Method and device for variable intake air preheating in motor vehicles with internal combustion engines

Abstract

Method for variable intake air preheating in motor vehicles with an internal combustion engine (5) with a main throttle valve (4) and power control via the fresh air quantity, characterized in that, for the purpose of reducing throttling of the engine in partial load operation, a heating device additionally heats the intake air and the air-conducting channels in the immediate vicinity of the engine inlet (11, 18), wherein a connection is made between a secondary line through which heated fresh air can flow and a main fresh air line downstream of the main throttle valve (4) for air quantity control, through which fresh air can bypass the main throttle valve (4), and in that, when transitioning to high engine load with opening of the main throttle valve (4) and deactivation of the heating device, this additional heating is quickly deactivated by the fact that, during operation of the heating device, the components in the area of ​​the air intake tract upstream of the heating device, and thus air-conducting pipes (1,1a) including an air filter (2), an air mass meter (3) and an intercooler (30) were kept close to the ambient air temperature by the ambient air and / or a limited leakage flow.

Description

[0001] The invention relates to a method and a device for variable intake air preheating in motor vehicles with internal combustion engines and power control via the fresh air quantity, in particular to vehicle engines with spark-ignition combustion and lambda-1 control of the air-fuel mixture. It is usable for engines without variable exhaust gas recirculation, but is particularly advantageous for engines that have variable internal or external exhaust gas recirculation.

[0002] It is a known practice in the past to use intake air preheating in gasoline engines to reduce throttling and ultimately save fuel. For example, US Patent 2,552,695 A from 1951 already shows a device in which the intake air, after passing through a carburetor and a main throttle valve, can be divided into a heated and an unheated air branch by means of a mixing valve, so that the internal combustion engine can be supplied with either heated or unheated air by means of appropriate control of the mixing valve. German Patent DE 32 14 205 A1 from 1982 also shows a device for heating the combustion air on demand. Such devices, and similar ones, which initially draw the intake air from a warm zone in the engine compartment or near the exhaust manifold by means of a thermostatically controlled switching device, and then, at higher engine or combustion temperatures, heat the fresh air to a warmer temperature, are also used in other applications.Coolant temperatures from a colder zone at the vehicle intake have proven in the past to help save fuel and, in some cases, reduce pollutant emissions. CO2, CO, and HC emissions during warm-up are generally reduced, while NOx emissions are sometimes slightly increased. Nevertheless, such devices have largely disappeared from the market for various reasons. The cost-benefit ratio and, above all, the loss of power during abrupt transitions to full load are primarily responsible. Furthermore, modern gasoline engines offer the ability for the engine control unit to intervene in the internal or external exhaust gas recirculation (EGR) system, enabling partial de-throttling that can be activated and deactivated much faster and with less delay in engine power delivery than conventional intake air heating systems. Therefore, optimized EGR recirculation is becoming increasingly common.This is considered the method of choice for partially removing throttling from gasoline engines, especially when no special / expensive intake and / or exhaust valve control is used for throttle-free load control. Additional intake air heating is generally considered ineffective, partly due to the described time delay in power delivery during a sudden transition to full load and because of the relatively unfavorable cost / benefit ratio.

[0003] In this context, JP 2004-150 384 A from 2002 describes a device for selectively heating and cooling the intake air of an internal combustion engine, which involves a correspondingly high level of complexity. The subsequently published document DE 10 2005 043 157 A1 revisits the previously described and well-established idea of ​​intake air preheating and proposes that, depending on the required cylinder filling, a specific amount of heat is supplied to the intake fresh gas and, if applicable, other gases. GB 681 811 A describes a heat exchanger that transfers heat from the non-recirculated exhaust gas into the intake air by means of contact between the fresh air pipes and parts of the exhaust system or by means of contact with the exhaust gas itself.

