An automated method for diagnosing an EGHR having a coolant path, an exhaust path, a heat exchanger, and a valve. The coolant path passes through the heat exchanger and the valve selectively directs the exhaust path through the heat exchanger. The method includes monitoring an inlet temperature and an outlet temperature of the coolant path, determining an instantaneous coolant power from the monitored inlet temperature and outlet temperature, and integrating the instantaneous coolant power to determine a total energy recovered by the coolant path. The method monitors an instantaneous exhaust power, determines an instantaneous available EGHR power from the instantaneous exhaust power, and integrates the instantaneous available EGHR power to determine a nominal EGHR energy. A differential is calculated between the nominal EGHR energy and the total energy recovered by the coolant path. If the calculated differential is greater than an allowable tolerance, an EGHR error signal is sent.

TECHNICAL FIELD

This disclosure relates to diagnostics and control of exhaust gas heat recovery (EGHR) mechanisms.

BACKGROUND

Some vehicles have exhaust gas heat recovery (EGHR) mechanisms. For example, discharge waste energy from the vehicle's exhaust may be extracted to enhance the warm-up of engine coolant. Additionally, the interior of the vehicle, liquid conditioned batteries, or thermal electric systems could also be warmed using exhaust heat energy.

SUMMARY

An automated method for diagnosing an exhaust gas heat recirculation (EGHR) mechanism is provided. The EGHR mechanism has a coolant path, an exhaust path, a heat exchanger, and a valve. The coolant path passes through the heat exchanger and the valve selectively routes, passes, or directs the exhaust path through the heat exchanger.

The automated method includes monitoring an inlet temperature of the coolant path and monitoring an outlet temperature of the coolant path. The method determines an instantaneous coolant power from the monitored inlet temperature and outlet temperature. The instantaneous coolant power is integrated to determine a total energy recovered by the coolant path.

The method also includes monitoring an instantaneous exhaust power and monitoring an instantaneous EGHR efficiency. The method determines an instantaneous available EGHR power from the instantaneous exhaust power and the instantaneous EGHR efficiency.

The method includes calculating at least one of a minimum average recovery and a maximum average recovery from the instantaneous available EGHR power and integrates the calculated minimum or maximum average recovery to determine at least one of a minimum energy tolerance and a maximum energy tolerance. The method includes comparing the total energy recovered to the minimum energy tolerance or maximum energy tolerance. If the total energy recovered is less than the determined minimum energy tolerance or if the total energy recovered is greater than the maximum energy tolerance, the method includes determining that there is an error with the EGHR mechanism and sends an EGHR error signal.

The above features and advantages, and other features and advantages, of the present invention are readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the invention, which is defined solely by the appended claims, when taken in connection with the accompanying drawings.

DETAILED DESCRIPTION

Referring to the drawings, like reference numbers correspond to like or similar components wherever possible throughout the several figures. There is shown inFIG. 1a portion of a powertrain10, which may be a conventional or hybrid powertrain. The schematic powertrain10shown includes an internal combustion engine12and an electric motor14. The engine12may be spark ignition or compression ignition.

While the present invention may be described with respect to automotive or vehicular applications, those skilled in the art will recognize the broader applicability of the invention. Those having ordinary skill in the art will recognize that terms such as “above,” “below,” “upward,” “downward,” et cetera, are used descriptively of the figures, and do not represent limitations on the scope of the invention, as defined by the appended claims. Any numerical designations, such as “first” or “second” are illustrative only and are not intended to limit the scope of the invention in any way.

Features shown in one figure may be combined with, substituted for, or modified by, features shown in any of the figures. Unless stated otherwise, no features, elements, or limitations are mutually exclusive of any other features, elements, or limitations. Furthermore, no features, elements, or limitations are absolutely required for operation. Any specific configurations shown in the figures are illustrative only and the specific configurations shown are not limiting of the claims or the description.

As shown inFIG. 1, a control system16is in communication with, and capable of operating, portions of the powertrain10. The control system16is illustrated in highly schematic fashion. The control system16is mounted on-board the vehicle and in communication with several components of the powertrain10. The control system16performs real-time, on-board detection, diagnostic, and calculation functions for the powertrain10.

The control system16may include one or more components with a storage medium and a suitable amount of programmable memory, which are capable of storing and executing one or more algorithms or methods to effect control of the powertrain10. Each component of the control system16may include distributed controller architecture, and may be part of an electronic control unit (ECU). Additional modules or processors may be present within the control system16. If the powertrain10is a hybrid powertrain, the control system16may alternatively be referred to as a Hybrid Control Processor (HCP).

