Abstract:
A controller moves a solenoid operated valve with a first solenoid operating pulse during a travel time. After a time interval, the controller applies a second pulse, which moves the valve towards its original position. The time interval may be varied, and a characteristic indicative of the return of the valve to the original position may be detected based on a comparison of the pulses.

Description:
RELATED APPLICATIONS 
     This application claims priority to, and the benefit of, United Kingdom patent application Serial No. GB0712538.8, filed on Jun. 28, 2007, entitled “Controller for a Solenoid Operated Valve.” 
     FIELD OF THE INVENTION 
     This invention relates to a controller for a solenoid operated valve and in particular but not exclusively, solenoid operated fuel injector valves, and valves used in diesel fuel injectors. 
     BACKGROUND OF THE INVENTION 
     The solenoid is often combined with a two-position valve, whereby the valve is pulled by the solenoid (when energized) and returned by a spring (when de-energized). The valve attached to the solenoid can be closed in one position and open in the second position, or it can be a changeover valve with two seats. In some applications, such as fuel injectors, it is desirable to measure and control the timing of the opening and closing positions of the solenoid operated valves. 
     Diesel fuel injectors need to have precise operating times. The valve determines the injection timing and also the injection duration (quantity of fuel) injected into a cylinder of a diesel engine. The performance of the engine (balance between cylinders, power, fuel consumption, emissions) is thus affected. 
     Known means exist to measure the impact point of the solenoid valve at the end of the energized stroke. For example Woodward U.S. Pat. No. 6,889,121 describes one such means. In this way the first (energized) travel time of the solenoid valve motion can be measured. It is desirable also to measure the impact of the solenoid valve at the end of the de-energized stroke. Thus information relating to the duration of the solenoid operation can be obtained for helping to control the amount of fuel supplied. This is particularly useful when the duration is short (as in diesel pilot injections)—small variations in duration can give large percentage variations in the output of a pilot injection. 
     A method of measuring the de-energized impact point is described in GB 2 110 373. In this patent specification, the method tries to measure the end of the solenoid movement by detecting a small change in the current to the solenoid caused by the back EMF when the solenoid stops moving (at the end of the de-energized stroke). This is very hard because of the small size of the change. Part of the reason for the small size of the change is that the gap between the solenoid armature and the stator is relatively large after de-energization. Often detecting this small current change is not possible because there is no current flowing at this time, and thus no change can be measured. 
     A further method is described in U.S. Pat. No. 5,650,909 in which a small current is added (to the solenoid) after the main current has been switched off. This is done to overcome the limitation above. The current must be small so that it does not affect the valve motion. Again there is difficulty in reliably measuring the small changes. 
     A yet further method involves adding a transducer to measure the valve motion directly. This can be a movement transducer or a pressure transducer (measuring some function of the valve attached to the solenoid). However, adding additional transducers considerably increases the system cost, and also increases complexity. 
     The Woodward U.S. Pat. No. 6,889,121 describes how to measure the end of the forward (energized) motion of the solenoid, and using this to control solenoid timing. This does not attempt to measure the solenoid return stoke. Changes in the operating conditions or parameters of the valves within a fuel injection system, for example wear, can lead to changes in the time of the valve return stroke. This in turn can lead to changes in the amount of fuel injected for a supply pulse of given duration and thus also to variations in the performance of the valves of a fuel injection system. 
     SUMMARY OF THE INVENTION 
     It is an aim of the present invention to alleviate the aforementioned problems and in particular to provide for accurate timing measurements in order to improve solenoid operated valve performance in, for example: fuel injection systems including diesel fuel common rail injector systems; diesel unit injectors; petrol injection solenoids; solenoids of the two-position type; particularly fast acting solenoids; solenoids for precise dosing of fluids; pilot valves for larger actuators; engine air intake and exhaust valves (if actuated, not cam driven); valves used in suspension or braking. 
