Fan Control advice needed, for automotive radiator

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1

Please help me with my electric fan controller program design for a vehicle radiator.

I can do the circuitry and coding fine, but I need advice on the target temperatures, strategies and timings. Here's where I'm at now -

My turbo diesel engine complies to Euro 3 regulations and is fitted with an 88°C thermostat in order to always run hot enough to reduce smoke and NOx pollution. The thermostat starts letting coolant go through the engine from 88°C (T3) and is full open at 99°C (T4). The coolant needs to be cooler than the first opening temperature by about 10°C, 78°C (T2), but NOT much cooler or the thermostat will over-react; either over-cool or stay closed too long. To ensure that T2 is quickly reached, active cooling (Fan just ON low) should only begin 10°C lower at ~68°C (T1). To avoid heat damage the maximum coolant exit temperature should be 110°C (T5), so extra active cooling should commence 10°C before this at 100°C and ramp up quickly.

too cold<-- T1 = 68°C target--> T2 = 78°C T3 = 88°C <--Thermostat--> T4 = 99°C T5 = 110°C -->too hot

My strategy is to monitor at the bottom and top of the radiator, Fan 1 will be run at a minimum of 30% while the vehicle is stationary, or if the air conditioning is On, or if the engine load is high, etc. Fan 1 and Fan 2 will try to maintain the bottom coolant available to the thermostat below 80°C, and Fan 3 will provide additional cooling if the coolant entering the radiator top is above 100°C. Fan 1 will also cool to T1 after the engine is turned off.
[Note that the 'Fans' may be separate devices or operational ranges of one or more larger Fans]

Thermofan profile
Thermofan profile733×407 16.8 KB

Is my reasoning sound ? Are my temperature targets valid ? If not, why not and what should they be ?

Edit - Ok, I've done some more research and some of these numbers (above) are wrong. See my next post for updates.

Additional information -

  • Temperature sensors - DS18B20 ('one-wire' 16 bit digital data)
  • Air Conditioning sensor - tap into existing air con Fan control wire (digital 0 / 12V)
  • Load Sensor - Tap into existing Mass Air Flow (MAF) sensor between air filter and inlet manifold (analog 0-5V)
  • Speed Sensor - air pressure module (MPS20N0040D Pressure Sensor + Hx710B ADC) in a Pitot Tube
  • Fan speeds controlled via Pulse Width Modulation (PWM) of 40A FETs
  • User Display - a single RGB LED. No Fans = Off, Fan 1 = Blue, Fan 2 = Green, Fan 1 + 2 = Cyan, Fan 3 = Red, Fan 1 + 2 + 3 = White
    Slow blinks = Sensor failure (or missing), Fast blinks = Fan failure
  • Sensing is performed once a second then, after smoothing, priority evaluation and hysterisis calculations, the Fan speeds are adjusted each 5 seconds.

bye.

2

Almost all radiator tops and bottoms are plastic. I hope you are actually monitoring the coolant and not the plastic surface.

3

Hi,
Can I suggest you bring fan 3 down in temperature so it is at 100% at the 100°C , that way you are giving yourself a safety margin.
A warning at 100°C would then sound.
Letting systems run to absolute maximums may cause damage, better safe than sorry.

The other thing is this can be adjusted in software when trialing the prototype.

Tom... :smiley: :+1: :coffee: :australia:
PS, Nice project :+1: :+1:

4

After some study of how cooling systems work and the target range for my engine (BMW M57) I'll add this summary -

