Method for the temperature regulation of an engine

Abstract

The invention concerns a method for regulating the temperature of an engine, in particular an internal combustion engine 12, in the case of which the engine is interconnected with a radiator 16 via at least one forward-delivery line 35 and at least one return-delivery line 44 within a cooling circuit 14, which said radiator can be bypassed via a valve-controlled bypass line 48 between the at least one forward-delivery line 35 and the at least one return-delivery line 44. Additionally, the cooling circuit 14 comprises at least one pump capable of being controlled via open-loop and/or closed-loop control, in particular an electric pump 34 for pumping a coolant through the connecting lines 32 of the cooling circuit 14, as well as an electronic control unit 52 that controls the cooling capacity of the cooling circuit 14 via open-loop and/or closed-loop control.

Description

BACKGROUND OF THE INVENTION

[0001] The invention is based on a method for regulating the temperature of an engine, in particular an internal combustion engine of a motor vehicle, according to the general class of the main claims.

[0002] The need to cool engines, in particular internal combustion engines, arises from the fact that excessive thermal stress on the engine can result in an impairment of its operation or even irreversible engine damage. For example, the surfaces that are in contact with hot gasses and the lubrication of said surfaces inside the cylinders of an internal combustion engine can only withstand the temperatures produced up to a certain extent without damage. Individual parts, such as spark plugs, nozzles, exhaust valves, prechambers, etc., or even piston heads must withstand particularly high mean temperatures. Such parts are therefore produced out of materials that have particularly high heat resistance and/or that dissipate heat well.

[0003] To dissipate heat, cooling systems are used, among other things, in the case of which a coolant flows through coolant passages that surround the cylinder head and engine block of the internal combustion engine, for example. At least a portion of the heat absorbed by the coolant is then released to the surroundings via a radiator, or it is used to heat the passenger compartment, for example, by means of an additional heat exchanger provided in the cooling system.

[0004] The coolant temperature can be measured by a temperature sensor that is located in the cooling circuit and that detects the actual temperature of the cooling water at that point in time and forwards it to an electronic control unit, for example. This open-loop control monitors the temperature of the coolant and compares it with a permissible maximum temperature for the coolant and/or for the engine through which coolant flows that must not be exceeded during operation.

[0005] A device and a method for cooling an internal combustion engine is made known in EP 0 442 489 A1, in the case of which a first temperature sensor detects the temperature of the coolant at the outlet of the cylinder head. Furthermore, the method described in EP 0 442 489 A1 comprises a further temperature sensor that is installed directly on the engine block and serves to determine the engine oil temperature. If the engine oil temperature rises above a specified value, the coolant flow that flows through the internal combustion engine is divided into two different branches. The first branch of the coolant flow continues to flow through the cylinder head, while the second, remaining part of the coolant flow flows through the cylinder block. The volumetric flow of coolant through the cylinder head can be controlled via closed-loop control in accordance with the engine oil temperature in the cylinder head.

[0006] Publication EP 0 894 953 A1 discloses a cooling system for the internal combustion engine of a motor vehicle having a plurality of sensors that measures a corresponding number of parameters of the engine during operation. For example, the cooling system described in EP 0 894 953 A1 comprises three temperature sensors, in particular, that are installed in the cylinder head cooling circuit, the engine block cooling circuit, and at the outlet of the cylinder head cooling circuit. Each of these sensors detects a temperature of the engine case and forwards the corresponding signals to a central electronic control unit of the cooling circuit.

[0007] Based on the different sensor signals, the central control unit of the cooling system controls various components of the cooling system located in the cooling circuit, such as a cooling-air fan, a coolant pump, or a throttle and/or bypass valve.

[0008] A disadvantage of the cooling system for the internal combustion engine of a motor vehicle disclosed in EP 0 894 953 A1 is the fact that a plurality of sensors, in particular temperature sensors, must be used to determine the engine temperature. Due to the high mechanical and thermal stresses in the engine compartment of an internal combustion engine, these sensors are highly susceptible to malfunction or total functional failure. Moreover, the use of a plurality of sensors represents a not-inconsequential cost factor as well as a marked increase in the complexity of the cooling system and/or its closed-loop control.

