DE10262435B3 - Method and device for the cost-efficient increase and use of waste heat from internal combustion engines - Google Patents

Abstract

Method for operating a cooling and heating circuit for motor vehicles with an internal combustion engine (1) cooled by coolant and with adjustment devices that can be influenced by an engine controller (20) to vary the combustion process within the internal combustion engine (1), characterized in that during operation with an increased waste heat requirement, a reduced coolant throughput is set by the internal combustion engine (1) in the direction of limit values permissible for safe engine operation and the fuel consumption of the internal combustion engine (1) is temporarily artificially increased by adjusting a fuel conversion in the direction of crankshaft settings with an increased combustion chamber volume, the increase in waste heat primarily for increasing the Exhaust gas temperature takes place, is used without considering the heating and with a coolant flow rate through the internal combustion engine (1) is close to zero.

Description

The invention relates to a method and a device for operating a cooling and heating circuit for motor vehicles with a coolant-cooled internal combustion engine, the coolant of which is conveyed by a coolant pump to the heating heat exchanger for the cabin and finally back to the internal combustion engine, with adjustment devices influenced by the engine control to vary the combustion process within the internal combustion engine. The variation measures are aimed at temporarily increasing the available waste heat for improved cabin heating and/or increasing the temperature of components in the exhaust aftertreatment system.

It is known that modern passenger cars with highly efficient diesel engines have additional heating components for cabin heating in winter, particularly in central European latitudes. Water-side auxiliary heating by means of fuel-operated auxiliary heaters derived from parking heaters or the electric heating of the cooling water or the direct electric heating of the cabin air by means of the well-known PTC auxiliary heaters are the usual solutions on the market.

It is also generally known that most car manufacturers have carried out extensive in-house investigations to increase the waste heat from direct-injection diesel engines for cabin heating purposes by adjusting the combustion inside the engine, with the well-known result that the auxiliary heating components mentioned above have not been omitted to this day could.
In this context, a study on the heat output in cars with consumption-optimized engines, financed by the German car manufacturers and accompanied by their experts, which was carried out by a generally recognized research institution for internal combustion engines - this is associated in particular with a well-known German university - summarizes, among other things, the Possibilities and limits of engine measures in May 2000 together (Source: Koch, Franz-Wilhelm; Haubner Frank; Klopstein, Stefan: Heat output in cars with consumption-optimized engines. In: FAT publication series, vol. 155, 2000, pp. 1-63. — ISSN 0933-50X). These are not only classified as very limited, but also as critical in terms of pollutant emissions, and this is already the case for the current EU III and EU IV regulations.
The research center selected operating points at 1500 rpm and 1.0 bar effective mean pressure as well as 2000 rpm and 2 bar mean effective pressure as representative operating points and measurements with different injection times on a 2.0 I TDI diesel engine with common rail injection system presented. A range from 16° CA before TDC to 1° CA before TDC with regard to the energy balance and pollutant emissions was measured as a physically meaningful variation range for the start of injection. The highest increase in the additional heat found in the engine cooling circuit was a little less than 1.5 kW at 1500/1 bar and approx. 3 kW at 2000/2 bar. This was found at maximum retard with an injection start of 1 or 2° CA before TDC and was immediately associated with a significant increase in emissions. If the injection is shifted to the early values up to 16°KW, the additional amount of heat introduced is almost negligible, but the total emission HC + NOx increases.
The measurement results lead to the conclusion published in consensus between the researcher and the contracting vehicle manufacturers: "Finally, as a result of the exhaust gas legislation, there is a very limited potential for increasing the heating output by shifting the combustion to the expansion phase."

Although a common-rail injection system (as is available in the engine used by the research center) allows for a significantly wider variation of the injection timing and, in particular, multiple injections, the research center decided to do this in consensus with the representatives of the automotive industry due to the lack of prospects of success didn't even try. Instead, it is proposed as an engine improvement method to artificially increase the exhaust gas back pressure by means of the supercharger with variable turbine geometry and thereby shift the operating point to a higher indicated mean pressure. The throttling of the exhaust gas mass flow - with VTG charger or throttle valve - in connection with an exhaust gas heat exchanger is described as particularly promising. Nevertheless, the exhaust gas heat exchanger has not yet been able to establish itself on the market and, as already mentioned, the external auxiliary heaters have not been omitted either.

In view of the above, it can be said that to date there is no efficient solution available or implemented on the market that is capable of replacing the additional auxiliary heating components such as burners, electric water heaters or PTC air heaters by means of engine measures alone. Internal engine measures to increase heating capacity are currently considered by experts - if at all - as supporting measures at best.

In addition to the motoric approaches described, in particular through an increased exhaust back pressure or retarding the injection timing away from the fuel consumption best point in the direction of increasing the heat input into the coolant, but new approaches are also known which, due to lower heat losses and particularly rapid local heating of components and coolants, improve the cabin heating performance without fuel consumption disadvantages.
With these solutions, there is a reduction in the coolant mass flow through the engine and the cabin heat exchanger and the use of highly efficient cabin heat exchangers, which still have a good level of efficiency even with low coolant throughput, so that passenger cars with petrol engines do not need any auxiliary heaters and passenger cars with diesel engines at least less auxiliary heating capacity to meet the existing ones heating performance criteria. On the one hand, the minimization of the heat-active masses of the engine and the heating circuit plays a decisive role, which is lower on average than with a high coolant throughput due to the increased temperature difference. On the other hand, the heat losses on the surface of the engine and the heating circuit and, thanks to the simultaneous reduction in the fresh air mass flow, also the heat losses in the cabin can be significantly limited in this way.

As a current publication by a well-known car manufacturer at the conference on heat management in motor vehicles shows, this hitherto unused potential for improvement with regard to the heating effect has now been identified and verified on the basis of detailed studies. As a pleasant side effect to the improved cabin heating effect, these measures also show a somewhat improved fuel consumption, which, according to the conference report, results from the faster engine heating and the lower pump drive power.
Despite the potential for improving the heating effect when using today's series heat exchangers, the conclusion of the publication remains that additional heating will be necessary even with optimized operation of the analyzed diesel vehicle, albeit with fuel consumption advantages due to a lower average additional heating capacity. Last but not least, the above-discussed publication of May 2000 should have been included in this assessment, which classifies the possibilities of artificially generating the missing heating output proportion via engine-internal measures as very limited and also extremely critical from the point of view of emissions.

In the DE 101 55 339 A1 In order to improve the cabin heat output, it is proposed that, in order to achieve or maintain a desired coolant temperature, a heating mode can be set in which the operating parameters of the internal combustion engine are set for a maximum possible heat input into the coolant and/or the exhaust gas when the requested power setpoint values are met. For this purpose, interventions by the engine controller in the operating parameters of the engine are proposed in order to provide increased engine waste heat for cabin heating purposes, in deviation from normal operation.

In contrast, the object of the present invention is to use the engine control and any additional devices that may be required to expand the adjustment range with regard to the artificial increase in engine waste heat with unchanged drive power for the vehicle drive in the direction of higher engine waste heat, without exceeding the typical passenger car engine limit values in terms of noise and pollutant emissions .

This object is achieved with the method according to claim 1 and with the device according to claim 10.

In particular, preferred embodiment variants of the invention solve the problem that the waste heat that can be generated is also available when driving under partial load in winter with a high need for cabin heating and is significantly higher than that achieved by engines on the market today by shifting combustion to an early or late direction, taking into account practical emission values. and that the total system cost of the vehicle is significantly lower than vehicles with known auxiliary heating systems utilizing fuel-driven off-engine auxiliary heaters. In particular, the waste heat that can be generated can safely reach a minimum value even with low engine load and engine speed, so that no external additional heaters are required in the cooling water or in the cabin air to support the cabin heating.
In particular, exemplary embodiments of the invention are described below in which the overall costs of the vehicle do not increase but decrease in comparison to the solutions used today. The same applies to fuel consumption, whereby in the special case of increased component costs, the effects relating to the component costs must be offset against a corresponding equivalent for the additional fuel consumption.

In particular, with the method according to the invention, including the associated claims, depending on the cost target, it is possible to implement fuel-consumption-neutral solutions with high cost savings or largely cost-neutral solutions with significantly lower fuel consumption than is usual today. The economic importance for the vehicle manufacturer but also for the end customer is corresponding.

