All-EV mode

I spend a lot of time in bumper-to-bumper traffic conditions, therefore like it or not, effectively the car will be running on EV-mode most of the time. And once the battery drains off, it will be recharged by the engine.

Question: Under such conditions, i.e. frequent recharging of the gasoline engine, is the Prius less efficient than a normal gasoline car? I would imagine that draining-recharging cycle should be less efficient than moving the car directly using the engine?

 

The traffic is often backed up for more than 2-3 kilometers. When it moves it leaves only a small gap of maybe 5-8 meters long. To drive that small distance and stop again, the battery drains pretty fast, and I do not get any regenerative braking at such low speeds.

One option is to wait for a bigger gap to open up, and then try to do a mini Pulse & Glide in order to let the engine drive the wheels directly and minimize battery use. But this is very difficult to pull off successfully and not to mention, it tends to annoy the other cars behind you and runs the risk of another car filling up the gap. Even if I managed to execute it, I noticed that it still uses a lot of battery power.

Therefore I have concluded that the best strategy is to just creep along on EV-mode like normal and let the engine regenerate the battery power. But it just leads me to the thought: is the gasoline engine much more efficient under such conditions?

Ignore for the moment the benefits of the Prius's engine not running while idling - this advantage may not be much if the traffic moves frequently with minimal idling time, yet the distance that opens up each time is very small.

 

That makes a lot of sense, thanks!

I was worried because my FC gauge was persistently above the maximum bar at 10L/100km during bumper-to-bumper traffic. I've also heard of people getting above average MPGs in city driving which sounds counter-intuitive to me, since the stop and go nature of city driving should be sub-optimal for fuel economy.

Does anyone have any idea (through experience, testing etc) what would be the impact on MPG by driving in all-EV mode at low speeds, with constant engine regen? I know this approach is not to be recommended, but is that actually highly detrimental to fuel economy? From my experience creeping through heavy traffic, the MPG at most would be 23.5 (converted from maximum bar 10L/100km shown on my screen - I do not know the actual figure since I did not reset my trip).

 

I have decided to try test out driving solely on the electric motor with constant regen (does this harm the engine/motor btw?) when the SOC drops too low.

Method 1:
With warm start, my round-trip journey based on all-electric mode yielded around 65-70mpg. Basically I tried to maintain the bar at around 50-75% of the EV region on the left whenever possible (i.e. level road or slight incline). The average speed is around 23kmph and the driving is almost continuous.

Method 2:
On the same route, I also tried a Pulse & Glide approach which gave me similar MPG but leaves me with higher SOC compared to the all-electric mode. Not surprisingly, the P&G method is better than all-electric.

But what really surprises me is the very good result that I have gotten with all-electric + constant regen, which is still highly efficient. But this may have to do with the fact that half my journey is a downward slope where I simply just glide/coast down. But since this is a round-trip experiment, I have to make up for it again with all-electric mode on the upward incline.

This experiment is also not consistent with the very poor results that I have gotten on bumper-to-bumper traffic. Perhaps this may have something to do with the constant accelerating from start, and the constant braking without regen?