  • Water pumps move coolant around the inside of an engine to maintain a desirable operating temperature while also evening out any hot or cold spots. When the coolant gets too hot it must be passed through an external cooling system.
  • Typically an air / coolant radiator is used to perform the cooling in a closed loop - old systems used the temperature gradient to allow natural syphoning of cold coolant from the bottom of the radiator to rise through the engine and be returned to the top of the radiator. Modern systems use a pump and control valve. In quite recent systems both of these are electrically operated in concert to provide the correct temperature regime.
  • Thermostatically or electrically controlled valves allow coolant to enter an engine. They act proportionally, that is they open more as the temperature rises (within a pre-defined range). An 88°C thermostat will allow a trickle to pass at 88°C, more at 93°C and maximum flow occurs at 99°C. Above 99°C they need external help to cool an engine effectively. In fact above 93°C (half way through the opening range) they need that help to start in order to not fully open before effectively cooling the engine back towards 88°C.
  • Cooling fans are simply not required while the coolant is colder than the lower opening temperature of a thermostat valve. This applies during engine warmup and at speeds above 40kph where ram air flow is normally enough. But not always.
  • Engines produce more heat when they work harder, so radiator size and air channel guides need to be designed for near maximum performance. Stop-start city driving at lower speeds and climbing steep hills while heavily loaded will require cooling fans to operate. Older systems un-necessarily operated fans all the time, thickening liquid (viscous) clutch mechanisms only turned mechanical fans when the liquid is heated enough, modern electric fans can be turned on & off as required.
  • To provide 'cooled enough' coolant to a thermostat requires monitoring of 1) supply coolant temperature from radiator 2) vehicle speed 3) engine load 4) radiator entry coolant temperature.

This was my first guess at operating parameters -
too cold<-- T1 = 68°C target--> T2 = 78°C T3 = 88°C <--Thermostat--> T4 = 99°C T5 = 110°C -->too hot

Here is a revised set of numbers -
too cold<-- T1 = 75°C target--> T2 = 85 °C T3 = 88°C <--Thermostat--> T4 = 99°C T5 = 110°C -->too hot
with the thermostat trying to maintain 90°C to 95°C.

new Thermofan profile
new Thermofan profile852×407 23.7 KB

Extra control -

  • Fan 1A establishes a flow through the engine bay and out the side vents well before the other fans start, this will keep engine bay temperatures lower before the real cooling regime starts. Especially in stop-start traffic.
  • Fans 1B & 2 need more than 35% power to start them, but are immediately throttled back to 25% once they are turning.
  • Considerable hysteresis is applied before turning these fans off.

Paul - its an all aluminium, cross flow radiator (tanks each side). Stainless steel encapsulated temperature probes will be wedged between horizontal water tubes near the entry and exit ports.

TomGeorge - Fans 1A & 1B SHOULD do 99% of the temperature management, bringing the outlet temperature down ~10°C as it passes down through the radiator. Fan 2 is monitoring the hot coolant being returned at the top of the radiator, not the cooled-down coolant being supplied to the thermostat, so it only needs to operate above the 10°C that the other fans are handling. Note the large undercooling hysteresis I've given it. Absolute maximum is closer to 120°C in modern vehicles so its already conservative.

bye for now.

5

More research has revealed more information.

N°1 is that my BMW M57 diesel engine has a dual valve thermostat, as one end gets slowly opened to admit coolant from the bottom of the radiator the second valve at the other end progrssively closes off the bypass so that eventually all heated coolant MUST go through the radiator. It starts to open ~88°C and will be 1/3 open at ~92°C which is the designed coolant INPUT temperature. The bypass is not fully sealed off till ~96°C while the coolant input keeps opening further up to 99°C.

N°2 is that the fan forced air flow from the viscous coupled clutch is very accurately adjusted to provide 91°C coolant to the thermostat/pump that it is attached to. It is not so good below its trigger point and quite agressive above it.

N°3 combustion becomes most efficient (and pollution is dramatically reduced) when the coolant at the top of the engine is above 80°C but below 110°C for diesel engines, petrol and gas can be operated a little hotter.

N°4 Fuel consumption drops ~2.5% as the inlet temperature rises from 90 to 120°C above which no further gains occur. Experiments show that the best practical temperature for low and moderate loading is 105°C while high loads require a lower temperature, closer to just 90°C.

N°5 warm up time can be shortened by keeping the thermostat closed, the fan off and the coolant pump off until the cylinder head is above 80°C. Can't do anything about the pump or thermostat, but I can at least keep the fan off till past 92°C.

