Low-Temperature Coolant Cooler

Abstract

The invention relates to a low-temperature coolant cooler, for the indirect charge-air cooling on an internal combustion engine, with a number of flat tubes, through which 700 to 1,800 litres per hour of coolant flow during operation, which open out in coolant collectors (4,8) and air guide devices, in particular, air guide fins are arranged between the flat tubes around which charge air for cooling flows. In order to guarantee a constant cooling power over a large operating range of coolant throughput, said low-temperature coolant cooler comprises the following features: a) the flat tubes have a depth (23) of less than or equal to 20 millimetres, b) the coolant flowing through the flat tubes is deflected a maximum of two times in the collectors (4, 8) and c) the flat tubes are provided with internal turbulence generating devices.

Description

The invention relates to a low-temperature coolant cooler for the indirect charge-air cooling of an internal combustion engine, having a plurality of flat tubes which, in operation, are traversed by 700 to 1800 liters of coolant per hour and open out into coolant collecting tanks, with air guide devices, in particular air guide plates, being arranged between the flat tubes, around which air guide plates flows charge air which is to be cooled.

In charge air coolers for internal combustion engines, the charge air which is to be cooled can reach temperatures of up to 220 degrees Celsius or higher. On account of the high temperatures, damage can occur at the inlet side of the cooler. For this reason, the German laid-open specification DE 199 62 391 A1 proposes a charge air cooler which is characterized by at least two cooling circuits with different coolant temperatures, which cooling circuits are each guided by heat exchanger blocks which are connected in series in the flow direction of the air. The known charge air cooler comprises a pre-cooler, a high-temperature charge air cooler and a low-temperature charge air cooler. The low-temperature charge air cooler receives coolant via a separate low-temperature circuit, and is therefore also referred to as a low-temperature coolant cooler. Upon entering the low-temperature coolant cooler, the coolant is for example at a temperature of 45 to 60 degrees Celsius. The low-temperature circuit is for example driven by an electric coolant pump which is also referred to as a low-temperature coolant pump. The coolant throughput of the low-temperature coolant cooler is relatively low and is around 700 to 1800 liters per hour. Known low-temperature coolant coolers have flat tubes which are smooth on the inside. In order to obtain sufficient flow speeds for the internal heat transfer, three or more deflections are necessary in the case of flat tubes which are smooth on the inside.

It is an object of the invention to provide a low-temperature coolant cooler for the indirect charge air cooling of an internal combustion engine, having a plurality of flat tubes which, in operation, are traversed by 700 to 1800 liters of coolant per hour and open out into coolant collecting tanks, with air guide devices, in particular air guide plates, being arranged between the flat tubes, around which air guide plates flows charge air which is to be cooled, which low-temperature coolant cooler ensures a constant cooling capacity over a wide operating range of the coolant throughput.

The object is achieved in a low-temperature coolant cooler for the indirect charge air cooling of an internal combustion engine, having a plurality of flat tubes which, in operation, are traversed by 700 to 1800 liters of coolant per hour and open out into coolant collecting tanks, with air guide devices, in particular air guide plates, being arranged between the flat tubes, around which air guide plates flows charge air which is to be cooled, by the following features: the flat tubes have a depth which is less than/equal to 20 millimeters; the coolant which traverses the flat tubes is deflected a maximum of two times in the collecting tanks; and the flat tubes are equipped at the inside with turbulence-generating devices. During operation, air flows around the air guide devices which are arranged between the flat tubes, which air extracts heat from the coolant in the interior of the flat tubes. The extent of the flat tubes in the air throughflow direction of the air guide devices is referred to as the depth of the flat tubes. Known low-temperature coolant coolers are equipped with flat tubes which are smooth on the inside. In order to obtain sufficient flow speeds for the internal heat transfer, three or more deflections are necessary in the collecting tanks. Within the context of the present invention, it was found that a coolant-side pressure drop observed in known low-temperature coolant coolers is to be attributed to a pronounced effect of the coolant viscosity and therefore ultimately to the ambient temperature. Together with a flat pump characteristic curve, the result is a strong dependency of the coolant throughput and the capacity on the ambient temperature. Despite multiple deflections, the flow in the known low-temperature coolant coolers with smooth on the inside tubes is laminar, or in the transition region, laminar to turbulent. The capacity of the known low-temperature coolant coolers is therefore strongly dependent on the coolant throughput. This can result, in particular at very low temperatures, in the pressure build-up of the low-temperature coolant pump being insufficient on account of the high resistance in the low-temperature coolant cooler. With the design according to the invention of the low-temperature coolant cooler, it is possible to maintain an approximately constant cooling capacity over a wide operating range of coolant throughput. This considerably diminishes the effects of the ambient temperature and of tolerances on the charge air cooling.

