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Discussion Starter · #1 ·
I had a very unusual experience last weekend when driving long downhill in Sport Mode. After stepping on the brake pedal the engine kept on running at very high rpm generating lots of noise. Felt like the transmission set itself into N position. Anyone with the hybrid model experienced the same?
 

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Sadly this is normal for hibrid. If your battery is full and you drive downhill without depressing acceleration pedal the engine goes high rpm to compensate energy generated by MG's.
I experienced it on a long descent and had a fuel consumotion 1.2L/100km without accelerating.
 

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miro said:
Sadly this is normal for hibrid. If your battery is full and you drive downhill without depressing acceleration pedal the engine goes high rpm to compensate energy generated by MG's.
I experienced it on a long descent and had a fuel consumotion 1.2L/100km without accelerating.
I'm on my 3rd hybrid now and never experienced that. It makes no sense either. Why would the engine rev to compensate for energy generated from MGs? The only time I have anything like it is when using B mode on a hill and it uses the engine to create drag ( when not braking)
 

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Strange you did not notice it on your past 2 hybrids.
The Toyota hybrid system uses power split device (PSD) that combines energy from MG1, MG2 and ICE. The ring gear is connected to MG2, ICE connected to planetary gears and MG1 connected to sun gear.
Vehicle can move forward by different combination of rotations of these components but always ring gear rotates forward when car goes forward.
If you release acceleration pedal on a slope the ICE will stop and make MG1 rotate in opposite direction (negative rpm value) that produces electricity and charges the battery. If battery is full this process must be stopped so MG1 speed should be equal to 0 or positive rpms (this mode will consume energy from battery). So here comes the ICE component that regulate speed of MG1. If ICE rpms are raised from 0 to 1500, the MG1 rpms are 0 or more depending on the speed of ring gear/vehicle speed.

This is a simulator of PSD http://eahart.com/prius/psd/
You can try it yourself making the car run forward (speed > 0) and set the MG1 rpms more than or equal to 0.
 

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When in sport mode decelerating im pretty sure the engine does not disengage. This means a faster response when you jump on the go pedal. I notice the car slows more like a normal car in sport.

So maybe this is why it sounds different to you. The ice is turning but not firing just like bmode.

My battery quickly depletes in sport mode and then feels slower than "normal" so ive given up messing with it.
 

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Hey guys, im not sure if we are talking about the same "issue" but i have the 1.2T and while im on downhill and i step little the brake pedal, RPMs go high (around 3k) and stays there until stop or if i step the gas pedal.
As i read this is normal and is called engine breaking and is used to prevent acceleration and to save your brakes.
 

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Discussion Starter · #9 ·
Chris said:
Hey guys, im not sure if we are talking about the same "issue" but i have the 1.2T and while im on downhill and i step little the brake pedal, RPMs go high (around 3k) and stays there until stop or if i step the gas pedal.
As i read this is normal and is called engine breaking and is used to prevent acceleration and to save your brakes.
Seen the RPMs going over 3K and stepping back on the gas pedal, after getting out of curves that is, made the engine go back to normal RPMs. Wouldn't call this engine breaking as driving in B gear which I would normally use on steeper downhills or snow. Felt more like the engine was not breaking at all just running crazy noisy in N gear (needed for heating or something?). It was a scary experience for all passengers. I immediately switched the driving mode from Sport to Normal mode and the engine behaved fine rest of the downhill.
 
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