Technical Evaluation

[Terry953]

Following a thread on the Toyota Hybrid forum regarding comparing the P position on a conventional auto gearbox where a sprag is engaged with the running gear to mechanically lock the transmission does the Auris HSD have a similar arrangement to do the same thing. It certainly feels like it if you select P - release the handbrake and try to push the car?

Another statement that I would like evaluating is as follows:-- "When in Drive and stationary with the brake pedal pressed, the Hybrid system will after a short time cut all power to the electric motors (creep function is disabled), so there isn't the stress as in a conventional automatic."

I've not tried this myself as I'm not in favour of holding a vehicle on the foot brake because I consider it unsafe - bad practice [blinding motorists behind me with my brake lights] - and consider the correct practice to be to apply the handbrake.

Here we are talking about the relative stresses on a torque converter-epicyclic gear train transmission when stationary - D selected- hand or foot brake ON, to the identical situation in an HSD where something is under stress because as soon as the brake is released the vehicle creeps without any throttle.

What is under stress ?

Should this scenario be treated only as a short time exercise ?

What damage could occur if this is prolonged or does the HSD system act as stated in the extracted statement to protect the transmission?

Regards TerryB

[Terry953]

UPDATE

From further research by studying various third party and Toyota Nomographs into the N and P differences in our HSDs I have come to the following conclusions.

SITUATION :--

Vehicle Stationary - Parking or foot brake ON - Electrics switched ON [i.e. READY] -

Transmission in ‘N’ =

Nothing moves, meaning =

The Engine is OFF -

The M/G [Motor/Generator] 1 is stationary - so not charging -

The M/G 2 is stationary. So vehicle is not moving.

Vehicle Stationary - Parking or foot brake ON - Electrics switched ON [i.e. READY] -

Transmission in ‘P’ =

Nothing moves, meaning =

The Engine is OFF - so not charging - But if the computer senses that power is required it will start up to charge the Battery.Bear in mind that our Atkinson engines idle &1000 rpm no less.]

The M/G [Motor-Generator] 1 is stationary - But if the computer senses that power is required the engine will start up and drive M/G 1to charge the Battery.

The M/G 2 is stationary. So vehicle is not moving.

Vehicle Stationary - Parking or foot brake ON - Electrics switched ON [i.E READY] -

‘D’ engaged =

The Engine is OFF - so not charging - But if the computer senses that power is required it will start up to charge the Battery.

The M/G [Motor-Generator] 1 is stationary - But if the computer senses that power is required the engine will start up and drive M/G 1to charge the battery.

As ‘D’ is engaged the computer wants to energise M/G 2 to move the vehicle but can’t because the parking or foot brake is applied. So energy is wasted, and the generated heat is dispersed by the transmission cooling system.

[Can’t find any reference to any inhibitors that will combat the build up of excessive heat in this situation. But it must waste energy anyway.]

Release the Brake = The vehicle moves off.

Conclusions for the vehicle stationary situation :--

1.Don't stay in 'N' for too long or excessive battery drain will occur [especially at night].

2.Don't stay in 'D' for too long as transmission overheating could occur and fuel/electrical energy waste will occur.

Or am I being pessimistic?

Must now do some practical testing.