More detail -
Most thermostats are driven by a wax pellet 'engine' which consists of a stationary metal pin, a shaped rubber bag containing the wax and a metal cup that holds the rubber bag in place around the pin. Mechanically the thermostat valve attached around the open end of the cup is pushed closed by a spring from a guide/frame and pushed open by the wax engine when the wax melts and expands.
Newer versions have an extension to a second spring loaded valve so that as the first opens to admit coolant from the bottom of a radiator the other closes to block off the radiator by-pass flow passage from the top of the engine, thus forcing all engine warmed coolant to pass into the top of the radiator.
Older engines positioned the thermostat at the engine coolant outlet with the radiator always part of the coolant circuit. Most current setups have it at the engine inlet with a radiator by-pass passage (or hose) parallel to the radiator. The cup (and wax) are positioned at the engine side of the thermostat housing to regulate the temperature of coolant going out of or into the engine cooling passages.
Here is a good Mahle video of dual action, although using older, vertical frame design - MAHLE Thermostats - How do they work? | Perfect Performance & Long Life for Combustion Engine - YouTube

Thermostat valve diameters and stroke length are engineered to allow a full flow to the coolant pump from either the bypass, the radiator outlet, or a proportion from each. Typically the tailored wax melts and expands over about a 11°C (20°F) range BUT doesn't solidify over the same range, it needs to be 'undercooled' an extra 2 or 3°C (5°F) to extract enough latent heat to crystallize.
Most contemporary dual valve thermostats are set to start opening at 88°C (190°F), then provide a mix of hot by-pass and cooler radiator outlet at ~93°C (200°F). If the mixture starts getting too hot the by-pass will be completely shut off at ~96°C (205°F) and the radiator valve gets to fully open at 99°C (210°F). On cooling it will remain partially open down to 85°C (185°F). Older systems are typically set 6°C (10°F) lower, while heavily loaded marine and heavy hauling/working engines are often set even lower.

Fuel consumption drops ~2.5% as the inlet temperature rises from 90 to 120°C above which no further gains occur. Experiments show that the best practical temperature for low and moderate loading is 105°C while high loads require a lower temperature, closer to just 90°C.
As 88 to 99°C seems a little low, why is this thermostat fitted? The thermostat (described above) attempts to regulate the coolant temperature pumped in to THE BOTTOM of a warmed-up engine to 93°C.
So how does this translate to what the temperature gauge shows from measuring the engine TOP temperatures? At low loads with air flow over the surface of the engine there will be very little increase, in fact with the thermostat part open the coolant pump will add too much from the cooled radiator output and the temperature throughout the engine will fall towards the 85°C closing point. At high loads, or when there is no air flow through the radiator or over the engine surface, the whole system will quickly get up to beyond 105°C (220°F), so active air flow cooling will be needed to keep the engine top at a safe temperature.

With active control of fan cooling it is possible to monitor engine load and adjust the radiator outlet temperture to suit. At consistantly light loads the coolant in the radiator can to be kept close to the by-pass shut off temperature (95°C in the example above) so that the engine top would be just over 100°C. As load increases then active cooling should be increased to bring the radiator outlet temperatures down below the thermostat opening temperature (87°C in the example above) so that it can control the engine top to be just around 95°C. This should keep the engine top temperatures closer to the optimums for various load conditions while also reducing the electric loading to only when really required.

These days engineers design in computer control for the pump rate, radiator to by-pass input mix, air duct shutter control, fan programs and even limit throttle position to keep engine top ends at optimum temperature. Older vehicles may be retrofitted with external pumps, mixing valves and electric shutter and fan controllers, with electric fan controllers being the easiest and cheapest upgrade to.

Thermo Fan Upgrade
How big of a fan, or how many fans, where to measure the coolant temperature and what temperatures to turn the fan(s) On and Off? Are any other inputs needed? What about manual over-ride, or extra cooldown, or ... ?

