Aptosuser

Newbie question. I take it that this mode is similar to the "B" position on our '12 Camry hybrid shifter, but more nuanced. Does anyone use it on a regular basis?

Droid13

The two lie at opposite ends of the spectrum (and not just on the alphabet). The Camry's "B" position is pure function, the "S" selector range on the RXh is pure fancy.While the Camry's B setting is mainly for engine braking the RXh S settings are mainly for sportiness. Sure, you could use the S settings for engine braking but that could have easily be achieved with a single selector position like the Camry. Keeping the engine rpms higher for a little more response could have also been implemented with a single selector position too, but yawn, boring. Instead they provide a simulation of an imaginary 6 speed transmission. Only thing missing is the optional sound track of an Indy car and the quarter slot.

It's cute and I suppose a bit fun when the mood strikes...

Aptosuser

Thanks. I think I'll just fuggeddaboudit. I seem to also recall reading some disparaging remarks about this feature elsewhere.

vlad_a

Are we talking about the Sport Mode or Manual Mode? The sport mode makes the accelerator pedal more sensitive and the speedometer lights up in red when putting the pedal to the metal. A side effect is nauseous passengers. In any case, I have little use for either one (no big hills to require engine braking around her).

Aptosuser

The mode where you manually shift from D to S. Actually, I tried it out today on a long downgrade, shifting from D to "4th" gear. It seemed to have the same effect as shifting from D to B in our Camry hybrid, using regenerative breaking to slow the car in place of applying the actual brakes; same thing as downshifting from 4th to 3rd with a manual transmission. I noticed that the eco light (as opposed to the eco mode light) was on the whole time. And per the energy display, the ICE was not running and the hybrid battery was charging. There was no engine revving, of course.

RXSF

Actually if you use S mode, you are using engine braking and it actually reduces mpg because the engine remains on while braking. you cannot look at the energy display since the regenerative braking arrows take over. After you come to a complete stop, the engine should be on

jrfiero

Quote Atpouser - "There was no engine revving, of course. "

There is engine reving in manual shift mode in my 2013. However, the fuel shuts off in overrun, so it doesn't decrease mileage. My energy display in this case shows charge, whereas if I used the brake it goes "past charge" in most cases because it needs mechanical braking in addition to regenerative, at least in the situations where I use the manual shifting which has recently been downhill towing a trailer.

Also, Sport Mode (not Manual Shift) changes the electric steering as well as the throttle response. I'm not fond of the throttle response change but I do like the steering change.

Jonas

Aptosuser

OK, now I'm totally confused. How does the engine rev if the fuel "shuts off"? We drive this route over the mountains from Santa Cruz to the SF Bay Area at least once a month. So what's the best way to drive on the downgrade to regain mpg?

RXSF

Have you noticed that sometimes, going down a downgrade with moderate to heavy braking, that the engine is still running by the time you come to a complete stop, even for an additional 2-3 seconds? Sport shift or not, my theory is that the engine will stay on to provide engine braking when necessary.

I feel it is best to leave everything in D and let the car do the thinking for you. Engine braking was used in conventional gasoline cars to prevent brakes from over heating and overuse of brake pads. This is essentially not necessary on a hybrid car since slowing down does not use brake pads at all, but the regenerative braking.

Aptosuser

OK, thank you; will do. And ditto for our '12 Camry hybrid.

jrfiero

Slowing with the brakes uses regenerative braking under light braking, then adds mechanical braking as necessary. Using the manual shift mode in a hybrid has the same brake-pad-saving advantages as in a non-hybrid but to a lesser extent. IMHO it is also more effective at charging because it uses the motor/generators rather than the regen brakes.

The engine revs because it is, more or less, mechnically connected to the front wheels through the transmission and electric motor components. Same as in non-hybrids. All modern electronic fuel injection systems shut off fuel in overrun. The transmission, although a Continuously Variable Transmission (CVT) mimics a 6-speed auto when in manual mode (as someone previously mentioned) and does so quite effectively (again, IMHO).

Jonas

Droid13

IMO...

Bringing a vehicle to stop requires converting kinetic energy to something else, hopefully not involving rapid deformation of the vehicle and occupants. That something else is typically:

(a) Heat from friction at the mechanical brakes, which is wasted energy from an efficiency aspect (unless you plan to fry eggs on your rotors after a drive).
(b) Heat from compression from engine braking, which is also wasted energy from an efficiency aspect, unless the engine is still warming up or it's brutally cold outside, then maybe a minor benefit.
(c) Heat and increase in energy storage within the battery from regenerative braking, which of course is more efficient because most of the energy is still available for use to power the vehicle.

Sometimes 2 or all 3 could be involved at once.

So, from an efficiency stand point, you want to stay away from (a) and (b). Any slowing involving mechanical brakes or increasing of engine rpms is just venting valuable energy out as heat to the environment.

The question is, what is going on with the dance between these 3 options at any given moment during braking. I think in "D" mode, a hybrid will use (c), then (a) to stop, minimizing (b) completely, either by stopping the engine completely or rotating it without fuel as slowly as it can, assuming cold temps are not a factor (the ratios defined within the CVT require the engine to physically rotate at speeds above 42mph for non-plug Toyota hybrids, no exceptions)

But the question of the day is, in the "S' range, it there a potential for improved efficiency in braking. I think, probably not, for most people. If you select down in "S" while coasting you might induce more regen braking, but you're also increasing engine rpms and therefore still just dumping excess heat energy to the environment just through a different means. It isn't much different that braking more quickly and forcing the mechanical brakes to also be applied in addition to regen. This isn't going to magically provide the vehicle with greater ability to recover energy into the battery. The regen capability is fixed, doesn't matter how it's triggered, it can only take up energy so fast within the limits of tire traction and charge rate.

As far as using downshifting in "S" for slowing, the only time I think this has any benefit, and this also includes "B" in other Toyota hybrids, is for long descents. In this situation, once the battery has reached max charge from regen, the vehicle no longer can use regen energy and mechanical brakes will be employed. Thus, in the end, the same reason for conventional cars is still applicable, to avoid wear and especially overheating of brakes during long periods of sustained braking.

DunWkg

I don't drive any hills large enough to downshift, however exiting the interstate I may downshift without braking. The computer recoups some energy to the battery and also prevents over rev'ing the engine by not permitting downshifting to too low of a gear. It beeps madly when I try. It takes years of experience to recognize "mad" beeping from "happy" beeping.