[0009] Advantages of the Invention

[0010] In contrast, the method according to the invention for regulating the temperature of an engine having the characterizing features of the main claim has the advantage that the number of sensors used in the cooling system can be reduced to a minimum. The engine temperature and/or the temperature of individual components of the engine can be determined in simple fashion by means of the coolant temperature and the volumetric flow of the coolant that is directed through the engine and/or individual components of the engine. In this manner, a plurality of detectors can be eliminated. On the other hand, however, due to the continuous diagnosis of the engine temperature, it is ensured that the heat-sensitive parts of the engine are not damaged.

[0011] Advantageous further developments and improvements of the method described in the main claim are possible due to the measures listed in the dependent claims.

[0012] It is particularly advantageous to determine the value for the volumetric flow of coolant that is required to determine the component temperature of the engine based on the electrical current required to operate the coolant circulation pump. During steady-state operation, an electrical pump for circulating coolant in the cooling circuit will deliver a constant volumetric flow given a constant electrical voltage U, a constant electrical current I, and a rotational speed N of the pump. The operating point of the pump, i.e., the pressure rise &Dgr;p, as well as the volumetric flow &Dgr;V/&Dgr;t, can be determined with reference to the known pump characteristics and the known resistance to flow of the cooling circuit when the values (U, I, N) mentioned hereinabove are known.

[0013] For example, the load on the pump and, therefore, the volumetric flow delivered by the pump, can be deduced from the rotational speed N of the pump when the state is known (i.e., constant electrical voltage U applied to the pump), if said pump always draws a constant electrical current I. In analogous fashion, if the pump maintains a constant rotational speed N, the load on the pump and, therefore, the volumetric flow of the coolant, can be deduced from the measurement of the electrical current I required by the pump.

[0014] In this manner, when data that are available anyway, e.g., the pump characteristics and the current required by the pump, are known, the volumetric flow that is delivered can be deduced and, therefore, when the coolant temperature is known, the sought-after engine temperature can be deduced as well. Existing operating parameters of the cooling system are therefore used in very advantageous fashion to obtain additional information about critical locations in the cooling circuit. When the method according to the invention is used, increased expenditure resulting from additional sensors used to detect the required data is not necessary, or is necessary only to a limited extent.

[0015] In advantageous fashion, a numeric model of the cooling circuit with its individual components, in particular the engine and/or a thermal model of the engine, the tube routing with the associated resistances to flow, the placement of the valves, and further parameters that describe the cooling circuit are stored in an electronic control unit belonging to the cooling circuit. A model and/or a data set is therefore stored in the electronic control unit that models the influence or the maximum permissible deviations of the volumetric flow of coolant on the component temperature. By comparing the actual component temperature at that point in time with the data on the associated setpoint component temperature stored in the electronic control unit, a correction signal and/or a manipulated variable can therefore be generated that changes the volumetric flow of coolant through the engine in a desired fashion in order to adjust the actual coolant temperature to the setpoint coolant temperature.

[0016] In advantageous fashion, the method according to the invention uses a second manipulated variable and/or a second correction signal to ensure that the cooling capacity of the cooling circuit works in an optional range for the engine. This second correction signal can be generated directly from the coolant temperature. To do this, the coolant temperature is detected, e.g, via a temperature sensor, and the change in coolant temperature over time is compared with a time-dependent model of the coolant temperature curve stored in the electronic control unit. For example, this time-dependent model of the coolant temperature stored in the electronic control unit can be a computer model of the coolant temperature curve during a cold start of the motor vehicle, or it can simulate another typical driving situation. The theoretical model makes it possible to detect whether the coolant temperature of the cooling circuit increases to the “correct extent”. To accomplish this, an optimum temperature band width for the engine—depending on the particular driving situation—can be stored in the electronic control unit, for example. If the actual coolant temperature deviates from the setpoint coolant temperature stored in the electronic control unit for the particular situation, or if the actual coolant temperature deviates from the specified temperature band width, a second correction signal is generated. The open-loop and/or closed-loop control of the cooling circuit by means of this second manipulated variable can supersede the corresponding closed-loop control of the volumetric flow, so that this second closed-loop control can be used as an additional safety control for the cooling circuit.