[0004] From DE 10 2005 015 844 A1, it is known that in a "homogeneous charge compression ignition engine," i.e., an engine with compression ignition, it is advantageous or even essential to preheat the intake air and, if necessary, to combine this with exhaust gas recirculation. WO 98 / 07 973 A1, with its detailed description of an "improved premixed charge compression (PCCI) engine," also teaches the same principle. Such engines attempt to operate with compression ignition as much as possible, or always, to minimize emissions and fuel consumption, and therefore place very specific demands on the temperature of the intake air and the combusted exhaust gas at the desired ignition point. The complexity and costs of this innovative type of engine are considerable, which is why they face significant challenges in gaining market acceptance.

[0005] In contrast, the task is to improve the cost-benefit ratio and the fuel savings achievable in practice of intake air preheating, and to optimize it so that switching from part-load operation with increased intake air temperature to full load with reduced intake air temperature can occur significantly faster than previously possible. This is particularly important because it allows intake air preheating to contribute to fuel savings not only during warm-up but also when the engine is at operating temperature, thus reducing throttling at part load and increasing cost efficiency. Furthermore, it prevents this measure from being automatically ruled out as a fuel-saving measure in future engines simply because the reduction of throttling at part load through intake air preheating is accompanied by unacceptable shortcomings in the rapid switchover to full load.

[0006] This problem is solved by the method according to claim 1.

[0007] The inventive method, in the "air preheating in partial load" operating mode, ensures that large areas of the intake tract, including the air filter, air mass meter, intake pipes, and optionally the charge air cooler, remain close to ambient temperature. Only the areas near the intake port, including the combustion chamber, are exposed to heated air and exhibit an elevated wall temperature. During a sudden full-load transition, cold fresh air is immediately supplied from these upstream zones, while the intake air heating is simultaneously deactivated, for example, by a valve in the auxiliary channel with heated fresh air. Only the increased wall temperatures in the area near the cylinder head or in the intake manifold, caused by the warmer intake air, have a slightly delayed effect on cylinder filling and potentially on the knock limit.For engines without control intervention in the exhaust gas recirculation, this means that the switch to full load is at least as fast as, for example, the deactivation of an external exhaust gas recirculation system in a comparable engine with controllable exhaust gas recirculation and with exhaust gas recirculation in a comparable position.

[0008] This is because exhaust gas recirculation also increases wall temperatures in the area near the cylinder head or in the intake manifold, and thus has a similarly delayed effect on cylinder filling and potentially a detrimental effect on the knock limit, as does the intake air preheating system according to the invention. A particular advantage of reducing throttling via intake air preheating is that switching to partial load with intake air preheating can occur with significantly less sensitivity to smooth running and a potential increase in soot formation at many operating points. In particular, the high efficiency of lambda-1-controlled exhaust aftertreatment systems often helps to reliably control the potential increase in NOx emissions at many operating points.

[0009] In the system for intake air preheating according to the invention, the simultaneous operation with a controllable exhaust gas recirculation offers a considerable additional benefit, given its rapid switchability. It is particularly advantageous if the exhaust gas recirculation control ensures that the contribution made by the intake air preheating to reducing throttling does not cause the exhaust gas recirculation rate to drop to reduced values ​​due to the lower pressure downstream of the main throttle valve, even with the position of the exhaust gas recirculation actuator remaining unchanged.

[0010] Against this background, some relatively unsuccessful laboratory experiments in the past should also be viewed. These experiments, which temporarily sacrificed maximum engine power when switching to full load, used conventional intake air preheating instead of thermostatic switching with a changeover valve actuated by the engine control unit in engines without variable exhaust gas recirculation. Here, depending on the engine, only a relatively small fuel consumption advantage from intake air preheating can be found, which, when considered in conjunction with the additional costs for air preheating, including the electronic changeover valve, leads to a negative cost assessment of the system. The reason for this lies, among other things, in the fact that the reduction in throttling caused by intake air preheating leads to a reduction in internal exhaust gas recirculation or the residual gas quantity in the cylinder, i.e., a counteracting effect with a partial reversal of the reduction in throttling. Depending on the engine – dhuaDepending on the valve overlap, in extreme cases the loss in internal exhaust gas recirculation or the residual gas volume can even outweigh the gains from thermal throttling. It is particularly important to note that internal exhaust gas recirculation provides both a throttling reduction due to the volume of combusted gas and a thermal reduction by heating the fresh gas. Depending on the base residual gas volume, a loss of residual gas therefore has a particularly negative impact. This fact must be taken into account when adapting the system according to the invention to engines without variable exhaust gas recirculation, if necessary by adjusting the base engine, especially the valve timing, and included in the cost / benefit analysis.

