Patent Application
20200165942
The present application relates to variable camshaft timing (VCT) and, more particularly, to controllers for variable camshaft timing devices.
Internal combustion engines (ICEs) use endless loops, such as a chain or a belt, that engage a crankshaft and a camshaft to communicate rotational force from the crankshaft to the camshaft. In the past, the angular relationship between the crankshaft and camshaft has been fixed. But many ICEs now use variable camshaft timing (VCT) to change the angular position of the camshaft relative to the crankshaft. The devices used to implement VCT and alter the angular position of the camshaft relative to the crankshaft can vary in design and be electrically- or hydraulically-actuated. Electrically-actuated VCT devices rely on electric motors that adjust the angular position of the camshaft relative to the crankshaft. The electric motors are controlled by control systems that can be implemented in a variety of ways. For example, a control system can receive an input that identifies the error between a commanded angular relationship of a crankshaft and camshaft and an actual angular relationship. However, control systems may lag or overshoot the commanded angular relationship and more accuracy and/or responsiveness can improve engine performance.
In one implementation, an electrically-actuated VCT device cascaded controller, comprises: a system processing device configured to receive inputs from one or more sensors and generate an output signal that is communicated to an electric phaser motor; the system processing device: receives data indicating an angular position of a camshaft relative to an angular position of a crankshaft at a primary control loop; receives data indicating an angular velocity of the crankshaft at a secondary control loop; and generates the output signal that controls the electric phaser motor using the primary control loop and the secondary control loop.
In another implementation, a method of controlling an electrically-actuated VCT device with a cascaded controller includes receiving data indicating an angular position of a camshaft relative to an angular position of a crankshaft at a primary control loop; receiving data indicating an angular velocity of the crankshaft at a secondary control loop; generating an output signal that controls the electric phaser motor using the primary control loop and the secondary control loop; transmitting the output signal to the electric phaser motor; and adjusting the angular position of the camshaft relative to the angular position of the crankshaft based on the output signal.
The following describes an electrically-actuated variable camshaft timing device cascaded controller (“cascaded controller” or “device controller”) and a method of controlling the electrically-actuated VCT device. The cascaded controller receives input indicating the angular position of the camshaft relative to the crankshaft, input indicating the angular velocity of the crankshaft, and input indicating an angular velocity of an electric motor output shaft actuating the VCT device to generate a control signal that is used to regulate the output shaft. The cascaded controller uses a cascaded control system that includes an outer/primary controller and an inner/secondary controller. The primary controller can receive input indicating the angular position of the camshaft relative to the angular position of the crankshaft; this can also be referred to as the phase relationship between the camshaft and crankshaft. And the secondary controller can receive input indicating the angular velocity of the crankshaft. The device controller can use these inputs to generate or output a control signal that directs the electric motor actuating the VCT device to increase or decrease the angular velocity of the output shaft of the electric motor or maintain the angular velocity of the output shaft. Maintaining angular velocity of the output shaft can maintain the relative angular position of the camshaft to the crankshaft while increasing or decreasing the angular velocity of the output shaft can change (advance or retard) the angular position of the camshaft relative to the crankshaft.
The actual angular position of the camshaft relative to the crankshaft compared to the target angular position of the camshaft relative to the crankshaft can reflect a primary variable for generating the control signal. However, as operating conditions of the internal combustion engine (ICE) change, providing an output signal to the electric motor solely based on the actual/measured angular relative position of the camshaft may not reflect the present operating condition of the ICE but instead reflect past operation. Outputting control signals based on rearward-looking data can reduce the responsiveness of the control system and delay the identification of and arrival at the target phase. In one example of a changing operating condition, an ICE operating at a relatively high level of revolutions per minute (RPM) may then be quickly brought to idle. Past, control systems have monitored the actual angular position of the camshaft relative to the target angular position of the camshaft and detected no difference between these two values despite a rapidly falling engine RPM. Despite the reduction in crankshaft RPM past control systems continue to detect zero error between an actual phase relative to a target phase. The past systems output a control signal directing the electric motor to maintain the angular velocity of the output shaft, which has been chosen for a higher-RPM camshaft angular velocity. As the RPMs of the crankshaft fall, so too do the RPM of the camshaft. Yet, the maintained output shaft angular velocity can unintentionally advance the angular position of the camshaft relative to the angular position of the crankshaft. An error value between the measured angular position and the target angular position may increase, and the controller can respond, but not before a period of time has passed during which the adjusted angular position of the camshaft is not optimal.
In contrast, the cascaded controller described herein implementing a cascaded control system uses phase error as well as angular velocity of the crankshaft to output a control signal for the electric motor that is more responsive to changes in RPM even though while zero error exists between an actual relative angular position of the camshaft relative to a target relative angular position of the camshaft, such as would exist during steady RPM values.
