Method to adaptively control and derive the control voltage of solenoid operated valves based on the valve closure point

The invention provides a computer implemented method to automate the calibration of the drive voltage waveform of a solenoid operated valve. An initial estimate of valve electromagnetic parameters and valve closure point is derived and the drive voltage waveform is created based in part on circuit constraints and the parameters and valve closure point. The drive voltage waveform is applied to the valve coil and the coil current feedback is obtained and used to update the initial estimate. This process is repeated until the coil current feedback meets predetermined criteria. The electromagnetic parameters include the L/R ratio of the valve during the pull-in time and decay time, the valve back emf during the pull-hold time, and the average resistance during hold when current is steady. The closure point is used to anchor the drive voltage waveform and is adjusted at a slower rate than the other parameters.

FIELD OF THE INVENTION

This invention pertains to controlling valves, and more particularly, to detecting and controlling the closure point of solenoid operated valves.

BACKGROUND OF THE INVENTION

Solenoid operated valves and pumps are driven in their simplest form by a coil and an armature that is free to move within the coil. The armature is normally spring loaded away from the energized position such that when a power pulse is applied to the coil, the armature is pulled into the energized position and in moving opens or closes the valve. It is known that once the solenoid has moved to the end of its operating stroke, no further work is done by the armature.

The amount of current flow through the coil determines the strength of the magnetic field acting upon the armature and the voltage applied to the coil determines the current flow through the coil. The duration of voltage application to the coil must be sufficiently long in order to permit the armature to complete its operating stroke. After the operating stroke has been completed, the current through the coil can be reduced to the amount of current necessary to hold the armature in place. This current is called the hold current. Current in excess of the hold current wastes power and reduces valve life.

In order to efficiently control the solenoid, the voltage waveform to drive the coil (i.e., a drive voltage waveform) is typically selected to provide sufficient power to drive the solenoid efficiently. The prior art requires extensive manual calibration and testing in order to find and tune a ‘suitable’ or optimum drive voltage waveform for a particular valve. In other words, ‘plug and play’ of the valves is not feasible. This is due to several reasons.

One reason is that the drive voltage may be fixed in operation. When the drive voltage is fixed in operation, the drive is in principle sub-optimal in operation because there is unit-to-unit variation of the valve electromagnetic and mechanical parameters.

Another reason is that there is also a very strong type-to-type variation. For example, the pull time, pull current, hold current and closure point can be significantly different between different manufacturer's valve for the same application. The prior art does not allow a simple replacement of one type for another without repeating the extensive manual calibration. For example, one cannot simply remove a valve manufactured by a valve manufacturer and install a valve manufactured by another valve manufacturer and vice-versa without repeating the manual calibration step.

Another reason is that the closure point detection (i.e., detecting when the solenoid closes) information from prior systems is not reliable. In these systems, a numerical algorithm detects closure by finding an inflection point in the current feedback from the coil. The current feedback signal typically exhibits several ‘non-linearities’ (e.g., inflections). In order to differentiate these from the closure point, the drive signal is compromised and the search window used to find the closure point has to be very narrowly defined. Additionally, finding inflections in a signal is very sensitive to noise. As a result, this technique is sensitive to cycle-to-cycle variation and unit-to-unit variation.

BRIEF SUMMARY OF THE INVENTION

The invention provides a computer implemented method to automate the calibration of the drive voltage waveform of a solenoid operated valve and adaptively control the drive voltage waveform of the solenoid coil and detect the closure point of the valve. An initial estimate of valve electromagnetic parameters and the valve closure point is derived and the drive voltage waveform is created based in part on circuit constraints and the parameters and valve closure point. The drive voltage waveform is applied to the valve coil and the coil current feedback is obtained and used to update the initial estimate. This process is repeated until the coil current feedback meets predetermined criteria. The electromagnetic parameters include the L/R ratio of the valve during the pull-in time and decay time, the valve back emf during the pull-hold time, and the average resistance during hold when current is steady. The closure point is used to anchor the drive voltage waveform and is adjusted at a slower rate than the other parameters.

