WO2003106825A1 - Method for operating a liquid-cooled internal combustion engine - Google Patents

Abstract

The coolant is circulated inside a closed coolant circuit by means of a coolant pump (11). According to a variable (TKW) characterising the temperature of the internal combustion engine (10), a modulator (12) enables the coolant means volume flow of a first coolant circuit (15, 16, 22, 23), which is connected to a coolant inlet (24) and a coolant outlet (14) of the internal combustion engine (10), to be switched to a second coolant circuit (15, 21, 22, 23) comprising a cooling element (18) of the internal combustion engine (10). According to the said variable (TKW), the coolant volume flow can be divided at the coolant outlet (14) of the internal combustion engine (10) into a first coolant volume flow (15, 16, 22, 23) in the first coolant circuit (15, 16, 22, 23) and into a second coolant volume flow in a bypass (30) containing at least one oil coolant heat exchanger (31).

Description

description

Method for operating a liquid-cooled internal combustion engine

The invention relates to a method for operating a liquid-cooled internal combustion engine according to the preamble of patent claim 1.

The operating behavior of internal combustion engines is significantly influenced by their operating temperature. Reaching the operating temperature quickly not only has a positive effect on the emission behavior and fuel consumption, but also on the comfort of the occupants with regard to rapid heating of the vehicle interior of the vehicle driven by the internal combustion engine.

Depending on the driving condition, ambient conditions, driving behavior, etc., a more or less long warm-up phase can be observed in every internal combustion engine. Design measures such as minimizing the internal cooling circuit volume, reducing the amount of engine oil or additional measures such as electrical or fossil coolant heaters can reduce the time until the operating temperature is reached.

On the other hand, when the fuel-air mixture is burned, peak temperatures of more than 2000 ° C. occur locally in the combustion chamber of an internal combustion engine. To prevent thermal overload of the materials used for the cylinder head,

To prevent valves, spark plugs, injection valve, cylinders, pistons, piston rings, seals, etc., cooling must be carried out. Forced cooling by means of a coolant has largely prevailed. The cylinder and cylinder head are double-walled. The intermediate space is filled with a cooling liquid and designed so that a coolant circuit is created. As a coolant a mixture of water, antifreeze and case-specific inhibitors.

Such conventional cooling systems usually include one either directly or indirectly via a movable traction means, e.g. V-belt coolant pump driven by the internal combustion engine and an expansion thermostat. The coolant pump therefore works in dependence on the engine speed and is designed in such a way that a sufficient coolant flow is made available in every operating state of the internal combustion engine. The coolant temperature is regulated in order to maintain a constant coolant temperature and thus also the internal combustion engine temperature. For this purpose, a temperature-dependent expansion regulator is provided, which actuates a valve which, when the coolant temperature drops, leads an increasing coolant flow past the cooler. Expansion regulator and valve form a structural unit and are generally referred to as a radiator thermostat.

Starting from the cold operating state of the internal combustion engine, the radiator thermostat is initially closed and the coolant circulation takes place exclusively in a bypass circuit of the internal combustion engine. This is also known as a "small cooling circuit". Above a certain coolant temperature, the cooler thermostat opens and the coolant flow flows to the cooler, where it is cooled due to the head wind and / or the cooler fan and returned to the internal combustion engine. This is also known as a "large cooling circuit".

From MTZ Motortechnische Zeitschrift 57 (1996) Issue 7/8, pages 424-428, a characteristic-controlled temperature control system for engine cooling circuits is known, in which an electrically controllable thermostatic valve is used. In contrast to a thermostatic valve in the design of a coolant thermostat insert without auxiliary energy, the control and regulating element is used in addition to the detection of the current one Coolant temperature provided the possibility of supplying electrical energy. This energy is introduced directly into the temperature-sensitive expansion material via an electrical resistance in the form of heat. This simulates a higher coolant temperature level for the control and actuating element, from which a temperature map can be generated. Appropriate control makes it possible to assign each operating point to the coolant temperature within this temperature field. This enables a thermally optimal operating point of the internal combustion engine to be set.

DE 32 38 919 AI describes a method and a device for operating a liquid-cooled internal combustion engine. After switching off the internal combustion engine, whose cylinder block with channels is provided for a circulation of coolant, the warm coolant is transported to an insulated reservoir. Before the internal combustion engine is started again, the warmed coolant is conducted from the reservoir back into the channels of the cylinder block, so that the cylinder block warms up before starting. For this purpose, an electrically driven coolant pump is provided, with which the coolant is pumped out of the channels of the cylinder block to the reservoir and back again. The reservoir is divided by a reciprocating piston into two chambers, each of which is connected to an associated end of the cooling channels of the cylinder block by a line. The coolant pump, which can be switched electrically with regard to its pumping direction, is interposed in one of the lines.