     According to the present invention, there is provided a controller comprising: means for supplying a first solenoid operating pulse for moving a valve from a first state to a second state, the movement from the first to the second state defining a travel time of said valve; means for supplying a second solenoid operating pulse after a time interval following said first pulse, during which interval the valve returns towards said first state; timing means operative for varying the time interval between said first and second solenoid operating pulses representing a pair of solenoid operating pulses; and detector means for detecting a characteristic indicative of the return of the valve to said first state from said second state based on a comparison between different pairs of pulses. 
     In a preferred embodiment, said characteristic is an advance in said travel time of said second solenoid operating pulse in at least one pair of solenoid operating pulses relative to a previous pair. The timing means may progressively decrease or increase the time interval from an initial predetermined time interval until at least one advance in travel time is detected. This may continue progressively until a maximum advance in the travel time is detected. 
     In a preferred embodiment, said valve may be a valve of a fuel injector, the first solenoid operating pulse may be a first fuel injection pulse for moving the valve of the fuel injector from the first state to the second state; and the second solenoid operating pulse may be a second fuel injection pulse. 
     The first and second fuel injection pulses advantageously represent test pulses for use during a calibration or adjustment phase of a fuel injection system. During normal injector operation, the controller is operative to supply drive fuel injection pulses to the fuel injector during a drive phase of the fuel injection system, these drive pulses tend to be supplied singly, the test pulses being supplied in pairs. The test pulses and said drive pulses may be supplied to a plurality of fuel injection valves, whereby the controller can adjust the duration of the drive fuel injection pulses supplied to respective ones of the fuel injection valves in dependence on a comparison based on the detected advance in the travel time and a reference such as to bring an operating characteristic of the injectors into alignment with one another 
     The preferred embodiment may include means for detecting an end point when the valve of the fuel injector reaches the second state from the first state. This end point detecting means may be configured for measuring an advance time period with reference to any timing event set or influenced by the controller such as the beginning or end of one of the test pulses, or even TDC (engine cylinder TDC). The advance time period may be taken with reference to said end point of the first fuel injection pulse or one of the beginning or end of said first fuel injection pulse. 
     According to a second aspect of the present invention, there is provided a method of controlling a timing of a solenoid, the method comprising: supplying a first solenoid operating pulse for moving a valve from a first state to a second state, the movement from the first to the second state defining a travel time of said valve; supplying a second solenoid operating pulse after a time interval following said first pulse, during which interval the valve returns towards said first state; varying the time interval between said first and second solenoid operating pulses representing a pair of solenoid operating pulses; and detecting a characteristic indicative of the return of the valve to said first state from said second state based on a comparison between different pairs of pulses. 
     In a preferred embodiment, the characteristic is an advance in said travel time of said second solenoid operating pulse in at least one pair of solenoid operating pulses relative to a previous pair. The method may include the step of progressively decreasing or increasing the time interval so that said detector means detects a maximum advance in said travel time. Alternatively, the change in the time interval may be in any order, that is to say, it could vary randomly, or step up and down in turn. 
     In a preferred embodiment, said valve may be a valve of a fuel injector, the first solenoid operating pulse may be a first fuel injection pulse for moving the valve of the fuel injector from the first state to the second state; and the second solenoid operating pulse may be a second fuel injection pulse. The first and second fuel injection pulses represent test pulses for use during a calibration or adjustment phase of a fuel injection system. The method may include supplying drive fuel injection pulses to the fuel injector during a drive phase of the fuel injection system and adjusting the duration of the drive fuel injection pulses supplied to the fuel injector in dependence upon the detected advance in the travel time. 
     The method may further include supplying said test pulses and said drive pulses to a plurality of fuel injection valves and adjusting the duration of the drive fuel injection pulses supplied to respective ones of the fuel injection valves in dependence on a comparison based on the detected advance in the travel time and a reference such as to bring an operating characteristic of the injectors into alignment or conformity with one another. 