The control system16may be configured to execute an automated method for diagnosing an exhaust gas heat recovery or recirculation mechanism, or simply EGHR mechanism20. Generally, the EGHR mechanism20allows the powertrain10to selectively capture thermal energy being expelled from the engine12as a result of combustion.

The EGHR mechanism20includes a heat exchanger22and a valve24. A coolant path30, which includes a coolant inlet31and a coolant outlet32, passes through the heat exchanger22. The coolant path30also passes or flows through the engine12, and may pass through other components, such as a transmission (not shown) or heater core (not shown).

In the highly schematic diagram shown, coolant fluid within the coolant path30flows substantially-constantly through the heat exchanger22. However, some systems may include a bypass channel or a variable pump to selectively prevent coolant from flowing through the heat exchanger22.

An exhaust path34, having an exhaust inlet35and an exhaust outlet36, also passes through the EGHR mechanism20. However, depending on operating conditions of the powertrain10, the valve24selectively directs flow of the exhaust path34through the heat exchanger22. The exhaust path34carries exhaust gases from the engine12to, ultimately, be expelled from the vehicle. The exhaust gases have varying levels of thermal energy (heat), some of which may be captured by the heat exchanger22of the EGHR mechanism20and redirected via the coolant path30to the engine12or other components.

The valve24is selectively movable or adjustable between at least two positions: a recovery mode and a bypass mode. The recovery mode is schematically illustrated inFIG. 1and is configured to direct the flow of exhaust gases through the exhaust path34through the heat exchanger22. In recovery mode the coolant path30and the exhaust path34are in direct heat-transfer communication through the heat exchanger22. Generally, when the valve24and the EGHR mechanism20are in recovery mode, the exhaust path34will transfer thermal energy to the coolant path30and will warm the coolant therein.

When the valve24and the EGHR mechanism20are in bypass mode, the exhaust path34does not pass through the heat exchanger22. Although the coolant path30and the exhaust path34are not in direct heat-transfer communication through the heat exchanger22, some thermal energy may be transferred from the exhaust path34to the coolant path30. This energy transfer may be referred to as parasitic heat and may be the result of the close proximity, even when in the bypass mode, of the coolant path30to the exhaust path34.

The valve24may be any suitable mechanism capable of switching the EGHR mechanism20between the recovery mode and the bypass mode. Note that the valve24may also be capable of directing only a portion of the exhaust path34through the heat exchanger22, which may be referred to as partial-recovery mode. The valve24may be, for example and without limitation: a wax motor or an electromechanical switch.

Wax motors may be actuated by temperature of the coolant within the coolant path30, such that the wax motor closes the heat exchanger22from the exhaust path34as the coolant warms. An electromechanical switch may respond to a signal from the control system16to place the valve24into either the bypass or recovery mode. Note that regardless of the mechanism used, the valve24may default to either the bypass mode or the recovery mode, depending upon system design.

A first sensor41is disposed within or adjacent to the coolant inlet31, such that the first sensor41determines the temperature of the coolant entering the EGHR mechanism20and the heat exchanger22. Similarly, a second sensor42is disposed within or adjacent to the coolant outlet32, such that the second sensor42determines the temperature of the coolant leaving the EGHR mechanism20and the heat exchanger22.

The first sensor41measures an inlet temperature, Ti, of the coolant and the second sensor measures an outlet temperature, To, of the coolant. The control system16reads the first temperature and the second temperature or receives the reading from other components, such as intermediate signal processors.

Referring now toFIG. 2, and with continued reference toFIG. 1, there is shown a chart50, which illustrates energy capture by the EGHR mechanism20in both the recovery mode and the bypass mode. The chart50includes an axis52, which represents time, and an axis54, which represents thermal energy recovered by the EGHR mechanism20to coolant within the coolant path30.

A mode-switch line56illustrates the approximate time at which the valve24switches from recovery mode to bypass mode. A first time period, to the left of the mode-switch line56, is representative of the EGHR mechanism20being in heat recover mode.

The first time period may occur just after startup of the engine20, such that it may be beneficial to capture thermal energy traveling through the exhaust path34and use that energy to warm the engine20or other components. During the first time period, the EGHR mechanism20should, ideally, capture as much of the thermal energy available in the exhaust path34. The second time period may occur after the engine20—and possibly also the heater core—is warm and no longer in need of recovered thermal energy.

Note that the mode-switch line56is representative of a desired change in the position of the valve24. In some instances, even though the control system16determines that the valve24should switch positions, the valve24may be stuck or there may be a problem with actuation of the valve24.