EP 01 101 914 A2 discloses a liquid-cooled internal combustion engine with a crankcase, at least one cylinder head, an exhaust gas manifold, an exhaust gas turbocharger, a charge air heat exchanger and a raw water heat exchanger, which together with a coolant pump to form a cooling middle circuit are interconnected. The coolant circuit in the flow direction behind the coolant pump is divided into an engine cooling circuit by the internal combustion engine with the crankcase and the cylinder head, an exhaust gas circuit with the exhaust gas collector pipe and the exhaust gas turbocharger, and a heat exchanger circuit with the charge air heat exchanger and the raw water heat exchanger in a parallel arrangement, these circles are brought together again before the coolant pump. A gear oil heat exchanger can also be connected in parallel with the charge air heat exchanger.

DE 196 37 817 AI describes a device for cooling and preheating, in particular gear oil in internal combustion engines for vehicles, with an expansion tank, with at least one water cooler which can be switched on by means of a motor thermostat when a predetermined temperature is reached in the cooling circuit and with a single one Water / oil heat exchanger, which can be used both for heating and for cooling operating materials, especially gear oil. The flow rate of the water / oil heat exchanger is in the

Heating phase can be branched off from the main cooling circuit of the internal combustion engine by means of a valve unit. In the cooling phase, the supply flow is taken from the low-temperature range of the water cooler by means of the same valve unit in the secondary coolant flow.

The invention is based on the object of specifying a method for operating a liquid-cooled internal combustion engine with which rapid heating of both the internal combustion engine itself and of operating materials of the internal combustion engine, in particular engine oil and / or transmission oil, can be achieved.

This object is achieved by the invention characterized in the independent claim. If necessary, the coolant is circulated within a closed coolant circuit by means of a coolant pump. Depending on a variable characterizing the temperature of the internal combustion engine, the coolant volume flow can be switched from a first coolant circuit connecting a coolant inlet and a coolant outlet of the internal combustion engine to a second coolant circuit containing a cooler of the internal combustion engine by means of an actuator. At the coolant outlet of the internal combustion engine, depending on the size, the coolant volume flow can be divided into a first coolant volume flow in the first coolant circuit and a second coolant volume flow into a bypass containing at least one oil / coolant heat exchanger.

As a result, after a cold start of the internal combustion engine has been recognized, the actuator can be actuated in such a way that the coolant volume flow is passed exclusively via the bypass containing oil / coolant heat exchanger, which leads to rapid heating of the operating materials such as engine oil and / or gear oil and / or hydraulic oil ,

A particularly rapid heating of the internal combustion engine and, consequently, of the operating materials results if, based on cold start conditions of the internal combustion engine, there is initially no circulation of the coolant, with the result that the relatively small coolant volume located in the cooling jacket of the internal combustion engine heats up very quickly.

According to a development of the invention, this is achieved by using an electrically driven coolant pump which is switched off at this operating point of the internal combustion engine.

Alternatively, however, a coolant pump mechanically driven by the internal combustion engine can also be used , it only has to be ensured that it can be uncoupled, for example, by means of a gear.

If a certain threshold temperature is exceeded, the warmed up coolant is passed through a bypass in which an oil / coolant heat exchanger is switched on. This leads to rapid heating of the operating fluids engine oil, gear oil, hydraulic oil and thus to an earlier reaching of the internal combustion engine temperature.

If an electric coolant pump is used, a coolant volume flow through the oil-coolant heat exchanger can be set, in which an optimal heat transfer in the oil-coolant heat exchanger is established.

The method according to the invention leads to a partially faster heating of the coolant and indirectly to a faster heating of the operating materials supplied to the oil-coolant heat exchanger, such as, for example, engine oil. Due to the lower oil viscosity, which is lower at higher temperatures, fuel consumption is reduced and more favorable emission behavior can also be observed.

Further advantageous embodiments of the invention are the subject of further dependent claims.

The invention is explained in more detail below with reference to the drawing using an exemplary embodiment.

It shows:

1 is a schematic representation of a coolant circuit of an internal combustion engine during a cold start,

Fig. 2 shows a schematic representation of a coolant circuit during the warm-up of the internal combustion engine and Fig. 3 shows a schematic representation of a coolant circuit when the internal combustion engine is at operating temperature.