During operation, the voltage waveform is adaptively adjusted to changing conditions by analyzing the coil current feedback and adjusting the drive voltage waveform accordingly and at a slower rate than during the initial calibration of the valve that determines the drive voltage waveform to be used. Adaptation of parameters is stopped if control pulses of the valve are such that the parameters (and closure point) cannot be derived.

Trends or patterns in the electromagnetic parameters and the closure point are used in one embodiment to determine the condition of the valve. Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

The present invention utilizes adaptive control and optimization to automate the calibration of a valve with respect to determine and tune the optimum drive voltage for a particular valve. Unlike prior art systems that find an inflection point in the coil current feedback, the invention controls the drive voltage such that the closure point of the valve corresponds to a minimum point of a “notch” in the coil current feedback. The invention reliably and repeatedly detects and controls the closure point of valves regardless of the type of valve, unit-to-unit variation, and operational variation between valves. In one embodiment, the closure point is controlled such that the lowest allowable current level to operate the valve is used. This reduces the system's power supply requirements, reduces heat generated in the valve coil drive circuitry and helps extend the life of the valves and valve controller.

FIG. 1shows an exemplary computing device100communicating with a valve102via voltage driver104for implementing an embodiment of the invention. Alternatively, the voltage driver104and valve102may be isolated from the computing device100and data manually entered into the computing device100. The valve102and voltage driver104are well known in the art and need not be described in detail herein. In its most basic configuration, the computing device100includes at least a processing unit106and a memory108. Depending on the exact configuration and type of computing device, the memory108may be volatile (such as RAM), non-volatile (such as ROM, flash memory, etc.) or some combination of the two. This most basic configuration is illustrated inFIG. 1by a dashed line110. Additionally, the device100may also have additional features/functionality. For example, the device100may also include additional storage (removable and/or non-removable) including, but not limited to, magnetic or optical disks or tapes. Such additional storage is illustrated inFIG. 1by a removable storage112and a non-removable storage114. Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. The memory108, the removable storage112and the non-removable storage116are all examples of computer storage media. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can accessed by the device100. Any such computer storage media may be part of the device100.

The device100may also have one or more input devices118such as keyboard, mouse, pen, voice input device, touch-input device, etc. One or more output devices120such as a display, speakers, printer, etc. may also be included. All these devices are well known in the art and need not be discussed at greater length here.

Turning now toFIG. 2, an example of a current waveform driven by a drive voltage derived in accordance with the invention for a valve is shown. The ordinate axis202is current magnitude and the abscissa axis204is time. The pull-time206is the time in which current in the valve coil rises to a first peak208. This current is called the pull current and the current rises linearly during this time. Controlling the valve with drive voltage makes the closure point correspond to a minimum point210of a “notch”212in the current waveform. When closure occurs during the pull-hold time214, the largest non-linearity in the pull-hold window214is due to a sudden decrease in the back emf (BEMF) that corresponds to valve closure. In other words, it is possible to get local minima due to other non-linearities, but the largest dip or the smallest minimum is due to closure of the valve. If the closure point information is reliable (i.e. no significant variation), then it can be used to anchor the drive voltage (e.g., it can be used as a datum to define an optimum drive voltage). Both the time value and current value of the closure point is used to determine the drive voltage. Once the pull-hold time passes, the current decays (this time is called the decay time216) until is reaches a current value218that is sufficiently above the valve hold current220to prevent the valve from prematurely opening.

Turning now toFIG. 3, the steps taken to derive and adapt the drive voltage (i.e., the control voltage) for the valve are shown. To derive the control voltage for a valve, four electromagnetic parameters of the valve are needed. These are the L/R ratio (inductance/resistance ratio of the valve coil) during the pull-in time of the valve coil (designated as L/R1), the back emf (BEMF) of the valve during the pull-hold time, the L/R ratio of the valve coil during the decay time (designated as L/R2), and the average resistance during hold (i.e., a hold resistance) when current is steady (e.g., current value216). Other parameters may also be used to derive the voltage waveform.

