The present disclosure relates to systems and methods for controlling an electronic throttle valve, such as a throttle valve of an internal combustion engine powering a marine propulsion device.
Many electronic throttle bodies have a limp home feature, in which a spring or springs force the throttle blade to a nominal high-idle condition in case of loss of control of the throttle valve, such as due to a signal or wiring failure. This spring requires that the throttle valve actuator, such as a motor geared to the throttle plate, apply a force to overcome the spring constant in order to move the throttle valve plate. The sign and amount of force required to move the throttle valve plate changes depending on whether the throttle valve is opening or closing, and depending on which side of the limp home position the throttle valve plate is located.
Additionally, a gear train that connects the motor to the throttle valve may have backlash that causes a delay in response of the throttle valve plate to actuation of the motor. Because teeth of meshed gears in the gear train may not be in tight contact with one another, they may have some play or lash between them, resulting in a delay between when a first gear in the gear train is moved until a second gear having teeth complementary to those of the first gear responds to such movement. Such backlash is most often seen when a switch from loading one side of a gear tooth to an opposite side thereof is required, such as when the gear train is actuated to change the direction of the throttle plate from opening to closing, or vice versa.
This Summary is provided to introduce a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.
One example of the present disclosure is of a method for controlling a position of an electronic throttle valve of an internal combustion engine. The method includes determining a desired throttle valve position. The method also includes determining a first feed forward signal based on a rate of change between a previous throttle valve position and the desired throttle valve position, and determining a second feed forward signal based on a comparison of the desired throttle valve position to a limp home position of the throttle valve, in which the throttle valve is biased open by a spring. The first and second feed forward signals are then summed to actuate the throttle valve. After the throttle valve is actuated according to the first and second feed forward signals, the method includes controlling the position of the throttle valve with a feedback controller so as to obtain the desired throttle valve position.
Another example of the present disclosure is of a system for controlling a position of an electronic throttle valve of an internal combustion engine to a desired throttle valve position. The system includes a motor coupled to the throttle valve, a throttle position sensor sensing a current throttle valve position, and a controller in signal communication with the motor and the throttle position sensor. The controller determines a first feed forward signal based on a rate of change between a previous throttle valve position and the desired throttle valve position. The controller also determines a second feed forward signal based on a comparison of the desired throttle valve position to a limp home position of the throttle valve, in which the throttle valve is biased open by a spring. The controller then combines the first and second feed forward signals and sends them to the motor to actuate the throttle valve. After actuating the throttle valve according to the first and second feed forward signals, the controller compares the current throttle valve position to the desired throttle valve position and generates a feedback signal to correct the position of the throttle valve.
The present disclosure is described with reference to the following Figures. The same numbers are used throughout the Figures to reference like features and like components.
In the present description, certain terms have been used for brevity, clarity, and understanding. No unnecessary limitations are to be inferred therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes only and are intended to be broadly construed.
Referring to
Returning to
According to the present disclosure, the controller 42 determines one or more feed forward signals to send to the motor 16 to move the throttle valve 12, which feed forward signals rectify backlash problems with prior art throttle control systems that rely solely on feedback control to achieve a desired position of the throttle valve 12 when the desired position is near the limp home position. For example, the controller 42 determines a first feed forward signal (velocity feed forward signal), using first feed forward calculator 44, based on the rate of change between a previous throttle valve position and the desired throttle valve position. Using a second feed forward calculator 46, the controller 42 determines a second feed forward signal (position feed forward signal) based on a comparison of the desired throttle valve position to the limp home position of the throttle valve 12, in which the throttle valve 12 is biased open by a spring 32. In one example, the desired throttle valve position and throttle valve velocity are limited by a limiter 52 before being sent to the throttle valve 12 as a throttle position and velocity setpoints. Limiting the velocity setpoint prevents an instantaneous spike in the feed forward velocity upon a step change. In one example, the limiter 52 uses a rate limit and an acceleration limit to limit the position setpoint (sent to second feed forward calculator 46 and feedback control section 40) and the velocity setpoint (sent to first feed forward calculator 44). The controller 42 determines the first feed forward signal from a look up table or similar input-output map of the first feed forward calculator 44. How the controller 42 determines the second feed forward signal will be discussed in greater detail herein below.