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The crankshaft 16 includes a crank wheel 28 that can be used to identify the angular position and/or the angular velocity of the crankshaft 16. The crank wheel 28 is mounted to the nose 24 of the crankshaft 16 adjacent to the crank sprocket 22 and can be implemented as a 60-2 crank wheel. This means that the crank wheel 28 includes 58 evenly-spaced teeth around the circumference of the wheel 28 and a space along the circumference where two teeth have purposefully been omitted. This space is also called a crank index 30 that identifies a defined point of crankshaft rotation relative to combustion, such as top-dead center (TDC). While this embodiment is described with regard to the 60-2 crank wheel, it should be appreciated that crank wheels having different numbers of teeth and index sizes could be used instead with equal success. As the crank wheel 28 rotates with the crankshaft 16, a crank position sensor 32 located in close proximity to the teeth on the crank wheel 28 generates a signal that indicates an absence or presence of the teeth on the crank wheel 28. The crank position sensor 32 can be implemented as a hall-effect sensor that generates a high-voltage level when a tooth passes the sensor 32 and a low-voltage level when the index 30 passes the sensor 32 or when the sensor 32 is located in between teeth on the crank wheel 28. The output from the crank position sensor 32 can be sent to a microcontroller that implements a variety of computing processes, including but not limited to the device controller disclosed herein. This will be discussed in more detail below. In response to an index on the crank wheel 28 that has eliminated teeth from a regularly spaced pattern, the microcontroller(s) may recognize the change and provide a signal in place of the missing signals. If the microcontroller is counting crank pulses, then the microcontroller may instead add the missing teeth to the count after passing and recognizing the index location.
The camshaft phaser 14 controls the angular position of the camshaft 18 relative to the angular position of the crankshaft 16. An electric phaser motor 34 regulates the phase of the camshaft 18 relative to the crankshaft 16 by driving a mechanical gearbox of the camshaft phaser 14 via an output shaft 46 of the electric phaser motor 34 according to a received motor control signal. The system 10 can be used with a variety of different cam phasers controlled by electric motors where the electric motor is rotating in order to maintain phase, such as the split-ring gear planetary cam phaser described in U.S. Patent Application Publication No. 2015/0315939, the contents of which are incorporated by reference. The electric motor driven cam phaser 14 includes the cam sprocket 20 and an electric phaser motor 34 that can be rotationally engaged with a sun gear of a planetary gearset (not shown) to alter the angular position of the camshaft relative to the angular position of the crankshaft. The planetary gearset engages two ring gears each of which have different numbers of teeth. One ring gear is included on a portion of the camshaft phaser 14 that is attached to the cam sprocket 20 whereas the other ring gear is attached to the camshaft 18. When the sun gear is rotated by the electric phaser motor 34 at the same speed as the two ring gears, a constant cam phase is maintained. However, when the electric phaser motor 34 drives the sun gear at a different speed than the ring gears, a slightly different speed of one ring gear to the other ring gear causes a change in cam phase. The camshaft 18 can be phase shifted over a range of angular positions that are defined by stops limiting changes in angular position of the camshaft 18 between a fully retarded position and a fully advanced position. In some implementations, this range can be as large as 140 degrees. It should be understood that this is one particular implementation of a cam phaser controlled by an electric motor and that other cam phaser designs including electric motors could also be successfully used.
The electric phaser motor 34 of the camshaft phaser 14 includes a defined number of magnets 38 located on a rotor 40 that is connected to an output shaft 46.
In an implementation in which the electric phaser motor 34 includes ten magnets 38 and three hall-effect sensors 48 located such that when the motor 34 is operational the magnets 38 induce a voltage in the hall-effect sensors 48 as the magnets 38 pass by along path (p), one 360-degree rotation of the output shaft 46 generates thirty high-voltage pulses from the sensors 48. The signals from the three sensors can be combined to produce a signal with 30 pulses. Alternatively, a signal with 15 pulses can be produced where a microcontroller interprets each rising or falling edge as the event used to calculate the motor movement and pulse frequency. The term high-voltage in this context can mean 5 volts (V) while low-voltage can refer to a 0 V value output by the hall-effect sensors 48 but other values are possible. A microprocessor in the form of an electric motor controller 54 can receive the output from the sensors 48 detecting passing magnets 38 of the electric phaser motor 34 and output an electric motor position signal indicating the frequency with which the magnets 38 are detected. The output from the sensors 48 can be used to determine the angular or rotational speed of the output shaft 46 of the electric phaser motor 34. In one embodiment, the electric motor controller 54 can be implemented using a three-phase brushless direct current (BLDC) motor controller and MOSFET driver.
