Patent Application
20130125847
The present disclosure relates to controlling a variable camshaft timing system of an engine.
Engines may utilize variable cam operation to adjust intake and exhaust valve operation in an engine cylinder. For example, the cam timing may be adjusted to improve engine operation across a range of conditions. In one example, a control system maintains the cam timing relative to crankshaft timing based on feedback information from cam and crankshaft sensors.
U.S. Pat. No. 6,932,033 describes one approach to control cam timing based on a toothed cam wheel with an additional index tooth. The index tooth indicates when a torque reversal occurs on the camshaft. The control system adjusts the cam actuator based on this information to provide improved cam timing control. Additionally, the uneven tooth can provide identification information used during engine starting to identify engine position, as the crankshaft does not uniquely identify engine position in a four-cycle engine.
The inventors herein have recognized some issues with the above approach. For example, while an increased number of evenly spaced teeth provide an increased data rate of sensed cam position, the single uneven tooth may lead to longer engine cranking. For example, up to two full crankshaft revolutions may occur before the uneven tooth is identified in order to identify engine position and commence sequential fuel injection. On the other hand, reducing the number of evenly spaced teeth in order to provide earlier engine position identification can lead to reduced data rates of sensed position during engine running.
The inventors herein have recognized that this apparent paradox can be at least partially addressed by incorporating information from uneven tooth edges into the feedback control of cam operation in one embodiment. For example, an engine method includes adjusting a variable cam actuator responsive to cam position feedback from even and uneven readings of a cam sensor.
In this way, it is possible to provide quick engine position identification during an engine start through a plurality of uneven tooth edges, while maintaining a high data rate of sensed cam position, and thus accurate control of cam operation, from both even and uneven tooth edges.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
An engine having variable valve operation, such as variable cam timing, is described in
Referring now to
Combustion chamber 30 may receive intake air from intake manifold 44 via intake passage 42 and may exhaust combustion gases via exhaust passage 48. Intake manifold 44 and exhaust passage 48 can selectively communicate with combustion chamber 30 via respective intake valve 52 and exhaust valve 54. In some embodiments, combustion chamber 30 may include two or more intake valves and/or two or more exhaust valves.
Intake valve 52 may open and close according to lobes of intake cam 51. Similarly, exhaust valve 54 may open and close according to lobes of exhaust cam 53. Phase of intake cam 51 and exhaust cam 53 may be varied with respect to crankshaft 40. Alternatively, the variable valve actuator may be electro hydraulic or another mechanism to enable valve actuation. During some conditions, controller 12 may vary the signals provided to actuators coupled to intake cam 51 and exhaust cam 53 to control the opening and closing timing of the respective intake and exhaust valves. The position of intake valve 52 and exhaust valve 54 may be determined by valve position sensors 146 and 57, respectively. In alternative embodiments, one or more of the intake and exhaust valves may be actuated by one or more cams, and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and/or variable valve lift (VVL) systems to vary valve operation. For example, cylinder 30 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT.
Fuel injector 66 is shown coupled directly to combustion chamber 30 for injecting fuel directly therein in proportion to the pulse width of signal FPW received from controller 12 via electronic driver 68. In this manner, fuel injector 66 provides what is known as direct injection of fuel into combustion chamber 30. The fuel injector may be mounted in the side of the combustion chamber or in the top of the combustion chamber, for example. Fuel may be delivered to fuel injector 66 by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail.
Ignition system 88 can provide an ignition spark to combustion chamber 30 via spark plug 92 in response to spark advance signal SA from controller 12, under select operating modes. Though spark ignition components are shown, in some embodiments, combustion chamber 30 or one or more other combustion chambers of engine 10 may be operated in a compression ignition mode, with or without an ignition spark.
Intake passage 42 may include throttles 62 and 63 having throttle plates 64 and 65, respectively. In this particular example, the positions of throttle plates 64 and 65 may be varied by controller 12 via signals provided to an electric motor or actuator included with throttles 62 and 63, a configuration that is commonly referred to as electronic throttle control (ETC). In this manner, throttles 62 and 63 may be operated to vary the intake air provided to combustion chamber 30 among other engine cylinders. The positions of throttle plates 64 and 65 may be provided to controller 12 by throttle position signals TP. Pressure, temperature, and mass air flow may be measured at various points along intake passage 42 and intake manifold 44. For example, intake passage 42 may include a mass air flow sensor 120 for measuring clean air mass flow entering through throttle 63. The clean air mass flow may be communicated to controller 12 via the MAF signal.
