Simple braking questions

Below about 7 MPH, Motor/Generator2 is not turning fast enough to slow the car, so at the end it is always friction brakes.

Motor/Generator2 (who's speed is always proportional to the wheel speed) is used as a generator while braking. There is a fairly low limit to how much electrical energy the regenerative process can convert to battery charge, the rest will be friction brakes. (or on long downhills, engine Braking. You can aid braking on long downhills with B)

 

There is a radiator for the inverter and transaxle that needs new coolant, same as the.engine. There is also.ATF WS lubricating and cooling the transaxle. Routine drain and fill with new ATF seems wise. 30,000, 90,000 and then every 90,000 miles

 

It isn't like the brakes which wear out from use, but is essentially a large alternator (also used as an electric motor) which is generating power as it takes kinetic energy from the movement of the car, slowing it down. It has proven extremely reliable, needing only routine maintenance of lubricant.

 

In a nutshell: the car has an electric motor, that can act as a motor, or, during braking, act as a generator.

 

Re: "going backwards" MG2 is connected by fixed gearing (and a chain, in some generations) to the differential and wheels, so it's always turning the same direction any time the car is going forward, the other direction when the car moves in reverse.

The only thing switching direction and "going backwards" when you brake is the electric current to/from the motor.

Even that isn't anything as simple to see as switching the + and - on DC connections, because the Prius MGs are AC motors. The difference between electrically 'forwards' and 'backwards' is just something you'd be able to see on a multichannel oscilloscope where you could watch the voltage and current waveforms together. (Or just using the Torque app or a ScanGauge, etc., which just asks the car's computer, which does the math for you.)

-Chap

 

Actually there have been MG coil failures on a small number of Prii requiring replacement of the HSD (both MGs are part of the HSD). That is why Jimbo repeats the oft stated suggestion to do regular ATF refreshes at 30k miles and every 60k miles thereafter. A good discussion of these failures in early Prii can be found at: VIDEO - Prius P3125, P3009, P3120 - MG2 repair - Luscious Garage | Hybrid Specialists
and at: Gen 2 Prius (2004-2009) Transmission Failure, P0AA6, P0A92, P0A7A - Luscious Garage | Hybrid Specialists in the Gen2 Prii.

JeffD

 

Most service intervals are miles OR months. I may just do another transaxle fluid change this fall. It's been three years since I last did one; it's been nowhere near 60,000 miles, or even 60,000 kms lol.

It's just: tri-yearly seems a good number, not onerous. And, time MAY be a factor, ie: a low mileage short trip vehicle may deteriorate the fluid faster. Who knows, it's a cheap and easy service.

 

I forget about time, as I do 30,000 miles a year so for me it is always miles. (now that I am retired, I may have to pay attention to time)