An actual coolant energy line60represents the total energy recovered by the EGHR mechanism20to the coolant path30. The total energy recovered is an accumulation of the instantaneous power captured by the coolant path30, as measured by the first sensor41and the second sensor42. The instantaneous coolant power may be determined by the first equation from mass flow of coolant, specific heat of the coolant, and temperature change.
{dot over (Q)}c={dot over (m)}c·cp(To−Ti)  (1)

The mass flow of the coolant in the coolant path30may be measured, such as by a flow meter, or may be estimated from operating conditions of other components. For example the speed of the engine12and the speed or power of pumps circulating the coolant may be used to estimate the mass flow. The specific heat may be estimated based upon the type of coolant and the ratio of coolant to water in the coolant path30.

The instantaneous coolant power may then be integrated to determine the total energy recovered, as shown in the second equation.
Qc=∫{dot over (Q)}cdt(2)

A nominal energy line62represents the total energy available to be recovered by the EGHR mechanism20into the coolant path30. The nominal energy line62is based upon the thermal power of the exhaust gases exiting the engine12.

When the EGHR mechanism20is operating at or near its optimal, the nominal energy line62and the actual coolant energy line60overlap. However, significant movements away from the nominal EGHR energy suggest that the EGHR mechanism20is not working properly, either because the EGHR mechanism20is recovering too little or too much of the available exhaust power. Possible causes of the fault may include, without limitation: a malfunctioning valve24; a blockage in the coolant path30or the heat exchanger22; a leak or failure in the exhaust path34; or other causes.

When there is a fault occurring with the EGHR mechanism20, regardless of the cause, the control system16sends or displays an error signal. For example, the control system16may display an error light or indicator light—such as a dashboard display icon—to alert the vehicle operator to the fault and may store an error code if the indicator light is not specific to the EGHR mechanism20, such as a check engine light. Alternatively, the control system16may utilize a communications network to alert a remote maintenance monitoring system, such as a phone, an email address, or a subscription-based centralized monitor.

To assess whether the actual coolant energy line60is too far from the nominal energy line62, the control system16may compare the difference between the actual coolant energy line60and the nominal energy line62to an allowable tolerance or variance. The allowable tolerance represents the amount by which the actual total energy recovered by the coolant path30may vary from the nominal EGHR energy. The allowance tolerance may be a fixed value or may vary based upon operating conditions.

Alternatively, as shown in the chart50, the control system16may compare the actual coolant energy line60to a minimum tolerance line64, below which is a fault zone65, or to a maximum tolerance line66, above which is a fault zone67. When the actual coolant energy line60falls below the minimum tolerance line64or moves above the maximum tolerance line66, the control system16may signal a fault in the EGHR mechanism20.

Whether the control system16uses differentials—such as the allowable tolerance—or compares the actual coolant energy line60to the minimum tolerance line64and the maximum tolerance line66, those comparison tolerances may be calculated as either fixed values or percentages of the nominal energy line62. Alternatively, the minimum tolerance line64or the maximum tolerance line66may be curves based upon integrating the instantaneous exhaust thermal power available to the EGHR mechanism20and the efficiency of the EGHR mechanism20.

In the illustrative example shown in the chart50, the engine12is outputting substantially constant thermal energy. The minimum tolerance line64is calculated based upon the EGHR mechanism20recovering approximately fifty-five percent of the available thermal power from the exhaust path34to the coolant path30while the valve24is in the recovery mode, which is shown to the left of the mode-switch line56.

Similarly, when the valve24is in the bypass mode, which is shown to the right of the mode-switch line56, the maximum tolerance line66is calculated based upon the EGHR mechanism20recovering approximately nine percent of the available thermal power from the exhaust path34to the coolant path30.

Note that when the exhaust path34is not carrying substantially constant thermal energy, the curves will vary more than in the chart50and there may be additional mode-switch lines56. However, the energy-capture rates used to establish the allowable tolerance may be the same.

The nominal energy line62is representative of the best performance that can be expected from the EGHR mechanism20. The nominal energy line62may also account for the efficiency of the EGHR mechanism20transferring that thermal power to the coolant path30, which is shown in the third equation. Note that the ideal efficiency may vary based upon operating conditions of the engine12.
Qnom=∫f({dot over (m)}ex,Tex)·Effideal·dt=∫{dot over (Q)}ex·Effideal·dt(3)

The exhaust temperature may be estimated based upon operating conditions of the engine12and any after-treatment systems. The mass flow of exhaust path34is based upon fuel and air entering the engine12, and may incorporate transport delays. If calculated, the specific heat of the exhaust is a function of the temperature of the exhaust. The allowable power flow is based upon minimum or maximum efficiency terms, as shown in the fourth equation.
{dot over (Q)}allow={dot over (Q)}ex·Effmix/max(4)
When the valve24is in the recovery mode, the control system16uses the recovery or minimum efficiency term, which may be approximately fifty-five percent; and when the valve24is in the bypass mode, the control system16uses the bypass or maximum efficiency term, which may be approximately nine percent. The allowable power flow may be integrated to establish the minimum tolerance line64and the maximum tolerance line66.

