Oil-coolant heat exchangers for motor vehicles

Abstract

Oil-coolant heat exchanger for motor vehicles, with heat exchange between a first liquid fluid with a strong temperature dependence of viscosity, in particular the coolant of the engine, and a second separately flowing liquid fluid, in particular the oil of the engine or the transmission, wherein at least one of the two fluids flows through a plurality of parallel fluid channels (3) and is in heat exchange with the second fluid there, characterized in that at least in the case of a liquid fluid with a strong temperature dependence of viscosity, at least two main fluid channels (5h) separated from each other and flowing in parallel are provided in the area of ​​the main heat transfer, which are formed by combining several fluid channels (3) distributed over the width of the heat exchanger and flowing in parallel into individual channel groups also flowing in parallel.and that the flow supply and / or flow discharge of at least one group of parallel main fluid channels (5h) is carried out via at least one separate flow limiting device (5b) per main fluid channel (5h).

Description

[0001] The invention relates to an oil-coolant heat exchanger for motor vehicles, with heat exchange between a first liquid fluid with a strong temperature dependence of viscosity, in particular the coolant of the drive engine, and a second separately flowing fluid, in particular the oil of the drive engine or the transmission, wherein at least one of the two fluids flows through a plurality of parallel fluid channels and is in heat exchange with the second fluid.

[0002] From EP 1 298 405 A2, a heat exchanger for automotive air conditioning systems is known in which refrigerant flows through a multitude of parallel fluid channels in the form of flat tubes and exchanges heat with air as the secondary fluid. Several parallel flat tubes are grouped together. The refrigerant is supplied via a manifold, in which it is divided by a throttling point into two groups, each containing three parallel flat tubes. A series connection with two further groups, each also containing three parallel flat tubes, is achieved by means of a 180° flow deflection.The refrigerant is split from a common inlet connection into two parallel flow paths, each of which passes in series through three groups of flat tubes, each containing three flat tubes, and exits the heat exchanger via a common outlet connection.

[0003] From DE 698 14 235 T2, a condenser with multi-stage separation of the gas and liquid phases is known, in which refrigerant flows through a multitude of parallel fluid channels in the form of flat tubes and exchanges heat with air as the second fluid. Several condenser tubes are grouped into tube groups through which the refrigerant flows in parallel. The refrigerant flows from the refrigerant inlet of the condenser via a manifold to a first tube group with a multitude of parallel tubes and is distributed via a 180° bend in a further manifold to a second tube group with several parallel tubes. After passing through the second tube group, the refrigerant is distributed to two further tube groups, each with several parallel tubes. These two further tube groups are also traversed by the refrigerant in parallel and exit the condenser via a common refrigerant outlet.

[0004] From DE 10 2004 024 255 A1 an oil-coolant heat exchanger for motor vehicles is known, wherein the coolant of the drive engine is in heat exchange with the oil.

[0005] From DE 38 03 885 A1 a tubular heat exchanger for engine cooling or passenger compartment heating is known, in which coolant of the drive engine is in heat exchange with air via heat exchanger tubes, wherein this is constructed with a water box added after the brazing of the heat exchanger matrix for supplying / removing the coolant to / from the coolant channels.

[0006] From EP 0 000 189 B2, a heating heat exchanger for motor vehicles is known in which the coolant of the engine is in heat exchange with air, the heat exchanger being constructed from a multitude of paired U-shaped pipes through which the coolant flows. The coolant flows from an inlet area of ​​a water box to the heat exchanger pipes, using an internal 180° bend without mixing, through parallel coolant channels in another water box, and back to an outlet area and the outlet connection of the water box.

[0007] From DE 30 50 963 C2 a heat exchanger (cooler) for motor vehicles is known, wherein the heat exchanger matrix determining the heat exchange is represented on the coolant side by parallel flow through tube groups (flat tubes) for the liquid coolant and on the air side by fins attached to these tubes and wherein the length of the parallel tubes is less than a factor of 1.3 than the total stack height of the parallel coolant-side tubes and air-side fins.

[0008] From DE 10 2004 001 786 A1 a heat exchanger for motor vehicles is known, wherein a 3- or 5-stage cross-counterflow design is used and wherein the two coolant connections of the fluid which is guided back and forth in cross-counterflow over the 3 or 5 stages lead to the same side of the heat exchanger matrix.

