Patent Application
20170145976
The present disclosure relates to a powertrain system having fault-tolerant coasting control logic.
In a powertrain having an internal combustion engine coupled to a transmission, a 12-volt DC auxiliary starter motor can be selectively energized to rotate a crankshaft of the engine and thereby start the engine. Hybrid powertrains use an engine in conjunction with one or more electric machines to optimize powertrain efficiency. One type of hybrid electric powertrain uses a belted-alternator-starter (BAS) in which the electric machine is coupled to the crankshaft, e.g., via a belt and pulley system. The auxiliary starter motor or the electric machine may be used to start the engine in some powertrain configurations, with torque from the engine used to power the electric machine in a generator mode to recharge an electrical storage system.
A method is disclosed herein for providing fault-tolerant coasting control of a powertrain system having an internal combustion engine, an auxiliary starter motor, a first energy storage system (ESS), and a controller. In an example embodiment, the method includes receiving, via the controller, a measured real impedance value of the first ESS from a frequency analyzer device at the calibrated frequency (ω), for instance 1000 Hz±500 Hz. This occurs while the engine is running. The method also includes comparing the measured real impedance value to a calibrated impedance value and enabling execution of a coasting maneuver of the powertrain system via the controller, i.e., turning off the engine above a threshold speed, e.g., vehicle or engine speed, only when the measured real impedance value is less than the calibrated threshold impedance value.
The method may also include starting the engine during the coasting maneuver using energy from a second ESS to thereby exit the coasting maneuver. This occurs when the measured real impedance value exceeds the calibrated impedance value. The method also includes preventing subsequent execution of the coasting maneuver in logic of the controller for as long as the measured real impedance value remains high relative to the calibrated impedance value.
An embodiment of the powertrain system is also disclosed herein having an engine, an auxiliary starter motor, a rechargeable ESS, a frequency analyzer device, and the controller noted above. The auxiliary starter motor is operatively connected to the engine and configured to selectively start the engine. The rechargeable ESS is electrically connected to the auxiliary starter motor. The controller is programmed to provide fault-tolerant coasting control of the powertrain system using the method noted above.
The second ESS in this embodiment may be a non-rechargeable or rechargeable device, e.g., a primary or secondary battery, respectively.
Starting the engine using energy from the second ESS may include activating a relay or other mechanical or semiconductor switch to connect the second ESS to the auxiliary starter motor. The second ESS may be a supercapacitor in some embodiments.
The detailed description and the drawings are supportive and descriptive of the disclosure, but the scope of the disclosure is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claims have been described in detail, various alternative designs and embodiments exist for practicing the disclosure defined in the appended claims.
Referring to the Figures, wherein like reference numbers indicate like or corresponding parts throughout the several views, a powertrain system 10 is shown schematically in
The vehicle 10 may include, in addition to the powertrain 12 and engine 14 noted above, a transmission (T) 16 and an electric machine 38, the latter of which is also labeled as MGU in
The powertrain 12 as configured herein includes an electrical system 22 operable for starting and stopping the engine 14 as needed, such as to conserve fuel. In the vehicle 10, this may occur while idling at a stoplight or at higher rates of speed of the vehicle 10 or engine 14 while coasting. As used herein, the terms “coasting” and “coasting maneuver” refer to an operating mode in which the vehicle 10 is operating above a particular speed, e.g., 50 MPH of ground speed, with the engine 14 turned off. Although omitted for illustrative clarity, the electrical system 22 may include other components such as power electronics, voltage regulators, power inverters, and the like.
A controller 50 is equipped with a frequency analyzer device SZ, e.g., a microchip or circuit operable for directly measuring the impedance across first energy storage system 54 (ESS1) at a calibrated frequency (ω) as set forth below with reference to
The controller 50 of
With respect to the example vehicle 10 of
The vehicle 10 may be equipped with a belted alternator-starter (BAS) system as shown. In such an embodiment, an endless rotatable drive member 37 such as a closed loop of belt or chain is driven via a first pulley 34 or a second pulley 48 depending on the operating mode. The first pulley 34 may be coupled to the crankshaft 23 such that the first pulley 34 and the crankshaft 23 can rotate in unison. The electric machine 38 is likewise selectively coupled to the engine 14, with torque from the electric machine 38, powered by the electrical system 22 via a power inverter module (PIM) 49 when the electric machine 38 is a polyphase device, possibly harnessed to assist torque from the engine 14 or to charge an energy storage system (ESS1) 54 in reducing fuel consumption and emissions of the vehicle 10. For example, in certain embodiments the electric machine 38 can start the engine 14 from the belt side of the engine 14 via a second pulley 48 or provide torque to the crankshaft 23 to assist in propelling the vehicle 10, such as while coasting or sailing with the engine 14 turned off. The electric machine 38 can also be selectively utilized as a generator to generate electrical current or recharge the first ESS 54 and, in some embodiments, the second ESS 56.
An auxiliary starter motor 45 (Ms) may be selectively activated to deliver torque to the crankshaft 23. For example, the starter motor 45 may draw power from the electrical system 22, again via the PIM 49 if the starter motor 45 is a polyphase device or directly if a DC motor device. Once energized, the starter motor 45 can deliver motor torque via a gear element 63 to a ring gear 30 connected to the crankshaft 23 as shown, drawing power from the electrical system 22 as set forth below. The starter motor 45 may be engaged with the electric machine 38 in some embodiments, e.g., via the gear element 60 shown schematically in
The electric machine 38 includes a rotor shaft 44 that selectively transfers motor torque to the crankshaft 23 to start the engine 14. The second pulley 48 is coupled to the rotor shaft 44. For certain operations, the rotor shaft 44 and the second pulley 48 can rotate in unison, while in other operations the rotor shaft 44 and the second pulley 48 are rotatable separately or one rotates while the other does not.
