another thermistor hack

<div class='quotetop'>QUOTE(ken1784 @ Aug 15 2007, 10:15 AM) [snapback]496123[/snapback]</div>

Thanks for that I might give it a go.

 

So, did you try this? If yes, how does it work?

 

No not as yet, just posted another thread on first 1 mile, in which using "N" during the warm up stage (negative ign angle phase) seems to have made a positive difference.

 

Are you using this to be able to initiate glide between 35-40 mph before s3/s4 temp is reached instead of only having ev glide available below 34?

 

Very nice! I was hoping a hack would come out for this. Great work, Ken and Bob!

 

Wow, I must have missed this thread the first time around [but
I did see all the discussion over on prius_technical_stuff, and
all the fun Bob was having..] The funny thing is while developing
the THW "linearizer" for the gauge, I wound up paralleling in
a test pot and running it a bit too far down, telling the car
that the coolant temp was WAY over 100C. Fans roared to life,
and the ToD popped on... but all that went right off again when
I brought the fake temp down to a reasonable level. The fans
seemed to kick on around 105C, if I remember.
.
Since I just use EV mode to work around various non-shutdown
issues in the early stages, I haven't played with THW fakeouts..
.
_H*

 

I would like to suggest one important and one "nice to have" modification to the middle circuit:

• forward bias signal diode with 240 ohm resistor
• low temperature disabler on "fake" (parallel mode)

Forward bias diode

One of the Prius Technical Group posters had suggested using a forward biased diode in the resistor network. The nominal 0.65V forward bias threshold means that when the thermistor reaches about 80C, the voltage across the diode will take out the adjustment resistance network. This is completely automatic so any high temperature events will be accurately detected.

Low temperature disabler

Originally suggested by Cor, the forward bias diode could be replaced by a pair of transistors so one keeps the resistor network transistor off until the thermistor reaches 30-40C. This would replace the mechanical switch and with the built-in, Si forward bias, fully automate operation. It should look something like this:


If someone has a working copy of SPICE, they could quickly optimize the design. Note that once the bias circuit enables, it also latches the enabler transistor, T1. I cheated by using a microprocessor to software control the thermistor bias and record the performance. It also allows me to software control disabling the bias when the ICE cools off, which this circuit lacks, and deal with initial states.

When the car is parked in "READY" facing a strong, cold wind, the ICE and coolant will get colder and colder. Once it reaches 60C, my 2003 Prius ICE turns on until it is warmed to 70C. With the microprocessor solution, it monitors the real ICE temperature and stops adjusting to allow the ICE to come on. I don't know how this dual-transistor circuit behaves during "READY" cooling.

Having a lower temperature, cut-off threshold may not be a problem. As the catalytic converter cools, it MAY on its own trigger ICE operation to keep them in an operational range but I have not done any testing with this circuit. The problem is if the ICE cools below 30C, I've seen unreliable operation including stalls.

One also has to be sensitive to startup voltage transients. You don't want T1 to 'turn ON' before voltages have settled. I suspect there is not a problem but a cap on the reference voltage network, lower resistor, might be a good idea. My software solution has a delay before it starts operating.

The simpler circuit may be a better answer but it needs more engineering and testing than I've been willing to invest. If someone has SPICE and an interest, I would recommend giving it a try and seeing how well it works.

Bob Wilson

 

Fantastic stuff guys! I few questions for the laymen in the group. The splice suggested in the "middle" diagram would require a splice "upstream" of the actual sensor. Is there an "easy" way to get to that part of the circuit. A possible simpler solution would be a "downstream" splice. My hope is that the sensor line goes into the ECU under the dash (not sure if this is true). Now if you can splice the line downstream under the dash, then you could hook it up to a reostat control (possibly next to the EV button). The reostat would add a positive delta to the "true" temp. Then you just dial the delta up or down as desired.

The "driving experience" I see is as follows.

1. Turn on NHW-20 then switch into EV.
2. While in EV adjust the reostat until the temp on SGII reads 85c (185f).
3. Drop out of EV and when the ICE lights it should jump strait to S4.
4. At the end of each pulse when the ICE is off, you dial the reostat to a "final" temp of around around 75c (165f)
5. During each glide you could also dial down the "delta dial" to zero to get a reading of the "true" temp.

Here are some strange S1 behaviors I've seen that might be of interest to this mod:

• IGN +6 in S1? New Prius Hack?
• New S1 Veto Prius II technique

11011011

 

Howdy,
Thanks guys for all the info, this thread was a great help in my own attempts to fix the whole warm up issue.