Referring now toFIG. 3, and with continued reference toFIGS. 1-2, there is shown a method100for controlling and diagnosing a powertrain with an EGHR mechanism, such as the powertrain10shown inFIG. 1. The method100may be executed completely or partially within the control system16.

FIG. 3shows only a high-level diagram of the method100. The exact order of the steps of the algorithm or method100shown may not be required. Steps may be reordered, steps may be omitted, and additional steps may be included. Steps shown in dashed or phantom lines may be optional. However, depending upon the specific configuration, any steps may be considered optional or may be implemented only selectively. Furthermore, the method100may be a portion or sub-routine of another algorithm or method.

For illustrative purposes, the method100is described with reference to elements and components shown and described in relation toFIG. 1and may be executed by the powertrain10itself or by the control system16. However, other components may be used to practice the method100or the invention defined in the appended claims. Any of the steps may be executed by multiple controls or components of the control system16.

The method100may begin at a start or initialization step, during which time the method100is made active and is monitoring operating conditions of the vehicle, the powertrain10and, particularly, the engine12and the EGHR mechanism20. Initiation may occur, for example, in response to the vehicle operator inserting the ignition key or the vehicle being placed into a mode in which the propulsion systems are active (i.e., the vehicle is ready to drive). The method100may be running constantly or looping constantly whenever the propulsion systems—including, at least, the engine12or the electric motor14—are in use.

Step112: Monitor Coolant Inlet and Outlet.

The method100includes monitoring an inlet temperature, Ti, of the coolant path30at the coolant inlet31, such as with the first sensor41. The method100also includes monitoring an outlet temperature, To, of the coolant path30at the coolant outlet32; such as with the second sensor42.

Any and all data output by the sensors shown and other sensors may be monitored by the method100. Furthermore, simple calculations within control system16or data provided by other modules or controllers are not described in detail and may be considered as monitored by the method100.

The method100finds the temperature difference between the coolant inlet31and the coolant outlet32. If the temperature changes, thermal power has been transferred to the coolant path30.

The100includes determining an instantaneous coolant power from the monitored inlet temperature and outlet temperature. The instantaneous coolant power may be determined from the equation above or a similar formula.

Step118: Calculate Total Energy Recovered.

The method100integrates the instantaneous coolant power to determine a total energy recovered by the coolant path30. Depending upon the operating mode, the control system16may be trying to recover high amounts of energy from the exhaust path34to the coolant path30.

The method100also monitors an instantaneous exhaust power. The instantaneous exhaust power may be determined as a function of the exhaust mass flow and the exhaust temperature. Alternatively, the instantaneous exhaust power may be determined from the amount of fuel combusted in the engine12or the torque produced by the engine12.

The method100includes monitoring an instantaneous EGHR efficiency of the EGHR mechanism20. The efficiency is the actual, and possibly ideal, ability of the EGHR mechanism20to transfer heat power of the exhaust path34to the coolant path30. The instantaneous EGHR efficiency varies with the temperature and flow conditions of the exhaust path34. Note that the method100may also use fixed values for the efficiency.

The maximum instantaneous EGHR efficiency may be around seventy percent. However, under many operating conditions, the efficiency will be in the sixty percent range, or less. The method100may also use the ideal efficiency to determine the allowable tolerance against which the total energy recovered by the coolant path30is compared.

The method100includes determining an instantaneous available EGHR power from the instantaneous exhaust power. The instantaneous available EGHR power may be determined by the instantaneous exhaust power multiplied by an assumed flat rate efficiency value. However, the instantaneous available EGHR power may also be determined from both the instantaneous exhaust power and the instantaneous EGHR efficiency. When variable efficiency is used, the method100may be more precise over a larger range of operating conditions of the engine12and the EGHR mechanism20.

The method100integrates the instantaneous available EGHR power to determine a nominal EGHR energy.

To determine whether a fault exists in the EGHR mechanism20, the method100includes calculating a differential between the nominal EGHR energy and the total energy recovered by the coolant path30. Alternatively, the method100may skip calculation of the energy differential, and directly compare the total energy recovered to minimum and maximum allowable tolerance levels.