[0009] DE 10 2004 044 861 A1 discloses an oil-coolant heat exchanger for motor vehicles, with heat exchange between a first liquid fluid (medium m1 coolant) with a strong temperature dependence of viscosity, and a second separately flowing fluid (medium m3 oil), wherein at least one of the two fluids flows through a plurality of parallel fluid channels and is in heat exchange with the second fluid there, wherein at least in the case of a liquid fluid with a strong temperature dependence of viscosity, at least two main fluid channels separated from each other and flowing through in parallel are present in the area of ​​the main heat transfer, and that the flow supply and / or the flow discharge of at least one group of parallel main fluid channels is effected via at least one separate flow limiting device per main fluid channel, wherein the oil side operates with parallel flow channels and has no inserted turbulence plates.

[0010] DE 43 05 060 A1 discloses an oil-coolant heat exchanger (oil cooler) for motor vehicles, with heat exchange between a first liquid fluid with a strong temperature dependence of viscosity, in particular the coolant of the drive engine, and a second separately flowing fluid (oil), in particular the oil of the drive engine or the transmission, wherein at least one of the two fluids flows through a plurality of parallel fluid channels (flat tubes) and is in heat exchange with the second fluid there.

[0011] DE 195 15 527 A1 discloses a heat exchanger in which, to optimize the power output without significant pressure losses, a common connecting pipe is proposed, from which the fluid flows through metering devices into intermediate chambers, each connecting several pipes.

[0012] It is also known to use high-efficiency oil-coolant heat exchangers or heat utilization rates in motor vehicles to cool the engine oil or transmission oil with the liquid coolant of the drive motor.

[0013] Furthermore, it is known to install oil coolers in the engine oil circuit and / or the transmission oil circuit. During warm-up, these coolers temporarily take on the additional task of transferring heat from the coolant to the oil, thereby reducing friction and fuel consumption. In particular, the targeted use of heat transfer from the coolant to the oil and vice versa requires highly efficient oil coolers that deliver good heat transfer across a wide range of fluid temperatures and flow rates. As practical testing shows, current oil coolers are only usable with certain limitations, especially because pressure losses on the oil side can increase significantly when the oil is cold, or the oil cooler efficiency can temporarily plummet.

[0014] In contrast, the task is to develop high-performance heat exchangers for separate fluids in motor vehicles that are capable of providing a higher maximum heat exchanger efficiency compared to current heat exchangers during warm-up and / or with coolant and / or oil temperature differences between heat exchanger inlet and outlet of more than 10K, while still enabling robust and reproducible heat transfer behavior, so that advantages in terms of fuel consumption can be reliably achieved.

[0015] This problem is solved with the device according to claim 1.

[0016] The at least two parallel flow-limiting elements 5b reduce the problem that an imbalance in the local heat transfer performance of the heat exchanger can easily occur when the fluid temperature of the oil or coolant decreases. Without the measures according to the invention, this imbalance results in particular from the fact that local subcooling of the coolant or oil, due to the significant increase in viscosity and the associated increased pressure drop, very easily leads to the coolant or engine oil migrating more readily to areas where there is less subcooling. The more the heat transfer performance is increased for a given coolant or oil flow rate, e.g., by increasing the installation space and / or the heat transfer surface area, the more susceptible the heat exchanger becomes to this effect. Similarly, a reduction in the coolant or oil flow rate leads to a similar effect.the oil throughput very quickly leads to a disproportionate and not always reproducible drop in heat transfer performance.

[0017] Presumably without thoroughly investigating this relationship, many automotive heat exchangers have accepted that heat exchange almost completely collapses at low fluid temperatures and / or low coolant and / or oil flow rates. This sensitivity applies to the coolant side of modern automotive heat exchangers, but especially to the oil side. In particular, the common approach of increasing the volume-specific heat exchanger capacity by adding or enlarging turbulators and / or turbulence plates on the coolant or oil side is of very limited help with modern automotive heat exchangers designed for high specific heat transfer capacity. This is because these measures, especially at low fluid temperatures, contribute significantly to a substantial drop in oil or coolant flow rate.