The interaction of a low coolant throughput through the engine and a high temperature drop in a highly efficient cabin heat exchanger of 25 K or preferably even 50 K and more makes it possible in this context in some exemplary embodiments of the invention, which will be described in detail below, to also use the usual injection times of diesel engines in the case of high heating output requirements, it should be moved further forward or further back than is the case with conventional engine cooling with a largely homogeneous temperature distribution of the cooling water and the combustion chamber walls. Depending on the type of heat exchanger and the integration of EGR coolers and/or exhaust gas heat exchangers, potentials with coolant temperature differences between the heat exchanger inlet and outlet of significantly more than 50 K are advantageous not only for highly effective cabin heating but also for significantly expanding the adjustment range for combustion.
As will become even clearer below, only the specific knowledge that such efficient cabin heat exchangers can be realized in passenger cars, even under the cost and package boundary conditions, opens up the full potential of the procedure according to the invention. In the method according to the invention, high wall temperatures in the combustion chamber are achieved with and without cabin heating and are therefore available in year-round operation, albeit with different additional fuel consumption. This is also particularly important for applications in which, in addition to improving the cabin heating, a temporary increase in the exhaust gas temperature is also required, in particular for burning off particle filters for diesel engines.

The increase in combustion chamber wall temperatures induced according to the invention, including the surfaces of the cylinder barrels that come into contact with the fresh air and the residual gas or the recirculated exhaust gas, has a very strong effect on the polytropic coefficient of compression, resulting in a higher final compression temperature.
Will now z. If, for example, an earlier injection compared to the best fuel consumption value is chosen to deliberately reduce the efficiency of the engine and thus to increase the heat input, this potential expands with reduced coolant throughput in the direction of "even earlier".
The same applies, again based on the injection timing of the optimum fuel consumption value, when shifting towards late, ie an “even later” injection is possible.

Both measures in turn increase fuel consumption, since the combustion or heat supply takes place at a lower effective compression ratio, but also the heat input into the combustion chamber walls and ultimately also the wall temperature. This effect builds up, especially when the injection timing is gradually adjusted in the direction of increased fuel consumption and the cooling water gradually warms up. If the injection timing is adjusted sufficiently, advancing the injection timing causes a greater increase in the wall temperature; retarding the injection timing shifts a larger proportion of the additional energy into the exhaust gas. As will be shown later - in contrast to the test results on the 2.0 l Common Rail TDI engine that have already been discussed and are generally recognized as representative and which give a clear recommendation for retarding the injection - both variants can be used sensibly depending on the optimization goal , whereby the combination of both measures is of particular interest with regard to maximizing the additional waste heat.

• Bei den geringen Lasten und Drehzahlen, die die Betriebspunkte mit Wärmedefizit auszeichnen, liegen i.a. nur geringe Temperaturdifferenzen für den Wärmeübergang im Metall und vom Metall an das Kühlwasser vor. Deshalb würde selbst eine Verdoppelung der Wärmezufuhr nur auf eine Wandtemperaturzunahme von wenigen Grad K führen. Ist jedoch der wasserseitige Wärmeübergangskoeffizient durch einen sehr geringen Kühlmitteldurchsatz herabgesetzt, so beträgt die lokale Temperaturdifferenz zwischen Brennraumwand und Kühlwasser z.B. 50 K anstelle von 5 K bei hohem Kühlmitteldurchsatz. Eine Verdoppelung der Wärmezufuhr, z.B. durch eine starke Verlagerung der Einspritzung in Richtung früh, bedeutet in diesem Zusammenhang in grober Näherung ebenfalls eine Verdoppelung der Temperaturdifferenz, d.h. 10 K in der Basis und 100 K bei reduziertem Kühlmitteldurchsatz.

Without the strong reduction in coolant mass flow, the change in wall temperature under this interplay would only be relatively small:

• At the low loads and speeds that characterize the operating points with a heat deficit, there are generally only small temperature differences for the heat transfer in the metal and from the metal to the cooling water. Therefore, even doubling the heat supply would only lead to a wall temperature increase of a few degrees K. However, if the water-side heat transfer coefficient is reduced due to a very low coolant throughput, the local temperature difference between the combustion chamber wall and the cooling water is, for example, 50 K instead of 5 K with a high coolant throughput. A doubling of the heat input, for example due to a strong advance of the injection, also roughly means a doubling of the temperature difference in this context, ie 10 K in the base and 100 K with a reduced coolant throughput.

In this context, it is particularly advantageous to induce the greatest possible increase in fuel consumption in the early phase of warm-up, so that high combustion chamber wall temperatures are achieved very quickly. In this context, the greatly increased friction loss of the engine during warm-up helps to get through the critical early phase quickly and at the same time to transfer enough heat to the combustion chamber walls that the injection parameters can also be adjusted sufficiently so that the rocking effect can continue to be used even with a partially heated engine . On the one hand, the high friction has a direct beneficial effect on the cylinder liner for the wall temperature, but also indirectly, via the indicated mean pressure required to overcome the friction, which leads to increased process temperatures and pressures. Since there is initially a relatively high basic fuel consumption in this very early phase of the warm-up, even a comparatively small adjustment of the injection timing causes a large amount of additional heat. At the same time, in view of the increased mean effective pressure, there is less sensitivity to adjusting the start of injection with regard to robust combustion. Last but not least, the higher fuel quantity as well as the increased boost pressure in TDI engines or the increased compression end pressure in Otto engines have an advantageous effect here.
Since the high friction loss of the engine in the early phase of warm-up is reduced particularly quickly in the method according to the invention due to the faster heating of the cylinder liner, it is important to use the potential for increasing the wall temperature by shifting the injection times as fully as possible in this phase.

The increased wall temperatures are important in the method according to the invention, on the one hand, in order to allow the adjustment of the injection times and in particular to use the above-described oscillating effect to maximize the adjustment. On the other hand, they are also important with regard to the cabin heating effect, in order to reach the area of nucleate boiling as quickly as possible, at least locally, so that the amount of heat given off to the coolant is sufficient for heating purposes even with a low coolant throughput through the engine. This requires a relatively large amount of additional heat in the early phase of warm-up, which can only be achieved through the interplay described.
For a rapid cabin heating effect, it is also advantageous to keep the amount of heat introduced in the early phase of the warm-up at values that are at least twice as large as in the warmed-up state. This takes into account the increasing heat extraction at the cabin heat exchanger with increasing coolant flow temperature, so that the well-known asymptotic approximation to the stationary final value of the coolant flow temperature does not result, but a much steeper curve. When the stationary value of the coolant temperature is finally reached after a relatively short time, the injection adjustment is then removed and the coolant flow temperature remains constant.

With this particularly effective procedure with maximized heat input in the early phase of warm-up, a relatively large amount of additional heat is induced very quickly, with the minimum wall temperature up to local nucleate boiling being initially reached quickly when the engine is relatively cold and the local component temperature then remaining approximately at this temperature level and changing Heat more and more component zones in the direction of nucleate boiling.
With this procedure, relatively high coolant flow temperatures for the cabin heat exchanger can be achieved quickly even when heat is drawn off for the cabin. A preferably good cabin heat exchanger efficiency up to very low coolant throughputs and the possibility to save additional energy by setting the air mass flow to reduced values in view of the coolant temperature reached, quickly lead to a stationary operating point at which additional energy is no longer required for warming up, but instead the entire cabin heat output from the waste heat can be contested at the best fuel consumption value.
Averaged over the winter driving time, this procedure generally results in fuel consumption that is below the usual values for external auxiliary heating methods. This is largely due to the shorter switch-on time of the engine-internal auxiliary heating as well as a large number of journeys in which the savings in heat losses and the reduced heat-active mass lead to the engine being operated at a higher average temperature or in which no artificial increase in fuel consumption is required at all. In addition, there are journeys where the system is used to increase the component temperatures in the partial load due to driving conditions with a higher basic load on the engine or limited cabin heating and saves fuel in this way. The fuel savings due to the weight advantages due to the omission of the external auxiliary heater components are also noticeable in year-round operation.

With regard to the practical implementation of the potential of the invention with a rapid increase in the combustion chamber wall temperature for high heat output, it should be noted that the engines and cabin heating circuits used today require a relatively high coolant throughput through the engine and cabin heat exchanger. In addition, the potential for reducing the fresh air mass flow through the cabin is only effective when a relatively high coolant temperature is reached. Last but not least against this background, the above-mentioned publication at the heat management conference shows the advantages of a reduced air mass flow only after a longer period of operation.
In other words, without the measures according to the invention already in the early phase of the warm-up and in particular without a special cabin heat exchanger for extremely low coolant throughputs, the need for relatively high coolant throughputs The temperature and pressure conditions in the combustion chamber generally result in such a high ignition delay that the tolerable noise limits are easily exceeded due to the rapid combustion of the premixed fuel-air mixture.
In addition, without sufficient temperature during combustion, problems with pollutant emissions are to be expected. In this context, unburned fuel fractions make a contribution to increasing fuel consumption and emissions, but not to the engine-side heat input. They are therefore generally disadvantageous even if the downstream catalytic converter still largely converts them.