In addition to the electric motor controller 54, the system 10 can include a system processing device 56 as another, separate microprocessor/microcontroller, such as an electronic control unit (ECU), that receives an electric motor position signal from the electric motor controller 54 as well as output from the crank position sensor 32 and electric controller 54. The system processing device 56 can use this information to execute the cascaded controller disclosed herein. The system processing device 56 can be any type of device capable of processing electronic instructions including microprocessors, microcontrollers, host processors, controllers, vehicle communication processors, and application specific integrated circuits (ASICs). It can be a dedicated processor used only to carry out the described methods or can be shared with other systems of an internal combustion engine or vehicle. It is possible to include the system processing device 56 within the electric motor controller 54 or to implement the device 56 as a separate and independent processing device. The system processing device 56 executes various types of digitally-stored instructions, such as software or firmware programs stored in memory. Communications between the sensors 32, 48, the electric motor controller 54, and the system processing device 56 can be carried out over a communications bus 58, such as those that are implemented using a controller area network (CAN) protocol. However, it should be appreciated that other implementations are possible in which at least some of these elements could be implemented together on a printed circuit board.
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The primary control loop 600 includes an error calculator 602 that calculates a phase error between the measured camshaft angular position and the target camshaft angular position. The primary control loop 502 also includes a proportional phase control element 604, an integral phase control element 606, a proportional temperature element 608, an integral temperature element 610, a primary proportional multiplier 612, and a primary integral multiplier 614. The phase error can be provided to the proportional phase control element 604 and the integral phase control element 606. The temperature input can be provided to the proportional temperature element 608 and the integral temperature element 610. The proportional elements can create an output that is proportional to the phase error and the integral elements can calculate an output that is the integral of past phase errors. The primary proportional multiplier 612 can receive output from the proportional phase control element 604, the proportional temperature element 608, and the phase error and create an output signal; the primary integral multiplier 614 can receive output from the integral phase control element 606, the integral temperature element 610, and the phase error. A primary proportional output signal is generated by the primary proportional multiplier 612 and a primary integral output signal is generated by the primary integral multiplier 614. The primary control loop 600 can also generate a speed change command for the electric phaser motor 34.
The secondary control loop 700 includes a crankshaft angular velocity divided by two plus speed change command summer 702, a speed limit regulator 704, an electric motor speed error calculator 706, a proportional speed element 708, a proportional temperature element 710, an integral speed element 712, an integral temperature element 714, a secondary proportional multiplier 716, a secondary integral multiplier 718, and an overall integral summer 720. The secondary control loop 700 receives a plurality of inputs. The inputs include the primary integral output signal, the calculated phase error, the speed change command, the measured angular velocity of the crankshaft 16, and a measured angular velocity of the output shaft 46. The angular velocity of the crankshaft can be provided to the electric phaser motor error calculator with the speed change command. The secondary control loop 700 can consider both the angular velocity of the crankshaft 16 along with a commanded angular velocity of the output shaft 46. The electric motor speed summer 702 outputs a target speed signal for controlling the output shaft 46 that is based on the angular velocity of the crankshaft 16 divided by two and the angular velocity of the output shaft 46. The target speed signal and the measured angular velocity of the crankshaft 16 divided by two are input into the electric motor speed error calculator 706, which can output an electric motor control command. The phase error is provided to the proportional speed element 708 and the integral speed element 712; the temperature is provided to the proportional temperature element 710 and the integral temperature element 714. The outputs from the proportional speed element 708 and proportional temperature element 710 are provided to the secondary proportional multiplier 716 along with the electric motor speed command. Outputs from the integral speed element 712 and integral temperature element 714 are provided to the secondary integral multiplier 718 along with the electric motor speed command. The overall integral summer 720 combines the outputs from the primary integral multiplier 614 and the secondary integral multiplier 718. The integral accumulator 722 stores the cumulative output of the overall integral summer 720.
A feed forward module 800 can include a feed forward temperature gain element 802, a feed forward crankshaft angular velocity element 804, and a feed forward summer 806. The module 800 can receive the angular velocity of the crankshaft 16 and a temperature value at the feed forward crankshaft velocity element 802 and the feed forward temperature gain element 804, respectively. Outputs from these elements can be passed to the feed forward summer 806 to generate a feed forward output signal. A master summer 900 receives output from the feed forward module 800, the primary proportional multiplier 612, the secondary proportional multiplier 716, and the integral accumulator 722. These signals can be combined into an output control signal that is communicated to the electric motor controller 54 where the signal is used to control the output shaft 46.
It is to be understood that the foregoing is a description of one or more embodiments of the invention. The invention is not limited to the particular embodiments) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.
As used in this specification and claims, the terms “e.g.,” “for example,” “for instance,” “such as,” and “like,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.
This application claims the benefit of U.S. Patent Application No. 62/771,276 filed on Nov. 26, 2018, the disclosure of which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62771276 | Nov 2018 | US |
