Patent Description:
A variety of internal combustion engines employ cooling systems in which a liquid engine coolant is pumped under pressure through the engine and a corresponding radiator in order to remove excess heat from the engine and keep the engine within a normal operating temperature range. Many such cooling systems employ a fan that can be turned on and off as appropriate in order to better control how much heat is being removed from the engine coolant flowing through the radiator. Cooling systems may employ a thermostat in order to control when engine coolant flows through the radiator and when engine coolant does not flow through the radiator. When an engine is below its normal operating temperature range, such as during a cold start, the thermostat may remain closed in order to allow the engine to warm up and more quickly reach its normal operating temperature range. As the engine coolant temperature approaches its normal operating temperature range, the thermostat will start to open, thereby allowing coolant flow through the radiator to enable cooling the engine.

Many thermostats are mechanical devices that can get stuck at an inappropriate thermostat position, particularly as thermostats age and/or become corroded. A thermostat that is stuck in an open or partially open position when coolant temperatures would otherwise indicate that the thermostat should be fully closed will cause the engine to run cooler than its normal operating temperature range. This can cause the engine to run inefficiently, burning more fuel, which results in additional pollutants, plug fouling and the like. Accordingly, there is a desire for the engine to reach its normal operating temperature as quickly as possible. A thermostat that is stuck in a closed or partially closed position can easily cause the engine to overheat as coolant evaporates. If carried to an extreme, overheating can also cause substantial engine damage and may cause a driver and/or passengers to become stranded.

Accordingly, there is a desire for methods and systems for determining when a thermostat is not working properly and to achieve early warning of possible problems. Documents cited during prosecution include <CIT>.

According to the invention, a method of monitoring performance of a thermostat according to claim <NUM> and an engine management system according to claim <NUM> are provided.

The present inventors have recognized, among other things, that a problem to be solved is the need for new and/or alternative approaches to determining if/when a thermostat is not working properly as part of an engine cooling system. The present inventors have determined that particular models that employ both measurable engine parameters as well as predictable engine parameters may be used to determine when a thermostat is malfunctioning before the thermostat malfunction results in an engine breakdown. The present inventors have determined that particular models may be used to provide an estimated coolant temperature and an estimated thermostat position. The estimated coolant temperature can be compared to an actual measured engine coolant temperature to diagnose whether there is a malfunction. Subsequently, based on this comparison, the thermostat position can be estimated and assessed to determine whether there is a risk of the thermostat being stuck at a position.

In an example being not part of the invention, a cooling system controller is configured to monitor performance of a cooling system that is configured to circulate engine coolant through an engine, the cooling system including a thermostat that controls engine coolant flow through a radiator. The controller includes an input port configured to receive an engine coolant temperature signal representative of an engine coolant temperature from an engine coolant temperature sensor and a controller that is operably coupled to the input port. The controller is configured to periodically execute a closed-loop healthy model, the closed-loop healthy model periodically outputting a healthy case thermostat position estimate and to periodically execute a closed-loop faulty model, the closed-loop faulty model periodically outputting a faulty case thermostat position estimate. The controller is configured to perform a statistical analysis on the periodically outputted healthy case thermostat position estimates and the faulty case thermostat position estimates in order to ascertain whether the thermostat is functioning appropriately and to output a warning signal when the thermostat is not functioning appropriately. An output port is operably coupled to the controller and is configured to provide the warning signal to an engine management system.

Alternatively or additionally, the closed-loop healthy model may include utilizing an Extended Kalman Filter (EKF) to estimate the healthy estimated thermostat position.

Alternatively or additionally, the closed-loop healthy model may further include utilizing an Extended Kalman Filter (EKF) to estimate a healthy estimated engine coolant temperature.

Alternatively or additionally, the closed-loop faulty model may include utilizing an Extended Kalman Filter (EKF) to estimate the faulty estimated thermostat position.

Alternatively or additionally, the closed-loop faulty model may further include utilizing an Extended Kalman Filter (EKF) to estimate a faulty estimated engine coolant temperature.

Alternatively or additionally, the controller may be further configured to utilize a comparison between the healthy estimated engine coolant temperature and the faulty estimated engine coolant temperature as a further indication of whether the thermostat is functioning appropriately.

