The present invention relates to internal combustion engines, and more particularly to balancing torque across cylinders of an internal combustion engine.
Internal combustion engines create drive torque that is transferred to a drivetrain via a crankshaft. More specifically, air is drawn into an engine and is mixed with fuel therein. The air and fuel mixture is combusted within cylinders to drive pistons. The pistons drive the crankshaft, generating drive torque.
In some instances, the individual cylinders do not produce an equivalent amount of drive torque. That is to say, some cylinders can be weaker than others, resulting in a torque imbalance across the cylinders. Such torque imbalances can generate noticeable vibrations throughout the drivetrain and can even result in engine stall if severe enough. Although traditional torque balance systems identify and increase the torque output to a chronically weak cylinder, such system fail to account for the torque increase and fail to balance the torque output across all cylinders.
Accordingly, the present invention provides an engine torque control system for balancing torque output across cylinders of an internal combustion engine. The engine torque control system includes a first module that determines a derivative term for each cylinder of the engine based on rotation of a crankshaft and a second module that determines a torque correction for a first cylinder based on an average derivative term associated with the first cylinder. The second module adjusts a torque output of the first cylinder based on the torque correction and adjusts a torque output of a second cylinder based on the torque correction.
In one feature, the second module compares the average derivative term to a derivative term threshold and adjusts the torque output when the average derivative term exceeds the derivative term threshold.
In another feature, the engine torque control system further includes a third module that determines a first derivative based on the rotation of the crankshaft and a fourth module that determines a second derivative based on the first derivative. The average derivative term is determined based on the first and second derivatives.
In another feature, the average derivative term is determined based on a first derivative that is determined for the first cylinder, a second derivative that is determined for the first cylinder and another second derivative that is determined for a recovery cylinder that is immediately after the first cylinder in a firing order.
In other features, the second module adjusts the torque output by increasing a torque output of the first cylinder. The torque output of the second cylinder is decreased in correspondence with a torque increase of the first cylinder.
In another feature, the second module increases a torque output of the first cylinder by an increase torque amount, decreases a torque output of the second cylinder by a first decrease torque amount and decreases a torque output of a third cylinder by a second decrease torque amount. A total of the first and second decrease torque amounts corresponds to the increase torque amount.
In still other features, the second module calculates a spark timing based on the average derivative term and induces combustion in the first cylinder based on the spark timing. The spark timing is further based on a spark versus thermal efficiency curve of the engine.
In yet another feature, the second module adjusts the torque output by regulating a fueling rate to the first cylinder.
In another aspect, the present invention provides an engine torque control system that balances torque output across cylinders of an internal combustion engine and includes a first module that determines a derivative term for each cylinder of the engine based on rotation of a crankshaft and a second module that determines an average derivative term for each cylinder. The second module adjusts a torque output of the cylinders based on their respective average derivative terms to balance the average derivative terms with respect to one another.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.
Referring now to
A control module 38 communicates with the engine 12 and various inputs and sensors as described herein. A vehicle operator manipulates an accelerator pedal 40 to regulate the throttle 13. More particularly, a pedal position sensor 42 generates a pedal position signal that is communicated to the control module 38. The control module 38 generates a throttle control signal based on the pedal position signal. A throttle actuator (not shown) adjusts the throttle 13 based on the throttle control signal to regulate airflow into the engine 12.
The vehicle operator manipulates a brake pedal 44 to regulate vehicle braking. More particularly, a brake position sensor 46 generates a brake pedal position signal that is communicated to the control module 38. The control module 38 generates a brake control signal based on the brake pedal position signal. A brake system (not shown) adjusts vehicle braking based on the brake control signal to regulate vehicle speed. An intake manifold absolute pressure (MAP) sensor 50 generates a signal based on a pressure of the intake manifold 20. A throttle position sensor (TPS) 52 generates a signal based on throttle position.
A crankshaft rotation sensor 48 generates a signal based on rotation of the crankshaft 30, which can be used to calculate engine speed. More specifically, the engine includes a crankshaft rotation mechanism (not shown), to which the crankshaft rotation sensor 48 is responsive. In one example, the crankshaft rotation mechanism includes a toothed wheel that is fixed for rotation with the crankshaft 30. The crankshaft rotation sensor 48 is responsive to the rising and falling edges of the teeth. An exemplary toothed wheel includes 58 teeth that are equally spaced about the circumference of the wheel, except in one location where two teeth are missing to provide a gap. Therefore, the gap accounts for approximately 12° of crankshaft rotation and each tooth accounts for approximately 6° of crankshaft rotation. The control module 38 determines the engine RPM based on the time it takes for a pre-determined number of teeth to pass.