[0011] After these explanations regarding potential fuel-saving losses with engines without variable exhaust gas recirculation, it becomes more understandable why the combination of variable exhaust gas recirculation and additional intake air heating is mentioned above: Adapting the actuator's position to the new situation with intake air preheating and thus higher intake manifold pressure, in such a way that the residual gas quantity does not drop too much, is maintained, or is even increased, leads to a synergistic interaction with considerable additional benefits regarding throttling reduction and fuel consumption.

[0012] Considering the limitations on exhaust gas recirculation due to engine smoothness restrictions, the increased air and fuel gas temperatures at ignition, and thus the improved combustion reaction kinetics, may even allow for a higher exhaust gas recirculation rate than without intake air preheating. As mentioned previously, this naturally depends on the development of NOx emissions and whether the catalytic converter can handle potentially increased NOx emissions resulting from the higher combustion temperatures. It is also important to ensure that the combustion process does not fall within the temperature range associated with increased soot formation.

[0013] Since the inventive method, despite its rapid switching capability, can result in a slight loss of spontaneity in power delivery, it is particularly advantageous to limit the intake air preheating and, if necessary, the EGR so that a sudden jump to full load can always be achieved with sufficient power reserves. A suitable criterion here is, for example, that at least the power output required under the nominal conditions under which the engine power is measured and published should always be available at every engine speed when transitioning to full load. Since significantly lower component temperatures are present under partial load than under full load, the rapid switching capability allows for considerable leeway to increase the intake air temperature and, to some extent, the EGR rate, even on a warmed-up engine.During warm-up, this margin is naturally even greater and is further improved in terms of available power and fuel consumption by the fact that the heated cylinder bores save some frictional power.

[0014] Taking into account the above limitations regarding NOx, soot and spontaneous power availability, it is very advantageous for some engines to increase the exhaust gas recirculation in parallel with the intake air preheating, e.g. by increasing the valve overlap in the case of internal EGR or a greater opening of the external EGR valve, until the engine – while maintaining a certain torque reserve with regard to the ignition angle for fast control – approaches a smooth running criterion.

[0015] The coordination of such a complete system is not entirely straightforward, but with careful planning it promises significant fuel consumption advantages with a comparatively low number of components.

[0016] Especially if the engine already has an external EGR system with corresponding piping and an EGR control valve, a system for intake air heating, similar in many respects, can be easily implemented, particularly with an identical control valve and a shared engine-side integration of the heated fresh air at the exhaust gas recirculation point(s). To fully utilize the potential, it is important to note that the original settings of the exhaust gas recirculation valve ia must be adjusted towards a wider opening to compensate for the loss of internal exhaust gas recirculation or residual gas volume due to the increase in intake manifold pressure behind the main throttle valve when the intake air is heated.

[0017] To further elaborate on the inventive concept, Fig. 1 An embodiment for carrying out the method according to the invention. The intake air has in Fig. During operation, the air at point 1 reaches approximately ambient temperature and pressure. It then passes through the air filter 2 and the mass airflow sensor 3 to the main throttle valve 4. Under lower partial load conditions, this valve is relatively closed, resulting in a significant vacuum relative to the ambient air at point 11. The fresh air then flows through the intake manifold 18 to the four cylinders of the engine 5. After combustion, the exhaust gas flows through the manifold 22 and the heat exchanger 7 to the exhaust aftertreatment system 8, which includes a catalytic converter and silencer, and then into the environment.