Alternatively or additionally, the thermostat may be configured to remain fully closed when the engine coolant temperature is below a first coolant temperature, be fully open when the engine coolant temperature is above a second coolant temperature and be partially open when the engine coolant temperature is between the first coolant temperature and the second coolant temperature. The controller may be further configured to confirm that the healthy estimated thermostat position corresponds to fully closed when the engine coolant temperature is below the first coolant temperature, to confirm that the healthy estimated thermostat position corresponds to fully open when the engine coolant temperature is above the second coolant temperature, to confirm that the healthy estimated thermostat position corresponds to a position between fully closed and fully open when the engine coolant temperature is between the first coolant temperature and the second coolant temperature and to output a warning signal when the healthy estimated thermostat position does not correspond to what the thermostat position should be given the engine coolant temperature.

Alternatively or additionally, the first coolant temperature and the second coolant temperature may be selectable based on specific engine requirements.

Alternatively or additionally, the first coolant temperature may range from about <NUM> degrees C to about <NUM> degrees C and the second coolant temperature may range from about <NUM> degrees C to about <NUM> degrees C.

Alternatively or additionally, the controller may be further configured, prior to issuing the warning signal, to ascertain whether a cumulative mass coolant flow rate through the radiator exceeds a threshold, and if so, to turn on the warning flag.

According to the invention, a method of monitoring performance of a thermostat within an engine cooling system according to claim <NUM> is provided. The engine cooling system includes a radiator and a coolant pump circulating coolant and the thermostat controls flow of coolant through the radiator. The method includes receiving an engine coolant temperature signal from an engine coolant temperature sensor, supplying the engine coolant temperature signal to an Extended Kalman Filter (EKF), the EKF estimating an estimated engine coolant temperature and an estimated thermostat position and comparing the estimated engine coolant temperature with an actual engine coolant temperature as indicated by the engine coolant temperature signal. When the estimated engine coolant temperature is within a temperature range centered on the actual engine coolant temperature, a determination is made that the thermostat position is appropriate. When the estimated engine coolant temperature is outside a temperature range centered on the actual engine coolant temperature, a determination is made that the thermostat position is not appropriate.

Alternatively or additionally, when the estimated engine coolant temperature is below the temperature range centered on the actual engine coolant temperature, a determination may be made that the thermostat is stuck open and a warning flag is turned on.

Alternatively or additionally, when the estimated engine coolant temperature is above the temperature range centered on the actual engine coolant temperature, a determination may be made that the thermostat is stuck closed and a warning flag is turned on.

According to the invention, the method includes comparing the estimated thermostat position with what an actual thermostat position should be based on the actual engine coolant temperature, and turning on the warning flag when there is a discrepancy between the estimated thermostat position and the actual thermostat position.

According to the invention, an engine management system according to claim <NUM> is provided.

In an example being not part of the invention, the controller may be configured to determine that a thermostat fault is present when the estimated engine coolant temperature varies by more than <NUM> degrees C from an actual engine coolant temperature as indicated by the engine coolant temperature signal.

In a further example being not part of the invention, the controller may be configured to determine that a thermostat fault is present when the estimated engine coolant temperature varies by more than <NUM> degrees C from an actual engine coolant temperature as indicated by the engine coolant temperature signal.

In a further example being not part of the invention, the one or more model inputs may include a mass flow rate of coolant through the engine.

In a further example being not part of the invention, the mass flow rate of coolant through the engine may be estimated using a rotational speed of a coolant pump circulating coolant through the engine and an estimated thermostat position.

In a further example being not part of the invention, the engine management system may further include using a reference model and the one or more model inputs to calculate the estimated engine coolant temperature.

This overview is intended to provide an introduction to the subject matter of the present patent application.

<FIG> is a schematic block diagram showing an engine cooling system <NUM> for an engine <NUM>. While the engine cooling system <NUM> is described with respect to an internal combustion engine such as a gasoline-fueled engine or a diesel engine, this is merely illustrative. The engine cooling system <NUM> may be used for cooling non-combustion engines such as an electric motor, a fuel cell, or a hydrogen-powered engine. The engine <NUM> (and hence the engine cooling system <NUM>) may be installed within any of a variety of different types of vehicles, such as but not limited to passenger vehicles, light duty pickup trucks, heavy duty pickup trucks, over the road trucks, construction vehicles and the like. The lines included in the schematic block diagram show possible coolant paths. When a thermostat <NUM> is open or partially open, meaning that the thermostat <NUM> permits at least some engine coolant to flow through the thermostat <NUM>, the engine coolant passing through the thermostat <NUM> passes to and through a radiator <NUM> where the engine coolant gives up heat as the engine coolant flows through the radiator <NUM>.

