This article was first published in 2000.
United States Patent No. 6,006,540 was awarded on December 28, 1999. Filed by Ford Global Technologies, Inc. (Dearborn, MI), the patent covers a novel intercooling method. Here's what they have come up with.
Engine designers seeking to obtain higher performance levels from automobile engines (particularly during intermittent high-load operation) have devised increasingly complex solutions. Systems are currently available for providing engines with nitrous oxide, and various schemes are used for supercharging or turbocharging engines. A drawback inherent with nitrous oxide arises from the fact that a nitrous bottle must be refilled frequently, because the amount of nitrous capable of being carried in most systems is quite low. And, although superchargers and turbochargers provide advantages, it is desirable to provide a much higher output from the engine intermittently, but without the need for either nitrous injection or the use of excessive boost pressures.
The Ford invention is a system that provides an engine with variable levels of charge-air cooling, including an intense intermittent level which can be accompanied by an increase in intake manifold pressure provided by a turbocharger or a mechanically-driven supercharger.
This is not the first system to take this approach - Japanese patent 93,118 also discloses a system for refrigerating air entering an engine air inlet. That approach does, however, suffer from a shortcoming because the refrigeration plant is used only for the purpose of refrigerating the air found within a surge tank. Such a system is necessarily limited in its capability because only a small quantity of air can be cooled, compared with the large quantity of air flowing through an engine in high speed and high load conditions.
The Ford invention overcomes the drawbacks of the Japanese system by providing a highly superior thermal reservoir. This takes the form of a liquid coolant tank, which is refrigerated by an on-board air conditioning compressor. The liquid coolant is then available to flood a charge air-to-liquid heat exchanger to provide extra densification of intake air for brief periods of time.
This provides increased engine output without the need for an oversized supercharger or turbocharger, and without the attendant drawbacks of nitrous oxide systems.
The Nuts and Bolts
The new intercooling system for an automotive engine consists of:
- a coolant reservoir containing a quantity of liquid coolant;
- a refrigeration system for removing heat from the liquid coolant within the reservoir;
- and a charge air-to-liquid heat exchanger that receives refrigerated coolant from the reservoir and chills the charge-air entering the engine.
The refrigeration system comprises:
- a refrigerant compressor driven by the engine;
- a condenser for receiving high pressure refrigerant vapour from the compressor and for liquefying the refrigerant;
- and an evaporator housed within the coolant reservoir, for receiving liquid refrigerant from the condenser, and for absorbing heat from the liquid coolant as the refrigerant returns to a gaseous state.
The system also includes an additional ambient air-to-liquid radiator for removing heat from the liquid coolant. This is used at times of low load, with the system switching to refrigerated coolant at times of high load. The refrigerant compressor of the intercooling system can also be used for supplying air-conditioning to the passenger cabin.
In this example the 'V' configuration engine (10) has supercharger (12), which is driven by a belt coupled to crankshaft (18). Charge air entering the engine's induction system through intake (16) flows through supercharger (12) and then ultimately through the air inlet (20). Prior to this, charge air moves through charge air-to-liquid heat exchanger (30). The recirculating fluid in this air-to-liquid heat exchanger is cooled by means of ambient air-to-liquid radiator (44) - so far, it's the same system used in conventional water/air intercooled turbo cars. However, during high load operation, refrigerated liquid coolant from the coolant reservoir (24) is used to flood the charge air-to-liquid heat exchanger (30), with the result that the intake air entering the engine is more dense, allowing more fuel to be supplied to the engine for a much greater power output.
The engine controller (50) operates three-way control valves 52 and 54 which control the flow of liquid coolant so that it either recirculates between charge air-to-liquid heat exchanger (30) and ambient air-to-liquid radiator (44), or between air-to-liquid heat exchanger (30) and the refrigerated reservoir (24). Thus, when valves 52 and 54 are set so as to bypass the intercooler radiator, liquid coolant is drawn from the refrigerated reservoir (24) and passes into the charge air-to-liquid heat exchanger (30). After liquid coolant has circulated through exchanger 30, valve 52 directs liquid coolant back to reservoir 24.
Heat is extracted from reservoir 24 by means of a compressor (32), which supplies compressed refrigerant vapour to the condenser (36), which in turn changes vapour to a liquid and sends it to the evaporator (34). The refrigerant changes phase to a vapour in the evaporator, thereby extracting heat from the liquid coolant (40) within reservoir 24. The engine controller (50) receives a signal from the throttle position sensor (56). When refrigerated liquid coolant from reservoir 24 is circulating through the heat exchanger (30), the ECU may increase the boost provided by the supercharger by means of the boost controller (22). Other inputs to the ECU include temperature sensors at 58 and 60.
The Pros & Cons
There are a number of significant advantages with taking this approach. Firstly, the intake air can be cooled to temperatures below ambient, giving an intercooler efficiency of over 100 per cent. This compares with typical traditional intercooler efficiencies of around 70 per cent. This very high efficiency has the potential to provide major power and/or knock resistance gains. Secondly, by constantly building up 'coolness' in the refrigerated intercooler coolant reservoir, and then using this to chill the intake air only at high loads, the refrigerant plant can be vastly smaller than if it were required to cool the intake air on a continuous basis. This makes it viable for the normal car air-conditioning system (perhaps with an uprated compressor) to be used in this application. Finally, if the system is integrated with the cabin air-conditioning system, the refrigeration part of the system will be automatically enabled by the driver (or climate control system) activating the compressor whenever the ambient temperature is high.
The are also a few disadvantages. The intercooling system will not be effective until the refrigeration system has had sufficient time to reduce the temperature of the intercooler coolant in the reservoir. The length of time that this takes will be dependent on the volume of fluid used and the power of the refrigeration system. This is one reason that the Ford patent uses ECU boost control, complete with intake air and intercooler coolant temperature inputs - the boost used depends on the intercooler fluid temperature. Secondly, the complexity of the system is much higher than for a simple air/air intercooling system. However, if an intercooling system is being designed from scratch, or if the car already has water/air intercooling, the system could still be relatively easily put into place.
And because the work of the intercooler refrigeration compressor is stored in the intercooler liquid reservoir, you could even turn off the air-conditioning compressor at high loads if you were after every last kilowatt!