A thermostat on its own can help keep the temperatures in the right range, but back-to-front for economy, engine longevity and pollution reduction; something else is needed! Old fashioned viscous clutch fans don't help here, and neither do simple on-off electric fans. However computer control is easy to add to monitor engine load, air speed and temperatures to allow better management of the radiator that is feeding the thermostat.
The amount of air being used by an engine is an indication of the load; most current vehicles have a Mass Air Flow (MAF) monitor fitted between the air filter and the intake manifold which provides 0 to 5V in proportion to the flow; ideal for input to a 5V microcontroller. Air pressure at the front of a vehicle will indicate air speed through the radiator, this is easy to measure with a $5 sensor. Temperature can be read with $5 'one-wire' sensors, these may be fitted at the radiator inlet and outlet. A simple computer program can then augment the thermostatic control.

2 fans allow targeted temperature control; both off allows the most rapid heating, both full on the most cooling. The fan closest to the outlet can fine tune the feed to the thermostat while the fan at the radiator inlet can provide additional rapid cooling when high engine loading is detected.
Computer programs can be written to identify 'states' and deliver 'strategies' to manage radiator temperature according to the conditions and loads.

Now to where I'm currently at -

So what states should we define and what strategies are appropriate to each?

  • Engine startup - collect initial data, set T1, T2 & L1 to falling
  • From engine start to radiator inlet temperature >95°C - no fans during warmup
  • If radiator inlet temperature >105°C - start fan2 at 25% 'tick over', increasing 15% per °C, set T2 rising
  • If radiator outlet >85°C - start fan1 at 25% 'tick over'
  • If radiator outlet >85°C increases 0.5°C - set T1 rising
  • If radiator outlet >85°C decreases 0.5°C - set T1 falling
  • While T1 rising, if load is low - allow radiator outlet temperature to rise to 97°C before increasing fan speed
  • if load is moderate - start to increase fan speed to take temperature to 92°C
  • if load is high - if off start second fan, increase both fan speeds to take temperature to 87°C
  • While T1 falling
    and still thinking about this ...

What I need -
I don't need chest beating wanna bees that say 'I fitted a thermo fan and its great' but i'm not gonna tell you what settings and trigger values I used because I don't know or care, but 'I fitted a thermo fan and its great'. If you can't contibute scientifically, stick to the forums where you can boast all you like to all your imaginary friends, but don't waste my time here.

I DO need real data on engine top temperatures and the fan turn On and speed changes made at different engine loads and vehicle speeds, etc to build a data table so that I can make informed decisions to design a program algorith with a fixed scope. Only then can I start to design an active fan system. And publish it here.

thanks in advance, bye.

6

Hello bgennette
Do you have a piggy bank that you can raid for the necessary design engineering work?

Have a nice day and enjoy programming in C++ and learning.

7

Hi,
Thanks of the information.

Can you post a diagram of the setup, or do BMW have a diagram explaining the physical arrangement of the cooling system?

Is it one of these?
Here;
https://www.bimmerworld.com/About-Us/BMW-Cooling-System-Tech/

Or here;

Thanks.. Tom... :smiley: :+1: :coffee: :australia:
PS. It looks like the BMW system, makes sure the water pump is flowing coolant all the time and is not blocked when the thermostat restricts/cutsoff flow through the radiator.

8

Hi TomGeorge,

The M57 was around for nearly 20 years, and for the first 10 used a conventional by-pass cooling system with a fan belt driven coolant pump, so always pumping through the engine from the bottom of the radiator or from the radiator by-pass from the top of the engine.
The diagrams you referenced are for later versions using electric coolant pumps and wax motor plus electricaly heated thermostats that introduced 2 extra control features that, unfortunately, can NOT be retrofitted to earlier engines :cry:

So, I can at least (or is that at most?) add smarter coolant management through clever fan control.

I've just about locked-down the scope of the project and have coded data collection and fan operating mechanisms, preparatory to writing a specification for putting it all together.

bye.

9

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