GB2501699A

GB2501699A - Refining electric thermostat duty cycle by estimating engine inlet temperature

Info

Publication number: GB2501699A
Application number: GB201207567A
Authority: GB
Inventors: Luca Borgia; Carmine Pezzella
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-04-30
Filing date: 2012-04-30
Publication date: 2013-11-06
Anticipated expiration: 2032-04-30
Also published as: GB201207567D0; GB2501699B

Abstract

A coolant inlet temperature T2 of an automotive internal combustion engine (fig 4) (with a water pump or a switchable water pump 710, a radiator 720 and an electric thermostat 730) is estimated by: ¢ reading 20 a coolant outlet temperature T1 of the engine, determining 21 if the coolant outlet temperature T1 is higher than a threshold TH1 and if yes, acquiring 22 a third temperature T3 at the radiator outlet, reading 23 the electric thermostat stroke h1 as function of the coolant outlet or inlet temperatures T1/T2 and then reading 24 a flow rate through the radiator and the electric thermostat as function of its stroke and the engine speed, calculating 25 the coolant inlet temperature T2 and then calculating 26 a difference T1-T2 between the coolant outlet and inlet temperatures, assessing 27 the difference against a target value from a map using engine load and speed, refining 28 the duty cycle on the electric thermostat by adjusting the supply voltage and then going back to the first step.

Description

METHOD OF ESTIMA TING THE COOLANT INLET TEMPERA TURE IN AN INTERNAL

COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of estimating the coolant INLET temperature in an internal combustion engine of an automotive system, the engine being provided with a coolant circuit, which comprises at least a water pump, a radiator and a thermostat. Preferably, the water pump is a switchable water pump and the thermostat is an electric thermostat type.

BACKGROUND

It is known that the coolant circuit of modem engines is provided with a switchable water pump, which can be switched off during engine startup. As an example, an engine control system for a vehicle could comprise a pump control module and a heating request determination module. The pump control module disengages the switchable water pump from an engine upon startup of the engine. The heating request determination module generates a heat request signal that indicates whether heating of a passenger cabin of the vehicle has been requested based on ambient air temperature, humidity of ambient air, and a status of an air conditioner clutch. The pump control module selectively engages the switchable water pump after the heat request signal is generated.

It is also known that modern coolant circuits are provided with an electric thermostat, which opens the circuit from the radiator to the engine, when the engine temperature reaches a certain threshold requiring the incoming of fresh water from the radiator. The electric thermostat is normally driven by a voltage duty cycle and its opening is based on the input coming from a temperature sensor located at the internal combustion engine outlet. The duty cycle signal determines the opening grade of the electric thermostat and therefore the water flowrate, which, together with the by-pass flowrate (coming from the oil cooler, the cab heater, the EGR cooler and so on), will be pushed by the water pump to the engine inlet.

The drawback of the known applications is related to the fact that the thermostat is driven by the value of the engine outlet temperature, which gives an absolute indication but cannot provide a value related to the heat transfer amount the engine needs. Such heat transfer is proportional to the difference between the engine inlet temperature and the engine outlet temperature. To estimate the former value, another temperature sensor would be needed, thus increasing the complexity and the costs of the engine management system.

Therefore a need exists for a method that accurately estimates the coolant temperature at the inlet of the intemal combustion engine, thus allowing a better water management without increasing costs and complexity of the engine management system.

An object of an embodiment of the invention is to provide a method that predicting the expected thermostat stroke and, consequently, the flowrate passing through it, is able to estimate the coolant temperature at the internal combustion engine inlet and then calculating the temperature difference between outlet and inlet of the engine, could provide a reliable signal to correctly drive the control of the electric thermostat.

Another object is to provide an apparatus which allows to perform the above method.

These objects are achieved by a method, by an apparatus, by an engine, by a computer program and computer program product, and by an electromagnetic signal having the features recited in the independent claims.

The dependent claims delineate preferred and/or especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides a method of estimating a coolant inlet temperature T2 of an internal combustion engine of an automotive system, the engine being provided with a coolant circuit, the coolant circuit comprising at least a water pump or a switchable water pump a radiator and an electric thermostat, the method comprising a cycle of following steps: a) reading a coolant outlet temperature Ti of the internal combustion engine, b) determining if the coolant outlet temperature TI is higher than a threshold TH1 and if yes, c) acquiring a third temperature 13 at the radiator outlet, then reading the electric thermostat stroke hi as function of the coolant outlet temperature Ti or the coolant inlet temperature T2 and then reading a flow rate thradj,j through the radiator and the electric thermostat as function of its stroke and the engine speed erpm, d) calculating the coolant inlet temperature 12 and then calculating a difference Tl-T2 between the coolant outlet temperature Ti and the coolant inlet temperatureT2, e) assessing the difference vs. a target value, derived from a map, having as input parameter the engine load and the engine speed, f) refining the duty cycle on the electric thermostat by adjusting the supply voltage and then going back to step a).