The previous description focuses in a very simplified manner on the positive effects of increasing the gas-side wall temperature. However, these positive effects are supported to a considerable extent by increasing the temperature of the residual gas and possibly the temperature of the recirculated exhaust gas. As is well known, it should be noted that even relatively small gas temperature differences at BDC with a correspondingly high polytropic coefficient cause a strong increase in the compression temperature at the time of injection. In simplified terms, this can be estimated using the polytropic compression with the polytropic coefficient κ according to T2=T1*(V1/V2) ^(1-k) : Insertion of engine-typical values shows that a gas temperature difference in the area of the bottom dead center of the compression (BDC) during compression from State 1 with volume V1 and temperature T1 leads to state 2 with V2 and T2, depending on the injection time, leading to a multiplication of the temperature difference compared to the temperature difference at BDC. The polytrope coefficient to be used for the simplified analysis is in turn dependent on the heat transfer and thus on the flow conditions and the wall temperature as well as the mixture composition but also on the injection time or, in the case of Otto engines, on the ignition time. Against this background, the physical significance of the temperature T1 for the temperature T2 that can be reached by the time of injection must be classified as significant. Not least against this background, the dependent claims with a specific assessment of the exhaust gas recirculation and with additional electric heating of the recirculated exhaust gas or the fresh air are of great technical and economic interest.

In order to maximize the amount of heat introduced, a double injection is preferably carried out in order to achieve the maximum deterioration in efficiency: With this procedure, the division of the fuel conversion causes in particular a minimization of the combustion noise. Among other things, the division into two "small" combustions with the unavoidable ignition delay and the sudden combustion of the premixed fuel-air mixture is involved, but also the natural limitation of the pressure increase due to the relatively large combustion chamber volume according to the invention during the fuel conversion.

Increasing the combustion chamber wall temperature by reducing coolant throughput and the associated increase in gas temperature at the time of injection and during fuel conversion is the decisive step towards a significant shift in fuel conversion towards increased combustion chamber volume. This applies to shifts in the direction of “much too early” and in the direction of “much too late” as well as for the combination of both measures. In contrast to known heat management measures, the reduced coolant throughput through the engine is not used to reduce fuel consumption by reducing friction on the cylinder liner and improving combustion, but rather to reduce fuel consumption, possibly even at the expense of a certain deterioration of combustion and emissions, to temporarily increase.

The advantages of the method according to the invention are not limited to the omission of the expensive cabin heating components, but in addition a significant fuel saving can be achieved on an annual average depending on the overall system design. In this context, it is in the nature of the procedure according to the invention that, depending on the configuration of the method, a greater or lesser proportion of the additionally introduced energy is lost due to an increase in the exhaust gas enthalpy.
Against this background, in the energetically most favorable application, an exhaust gas heat exchanger is used, which not only uses this additional energy, but also a large part of the exhaust gas enthalpy of the basic calibration close to the consumption best value of the currently delivered engine drive power. Vehicles with exhaust gas heat exchangers generally get by with very moderate adjustments to the injection times even when there is an extremely high need for cabin heating, but the procedure according to the invention is of fundamental interest, especially in the very early warm-up phase, since it can be used to realize time gradients in cabin heating that were previously considered physically impossible. In addition, the exhaust gas heat exchanger heats up the engine more quickly in both summer and winter and thus makes a fundamental contribution to fuel savings. Despite all of these benefits, there are costs First of all, variants of the method according to the invention are of particular interest, which provide sufficient heat output even without an exhaust gas heat exchanger.

As has already been described in detail but in a greatly simplified manner, a sufficient temperature at the time of injection is a necessary condition for shifting the injection times according to the invention in the direction of a larger combustion chamber volume. However, another very important parameter for the combustion process is the combustion chamber pressure - in addition to other parameters that are not adjusted here, such as charge movement in the combustion chamber and spray characteristics.
In this context, the shifting of the injection times according to the invention means that even if the same gas temperature is reached, the boundary conditions for the ignition of the mixture and the further course of combustion are not the same. Rather, the reduced pressure inevitably results in an increased ignition delay, which must be compensated for by the fact that the temperature at the time of injection is not only identical, but also significantly higher than at the same temperature and higher pressure. It is therefore essential to use the potential for reducing the coolant throughput as far as possible in order to increase the cabin heating capacity. If, on the other hand, only the exhaust gas temperature is to be increased to burn off soot particle filters without taking the heating into account, then the scope for increasing the combustion chamber wall temperature is only limited by the permissible engine temperatures and is therefore significantly greater. In the borderline case, it is even possible to work with coolant throughputs close to zero.
1 shows a particularly advantageous embodiment of an engine and vehicle cooling system for carrying out the method according to the invention, including as an example important measuring and control lines 20a-20f of engine control unit 20 that are helpful for the method-based control of the coolant throughput and the fuel injection of a diesel engine with cooled exhaust gas recirculation.

The coolant is according to 1 conveyed through the engine 1 by the cooling water pump 7 of the engine. From the engine outlet, the coolant flows in a first circuit 9a to the water tank 9 and then via the thermostat 6 back to the engine 1. This branch is used for ventilation and degassing and contains, in particular, a throttle point (not shown) for reducing heat losses during warm-up and for safe degassing the coolant throughput to values close to zero at low engine speeds. Alternatively, a two-way valve can be used instead of the throttling point for even more precise control or temporary shutdown during warm-up.
A second branch of the cooling system goes via the line 6a and the vehicle radiator 8 to the thermostat 6 or via the switchable by means of the engine control line 20c bypass branch with switching valve 6b directly to the thermostat 6. Above a certain operating temperature, the thermostat 6 opens the radiator Branch 6a more and more and closes the bypass branch 6b in an analogous manner. Alternatively, instead of the conventional thermostat 6, a control valve controlled by the engine control according to the cooling requirement can also be used, optionally with the additional integration of the bypass valve 6b.

In addition to the branches 6a, 6b and 9a for engine cooling and ventilation of the cooling system, branch 4a is used to heat the vehicle cabin. The coolant is conveyed by the electric auxiliary pump 2 via the EGR cooler 3 and the temperature sensor 15 to the cabin heat exchanger 4 and then back to the thermostat 6.

The internal combustion engine is supplied with combustion air via the fresh air line 10 , which mixes with the recirculated exhaust gas from the EGR branch 11 in line 12 . The electric EGR auxiliary heater 30 is optionally connected downstream of the EGR cooler 3 .
The exhaust gas leaves the engine via the exhaust manifold 13 and is divided by the exhaust gas recirculation valve 14 into the EGR branch 11 and the exhaust gas line 17 depending on the need for exhaust gas recirculation.

The coolant volume flow is deliberately set to low values of, for example, only 2 l/min, at least in the event of a heat deficit, in that the line cross-sections in the heating branch 4a have an inner diameter of only 4-6 mm instead of the usual 16-20 mm, and the bypass branch 6b and the Cooler branch 6a are closed at heat output deficit. The cabin heat exchanger is also designed for a relatively high pressure drop in order to achieve high coolant flow rates in the individual heat transfer tubes and good heat transfer. In contrast to the cross-flow heat exchanger design typical for passenger cars, the counter-flow design is preferably used here, which usually has a greater pressure loss on the water side anyway.

The installation of the additional electric pump 2, which, in contrast to the centrifugal pumps commonly used in vehicle cooling, is particularly advantageously designed as a membrane, piston or gear pump, results in the heating circuit in connection with a particularly preferred design of the cabin heat exchanger and the coolant line Due to a very low coolant volume flow and high pressure losses, the coolant flow rate is largely independent of the engine speed. Last but not least, the fact that for the cooling system of today's internal combustion engines the most moderate possible pressure and power requirement of the coolant pump 7 on the engine side is aimed at is involved in this situation. When using a gear pump as the additional pump 2, for example, the flow through the cabin heat exchanger is determined in a first approximation by the electrical power of the gear pump and not by the motor pump.
In comparison to today's cooling and heating systems, an overall system designed in this way leads to a dramatic improvement in the cabin heating capacity even without additional measures to artificially increase the engine waste heat. The physical mechanisms of action used here have already been described in detail.