[0018] Heat exchanger 7 consists, for example, of an air-gap insulated exhaust pipe, as is already known for rapid catalyst heating. Here, however, it is a separate component used for intake air preheating and only has a fresh air inlet and outlet. To save costs, an existing air-gap insulated pipe or air-gap insulation on the outer casing of the catalyst can also be used, in which case the heat exchanger is preferably only used for intake air preheating after the catalyst's light-off temperature has been reached. As a frequently desirable side effect, this also improves heat protection, meaning that critical peak temperatures of the vehicle after prolonged full-load driving can be avoided.

[0019] The heat exchanger 7 for heating the intake air can also simply consist of one or more fresh air pipe channels and transfer heat from the non-recirculated exhaust gas into the intake air by means of heat-conducting contact of the fresh air pipes to parts of the exhaust system or by means of direct contact with the exhaust gas itself.

[0020] According to the engine Fig. 1. Fresh air to be heated is drawn downstream of the air mass meter 3, routed via line 1b to the heat exchanger 7, and flows downstream of the main throttle valve 4 to the intake manifold 18 via the switching or control valve 10. At lower engine partial loads, a significant vacuum ensures that, despite relatively small cross-sections and relatively high pressure losses in the intake air heating circuit, a substantial air mass flow passes through this branch and is heated. Taking into account the total air mass flow measured by the air mass meter 3, the throttle valve is almost completely closed by the engine control unit 16. If necessary, switching off or controlling the valve 10 ensures that a control reserve for the air mass flow is always available to adjust the currently desired engine output. In some cases, it seems advantageous for the control valve 10 to regulate the air mass flow in the Fig. The idle air control valve (not shown for clarity), i.e., the auxiliary air control valve for metering the particularly small idle air quantities when the throttle valve is closed, is replaced. Additionally, the engine features... Fig. 1. An external exhaust gas recirculation branch 6b is provided, in which an EGR control valve 9, in conjunction with the engine control unit 16, adjusts the recirculated exhaust gas quantity to the respective requirements. The integration of EGR and intake air preheating is located downstream of the throttle valve, thus heating only a fraction of the intake tract. This makes a significant contribution to the rapid switching between partial and full load. Equally important, however, is the implementation of the inventive concept described in detail above, such that when intake air heating is integrated, completely new settings of the EGR valve must be applied simultaneously in many operating ranges to ensure that the two measures do not partially cancel each other out. Depending on the extent of the intake air heating, the desired degree of fuel savings is only achieved when the position of the EGR valve is shifted significantly towards a wider opening.Conversely, in near-idle operation, significant external exhaust gas recirculation is not always possible for reasons of smooth running; some engines operate entirely without external exhaust gas recirculation in this environment. The engine according to the invention... Fig. 1 at least enables the reduction of throttling by heating the exhaust gas while compensating for the loss in internal exhaust gas recirculation rate through a slight opening of the external EGR branch. Furthermore, in many cases, the increase in intake air and combustion temperatures according to the invention allows for somewhat smoother running and ultimately a slight increase in the overall exhaust gas recirculation rate / residual gas quantity compared to the baseline with the intake air heating switched off.

[0021] Compared to Fig. 1 shows Fig. 2. A system with intake air heating with a modified extraction point for the heated intake air: Here, the air is drawn directly from the ambient air at a hot point or at a heat exchanger 7 and then guided via line 1b to the inlet of the air intake tract, where a switching valve 10ab, actuated by the engine control unit 16, switches from normal operation to air preheating operation. While the modification of the air supply to the heat exchanger 7 also occurs in Fig. 1 can be used, a corresponding circuit shows Fig. 3, where the additional air filter 2z becomes absolutely necessary, the engine exhibits according to Fig. 2. The inventive advantage of very rapid deactivation of the air preheating during a sudden transition to full load is not present. However, the motor does exhibit, according to... Fig. 2 the potential according to the invention to improve the part load consumption by means of the simultaneous use of variable exhaust gas recirculation and intake air preheating - without dispensing with the rapid switching from part load to full load.