The valve holding current is acquired (step300). This is a known parameter of the valve and is based upon valve size and valve magnetic parameters. An initial estimate of the four electromagnetic parameters and closure point (hereafter, collectively called “the parameters) is determined (step302). The initial estimates may be guessed or be based upon similar valve designs. For example, parameters for similar devices could be stored in a database and these stored parameters could be used as the initial estimate of the parameters. The initial estimate can also be determined by defining a standard very low energy starting voltage waveform. This approach is used when very little or nothing is known about the valve. The resulting coil current feedback is used to derive the four parameters and closure point. While using a very low energy starting voltage waveform will not produce a satisfactory result initially, the method described herein reaches a satisfactory result after a number of iterations.

Once the initial estimate is determined, a voltage drive waveform is derived based on circuit constraints and the estimated parameters and closure point (step304). The circuit constraints may include maximum driver current, voltage limits, slew rate (i.e., voltage and/or current rise times) (to reduce electromagnetic interference), and the like.

The derived voltage waveform is tested on the valve coil and the coil current feedback is obtained (step306). The coil current is analyzed to determine if the drive voltage waveform is acceptable (step308). The analysis includes determining the time and current value of the parameters (i.e., closure point and electromagnetic parameters). For example, the R value is determined by looking at the tail end of the coil current feedback where this is no significant dI/dt and solving R from V=IR where V is the magnitude of the drive voltage and I is the current. L/R1 is determined by solving dI/dt=(V−IR)/L during the current rise time. L/R2 is determined similarly by looking at the current decay from the pull current value to the hold current value. The BEMF is the average extra voltage required to return the current to the same pull current value before decay starts.

The drive voltage waveform and current feedback are compared to previously acquired waveforms for the valve (or stored waveforms for similar valves) and the parameters are adjusted accordingly. If the parameters need to be adjusted, the estimate of the parameters is updated (step310) from the coil current feedback and voltage waveform as described above. The process of steps304-310is repeated until the coil current feedback meets predetermined criteria. The criteria may include the closure point not having a significant variation from shot to shot, the area under the current curve is minimized to reduce power dissipation in the coil, etc. In one embodiment, if the coil current feedback is acceptable, the drive voltage waveform is applied to the coil for a predetermined number of times to verify that the drive voltage waveform consistently results in a desired coil current feedback.

In the steps described above, there are two types of basic adaptation that are taking place. The first type is the adaptation of the four electromagnetic parameters. An adjustment of these electromagnetic parameters results in a change in the drive voltage levels. The second type is the adaptation of the closure point. Since this is used an anchor in the drive voltage waveform, an adjustment in the closure point results in a change in the time values that define the drive voltage windows (e.g., pull time, pull-hold time, etc.). In principle, the two adaptations above form an algebraic loop. For example, a change in the electromagnetic parameters causes a change in the closure point that in turn causes a bigger change in the parameters, and so on. This potential problem is resolved by forcing the closure point adaptation to occur at a much lower frequency than the parametric adaptation so that they do not adversely interfere with each other. Additionally, knowledge of the parameters provides an information link between the time values, the drive voltage, and current levels. This information is used in feed forward fashion to reduce the degree of the algebraic loop.

Once the voltage waveform has been derived, the coil current feedback is monitored and the voltage waveform is adjusted during valve operation to optimize the coil current feedback. Turning now toFIG. 4, the coil current feedback is sampled during operation (step400). The samples are analyzed as described above (step402). A determination is made of whether the drive voltage waveform needs to be changed (step404). If the samples indicate no change in the drive voltage waveform is needed, steps400-404are repeated. If the samples indicate that a change in the drive voltage waveform is needed, the process enters into a maintenance mode (step406). In the maintenance mode, a determination is made as to whether the drive voltage waveform should be adjusted and/or maintenance activity signaled. Trends or patterns in the electromagnetic parameters and the closure point contain information about the condition of the valve. For example, a gradual fouling of a sticky valve can be diagnosed and predicted in advance by the change in parameters and an indication can be provided of the condition to a system controller and/or a visual indication can be provided. Prediction of valve failure and preventive maintenance (e.g., prognostics) can be performed by comparing the current feedback of valves and the calculated valve parameters (e.g., the electromagnetic parameters) to other valves in an engine. For example, if a valve's parameters begin to change at a faster rate than other valves, the valve can be checked to determine if the valve should be replaced. If the drive voltage waveform needs to be adjusted, steps304to310are repeated.