One preferred exemplary embodiment of the low-temperature coolant cooler is characterized in that the flat tubes with the turbulence-generating devices are designed in such a way that the ratio between the maximum and minimum pressure loss in the flat tubes is less than 3 for a coolant throughput of 700 to 1800 liters per hour. This provides a faster response of the indirect charge air cooling at low ambient temperatures.

A further preferred exemplary embodiment of the low-temperature coolant cooler is characterized in that the ratio between the maximum and minimum Nusselt number in the flat tubes is less than 3 for a coolant throughput of 700 to 1800 liters per hour. The Nusselt number is calculated from the ratio between the product of the heat transfer coefficient and a characteristic length, and the thermal conductivity of the material used. The material used is preferably aluminum sheet.

A further preferred exemplary embodiment of the low-temperature coolant cooler is characterized in that the flat tubes have inwardly aligned indentations on at least one of their flat sides. The indentations are preferably formed corresponding to the exemplary embodiments which are disclosed in the German laid-open specification DE 101 27 084 A1.

A further preferred exemplary embodiment of the low-temperature coolant cooler is characterized in that turbulence inserts are arranged in the flat tubes. The turbulence inserts are preferably equipped with similar indentations to the flat tubes described above.

Further advantages, features and details of the invention can be gathered from the following description, in which various exemplary embodiments are described in detail with reference to the drawing. Here, the features mentioned in the claims and in the description can be essential to the invention in each case individually or in any desired combination. In the drawing:

FIG. 1 is a schematic, perspective illustration of a low-temperature coolant cooler according to a first exemplary embodiment;

FIG. 2 is a similar illustration to that in FIG. 1, according to a further exemplary embodiment;

FIG. 3 shows a Cartesian coordinate diagram in which the charge air temperature downstream of the charge air cooler is plotted against the coolant throughput;

FIG. 4 shows a Cartesian coordinate diagram in which the coolant pressure is plotted against the coolant throughput, and

FIG. 5 shows a Cartesian coordinate diagram in which the Nusselt number normalized to a minimum Nusselt number, or the pressure loss normalized to a minimum pressure loss, in the cooler network is plotted against the coolant throughput.

FIG. 1 is a schematic perspective illustration of a low-temperature coolant cooler 1 according to the invention. The low-temperature coolant cooler 1 comprises an upper collecting tank 4, on which is provided an inlet connecting pipe 5 for coolant. An arrow 6 indicates the coolant entering into the upper collecting tank 4. The coolant throughput through the low-temperature coolant cooler 1 according to the invention is greater than 0.2 and less than 0.5 kg/s.

The low-temperature coolant cooler 1 also has a lower collecting tank 8, on which is provided an outlet connecting pipe 9 for the coolant. The coolant passing out of the lower collecting tank 8 is indicated by an arrow 10. The coolant is preferably water with special additives.

Provided between the upper collecting tank 4 and the lower collecting tank 8 is a heat exchanger block 12 which comprises a plurality of flat tubes (not illustrated) which run between the collecting tanks 4 and 8, which are also referred to as coolant collecting tanks. Air guide plates, for example in the form of corrugated fins, are arranged between the flat tubes, around which air guide plates flows charge air which is to be cooled.