Step130: Compare Energy Differential to Allowable Tolerance.

The method100includes comparing the differential to an allowable tolerance. Thermal power spikes or fluctuations, particularly during transient operating conditions of the engine12, are not representative of problems with the EGHR mechanism20. Therefore, the control system16and the method100account for transient conditions without improperly diagnosing an error in the EGHR mechanism20. By integrating the instantaneous coolant power to determine the total energy recovered, thermal power fluctuations do not drastically alter the total energy values. For example, even if the instantaneous power unexpectedly doubles for two seconds, the relative change in the total energy recovered will not trigger the method100to signal an error.

Whether comparing a differential to an allowable tolerance or directly comparing the total energy recovered to minimum and maximum values, the method may use average capture rates as comparisons. For example, the method100may use a minimum average recovery of fifty-five percent of the instantaneous exhaust power when the EGHR mechanism20is in the recovery mode, and may use a maximum average recovery of nine percent of the instantaneous exhaust power when the EGHR mechanism20is in the bypass mode.

If there is no fault with the EGHR mechanism20, such that there is no need to signal a fault or error code, the method100may end or repeat. The method100may continually loop or iterate.

If the calculated differential is greater than an allowable tolerance, the method100sends an EGHR error signal because there may be a fault with the EGHR mechanism20. The method100may signal the fault to an indicator light to alert the operator of the vehicle or may signal to a communications network.

The EGHR error signal indicates that there is a fault with the EGHR mechanism, but may not indicate the source or cause of the fault, which may be due to a malfunctioning valve24, faulty heat exchanger22, or other causes. Alternatively, the control system16may directly compare the total energy recovered by the coolant path30to minimum values, maximum values, or both. For example, the allowable tolerance may be calculated by comparing the nominal EGHR energy to one of the minimum tolerance line64and the maximum tolerance line66.

Regardless of the reasons for the error, the EGHR mechanism20needs to be inspected to determine where the fault exists, so the control system16sends a notification of the error. After signaling the fault, the method100may return to looping or iterating.

The method100may also incorporate the state command for the valve24and determine whether the EGHR mechanism20is in recovery mode or bypass mode. Determining the state command may assist the method100in determining the allowable tolerance for the total energy recovered by the coolant path30.

However, in some configurations, the method100may determine the state based upon the average of the instantaneous coolant power. For example, when the EGHR mechanism20is recovering less than twenty-five percent of the available exhaust energy, the method100may assume that the EGHR mechanism is in the bypass mode.

When the method100is determining the state command, the control system16may command the valve24into a recovery mode, in which both the coolant path30and the exhaust path34pass through the heat exchanger22, for a first time period. Then, the method100may calculate the allowable tolerance from the minimum line during the first time period.

The first time period is illustrated in the chart50as the area to the left of the mode-switch line56. During the first time period, if the total energy recovered falls into the fault zone65, then the control system16signals an error or fault with the EGHR mechanism20.

The control system16may also command the valve24into the bypass mode, in which only the coolant path30passes through the heat exchanger22, for a second time period. Then, the method100may calculate the allowable tolerance from the maximum line64during the second time period. The second time period is different from the first time period and is illustrated in the chart50as the area to the right of the mode-switch line56.

The method100may include validating the temperature sensors from the state and temperature information. The control system16may prevent flow through the exhaust path34during a third time period. For example, the control system16may shut down the engine12, such that no exhaust gases are being produced, during periods in which the powertrain10is propelled by the electric motor14or other hybrid propulsion systems. Furthermore, extended deceleration fuel cut-off (DFCO) periods may reduce thermal energy passing through the exhaust path34.

Following lapse of the third time period, the control system16compares the monitored inlet temperature to the monitored outlet temperature. The third time period is configured to be sufficient length that any remaining thermal energy in the exhaust path34or the heat exchanger22has dissipated or transferred to the coolant path30. Therefore, monitored inlet temperature and the monitored outlet temperature should come together and become substantially equal.

However, if the monitored outlet temperature is not substantially equal to the monitored inlet temperature, there may be an error with either the first sensor41or the second sensor42. Therefore, the control system16may send a sensor error signal.

Additionally, the method100may validate temperature sensors by monitoring temperature behavior after start-up of the engine12following long vehicle-off periods. For example, if the vehicle has been sitting in eighty-degree ambient weather for six hours, the inlet and outlet temperatures should begin at around eighty degrees. However, the temperatures of the coolant in the coolant path30should increase as a result of thermal heat extracted from the EGHR heat exchanger22and also thermal energy generated within the engine12.