldn't be surprised if the algorithms are designed to produce as little excess energy as possible during cruise control. Generally, the slower you charge the battery the longer its lifespan is. Also you need to leave some room to recoup the energy when you regeneratively brake.

 

I found that I got better fuel mileage on flat interstate roads with the cruise control as compared to without the cruise control. Of course am not comparing cruise control mileage to "gliding" mileage. Also, I set the cruise control to about 60 mpg and that was a good balance between being run over and good fuel mileage.