If this improvement in heating output is still not sufficient, with this configuration it is easily possible to increase the heat input into the coolant or the exhaust gas by retarding the injection timing comparatively moderately. The highest possible exhaust gas recirculation rate helps ensure that a significant proportion of the exhaust gas enthalpy remains in the engine/cabin heating system. Increased combustion chamber wall temperatures and the heating of the fresh air by the residual heat of the recirculated exhaust gas ensure that the slight shift in the injection timing has hardly any negative effects on the combustion noise and the exhaust gas emissions.
The low coolant throughput through the EGR cooler and its low heat-active mass very quickly results in a high coolant flow temperature at the cabin heat exchanger, i.e. the low coolant throughput through the EGR cooler already focuses a large proportion of the enthalpy of the recirculated exhaust gas on the cabin heat exchanger before the entire heat-active one Mass of the engine must be heated. At the same time, the relatively high coolant temperature in the EGR cooler ensures that the recirculated exhaust gas is not overcooled in the early phase of warm-up. In this context, the closing of the engine-side bypass 6b helps to achieve additional advantages by minimizing the thermally active mass of the engine.

Such a heater is sufficient in most engine/vehicle combinations to meet all current comfort requirements without any external auxiliary heating components. The slight retardation is i.a. only required in extremely cold weather, so that on average in winter there is a fuel saving of several % compared to external auxiliary heaters, in particular to el. PTC auxiliary heaters. The fuel savings are still noticeable even in a direct comparison of the slight retardation with the external additional burner, which is currently considered by experts to be the least harmful in terms of energy. This is due in particular to the fact that the recirculated exhaust gas is initially used primarily for heating the cabin and not for heating the engine, and at the same time the engine makes an additional contribution due to the temperature stratification between the inlet and outlet or between the interior and exterior of the engine. The additional fuel consumption due to the delayed injection is characterized on the one hand by an additional consumption portion that goes directly into the engine structure, on the other hand by the remainder, of which up to 50% - with cabin-focused utilization in the EGR cooler - is lost due to high EGR rates System engine cabin heating remain. The overall degree of utilization in relation to the direct heat input into the engine and heating circuit system thus remains only relatively slightly below the corresponding efficiency of the burner of 80-85%. EGG. Auxiliary heating systems cut due to the high losses in the alternator - these are i.a. 100% lost - and further losses in the exhaust gas in terms of fuel consumption are even worse.

In view of the previous statements, it is obvious that the integration of an additional exhaust gas heat exchanger to use the residual enthalpy in the exhaust system 17, which is preferably carried out on the coolant side between the engine and the EGR cooler, can achieve an additional increase in cabin heating capacity or additional fuel savings. However, the relatively high cost of the exhaust gas heat exchanger makes the series introduction of such systems highly dependent on the development of exhaust gas legislation and fuel prices.

In addition, it represents a considerable competitive advantage if a motor vehicle manufacturer can offer heating comfort that is far above the level customary today by offering previously unknown cabin heating rates in its vehicles. This initially applies independently of fuel consumption, ie there are boundary conditions under which the customer would rather accept higher fuel consumption than wait a long time for the cabin to heat up.
The variants according to the invention offer considerable scope here to gain a competitive advantage through reliable technical control of an extended range of variation with regard to fuel consumption or with regard to waste heat for heating purposes. Alternatively, the potential of the invention can also - under Acceptance of reduced fuel consumption - used to work with cheaper components in the cooling or heating circuit or to use package advantages. This applies in particular to the coolant lines, the heat exchanger and the number and control quality of the control and control goods used.

Even with internal combustion engines without the EGR cooling, which is particularly helpful for cabin heating purposes, or if the series connection of the EGR cooling according to 1 is not possible, the approaches according to the invention can be used advantageously. A corresponding configuration shows 4 .

High EGR rates keep the waste heat, which is additionally generated by late injection, still to a significant extent in the overall engine-cabin heating circuit system. Nevertheless, in principle it is advantageous to work with the "too early + too late" variant. If the injection is too early, there is naturally a longer period of time for the heat transfer from the fuel gas to the combustion chamber walls, so that the exhaust gas temperatures are lower and a larger proportion of the fuel quantity to be dissipated contributes to heating the combustion chamber walls and the coolant.

This fact is in accordance with the application of the variant of the method according to the invention 5 to a much greater extent where no exhaust gas recirculation is available to support air preheating. The use of later injection in diesel engines or later ignition in Otto engines is definitely possible within certain limits. Nevertheless, only a comparatively small proportion goes into the engine structure, the majority is lost in the exhaust gas due to the lack of exhaust gas recirculation. The calculation results of a corresponding numerical simulation of the combustion and the heat transfer according to 6 estimate this effect. It should be clear that the assumption of identical combustion processes does not exist in practice or can only be realized to a very limited extent and that the 1-D calculation of the gas exchange and combustion with heat transfer using the heat transfer calculation method according to Woschni only has a limited resolution of physics delivers.

1. 1. die Abgastemperatur (Rechtecke, linke Ordinate)
2. 2. die in Form von Kraftstoff zugeführte Energie (Kreise, rechte Ordinate) und
3. 3. die Abgasenthalpie (Rauten, rechte Ordinate).

For a cold engine with a constant indicated mean effective pressure of 2 bar and a speed of 1500 rpm as well as a constant combustion period of 30°CA, in 6 plotted over the start of combustion:

1. 1. the exhaust gas temperature (rectangles, left ordinate)
2. 2. the energy supplied in the form of fuel (circles, right ordinate) and
3. 3. the exhaust gas enthalpy (diamonds, right ordinate).

The results of the calculations confirm what has been said so far, that retarding combustion with constant engine power output leads to increased exhaust gas enthalpy compared to retarding combustion early. Without EGR, this portion of the additional fuel energy input is lost.
In addition, it becomes clear that, in order to improve engine warm-up, it is in principle more favorable to work with early combustion, since with the same amount of displacement angle relative to TDC, a higher total fuel quantity can be converted with the same torque on the shaft. The reason for this is the increased wall heat loss of the fuel gas, which is available for heating the engine and coolant.

Based on 6 It is also clear that for the practical implementation of the method according to the invention, which in particular wants to induce very high additional heat, a far greater adjustment of the injection is necessary than in the measurements on a 2.0 I common rail TDI engine described above case was. As already mentioned, due to the lack of knowledge of the measures and interactions according to the invention, only a total variation range of 15° CA was considered for the potential variation scope. And even here, in view of the emission values measured, there were doubts about the practical feasibility.

In this context, it must be taken into account that comparable combustion durations and combustion processes with a very large shift in the crankshaft position of the fuel conversion, as is the case for the statements according to 6 was assumed to clarify the physical relationships, cannot be implemented without additional measures. The same applies to the combustion noise. The scope for "too early" injection is also fundamentally limited here, as with "too late" injection, due to the increase in combustion noise and the quality of fuel conversion. However, the very low coolant throughputs help significantly to expand the scope. In the interaction of the parameters with greatly increased temperatures on the combustion chamber side and a simultaneous increase in heat input due to the postponement of the start of injection "too early", variation bands for the engine waste heat have finally moved into the realm of feasibility that previously had not been thought possible. This applies in principle, but especially in connection with exhaust gas recirculation.

The particularly attractive “too early and too late” process variant opens up a particularly large potential for maximizing the heat input and minimizing the combustion noise. Since the injected fuel quantity with the atomization quality of modern injection systems at low speed and load is largely converted to a fuel conversion within less than 10° CA, the effective compression ratio of the fuel conversion and thus the efficiency and the amount of waste heat can be varied within a very wide range . How out 6 can be derived, if there is a lot of additional waste heat to be introduced into the cooling water, the injection would have to be so late in the case of pure shifting to "too late" that the gas pressure and gas temperature in the combustion chamber drop to intolerable values, associated with problems with ignition/self-ignition , the ignition delay and the burnout, not to mention the exhaust gas quality. The variant according to the invention “too early and too late” is significantly less critical here and still ensures that the heat is supplied at the lowest possible compression ratio and thus at the worst achievable thermodynamic efficiency. Added to this are the increased heat losses of the first combustion and the preheating of the gas for the second combustion, combined with the potential for this to be a little later.
In this context, it is not new to use multiple injections in diesel engines to increase exhaust gas temperatures. However, the first injection generally takes place relatively close to TDC, not least in order to keep the combustion noise low and to provide sufficient temperatures for the subsequent injections or combustion. This inevitably makes a negative contribution to maximizing the waste heat, since the fuel conversion takes place at a high compression ratio. The result is a limitation of the achievable increase in fuel consumption at a given engine torque, coupled with the effect that the majority of the additional waste heat escapes unused via the exhaust system. In the case of cabin heating, this is particularly inefficient in engines without EGR, but also to a lesser extent in engines with EGR. This problem with regard to efficiency when combustion is shifted to the expansion phase is actually only mitigated if an EGR cooler is arranged between the engine outlet and the cabin heat exchanger inlet and focuses the majority of the EGR enthalpy on the cabin, such as in 1 shown. Depending on the overall engine heating circuit system and especially with a limited EGR rate, the "too early" and "too early and too late" variants are not only characterized by a higher additional heating potential, but also by a significantly better efficiency with regard to the required additional fuel consumption .
On the other hand, if the aim is to have the highest possible exhaust gas temperature, for example for burning off particle filters or NOx storage, these statements regarding efficiency are largely reversed in accordance with the task at hand.