[0022] The simultaneous use of exhaust gas recirculation adjustable by the engine control unit 16 and intake air heating also adjustable / switchable by the engine control unit 16 in a passenger car is not only novel but also offers previously untapped advantages that are exceptionally attractive in themselves. Against this background, the inventive method with simultaneous use of exhaust gas recirculation and intake air preheating is claimed in a separate patent claim, independent of the rapid switching capability of the main claim. Fig. 2 is merely one example of this. Specifically in Fig. 2. The loss of functionality is offset in particular by a certain simplification in the tuning, since valve 10ab interacts less strongly with the main throttle valve in the individual positions. Even if the temporary full-load disadvantages currently seem unacceptable, this could easily change in the future depending on the vehicle type, engine installation situation, and future fuel cost developments.

[0023] To further improve costs and efficiency with regard to the fastest possible switchover between partial load with intake air preheating and full load, we show Fig. 4 and Fig. 5. A common connection line 19 is used for supplying the heated air and the recirculated exhaust gas. This common line reduces costs. Furthermore, the connection with separate supply points 18a at each individual cylinder, particularly in the flange between the intake manifold and the cylinder head, further reduces the areas where the intake manifold is heated by the recirculated exhaust gas or the heated air. Even with relatively large pulsation / backflow in the intake manifold due to gas dynamic effects during the charge exchange, only a relatively small amount of the intake manifold surface is heated.

[0024] Fig. Figure 6 shows a further circuit for implementing the concept of the invention. Here, two coupled valves 10 and 20 handle the switching between operation with and without intake air preheating. Alternatively, a corresponding multi-way valve can perform the same function. The particular advantage in Fig. 6 is in comparison to Fig. 2. This ensures that at least some areas of the intake tract are not heated, which benefits the rapid switching. Furthermore, this means that the air mass meter 3 is still located in a zone where the intake air temperature is low and less subject to fluctuations. Both of these factors improve the accuracy of the air mass flow measurement.

[0025] Fig. Figure 7 shows a variant of the inventive concept on a turbocharged engine. Here, too, the throttling losses at the main throttle valve play a significant role with regard to fuel consumption. Fig. The increase in intake air temperature is not provided by an external heat source, but by the compressor 40 itself. The bypassing of the charge air cooler 30 - in Fig. 7, exemplified by the coupled valves 10 and 20, leads to the desired increase in intake air temperature under partial load and thus to the desired reduction in throttling. Here again, the control of the exhaust gas recirculation plays a crucial role in maximizing its benefits. A significant advantage is that, during phases of intake air heating, the temperature of the charge air cooler itself and the air it contains is completely reduced to ambient temperature by the airflow, making exceptionally cold air available for sudden load changes.

[0026] The previous systems according Fig. Figures 1-7 all show a valve controlled by the engine control unit 16 for activating / deactivating the intake air heating. This is also necessary to maximize the utilization range of the inventive method. If cost is the primary concern and therefore only the warm-up phase is to be optimized, this valve can also be thermostatically actuated. The necessary thermal safety margin with respect to full load can be provided by a correspondingly low switching temperature, e.g., a coolant temperature of 75°C.

[0027] Alternatively, this shows Fig. 8 a pressure-dependent valve 10dv that only opens when there is a sufficiently low intake manifold vacuum or a sufficiently large pressure difference between the exhaust manifold and the intake manifold.

[0028] In both cases, i.e., with both thermostatically and pressure-operated valve 10dv, additional throttling via the pipe cross-sections or a perforated orifice is necessary when integrating it downstream of the main throttle valve. This ensures that even with the main throttle valve 4 fully closed, slightly less than the idle air mass flow passes through the heated intake air branch. Only in this way can stable power control be guaranteed. The potential losses resulting from this approach are relatively significant, so it will likely remain limited to exceptional cases, such as those where particularly inexpensive warm intake air is available from an existing air-insulated manifold.

[0029] Beyond the intake air heating methods described above, there are numerous other ways to implement switchable intake air heating. For example, well-known thermal management methods induce higher coolant temperatures, and consequently higher combustion chamber wall temperatures and higher temperatures in the air intake ports, by increasing the thermostat opening temperature during partial engine load. A similar principle applies to approaches that initially restrict or even temporarily stop the coolant flow through the engine during warm-up. The effectiveness of such thermal management methods in warming the intake air is not without controversy in the professional community. The prevailing opinion is that the primary effect of these thermal management measures stems from increasing cylinder liner temperatures and, later in the warm-up phase, from increasing the oil temperature.Thermal throttling through increased coolant temperatures is mentioned in the technical literature, but according to the current opinion of many experts, it does not play a significant role.

