One of the aspects I like most about hybrid and electric-powered vehicles is regenerative braking.

Regeneration braking (“regen”) occurs when the electric motor is used as a generator, so charging the battery and in turn slowing the vehicle.

Regen is important for energy-efficiency – the energy that would normally be wasted in friction braking is instead utilised. In many driving conditions this can result in a substantial improvement in fuel economy (hybrids) or driving range (battery electric).

However, I like regen most because it is really effective from a driving perspective.

Unlike friction braking, the faster that you are going, the better regen works. The faster-moving vehicle has more potential energy that in turn can be turned into more electric energy. That’s the case with friction braking as well (the potential energy is higher so more heat energy can be generated) but since conventional brakes reduce in effectiveness as they are required to do more work, the feeling is not the same.

Regen braking can feel like the ‘inexorable giant hand’ pulling you back, all with smoothness and a degree of control that is impossible to obtain with friction brakes.

And let’s look at the subject of control for a moment.

Traditional cars use separate pedals for the accelerator and the brake only because of the origins of the technology. The ‘brakes’ and the ‘engine’ have always been effectively two separate systems. Even today, in most cars the only link between the engine and the brakes is the vacuum brake booster line.

Having separate pedals for ‘go’ and ‘stop’ seems to me to be absurd. If the parameter is ‘acceleration’, and that parameter needs to be varied on a continuum from maximum negative to maximum positive acceleration, why shouldn’t one driver input do it?

Some electric cars almost achieve this by controlling both electric motor power and regen braking with the one pedal. At (say) the half-way point in the pedal travel, the car is neither braking nor accelerating. At full accelerator pedal travel, it is accelerating as hard as it can. At full lift-off, it is (regen) braking as hard as it can. In these cars, the friction brakes are used just for the last few metres of a normal stop, and also for emergency braking.

(If you’re prepared to trade-off some energy efficiency, the electric motor braking can bring you to a complete halt – and probably also do emergency braking. You just drive the electric motor backwards – or try to drive it backwards, anyway!)

An electric car I drove some time ago used the one pedal for both regen braking and acceleration. At that time I wrote a commentary saying how good the combined brake/accelerator pedal approach was, only to have people suggest that the braking side would feel awful – like a traditional car that needed to have its brakes bled!

But I think that comment was simply because the people were stuck in a paradigm of conventional car control.

Think instead of sailing a boat. Long ago I used to have a small catamaran. Flying one hull (something at which I was rather inexpert) was for me the greatest buzz. With one hull up in the air, too much propulsion from the sail would overturn the boat; too little would settle the flying hull back into the water.

The amount of power being generated by the sail was controlled by the mainsheet – the rope that controlled the angle of the boom to the wind. Let the mainsheet right out and the boat would brake strongly, the hulls sinking into the water. Pull the mainsheet in and the boat would accelerate.

Both braking and acceleration were controlled by the one rope, a system that allowed you to play wonderful nuances with the angle of boat heel. The idea that you might need to grab another rope to slow the boat is absurd, and certainly for this novice sailor it would have made everything very hard indeed.

However, major hybrid and electric car manufacturers have steered clear of using a combined accelerator/regen braking pedal. Instead, they typically apply a little regen when the throttle is fully lifted, and then apply more regen as the brake pedal is pressed. Some hybrid vehicles (like the Prius) monitor hydraulic braking pressure and alter regen in sympathy with friction brake use, while others (like the Honda Insight) apply regen in the first portion of brake pedal travel and then allow hydraulic braking to take over.

And it’s my hybrid Honda Insight that made me think about this topic.

I’ve modified the throttle control of the car so that a number of non-standard things happen. One new outcome is that rather than the car regen braking as soon as the throttle is quickly lifted, there is a pause of a few seconds before the regen then smoothly comes in.

This works extremely effective in practice. Think about it for a moment. Quite often in normal driving you might take your foot off the throttle – eg when going downhill and not wanting to exceed a speed limit, or maintaining a gap to a car in front that is slowing. However, equally often that throttle-lift will be only momentary. But if you have your foot off the throttle for more than few seconds, it’s usually because you really want to slow down.

So regen that takes a few seconds of throttle-lift to come into effect works rather well. You can roll the car by lifting the throttle, or brake the car by simply keeping your foot lifted for longer.

Such braking behaviour is of course impossible with a normal friction braked car.

And you can take it further. What about mapping throttle-lift regen braking against vehicle speed (and so actual potential energy)? Or having switchable sporty mode regen braking that is much stronger than normal? (The pictured GM Hybrid bus I drove could be configured to have regen braking strong enough to lock the wheels!)

It’s not something that many ‘green’ vehicle enthusiasts seem to stress, but regen brakes that work seamlessly and strongly with infinite control, and can have their behaviour mapped against other car parameters, make traditional hydraulic brakes look like the 100 year old technology they really are.

I think that regen braking has the potential to make a whole new generation of driving enthusiasts…