[Quietcars] Regression testing 2010 Prius

[Robert Wilson]

Hi,

. . .
> What is the pump noise?  Is it the same as a gasoline engine's fuel
> injection pump noise as a short burst, maybe listing a  couple of seconds?  

The consensus is the power brake accumulator pump is running. To me, it seems a little like an aquarium pump in tone but at a slower rate. Sorry, but words are a poor way to describe a sound. By the time I have my hand on the door, it is unlocking and I hear the pump sound as I slide into the seat. Then I can't hear it any longer in the cabin, suggesting it is on the other side of the engine firewall.

> The other noises you refer to are generator noises?  

I suspect it is more the power feeding the main power motor, MG2.  There is a lot more is going on with the inverter than just the generator.

Let me try to explain the central purpose of the inverter, which has three major functions:
(1) it is a switching power supply connecting the 208 V DC battery to the motor generators
(2) it is the 'commutator' for the generator (called motor generator 1 or MG1)
(3) it is the 'commutator' for the motor (called motor generator 2 or MG2)

The inverter is metal box a little over one foot by one foot nearly a cube locate just behind the radiator on the right-hand side of the engine compartment when facing the compartment. This inverter box contains a cluster of high-power transistors, capacitors and control logic that switches the power between the battery, MG1 and MG2 to run the car. 

The inverter interfaces the 208 V traction battery to the 650 V, alternating current (AC) needed to power either MG1 or MG2. By changing the timing of when these power transistors switch on or off, they can draw electric power from MG1 or MG2 so either one can work like a generator. When there is excess power, the inverter converts the 650 V AC back down to 208 V direct current (DC) to charge the battery.

The inverter frequency we are hearing is pretty high and I'd estimate closer to 12 kHz but that really needs to be tested. It reminds me of a mosquito but it is difficult to hear from the cabin. If my windows are down and I am near a wall, I can hear the reflected sound. I have no idea of the sound pattern and level. We don't know which power flow or flows are associated with its generation but it is loud enough that experience Prius owners notice it.

> You must be assured that under a high traffic situation that these noises
> couldn't be apparently heard over the noise of automobiles and trucks around
> the hybrid, for they can't be tat loud.  The writer claims that he or "they"
> are in a parking lot.  Is the parking lot deserted and is the Prius the only
> vehicle moving at the time?  

At Hybridfest, they like to arrange the Prius for display so they would have been away from ordinary traffic. The inverter sound is distinct from ordinary traffic sounds, which is why I mentioned it here. Past audio testers would not have had it available from the NHW20 model (2004 through 2009.)

> If one is truly serious about this discovery and the noises emitted from the
> Prius are that discernable, then, let's test the car n real world
> conditions, in traffic, at stop lights with cars, trucks and other noises
> abounding.  

I'm not a mobility expert but I suspect the 2010 (model ZVW30) inverter sounds may be a useful audio signal that can be learned and mastered. The two pumps, inverter coolant and brake accumulator, are another area that I suspect may be useful in the future. A new technology, hybrid electric vehicles, have introduced 'different' sounds and there may yet be an approach that makes sense.

The hybrid electric vehicles generate a different set of sounds, unique to their systems:
(1) inverter - which is liquid cooled and in some modes, makes a high frequency sound
(2) inverter pump - which constantly circulates the inverter coolant
(3) brake accumulator pump - which maintains the power brake system pressure

I would have no problem if one or more of these parts were mounted on the front engine compartment plate that mounts the radiator so their sounds 'leaked' out the front radiator, air inlet. Anyone who has been around an espresso machine knows that recipricating, liquid pumps are not so quiet.

Unlike 'add-on' noise generators, these hybrid electric parts avoid patent or licensing issues because they are intrinsic to hybrid vehicle operation. There would be no easy way to disable them without also disabling the vehicle. 

Front mounted, they would be further removed from the cabin making the hybrid owner's driving experience quieter (and the mosquito-like noise would annoy the exhaust belching SUV in front of me.) 

>From a maintenance standpoint, it would be easier for a mechanic to diagnose potential problems like inverter pump failure. The sounds from these parts are the distinct audio signature of a hybrid electric vehicle and may stand out from ordinary traffic. 

Regardless, the 2010 Prius inverter noise has been noticed by experienced Prius owners and we like it quiet.

Bob Wilson

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