Arranged in the upper collecting tank 4 is a first partition 17, by means of which the coolant which enters into the low-temperature coolant cooler 1 through the inlet connecting pipe 5 is deflected for a first time along an arrow 18. Arranged in the lower collecting tank 8 is a second partition 20, by means of which the coolant is deflected for a second time in the low-temperature coolant cooler 1 along an arrow 21, before exiting the low-temperature coolant cooler 1 through the outlet connecting pipe 9.

The low-temperature coolant cooler 1 is preferably made from aluminum sheet and has a depth 23 of less than/equal to 20 millimeters. Advantageously under some circumstances, the low-temperature coolant cooler according to the invention has a greater width than height, as illustrated by way of example in FIG. 1.

FIG. 2 is a schematic, perspective illustration of a low-temperature coolant cooler 31. The low-temperature coolant cooler 31 comprises a left-hand collecting tank 34 which is equipped with an inlet connecting pipe 35. Coolant enters into the left-hand collecting tank 34 through the inlet connecting pipe 35 as indicated by an arrow 36. The mass throughput of coolant is greater than 0.2 and less than 0.5 kg/s. In addition, the left-hand collecting tank 34 is provided with an outlet connecting pipe 38. The coolant passes out of the low-temperature coolant cooler 31 through the outlet connecting pipe 38.

In addition, the low-temperature coolant cooler 31 has a right-hand collecting tank 42. Formed between the left-hand collecting tank 34 and the right-hand collecting tank 42 is a heat exchanger block 44. The heat exchanger block 44 comprises a plurality of flat tubes (not illustrated) which run in the horizontal direction between the left-hand collecting tank 34 and the right-hand collecting tank 42. Arranged between the flat tubes are air guide plates, for example in the form of corrugated fins, around which flows charge air which is to be cooled.

Provided in the left-hand collecting tank 34 is a first partition 48, by means of which the coolant which enters into the low-temperature coolant cooler 31 through the inlet connecting pipe 35 is deflected a single time along an arrow 49, before exiting through the outlet connecting pipe 38. The low-temperature coolant cooler 31 illustrated in FIG. 2 has a depth 51 of at most 20 millimeters.

The low-temperature coolant coolers illustrated in FIGS. 1 and 2 have in each case an installation depth of at most 20 millimeters. The flat tubes of the low-temperature coolant coolers are equipped with turbulence-generating surfaces as are disclosed in FIGS. 2 to 8 of the German laid-open specification DE 101 27 084 A1, or with turbulence-generating inserts which are also referred to as turbulators, and with a maximum of two deflections. This provides that the ratio of the pressure loss in the tubes at a minimum/maximum mass flow rate (0.2 kg/s<mass flow rate <0.5 kg/s) is less than 3. At the same time, the Nusselt number varies at most by a factor of 3 between the maximum and minimum coolant throughput.

As illustrated by way of example in FIG. 2, it is under some circumstances advantageous for the low-temperature cooler according to the invention to have a width which is smaller than its height. Here, the height is the dimension in the tube longitudinal direction.

In FIG. 3, the charge air temperature downstream of the coolant-cooled charge air cooler in degrees Celsius is plotted against the coolant throughput in kg/s. The effect of the design according to the invention on the charge air cooling is illustrated on the basis of various characteristic curves. The charge air cooling for coolers without a turbulence-enhancing tube inner side, with a laminar tube flow or a tube flow in the deflection region between laminar and turbulent, is illustrated on the basis of two characteristic curves 53. 54 denotes a region which is to be avoided on account of undesired boiling in the coolant-cooled charge air cooler. 56 denotes a characteristic curve of a low-temperature coolant cooler according to the invention, which is also referred to as a charge air cooler. The low-temperature coolant cooler according to the invention is equipped with a turbulence-enhancing tube inner side. This ensures improved and approximately constant charge air cooling over a wide coolant throughput range. 58 and 59 denote operating points with a tolerance-induced scatter band.

