Basic Hypermiling Concepts For The Toyota Hybrid

February 15, 2014

I’m posting this topic on request from another thread. I suspect for many people this may be of minimal interest! Hypermiling is too big a subject for one post, so the idea behind this one is to focus on those aspects relevant to Toyota Hybirds, to raise some awareness and perhaps stimulate some discussion.

[Disclaimer: I am acting as a messenger here. Simply passing on information without judgement. I am aware that some/many of the ideas and driving techniques may be considered nuts and even downright dangerous.]

Hypermiling Background:
Put simply, ‘hypermiling’ encompasses the range of actions which may be taken by drivers to improve fuel economy. These may apply to any vehicle. Some are easier to do than others. Some have greater impact than others. The best way to save fuel is of course not to drive at all! One way to look at it is, if you *had* to drive, what are all the options available to you to use the least amount of fuel for the journey. Here are some generic examples suitable for all cars. I have put two suggestions in each category to stimulate discussion. I’m sure there are many who can think of other ideas to fit into each category:

Simple actions with noticeable gains:

Maintaining tyre pressures & using the maximum permitted tyre pressures
Anticipating traffic

Simple actions but not really practical:

Choosing a different time to travel
Taking no passengers and removing all excess weight

More costly with questionable gains:
Reducing aerodynamic drag, lowering and stiffening the car.
Low rolling resistance tyres

Downright nuts:

Drafting (driving at speed close behind a large truck to shield from wind resistance)
Driving at speeds much lower than others

[n.b., there is a list of more ideas in the last link of this post!]

Hypermiling for the Toyota Hybrids (specifically the Prius)

The following are brief descriptions of 4 important concepts which relate to the Prius but may also apply to other Toyota Hybrids:

1. Five stages of Hybrid operation (engine warm-up)
These hybrids are cold blooded creatures and it can take a long time for the ICE to reach its preferred operating temperature of 73 – 93 C. Under certain conditions I can complete a 30 minute commute with the engine block only reaching 50 C. Knowledge of the Five Stages allows understanding of the car’s operation which might appear odd (like why the ICE shuts off in some situations and not others).

Hybrid Hypermiling before the engine is fully warmed (Stage 4) is mostly done in Stage 2. You need to switch off cabin heating, and anything else you can do without, to prevent the ICE from coming on. You need additional instrumentation like ScanGauge to read the ICE temperature and anticipate the car's behaviour.

More on the Five Stages can be found here:

http://priuschat.com/threads/the-five-stages-of-prius-hybrid-operation.12919/

2. Pulse and Glide (under 40 mph)

The simple concept here is that you will expend less overall energy by intermittently accelerating and coasting, allowing your speed to rise and fall, than by continuous driving and maintaining a constant speed. Bicyclists do this naturally and there are many examples in nature which have evolved to save energy this way, e.g., birds (flap and glide) & fish (twitch and glide).

Hybrid Hypermilers will aim to Pulse by running the ICE *only* at the engine’s most efficient RPM (peak BSFC). This is a fairly brisk acceleration (to the right of the HSI on a Gen 3):

See the first graphs here: http://techno-fandom.org/~hobbit/cars/sweet/refl.html

There is a difference between ‘coasting’ and ‘gliding’. Coasting is when you take your foot completely off the accelerator and allow the car to slow down (as with normal cars). Gliding is when you apply a gentle touch on the accelerator, just enough to cancel the HV Battery regeneration, in a method described as ‘feathering’ the accelerator pedal. You can use the MFD or HSI to help with this or additional instrumentation like ScanGauge, but after a bit of practice you can do this by just ‘feeling’ the car’s behaviour.

It may take some practice but not that difficult to P&G between 15 - 25 mph or 20 – 30 mph in urban areas and between 30 – 40 mph on busy A roads, without your passenger(s) or other drivers realising you are doing it.

Ideally the engine needs to be warm. The glide phase should be 3 – 5 times longer than the pulse phase.

3. Warp Stealth (40 – 50 mph):

This is the higher speed equivalent of the glide situation when travelling at speeds above 42 mph. P&G is increasingly difficult at higher speeds (see below), so the best time to apply this is when on a long slight downhill.

Hybrid Hypermilers need to know that above 42 mph, the car has to spin the ICE in order to protect one of the electric motors (MG1) from spinning backwards too quickly. You can initiate warp stealth by lifting your foot off the accelerator completely for a moment and then feathering. The other factors that come into play when you do this can be found here, written by ‘Hobbit’ who coined the phrase:

http://techno-fandom.org/~hobbit/cars/warpstealth.html

4. Super highway mode (around 50 - 60 mph):

From about 40 mph upwards, wind resistance becomes the dominant force against which you are burning petrol. The glide phase of any attempt at P&G becomes increasingly short and difficult to maintain. So for situations higher speeds, this technique is used to find the ‘sweet spot’ of fuel efficiency at these speeds. The end result, by using extra gauges, is to just hold your speed or only allow it to bleed off *very* slowly, thereby minimising fuel consumption during this phase, before having to accelerate back up again.