[0018] In contrast, the inventive method with the flow limiting devices 5b provides means that ensure that the viscosity-related effects described above are significantly less pronounced than in conventional car heat exchangers.

[0019] In this context, it is important to depart from the usual approach to passenger car heat exchanger design, which generally uses available pressure reserves to increase heat transfer performance by increasing the channel density or flow velocities in the individual channels and / or by using embossed turbulators or inserted turbulence plates to ensure improved local mixing. In contrast, the inventive method introduces local pressure loss sources 5b that initially do not directly contribute to improving the heat transfer coefficient or increasing the heat-transferring area. However, as practice shows, a surprisingly high efficiency of this measure can be achieved indirectly via the flow uniformity distribution. Simple perforated orifices 5b are the easiest to use for this purpose.A particular advantage of the inventive method is that the pressure loss source 5b can be designed in such a way that, at very low temperatures of the coolant and / or the oil, the pressure loss increases significantly less – in contrast to conventional oil coolers – since here the dynamic component of the pressure loss at the orifice plate is greatly subordinate to the viscous component in the fluid channels of the coolant or the oil.

[0020] As an example, consider the extremely high oil-side pressure drop of modern passenger car oil coolers at low oil temperatures, which can generally only be managed by means of bypass lines, possibly with an additional pressure relief valve. While a high plate density and additionally inserted turbulence baffles result in good heat transfer when functioning as an oil cooler (i.e., with hot oil), these standard oil coolers are often largely deactivated during the engine's warm-up phase via the oil-side oil cooler bypass or the oil pressure relief valve. The already low oil flow rate is then compounded by the flow distribution problems described above. The inventive method for improving flow distribution provides a significant improvement on both the oil and water sides.Specifically in the operating mode "heat transfer from coolant to engine oil during warm-up", the improvement in oil heating leads more quickly to the point where little or no oil flows through the oil-side bypass and therefore does not participate in the oil heating in the oil cooler.

[0021] In conventional oil coolers, the significant increase in viscosity of both fluids with decreasing temperature leads to the described risk of the coolant and oil flow rate concentrating in local areas of the oil cooler. In contrast, the throttling devices 5b according to the invention stabilize the flow distribution. With certain limitations, this also applies, in particular, even if only one of the two fluids is stabilized with throttling devices 5b. For example, a stable, uniform flow and temperature distribution on the water side during warm-up can be used to promote oil transport to all areas of the heat exchanger on the oil side.

[0022] To illustrate the concept of the invention, the following is shown Fig. 1. A heat exchanger with coolant-side flow channels 3 in the plane of the image and oil-side flow channels (essentially) perpendicular to the plane of the image, formed by the outer surface of the coolant-side flow channels 3. The coolant flows into Fig. 1 at the supply line 1 into the water tank 5 and is distributed via the four perforated plates 5b of the partition 5c into four parallel rows of flow channels formed by the partition 5c. In claim 1, these four parallel rows of flow channels are referred to as main fluid channels 5h. To illustrate this, the figure shows Fig. 1a the Fig. 1 with the four main fluid channels 5h marked by a dashed frame that outlines the flow channels 3 affected by each main fluid channel. In the water box 6, the coolant from the four parallel rows (i.e., the four main fluid channels 5h) is recombined and leaves the heat exchanger via line 2. In the simplest case, i.e., with only 2 instead of as in Fig. For four main fluid channels, one baffle plate 5c and one baffle plate 5a with two perforated plates 5b are sufficient to improve the heat exchanger. However, three or more baffles 5c and a corresponding number of perforated plates 5b are preferred, as shown in [reference]. Fig. 1 or Fig. 1a is used because it achieves very good flow uniformity at minimal cost. If necessary, two or more orifices 5b with reduced diameter can be used per channel group. This provides even better flow uniformity but also increases the risk of clogging. In special applications designed for low flow rates, the hole diameter of the orifices on the coolant side can be less than 4 mm to achieve the best possible flow uniformity.