The controller 42 combines the first and second feed forward signals, for example at summer 48, and sends the combined signal to the motor 16 to actuate the throttle valve 12. After the throttle valve 12 has been actuated according to the combined first and second feed forward signals, the controller 42 compares the current throttle valve position to the desired throttle valve position and generates a feedback signal, using feedback control section 40, to correct the position of the throttle valve 12. During the next iteration of control, each of the outputs from the feedback control section 40, first feed forward calculator 44, and second feed forward calculator 46 are summed together at summer 48 and sent as a signal to the motor 16 to actuate the throttle valve 12.
Now turning to
This response of the throttle valve position to the change in duty cycle illustrates the effects of both backlash in the gear train 18 as well as a change from loading one side of the spring 32 to loading an opposite side of the spring 32 as the throttle blade 22 crosses over the limp home position. In one example of the present system, the second feed forward calculator determines a second feed forward signal that compensates for both the backlash of the gear train 18 and for the shift in load due to the different spring constant as the throttle blade 22 crosses over the limp home position. To do so, the controller 42 varies the second feed forward signal depending on whether moving the throttle valve 12 from the previous position to the desired position requires a directional change in movement of the throttle valve 12. If a directional change is not required, the controller 42 will either add or subtract an incremental duty cycle using a second feed forward signal that is based on a difference between the desired throttle position and the previous throttle position. For example, if the controller 42 determines that the desired throttle position is in the neutral zone and is increasing, the controller 42 may add an incremental duty cycle to step over the backlash in the system represented at arrow 301. In other words, the controller 42 increments the duty cycle high enough to effect a change in the throttle valve position and shift it out of the neutral zone 313.
On the other hand, if a directional change of the throttle blade 22 is required (i.e. the throttle valve is changing from opening to closing, or vice versa), the controller 42 may either add or subtract a step change in duty cycle using the second feed forward signal so as to overcome the backlash of the gear train 18. To do so, the controller 42 could effelctively add or subtract a step change that would bring the throttle position all the way from the area where the backlash shown by arrows 301 and 305 begins, to where the backlash ends. In effect, the duty cycle step change provided by the second feed forward signal would cause the load on the gear teeth to jump from one side to the other. Providing this switched loading on the gear teeth with a tfeed forward signal avoids problems associated with prior art feedback-only control, in which the feedback controller would wind up to the provide the required switched loading and eventually slam the loading in the opposite direction, which required that the feedback control section later unwind.
Continuing the example in which the duty cycle is increasing, once the duty cycle has increased as shown at arrow 303 so much that the throttle valve position exits the neutral zone 313, the response of the throttle valve position to the duty cycle begins to level off, as shown at arrow 309. This means that roughly the same duty cycle is required to effect any given position of the throttle valve 12. Similarly, as the duty cycle is decreasing as shown by arrow 307, the response of the system eventually levels off as shown by arrow 311, where the duty cycle required to maintain a particular throttle valve position is roughly constant.
Turning to
Still referring to
In one example, the curve 407 includes a neutral point 410, representing a position of the throttle valve 12 when the applied duty cycle is zero, i.e. the limp home position. This limp home position 410 may or may not correspond exactly to a 0% throttle valve position depending on whether a biasing force is present, e.g. the throttle blade shaft 20 is slightly offset or there is an air foil/wedge on one side of the throttle blade 22. The second feed forward signal can be determined from this curve 407: for example, the required duty cycle can be calculated using one or more linear equations representing the curve 407, given an input desired throttle valve position. In one example, the curve 407 may have two different slopes, i.e. between point 409 and 410, and between point 410 and 411, and therefore two different linear relationships between the input desired throttle valve position and the output second feed forward term. In another example, the curve 407 may have one slope and may extend directly from point 409 to 411.
