Patent Application
20050149249
1. Field of the Invention
The present invention generally relates to a system and method for tracking the angular position of an engine's crankshaft.
2. Description of Related Art
Various systems for tracking the angle of an engine are known. Known systems determine the engine position from a sensor that generally works only above a minimum speed. These systems are based on a profile of the rotation of two engine position wheels, one on the crankshaft and one on the camshaft. In addition, at start-up these systems require the engine to initially rotate through an angle before the engine position becomes known. The amount of requisite angular displacement is dependent on the initial engine position.
It is desirable to know the engine position at engine startup, as this allows the system to fuel and ignite the very first possible cylinder. In the example of a port injected engine, the first possible cylinder would be the cylinder with an open or about to be opened intake valve. The benefits available from early ignition include minimization of tailpipe hydrocarbon emissions due to “crank-through” of fuel vapors from the intake manifold to the exhaust manifold, the minimization of crank time, and the reduction of crank time variability.
Typically, determination of engine position or engine tracking begins at engine crank and is not complete until some amount of engine rotation. The requisite rotation can slightly exceed two revolutions, depending on configuration. People have proposed systems that leave the controller powered after the engine off command and track the engine position until it comes to rest. However, known sensors have difficulty identifying engine reversals as the engine slows to a stop. Further, methods to detect the reversals are complex and can become unreliable in the presence of missing teeth on the position encoder wheel.
In view of the above, it is apparent that there exists a need for an improved engine position tracking system.
In satisfying the above need, as well as overcoming the enumerated drawbacks and other limitations of the related art, an embodiment of the present invention provides a system that includes an engine tracking subsystem for determining engine angle and a throttle configured to lower air pressure in the engine's intake manifold and thus lower the ingested air thereby reducing the cylinders compression torque based on an engine shutdown signal.
The engine tracking subsystem is coupled to the engine and determines the angle of the engine by sensing rotation of the crankshaft. As the engine controller receives an engine shutdown signal, the throttle is controlled to lower the air pressure in the intake manifold of the engine. The air pressure is lowered such that the resulting reversal torque caused by compression of air in the cylinders is smaller than the friction torque of the engine thereby minimizing or eliminating engine reversal. To lower the air pressure, the throttle is closed and remains closed until the engine is stopped. Thereafter, the throttle is slightly opened increasing the air pressure in the engine to avoid the drawing of exhaust fumes back into the intake manifold. When the engine is stopped, the engine tracking system stores the engine angle for use during engine startup. Because engine reversal has been eliminated, the stored engine angle remains the correct engine position for the next startup. Alternatively, if valve actuation is available (Variable Cam Timing, or Electrically Actuated Valves) a cylinder's compression torque can be reduced by altering the valve timing, (for example: late closing of the intake valve).
In a foot-operated throttle system, a throttle bypass valve provides air control when the driver's foot is off the accelerator pedal. Alternatively, instead of a throttle valve being commanded to close at the engine-off command, a throttle bypass valve could be commanded to close.
In another aspect of the invention, the throttle is closed immediately upon key-off. The fuel injection system is configured to continue injecting for a predetermined time after key-off. Further, the ignition system is configured to continue sparking after the fuel injection has ceased. By allowing fuel injection and spark ignition for a short time after engine-off request, while still closing the throttle at the engine-off request, the intake manifold pressure is lower than it would otherwise be if all the actions were taken simultaneously.
Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification.
Referring now to
The engine 10 is shown as an internal combustion engine having a throttle 30, a piston 22, and a cylinder 20. As will be apparent from the discussion that follows, the engine 10 could be provided with any number of cylinders and the system 8 readily adapted thereto. Each cylinder 20 houses a piston 22 mounted for reciprocal movement therein. Combustion in the cylinder 20 will cause movement of the piston 22 resulting in a rotation of the crankshaft 48, which is used to transfer power from the engine 10 to the drivetrain and other systems within the vehicle.
Air entering the cylinder 20 from the intake manifold 28 is controlled by the throttle 30 and is combined with fuel, injected from a fuel injector 26, to form a gas/air mixture in the cylinder 20. The fuel injector may inject directly into the cylinder as shown or it may inject into the intake port. A spark is generated by a spark plug 24 to initiate combustion in the cylinder 20 thereby creating motion of the piston 22. To create continuous rotation of the crank shaft 48, the pistons 22 are positioned at varying engine angles relative to the crank shaft 48 and the controller 12 synchronizes combustion in each cylinder to cause a smooth rotation of the crank shaft 48. After combustion, exhaust gasses are forced out of the cylinders 14, as the piston 22 rises on the next part of its cycle and exit through the exhaust manifold 32.
As the engine 10 produces continuous rotation of the crankshaft 48, a flywheel 52 is also rotated. Teeth 50 are provided at equally spaced positions around the circumference or perimeter of the flywheel 52 with one or two teeth missing. A sensor 54, located proximate to the flywheel 52, produces a signal as each tooth 50 is rotated therepast. This signal is provided to the controller 12 along line 56. The controller 12 includes a microprocessor 40 which counts the number of signals provided from the sensor 54. By counting the signals, the microprocessor 40 can keep track of the engine position or angle.
Additionally, the microprocessor 40 optimizes the engine's performance by controlling the fuel injectors 26, the timing of the spark plugs 24, and the throughput of the throttle 30. The position of the throttle 30 controls the amount of air allowed to flow through the intake manifold plenum 31 to the intake manifold 28 and into the cylinder 20. The position of the throttle 30 is manipulated by the controller 12 through the throttle actuator 29. The air flow into the cylinder 20 can also be controlled through cam timing. The timing of the cam shafts 66 can be manipulated by the controller 12 through the cam timing actuator 64. The cam shafts 66 drive the opening and closing of the intake valve 67 and exhaust valve 68.
As a key switch 62 is switched to the off position, an engine shutdown signal is sent along line 60 to the controller 12 thereby initiating an engine shutdown sequence in the microprocessor 40. During the shutdown sequence, engine position continues to be monitored by the sensor 54 and the controller 12. After the engine has stopped, the last engine position is stored in a memory 46 of the controller 12 for use in the next engine startup.
The engine shutdown sequence operates to reduce the engine's maximum compression torque to near or lower than the engine's friction torque in order to eliminate or reduce engine reversal on spin down. Lowering compression torque is readily accomplished by closing the throttle 30.
In addition, various forms of valve timing control are coming into use on automotive engines. Since valve timing influences the mass of gasses that are compressed in the cylinder 20, valve timing is a way to either augment or substitute for closing the throttle 30. While many compression torque reducing schemes are contemplated, the most readily accomplished scheme is to close the intake valve 67 later than normal. With ideal valving, the intake valve 67 is closed at the beginning of the compression stroke. If the intake valve 67 closing is delayed, then some gas consisting of air and residual combustion products can be pushed backwards out of the intake valve 67 instead of being compressed in the cylinder 20. Effectively, this reduces the engine's compression ratio and compression torque is reduced, thus reducing the engine's propensity to reverse as it slows to a stop.
An engine shutdown sequence in accordance with the present invention is shown in
Now referring to
As noted above, the lowering of the air pressure in the intake manifold 28 is instrumental in preventing engine reversals. Now referring to
When closing the throttle 30 to lower the manifold pressure in accordance with the present invention, referring to
As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.
