Hybrid Battery Temperature Control

Has anyone ever wondered what is going on with their hybrid battery temperature and cooling fan (you know, the one under the rear seat)?

If I am interpreting the logs correctly, at cabin temperatures of 25-30ºC, the cooling fan is activated when Hybrid Battery Temperature reaches ~35ºC. The fan (Hybrid Battery Cooling Fan 1) runs between 120-200 Hz, maybe more if things get hotter. It is controlled by Hybrid Battery Cooling Fan Drive Request (which seems to operate between 40-60%, maybe more if things get hotter).

This controller does respond to Cabin Temperature and Hybrid Battery Temperature (probably in a series of steps, which can be seen in Hybrid Battery Cooling Fan {Status}, though they are not plotted here). You can see the effects in the second graph, where the cabin temperature started higher (because the car was parked in the sun) and Hybrid Battery Temperature 2 got above 45ºC.

But it is far more responsive to - can you guess? The answer, which I did not anticipate, is … Vehicle Speed! There is an almost exact match in the patterns, with the Fan Drive Request dropping to 40% when the car stops, then ramping up with car speed.



What should you do about this? Probably nothing (though you could try the excuse that “I was just trying to cool my hybrid battery”).

PS: What is a lone in the Forum Header: "Come learn, share, and discuss Toyota's lone of electrified vehicles!"? The brand is good, but surely not a_lone!

 

Alan, you are lucky if there is just RADAR around a corner. I generally find LIDAR (which is much harder to contest) at the bottom of a hill. Ah well, at least these cars have regenerative braking.

burrito, that would explain it. I wonder if it is worthwhile given all the other whirs and clunks in these hybrids? When I first drove the car, I thought someone must have hidden a cat in the back. Even now, I sometimes look in the rear-view mirror, wondering: "Where is the emergency vehicle with the siren?"

Anyhow, this approach to hybrid battery temperature control must be effective enough, given the long battery warranty.
(TMC may be a_lone but it is probably not a_lune.)

That said, if I ever saw hybrid battery temperatures around 50ºC, I would look into improved cooling, even for NIMH.

 

Following up on the lead given by burrito, I saw that the link between hybrid battery cooling fan speed and car speed has been mentioned before in the forum (though now despite searching the forum and my browser history I can not find the post). Some people have said it does not exist and only fan speed drive number matters (Hybrid Battery Fan Speeds | PriusChat; Gen 3 Prius Battery Fan Operation | PriusChat), so maybe it varies with model. The approach to mask fan noise has been explored in academic detail (https://www.jstor.org/stable/26562342).

Out of idle curiosity, I was interested in how ‘Hybrid Battery Cooling Fan 1 Drive / Status’ (number 1-6, maybe more) modulates the effect of ‘Hybrid Battery Cooling Fan 1 Drive Request (%)’ on ‘Hybrid Battery Cooling Fan 1 Frequency (Hz)’.

From the plots, I can not discern any effect from fan drive / status number 1-3 in my gen5 rav4 hybrid. But there is a discernible step change (albeit a small one) from number 3-4. It is evident when battery cooling fan frequency at the same car speed is compared either side of the step from 3 to 4. I guess (and hope, for NiMH battery life) that the effect might be bigger at higher fan drive / status numbers, if things get hotter.

There must be something that I do not understand in the units, because I figure that for a DC motor 150 Hz = 9000 rpm, which already seems too high for a cooling fan speed.

 

Hi ChapmanF, as mentioned in post #5 above (but obviously not prominently enough) the car I have logged is a gen5 rav4 hybrid (2019). I have only the PID names, which the OBDLink company says come from Toyota. As commented in another thread (Techstream Question | PriusChat), I find some of the PID names a bit cryptic, but I have not found more detailed PID descriptions (even under Data List Manager > Parameter Information in several {pirated} versions of Techstream). The PID name is 'Hybrid Battery Cooling Fan 1 Frequency (Hz)', and I take this to mean that it is Hz (cycles per second) of Hybrid Battery Cooling Fan 1. As far as I know, there is only one Hybrid Battery Cooling Fan in the car. As you say, it must provide this information into the CAN bus.

But there must be something that I do not understand in the units. As burrito points out, it must not be as simple as multiplying Hz by 60 to obtain rpm (even for this DC cooling fan motor). It probably does not alter the main interpretation, just tying up loose ends.

 

Thanks ChapmanF. It is interesting that there are other cases where Toyota OBD DC motor 'frequency' does not follow the conversion rpm = Hz * 60. But at least it was a linear conversion as you recall. My guess for the rav4 hybrid battery cooling fan is that rpm = 'OBD frequency' (Hz) * (60/2 or 60/4). But it does not alter the main interpretation.

If anyone is interested to be sure of actual rpm, they can try a strobe as you suggest. Most readers are probably more interested in the patterns of relative fan speed, which should follow the plots above. (If the conversion is non-linear, which might be tricky to discern even with a strobe, the ratios will change but the ranking will still be right. Air speed will probably not be a linear function of fan speed across the entire fan speed range in any case, but the ranking should be right).

 

This is getting well away from the original purpose of the thread, and most readers can safely ignore it, but one of the special features of this forum is that some participants are really interested in how these cars work.

