Systems, methods, and devices for valve stem position sensing
A linear variable differential transformer (LVDT) for monitoring engine valve position is disclosed. The system includes a valve guide having an elongated recess through it. The engine valve has a valve head and a valve stem with two adjacent materials having different magnetic properties meeting at an interface. The valve stem fits and moves linearly within the valve guide, and the valve head closes an engine combustion chamber. It also includes monitoring coils within the valve guide that create a signal related to the position of the interface within the valve guide. An engine control unit (ECU) is coupled to the monitoring coils and receives and analyzes the signal from the monitoring coils to determine operation of the valve.
1. A system for monitoring positions of an engine valve comprising:
a valve guide having a central recess passing through a length of the valve guide, wherein said engine valve comprises:
a valve stem having a first section with a first magnetic property adjacent to a second section with a second magnetic property, the first section and the second section having a same diameter and creating an interface between the two sections, wherein the valve stem is received by the central recess and the valve stem is allowed to move linearly through the central recess;
a powered coil surrounding said valve guide recess; and
a sensor coil also surrounding the valve guide recess, adjacent the powered coil, wherein the valve stem changes a coupling between the coils as it moves relative to the coils, thereby generating a signal within the sensor coil that is directly related to a position of the valve stem relative to the coils.
2. The system of claim 1 wherein the coils are located at a coolest portion of the valve guide that will encompass motion of the interface.
3. The system of claim 1 wherein the powered coil creates an alternating magnetic field.
4. The system of claim 1 wherein the interface of the valve stem is a magnetic discontinuity.
5. The system of claim 1 wherein the interface is between metals having dissimilar magnetic permeabilities.
6. The system of claim 1 wherein the interface is a weld interface.
7. The system of claim 1 wherein the interface is between a ferromagnetic material and a non-ferromagnetic material.
8. The system of claim 1 wherein the interface is between a solid portion of the valve stem and a hollow portion of the valve stem.
9. The system of claim 1 , further comprising a switching rocker arm assembly adapted to drive the engine valve in one of a high lift mode and a low lift mode wherein the high lift mode causes the valve stem interface to move through a first linear distance and the low-lift mode causes the valve to move through a second distance smaller than the first distance.
10. A linear variable differential transformer (LVDT) for monitoring engine valve position comprising:
a valve guide having an elongated recess through a length of the valve guide,
an engine valve comprising:
a valve stem with two adjacent portions made of materials having different magnetic properties, the two adjacent portions meeting at an interface, the two adjacent portions having a same diameter, wherein the valve stem fits and moves linearly within the valve guide;
monitoring coils within the valve guide that create a signal related to a position of the interface within the valve guide by coupling between the coils; and
an engine control unit (ECU) coupled to the monitoring coils, the ECU adapted to receive and analyze the signal from the monitoring coils to determine operation of the valve.
11. The LVDT of claim 10 wherein the ECU determines that the valve is operating in a high-lift mode.
12. The LVDT of claim 10 wherein the ECU determines that the valve is operating in a low-lift mode.
13. The LVDT of claim 10 wherein the ECU determines that the valve is failing to close.
14. The LVDT of claim 10 wherein the ECU determines that the valve is operating out of sequence with the engine.
15. The LVDT of claim 10 , further comprising a switching rocker arm assembly adapted to drive the engine valve in one of a high lift mode and a low lift mode, the switching rocker arm assembly comprising an inner arm, an outer arm and a latch for latching the inner arm to the outer arm for a high lift mode of operation and causing the valve stem interface to move through a first distance, the latch also suitable for unlatching the inner arm from the outer arm for a low lift mode of operation and causing the valve to move through a second distance smaller than the first distance.