In many cases, the radiator <NUM> is positioned within the vehicle such that air passes through the radiator <NUM> as a result of the vehicle moving. The cooling system <NUM> may include a fan <NUM> that can be turned on or off to increase air flow through the radiator <NUM> and thus increase heat transfer from the engine coolant as desired. The fan <NUM> may be an electronic fan, for example, and may include one larger fan or two relatively smaller fans. In some older vehicles, the fan <NUM> may have a thermostatically controlled clutch and thus be belt driven off the engine <NUM>. Engine coolant passing through the radiator <NUM> will then revert back to a pump <NUM>. The pump <NUM> may be belt driven off the engine <NUM>.

When the thermostat <NUM> is fully closed, meaning that no engine coolant is permitted to pass through the thermostat <NUM> and reach the radiator <NUM>, the engine coolant will revert back to the pump <NUM>. In some cases, at least some of the engine coolant circulating through the engine cooling system <NUM> may be used to heat a passenger space of the vehicle. The engine coolant may pass through a heater <NUM>, sometimes referred to as a heater core. The heater <NUM> is essentially another radiator. Hot engine coolant passes through the heater <NUM> and gives up heat to air being blown through the heater <NUM>. In this case, however, the air being blown through the heater <NUM> is being driven by an electrical fan that is used to blow the air through the heater <NUM> and through a duct system into the passenger space in order to heat the passenger space. In some cases, at least some engine coolant may pass through a cooler <NUM> which can be used for heat dissipation from engine oil, transmission fluid or exhaust gases. In some cases, the cooler <NUM> may be an oil cooler, a transmission cooler, a high pressure or low pressure EGR cooler or an exhaust intercooler.

The engine cooling system <NUM> includes a bottle <NUM>, which may also be referred to in some cases as a coolant recovery tank or a coolant expansion tank. It will be appreciated that engine coolant, which is generally a mix of propylene glycol and water, and minor amounts of various additives, will expand as it becomes hot. The bottle <NUM> provides a place for the expanded engine coolant to flow into. Because the engine cooling system <NUM> is pressurized, at least in part in order to increase the effective boiling point of the engine coolant, excess engine coolant may flow into the bottle <NUM> as the engine coolant heats up and subsequently as the engine coolant cools down, engine coolant may be drawn out of the bottle <NUM> and back into circulation.

An engine coolant temperature sensor <NUM> is shown adjacent the engine <NUM>. In some cases, there may be more than one engine coolant temperature sensor <NUM>, and the one or more engine coolant temperature sensor(s) <NUM> may be located in other positions. In some cases, placing the engine coolant temperature sensor <NUM> adjacent to where the engine coolant exits the engine block provides the most accurate indication of engine coolant temperatures and thus the actual temperature of the engine block itself. The engine coolant temperature sensor <NUM> may output an engine coolant temperature signal that is representative of the engine coolant temperature. The engine coolant temperature signal may be provided to a cooling system controller, as shown for example in <FIG>, as an Extended Kalman Filter needs an observable condition as an input.

<FIG> is a schematic block diagram of an illustrative cooling system controller <NUM>. The cooling system controller <NUM> may be configured to monitor performance of a cooling system such as the cooling system <NUM>. The cooling system controller <NUM> includes an input port <NUM> that is configured to receive an engine coolant temperature signal representative of an engine cooling temperature from an engine coolant temperature sensor such as the engine coolant temperature sensor <NUM>. The input port <NUM> may represent a logical input. The input port <NUM> may represent a wiring terminal or terminals configured to receive one or more wires carrying the engine coolant temperature signal. The input port <NUM> may be configured to receive a variety of different signals from a variety of different sensors, for example.