All figures have in common that only the components necessary for understanding the invention are shown. In particular, the heating heat exchanger and the coolant expansion tank, which are used to heat a vehicle interior, and the associated line branches are omitted. The path of the coolant volume flow within the coolant circuit is shown with arrow symbols.

The same components are provided with the same reference symbols in all figures and are usually only explained once.

The coolant circuit of the internal combustion engine 10 has a coolant pump 11, which in the exemplary embodiment shown is designed as an electrically driven coolant pump. In particular, a coolant pump that is reversible with regard to its pumping direction can also be used, for example, and the speed of rotation can also be regulated. In a simpler embodiment of the invention, the coolant pump is designed as a pump mechanically driven by the internal combustion engine. In a preferred one

In this embodiment, the drive of this mechanical coolant pump can be decoupled from the internal combustion engine by means of a device, for example a clutch, and its pumping direction can be reversed, for example, by means of a gear.

Instead of the conventional radiator thermostat, an electrically controllable actuator 12 is provided in the form of a 3/2 way valve. This actuator has three connections I, II, III, in the following the connections I and II are also referred to as inputs and the connection III also as an output. By appropriate control of the The coolant volume flow can be divided according to the operating range of the internal combustion engine 10, as will be explained in more detail later.

The internal combustion engine 10 has one, not shown

Cooling jacket around the cylinder 13 and the coolant pump 11 conveys the coolant into the cooling jacket around the cylinder 13, it flushes around it and reaches the cylinder head through through bores. At the cylinder head of the internal combustion engine 10, a coolant outlet 14 is provided, to which a line 15 is connected. The line 15 leads to a coolant inlet 17 of a cooler 18. In the cooler 18, the waste heat generated in the internal combustion engine 10 is dissipated to the surroundings via the coolant. In order to achieve high cooling capacities even at low vehicle speeds, at least one electrically driven fan 19 is additionally provided. The fan 19 is generally switched on or off in a temperature-controlled manner.

A coolant outlet 20 of the cooler 18 is connected via a line 21 to the input I of the actuator 12. In the line 15, which connects the coolant outlet 14 on the engine side to the coolant inlet 17 on the cooler 18, a branch is provided for a bypass line 16, which leads to the input II of the actuator 12. The output III of the actuator 12 is connected via a line 23 to an inlet (suction side) of the coolant pump 11, which is not specified. The outlet (pump side) of the coolant pump 11 is connected via a line 22 to an engine-side coolant inlet 24.

A bypass line 30 branches off from the line 15 in the vicinity of the engine-specific coolant outlet 14 and opens into the line 23, which connects the actuator 12 to the suction side of the coolant pump 11. In the bypass line 30 there is an oil-coolant heat exchanger 31, each with a coolant inlet 32 and a coolant outlet 33, as well as an inlet leave on 34 and an outlet 35 for the oil to be heated. The oil to be heated is preferably the lubricating oil (engine oil) of the internal combustion engine 10 or the gear oil, a gearbox connected to the internal combustion engine 10 for gear selection. Hydraulic oils, for example for servo pumps, can also be heated by the coolant in the oil-coolant heat exchanger 31. The oil-coolant heat exchanger 31 is arranged in the vicinity of the Brerin engine in order to keep the line length and thus the volumes of the coolant to be transported to the oil-coolant heat exchanger 31 small.

The oil-coolant heat exchanger 31 can also be designed such that there are several inlets and outlets for different fluids to be heated, for example engine oil and transmission oil, each of which absorbs part of the heat of the coolant in separate chambers.

Furthermore, it is possible for a plurality of separate oil-coolant heat exchangers to be connected in series or in parallel in the bypass, one oil-coolant heat exchanger for the engine oil and another oil-coolant heat exchanger for the transmission oil, for example.

In order to set the coolant volume flow through the internal combustion engine 10 by means of appropriate control by means of electrical signals, the actuator 12 is connected to a control device 26 via a control line 25. Such electronic control devices, which as a rule contain one or more microprocessors and a time counter 29 and which, in addition to fuel injection, also take on a large number of other control and regulating tasks for the internal combustion engine 10, are known per se, so that in the following only the related the relevant structure and its mode of operation are discussed. A temperature sensor 27 on the coolant outlet 14 on the engine side supplies a signal TKW corresponding to the temperature of the coolant at the engine's own outlet to the control device 26 for the actuation of the actuator 12 as required designated, fed. The individual actuators and components that are necessary for operating the internal combustion engine 10 are controlled via output signals AS.

The electrical coolant pump 11 and the fan 19 are likewise connected to the control device 26 via control lines.