[0023] This shows, for example, Fig. 1 or Fig. 1a A configuration with an oil / coolant heat exchanger with coolant-side connections 1 and 2 and oil-side connections 1oel and 2oel. A corresponding housing design on the oil side ensures that the oil flows through the oil channels 4oel along the surface of the coolant-side flow channels, similar to air in a heating heat exchanger. A sufficiently large oil inlet area with only a small local oil-side pressure gradient upstream and downstream of the actual heat exchange zone, as well as the relatively large pressure drop in the individual oil channels 4oel, ensure that a reasonably homogeneous oil-side heat exchanger flow is achieved despite the relatively small oil inlets and outlets 1oel and 2oel. The in Fig. 1 and Fig. 1a The dotted oil flow arrow, in such an optimized design, will generally primarily exhibit a flow component flowing perpendicular to the plane of the image, i.e., the one in Fig. 1 or Fig. 1a The dotted oil flow component opposite the coolant flow direction is only relatively small.

[0024] The coolant-side grouping into four parallel-flow channel groups with throttle plates 5b significantly contributes to ensuring that not only the coolant but also the oil is distributed particularly evenly across the entire heat exchanger area. This is especially helpful in dissipating areas with initially very low oil flow when the oil is very cold, as would be the case without the measures according to the invention on the coolant side. This results in improved heat transfer during warm-up and a slightly lower pressure drop on the oil side. Both effects ultimately contribute to improved fuel consumption.

[0025] Further improvements in oil cooler efficiency can be achieved by using a similar approach on the oil side, grouping the oil channels and employing oil-side throttle plates 5b, which contributes to more uniform flow. Starting from Fig. For example, three additional oil-side partitions are advantageous for creating four main oil channels, each supplied with oil via oil-side orifice plates 5b on the oil inlet or outlet side. Even though it is not entirely easy to manufacture the three oil-side partitions perpendicular to the coolant channels 3, this is nevertheless worthwhile, especially when oil coolers with particularly low oil-side pressure loss at cold oil temperatures are required.

[0026] Another particularly advantageous design of an oil cooler according to the invention shows Fig. 2 in the form of a plate oil cooler. Fig. 2a shows four main fluid channels in a dashed outline 5h (analogous to the representation in Fig. 1a) Plate oil coolers are generally known and typically have two coolant-side connections 1 and 2, as well as - in Fig. 2 and Fig. 2a is offset in the depth direction of the drawing plane and therefore not shown – two oil-side connections 1oel and 2oel. The ability to generate the four connections and, if necessary, the oil cooler housing solely through deep drawing and brazing of the heat exchanger plates makes such oil coolers very cost-effective. The efficiency of known heat exchangers of this stacked design for the application of "oil cooling" as overheat protection is also very good due to the turbulators typically incorporated on the oil side or the turbulence or mixing plates inserted on the oil side. However, the viscosity effects described extensively above also limit the efficiency of this design, especially in the operating mode "heat transfer from water to oil during warm-up," i.e., for faster oil heating. Against this background, in Fig. 2 - largely analogous to Fig. 1 - On the coolant side, the supply pipe 1 is inserted, with the coolant channels grouped into 4 main coolant flow paths at the joints 5c and with coolant throttling at the 4 orifices 5b. Particularly with existing passenger car oil coolers, it is very simple and cost-effective to implement the flow guidance according to the invention by inserting molded parts with sealing rings at the joints 5c. Alternatively, the joining or soldering process can also be extended to include the additional components according to the invention.

[0027] The design according to Fig. Design 2 has the distinct advantage that, with minimal effort, flow groups (main fluid channels) with throttle plates can be selectively implemented on the coolant side and / or on the oil side. Furthermore, these oil coolers can also be easily calibrated to specific engines, particularly by inserting molded parts 1 with seals at the interfaces 5c and perforated plates 5b.

[0028] Compared to, for example, water / glycol mixtures on the coolant side, passenger car engine and transmission oils generally exhibit a significantly more dramatic increase in oil viscosity with decreasing temperature. This represents a certain limitation of the design according to the invention, since at very low oil temperatures the influence of oil viscosity is very dominant, and the improvement approach according to the invention, which is primarily based on the dissipation of the dynamic pressure specifically built up in the orifice plate, initially has only a relatively minor effect. However, during the warm-up phase, the approach according to the invention also shows quite significant advantages on the oil side.