[0030] In light of the detailed explanations above regarding the interaction between external intake air preheating and external or internal exhaust gas recirculation, it can ultimately be indirectly deduced that only the active engine control unit-side integration of variable exhaust gas recirculation with "internal" intake air preheating through thermal management measures fully exploits the fuel-saving potential of these measures. Here, too, the control unit's setting for metering the exhaust gas recirculation rate must be adjusted towards higher recirculation rates at increased component and thus intake air temperatures in order to restore the original exhaust gas recirculation rates and utilize the full reduction in throttling.

[0031] Ultimately, the combination of variable exhaust gas recirculation with external intake air preheating via a switchable or controllable airflow branch, e.g., using the coolant, the non-recirculated exhaust gases, or by bypassing a charge air cooler, can be particularly advantageously supplemented with switchable thermal management measures, i.e., in particular, internal intake air heating by reducing heat dissipation on the coolant side. Crucially, the exhaust gas recirculation rate is adjusted towards higher values, deviating from conventional approaches, and does not remain unchanged as it would without intake air preheating. This is fundamentally possible for any type of intake air preheating when considering only engine part-load operation. In practice, i.e.,However, when considering partial and full load operation and the entire relevant engine temperature range, this combination is particularly advantageous when implemented in conjunction with the inventive option of rapidly deactivating the intake air heating. To achieve a rapid temperature reduction, this is accomplished in particular by simultaneously deactivating the exhaust gas recirculation to an unavoidable minimum, deactivating the heated intake air branch, and spontaneously increasing the engine coolant flow rate until the vehicle coolant radiator opens.

[0032] Concerns about the increased component temperatures at partial load associated with this approach are, upon closer examination, only partially justified, since at a wide range of operating points there is an extremely high safety margin to potential component overheating: A load step from 80% load to 100% load when operating without the temperature increase according to the invention – assuming correct map programming – shows significantly fewer power reserves than a load step from 20% load to 100% load. This difference is even greater during warm-up.

[0033] Devices for controlling internally and / or externally recirculated exhaust gas have so far primarily involved external exhaust gas recirculation and / or internal exhaust gas recirculation with variable valve timing. However, a number of other components, such as an additional throttle valve in the exhaust system and / or an adjustable back pressure of an exhaust gas turbocharger, can also be adjusted by the engine control unit towards a position of increased exhaust gas recirculation potential.

[0034] It has already been described that, in order to maximize fuel savings, it can be particularly advantageous to increase the heating of the intake air and / or the exhaust gas recirculation until an upper limit of a smooth running criterion of the engine control is reached.

[0035] It is particularly important to note that the heating of the intake air and / or the increase in exhaust gas recirculation is limited by adhering to an upper limit value of the maps stored in the engine control unit for NOx limitation.

[0036] The same applies to the potential increase in soot emissions and to the minimum engine power that must be available at all times without delay.

[0037] Depending on the control potential of the intake air heating valve, the main throttle valve has a certain amount of unheated leakage. However, this is not a disadvantage but rather an advantage, because it prevents the main intake tract from being heated by locally warmed air or by heat radiation, so that cold air is drawn in immediately after the intake air preheating is deactivated.