     The method advantageously includes detecting an end point when the valve of the fuel injector reaches the second state from the first state, and measuring, on detection of said advance, an advance time period with reference to the first fuel injection pulse and the detection of said end point corresponding to the second fuel injection pulse. 
     Insofar as they apply to fuel injection systems, embodiments of the invention allow for the drive fuel supply pulses to be individually adjusted in time so that the ‘end stop to end stop’ timing of the valves within the fuel supply system can be standardised with reference to a predetermined characteristic. This characteristic may be that the valves have the same ‘end stop to end stop’ timing values and that these are substantially equal to a predetermined reference. Periodic calibration of the valves can therefore be carried out so as to achieve an adaptive control capability in the engine management system to which the controller is applied, thereby improving engine performance. The (electronic) controller of the solenoid can perform this calibration task in an algorithm on a periodic basis. For a number of solenoids, the start and stop times of the current pulses can then be set so that the performance of all the solenoids can be matched. In this way the performance of a diesel engine (that uses many injectors, each with a solenoid) can be improved. 
     Further advantages may arise from embodiments of the invention as follows: closer matching of pilot injection quantities; closer matching of main injection quantities; close matching of post injection quantities; improvement of engine cylinder balance; reduced engine emissions; improved fuel economy; lower hardware manufacturing costs (arising from a lower need for tight tolerances); better diagnostic checking of the solenoid valve (from greater knowledge of the solenoid performance). 
     Embodiments may be advantageously applied to: diesel fuel common rail injector systems; diesel unit injectors; petrol injection solenoids; solenoids of the two-position type; particularly fast acting solenoids (where the time taken to move from one state to another is less than 2 milliseconds, preferably less than 0.5 milliseconds); solenoids for precise dosing of fluids; pilot valves for larger actuators; engine air intake and exhaust valves (if actuated, not cam driven); solenoid operated valves used in suspension or braking systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be further described by way of example with reference to the accompanying drawings in which: 
         FIG. 1  is a schematic diagram of a solenoid operated valve for explaining the context of the present invention; 
         FIG. 2  shows a profile of a valve lift for a given logic pulse and supply current pulse according to the prior art; 
         FIG. 3  shows a valve lift for a pair of consecutive supply current pulses separated by a relatively large gap in time; 
         FIG. 4  shows a valve lift when the current pulses are separated by a gap of medium duration; 
         FIG. 5  shows the lift in the case of a relatively small gap between the current pulses; 
         FIG. 6  is a graph showing how the second current pulse advances the valve forward travel with gap size; and 
         FIGS. 7   a  to  7   c  show adjustments in solenoid operated pulses to compensate for short or long valve return times relative to a standard. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     In  FIG. 1 , a solenoid valve shown generally by numeral  1  comprises a valve  2  is moveable between mechanical stops  3   a  and  3   b . The valve  2  is driven by a solenoid having a stator  7 , solenoid coil  9 , return spring  11 , and armature  13 . This operates in accordance with conventional solenoid valves, namely, that when a current is applied to the solenoid valve  1  from a governor controller  4 , the armature  13  is pulled from its stable state towards the stator  7  thus bringing the valve  2  to the mechanical stop or seat  3   b . When the current is switched off, the return spring  11  pushes the armature  13  and hence the valve  2  back to the stop  3   a . On impacting the stop  3   a , it can bounce up to 10 or 20% (example percentage only) of the return travel distance. Experimental evidence shows that there may be a second and possibly a third bounce as is explained below with reference to  FIG. 6 . In embodiments of the invention, the valve may be of various types, for example, may have a single seat that forms one of the two mechanical stops. An alternative valve can have two seats, each of which forms a mechanical stop. 