[0017] In advantageous fashion, the delivery amount of the circulation pump, i.e., its rotational speed, in particular, can be varied in accordance with the correction signals generated. It is possible, for example, to vary the volumetric flow of coolant and, therefore, the engine temperature, as needed.

[0018] In addition to the open-loop and/or closed-loop control of the coolant pump, the valves located in the cooling circuit and further components associated with the cooling circuit, e.g., a cooling fan for the radiator of the cooling circuit, can be controlled via closed-loop control by the electronic control unit as needed in accordance with the generated correction signals, so that a volumetric flow of coolant adjusted in optimum fashion for the particular driving situation and/or an optimized coolant temperature prevails in the cooling circuit at all times.

[0019] Advantageously, the method according to the invention also makes it possible for the electronic control unit to control—via closed-loop control—the cooling capacity of the cooling circuit and, in particular, the volumetric flow of coolant through the engine with consideration for further operating parameters of the vehicle. One example of this is the optimized pollutant emission of the engine as a function of the cooling capacity delivered to the engine. A pollutant sensor can forward an appropriate signal to the electronic control unit of the cooling circuit, so that the electronic control unit implements an optimized configuration of the active setting elements of the cooling circuit to obtain minimal pollutant emissions based on an optimized engine temperature. For this purpose, a model and/or a data set in the form of a program map or a data base is contained in the electronic control unit—in an analogous fashion to the temperature behavior described hereinabove—that describes the influence of the volumetric flow of coolant on the pollutant emission of the vehicle.

[0020] Deviations from the engine parameters that are calculated or that were stored previously in the electronic control unit can be not only diagnosed but actively corrected as well by the electronic control unit. In addition to adjusting the adjustable cooling circuit components, the electronic control unit can also inform the vehicle driver about deviations in the cooling system using appropriate warning signals. The “on-board diagnosis” also makes it possible to detect errors or defects in the cooling system, such as blocked valves, pinched connecting lines, or defective pumps.

[0021] In advantageous fashion, the electronic control unit that controls—via closed-loop control—the active components can be an engine control unit.

SUMMARY OF THE DRAWINGS

[0022] An exemplary embodiment of the invention is shown schematically in the drawings and it is described in greater detail in the subsequent description.

[0023] FIG. 1 is a simplified view of an engine compartment of a vehicle, in which a vehicle motor with a cooling circuit for this engine is located.

[0024] FIG. 2 is a block diagram for the temperature regulation of a vehicle engine according to an exemplary embodiment of the method according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The description, the figures, and the claims contain numerous features in combination. One skilled in the art will advantageously consider them individually as well and combine them into reasonable further combinations.

[0026] FIG. 1 is a simplified, schematic illustration of an engine compartment 10 of a vehicle, in which an internal combustion engine 12 and a cooling circuit 14 for this internal combustion engine 12 are located. The heat given off by the internal combustion engine 12 is dissipated—preferably outwardly—via the cooling circuit 14, which forms a cooling system. For this purpose, the cooling circuit comprises a radiator 16 that is located in the cooling air stream 18 of the moving vehicle. The cooling air stream 18 and, indirectly, therefore, the cooling capacity of the cooling system, can be controlled via air flaps 20 that are installed in the body 22 of the vehicle. The cooling capacity of the cooling circuit is a function of the temperature of the coolant at that point in time and the volumetric flow of coolant pumped through the cooling system.

[0027] Additionally, to improve the cooling capacity of the cooling system, at least one fan is located in the region of the radiator 16 that is composed of a fan wheel 26 and an electric motor 28 driving this fan wheel 26. As an alternative, the air flaps 20 or additional, further air flaps can also be located between the radiator 16 and the fan 24.

