Jboswald

I stumbled across a method to increase the amount of energy recovered by regen braking - and it doesn't require any modification to the car.
In a NON-hybrid car the cruise control will adjust the throttle to maintain a constant speed. However when the car starts down a long hill the most the cruise control can do is just close the throttle and hope that engine braking is sufficient to keep the car from exceeding the set speed - and depending on the grade level of the hill the car may continue to speed up over the cruise control set speed.

In the Lexus hybrid system the cruise control is a bit smarter and will work with the power train controller to apply additional regenerative braking to keep the car from exceeding the set cruise speed. Normally when you take your foot off the accelerator the car will use some regenerative braking to emulate what a normal car would experience with normal engine braking - however the cruise control will apply additional regenerative braking to slow the car down.

To exploit this feature, I enable the cruise control when I first get in the car (Push the button in so you get the green light on dash). Then SET the cruise control at the lowest possible speed (around 25 MPH I believe - push DOWN on the cruise control). Now you can either cancel the cruise control at this point by pulling the control TOWARD you - or simply override the control by using the accelerator and driving normally. The cruise control will remember the 25 MPH set point until you either turn OFF the cruise control or shut the car off or set a higher setpoint.

If you are over the cruise speed setpoint and you take your foot off the gas pedal while the cruise control is active (You can activate it by pushing the control UP to RESUME if it is not set) the cruise control will use regenerative braking to reduce the speed of the car till it gets down to the set point. If you were to use the BRAKE PEDAL to slow the car down in addition to the regenerative braking the friction brakes would also be applied which wastes some energy. The cruise control solution does not use the friction brakes so it allows you to recover more of your energy and put it in the battery.

When you do apply the foot brake the cruise control will be disengaged but it will still remember its original setpoint. You can re-activate the cruise control by pulling the control up (Resume) and it will be available again to provide additional braking anytime you take your foot off the accelerator and you are above the cruise speed setpoint.

jollick

You do know that when you hit the brakes the hybrid system uses regenerative braking first, then the brake pads. So, I do not believe your technique is any more effective. This is the reason Toyota/Lexus hybrid brake pads last so long, they hardly get used.

Jboswald

The regenerative braking applies to the front wheels only, when you step on the brake all 4 wheels participate in the braking effort. Toyota isn't going to compromise the safety and stability of the car by only using two wheels to slow the car since there is the possibility of rain slick roads or ice. The percentage of brake effort on the front wheels apportioned between regenerative / friction brakes may vary from 95/5 percent to 0/100 percent based on speed, pedal pressure, battery charge, component temperature, etc.. But 100% of the brake effort on the rear wheels is wasted as heat. Granted the front wheels provide the majority of braking effort, but regenerative braking can only recover a percentage of that energy. The percentage will vary considerably based on many considerations, especially the driving habits of the driver.

jim256

Not actually true. Regenerative braking is controlling other than in panic stops or the last few yards before you stop, when there is not enough motor power to give adequate braking action. Your pedal is actually brake by wire, with some safeguards for failure, so the car is not activating the friction brakes until needed. You might search the Prius Chat Technical forum for many particulars on how braking works, as well as all aspects of the Toyota/Lexus drive system.

PirelliRC

I also use the cruise control feature quite frequently to maximize effeciency. However, i only engage it on open roads and the highway. The problem that i see with what you are suggesting is that the cruise control can be dangerous if you enable it at a low speed or have it on constantly, because if you set it at 25 mph, and forget about it or get distracted by an event, you can have a crash.