Exhaust passage 48 can receive exhaust gases from other cylinders of engine 10 in addition to cylinder 30. Exhaust gas sensor 126 is shown coupled to exhaust manifold 48 upstream of catalytic converter 70 (where sensor 76 can correspond to various different sensors). For example, sensor 126 may be any of many known sensors for providing an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor, a UEGO, a two-state oxygen sensor, an EGO, a HEGO, or an HC or CO sensor.
Controller 12 is shown in
Storage medium read-only memory 106 can be programmed with computer readable data representing instructions executable by processor 102 for performing the methods described below as well as other variants that are anticipated but not specifically listed.
Continuing with
Camshaft 142 is directly coupled to housing 144. Housing 144 forms a toothed wheel having a plurality of teeth 148. Housing 144 is hydraulically coupled to crankshaft 40 via a timing chain or belt (not shown). Therefore, housing 144 and camshaft 142 rotate at a speed substantially equivalent to the crankshaft or a multiple thereof. However, by manipulation of the hydraulic coupling as will be described later herein, the relative position of camshaft 142 to crankshaft 40 can be varied by hydraulic pressures in advance chamber 150 and retard chamber 152. By allowing high pressure hydraulic fluid to enter advance chamber 150, the relative relationship between camshaft 142 and crankshaft 40 is advanced. Thus, intake valve 52 opens and closes at a time earlier than normal relative to crankshaft 40. Similarly, by allowing high pressure hydraulic fluid to enter retard chamber 152, the relative relationship between camshaft 142 and crankshaft 40 is retarded. Thus, intake valve 52 opens and closes at a time later than normal relative to crankshaft 40.
While this example shows a system in which only the intake valve timing is controlled, concurrent intake and exhaust cam timing, variable exhaust cam timing, dual independent variable cam timing, dual equal variable cam timing, or fixed cam timing may be used. Further, variable valve lift may also be used. Camshaft profile switching may be used to provide different cam profiles under different operating conditions. Further still, the valvetrain may be roller finger follower, direct acting mechanical bucket, electromechanical, electrohydraulic, or other alternatives.
Continuing with the variable cam timing system, teeth 148, being coupled to housing 144 and camshaft 142, allow for measurement of relative cam position via cam timing sensor 146 providing signal VCT to controller 12. Teeth, such as tooth 148, may be used for measurement of cam timing and may have at least some edges that are equally spaced (for example, spaced 180 degrees apart from one another) and edges that are unequally spaced. In addition, controller 12 sends control signals (LACT, RACT) to conventional solenoid valves (not shown) to control the flow of hydraulic fluid either into advance chamber 150, retard chamber 152, or neither.
Relative cam timing can be measured in a variety of ways. In general terms, the time, or rotation angle, between the rising edge of the PIP signal and receiving a signal from one of the plurality of teeth 148 on housing 144 gives a measure of the relative cam timing. Additional details on measuring cam timing are described below. Under some conditions in the example of a V-8 engine, with two cylinder banks and toothed wheel with four even and four uneven teeth edges, an equally spaced measure of cam timing for a particular bank is received four times per revolution, with the uneven edges used for cylinder identification. However, under other conditions, a measure of cam timing may be based on both evenly spaced tooth edges and unevenly spaced tooth edges.
As described above,
Referring now to
Cam wheel 200 includes a plurality of teeth, A-D, including two teeth C, D that are narrower in width (rotational angle) and two teeth A, B that are wider in width. The narrow teeth C, D may be arranged adjacent on cam wheel 200.
Each tooth has a rising edge and a falling edge, relative to the axis of rotation of the cam wheel 200. As depicted in
Thus, the cam wheel 200 may include four teeth, with two teeth having a smaller tooth width and two teeth having a greater tooth width. One edge of each tooth may be evenly spaced around the wheel to generate the even readings, and another edge of each tooth may be unevenly spaced around the wheel to generate the uneven readings.