     The solenoid operated valve of  FIG. 1  may be used to control the valve in a fuel injector. Although  FIGS. 2 to 7  below are described with reference to the control of a fuel injector valve, the control may be applied to other situations such as: solenoids of the two-position type; particularly fast acting solenoids; solenoids for precise dosing of fluids; pilot valves for larger actuators; engine air intake and exhaust valves (if actuated, not cam driven); solenoid operated valves used in suspension or braking systems. An example of a solenoid valve assembly that may be employed in embodiments of the present invention is one manufactured by Woodward Diesel Systems and known as “Balanced Valve Assembly”, part number G50010255. This is used in a unit injector. It can be operated by the controller  4 . An example of a controller  4  that could be employed in embodiments of the present invention is a Woodward Diesel Systems manufactured “In-Pulse II” part number 82371006. This is a typical controller suitable for controlling solenoid valves (in fuel injection systems). In  FIG. 2 , a valve lift trace  21  for a fuel injector for a given current pulse  23  is shown. A “logic” pulse  25  represents the duration of the current pulse  23  supplied to the solenoid coil  9 , from the controller  4 , which in turn lifts the valve  2  of the fuel injector. The current pulse  23  profile versus time can take various shapes relative to the one shown in  FIG. 2 , depending on the drive circuitry and control used to supply the current. The profile of the current pulse  23  is such that it typically rises fast to a high value H. This causes the valve  2  to move between the first and second positions, namely, from the stop  3   a  to the stop  3   b . When the valve  2  has reached an end point L in its forward travel F 1 , then the current is set to a lower value to save power (see the dip in the “M” shape part of the current pulse  23  trace in  FIG. 2 ). The time between the start  26  of the logic pulse  25  and the end of forward travel F 1  of the solenoid (where the valve lift reaches a maximum) is shown as FT 1 . The method of measuring the valve forward stroke as described in U.S. Pat. No. 6,889,121 is used to trace the shape of the current shown in the Figures. 
     After the current pulse  23  has been switched off and has fallen to zero (see point O in  FIG. 2 ), then the valve starts to move on its return stroke, under the action of the return spring  11 . The valve starts its return stroke  27  slowly and accelerates until it hits an end stop  29 . The time period between the end of the logic pulse  25  and the point at which the valve  2  reaches the end stop  29  is RT 1 . The valve typically bounces by as much as 20% of its travel as shown by the peak P in  FIG. 2 . 
       FIG. 3  shows a valve lift profile  31  in a case where the current supplied to the solenoid  9  comprises a pair of consecutive current pulses  33   a ,  33   b . These correspond to a pair of logic pulses  35   a ,  35   b  separated by a relatively large time gap T 1 . As is apparent from  FIG. 3 , the forward travel times FT 1  are the same for both valve lifts  31   a ,  31   b  in this train of pulses. This is as expected. The time when the forward travel F 2  of the second valve lift  31   b  has been completed depends only on the time gap T 1  between the current pulses  33   a,b . As the time gap represented by T 1  between the current pulses is reduced then the forward travel F 2  of the second valve lift  31   b  will be completed earlier. 
     This is illustrated in  FIG. 4  in which a time gap T 2  between consecutive logic pulses  45   a  and  45   b  is reduced relative to the time gap T 1  of  FIG. 3 . In this case, the time gap between the two current pulses is smaller, and the second forward travel time FT 2  has been reduced relative to FT 1 . This is because the valve  2  has bounced on the end stop  29  in  FIG. 2  at the end of its return stroke. Thus the valve  2  is already travelling forward, when energized with the second current pulse, and completes its second forward travel F 2  quickly relative to the forward travel F 1  of the first valve lift  41   a . The second forward travel time FT 2  is therefore completed (i.e. the end point L is reached earlier) in advance of that which would be otherwise expected from the timing of the two current pulses  43   a ,  43   b . That is, there is an advance in the timing of point L in the current pulse  43   b  relative to what it would have been in the absence of the bounce. The time period Ta is thus shorter than it would have been in the absence of the bounce. The time period Ta is referenced relative to the start of the logic pulse  45   a  but could alternatively be taken from any known timing point. 
