Abstract:
A method and apparatus for detecting a valve position includes the step of providing a non-actuating alternating current signal ( 24 ) to a drive coil signal ( 22 ). As a valve plunger ( 14 ) moves within the coil, the non-actuating signal changes. By monitoring ( 26,29 ) the non-actuating signal a control can predict when the plunger reaches a particular position. This invention thus provides a simplified way of detecting an end of travel position (FIG.  1 ).

Description:
This application claims priority to Provisional Patent Application Ser. No. 60/223,946 filed Aug. 9, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     This application relates to a method for detecting valve position in a valve driven by at least one electromagnetic coil, wherein changes in a signal applied to the coil are sensed. 
     For purposes of this application, the term “coil” will refer to any type of device such as a solenoid, etc., which receives an electric signal to in turn move a plunger. The plunger may be a permanent magnet, or simply a material such as iron which is subject to magnetic attraction. 
     Valves are typically utilized in vehicle engines to control the supply of fuel and air to the engine cylinders. One type of valve is driven by a pair of coils, and is utilized as part of a fuel injector. In such a valve the two coils are selectively and alternatively powered to drive the plunger between two positions and control the supply of fuel. With such systems, it is very difficult to accurately track the timing of the valve, and to determine its position as it moves. 
     Other types of valves are driven by a single coil in one direction, and moved in the other direction by a spring force. The same concerns with regard to tracking the movement of the plunger exists in these systems. 
     Another application for vehicle control is the air supply and exhaust valves on an engine. Historically these valves have been controlled to open in sequence by a cam shaft and rocker arms. More recently camless control systems have been utilized. However, these camless systems have the same problem as mentioned above with regard to detection of the actual position of the valve plunger. 
     The present invention provides a simple method for detecting plunger position. 
     SUMMARY OF THE INVENTION 
     In a disclosed method and apparatus of this invention, two signals are supplied to a coil for driving a valve plunger. A first actuating signal powers the coil to drive the plunger. A second non-actuating signal is applied to at least one coil associated with the plunger. As the plunger moves, it will produce changes in this non-actuating signal. These changes are identified by a control such that by monitoring the changes the system will be able to predict at least when the plunger has approached an end of travel position. Most preferably, the change is compared to a reference signal. 
     In one embodiment there is only one coil for powering the plunger. In a second embodiment there are a pair of spaced coils. In this embodiment the non-actuating signal could be applied to the activated coil, or the deactivated coil. 
     In the embodiment having two drive coils, it could be the non-actuated coil which is utilized to provide the reference. In particular, a valve plunger other than the one that is being driven may also have a non-actuating signal applied to one of its coils. The changes in that signal are compared to the changes in the signal from the moving plunger coil. In this way, the system is better able to accurately track when changes in the non-actuating signal are in fact indicative of an end of travel position. 
     These and other features of the present invention can be best understood from the following specification and drawings, and the following which is a brief description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a first embodiment of the invention. 
     FIG. 2 shows another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIG. 1, valve  10  including a plunger  14  which is spring biased by a spring  16  to a position where it blocks flow through a fluid path  18 . A coil  15  is selectively actuated to pull the plunger in an opposed direction. As illustrated, a DC actuating circuit  22  and an AC supply circuit, such as an oscillator,  24 , apply both an actuating (DC) and a non-actuating (AC) signal to the coil  15 . A phase shift detector  26  detects any change in the phase supplied by the AC source  24 , which may be modified by the movement of the plunger  14 . A second signal is taken from a second reference source  27 , which could be a plunger which is non-actuated. As an example, these systems are typically employed in internal combustion engines having a number of cylinders, and there are typically several of the plungers which would be non-actuated. Reference signal source  27  may be taken from one of those non-actuated plungers. The signals from both a non-actuated system phase shift detector  28  and phase shift detector  26  associated with the activated system are both supplied to a control  29 . In the disclosed embodiment, the control  29  has differentiating applier  31 , a differentiator  30  and in turn to a microprocessor control  32 . The control is shown as partially hardware, but of course all of these steps can also be taken in software within the scope of this invention. Essentially, the system compares the change in phase shift between the two phase shift detectors, and if a significant difference exists, then a determination can be made that the plunger is at a particular position. 
     Applicant has learned that when movement of the plunger begins or when it approaches an end of travel position, there are distinct changes in the super imposed AC signal that the detectors from the two coils will be able to detect. As the plunger moves, the phase will change, and the phase shift detector will detect those changes. Alternatively, the amplitude or frequency could also be monitored for change. By monitoring these changes as the plunger is moved, the inventor of this system has learned it can identify particular points during the movement path of the plunger. 
     By utilizing the reference plunger  27  which is non-actuated, the system is able to eliminate “noise” or other false indications of a particular point in travel, that could have been erroneously based upon a change in the signal for some reason other than plunger position. As an example, vibration, or other variables that will be experienced by the vehicle could also result in a phase shift. By looking at the non-actuated plunger, the system is able to filter out any such false readings. That is, if the non-actuated plunger is undergoing a similar phase shift to the one in the plunger being monitored, then the control will be able to identify that it is not an end of travel position but instead some other variable which has caused the phase shift. 
     As shown in FIG. 2, another common type plunger has two drive coils rather than a spring. The drive coils  40  and  42  are selectively actuated to move the plunger  44  between two positions. Each of the two coils is provided with its own drive circuit  50 , and those two circuits send signals from phase shift detectors to a control  52 . The circuit  50  and control  52  may be generally as shown in FIG.  1 . This two-coil system could also be monitored by taking a reference from another non-actuated plunger. 
     Moreover, it may be that a certain expected phase shift for a particular point in the plunger movement could be stored in a control, rather than requiring comparison with a reference. However, it is preferred that the reference signal be utilized. Finally, while the non-actuated signal is preferably applied to the coil which is actuated, it may also be applied to the non-actuated coil, and it would be expected that some change would occur even in the non-actuated coil as the plunger moves. 
     The aforementioned description is exemplary rather then limiting. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed. However, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. Hence, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For this reason the following claims should be studied to determine the true scope and content of this invention.