Consequently, an apparatus is disclosed for estimating the coolant inlet temperature in an internal combustion engine of an automotive system, comprising: a) means for reading a coolant outlet temperature Ti of the internal combustion engine, b) means for determining if the coolant outlet temperature TI is higher than a threshold THi and if yes, c) means for acquiring a third temperature T3 at the radiator outlet, then means for reading the electric thermostat stroke hi as function of the coolant outlet temperature Ti or the coolant inlet temperature T2 and then means for reading a flow rate thradjyjnr through the radiator and the electric thermostat as function of its stroke and the engine speed erpm, d) means for calculating the coolant inlet temperature 12 and then means for calculating a difference T1-12 between the coolant outlet temperature Ti and the coolant inlet temperature 12, e) means for assessing the difference vs. a target value, derived from a map, having as input parameter the engine load and the engine speed, f) means for refining the duty cycle on the electric thermostat by adjusting the supply voltage and then going back to step a).

An advantage of this embodiment is that it allows to estimate the coolant temperature at the inlet of an internal combustion engine, thus improving the water management, without increasing the cost and complexity of the system, more in detail, improving the electric thermostat control having a virtual feedback signal for the stroke position and monitoring the heat exchange on the engine during any running condition.

According to a further embodiment of the invention, if the temperature Ti is lower or equal than said threshold TH1, then the assumption that the coolant inlet temperature T2 is equal to the coolant outlet temperature Ti is taken and the method go back to the step a).

An advantage of this embodiment is to allow the estimation of the inlet engine coolant temperature, also in condition of closed thermostat, in other words when the engine is still cold and does not transfer heat to the water.

According to an embodiment of the invention, if the temperature Ti is higher than the threshold TH1, the temperature T2 is calculated by the formula: T2 = r) + (thradiator. q) (thmdatar + where: Thbypass = is the flowrate through the by-pass coolant circuit and 1mdicnor + = -pump with pump being the total flowrate through the water pump and thm&aror being the flowrate at the radiator exit then, knowing the water pump (710) flowrate (based on electric thermostat stroke position), the by-pass flowrate can be calculated as difference between the water pump (710) flowrate and the radiator 720 flowrate.

An advantage of this embodiment is that it allows to estimate the coolant temperature at the inlet of an internal combustion engine, without using any further temperature sensor or equivalent measurement equipments.

According to another embodiment of the invention, said electric thermostat stroke hi is read from a map in which the hysteresis effects respect to the temperature are neglected.

An advantage of this embodiment is that it allows to determine the electric thermostat stroke in a simple and reliable way, without using any position sensor.

According to an aspect of the invention, during the first iteration the electric thermostat stroke hi is read as function of the coolant outlet temperature TI.

According to another aspect of the invention, during the further iterations said electric thermostat stroke hi is read as function of the coolant inlet temperature 12.

According to a further embodiment of the invention, said TH1 is equal to the "start to open" Sb temperature of the electric thermostat, said temperature increased by 2 kelvin.

An advantage of this embodiment is to provide a coolant temperature estimation also when the engine is still cold and does not transfer heat to the water, by using a safe tolerance to avoid misdetection.

According to another embodiment, the invention provides an internal combustion engine of an automotive system, equipped with a coolant circuit, the coolant circuit comprising at least water pump, a radiator and an electric thermostat, the automotive system comprising an electronic control unit configured for carrying out the above method for estimating the coolant temperature at the engine inlet.

The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the font of computer program product comprising the computer program.

The computer program product can be embodied as a control apparatus for an internal combustion engine, comprising an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program all the steps of the method described above are carried out.

The method according to a further aspect can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represents a computer program to carry out all steps of the method.

A still further aspect of the disclosure provides an internal combustion engine specially arranged for carrying out the method claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an automotive system.

Figure 2 is a section of an internal combustion engine belonging to the automotive system of figure 1.

Figure 3 is a graph showing the behavior of the thermostat stroke as function of the coolant temperature.

Figure 4 is a graph depicting the behavior of the flow rate th,Qdj,,,or through the radiator and the thermostat as function of its stroke and the engine speed.