[0029] To achieve comparably good heat transfer with a conventional automotive oil cooler design, especially at relatively low flow rates and / or during warm-up, as with the oil cooler according to the invention, a significant increase in the oil-side flow velocity or an increase in the pressure drop would be necessary for the same installation space. Common methods for increasing efficiency would be increasing the plate density, i.e., reducing the oil-side gap height, using turbulence plates with increased pressure drop, or connecting individual heat exchanger sections in series on the oil side by means of multiple oil deflections. All these measures mean that, with very cold oil, significantly less oil flows through the oil cooler due to viscosity. Against this background, current engine oil circuits generally...Even conventional oil coolers have bypass branches to bypass the oil cooler, firstly to ensure the engine's oil supply, and secondly to prevent the oil cooler from bursting due to excessive pressure. During warm-up, it's inherent in the design that the oil flowing through the bypass flows to the engine and bearings without being heated in the oil cooler, thus wasting potential heat transfer from the coolant, which generally heats up more quickly, to the oil.

[0030] The performance enhancement of the oil cooler according to the invention, achieved through the throttle plates 5b on the water and / or oil side, unlike the conventional improvements described for passenger car oil coolers, does not contribute significantly to the oil-side pressure loss of the oil cooler, especially at low oil temperatures. In other words, if an oil cooler according to the invention is designed for the same heat transfer performance as a standard oil cooler when the oil is largely at operating temperature, it will exhibit significantly better heat transfer performance during practical engine operation during warm-up, resulting in corresponding fuel consumption advantages.

[0031] If necessary, the structural requirements of the omitted turbulence plates can be met by simpler webs running in the longitudinal direction of the flow or by supporting nubs. Besides cost considerations, the advantages with cold oil are particularly important here. Especially with only partially warmed oil, this ensures that the oil cooler is used more effectively for oil heating and is not largely blocked by a high pressure drop on the oil side. The same applies to methods that incorporate significant corrugations into the sheet metal structure to increase oil cooler efficiency. Depending on the engine oil system, it is particularly advantageous for warm-up to completely eliminate such turbulators and ensure the target heat transfer values ​​with warm oil through component dimensioning, including optimization of fluid flow rates and flow / temperature distribution within the oil cooler.The specific constraints of passenger car engines sometimes result in configurations where it is particularly advantageous to use flow channels on the oil side that, unlike current high-performance passenger car oil coolers on the market, have a minimum flow cross-section of more than 2 mm. This is especially common in engines where the oil pressure regulating valve is located downstream of the oil cooler or oil filter.

[0032] It is inherent in the nature of the inventive method that careful dimensioning of the orifice plates is required. On the one hand, the dynamic pressure that builds up in the orifice plates and is subsequently largely dissipated must be high enough to achieve a sufficient uniform distribution effect relative to the pressure drop of the generally laminar flow, at least during warm-up, in the fluid channels of the oil or coolant. On the other hand, the pressure drop must not be so high that the fluid flow rate falls to unacceptable values, given the available delivery pressures of the coolant pump or the oil pump. In this context, even the best flow uniformity is of no use if the enthalpy flow of the relevant fluid becomes too low.

[0033] To avoid excessive pressure losses, especially when the viscosity ia is highly temperature-dependent, it is preferable to design the system such that the throttling elements 5b play only a very minor role in the extremely low temperature range. The dimensioning is preferably carried out such that, during warm-up after exceeding a limit temperature, the at least two parallel flow-limiting elements 5b generate a greater increase in inflow and / or outflow pressure loss in the respective main fluid channel with increasing volume flow than the heat-transferring inner area of ​​the main fluid channel itself. This results in a situation where the opposing and disproportionate change in pressure loss at the orifices with slightly increased flow has a greater effect at the orifices with reduced flow than the potential increase in viscosity due to excessive local cooling caused by insufficient flow at those orifices.

[0034] If necessary, and if the pump has sufficient delivery pressure reserves, the flow can be throttled more strongly at the orifices. For oil coolers in passenger cars, temperature values ​​between 20 °C and 90 °C have proven particularly suitable for fulfilling this condition, especially with regard to optimal use during warm-up. The usable area of ​​the heat exchangers, as well as the effort required for vehicle-specific tuning, can be further improved if the at least two parallel flow restrictors 5b release an additional flow cross-section when an opening pressure differential is exceeded. This can be achieved, in particular, by having spring-loaded valves with leakage flow open additionally via orifice plates under the influence of the pressure differential.

