kona44

After letting off the gas from 45mph or so, is it harmful to slap the transmission down to 4th to let the engine/tranny brake in slowing down? Being a hybrid, are there energy/gas saving advantages or does this downshift do more harm than good?

It's so easy to move the transmission lever from drive to 4th and back.

Regards, kona44

happy1977

I thought at that speed, you'd still be at 4th gear. And just curious as to why you chose to shift manually?

Stormforge

i doubt there are any energy/gas saving advantages for manually downshifting. the tranny should be strong enough to handle when popping the shifter from auto to manual



when driving aggressively, you sometimes need to stop more quickly when just stomping on the brakes just won't do. so what i do sometimes is brake, pop the shifter to manual and downshift to create engine braking. it helps to slow down really quickly!

Cruiter

If you own a 450h, you need to know how it works.

When you let off the gas, the engines stops 'completely'. There is more natural deceleration than the 350 due to the electric motors providing light to moderate braking to charge the batteries. Your front pads should last well over 100,000 miles.

D/shifting is more an advertising feature than really helpful. I've tried in the mountains and it does provide some good there but that would be the biggest advantage.

happy1977

I know that, it just seems the OP's post was asking about down shifting without braking first.

kona44

Thanks for the replies. It was pointed out that since the engine stops when lifting the gas, it becomes moot if downshifting saves gas, my concern, and marginal saved brake pads. Great answers!

Regards, kona44

kitlz

kona, I downshift going down a hill by me in the morning. It winds with a few blind turns. Can't forget the occasional deer crossing the road. I usually go down to third combined with the brakes. The gauge is at the beginning of the blue charge area, like the car isn't on. Then when I eventually stop, I shift up to six and move the shifter over to drive. Kinda neat seeing sixth gear I haven't noticed any increase or decrease in mileage.

LAMark

OK, As a 450 owner I should know this, but with the CVT, what does "downshifting" actually mean? For that matter what do "3rd gear" and "4th gear" mean? I know there are labels on the "shifter", but I thought they were more for a placebo effect to satisfy drivers used to conventional transmissions.

lucasb7

This is a fairly complicated question. But you are correct that the transmission is simply imitating preset gear ratios set by the engineers. I will try to use this Synergy Drive simulator to explain what (to the best of my knowledge is going on). These numbers are for a G2 Prius so motor speeds and ICE redline are different.

First, note that MG2 is the only slider that affects speed; it is the only thing that a direct connection to the wheels. Now, if you drag MG2 to 35 mph, in D the transmission would try to keep the ICE off or as low as possible (probably around 1100 RPM unless you try to accelerate or go up a hill). When you use the manually selected gears it is just bumping the ICE and MG1 sliders up at some preset ratio. In D, the computer will chose from a near infinite combination of ICE and MG1 speeds to optimize mileage.

It is important to say that using the manual gears will not improve mileage. The only time I would advise using them is when you are descending a hill where you know that the battery will be full (all bars, no regen available...ie the gauge doesn't go into charge anymore). Otherwise, you are wasting energy that could be captured as electricity as heat in the ICE. The manual gears will increase regen (while making the engine spin unnecessarily) but no more than light brake pressure would do.

kona44

Great answer, thanks for your time and explanation. kona44

wa3cuj

My dash display can show the ICE as the only thing driving the wheels, yet when I let MG2 at 0 and run the ICE in the simulator, the simulator shows 0 mph. Am I missunderstanding something, or is the dash display not giving an accurate picture of what is going on at all times?

lucasb7

Both are correct in a sense. The ICE can be the only thing that is providing motive power to the wheels, but MG2 will always be spinning if the wheels are moving. So the dash display is correct that the ICE is driving the wheels but the power is routed through MG2.

Note that MG2 is the outer ring and ICE is the planetary gear set. So if ICE is turning the planetary gear set and MG1 is providing some resistance (shown by the constant regen to the battery, which is there most of the time) then MG2 is forced to move and turn the wheels even if it isn't providing power.

The more and more I learn about this transmission the more my respect for Toyota's engineers increases. It really is an amazing feat of simplicity and efficiency. And people wonder why other automakers have had trouble producing hybrids as efficient as Toyota's...

wa3cuj

Thanks for the explanation. Now, after being in retirement for 5 years, I know why I became an Electrical Engineer I hope the guy that dreamed this up got some kind of bonus!!

wa3cuj

I know that the wheels of justice can turn slow, but that article is 5 years old. Are you aware of any resolution in the matter?