In FIG. 4, the coolant pressure in bar is plotted against the coolant throughput in kg/s. 62 denotes a pump characteristic curve. 64 to 67 denote various system characteristic curves of a heat exchanger according to the invention (64, 65) and of a known heat exchanger (66, 67). The system characteristic curve 64 corresponds to an ambient temperature of 35 degrees Celsius. The associated system characteristic curve 65 corresponds to an ambient temperature of −5 degrees Celsius. The system characteristic curve 66 in turn corresponds to an ambient temperature of 35 degrees Celsius. The associated system characteristic curve 67 corresponds to an ambient temperature of −5 degrees Celsius. FIG. 4 shows an advantageous reduction, by means of the present invention, of the pressure required for a desired coolant throughput.

70 denotes the difference in the coolant throughput at the different ambient temperatures in a design according to the prior art. Since the temperature influence on the coolant throughput is very high in a design according to the prior art, the difference 70 is likewise very high. 71 denotes the difference in the mass throughputs at different temperatures in a design according to the invention with a turbulence-enhancing inner, side. A comparison between 70 and 71 makes it clear that the temperature influence can be considerably reduced by means of the design according to the invention.

In FIG. 5, the Nusselt number normalized to a minimum Nusselt number, or the pressure loss normalized to a minimum pressure loss, in the flat tubes is plotted against the coolant throughput. Since all of the plotted variables rise continuously with increasing coolant throughput, and are a minimum at 0.2 kg/s, all of the curves begin at 0.2 kg/s with the value 1.

74 denotes the normalized Nusselt number for smooth tubes with three deflections. 75 denotes the normalized pressure loss for smooth tubes with three deflections. 76 denotes the normalized pressure loss for a design according to the invention with one deflection. 77 denotes the normalized Nusselt number for the new design with one deflection. FIG. 5 shows that the influence of the coolant quantity on the heat transfer function and on the coolant-side pressure loss can be reduced by means of the measures according to the invention.

Claims

1. A low-temperature coolant cooler for the indirect charge air cooling of an internal combustion engine, comprising a plurality of flat tubes which, in operation, are traversed by 700 to 1800 liters of coolant per hour and are connected to coolant collecting tanks, and air guide devices arranged between the flat tubes, around whereby charge air which is to be cooled flows the air guide devices for cooling wherein:

a) the flat tubes have a depth which is less than/equal to 20 millimeters;

b) the coolant which traverses the flat tubes changes flow direction a maximum of two times in the collecting tanks; and

c) the flat tubes are equipped at the inside with turbulence-generating devices.

2. The low-temperature coolant cooler as claimed in claim 1, wherein the flat tubes with the turbulence-generating devices are designed in such a way that the ratio between the maximum and minimum pressure loss in the flat tubes is less than 3 for coolant throughputs of 700 to 1800 liters per hour.

3. The low-temperature coolant cooler as claimed in claim 2, wherein the ratio between the maximum and minimum Nusselt number in the flat tubes is less than 3 for coolant throughputs of 700 to 1800 liters per hour or of 0.2 to 0.5 kg/s.

4. The low-temperature coolant cooler as claimed in claim 1, wherein the flat tubes have inwardly aligned indentations on at least one of their flat sides.

5. The low-temperature coolant cooler as claimed in claim 1, wherein turbulence inserts are arranged in the flat tubes.

6. The low-temperature coolant cooler as claimed in claim 2, wherein the flat tubes have inwardly aligned indentations on at least one of their flat sides.

7. The low-temperature coolant cooler as claimed in claim 3, wherein the flat tubes have inwardly aligned indentations on at least one of their flat sides.

8. The low-temperature coolant cooler as claimed in claim 2, wherein turbulence inserts are arranged in the flat tubes.

9. The low-temperature coolant cooler as claimed in claim 3, wherein turbulence inserts are arranged in the flat tubes.

10. The low-temperature coolant cooler as claimed in claim 4, wherein turbulence inserts are arranged in the flat tubes.