With respect to the electrical system 22 of
To achieve the desired ends, the controller 50 may include or be placed in communication with the frequency analyzer device SZ, which is operable for measuring a total impedance Z(ω) across the first ESS 54 at a calibrated frequency (ω) when the engine 14 is running. The second ESS 56 may be evaluated in the same manner. In a particular non-limiting example embodiment, the calibrated frequency (ω) is about 1000 Hz. That is, a typical duration (T) of a peak power pulse when cranking and starting the engine 14 is about 1 millisecond, which corresponds to a frequency (ω) equal to
or 1000 Hz. Sufficient performance may be enjoyed within a reasonable band of this frequency, e.g., 1000 Hz±500 Hz. Embodiments of greater than 1500 Hz or less than 500 Hz may be used within the scope of the disclosure, e.g., 1 Hz-1 MHz. However, at least with respect to higher frequencies, inductive effects can result that may be difficult to characterize.
In the example embodiment of
Referring briefly to
Z(ω)=√{square root over ([(ZIM)2+(ZR)2])}
A calibrated new ESS 54 may have the total impedance curve Z(ω), with a high-frequency intercept point 62 indicative of pure ohmic drop. As a given ESS experiences a high-frequency failure such as an electrical short or loss of conductivity, e.g., due to age, the impedance curve will shift to the right in
The controller 50 can request measurement of the total impendence of the ESS 54 or 56 at the calibrated frequency (ω) using the frequency analyzer device SZ, compare the measured impedance to a calibrated impedance value, and execute a control action with respect to the powertrain 12 if and when the measured impedance exceeds the calibrated impedance value. That is, the controller 50 can ensure that the engine 14 is not turned off when the measured impedance exceeds the calibrated impedance value, in addition to executing other control actions prompting service. In a particular embodiment, the frequency analyzer device SZ may be an integrated circuit or chip operable for directly measuring the impedance to a high degree of accuracy. As electrical currents are generally low in the electrical system 22, calculation of the impedance from voltage and current may not produce optimal accuracy, and therefore the frequency analyzer device SZ provides an accurate hardware solution that may be used as part of the electrical system 22.
Referring to
In
Referring to
Step S104 includes comparing the measured impedance value from step S102 to a calibrated impedance value. The method 100 proceeds to step S106 when a value less than the calibrated impedance value is detected, or to step S108 in the alternative when a value exceeding the calibrated impedance value is detected, or as noted below, an impedance trajectory indicates that the measured impedance will likely exceed the calibrated impedance value during the coasting maneuver.
At step S106, the controller 50 enables the coasting/sailing maneuver. Step S106 may entail setting a bit flag or permission in memory (M) such that a separate controller, or the controller 50, can thereafter allow the engine 14 to turn off and coasting to commence. The method 100 then proceeds to step S110.
At step S108, the controller 50 disables the coasting maneuver. Step S108 may entail setting a bit flag or permission in memory (M) such that a separate controller, or the controller 50, can thereafter prevent the engine 14 from turning off and coasting. Step S108 may also include setting a diagnostic code in memory (M) and possibly activating an indicator lamp within the vehicle 10, sending a text message, or otherwise alerting an operator of the vehicle 10 to the need to service the first ESS 54, or the second ESS 56 or 156 depending on which device is being evaluated.
Step S110 includes determining, while coasting, whether the received impedance value remains less than the calibrated impedance value noted above. That is, the first ESS 54 may experience a fault while the powertrain 12 is actively coasting, or the controller 50 may determine that such a fault is likely to occur after entering the coasting maneuver as set forth below. In this event, the method 100 proceeds to step S112.
At step S112, the controller 50 may execute another control action with respect to the powertrain 12. In this instance, the controller 50 may activate the first switch S1 of
Those of ordinary skill in the art will appreciate that other variations of the method 100 may be contemplated. For instance, a look-ahead or preemptive embodiment may be envisioned in which the engine 14 of
That is, rather than evaluating the impedance of the first ESS 54 at the point in time at which the coasting maneuver is to be commanded or enabled by the controller 50, the controller 50 may calculate an impedance trajectory using the measured real impedance value, and then enable the coasting maneuver only when the measured real impedance value is less than the calibrated impedance value and the impedance trajectory will not result in the measured impedance value exceeding the calibrated impedance value during the duration of the coasting maneuver.
For instance, the controller 50 may evaluate the change in impedance at a plurality of different time points over a calibrated interval prior to entry into the coasting maneuver. By projecting the change in impedance forward in time over a likely duration of the coasting maneuver, the controller 50 can quickly determine whether the impedance of the first ESS 54 will rise above the calibrated impedance value during the course of the coasting maneuver. In such an event, the controller 50 can prevent entry into the coasting maneuver in a preemptive manner and execute the required control actions noted above, e.g., setting a diagnostic code or otherwise alerting an operator as to the current state of the ESS 54.
While the best modes for carrying out the disclosure have been described in detail, those familiar with the art to which this disclosure relates will recognize various alternative designs and embodiments for practicing the disclosure within the scope of the appended claims. Furthermore, the embodiments shown in the drawings or the characteristics of various embodiments mentioned in the present description are not necessarily to be understood as embodiments independent of each other. Rather, it is possible that each of the characteristics described in one of the examples of an embodiment can be combined with one or a plurality of other desired characteristics from other embodiments, resulting in other embodiments not described in words or by reference to the drawings. Accordingly, such other embodiments fall within the framework of the scope of the appended claims.
