Thursday, 7 February 2013

Cooling

A critical aspect of the BMW F10 M5 engine is its cooling. Because of the high RPM's and boost pressures, considerable heat is thrown off in spirited driving that must be tamed. To start, notice all the air intakes and radiators at the front of the car. 


Neither fog lights nor front-looking radar, both available on the standard F10 5-Series, are available for the M5 because of the cooling needs of the car. There are in fact 10 separate coolers in the car. 

The engine and turbo water coolant circuit is shown in the diagram below, with the charge air and computer cooling circuit shown dimmed for now.

The coolant is circulated through the radiator (1) by a belt-driven pump (not shown). From there, it flows to an electric pump (5) which drives coolant through the engine block. On exit it is monitored by the coolant temperature sensor (11). At this point the thermostat (4) either sends it back into the engine during warmup, or directs it back to the radiator to get cooled down. An electric motor (10) directs heated coolant through a valve (8) to the cabin heat exchanger (7). Electric motor (9) sends coolant through to the turbos (6). As the pressure gets higher, coolant is bled off into two expansion tanks (3 & 12) where it can be recycled when needed.

The illustration below shows the expansion tank (1), coolant filler pipe (2), coolant level sensor (15), main pump (4), electric fan (5), radiator (6), and thermostat (9). The cold coolant heads to the engine at (12) and returns hot at (11). The passenger compartment heat exchanger is (14), powered by an auxiliary electric pump (13). 


The main pump has a modified design that achieves a higher coolant flow rate through different impeller geometry. As well, the cylinder head cooling has been optimized.

After the engine is shut down, there is an auxiliary electric coolant pump that can run for up to 30 minutes, with the electric fan running for up to 11 minutes to improve cooling.

The turbochargers are also liquid cooled. This is not critical during operation, as the intake airflow and the oil lubrication keep the turbo within acceptable operating temperature ranges. However, after the engine is shut down and no further airflow or oil flow occurs, the exhaust manifold retains heat which will be absorbed into the turbo bearings which can cause damage.


For this reason there is an electric motor (3) driven cooling circuit for the turbocharger bearings as shown below. Its coolant flows in after it has already exited the engine so as not to detract from engine cooling during operation. After the engine shuts down is when the turbo bearings need cooling.



In addition, there is a second "low temperature" cooling circuit shown below dedicated to the charge air coolers (aka "turbo intercoolers") (D,H) and the DME computers (F,G).


There are three radiators (A,B,J) located beneath and to the sides of the main radiator. These cooling circuits are driven off two electric pumps (C,I) and the circuit has its own reservoir (E).

The low temperature cooling circuit is shown below. It cools the DME's (F,G) and the charge air (D,H) using radiators (A,B,J) and electric pumps (C,I). It also has its own expansion tank (E).


This circuit has the two air-to-water charge air coolers and the three radiators, for a total of five coolers. Add to this the main engine radiator, a radiator for the engine oil, one for the transmission oil, one for the power steering, and the air conditioner's condenser, and that's the total of 10. In addition there are cooling fins on the rear diff under its aluminium oil tray. Eleven in all really, but whose counting any more?

When the engine is generating as much power as does the M5's, cooling is not something you want to treat as an afterthought. If the cooling system fails, it is quite possible to melt the engine very thoroughly. If it is even a bit off, heat can accumulate at sensitive places and cause a lot of damage, shortening the longevity of the engine.

6 comments:

  1. Cars radiators right? How does that idea correlated with Cooling towers?

    ReplyDelete
  2. very nice blog post. I also found a very good website who are working in Intercoolers Suppliers Australia.

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  3. Fantastic post. Thanks for helping us to understand an incredible piece of engineering. It's amazing all this works and continues to work under pressure and hot temperatures! *hats off to the engineers*

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