Claims

[1] Method for variable intake air preheating in motor vehicles with internal combustion engine (5) with a main throttle valve (4) and power control via the fresh air quantity, characterized by, that to reduce air-side throttling of the engine in partial load operation, a heating device additionally heats the intake air and the air-conducting channels in the immediate vicinity of the engine inlet (11, 18), wherein a secondary line through which heated fresh air flows is connected to a main fresh air line downstream of the main throttle valve (4) for air volume control, through which fresh air can bypass the main throttle valve (4), and that when transitioning to high engine load with opening of the main throttle valve (4) and deactivation of the heating device, this additional heating is quickly deactivated by the fact that during operation of the heating device the components in the area of ​​the air intake tract upstream of the heating device and thus air-conducting pipes (1, 1a) including an air filter (2), an air mass meter (3) and an intercooler (30) were kept close to the ambient air temperature by the ambient air and / or a limited leakage flow. [2] Method according to claim 1, characterized by , that in addition to the first device for temporarily heating the intake combustion air, a second device for controlling the internally and / or externally recirculated exhaust gas, in particular an external exhaust gas recirculation and / or an internal exhaust gas recirculation with variable valve timing and / or an additional throttle valve in the exhaust system and / or an adjustable back pressure of an exhaust gas turbocharger, is simultaneously adjusted by the engine control towards a position of increased exhaust gas recirculation potential. [3] Method according to one of claims 1-2, characterized by , that the exhaust gas recirculation rates are increased beyond the basic exhaust gas recirculation values ​​during phases with strong heating of the combustion air by means of the heating device at the same load and power. [4] Method according to one of claims 1-3, wherein the heating of the intake air and / or the exhaust gas recirculation is increased to such an extent that an upper limit of a smooth running criterion of the engine control is reached. [5] Method according to any one of claims 1-4, characterized by , that the heating of the intake air and / or the increase in exhaust gas recirculation is limited by reaching an upper limit of a NOx criterion stored in the engine control unit. [6] Method according to any one of claims 1-4, characterized by , that the heating of the intake air and / or the increase in exhaust gas recirculation is limited by reaching an upper limit of a soot criterion stored in the engine control unit. [7] Method according to any one of claims 1-4, characterized by, that the heating of the intake air and / or the increase in exhaust gas recirculation are limited by reaching an upper limit of a performance criterion stored in the engine control unit, in particular a criterion for a minimum power output that is available at all times without delay. [8] Device for variable intake air preheating in motor vehicles with internal combustion engine (5) with a main throttle valve (4) and power control via the fresh air quantity, characterized by , that for the purpose of reducing air-side throttling of the engine in partial load operation, a heating device additionally heats the intake air and the air-conducting channels in the immediate vicinity of the engine inlet (11, 18), wherein a connection is made between a secondary line through which heated fresh air can flow and a main fresh air line downstream of the main throttle valve (4) for air quantity control, through which fresh air can bypass the main throttle valve (4). [9] Device according to claim 8, characterized by , that when transitioning to high engine load with opening of the main throttle valve (4) and deactivation of the heating device, this heating can be quickly deactivated by keeping the components in the area of ​​the air intake tract upstream of the heating device and thus air-carrying pipes (1, 1a) including an air filter (2), an air mass meter (3) and an intercooler (30) near the ambient air temperature by the ambient air and / or a limited leakage flow during operation of the heating device. [10] Device according to claims 8 and 9, characterized by , that the heating device is a secondary air branch in the air intake tract, arranged at least partially parallel to the main fresh air branch and with only a small amount of fresh air flowing through it under high engine load, which transfers heat, in particular from the non-recirculated exhaust gas or the coolant, into the intake air via a heat exchanger. [11] Device according to claims 8 and 9, characterized by , that the heating device is a separate secondary air branch in the air intake tract, through which only a small amount of fresh air flows under high engine load, and which transfers heat, in particular from the non-recirculated exhaust gas or the coolant, into the intake air via a heat exchanger. [12] Device according to claims 8 and 9, characterized by , that the heating device is a separate secondary air branch in the air intake tract, through which only a small amount of fresh air flows under high engine load, and which directly draws air from a particularly warm point, especially near the exhaust system. [13] Device according to claims 8 and 9, characterized by, that the heating device is a temperature- and / or load-dependent switching thermal management device or is supported by such a thermal