[0028] The cooling system has an electric coolant pump 34 to pump a coolant 30 through the connecting lines 32 of the cooling system. Water is used preferably as coolant, and an appropriate cold protective can be added to said water for low temperatures.

[0029] The coolant 30, coming from the radiator 16, is directed by the coolant pump 34 through a forward-delivery line 35 to the engine 12. To determine the coolant temperature, a temperature sensor 38 is located in the cooling circuit in the region of a coolant inlet 36 of the engine 12. The coolant 30 flows through the engine 12 along paths not shown further in FIG. 1, and it absorbs a certain amount of heat from the engine 12, then it exits said engine through a coolant outlet 40. Moreover, in the exemplary embodiment according to FIG. 1, the internal combustion engine 12 comprises a second coolant inlet 50, via which a portion of the heated coolant can be directed to a heat exchanger, e.g., for the passenger compartment of the motor vehicle.

[0030] In further exemplary embodiments of the invention, the use of a plurality of coolant inlets and coolant outlets is possible. Cooling circuit architectures that are more complex than the cooling system shown in the exemplary embodiment in FIG. 1 can also be combined with the method according to the invention. Only one highly simplified, schematic cooling circuit is shown in FIG. 1 to describe the method. It is not intended to represent a limitation of the possible cooling circuit architecture.

[0031] A further, second temperature sensor 42 that detects the temperature of the coolant 30 after it leaves the engine 12 is located in the region of the coolant outlet 40 of the engine 12. The coolant 30 travels through a return-delivery line 44 back to the radiator 16 of the cooling circuit. A valve 46 is provided in the return-delivery line 44 that allows the coolant to bypass the radiator 16 via a bypass line 48. During a cold start of the vehicle, for example, it is possible to direct the heated coolant 30 back to the engine 12 immediately after it leaves said engine, without the temperature of the coolant dropping substantially. This allows the engine to warm up faster. This results in a marked reduction in pollutant levels during the starting phase of the motor vehicle.

[0032] The active components of the cooling system, e.g., the air flaps 20, the fan 24, the coolant pump 34, the bypass valve 46, and further components of the cooling circuit not shown explicitly in the exemplary embodiment, are adjusted and/or controlled via closed-loop control—with the aid of an electronic control unit 52 that comprises a memory 54, a processing block 66, and a comparing element 68—over data lines 56 in such a fashion that the engine 12 of the vehicle has a optimum temperature and/or temperature distribution at any point in time during a driving schedule. This optimum temperature can be characterized, for example, by the lowest possible fuel consumption or the lowest possible pollutant emission of the engine. A pollutant sensor 72 that is also interconnected with the electronic control unit 52 via a data line 74 is provided to detect the current pollutant emission.

[0033] The method according to the invention for regulating the temperature of an engine will be explained further hereinbelow with reference to a block diagram shown in FIG. 2. The active, adjustable components of the cooling system, such as the air flaps 20, the fan 23, the coolant pump 34, the bypass valve 46, and further components of the cooling circuit not defined explicitly in the exemplary embodiment are interconnected with the electronic control unit 52 via signal lines 56 that also supply the electrical current to these adjustable components. The further components 60 of the cooling circuit can be additional, adjustable valves or an additional coolant pump, for example. The temperature sensors 38 and/or 42 for determining the coolant temperature are also interconnected with the electronic control unit 52 via appropriate data lines 58.

[0034] The electric coolant pump 34 has an energy supply 62 that can be coupled to the vehicle's electrical supply system via the electronic control unit 52, for example. The electronic control unit 52 detects the working point of the coolant pump 34, i.e., the volumetric flow delivered by the pump—in the exemplary embodiment shown in FIG. 22—based on the electrical current I that the electric pump requires from the energy supply. This signal is also forwarded to the electronic control unit 52 via a data line 64.

[0035] Based on the actual parameters of the cooling circuit existing at that point in time, e.g., the actual, detected coolant temperature and/or the electrical current I required by the coolant pump 34, the electronic control unit 52 calculates the volumetric flow of coolant pumped through the cooling circuit, and, based on this, the engine temperature and/or the temperatures of various engine components.

