high pitched pump sound? Stopping strategy?

[nonseqpriapus]

Hi,
I got my prius recently. Having been a tech for narrow aisle electric lifts in a former life, I suspect that prii stop by reversing armature polarity in the traction motor (while shunting some current through the regen) and then apply the main drum and rotor brakes to affect a full stop. Is this correct? Also, what is the high pitched pump noise after shutting the car off? Perhaps circulating coolant around the drive motor?

Also, has anyone added an amplifier to the factory audio with JBL's? I believe the factory radio is quite susceptible to amplitude clipping and wonder if the JBL's would give a more natural response at moderate levels with a modest amp.

I'm very happy with my prius and can't imagine going back to a conventional car. Thanks to all who wish to reply!

[dogfriend]

Welcome to the forum!


Under normal circumstances, most of the braking is regenerative until the speed drops to approximately 7 mph, then the friction brakes take over. MG2 (the traction motor) becomes a generator when coasting with your foot off the accelerator pedal or when braking. MG2 is a 3 phase AC induction motor, as is MG1. The Skid Control ECU handles braking; it negotiates with the HV ECU to determine how much braking is regenerative vs. friction.

The high pitched pump sound you hear after shutting down is the Coolant Heat Storage Pump. There is a "thermos bottle" which can store hot coolant for up to 3 days. When you shut down, the pump activates to fill the bottle with hot coolant. Then at the next start up, the pump circulates hot coolant to preheat the cylinder head. This is done primarily to reduce start up emissions.

I think that some have added aftermarket amps. I would try a search in the Audio section of the forum.

[Bill Merchant]

Hi nonseqpriapus, welcome to PriusChat!
The coolant transfer pump is just one of those sounds, like the brake accumulator pump, that you get used to. Also the non-sound of sitting silently at a stop light while everybody else around you idles.

The JBL amp is integrated into the car and nav. Beeps originate in the amp on order from the AV LAN. Also, the speakers are wired oddly; the rear doors get a left and right signal with a crossover wired into the tweeter, the front doors have separate circuits for the tweeters and mid/base. The sound stage is improved by disconnecting the dash center speaker, in my opinion.