management device, which increases the surface temperatures of the engine-adjacent areas of the intake manifold and / or the intake ports in the cylinder head including the intake valves and / or the surface temperatures of the other surfaces facing the combustion chamber and coming into contact with the fresh gas, and that this switchable thermal management device temporarily operates with increased coolant temperatures and / or reduced coolant-side heat transfer at reduced coolant flow during partial engine load. [14] Device according to claims 8 and 9, characterized by, that the integration of the second line downstream of the main throttle valve (4) is used to manage with the smallest possible line cross-sections and, in particular, to use largely the same components as in external exhaust gas recirculation systems. [15] Device according to claims 8 and 9 or 14, characterized by , that the integration of the second line downstream of the main throttle valve (4) is used to manage with the smallest possible line cross-sections, whereby the narrowest line cross-section ensures that even with a very strong pressure difference at the main throttle valve (4) only a limited air mass flow passes through the second line and is heated, so that the conventional throttle valve control retains control over the regulation of the total fresh air mass flow. [16] Device according to claim 15, characterized by , that a separate shut-off valve in the auxiliary air branch is omitted. [17] Device according to claims 9 and 10 or 15, characterized by , that an air mass flow sensor is used for control and is positioned at a point where both partial air mass flows pass by. [18] Device for variable intake air preheating in motor vehicles with internal combustion engine with air-volume-controlled power regulation, with a main throttle valve (4), spark-ignition combustion and lambda-1 control of the air-fuel mixture, characterized by, that the internal combustion engine has an external exhaust gas recirculation with a control valve and a secondary line that feeds heated fresh air downstream of the main throttle valve (4) for engine power control at partial engine load for de-throttling, wherein, for de-throttling at partial engine load, a first device, which is largely deactivated by the engine control at high engine load, temporarily heats the intake air more intensely, and simultaneously a second device for controlling the internally and / or externally recirculated exhaust gas is adjusted by the engine control relative to a base exhaust gas recirculation value at the same load and power without the increased heating towards a position of increased exhaust gas recirculation potential. [19] Device according to one of claims 8 or 18, characterized by, that the supply of the heated fresh air takes place particularly far downstream of the main throttle valve (4) by assigning each cylinder its own cylinder head-adjacent connection point for the heated fresh air at the end of the individual intake manifolds. [20] Device according to one of claims 8 or 18 to 19, characterized by , that a supply of heated fresh air and externally recirculated exhaust gas takes place at the same connection point(s) downstream of the main throttle valve (4). [21] Device according to one of claims 8 or 18 to 20, characterized by , that a secondary line draws fresh air from a position downstream of the air filter and upstream of any charge air cooler that may be present, and directs it at least temporarily through a heat exchanger during partial engine load, whereby rapid deactivation of the air preheating is achieved by largely closing the secondary line under high engine load. [22] Device according to one of claims 8 or 18 to 21, characterized by , that a secondary line extracts fresh air by means of a separate secondary air filter, in particular without flowing through a charge air cooler if present, and directs it at least temporarily via a heat exchanger during partial engine load or has already extracted it from a warm point, whereby rapid deactivation of the air preheating is achieved by largely closing the secondary line at high engine load. [23] Device according to one of claims 8 or 18 to 22, characterized by , that a reduction / deactivation of the air preheating is achieved by partially / fully closing a valve in the secondary line from the engine control unit. [24] Device according to one of claims 8 or 18 to 23, characterized by, that a reduction / deactivation of the air preheating is achieved by a differential pressure valve in the secondary line partially / completely closing as soon as there is only a small intake manifold vacuum at high engine load. [25] Device according to one of claims 8 or 18 to 24, characterized by , that a reduction and largely deactivation of air preheating occurs because, at high engine load, there is only a very low intake manifold vacuum, and in conjunction with a high throttling effect of a perforated plate or small secondary line cross-sections, only a relatively small mass airflow results in the secondary line at full load. [26] Device according to one of claims 8 or 18 to 25, characterized by, that the secondary line draws fresh air from a position downstream of the air filter and upstream of any charge air cooler that may be present, and directs it at least temporarily through a heat exchanger during partial engine load, whereby rapid deactivation of the air preheating by means of two valves or a three-way valve is achieved by closing the secondary line and opening the main line at high engine load.

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