In 1 is optionally an el. Heating 30 of the recirculated exhaust gas integrated. This additional measure is very effective with and without cooling the recirculated exhaust gas, in order to further expand the variation range of the waste heat over even higher compression temperatures at the time of injection or ignition.
On the one hand, the integration in the EGR branch has the advantage that this area, in contrast to the charge air lines, which are often made of plastic or rubber, is already very robust with regard to increased temperatures, so that the electric heating can be counteracted with less effort el. Overheating must be secured. In the simplest case, there is electrical heating with resistance wires, which, if there is no air flow, give off their excess heat to the environment or the flanged metal pipes, the engine and the exhaust system components through radiation or heat conduction. On the other hand, there is the very special advantage that the pressure loss of the electric EGR heating does not have any negative effects on the nominal output, since the EGR is generally deactivated there.

At first glance, it may not appear to be very effective, for example, to save the electric PTC heater on the side of the cabin air and, in return, to add an electric heater in the EGR branch.
The following technical developments of the EGR heating and the equally advantageous heating of the fresh air will show that there are nevertheless cost advantages here.

It is much more significant, however, that the potential for rapid cabin heating can be increased extremely far beyond the previously known level. In addition, in many future diesel engines, the measures according to the invention are also very helpful for safely burning the diesel particle filter clean. Here, too, the enormously increased range of applications in the direction of low engine load, low engine speed and low ambient temperature is of importance that should not be underestimated.
The additional mechanical engine load to provide, for example, 800 W electrical power is not insignificant in this context, with a higher base engine load not only fundamentally increasing the heat input and also measured in absolute numbers the waste heat per °KW Adjustment of the injection is also significantly increased, but this also increases the scope for adjusting the injection timing.

In a particularly cost-effective variant, the consistent application of the ideas according to the invention with electric EGR auxiliary heating according to 1 to the omission of the glow plugs found throughout the combustion chamber of today's passenger car diesel engines. As is well known, these ensure reliable starting of the diesel engine by means of a preheating time dependent on the ambient temperature and, by means of afterglowing during the early phase of the warm-up phase, ensure adequate combustion quality and an acceptable combustion noise level.
Up until now, only diesel trucks in motor vehicles have been able to do without glow plugs in the combustion chamber. In this context, passenger car diesel engines generally have a higher compression ratio than truck diesel engines, but this advantage is more than offset by the unfavorable ratio of combustion chamber surface to combustion chamber volume and the increased requirements with regard to noise emissions from passenger car diesel engines, so that glow plugs inside the combustion chamber have been required up to now .

In this context, the procedure according to the invention with EGR auxiliary heating makes it possible to bring the final compression temperature to a comparatively high temperature level so quickly that the glow plug inside the combustion chamber is no longer absolutely necessary to reduce the ignition delay and to stabilize the combustion.
In the optimal variant, this means that a previously unimaginable time constant during cabin warm-up and the burning off of particle filters can be achieved at least cost-neutrally, namely by offsetting the costs of the EGR auxiliary heating with the cost savings for eliminating the glow plugs.
The 1:1 calculation of the advantages of the simplified cylinder head, the reduction in the number of plugs and lines together with the package volume released in the engine compartment and the additional degrees of freedom for the arrangement of the injection nozzles and combustion chamber design should certainly be a very moderate classification of potential. But even then, the economic importance is clearly evident.

This statement applies to the preferred heating of the air by means of electrical heating of the recirculated exhaust gas, but also to solutions with electrical heating of the fresh air.

The proposed arrangement of the el. Additional heater 30 according to 2 has the advantage of simplicity and particularly high operational reliability: A simple query of the engine speed as a criterion for switching on and off is sufficient to ensure that, for example, an electric flat-wire resistance heater cannot burn out in view of the minimum fresh air throughput through the engine that is typical when idling. This advantage, which should not be underestimated, is accompanied by potential disadvantages in terms of pressure loss or the size and heat-active mass of the electric heating elements.

The arrangement of the el. auxiliary heating in the EGR branch according to 1 as well as in the fresh air branch in 2 When using charge air cooling, this has the disadvantage that a certain potential for increasing the temperature of the fresh air is wasted at the charge air cooler. The arrangement according to 3 is particularly beneficial to this disadvantage and also the disadvantages of 2 regarding the pressure drop at full load. The not inconsiderable costs for the bypass as well as the additional costs for the safety monitoring of the electric auxiliary heater must be offset against the advantages for the specific application.

The use of the method and device variants according to the invention in year-round operation is made possible not least by the free control of the bypass valve 6b. The application in engine map areas with and without heat deficit depends on the temperature limits and minimum flow rates permitted for the engine. In the case of the heat input according to the invention, in particular the exhaustion of the potentials is particularly simple if the emissions are monitored or controlled by means of the smooth-running control or other measured variables.

The additional fuel saving potential of the various "hot cooling variants" in the statutory exhaust gas test between 20 and 30 °C ambient temperature and without cabin heating, which result from the gradual increase in the coolant flow through the engine, starting from a flow rate close to zero up to a fully open bypass 6b or cooler circuit are known and need not be repeated here.

The specific advantages of the "too early and too late" variant have already been discussed in detail. A variant of the method is of particular interest in which the fuel is introduced primarily in the first and the last injection, in particular that exactly two injections take place. As long as the ignition delay and the combustion time due to the engine design are only a few degrees of crank angle, it is appropriate here, for example, for the application 5 most effectively with two approximately equal injection quantities of the first and last injection to work. The implementation of the first combustion process is then generally completed well before TDC and the second combustion begins well after TDC, which benefits the conversion of an increased fuel quantity.
However, if the sum of ignition delay and combustion duration is relatively large, it is more favorable if the fuel quantity injected in the last injection is larger than the quantity of the first injection. This applies in particular to variants with a focus on increasing the exhaust gas temperature or with optimized EGR utilization for preheating the combustion air and with cab heating output-optimized integration of the EGR cooler.
In the case of multiple injections, the first and last injection times are advantageously selected such that the pressure and temperature of the combustion gas at the time of injection are defined using a map for the ignition delay with additional consideration of the reduced coolant throughput. In this way it is achieved that the ignition delay is approximately at the same level for both injection processes.

The cooling of the recirculated exhaust gas according to 1 is a highly efficient method of achieving rapid cabin warm-up with little additional fuel consumption. Overcooling of the exhaust gas is generally not to be expected due to the rapid heating of the cooling water in the EGR cooler. In the early phase, however, where even the smallest amounts of air preheating are required, it is advantageous, in part to maximize combustion advance and the described blow-up effect, to use reduced EGR cooling or no EGR cooling at all. This means that the temperature level for reliable initiation of combustion can already be achieved at very early and/or very late injection times. Although the cabin heating-promoting effect is only indirect, via the extended control range for the fuel injection and the minimized effective heat-active mass of the engine and cabin heat exchanger, the cabin heating capacity can be significantly improved in this way. This procedure can be very effective, especially with moderate EGR rates.

As already described, it is advantageous for a rapid increase in the cabin heat output to make the additional amount of fuel introduced into the internal combustion engine as large as possible in the early phase of the warm-up, in particular in order to activate the oscillating effects. For this purpose, it is particularly advantageous to provide that the total amount of fuel introduced into the internal combustion engine is more than twice as large as at the steady-state final temperature value of the coolant.

The enormous potential of the method according to the invention to bring about very rapid cabin heating involves a certain risk in the vehicle-specific application that an imbalance in the target values of maximum cabin heating effect and minimum fuel consumption is induced. This danger exists in particular because the homologation of fuel consumption is currently only carried out without cabin heating, so that depending on the development process at the vehicle manufacturer, heating is only found to be overweighted very late or even at the customer's. In addition, it is only marketable to a limited extent from an environmental point of view to save on the external auxiliary heating components, but at the same time to increase fuel consumption. Therefore, a particularly advantageous variant of the method according to the invention provides that the artificially induced additional fuel consumption due to the adjustment of the combustion processes are limited in such a way that they are compensated by energy savings due to faster engine heating, reduced heat losses to the environment and in particular by compared to el Cabin air lower mass and duty cycle, at least averaged over the average vehicle service life, are compensated.
For the practical implementation of these considerations regarding the increase in cabin heat output with moderate fuel consumption, it is particularly advantageous that the early phase is provided with a time limit depending on the coolant or ambient temperature and/or is limited to the time until a target coolant temperature is reached.