A controller <NUM> is operably coupled to the input port <NUM>. An output port <NUM> is operably coupled to the controller <NUM> and is configured to provide a warning signal to an engine management system <NUM>. In some instances, the cooling system controller <NUM> may be a standalone controller that is distinct from the engine management system <NUM>. In some cases, the cooling system controller <NUM> may be incorporated into the engine management system <NUM>. The engine management system <NUM> may represent a collection of control systems that regulate operation of various systems within a vehicle in which the engine management system <NUM> is installed. The engine management system <NUM> may represent a compilation of both hardware and software, for example. The controller <NUM> may be configured to carry out a number of steps in monitoring thermostat performance. Some of these steps are outlined in <FIG>.

<FIG> is a flow diagram showing an illustrative series <NUM> of steps that the controller <NUM> may be configured to carry out. The controller <NUM> may be configured to periodically execute a closed-loop healthy model, the closed-loop healthy model periodically outputting a healthy case thermostat position estimate, as indicated at block <NUM>. The controller <NUM> may be configured to periodically execute a closed-loop faulty model, the closed-loop faulty model periodically outputting a faulty case thermostat position estimate, as indicated at block <NUM>. The controller <NUM> may be configured to perform a statistical analysis on the periodically outputted healthy case thermostat position estimates and the faulty case thermostat position estimates in order to ascertain whether the thermostat is functioning appropriately, as indicated at block <NUM>. The controller <NUM> may be configured to output a warning signal when the thermostat is not functioning appropriately, as indicated at block <NUM>.

In some instances, the closed-loop healthy model includes utilizing an Extended Kalman Filter (EKF) to estimate the healthy estimated thermostat position. The closed-loop healthy model may further include utilizing the Extended Kalman Filter (EKF) to estimate a healthy estimated engine coolant temperature. In some instances, the closed-loop faulty model may include utilizing an Extended Kalman Filter (EKF) to estimate the faulty estimated thermostat position. The closed-loop faulty model may further include utilizing the Extended Kalman Filter (EKF) to estimate a faulty estimated engine coolant temperature. In some instances, the controller <NUM> may be further configured to utilize a comparison between the healthy estimated engine coolant temperature and the faulty estimated engine coolant temperature as a further indication of whether the thermostat is functioning appropriately.

With reference to <FIG>, the controller <NUM> may be configured to execute comparison and hypothesis testing. It will be appreciated that a thermostat such as the thermostat <NUM> may be configured to remain fully closed when the engine coolant temperature is below a first coolant temperature, which can be identified as Tc,min and to be fully open when the engine coolant temperature is above a second coolant temperature, which can be identified as Tc,max. The thermostat may be configured to be partially open (at a position between fully closed and fully open) when the engine coolant temperature is between the first coolant temperature Tc,min and the second coolant temperature Tc,max. In some cases, the first coolant temperature and the second coolant temperature are selectable based on thermostat characteristics and the particular type of thermostat that the engine <NUM> has. As an example, the first coolant temperature may range from about <NUM> degrees C to about <NUM> degrees C and the second coolant temperature may range from about <NUM> degrees C to about <NUM> degrees C.

<FIG> provides an example <NUM> of how the controller <NUM> may ascertain whether the thermostat is functioning properly. The controller <NUM> may compare and test hypothesis, as indicated at block <NUM>. In some case, the engine coolant temperature may be below Tc,min, as indicated at block <NUM>. In some cases, the engine coolant temperature may be above Tc,max, as indicated at block <NUM>. In some cases, the engine coolant temperature may be between Tc,min and Tc,max, as indicated at block <NUM>. If the engine coolant temperature is below Tc,min, as indicated at block <NUM>, then all models including the closed-loop healthy model and the closed-loop faulty model should all indicate that the thermostat is fully closed, as indicated at block <NUM>. If the engine coolant temperature is above Tc,max, as indicated at block <NUM>, then all models should indicate that the thermostat is fully open, as indicated at block <NUM>. If the engine coolant temperature is between Tc,min and Tc,max, as indicated at block <NUM>, then all of the models should indicate that the thermostat position is somewhere between fully closed and fully open, as indicated at block <NUM>. If any of these are not true, the controller <NUM> may perform further checks, such as but not limited to determining whether the cumulative radiator mass flow rate is above a threshold, as indicated at block <NUM>. If so, the controller <NUM> may determine that the thermostat is not functioning correctly, as indicated at block <NUM>.

