Patent Application
20060081202
This invention relates to engine valve lift position sensors and, more particularly, to an engine valve lift sensor capable of providing a linear output signal which varies with the position of an engine valve during an engine valve cycle.
Hall effect sensors are known in the art for tracking engine valve operation. However, Hall effect sensors provide a non linear output signal which is not capable of accurately detecting the position of the engine valve during an engine valve cycle.
A low cost valve sensor capable of providing a linear output signal for accurately determining the position of an engine valve during an engine valve cycle is desired.
The present invention provides a low cost engine valve sensor capable of providing a linear output signal which varies with the position of an engine valve during an engine valve cycle.
The engine valve sensor is carried by an engine valve assembly. In an exemplary embodiment, the engine valve assembly includes an engine valve housing such as a cylinder head carrying an engine valve having a valve stem and a valve head at one end of the valve stem. The stem extends into the valve housing and is sealed by a valve stem seal. A valve spring retainer is carried by the stem, and axially spaced from the valve stem seal. A spring extends between the valve stem seal and the valve spring retainer to bias the engine valve toward a closed position.
The sensor assembly includes a signal generator, such as an oscillator, which excites a stationary coil, carried directly or indirectly by the engine valve housing and a current measuring device such as a resistor in series with the coil. Spaced adjacent the coil is a movable electrically conductive target, for example metallic, carried directly or indirectly by the valve. The coil, when energized by the signal generator creates an oscillating magnetic field which induces eddy currents in the target to the degree in which the magnetic field engages the target. The eddy currents in the target result in an energy loss which causes a phase lag in the coil current and the voltage across the resistor relative to the signal generator voltage that varies with the valve lift position. A comparator, such as an Exclusive OR gate integrated circuit, can thus determine the position of the target and the engine valve based upon the degree of phase lag from the generated driving signal.
The position of the target and the coil within the valve spring and the use of an Exclusive OR gate comparator circuit define a system that can be applied to a multicylinder engine at a comparatively low cost.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.
Referring first to
A valve stem seal 24, fitted into a recess 26 of the valve housing 14 engages the circumferential surface-of the valve stem 20 to seal against oil leakage into the valve port 15. A valve spring retainer 28 is carried on the valve stem 20 and is axially spaced a distance from the valve stem seal 24. An engine valve spring 30 is disposed about the valve stem 20 between the valve housing 14 and the valve spring retainer 28 to bias the engine valve 18 toward the closed position so that the valve head 22 closes the opening 16, as shown in
A sensor assembly 32, as illustrated in
Referring now to
In operation, the engine valve 18 is moved between the closed position and the opened position to allow fluids to be transferred in and out of an associated combustion chamber for engine operation.
The position of the engine valve 18 is monitored by the sensor assembly 32. The signal generator 34 energizes the coil 36 with an oscillating voltage to create an oscillating magnetic field, which is concentric to the coil. The oscillating magnetic field induces eddy currents in the target which in turn create reactive magnetic fields. These increase in strength as the valve is opened and the target engages more of the coil magnetic field so that the eddy currents increase and a greater phase shift results between voltage of the signal generator and the current in the coil and the resistor.
The reactive fields of the eddy currents affect current flow through the coil by creating a lag in the current phase of the coil 36 and the resistor 38 relative to the phase of voltage supplied by the signal generator 34. The phase of current in the resistor 38 is then compared to the phase of voltage from the signal generator 34 in the comparator 40. The comparator 40 then provides a pulse-width-modulated signal with a duty cycle proportional to the valve lift. This signal can be read directly by an engine valve controller, not shown, using a digital timing circuit. Alternatively, the output of the comparator 40 can be converted to an analog signal using a filter, not shown.
In the subject invention, the supply power is lost to heat by both the resistor and eddy currents dependent on the amount of engagement of the target with the magnetic field of the coil. This engagement is directly proportional to the engine valve lift when the target is affixed to the valve and the coil is affixed to the cylinder head as shown in
As the target 42 moves closer to the coil 36, in an engine valve 18 open position, the amount of phase lag in the coil and the resistor increases. As the target 42 moves away from the coil 36, in an engine valve 18 closing position, the amount of phase lag in the coil and the resistor decreases. Accordingly, the position of the target 42 (and the valve) relative to the coil 36 can be measured by comparing the amount of phase shift/lag between the current or the voltage drop across the resistor 38 and the supply voltage from the signal generator 34.
The lower portion of the graph illustrates the Exclusive OR output signal relative to the upper portion of the graph. Line 50 represents a variable duty cycle digital signal with a frequency twice that of the signal generator frequency. Specifically, for each signal generator cycle two output signals are generated, shown as peaks 52 and 54. The width of each output signal is proportional to the response delay (phase lag) of the resistor voltage relative to the signal generator voltage.
The Exclusive OR output signal is determined according to the following logic. When the state of the signal generator voltage and the resistor voltage are the same, the output signal is “Low”, as illustrated by portions 56 of line 50. However, when the state of the signal generator voltage and the resistor voltage are different, a “High” output signal is generated, as illustrated by portions 52 and 54 of line 50, until the states become the same. Thus, the duty cycle (or width) of the output signals 52, 54 is proportional to the response delay (phase lag) of the resistor voltage, which is proportional to valve lift.
If desired, the sensor assembly 32 may be modified so that the signal generator 34 supplies voltage, in parallel, to multiple sensor assemblies, similar to sensor assembly 32, positioned throughout an engine valve train to track the positions of multiple engine valves.
In the illustrated embodiment, the valve spring extends between a valve seat on the cylinder head and a valve retainer attached to the valve stem and biases the valve toward a closed position. However, the present invention can also be applied to other forms of valve springs which bias a valve to a mid position or an open position as well to valves actuated without valve springs.
While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.