As is well known, driving conditions with a low engine load and low engine speed are particularly critical with regard to potential heat deficits. Last but not least, the example in 6 makes it clear that only a comparatively small artificial increase in fuel consumption can be achieved with small adjustments in the fuel conversion in the ranges of a maximum of 10-15° CA that are usually applicable today. This severely limits both the options for engine control to increase the exhaust gas temperature to burn off components in the exhaust system and to improve the cabin heating effect.

In contrast, the procedure according to the invention results in the potential adjustment range being considerably expanded. If necessary, it is even possible to adjust the fuel conversion by more than 20° CA in both directions relative to TDC at low engine speeds. How 6 shows, this is also necessary in order to provide the necessary energy, so that some particularly cost-effective process variants can be put into practice. This means that new users in particular It can be used advantageously for maximizing the waste heat in which the first injection begins more than 25° CA before the compression dead center when there is a high waste heat requirement and a low engine load, temporarily also at engine speeds of less than 1500 rpm and engine loads of less than 10%.
In addition, or when using the "too early and too late" process variant, it is advantageous for maximizing the waste heat in specific application variants that the last injection takes place when there is a high demand for waste heat and a low engine load, temporarily also at engine speeds of less than 1500 rpm and engine loads of less than 10%. more than 30° CA after compression dead center.
Especially for today's diesel engines, these are areas that are generally not even approached when measuring the engine characteristic maps, since without the measures according to the invention the combustion noise and the exhaust gas emissions would increase immeasurably.
In Otto engines, such large displacements are already possible with today's engines - as is well known, retardation is a very tried and tested means of rapid catalytic converter heating - but here too the procedure according to the invention helps to expand the adjustment range. This is particularly important so that the good emission values in the statutory exhaust gas test can also be achieved in real winter driving without cab heating. For driving states with and without cabin heat output extraction, the reduction in coolant throughput also reduces the required additional fuel consumption for the same values of waste heat increase.

The procedures according to the invention can be used particularly advantageously in the warm-up phase. The engine is initially started completely normally and operated for a few seconds. In the further course of the very early warm-up phase, which is characterized by extremely high friction on the cylinder liner and lasts less than 2 minutes in particular, the conventional injection angles are then gradually adjusted to increase the waste heat. The resulting oscillating effects of migratory heating can be induced particularly well in this very early phase of warm-up, in particular because the engine’s friction loss is still extremely high here and even relatively small adjustments to the injection angles release a significant amount of additional heat in view of the relatively high basic fuel consumption. The accelerated heating of the cylinder liners according to the invention leads to a reduction in the friction loss of the piston group, but the other components help in the further course of the warm-up due to the still low oil temperature, so that the base engine load is not so low that the desired increase in wall temperatures in view of the low base engine load is interrupted. This is particularly important in order to quickly reach the area of local nucleate boiling of the cooling water and thus to provide a sufficient amount of heat for the cabin even with a very small coolant throughput of the engine.

The use of external electrical heating of the combustion air is also of particular interest in connection with the basic engine load: For reasons of durability, conventional glow plugs in the cylinder head of passenger car diesel engines must be reduced in performance or switched off completely after a relatively short afterglow time. This is according to the external electric heating 1-3 not the case. The external heating helps here in the first few minutes of the warm-up not only through the electrical energy supplied but also through the additional increase in the basic engine load. It is also of very particular economic and technical interest that an external electrical preheating of the combustion air is used and that this preheating in connection with the method according to the invention also fulfills the tasks of the glow plugs for pre-glowing and after-glowing, which are otherwise usually found in the cylinder head of passenger car diesel engines .

In the 1-5 Assemblies and system integration variants shown show that the ideas according to the invention are very versatile.

The design according to 4 should finally be used again to deepen the procedure according to the invention using an example of a particularly advantageous strategy for increasing the waste heat for cabin heating purposes. The variant with an EGR cooler between the engine outlet and the cabin heat exchanger inlet, which is often more favorable in terms of energy, is deliberately not used in order to show the far-reaching consequences and the wide field of application of the procedure according to the invention. In this context, the following statements also apply in particular to diesel engines with an EGR cooler, which is arranged parallel to the heating circuit due to the cooling system and has a sufficiently sensitive flow limitation, in particular with a thermostat that only fully opens when a minimum temperature is reached.

• • ein Stellglied (6b) zusätzlich zu dem serienüblichen Thermostaten 6 den Kühlmitteldurchfluss durch den Motor reduziert und damit die Brennraumwandtemperatur steigert und
• • eine Zahnradpumpe (2) sicherstellt, dass auch durch den Kabinenwärmetauscher ein geringer Kühlmitteldurchfluss vorliegt und eine Kühlwassertemperaturdifferenz zwischen Ein- und Austritt von mehr als 25 K vorliegt und
• • ein hocheffizienter Kabinenwärmetauscher 4, mit mehr als 75% Wirkungsgrad bei 25 K Kühlwassertemperaturdifferenz Verwendung findet und
• • mittels der Motorsteuerung 20 hohe EGR-Raten eingestellt werden und
• • mittels der Motorsteuerung 20 der Einspritzzeitpunkt der ersten Kraftstoffeinspritzung anhand eines Kennfeldes für den Zündverzug unter zusätzlicher Berücksichtigung der Kühlmitteldurchflussabhängigkeit der momentanen Brenngastemperatur in Richtung früh verstellt wird und
• • mittels der Motorsteuerung der Einspritzzeitpunkt der letzten Kraftstoffeinspritzung anhand eines Kennfeldes für den Zündverzug unter zusätzlicher Berücksichtigung der kühlmitteldurchflussabhängigen momentanen Brenngastemperatur in Richtung spät verstellt wird.

If, for example, there is an increased waste heat requirement with a high cabin heating requirement, this is the case with the example configuration of the circuit according to 4 with concrete hardware particularly advantageous that

• • an actuator (6b) in addition to the standard series thermostat 6 the coolant flow reduced by the engine and thus the combustion chamber wall temperature increases and
• • a gear pump (2) ensures that there is also a low coolant flow rate through the cabin heat exchanger and that there is a cooling water temperature difference of more than 25 K between the inlet and outlet and
• • a highly efficient cabin heat exchanger 4, with more than 75% efficiency at 25 K cooling water temperature difference is used and
• • high EGR rates are set by means of the engine control 20 and
• • The injection timing of the first fuel injection is advanced by means of the engine controller 20 based on a map for the ignition delay, also taking into account the coolant flow dependency of the instantaneous combustion gas temperature and
• • The injection timing of the last fuel injection is retarded by means of the engine control using a map for the ignition delay, also taking into account the coolant flow-dependent instantaneous combustion gas temperature.

The variant "too early and too late" is selected specifically for the engine in order to achieve a very high heat input on the one hand and to keep noise development within limits on the other. From a purely energetic point of view, the "too early" variant is a little cheaper here, but the slightly higher EGR temperature of the "too early and too late" variant is used in the application shown to preheat the combustion air and thus expand the variation range. If the need for additional heating is reduced, it may also be advantageous with this engine to switch to the “too early” variant in order to save fuel. There are also combustion engines with reduced EGR compatibility, where the "too early" variant is also of particular interest.
In all control variants, the extent of the adjustment is preferably additionally monitored or limited by means of a smooth-running control.

By using these special possibilities of artificially increasing the fuel consumption to support the cabin heating effect, the temporal control strategy with regard to the set fuel consumption is in accordance with it
7 advantageous.
For an idling point, ie the engine friction power and the electrical consumers define the fuel consumption, the solid line shows measurement data for the fuel consumption curve over time. The actually required additional burner with 5KW heat output was deactivated. The dashed line shows an exemplary course of the fuel consumption, as provided by the method according to the invention. After a few seconds of largely identical fuel consumption, the injection is adjusted according to the invention in this exemplary embodiment. Since the frictional loss is still very high at this point in time, a positive gradient in the development of fuel consumption over time can even be temporarily achieved with the process control according to the invention by gradually adjusting the injection and the build-up effects already described in detail, despite a sharp drop in frictional loss. In the given case, this is stabilized at around 19 kW in interaction with the increasing average system temperature. As given the example in 6 already to be expected, a very significant adjustment of the injection in the direction "too early and too late" is required here. Measures to advance to such extreme values in passenger car diesel engines have already been described. The basic rule here is that near-idling operation at extremely high fuel consumption levels of e.g. 19 kW at approx. 900 rpm is made considerably more difficult by means of measures on the engine control system due to the decrease in engine friction over time and can often only be maintained for the first 3-5 minutes . In the example shown according to 7 The fuel quantity that can be converted therefore falls below 19 kW again after about 3 minutes. Last but not least, it is very important to start adjusting the combustion according to the invention as early as possible, with a strong reduction in the coolant mass flow. Although a volume flow rate close to zero would be most favorable for adjusting the combustion, the cabin heating requires its share of heat output immediately after the start, and doing without during the first few minutes is unthinkable, not least for safety reasons. Therefore, the simultaneous integration of a highly efficient cabin heat exchanger, with high efficiencies at low coolant flow, makes the method according to the invention particularly effective for use in passenger cars.