[0036] A thermal model of the cooling circuit with its components, e.g, the line routing, the viscosity change of the coolant, the position of the valves, the cooling capacity of the radiator 16 and the fan 24, and further parameters that describe the cooling system, is stored in the memory 54 of the electronic control unit 52. A data set is therefore contained in the electronic control unit 52 that models the influence of a certain volumetric flow of coolant on the engine temperature and/or on the temperature of various engine components.

[0037] The characteristics of the coolant pump 34 are also stored in the memory 54 of the electronic control unit 52. The electric pump 34—during steady-state operation—will deliver a constant volumetric flow. This takes place with a constant electrical voltage U, a constant electrical current I, and a specifiable rotational speed N of the pump. The particular operating point of the pump, i.e., the pressure rise &Dgr;P and the volumetric flow &Dgr;V/&Dgr;t, can therefore be determined by the electronic control unit with reference to the pump characteristics and the stored resistances to flow of the cooling circuit when the values for electrical voltage U, electrical current I and rotational speed N of the pump are known. For example, based on the measurement of the electrical current I that the pump draws during steady-state operation given a constant electrical voltage U and a constant rotational speed N, the electronic control unit can deduce the volumetric flow delivered by the pump. The electrical current I required by the coolant pump can therefore be used to evaluate and diagnose the volumetric flow of coolant delivered by the pump 34. The volumetric flow of coolant diagnosed in this fashion via the electrical current of the pump 34 is used together with the coolant temperature determined, e.g., by the temperature sensor 42, by the electronic control unit to calculate the actual engine temperature.

[0038] The data—from the processing block 66—on the determined, actual engine temperature at that point in time and/or the volumetric flow of coolant representing this engine temperature is compared with the model for the optimum coolant temperature and the optimum volumetric flow of coolant stored in the memory 54 of the electronic control unit 52 in a comparing element 68 of the electronic control unit 52. By way of the comparing element 68, the electronic control unit 52 generates one or more correction signals 56. The correction signal is used to control and/or adjust the active elements of the cooling circuit, such as the coolant pump 34, the cooling air fan 24, the bypass valve 46 or the air flaps 20. For example, controlling the coolant pump 34 via closed-loop control makes it possible to adjust the volumetric flow of coolant through the engine 12 and optimize the temperature of the engine and/or the temperatures of diverse engine components with regard for fuel consumption and/or pollutant emission.

[0039] In analogous fashion, the electronic control unit 52 also delivers a command and control signal to the bypass valve 46 that can adjust the temperature of the coolant at the coolant inlet 36 to the desired value by opening and/or closing the bypass line 48. To check the operational capability of this control mechanism, the temperature sensor 38 can determine the coolant temperature in front of the coolant inlet 36 of the engine 12 and forward this signal to the electronic control unit 52. In this fashion, it is possible to detect a defective component in the cooling circuit if it does not meet the thermal specifications of the electronic control unit 52 and the thermal model stored in the electronic control unit.

[0040] Specifically, in this fashion, the change in temperature of the coolant over time during the starting phase of the internal combustion engine can be compared with a time-dependent model of the coolant temperature for this phase stored in the electronic control unit. If the actual temperature values deviate from the specified setpoint temperature values—which can be stored in the memory 54 of the electronic control unit 52 in the form of a temperature range—the electronic control unit 52 also issues an appropriate warning signal that indicates the presence of a malfunction in the cooling circuit and, therefore, a possible defective component.

[0041] Moreover, the electronic control unit also has appropriate pollutant sensors 72, for example, that detect the actual pollutant emission of the internal combustion engine and report the result to the processing block 66 of the electronic control unit 52 via a line 74. The pollutant sensors 72 therefore make it possible to also adjust the engine temperature to its particular optimum value by running a comparison 68 with corresponding data stored in the memory 54 of the electronic control unit.

[0042] The method according to the invention is not limited to the exemplary embodiment described.