[0035] In particular, practical testing on passenger cars has shown that it is especially advantageous to dimension the number of parallel sub-fluid channels per main fluid channel such that the mean flow velocity in the sub-fluid channels is less than 30% of the mean flow velocity of the flow restricting device 5b assigned to the respective channel group. This generally allows for a usable flow distribution with moderate pressure loss.

[0036] The dimensions of connections 1, 2 and 1oel and 2oel are preferably smaller in the areas where the orifice plates 5b are located. The orifice plates are preferably located on the warm fluid side. This ultimately offers advantages in terms of installation space and thermal mass, while also providing more quickly defined temperature and flow conditions with defined pressure dissipation at this location. In particular, this approach makes it especially advantageous to implement the plate design with unchanged external dimensions and / or to simultaneously work with fluid-side inflow cross-sections that are less than 70% of the outflows.

[0037] Another aspect of the dimensioning is that the orifice plates used should not be arbitrarily small, as this could lead to clogging by dirt particles. Grouping the subfluid channels has proven to be a significant advantage in increasing operational reliability and allows for a very wide range of variations in the orifice plate pressure drop design. For automotive applications, particularly on the coolant side of heater cores and oil coolers, orifice plates with a diameter of less than 4 mm have proven very effective, with the diameter of the orifice plates preferably being larger than the narrowest diameter of the subfluid channels.

[0038] How Fig.As shown in Figure 1, the inventive method with orifice plates 5b can already be advantageously used in cross-flow heat exchangers. However, it is particularly advantageous if the two fluid flows are to experience a high temperature difference when passing through the heat exchanger. This is achieved by connecting exactly three or four individual heat exchanger levels in series in a cross-counterflow configuration and by using exactly one row of orifice plates 5b for all three or four individual heat exchanger levels, thus achieving a pressure-loss-optimized counterflow characteristic. Such a heat exchanger design is particularly advantageous when, with a controlled engine oil pump, only a small oil volume flow is to be delivered through the oil cooler and subsequently through the engine.The high efficiency of the 3-4 stages in cross-counterflow maximizes the oil temperature rise at the oil cooler during warm-up, minimizes pressure losses in the oil cooler and oil filter, and ultimately even leads to an increase in the oil supply temperature to the engine bearings. These effects, in turn, are associated with fuel consumption benefits. Without the additional measures according to the invention, known oil cooler designs can only be used to a very limited extent, since the efficiency of heat transfer to the engine oil during warm-up is relatively low, especially with low oil flow through the engine oil cooler. The flow-stabilizing measures on the water side already make a significant contribution here, as does the cross-counterflow configuration. If necessary, the measures according to the invention can also be used additionally or independently on the oil side.

Claims

[1] Oil-coolant heat exchanger for motor vehicles, with heat exchange between a first liquid fluid with a strong temperature dependence of viscosity, in particular the coolant of the engine, and a second separately flowing liquid fluid, in particular the oil of the engine or the transmission, wherein at least one of the two fluids flows through a plurality of parallel fluid channels (3) and is in heat exchange with the second fluid there, characterized by, that at least in the case of a liquid fluid with a strong temperature dependence of viscosity, at least two main fluid channels (5h) separated from each other and flowing through in parallel are present in the area of ​​the main heat transfer, which are formed by combining several fluid channels (3) distributed over the width of the heat exchanger and flowing through in parallel into individual channel groups also flowing through in parallel, and that the flow supply and / or the flow discharge of at least one group of main fluid channels (5h) flowing through in parallel is carried out via at least one separate flow limiting device (5b) per main fluid channel (5h). [2] Oil-coolant heat exchanger for motor vehicles according to claim 1, characterized by , that in the area of ​​the parallel fluid channels (3) the flow directions of the two fluids are perpendicular to each other. [3] Oil-coolant heat exchanger for motor vehicles according to one of claims 1-2, characterized bythat the oil flow component opposite the coolant flow direction is only relatively small.

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