The cylinder torque balancing control of the present invention identifies weak cylinders based on rotation of the crankshaft and balances the cylinder torque output across the cylinders. More specifically, the cylinder torque balancing control monitors the crankshaft signal generated by the crankshaft rotation sensor 48. The time it takes the crankshaft 30 to rotate a predetermined angle (e.g., 90°) during the expansion stroke of a particular cylinder is provided as tCS.
An average derivative term (DTAVG) for each cylinder is calculated. DTAVG is determined based on first and second crankshaft speed derivatives FD and SD, respectively. More specifically, FD is determined for the monitored cylinder k-1 and is denoted FDk-1. As used herein, k is the recovery cylinder, which fires after the monitored cylinder k-1 (i.e., the recovery cylinder is next in the firing order after the monitored cylinder). SD is determined for both the recovery cylinder (i.e., the currently firing cylinder) and the monitored cylinder, which are provided as SDk and SDk-1, respectively. A derivative term (DT) for a particular cylinder is sampled over several engine cycles and DTAVG is determined as the average thereof.
If DTAVG of a particular cylinder exceeds a threshold (DTTHR), that cylinder is deemed weak. Accordingly, the torque output of the particular cylinder (TQk) is increased. Concurrently, the torque output of another cylinder or other cylinders is correspondingly decreased. That is to say, if the torque output of the weak cylinder is increased by X Nm, the torque output of another cylinder is decreased by X Nm. Alternatively, the torque output of each of a plurality of other cylinders can be decreased, whereby the total torque output decrease is equal to X Nm.
In another aspect of the present invention, the cylinder torque balancing control can actively balance the torque output of each cylinder with respect to the total torque output across the cylinders. More specifically, the cylinder torque balancing control monitors DTAVG for each cylinder and increases or decreases the torque output of the individual cylinders to balance DTAVG across the cylinders. DTAVG can be balanced so that it is approximately equal for all cylinders. Alternatively, DTAVG can be balanced so that each DTAVG is within a predetermined range. That is to say that DTAVG is within a range defined between a predetermined minimum DT (DTMIN) and a predetermined maximum DT (DTMAX).
The torque output of the individual cylinders can be regulated by adjusting the spark timing of the particular cylinder. More specifically, the spark timing can be retarded or advanced to respectively decrease and increase the torque output of the particular cylinder. The spark versus thermal efficiency curve for the particular engine can be implemented to determine the spark adjustment to achieve the desired torque adjustment. If an engine exhibits a steep relationship of spark timing to thermal efficiency, a pure spark correction will vary in delivered torque as a function of the base spark timing. For example, the torque versus spark timing slope is different at 8° base spark timing when compared to 15° timing. In the case of a diesel engine, the torque output can be regulated by adjusting the fueling to the particular cylinder, whereby the fuel to torque relationship is used to determine the fuel adjustment required to achieve the desired torque change.
Referring now to
Referring now to
Referring now to
In step 410, control determines whether DTAVGk-1 (i.e., for the currently firing cylinder) exceeds DTTHR. If DTAVGk-1 does not exceed DTTHR, control ends. If DTAVGk-1 exceeds DTTHR, control increases TQk-1, based on DTAVGk-1, during the next firing event for the monitored cylinder k-1 in step 412. In step 414, control increases TQ for either or both of the previous firing cylinder k-2 and the recovery cylinder k based on the increase to TQk-1, and control ends.
Referring now to
The maximum module 504 clamps FDk and the minimum module 506 clamps SDk to minimize noise. The buffer modules 508, 510 output SDk-1, and FDk-1 to the gain modules 512, 516, respectively, and the minimum module 506 outputs SDk to the gain module 514. The gain modules 512, 514, 516 multiply SDk-1, SDk and FDk-1, by respective gains A, B and C. The gains can be used to adjust the influence or weight of a particular derivative (i.e., SDk-1, SDk and FDk-1) or to turn OFF a derivative (e.g., gain set equal to 0).
The summer 518 sums FDk-1, and SDk-1 and subtracts SDk to provide DTk-1. DTk-1 is output to the maximum module 520, which clamps DTk-1 to minimize noise. DTk-1 is output to the cylinder torque module 522, which calculates DTAVG for each cylinder and generates control signals to regulate the torque output of the individual cylinders.
Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.
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Number | Date | Country | |
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20070261669 A1 | Nov 2007 | US |