Furthermore, the control device 26 is connected to a memory 28, in which, among other things, predetermined threshold values SW1-SW4 for the temperature of the coolant TKW are stored. .

With reference to FIG. 1, it is now explained how the coolant volume flow is set when the internal combustion engine 10 is cold started, so that, in addition to rapid heating of the internal combustion engine, the engine oil and / or the transmission oil can be heated as quickly as possible.

The signal TKW of the temperature sensor 27 is read in at the start of the internal combustion engine 10 and compared with a predetermined threshold value SW1, which characterizes a cold internal combustion engine and is stored in the memory 28. If the value of the coolant temperature is below this threshold value SW1, a cold start of the internal combustion engine is concluded and the actuator 12 is controlled by an electrical signal from the control device 26 such that the connection between the input I and the

Exit III, as well as between the entrance II and the exit III is interrupted. The position of a rotary valve associated with the actuator 12 is shown schematically.

With the help of the coolant pump 11, a coolant flow through the cooling jacket of the internal combustion engine 10 and through the bypass 30 and thus through the oil-coolant heat exchanger 31 in the direction indicated by arrow symbols is possible due to this position. This results in rapid heating of the oil, which in turn leads to the operating temperature of the internal combustion engine 10 being reached early.

Even faster heating of the internal combustion engine 10 can be achieved if the circulation of the coolant is completely interrupted for a certain period of time when the internal combustion engine 10 is cold started.

This can be achieved, for example, in the case of a coolant pump mechanically driven by the internal combustion engine, by providing a switchable clutch. In cooling systems with an electrically driven coolant pump, the cooling circuit can be interrupted in a simple manner by switching off the electric motor of the coolant pump. Since the coolant is no longer circulating here, one speaks of a "standing coolant". As a result, the small volume of coolant contained in the cooling jacket of the internal combustion engine 10 heats up very quickly. After the predetermined period of time determined by tests has elapsed, the coolant pump is switched on and the heated coolant flows via the bypass 30 and thus to the oil / coolant heat exchanger 31.

A further possibility of achieving particularly rapid heating of the internal combustion engine 10 and, as a result, rapid heating of the oil, is to use an electrical coolant pump which is reversible with regard to its pumping direction. Such a coolant pump will be recognized of a cold start of the internal combustion engine for a period of time T _in such a way that a coolant volume flow flows via line 22, the cooling jacket of internal combustion engine 10 to the location of temperature sensor 27. The time period T _before , during which the coolant pump 11 is activated so that a coolant flow takes place up to the location of the temperature sensor 27, is determined experimentally for the internal combustion engine 10 in question. It essentially depends on the structural design of the internal combustion engine, in particular on the mass, the number of cylinders and the dimensioning of the cooling jacket. This time period T _before is monitored by the time counter 29 of the control device 26 and is generally in the range of seconds.

After the time period T _before , the coolant pump 11 is deactivated again. The signal from the temperature sensor 27 is constantly read in and compared with a further threshold value SW2, which characterizes a warm internal combustion engine.

If the currently detected value TKW of the coolant temperature is below this threshold value SW2, the coolant pump 11 is reactivated after a further period of time T ^ ait, which is also determined experimentally. However, the coolant pump is now controlled in such a way that the coolant is now conveyed in the opposite direction by the internal combustion engine 10. The time period T _ruc k; during which the coolant pump 11 pumps the coolant 11 in the opposite direction is preferably identical to the above-mentioned time period T _before .

These two pump cycles are repeated until the signal TKW of the temperature sensor 27 reaches the threshold value SW2. If this is the case, the coolant pump 11 is activated in such a way that a continuous coolant flow in the direction shown by arrow symbols takes place via the bypass 30 and the oil-coolant heat exchanger 31. gives. The slide of the control valve 12 is in the position already described above.

The use of an electrical coolant pump that is adjustable in speed also has the advantage that it can be used to set a coolant volume flow in which there is an optimal heat transfer between coolant and oil in the oil-coolant heat exchanger 31.

FIG. 2 shows a schematic representation of the coolant circuit while the internal combustion engine is warming up. If the temperature TKW exceeds a further threshold value SW3, by actuating the actuator 12, the input II is connected to the output III, so that a coolant volume flow both via the bypass 30 and the oil / coolant heat exchanger 31, and also via the small coolant circuit, i.e. can flow through the bypass 16. The coolant pump 11 is controlled in such a way that a continuous coolant volume flow can circulate in a single direction.