Figure 5 is a simplified scheme of the coolant circuit according to the invention.

B

Figure 6 is a flowchart of a method for estimate the coolant temperature in an internal combustion engine, according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 100, as shown in Figures land 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145.

A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150.

A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received a fuel source 190. Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the pod 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200.

An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other ernbodinients, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include1 but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters. Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110 and equipped with a data carrier 40. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system and an interlace bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send1 receive, and modulate analog and/or digital signals to/from the various sensors and control devices.

The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

Turning back to the internal combustion engine 110, in Fig. 5 a schematic coolant circuit 700 is represented. A water pump 710, preferably a switchable water pump 710, ensure the water circulation from the radiator 720 to the engine 110. The coolant circuit is also provided with a thermostat 730, preferably an electric thermostat 730, which opens the circuit from the radiator to the engine when the engine temperature reaches a certain threshold, requiring the incoming of fresh water from the radiator. When the thermostat is closed, the water pump 710 let the water flows through the engine and through the by-pass circuit (passing through, for example, the oil cooler 740, the heater 750, the EGR cooler 760). In this case, the flowrate equation is -,,,,,,, = being no water flowing through the radiator 720.

When the thermostat opens, then the mass equation changes in the followings: + = tot pIJfflf2 Whereby, the flowrate parameters have been previously defined.

The electric thermostat is normally driven by a voltage duty cycle and its opening is based on the input coming from a temperature sensor located at the internal engine outlet Ti. The duty cycle signal determines the opening grade of the thermostat and therefore the water flowrate, which, together with the by-pass flowrate (coming from the oil cooler, the cab heater, the EGR cooler and so on), will be pushed by the water pump to the engine inlet.

Engine technology is now challenging to develop day by day more efficient engines. In this direction, thermal management is a key player to optimize engine efficiency through a better usage of the generated heat. For this reason, electric controlled thermostats have been introduced to maximize fuel economy, especially at partial load. Being not available the coolant temperature at engine inlet T2, it is not possible to have a real heat exchange monitoring during engine running.

Of course, a specific control strategy needs to be implemented to use them. The invention is about how to improve the control of this device without having a feedback position sensor but using a stroke prediction curve. The electric thermostat can be controlled via duty cycle, There is no feedback signal in the control chain, so it is not possible to correlate duty cycle vs. the thermostat stroke position hi, in other words versus the real temperature at engine inlet T2.

The method according to the invention is able to estimate the coolant temperature at the internal combustion engine inlet and then, calculating the temperature difference between outlet and inlet of the engine, could provide a reliable signal to correctly drive the opening of the electrical thermostat.

In more detail, looking at the flow chart in Fig. 6, the method comprising the steps of: a) reading 20 a coolant outlet temperature Ti of the internal combustion engine b) determining 21 if the coolant outlet temperature Ti is higher than a threshold TH1 and if yes, c) acquiring 22 a third temperature 13 at the radiator 720 outlet, then reading 23 the electric thermostat 730 stroke hi as function of the coolant outlet temperature Ti or the coolant inlet temperature T2 and then reading 24 a flow rate th,UdfG, through the radiator 720 and the electric thermostat 710 as function of its stroke and the engine speed erpm, d) calculating 25 the coolant inlet temperature T2 and then calculating 26 a difference T1-T2 between the coolant outlet temperature Ti and the coolant inlet temperature T2, e) assessing 27 the difference vs. a target value, derived from a map, having as input parameter the engine load and the engine speed, f) refining 28 the duty cycle on the electric thermostat 730 by adjusting the supply voltage and then going back to step a).

The temperature target value is derivable from a calibratable map, having two entries (engine load and engine speed), whose outcome is an estimated temperature difference between engine inlet and engine outlet, due to the overall heat transfer, operated by the cooling system.

Advantageously, said threshold ThU is equal to the "start to open" STO temperature increased by 2 Kelvin, as safe tolerance. If the temperature at the engine outlet will be lower than TH1, the thermostat will remain closed and the temperature T2 at the engine inlet can be assumed equal toll. On the contrary, if the temperature TI is higher than the threshold TH1, then the temperature T2 is calculated by the formula: T = (thypass. T)+ (thraaiaior. +

where: = is the flowrate through the by-pass coolant circuit and thradiator + = with iii,,,, being the total flowrate through the water pump and 2 5 thrfld,,J,or being the flowrate at the radiator exit In this way, knowing the water pump 710 flowrate from the pump characteristic (based on thermostat stroke position), the by-pass flowrate can be calculated as difference between the switchable water pump flowrate and the radiator flowrate, which in its turn, is calculated from the map in Fig. 4.