So yes, if my interpretation is correct, 'Hybrid Battery Cooling Fan 1 Frequency (Hz)' is reporting on fan rotation. This is an improvement on the previous approach of reporting fan voltage, which was presumably the input voltage and it did not really tell us whether the fan was rotating in response. In the gen5 rav4, if my interpretation is correct, the input indicator is ‘Hybrid Battery Cooling Fan 1 Drive / Status’ (possibly a choice of resistors to reduce the system voltage) in combination with ‘Hybrid Battery Cooling Fan 1 Drive Request’ (% of thus modulated system voltage?).

I could be wrong. There are ways of controlling DC motor speed based on frequency of DC pulses (PWM). But typically, these would work at frequencies higher than 150 Hz (pwm - Calculate DC motor frequency - Electrical Engineering Stack Exchange).

There are various ways to sense motor speed in Hz, using optical or Hall effect or back-EMF or maybe other sensors (How to Power and Control Brushless DC Motors | DigiKey). I agree that these are likely to have a linear relationship to motor rpm. Cooling (heat transfer coefficient) is unlikely to have a linear relationship to fan rpm (www.offroadvw.net/tech/wes/fan.html), but cooling will increase if fan speed increases.

I do not know for sure how Toyota has designed any of this in the ray4, and I am not a physicist or electrical or aircon engineer.

 

Interestingly, quite a few people believe that hybrid battery cooling fan speed depends on car speed, from gen 2 Prius on:

HV Battery Fan Running Higher Then Normal On FWY | PriusChat

Gen 3 Prius Battery Fan Operation | PriusChat

Scanguage command to turn on hv battery cooling fan | Page 2 | PriusChat

Battery Cooling Fan Constantly Runs Every Highway Trip - Normal? | PriusChat

Inverter cooling fan coming on | PriusChat

GenII hv blower control codes for android torque app | PriusChat

Others think otherwise. The last post is the one I could not find when mentioned above. It even gives a ratio: "Hv cooling fan gets one extra volt of electricity per 10 mph road speed increase (approximate)."

As an aside, it seems reasonable that DC fan speed control used the old approach (voltage) for old technology motors (brushes and commutator); and a newer approach (PWM) for newer technology (brushless DC motors). But there are probably exceptions, and I don't know what Toyota or other HV manufacturers used in each model and year.

In any case, the logs above do not lie for the gen5 rav4HV; and it seems beyond reasonable doubt that ‘Hybrid Battery Cooling Fan 1 Frequency (Hz)’ is a measure of fan speed.

 

This log gives us some more insight:


When the car is stopped (in READY), the ‘Hybrid Battery Cooling Fan 1 Drive Request’ increases from 39.5% at ‘Drive Status 3’ to 43.5% at ‘Drive Status 4’.

At all car speeds, the ratio of ‘Fan Frequency’ to ‘Drive Request’ is higher at ‘Drive Status 4’ than at ‘Drive Statue 3’.

At any given ‘Drive Status’, ‘Fan Frequency’ increases in linear proportion to ‘Drive Request’. Both increase in approximate proportion to the logarithm of car speed above 20 KPH (I do not know the exact algorithm).

From specs of replacement blowers, the reported value from the fan tachometer ‘Fan Frequency’ is most likely 4 times the speed of physical fan rotation. Thus cooling fan rpm = ‘Fan Frequency (Hz)’ * 60/4 or, put another way, cooling fan rpm = Hz * 15. At a reported 200 Hz, the cooling fan is probably working at a reasonable 3,000 rpm.

At a cabin temperature up to 30 ºC, the cooling fan at the automatically selected ‘Drive Status 4’ seems to keep the gen5 rav4 HV hybrid battery temperature below 45 ºC under these moderate (non-towing) driving conditions. The system has some headroom (Cooling Fan Drive Status 5-6) if needed.

It might be interesting to look at hybrid battery temperature after a long urban run (to warm the traction battery) followed by turning the car off (which turns the cooling fan off).

 

Hi SmellyTofu. I can't answer all your questions, and there are others who know more in this forum, but I will offer a few insights:

1. There are now many more registered rav4 hybrids than Pii, but it seems there are many more technically-adept Prius owners.

2. The rav4 hybrid will absolutely activate the ICE before 1/4 throttle. At low acceleration it will run on the electrical motors alone for a while, but mostly it integrates ICE with electric. This is the design. It still manages around 5l/100k, which is fairly good for a car that size.

3. I don't think that 44ºC is a problem for the NiMH traction battery. Some NiMH batteries are designed to operate above 60ºC (https://industrial.panasonic.com/cdbs/www-data/pdf/ACG4000/ACG4000COL12.pdf); though until I know the Toyota specs (at least) I am happiest if the hybrid battery stays below 50ºC.

4. I am not sure if you can log using the scangauge (I use OBDLink with MX+), but personally I would want to look at a log of how parameters relevant to hybrid battery cooling in the rav4 hybrid are going during some drives before I tinkered with anything. From what you have said, it may be working just fine with the OEM algorithms.

5. I have not pulled the rav4 hybrid apart to understand the hybrid battery cooling air flow, but from what I can see it does not have an exhaust duct to the auxiliary battery area (as in some Prii). I assume it mostly stays in the volume under the trim, and exits the vehicle via the vent with rubber flap into the exterior behind the rear left quarter panel. This vent is visible from the luggage compartment if the inspection port at rear left is popped.

6. Hybrid Assistant does not support Aus gen5 rav4, and I am not sure that it can modulate fan speed in any rav4; but as mentioned above I would personally not tinker anyway unless I could see that there was a flaw in the OEM design.