In practice, the rate of adaptation of the parameters (and the drive voltage waveform) should be controlled to suit a particular mode of the engine or activity. For example, during the initial calibration, a high convergence rate is recommended. However, during run time, the convergence rate has to be low so that no unwanted adaptation takes place during unusual or abrupt changes to the engine. There are also situations where the adaptation has to be switched off for events, including when the injection event is cancelled during a maintenance or monitoring activity. For example, if the engine controller requests a very short injection pulse which is shorter than the time necessary to decay the current to the hold value, the R and L/R2 adaptation is disabled. If the required pulse is so short that it cuts into the closure window, then BEMF and closure point adaptation are disabled. If the closure point can't be detected during normal operation (i.e., during the time of a normal valve closure), the system user is alerted of a possible valve failure.

The overall steps have been described. Returning now toFIG. 2, an actual converged waveform during a bench test on an ERV (electronic rail valve) is shown. It can be seen that the closure point is within the pull-hold window214and is at the minimum current value in the pull-hold window214. The converged waveform may be different for other valve types and units of valves. The invention finds the optimum current waveform for the pull-time206, pull-hold time214, decay time216and the optimum values for the first peak208, the closure point (i.e., minimum point210), “notch”212, and current value218using the techniques described herein.

FIG. 5shows how the current feedback trace converges from its initial state500to its final state506using the procedure described above. Intermediate states are represented by curves502and504. Any number of intermediate states may be needed for convergence. The procedure purposely causes a notch (e.g., notch212) that corresponds to the closure point and never loses track of it. The closure point value is the location in time corresponding to the minimum point of the notch.

It should be noted that the power source does not have to be a stiff source for the invention to work. The invention accounts for any change in the voltage level (e.g., supply voltage sagging as a result of current being drawn) by lumping source characteristics in the electromagnetic parameters. For example, the derivation of the L/R1 constant accounts for the change in voltage during the pull-time.FIG. 6shows how the corresponding duty cycle of the drive voltage waveform changes with iterations. Note that the initial state600and final state606are different. An intermediate state604is also shown. The initial state600corresponds to curve500, intermediate state604corresponds to curve504, and the final state606corresponds to curve506. The intermediate state606overlays the initial state600for a portion of the time from the start (time=0 μsec) until it drops to zero. It also overlays the final state606as shown until the end of the cycle. The drive voltage waveform tracks the duty cycle. For example, if the power source is a stiff source, the average voltage delivered to the valve coil is the duty cycle times the power source output voltage level. Those skilled in the art will recognize that any type of PWM (Pulse width modulation) control may be used. PWM control is known in the art and need not be discussed herein.

FIGS. 7 and 8illustrates the convergence of the basic four parameters.FIG. 7illustrates the convergence of L/R1 (curve700) and L/R2 (curve702).FIG. 8illustrates the convergence of the back EMF (curve800) and the average resistance (R) during hold (curve802). The adaptations are initially large and then reach equilibrium. Note that the adaptations of these parameters are the high frequency adaptations previously described, as opposed to the low frequency adaptations that are related to the movement of the closure point in time and in current as shown in FIG.9. The L/R1 and L/R2 values converge to different values even though there is only one valve coil and one resistance. The reason for this is that the coils typically exhibit non-linearity and the current rise during pull time206is not necessarily controlled by the same average characteristic parameters than the current fall during decay216. L/R is used rather than L in order to decouple any disturbance that might come from R adaptation on the rise and fall time constant.

FIG. 9shows how the closure point location in time and in current is moved during the search for the optimum drive voltage. Curve900is the closure point location, curve902is the current at the closure point, and curve904is the pull-time. It can be seen that the curves are smooth and stable and that the adaptation occurs at a low frequency as described above. If the closure point moves in time during operation, the controller can bias the injection timing to adjust for this movement and precisely control when fuel is injected.

It can be seen from the foregoing description that a method to reliably and repeatedly detect and control the closure point of valves regardless of the type of valve, unit-to-unit variation, and operational variation between valves has been described. Closure point is reliably and repeatedly detected and controlled, which results in the coil current and closure point time being controlled to optimum values.