If the operating temperature of the internal combustion engine 10 is reached (exceeding a further threshold value SW4), the input I is connected to the output III by actuating the actuator 12, so that a coolant volume flow through both the bypass 30 and the oil-coolant heat exchanger 31 as also via the large coolant circuit, d. H. can flow through the cooler 18. As a result, heat is emitted in the cooler 18, as a result of which overheating of the internal combustion engine 10 is avoided even at full load. The bypass line 16 is switched off, i.e. there is no connection between the input II and the output III of the actuator 12 (FIG. 3). The direction of the coolant volume flow is again drawn with arrow symbols.

Instead of the electrically controlled actuator 12, a temperature-controlled switching valve in the form of a Thermostatic valve can be used. It is only crucial that both the small and the large cooling circuit can be shut off.

Claims

claims 1. Method for operating a liquid-cooled internal combustion engine (10), in which - If necessary, the coolant is circulated within a closed coolant circuit by means of a coolant pump (11), - Depending on a variable (TKW) characterizing the temperature of the internal combustion engine (10), the coolant volume flow of a first coolant circuit (15, 16, 22, 23) connecting a coolant inlet (24) and a coolant outlet (14) of the internal combustion engine (10) can be switched to a second coolant circuit (15, 21, 22, 23) containing a cooler (18) of the internal combustion engine (10) by means of an actuator (12), characterized in that - At the coolant outlet (14) of the internal combustion engine (10) in Depending on the temperature (TKW) characterizing the temperature of the internal combustion engine (TKW), the coolant volume flow into a first coolant volume flow in the first coolant circuit (15, 16, 22, 23) and into a second coolant volume flow into one, at least one oil-coolant heat exchanger (31) containing bypass (30) can be divided. 2. The method according to claim 1, characterized in that after detection of a cold start of the internal combustion engine (10), the actuator (12) is controlled such that the coolant volume flow exclusively via the bypass (30) with the at least one oil-coolant heat exchanger (31 ) is conducted. 3. The method according to claim 1, characterized in that - After detection of a cold start of the internal combustion engine (10), the coolant pump (11) remains deactivated until a predetermined threshold value (SWl) for the quantity (TKW) characterizing the temperature of the internal combustion engine (10) is exceeded, - if the threshold value (SWl) is exceeded, the actuator (12) is actuated such that the coolant volume flow is exclusively via the bypass (30 ) with the at least one oil-coolant heat exchanger (31). 4. The method according to claim 1, characterized in that after detection of a cold start of the internal combustion engine (10), the coolant pump (11) is controlled such that the coolant volume located between the coolant inlet (24) and the coolant outlet (14) alternately from the internal combustion engine (10) is pumped out and in and the alternating operation of the coolant pump (11) is ended when the variable (TKW) characterizing the temperature of the internal combustion engine (10) has reached a predetermined threshold value (SW2). 5. The method according to any one of the preceding claims, characterized in that the temperature of the coolant is used as the variable (TKW) characterizing the temperature of the internal combustion engine (10). 6. The method according to claim 5, characterized in that the temperature (TKW) of the coolant at the coolant outlet (14) is detected by means of a temperature sensor (27). 7. The method according to claim 4, characterized in that the durations (T _ago, T _r Ueck) during which the coolant pump (11) in the one and the other direction is activated, are identical. 8. The method according to claim 4, characterized in that the switching between the two pump directions only after A predetermined period of time (T _wa j_t) has elapsed. 9. The method according to claim 7 and 8, characterized in that the durations (T _ago, T _r ü _C k. ^Τ wait) experimentally depen ^¬ be determined gig of the structural design of the internal combustion engine (10). 10. The method according to claim 1, characterized in that an electrically driven coolant pump (11) is used. 11. The method according to claim 1, characterized in that a mechanically driven by the internal combustion engine (10) coolant pump (11) is used. 12. The method according to claim 4, characterized in that when the threshold value (SW2) is reached, the coolant pump (11) is controlled such that the coolant volume flow is continuously pumped in one direction. 13. The method according to claim 12, characterized in that when the threshold value (SW2) is reached, the coolant volume flow is passed exclusively via the bypass (30) with the at least one oil-coolant heat exchanger (31). 14. The method according to any one of the preceding claims, characterized in that a plurality of individual oil-coolant heat exchangers (31) are provided in the bypass (30), which are used for the individual heating of engine oil, transmission oil and hydraulic oil of the internal combustion engine (10 ) serve. 15. The method according to any one of claims 1-13, characterized in that a single oil-coolant heat exchanger (31) is provided in the bypass (30), which for the common heating of engine oil ^' and / or gear oil and / or hydraulic oil Internal combustion engine (10) is used.