With brief reference to <FIG>, it will be appreciated that a thermostat position ut is a dynamic model that can be described with the help of a heating curve ft<NUM>(Tc ) and a cooling curve ft<NUM>(Tc ) where Tc denotes the coolant temperature. Hysteresis may be defined as follows: <MAT>.

The hysteresis model of a thermostat opening ut may be given as a min-max operator over hysteresis curves ft<NUM>(Tc ) and ft<NUM> (Tc )) and past thermostat opening uT (k - <NUM>) as the following: <MAT>.

A temperature control model <NUM> can be created. Assuming, for simplicity, a sampling rate of <NUM> per second, the combustion dynamic model may be given by two difference equations that abstract the heat transfer from the generated heat to the coolant and to the ambient. The coolant temperature at the engine outlet may be given by the following: <MAT>.

A temperature control model <NUM> can be created. According to cooling system configuration, the coolant temperature at the engine inlet is given by flow mixing of radiator coolant flow ṁc,rad with temperature Tc,RadOut with the coolant flow ṁc,m and temperature Tc,m. This can be seen below: <MAT>.

Inserting inside the combustion difference equation yields the following first order model: <MAT>.

It will be appreciated that the radiator coolant flow ṁc,rad, the engine coolant flow ṁc,eng and other flows through the cooler, heater ṁc,m depend on the thermostat position ut and revolutions of the pump Npump. Temperatures at the component outlets Tc,RadOut and Tc,m can be modeled based on the engine data and with the help of physical-based models. Other inputs such as combustion heat Q̇Comb can be determined from engine data.

<FIG> is a schematic block diagram of a method <NUM> for predicting a thermostat fault. In the method <NUM>, the controller <NUM> executes a closed-loop healthy model <NUM> as well as a closed-loop faulty model <NUM>. The closed-loop healthy model <NUM> and the closed-loop faulty model <NUM> are executed simultaneously. One of the outputs of the closed-loop healthy model is an estimated healthy thermostat opening ût and one of the outputs of the closed-loop faulty model is an estimated faulty thermostat opening ûf. These two values are compared at a block <NUM>, which leads to a determination of a detected leak, as indicated at block <NUM>. In this, the thermostat is considered to be leaking if the actual thermostat position is different than expected, based on engine coolant temperatures. In some instances, the thermostat may be considered to be leaking if the thermostat is stuck at any particular position, whether fully open, fully closed or somewhere in between, regardless of engine coolant temperatures.

The Extended Kalman Filter (EKF) is a non-linear estimator of the internal dynamical states for a state-space system that is affected by additive noise. The internal model may be augmented with noise, as indicated below: <MAT>.

In this, wk is the process noise with a covariance <MAT> and νk is the measurement noise with a covariance <MAT>.

The closed-loop model of a healthy system includes measured coolant temperature Tc,EngOut with the Kalman gains LT and Lu, and is described by the following: <MAT>.

The output of EKF (Extended Kalman Filter) is an estimated coolant temperature T̂c,EngOut and estimated thermostat position ût. It will be appreciated that estimated radiator flow may be determined from a flow model of engine coolant through the radiator <NUM> that depends on the estimated thermostat opening ût and a pump speed Npump. The estimated radiator flow may be indicated as ṁc,rad (ût, Npump).

The closed-loop model of a faulty system includes measured coolant temperature T̂c,EngOut with the Kalman gains LT and Lu and the faulty thermostat position ûf, and is described by the following: <MAT>.

The output of EKF (Extended Kalman Filter) is an estimated coolant temperature T̂c,EngOut and estimated thermostat position ûf in a fault case. Fault case is considered when the thermostat model does not follow the heating and cooling curves at nominal characteristics. It will be appreciated that estimated radiator flow may be determined from a flow model of engine coolant through the radiator <NUM> that depends on the estimated thermostat position ûf and a pump speed Npump. The estimated radiator flow may be indicated as ṁc,rad(ûf, Npump).

<FIG> is a graphical representation <NUM> showing an example of measured data. In the graphical representation <NUM>, the vertical axis denotes number of drive cycles and the horizontal axis denotes the measured cumulative radiator flow per minute. A number of healthy cases are indicated within a healthy case ellipse <NUM> and a number of faulty cases are indicated within a faulty case ellipse <NUM>. It can be seen that a separation threshold <NUM> is defined therebetween.