       FIG. 5  illustrates the case where a time gap T 3  between the logic pulses  55   a ,  55   b  is reduced further relative to the time gap T 1 . In this case, the duration of the gap between the current pulses  53   a ,  53   b  is insufficient to allow time for the valve  2  to reach the end stop  3   a  before the solenoid is re-energised by the current pulse  53   b . That is, the forward movement of the valve  2  is started before the return stroke of the previous pulse has finished. In this case, the valve  2  forward travel on the second lift  51   b  does not receive any assistance because of the absence of bounce at the end of the return stroke of the first lift  51   a . Consequently, the forward travel time FT 3  of the second valve lift  51   b  is similar to the forward travel time FT 1  of the first valve lift  51   a.    
       FIG. 6  is a graph showing the change in forward travel time FT 2  as the gap between the pair of pulses progressively decreases from a relatively large value. It shows a small peak at a gap of 2 milliseconds, suggestive of an advance in timing arising from a third bounce. As the gap decreases to about 1.7 milliseconds, a second larger peak is detected indicating a second bounce eventually reaching a maximum advance at about 1.2 milliseconds. Detection of this maximum advance is a way of determining the recent occurrence of the end of return travel of the valve  2 , indicated by reference numeral  29  in  FIG. 2 . This allows for ‘end to end point’ timing to be measured for the injector valve as well as comparisons between different valves in a fuel injection system comprising many valves. 
       FIGS. 7   a  to  7   c  illustrate how a drive fuel injection pulse duration in respect of a valve is adjusted in order to equalise the injection timing between valves. 
       FIG. 7   a  corresponds to  FIG. 4  in which a maximum advance time Tmax-adv is detected. In this case it is with reference to the time period between the end of the first logic pulse  75   a  and the end point L of the second valve lift  71   b . The logic pulses  75   a  and  75   b  correspond to test fuel injection pulses for detecting the return time of the valve.  FIG. 7   a  shows a drive fuel injection pulse  77  which delivers the current pulse  78 , which in turn lifts the valve  2  in accordance with the lift profile  79 . The value Tmax-adv corresponds to a desired reference value for the fuel injector valve, indicating that the valve is delivering the correct fuel injection quantity. 
     During a calibration phase of the governor controller  4 , the time between the test pulses  75   a,b  is progressively decreased until a maximum advance T′max-adv is detected as shown in  FIG. 7   b . The controller  4  has a comparator (not shown) for comparing the time Tmax-adv with T′max-adv, the difference representing an increase in the return travel time of the valve return stroke relative to the valve under test in  FIG. 7   a . This increase may arise from initial manufacture, wear or other change in the operating environment of the valve. The controller  4  is operative to shorten the drive fuel injection pulse  77  for this valve by an amount Tdiff so that the return stroke follows the dotted line  80 , this corresponding to the correct valve time for this valve (see dotted line  82  which shows the end point  29  shifting to coincide with the end point  29  of  FIG. 7   a.    
     A valve with a shorter return stoke requires a lengthening of the drive fuel injection pulse as illustrated in  FIG. 7   c . In this case, the time period T″max-adv is shorter than Tmax-adv indicating that a corresponding increase T′diff in the drive fuel injection pulse is required by the controller  4 . 
     It is apparent that the controller  4  is operative for carrying out periodic calibration routines by applying pairs of test pulses having progressively reducing gaps between them in order to gain a comparison between the return timings, and hence ‘end stop to end stop’ timings. Changes in the fuel injection times of the valves can therefore be measured and compensated for on a periodic basis. 
     A calibration test procedure can be run when the solenoid valves are not required for normal operation, for example:
         1) When the engine is not operating and no fuel pressure is present. The solenoid valve motion will not then cause any problems.   2) In a unit injector (or a pump pipe injector) the engine can be operating. In this case the test pulses can be timed to be out of phase with the cam lobe rise. Therefore no fuel will be injected into the engine cylinders.   3) It is preferable to have the engine operating and thus the temperatures and pressures are at normal levels. In this case the two test pulses can be timed to fit in the time interval of one normal drive pulse. Therefore the engine cylinder associated with the injector being tested will not be over-loaded.