[0043] For example, the actual engine temperature and/or component temperature of the engine can be diagnosed indirectly via other characteristic values of the coolant pump. If the pump always draws a constant electrical current I during steady-state operation, i.e., when electrical voltage U is constant, then the load on the pump and, therefore, the volumetric flow that is delivered can be deduced from the rotational speed N of the pump. By using the volumetric flow detected in this fashion and the measured coolant temperature, then, in turn, a component temperature of the engine can be deduced.

[0044] If another physical variable is used to control the coolant pump, e.g., electrical current I, then the other characteristic values (U, N) of the coolant pump must be detected and processed by the electronic control unit 52. The measurement variables (U, I, N) are evaluated currently by the electronic control unit 52, where they are then compared with the computer model and the stored pump characteristics. Deviations from the data that were calculated or stored previously in the electronic control unit make it possible, therefore, to detect faults in the cooling system, e.g., caused by blocked valves, defective lines, or an inoperative coolant pump.

[0045] With the method according to the invention, it is possible to perform an “on-board diagnosis” of the cooling circuit of a motor vehicle in simple, efficient fashion, which can also ensure, in particular, that certain pollutant emissions of the internal combustion engine are adhered to.

Claims

1. A method for regulating the temperature of an engine, in particular an internal combustion engine (12), in the case of which the engine is interconnected with a radiator (16) via at least one forward-delivery line (35) and at least one return-delivery line (44) within a cooling circuit (14), which said radiator can be bypassed via a valve-controlled bypass line (48) between the at least one forward-delivery line (35) and the at least one return-delivery line (44), and comprising at least one pump capable of being controlled via open-loop and/or closed-loop control, in particular an electric pump (34) for pumping a coolant through the cooling circuit (14), whereby an electronic control unit (52) controls the cooling capacity of the cooling circuit (14) via open-loop and/or closed-loop control,

wherein at least one component temperature of the engine (12) is determined based on a coolant temperature and a volumetric flow of the coolant through the engine (12).

2. The method according to claim 1,

wherein the volumetric flow of the coolant pumped through the engine (12) is determined based on the electrical current (I) required by the pump (34).

3. The method according to claim 1,

wherein the volumetric flow of coolant pumped through the engine (12) is determined based on the electrical voltage (U) applied to the pump (34).

4. The method according to one of the preceding claims,

wherein a numeric model of the cooling circuit (14) with its components—in particular the engine (12), the pump (34), and its load curve and the connecting lines (32)—is stored in data form in the electronic control unit (52), which said model describes the dependence of at least one component temperature of the engine (12) on the volumetric flow of coolant.

5. The method according to claim 4,

wherein, to change the volumetric flow of coolant, at least one correction signal (55) is generated by comparing at least one determined actual component temperature with the data on the associated setpoint component temperature stored in the electronic control unit (52).

6. The method according to one of the preceding claims,

wherein the coolant temperature is detected via at least one temperature sensor (72).

7. The method according to claim 6,

wherein the change in temperature of the coolant over time is compared with a time-dependent model for the coolant temperature stored in the electronic control unit (52), and at least one second correction signal (56) is generated in accordance with a present deviation of the actual coolant temperature from the setpoint coolant temperature.

8. The method according to claim 1,

wherein the delivery quantity of the pump (34) is controlled via open-loop and/or closed-loop control in accordance with the at least one first (55) and/or the at least one second (56) correction signal in order to change the volumetric flow of coolant.

9. The method according to one of the preceding claims,

wherein at least one valve located in the cooling circuit (14), in particular an electrically controllable valve (46) and/or a radiator blower (24) associated with the radiator (16), and/or air flaps (20), are controlled via open-loop and/or closed-loop control in accordance with at least a first (55) and/or the at least one second (56) correction signal to obtain a specifiable volumetric flow of coolant and/or a specifiable coolant temperature.

10. The method according to one of the preceding claims,

wherein the electronic control unit (52) controls—via open-loop and/or closed-loop control—the cooling capacity of the cooling circuit (14) and, in particular, the volumetric flow of coolant with consideration for at least one further parameter, in particular the pollutant emission of the engine (12)