<FIG> is a schematic block diagram of a model <NUM> that may be used to estimate an unmeasured radiator flow via an Extended Kalman Filtering approach. Model inputs <NUM> are fed to a reference model <NUM>. An output of the reference model <NUM> is an estimated temperature <NUM>. The estimated temperature <NUM> and a measured temperature <NUM> from an engine coolant temperature sensor are fed to a summation point <NUM>, and then to an EKF (Extended Kalman Filter) <NUM>. An estimated thermostat position is outputted from the EKF <NUM>. Given the estimated thermostat position and pump speed, the estimated radiator flow can be determined.

<FIG> is a flow diagram showing an illustrative series <NUM> of steps that the controller <NUM> or an engine management system including the functionality of the controller <NUM> is configured to carry out. The controller <NUM> may be configured to receive one or more model inputs including data related to operation of the engine, and calculate an estimated engine coolant temperature, as indicated at block <NUM>. The one or more model inputs may include, for example, a mass flow rate of coolant through the engine. The mass flow rate of coolant through the engine may be estimated using a rotational speed of a coolant pump circulating coolant through the engine and an estimated thermostat position.

The controller <NUM> may be configured to receive an engine coolant temperature signal from the engine coolant temperature sensor, as indicated at block <NUM>. The controller <NUM> may be configured to analyze the engine coolant temperature signal and the estimated engine coolant temperature to determine whether a thermostat fault is present, as indicated at block <NUM>. The controller <NUM> may be configured to determine that a thermostat fault is present when the estimated engine coolant temperature varies by more than <NUM> degrees C, or perhaps <NUM> degrees C, from an actual engine coolant temperature as indicated by the engine coolant temperature signal. The controller <NUM> may be configured to issue a warning signal responsive to the presence of the thermostat fault, as indicated at block <NUM>. In some cases, the controller <NUM> may also be configured to use a reference model and the one or more model inputs to calculate the estimated engine coolant temperature.

<FIG> is a flow diagram showing an illustrative method <NUM> of monitoring performance of a thermostat within an engine cooling system, the engine cooling thermostat including a radiator and a coolant pump circulating coolant, the thermostat controlling flow of coolant through the radiator. The method includes receiving an engine coolant temperature signal from an engine coolant temperature sensor, as indicated at block <NUM>. The engine coolant temperature signal is supplied to an Extended Kalman Filter (EKF), the EKF estimating an estimated engine coolant temperature and an estimated thermostat position, as indicated at block <NUM>. The estimated engine coolant temperature is compared with an actual engine coolant temperature as indicated by the engine coolant temperature signal, as indicated at block <NUM>.

When the estimated engine coolant temperature is within a temperature range centered on the actual engine coolant temperature, a determination may be made that the thermostat position is appropriate, as indicated at block <NUM>. When the estimated engine coolant temperature is outside a temperature range centered on the actual engine coolant temperature, a determination may be made that the thermostat position is not appropriate, as indicated at block <NUM>. In some cases, the method <NUM> may further include comparing the estimated thermostat position with what an actual thermostat position should be based on the actual engine coolant temperature, and turning on the warning flag when there is a discrepancy between the estimated thermostat position and the actual thermostat position, as indicated at block <NUM>.

Claim 1:
A method of monitoring performance of a thermostat within an engine cooling system, the engine cooling system including a radiator and a coolant pump circulating coolant, the thermostat controlling flow of coolant through the radiator, the method comprising:
receiving (<NUM>) an engine coolant temperature signal from an engine coolant temperature sensor;
supplying (<NUM>) the engine coolant temperature signal to an Extended Kalman Filter (EKF), the EKF estimating an estimated engine coolant temperature and an estimated thermostat position;
comparing (<NUM>) the estimated engine coolant temperature with an actual engine coolant temperature as indicated by the engine coolant temperature signal;
wherein when the estimated engine coolant temperature is within a temperature range centered on the actual engine coolant temperature, determining (<NUM>) that the thermostat position is appropriate;
and when the estimated engine coolant temperature is outside a temperature range centered on the actual engine coolant temperature, determining (<NUM>) that the thermostat position is not appropriate; and
comparing (<NUM>) the estimated thermostat position with what an actual thermostat position should be based on the actual engine coolant temperature, and turning on a warning flag when there is a discrepancy between the estimated thermostat position and the actual thermostat position.