In 7 After approx. 4-5 minutes, a sufficient coolant flow temperature is reached at the cabin heat exchanger so that the additional engine-internal measure can be deactivated. Given the still low coolant throughput through the engine, fuel consumption now falls well below the baseline with conventional coolant throughput. Compared to the differences in fuel consumption with different coolant throughputs previously known from publications on hot cooling, it is noticeable that the consumption advantage of the method according to the invention is relatively large here. This is because that the basis is still at a relatively low temperature level even after a long period of operation due to the low engine load with high heat extraction for the cabin. The strongly progressive increase in friction with decreasing oil or cylinder wall temperature is only one of the reasons for this difference. Another effect that should not be neglected results from the process-related advantage that, with a higher coolant flow temperature, it is also possible to work with a lower fresh air mass flow through the cabin heat exchanger, which not only improves its efficiency but also saves additional heat losses to the environment. This is also urgently needed in order to heat the cabin sufficiently given the steady-state fuel consumption shown.

The integration of the time curves of the fuel curves makes it particularly clear that the duration of the journey has a decisive influence on whether a procedure according to the dashed line according to the invention is more favorable for the respective journey or the basis according to the solid line. The additional output of the burner must be included in the base.

A further deepening of the interactions would go too far at this point, but the exemplary character of the above explanations should be based on the configuration according to 4 be clear. In particular, the explicit naming of specific consumption target values - in 7 Extreme values were deliberately used that are not required in many applications - and the naming of specific hardware is only to be seen as an example. Especially in the case of engines without a bypass branch 6b, the valve 6b can of course also be omitted, or the valve 6b can be implemented in a functional unit with an electric valve 6, which replaces the thermostat.

The advantages that can be achieved by using external electric heating of the combustion air, in particular for the additional extension of the combustion adjustment range with simultaneous elimination of the engine-internal glow plugs for pre- and after-glowing, have already been described.
For this purpose, low-cost external auxiliary heating components are of particular interest, which are characterized by low costs, quick response and the possibility of continuous operation. The preheating of the exhaust gas or the air by means of directly electrically heated resistance heating wires offers these features. To simplify production, heating resistance wires made of flat wire, in particular made of corrosion-resistant steel or anodized aluminum, are preferably used.

In one variant, which is particularly attractive in terms of size and rapid response, the flat wire consists of aluminum sheeting which, to improve heat transfer, has a large number of oblique cuts perpendicular to the air flow, the so-called louvres 42a and 42b
8th , is provided.
In particular, aluminum ribs that are already available from car heating heat exchanger construction can be used as the base material. Here, the stacking of zigzag bands 41 known from heating heat exchanger construction is preferably used for the aluminum sheet, with intermediate layers of electrically insulated separating sheets 40 being used instead of the heat exchanger tubes. Anodized aluminum tape is a particularly cost-effective and robust solution with the interposition of an insulating tape. The zigzag tape is preferably wound up, resulting in a round or oval outer geometry. This simplifies the integration of the electric heater into the pipes of the air or EGR distribution system, where, as is well known, predominantly round and oval cross-section geometries are used. The electrical contact is preferably made on the outside of the outer cladding tube, so that the anodized aluminum surfaces can also be routed through a metal jacket without additional effort.

Especially when aluminum is used as the heating resistor, it is particularly advantageous to manufacture the heating ribs 41 from anodized aluminum, in which case the anodized layer is used for electrical insulation. Anodized aluminum has the additional advantage that the anodized layer represents very good protection against corrosion.
The design with regard to the thickness of the anodized layer depends not least on the required material thickness in order to ensure sufficient strength and durability in the pulsating flow in the EGR branch or in the intake duct, without making the required construction volume too large.
The good electrical conductivity of aluminum is initially a hindrance here, since either the material thicknesses are too thin and therefore too sensitive, or the construction volume is very large due to the required wire length. Against this background, known heating flanges for truck diesel engines work with conventional heating conductor materials which have a significantly higher specific electrical resistance. In addition to the increased material price, these materials are partly closed to the use of the heating fin design from cabin heating heat exchanger construction with the so-called Louvres, which is preferred for reasons of efficiency with regard to heat transfer and heat-active mass.

Especially the good heat transfer of the heating fins according to 8th allows per surface very transfer high el. Heat output to the gas to be heated. Against this background, in order to maximize the specific heating output per surface, it is particularly advantageous to manufacture the heating fins from anodized aluminum, in which the thickness of the anodized layer is used to adjust the flexural rigidity and/or the application-specific electrical output per heating surface, and in particular that the thickness of the anodized layer is greater than half the thickness of the metal layer. With good flexural rigidity, this results in a very high specific output with a small installation space and low pressure loss. If, for example, aluminum with a base thickness of 70 µm is anodized as the starting material and provided with an anodized layer of approx. 25 µm on both sides, a conductive metal layer of 20 µm remains. The use of non-anodized base material of 20 µm in order to achieve the same output per area would be difficult to handle in production on the one hand, and on the other hand it would also be very sensitive to vibration and corrosion during operation.

A high electrical power per surface is particularly important to achieve rapid heating of the air. The high output per surface leads to a minimization of the masses to be heated, but also to the fact that the heat-active masses to be heated reach the state of equilibrium between the electrical power supplied and the heat output emitted even at a lower material temperature.
Against this background, the Louvres in particular are of particular importance for maximizing the heat transfer per material used. This applies both to anodized aluminum and to non-anodized materials, especially when using conventional stainless steel, which is also significantly cheaper than known heating resistance materials, eg based on CuNi or NiCr. In this context, the highly efficient design with Louvres helps in particular to ensure that the not-so-low temperature gradient of the electrical resistance of aluminum or stainless steel does not lead to durability problems in view of local overheating: the relatively low excess temperature for providing the required temperature gradient for heat transfer increases the safety reserves considerably , so that the increase in resistance due to the global warming of all heating wire zones compared to the local heating of zones with increased thermal stress, in particular due to reduced local flow around it, causes a reduction in the wire sensitivity to overheating via the increase in total resistance. In addition, this increase in resistance with wire temperature is preferably used for temperature monitoring or regulation. In other words, the use of the Louvres in particular provides the optimal robustness of the electric heating system, which allows it to get close to the permissible material temperatures. When using conventional heating conductors, this means in particular a minimization of the heat-active mass, with conventional metals such as aluminum or stainless steel both the heat-active mass and the robustness against local overheating are significantly improved.

For installation situations in which a low heat-active mass and/or the installation space is less important, existing designs from heating construction can also be used.
Due to the availability and years of proven use in PTC auxiliary heaters for the cabin air, the preheating of the exhaust gas or the air using electrically heated PTC heating ceramics can also be successfully adapted here, which are at least partially encased and transfer the energy to the outer heating fins by heat conduction.
In contrast to electric cabin heating, a conventional heating resistor can also be used instead of the intrinsically safe PTC ceramic due to the special application in the intake manifold or in the EGR branch, with a basically available monitoring of the air and EGR mass flow by means of the engine control . Here, too, anodized aluminum sheet, which is clamped between the cooling fins instead of the PTC ceramic, is a very cost-effective and robust solution.

The potential to replace the glow plugs in passenger car diesel engines with an external electric heating of the combustion air optimized in the direction of low thermal inertia has already been outlined. It should be clear that in modern cars only preheating times in the range of seconds are still salable. Hence the efforts specific to the invention to provide the fastest possible electrical heating. The effort required to bring the external heater to the stationary final temperature as quickly as a glow plug in the combustion chamber is not inconsiderable. This applies in particular to the glow plugs with PWM control that are now available, which heat up in a matter of seconds and are then kept at the target temperature using PWM. In addition, there is the air volume between the external heater and the combustion chamber, which must first be emptied and then filled with heated air.
The almost exclusive use of direct-injection combustion processes and the high injection pressures of modern injection systems, in conjunction with a very high atomization quality and very fine dosing with multiple injections, help in this context that passenger car diesel engines no longer actually need preheating to start when the ambient temperature is not too low . The glow plugs serve here rather the improvement of the combustion quality during warm-up. However, the external electric heater according to the invention can be implemented with moderate effort specifically to support the warm-up and is additionally supported by the reduced coolant flow. From this follows the possibility, especially for customers who are willing to put up with some pre-heating time at high minus temperatures, to realize significant cost savings through particularly inexpensive versions of the external electric pre-heating of the combustion air. In particular, such systems are less expensive than systems with engine-internal glow plugs, not to mention the additional cost advantages, in particular due to the elimination of external cabin heating by means of PTC or burners.