I ended up making a circuit of my own, based in no small part on what you guys did.

I tried some of the circuits shown but had some issues with ensuring that I didn't affect the engine temp after the warmup phase. Both the simple resistor and the simple diode setups affected the engine temp after warmup, causing the cooling fans to come on too early and force the engine to always run too cool.

I attached a picture of the enable/dissable switch, the circuit I ended up using, and a picture of the circuit board.

The circuit uses a capacitor to provide a voltage that the car can read.
A set of transistors compares the capacitor voltage to a reference voltage and discharges the capacitor as needed (Purple stuff). Another set of transistors prevents the system from operating until the car is sufficiently warmed up (blue stuff). Lastly another capacitor delays start up, and ensures an orderly "boot" sequence (green stuff).

Effectively the circuit allows the car to warm up to 42C, then suddenly boosts the temp to 73C. The circuit has no effect if the car gets warmer than 73C

I have found this circuit doubles my fuel efficiency.

I should note that I have a Toyota Highlander, not a prius. You would need to atach the leads to the corresponding pinouts for a prius, but it should still work.

As an unanticipated bonus, the circuit also informs you that you have entered "mode three". As you start the car and drive off the temp needle will be pegged low, it will just be comming off of the peg when the circuit swoops it up to just under normal operating temp. As soon as you see the needle in this high temp region you are capable of entering full hybrid mode, but in fact you will be stuck in mode three. So l pull over, stop for ten seconds and voila.

Thanks again for the help, hope someone else finds this circuit usefull.

Legal Note:
I am sure this voids your warranty. There is a risk of damage to the car and or engine. Tinkering with electrical components also can cause fires. Use at own risk.

(so far I have seen no ill effects on my engine, perhaps because I have set the min required warmup to 42, (just past mode1) certainly the car will behave badly if it really is at -5 and you tell the computer it is at 73.)

 

j

 

Does anyone happen to have a picture of where to locate pin E4-19 of engine ECU? Are the plugs labled under the dash? I would hate to get the wrong one.

 

Can somebody explain how doing this to a cold engine can cause damage? As far as I can tell, cold oil will work just as well as normal temp oil...

 

I don't think it WILL cause damage, the statement was simply that it MAY cause damage.

Another way of stating it would be:
"All the PhDs at Toyota say not to do this, but if you want to do it anyway.... here's how".

There are 1000's of decisions the Prius makes every second and a large portion of them take temperature into account. By operating outside of the operational parameters of the Toyota PhD's you may come across something that they have never seen before, and as such, never tested for before.

Fantasy below

For all we know the 60+ second S1 warm up phase may be masking some obscure gasket that doesn't react to pressure properly when cold. It may have never shown up under testing because the S1 warm up phase gets the gasket warm before it takes high pressure. With the thermo hack, you can reduce what could have been (in Canada) a 15 minute slow transition from S1->S2->S3 into a 10 second S1->S3.
​

So basically you will be operating your vehicle in a configuration that may not have been fully tested or planned for. For me... I'd do it in a heartbeat... I think the Prius is much tougher than the Toyota PhD's spec'd it for, but to be fair to Ken, it is kinda necessary to warn people to do this at their own risk.

11011011

 

Can anyone that has used this hack, or has more knowledge of EE than I do, provide some more info? If I print out this schematic of the new "complex" version of the hack and take it to Radio shack or similar, would they be likely to know how to interpret this and provide me with everything I need? Also, is this hack the same as the one of the guy on the CNN clip on cleanmpg - he can instantly get feedback from one of his SGII's and turn the temperature up to where ever he wants- same or no? Thanks to anyone who can help!

 

I'd imagine the 1k variable resistor to be some sort of dial resistor, where you can turn up or down the resistor value. the 240 is fixed.

I just thought of something... what temp would the car think its running at on the complex diagram when your in the middle of switching to the fake circuit (100% resistance or wire cut)?

 

I'm wanting to build jstcd's design but I'm not sure on what some of the stuff is in his schematic.

Can someone tell me what the transistor values are? And can someone tell me what the "NOT" gate is? Is it just a connection or is there an actual NOT gate there?

 

Any recomendations for someone who doesn't know anything about circuit boards? I have a hymotioned prius, less than a 5 mile commute and would like to operate all electric. I would be interested in purchasing one of these hacked boards from someone with some detailed information about what it is doing and that the same board has been used on an existing prius....