Referring now to
At 302, the routine determines if the engine is running. If not, routine 300 ends. If the engine is running, routine 300 proceeds to 304 to determine if engine start is complete. During start of the engine, the engine may be cranked by a starter motor, for example, rather than operating with fuel injection. If the engine start is not complete (e.g., the engine is still cranking), routine 300 continues to 306 to determine engine position during engine cranking so that sequential fuel injection can commence. In one example, the routine identifies crankshaft position from the crankshaft sensor in order to identify that the engine is in one of two positions. Then, the position is selected form the two options based on identification of engine position via one or more cam sensor readings. For example, the routine may identify the location of rising and falling edges of the toothed cam wheel sensor and once enough edges have been detected to identify the pattern and determine cam position, engine position is identified. For example, the routine may identify cam position from one of four patterns including: narrow-narrow; narrow-wide; wide-wide; and wide-narrow.
Additionally, or alternatively, engine position and cam position may be stored upon shutdown, and then assumed to have remained substantially fixed during the shutdown such that engine position and cam position are known upon engine start, even before any toothed cam wheel sensor edges are detected.
Additionally, cam timing may be controlled during engine start/cranking based on the stored shutdown information to move the cam timing to a desired position for engine starting, such that the cam timing may be adjusted before a first combustion event in a cylinder from engine rest.
Continuing with
The determined edge timing is compared to a base position table at 312. The base position table may be stored in the memory of the controller, and may include position timing for each edge of the cam wheel at the base position, e.g., the normal, non-adjusted cam position. An example base position table, Table 1, is described in more detail below.
At 314, routine 300 determines if engine speed is below a threshold. The threshold engine speed may be a speed below which the control response timing for adjusting cam position based on operating parameters may exceed the feedback response timing from the even edges, e.g., 600 RPM. If the answer is yes, and engine speed is below the threshold, cam position may be controlled at 318 based on even and uneven edge-based cam position with a first gain set in order to increase the feedback response timing and take advantage of the higher data rate sensor information regarding cam timing.
At 316, if the engine speed is not below the threshold, the cam position may be controlled based on only even edge-based cam position with a second gain set. Upon controlling cam position, routine 300 exits.
In this way, increased samples of cam timing during low speed operation can be provided. The above-described adjusting of the variable cam actuator may occur during feedback position control of cam timing during warmed-up engine operation. In one embodiment, the cam position may be a relative angle between cam position and crankshaft position, measured in crankshaft angle degrees, and the relative angle may be further relative to a base cam position. Further, control routine 300 provides for adjusting a variable cam actuator responsive to cam position feedback from even and uneven readings of a cam sensor. This adjusting may be responsive to cam position feedback from even and uneven readings during engine speed below a threshold speed, and adjusted responsive to cam position feedback from only the even readings when engine speed is above the threshold speed. During engine speed operation below the threshold, a first controller gain may adjust the variable cam actuator responsive to an error between a desired position (e.g., a position set by the controller based on operating parameters) and the feedback cam position, and during engine speed operation above the threshold, a second controller gain may adjust the variable cam actuator responsive to the error between the desired position and the feedback cam position.
The two different gains, or gain sets in one example, utilized in the above described control routine may be selected based on engine speed as described. For example, the first set may be used at engine speeds below the threshold while the second set may be used at engine speeds above the threshold. The gain sets may be determined based on an off-line model to optimize the control performance and minimize noise, based on engine speed, and stored in the controller memory. However, in some embodiments, the controller gains may be based on other parameters, such as even/uneven readings. In this way, a first feedback control adjustment gain may be applied when using feedback based on only even readings, and a second, different feedback control adjustment gain may be applied to feedback from both even and uneven readings. In this way, it is possible to take advantage of the higher data rate sensing at lower engine speeds by using a more optimized controller gain for these situations to provide faster control, while still retaining controller stability at both higher and lower engine speed ranges. Alternatively, a constant controller gain may be used at both high and low engine speed and with both even and unevenly spaced cam timing sensed positions.
Referring now to
At 406, the determined CA° is compared to the base position in the base timing table stored in the memory of the controller, such as Table 1 below. At 408, the current camshaft angle is determined based on the difference between the determined CA° and the base position from the table. For example, if the identified edge has a crankshaft angle of 180° at the base position, but is identified at 185° CA, the camshaft position is determined to be advanced 5° CA.