• Wie in 7 exemplarisch gezeigt, erfolgt die Verstellung der Verbrennung bevorzugt erst, nachdem zunächst ein ganz normaler Start erfolgt ist. Dadurch ist sichergestellt, dass der Motor sicher hochläuft und insbesondere die Motorsteuerung mittels der üblichen Überwachung der wichtigsten Betriebsparameter verifiziert hat, dass alle Systeme arbeiten und nicht eine eingeschränkte Funktion bezüglich wichtiger Regelparameter vorliegt. Ist eine el. Heizung mit hoher Leistung installiert und diese hohe el. Leistung auch verfügbar, so wird diese bevorzugt von Anfang an abgerufen, um den Warmlauf zu unterstützen.

However, the process variant according to the invention with external electrical heating is also suitable for applications in which the specific boundary conditions, in particular the characteristics of the combustion process used or particularly extreme requirements with regard to the quick start properties at high sub-zero temperatures, mean that the engine-internal glow plug should not be dispensed with Combustion air is still of great benefit given the remaining benefits:

• As in 7 shown as an example, the combustion is preferably only adjusted after a completely normal start has taken place. This ensures that the engine runs up safely and, in particular, that the engine control has verified by means of the usual monitoring of the most important operating parameters that all systems are working and that there is no restricted function with regard to important control parameters. If an electric heater with a high output is installed and this high electric output is also available, it is preferably used from the start to support the warm-up.

In many cases, however, there is not enough electrical power available, particularly when the vehicle electrical system is heavily loaded with auxiliary consumers or when the battery is weak. In the extreme case, this can mean that without the electrical energy available in the normal state, a transition to the operation according to the invention with a very strong adjustment of the injection in the direction of increased fuel consumption is also not possible. Compared to the direct PTC auxiliary heater in the cabin air mass flow, this still does not represent a deterioration, since it cannot be operated under such boundary conditions, but this is only an unsatisfactory situation for the driver. If the measure for temporarily increasing waste heat is also emission-relevant, e.g. for burning the diesel filter free, then, in addition to the loss of comfort, durability aspects and the risk of violating exhaust gas laws quickly come into play.

For these operating conditions, it is proposed as a further refinement of the method according to the invention to heat the device 30 for the external electrical heating of the combustion air but not or only very little gas to flow through it, for example by deactivating the exhaust gas recirculation so that the electrical Heating device heats up to a high temperature and to initiate the inventive method only after heating. The stored amount of heat is then suddenly available, for example by activating the exhaust gas recirculation, and thus allows a very far-reaching adjustment of the combustion. How based 6 becomes clear, a very large amount of heat can be generated suddenly, with the exhaust gas temperature also increasing at the same time. The rising exhaust gas temperature gradually compensates for the drop in the amount of heat available at the electric heating device. In this way, it is possible to get into the area of greatly increased waste heat despite the limited electrical output. Without this refinement, it is possible under comparable boundary conditions, at best by accepting transient phases of increased combustion noise, to convert the critical amount of additional heat in order to initiate full adjustment of the combustion with limited electrical power.

In principle, this procedure is possible during the warm-up and is particularly advantageous in order to keep the costs for the electrical heating and the associated system components low.
However, this process variant with transient use of the external electrical heating of the combustion air is also of particular interest for applications that want to generate a high level of waste heat when the engine is partially or completely heated and thus with relatively low friction. Even if, for example, only 10A can be provided in the 12V on-board voltage network for the electrical heating, it is ultimately possible to advance into areas of very high adjustment of the fuel conversion, as is the case with permanent gas flow through the electrical auxiliary heating only with a multiple of the electrical current, ie eg 100A instead of 10A, would be possible.

The measures according to the invention, which are aimed in particular at driving situations in passenger cars with highly efficient TDI engines with a waste heat deficit, are in the case of additional external el. Preheating of the combustion air in competition with the basic possibility of ultramodern passenger car diesel engines, in connection with the other features of the method according to the invention to achieve sufficient adjustment potential even without the electrical preheating.

6 Using the values for the fuel consumption and the gas temperatures as a function of the start of combustion, which can be seen in particular in connection with the associated values for the pressure and for the ignition delay significantly influenced by pressure and temperature, shows that the method according to the invention in particular proposes all the usual limits of today's passenger car TDI diesel engines with regard to the adjustment of the start of combustion at low engine speeds and loads.
This would only be possible to a very limited extent without the specific reduction in coolant throughput and sometimes also without the transient methods for transitioning from normal operation to operation with extreme adjustment. In particular, the external electric heating helps to meet even the most extreme requirements. Especially in comparison to the procedure described, using several very short and very early injections or combustions to raise the temperature and pressure level of the second and, if necessary, third and fourth injection and thus to minimize the combustion noise, the external electrical heating remains in relation to maximization advantage of waste heat. On the one hand, this is due to the fact that the fuel conversion of the individual injections can be selected to be higher with the same noise level, so that the conversion takes place earlier on average over time. What is also very important is the fact that the heating of the fuel gas by means of the first combustion always contributes to the torque of the engine, despite the considerable wall heat losses in the case of early injection. However, this is precisely what is not desired in the case of a waste heat deficit and limits the potential for variation with regard to the fuel energy that can be converted. The same applies to the variant with multiple late injections, where the heat balance with regard to the engine's internal heating is even worse. In contrast, the electrical heating takes place outside the combustion chamber and does not contribute to the engine torque. On the contrary, the increased electrical load even increases the motor torque and in this way leads to an additional expansion of the realizable waste heat.
Against this background, it should be noted that the economic importance of the method according to the invention and the associated components extends to vehicles with and without external electrical heating of the combustion air and not least depends on the extent of the heat deficit.

Claims (12)

Method for operating a cooling and heating circuit for motor vehicles with an internal combustion engine (1) cooled by coolant and with adjustment devices that can be influenced by an engine control (20) for varying the combustion process within the internal combustion engine (1), characterized in that in operation with an increased waste heat requirement a reduced coolant throughput through the internal combustion engine (1) is set in the direction of limit values permissible for safe engine operation and the fuel consumption of the internal combustion engine (1) is temporarily artificially increased by adjusting fuel conversion in the direction of crankshaft settings with an increased combustion chamber volume, with the increase in waste heat takes place primarily to increase the exhaust gas temperature, is used without considering the heating and is used with a coolant throughput through the internal combustion engine (1) close to zero. procedure after claim 1 , characterized in that the waste heat is not increased for the purpose of providing satisfactory heating comfort. Procedure according to one of Claims 1 - 2 , characterized in that an external exhaust gas recirculation (13, 11, 12) is provided and activated. Procedure according to one of Claims 1 - 3 , characterized in that the internal combustion engine (1) supplied fresh air (10) is additionally electrically heated (30). Procedure according to one of Claims 1 - 4 , characterized in that a point in time of the fuel conversion is determined by a point in time of injection of the fuel. Procedure according to one of Claims 1 - 5 , characterized in that an injection is shifted in such a late direction that it begins after top dead center of the compression stroke. Procedure according to one of Claims 1 - 4 , characterized in that the internal combustion engine (1) is an Otto engine. Internal combustion engine (1) for motor vehicles with a cooling and heating circuit with a in the engine control (20) and stored by the Engine control (20) controlled method according to one of Claims 1 - 7 . Motor vehicle with an internal combustion engine (1). claim 8 . Device for operating a cooling and heating circuit for motor vehicles with an internal combustion engine (1) cooled by coolant, the coolant of which is conveyed by a coolant pump (7, 2) to a heating heat exchanger (4) for the cabin and finally back to the internal combustion engine (1), with adjustment devices influenced by an engine controller for varying the combustion process within the internal combustion engine, characterized in that the fuel consumption of the internal combustion engine is artificially increased when there is an increased waste heat requirement in that a reduction in the Coolant throughput through the internal combustion engine takes place in the direction of the limit values permissible for safe engine operation and that at the same time there is an adjustment in the fuel conversion in the direction of crankshaft positions with an increased combustion chamber volume, with the increase in waste heat primarily taking place to increase the exhaust gas temperature and without taking the heating into account. device after claim 10 , characterized in that with a coolant flow rate through the internal combustion engine (1) is close to zero. Device according to one of Claims 10 - 11 , characterized in that the waste heat is not increased for the purpose of providing satisfactory heating comfort.

Images