According to a preferred embodiment, the electric thermostat 730 stroke hi is read from a map in which the hysteresis effects, with respect to the temperature, are neglected.

More particularly, during the first iteration said electric thermostat 730 stroke hi is read as function of the temperature Ti, not having the T2 temperature still available, while during the further iterations (Fig. 3) the electric thermostat 730 stroke hi is more precisely read as function of the temperature T2. In fact, in Fig. 3 the hatched curve h(T2) represents the function thermostat stroke vs. engine inlet temperature, neglecting the hysteresis effects. Txl is the maximum temperature value for which the thermostat is still closed (stroke = 0), while Tx2 is an exemplary value giving a thermostat stroke hi (Tx2).

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS block

21 block 22 block 23 block 24 block block 26 block 27 block 28 block 29 block data carrier automotive system internal combustion engine 120 engine block cylinder cylinder head camshaft piston 145 crankshaft combustion chamber cam phaser fuel injector fuel rail 180 fuel pump fuel source intake manifold 205 air intake pipe 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 turbine 260 intercooter 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 290 VGT actuator 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU 700 coolant circuit 710 water pump/ switchable water pump 720 radiator 730 thermostat I electric thermostat 740 oil cooler 750 heater 760 EGR cooler hi electric thermostat stroke erpm engine speed Ti engine cutlet temperature T2 engineinlettemperature T3 radiator temperature by-pass ecolant circuit flowrate th,0, , water pump flowrate radiator flowrate ivdeazor

Claims

CLAIMS1. Method of estimating a coolant inlet temperature (T2) of an internal combustion engine (110) of an automotive system (100), the engine being provided with a coolant circuit (700), the coolant circuit comprising at least a water pump or a switchable water pump (710) a radiator (720) and an electric thermostat (730), the method comprising a cycle of following steps: a) reading (20) a coolant outlet temperature (Ti) of the internal combustion engine (110), b) determining (21) if the coolant outlet temperature (Ti) is higher than a threshold (TH1) and if yes, c) acquiring (22) a third temperature (T3) at the radiator (720) outlet, then reading (23) the electric thermostat (730) stroke (hi) as function of the coolant outlet temperature (Ti) or the coolant inlet temperature (T2) and then reading (24) a flow rate thrajato, through the radiator (720) and the electric thermostat (710) as function of its stroke and the engine speed (erpm), d) calculating (25) the coolant inlet temperature (T2) and then calculating (26) a difference (T1-T2) between the coolant outlet temperature (Ti) and the coolant inlet temperature (12), e) assessing (27) the difference vs. a target value, derived from a map, having as input parameter the engine load and the engine speed, f) refining (28) the duty cycle on the electric thermostat (730) by adjusting the supply voltage and then going back to step a).
2. Method according to claim i, wherein if the temperature (TI) is lower or equal than said threshold (TH1), then the assumption (29) that the coolant inlet temperature (T2) is equal to the coolant outlet temperature (Ti) is taken and the method go back to the step a).
3. Method according to claim 1, wherein the temperature (T2) is calculated by the formula: = *i) + (thrth tarot + where: = is the flowrate through the by-pass coolant circuit and thradiajor being the flowrate at the radiator exit then, knowing the water pump or the switchable water pump (710) flowrate, based on thermostat stroke position, the by-pass flowrate can be calculated as difference between the water pump or the switchable water pump (710) flowrate and the radiator (720) flowrate.
4. Method according to claim 1, wherein said thermostat or electric thermostat (730) stroke (hi) is read from a map in which hysteresis effects, with respect to the temperature, are neglected.
5. Method according to claim 4, wherein during the first iteration said thermostat or electric thermostat (730) stroke (hi) is read as function of the coolant outlet temperature (Ti).
6. Method according to claim 4, wherein during the further iterations said thermostat or electric thermostat (730) stroke (hi) is read as function of the coolant inlet temperature (12).
7. Method according to claim 1, wherein said threshold TH1 is equal to the start to open" (STO) temperature increased by 2 kelvin.
8. Internal combustion engine (110) of an automotive system (100) equipped with a coolant circuit (700), the coolant circuit comprising at least a water pump (710) a radiator (720) and a thermostat (730), the automotive system (100) comprising an electronic control unit (450) configured for carrying out the method according to claims 1-7.
9. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-7.
10. Computer program product on which the computer program according to claim 9 is stored.
11. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (40) associated to the Electronic Control Unit (450) and a computer program according to claim 9 stored in the data carrier (40).
12. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 9.