Referring now to
At 504, routine 500 determines if engine speed is below a threshold, such as 600 RPMs. If engine speed is lower than the threshold, the cam position feedback provided by only the even edges may not be reported at a fast enough rate to maintain stable control performance (e.g., the control to the camshaft position may occur more frequently than the feedback). Thus, at 506, routine 500 includes determining and sending actuator output at each detected edge, including both the even and uneven edges. The actuator output may be based on the determined cam angle relative to crankshaft angle detected from each edge (as determined based on routine 400, described above with respect to
If engine speed is not below the threshold, the position reported by the even edges may be sufficient to maintain optimal control performance, and at 508, routine 500 includes determining and sending actuator output at the even edges only. This may be based on the determined cam angle relative to crankshaft angle detected from the even edges, and further based on the selected gain set. In one example, the controller update rate is interrupt driven upon receiving a sensed edge—with both rising and falling edges triggering a controller algorithm update and corresponding actuator signal update at lower engine speeds, and only even rising edges triggering the update at higher engine speeds.
In this way, the actuator output, such as movement of a valve spool to control the hydraulic fluid in a chamber of the cam phaser, may be controlled based on the determined cam position from either the even edges only, or from all edges, depending on engine speed. In one embodiment, during higher engine speeds, a variable cam timing (VCT) actuator may be adjusted responsive to cam timing feedback from even and uneven edge readings of a toothed cam sensor wheel. During lower engine speeds, the VCT actuator may be adjusted responsive to cam timing feedback only from even edge readings, and independent of the uneven readings, of the toothed cam sensor wheel.
In another example, the controller may include non-transitory code to adjust the actuator responsive to readings from both even and uneven edges during a first condition and responsive to readings from only even edges during a second condition. The first condition may include engine speed below a threshold, while the second condition may include engine speed above the threshold. The threshold engine speed may be constant, e.g., may be set in advance without changing regardless of engine conditions. However, in other embodiments, the threshold engine speed may be adjusted based on operating conditions, such as transient conditions. In one example, the threshold speed may be lowered during a tip-in event.
Referring back now to
As noted above, the feedback control can further include adjustments to the gain values to take into account the fact that when using both even and uneven edges for cam timing sensing and control, multiple samples can occur closer to one another during some conditions and further apart during other conditions in a repeating pattern as the cam toothed wheel rotates. This is in contrast to the conditions where only even spaced data is utilized, in which case the samples occur at even spacing. In one approach, even when unevenly spaced readings are utilized, the controller can ignore the variation in sample spacing and simply determine control output based on the determined error values at each sample (and possibly based on one or more previous samples) without regard to the variation in controller updates.
In another example, rather than ignoring the uneven sample spacing for controller design, the controller may vary one or more control gains. For example, each particular edge reading may correspond to a specific controller gain corresponding to its particular relative sensing position as compared to an even tooth. An example base position table, Table 1, is shown below, that includes base position for each edge, and example gain sets. For the first edge, rising edge A (AR), a sample reading timing and position are included. For each other edge in the table, sample reading of timing and position would be determined in a similar manner (e.g., the position of falling edge A would be y-bAF, etc.).
Because falling edges come evenly, a first controller with a common gain may be used for any falling edge data point, but for uneven edges, the controller gain may be adjusted to the specific edge. In this embodiment, two controllers may be run as follows:
Upon detection of a falling edge:
e(k)=difference between base crank position and crank position measured at falling edge for current sample (see Table 1 above).
uF(k)=pF1*e(k)+ . . . where k is incremented upon each falling edge. This example shows proportional control only, however, various other types of control may be added in other embodiments, such as integral, derivative, non-linear, etc. (e.g., pF2*e(k−1) may be added to the end of the series).
Upon detection of a rising edge:
e(i)=difference between base crank position and crank position measured at falling edge for current sample (see Table 1 above).
Here, the gain may be tracked to the sample order, as indicated in the Table 1 above. For example, when reading the rising edge of period D, the following applies:
uR(i)=pRD*e(i)+ . . . where i is incremented upon each rising edge.
Likewise, specific filtering gains may be applied depending on whether even or uneven spaced cam position data is utilized. Further, specific filter parameters may be included for each of the uneven data points depending on which uneven data point is sampled, according to the Table above, as described for the controller gains.
It will be appreciated that the configurations and methods disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.
The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.