Because the response of the system 10 to a signal's duty cycle is predictable above and below the upper and lower throttle valve position thresholds 401, 403, respectively, a calibratable feed forward signal may be provided as the second feed forward signal above and below these thresholds 401, 403. For example, the second feed forward signal may be a first predetermined duty cycle (in the example, 20%) when the desired throttle valve position is above the upper throttle valve position threshold 401, and may be a second predetermined duty cycle (in the example, −20%) when the desired throttle valve position is below the lower throttle valve position threshold 403. These exemplary duty cycles would of course vary depending on the particular throttle valve 12, motor 16, and other components of the system 10. The predetermined duty cycles can be calibrated values that are retrieved by the second feed forward calculator 46, or can be adapted as the system learns the neutral point of the throttle valve 12.
In one example, the controller 42 learns the limp home position 410 of the throttle valve 12 on the duty cycle curve 407 when a commanded duty cycle is zero and an actual position of the throttle valve 12 is within a predetermined range of an estimate of the limp home position. The limp home position can be learned or adapted and stored in the memory 54 between key cycles. The learning of the limp home position of the throttle valve occurs during normal operation of the throttle valve 12 and is non-intrusive. Any time the commanded duty cycle is zero (within a calibratable window), actual position is within a calibratable range of the estimated neutral point, and there is not a throttle control error present, the learning will occur.
After the desired throttle position shifts firom one feed forward zone to another, the second feed forward calculator 46 may optionally reset the output of the feedback control section 40, as the feedback from control in the prior zone is not relevant to feedback from control that will occur in the new zone. In another example, the PID outputs are blended out as the system shifts from one feed forward zone to another.
As mentioned above, after the throttle valve 12 has been moved according to the feed forward signals, the feedback control section 40 accounts for any error in the position of the throttle valve 12. However, by providing appropriate compensations in the neutral zone of the throttle valve 12, the electronic throttle control system now relies less on the feedback control section 40 to achieve the desired throttle valve position. This allows for a faster response and more robust control.
Referring to
In one example, the second feed forward signal also compensates for backlash of a gear train that couples a motor to the throttle valve. The second feed forward signal may vary depending on whether moving the throttle valve from the previous position to the desired position requires a directional change in movement of the throttle valve. In one example, the method includes one of adding and subtracting an incremental duty cycle with the second feed forward signal based on a difference between the desired throttle position and the previous throttle position if the directional change is not required. In another example, the method further comprises one of adding and subtracting a step change in duty cycle with the second feed forward signal so as to overcome the backlash if the directional change is required.
The method may alternatively comprise detennining the second feed forward signal from a duty cycle curve that extends between an upper throttle valve position threshold and a lower throttle valve position threshold representing a deadband around the limp home position. The upper throttle valve position threshold corresponds to a first duty cycle required to overcome a force of the spring in a first direction and the backlash of the gear train as the throttle valve is opening, and the lower throttle valve position threshold corresponds to a second duty cycle required to overcome a force of the spring in a second direction and the backlash of the gear train as the throttle valve is closing. The second feed forward signal is a first predetermined duty cycle when the desired throttle valve position is above the upper throttle valve position threshold, and is a second predetermined duty cycle when the desired throttle valve position is below the lower throttle valve position threshold. The method may further include learning the limp home position of the throttle valve on the duty cycle curve when a commanded duty cycle is zero and an actual position of the throttle valve is within a predetermined range of an estimate of the limp home position.
In the above description, certain terms have been used for brevity, clarity, and understanding. No unnecessary limitations are to be inferred therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different systems and method steps described herein may be used alone or in combination with other systems and methods. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims.
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