[Quietcars] Regression testing 2010 Prius

Thu Jul 23 13:21:44 UTC 2009

Bob, thanks so much for the explanations regarding what I'd written about
pump noise and other factors during this testing.  Though many of these
things seem to be Greek to me, you'd explained them in a clear manner, and I
understand now what you were referring to.  

It appears that though these noises are somewhat audible, they will come up
short in helping anyone detect the presence of a Hybrid, and that the true
solution to this noiseless or quiet automobile has yet to be agreed upon,
though there are several possibilities that are now available for
implementation.  I wonder if the ACB and NFb have made any progress on the
legislative effort, as well as representative Towns's effort from NY?  I
think that hybrid technology is a stopgap to seeking measures to lessen our
dependence on foreign dependence on oil, and that diesel engines or gasoline
engines with turbos may be the clue if their further development continues
along the progress that VW and the newly organized Chrysler and GM are
considering.  

Your points about cars becoming more "electronic" dependent is well taken as
well as many cars have drive by wire which essentially eliminates the
throttle linkage and replaces it with TPS switches and computerization to
control how one accelerates and decelerates.  Electronic braking is the next
step, as electric steering is in place on several fronts today.  

I would like to suggest that maybe, if you or someone else on list who has a
hybrid has a moment, that you take a spin in the 2010 Honda Insight, which
has been newly revamped and outfitted for a sportier appearance and driving
posture for the model year, to see how it compares in performance and
technology to the Prius.  

Thanks again for your efforts and keep us posted on your 2010 Prius.  

Mike T in NJ

-----Original Message-----
From: quietcars-bounces at nfbnet.org [mailto:quietcars-bounces at nfbnet.org] On
Behalf Of Robert Wilson
Sent: Thursday, July 23, 2009 5:02 AM
To: quietcars at nfbnet.org
Subject: Re: [Quietcars] Regression testing 2010 Prius

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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