The present invention relates to a circuit for driving an electric actuator, in particular an electric fuel injector for an internal-combustion engine.
More specifically the invention relates to a control circuit of the type defined in the introductory part of claim 1.
Such a control circuit is schematically shown in
In this figure, 1 denotes a direct voltage source, for example a battery in a motor vehicle. In the embodiment shown the voltage source 1 has its negative pole connected to earth GND and its positive pole connected to a chopper circuit denoted overall by 2. An electric actuator 3, such as an electric fuel injector of an internal-combustion engine, is connected to the chopper circuit 2.
4 denotes an electronic control unit designed to apply to the chopper circuit 2, for an activation time ti which is in each case predetermined and included between an initial instant ts and a final instant te, a command signal CS essentially of the PWM (Pulse-Width Modulation) type, with a predefined ON/OFF switching period p and a variable duty cycle.
Correspondingly, the chopper circuit 2 causes the flow, within the electric actuator 3, of a correspondingly choppered current I having a nominal duration corresponding to the abovementioned activation time ti.
In control circuits for driving electric injectors, the current choppering frequency is not particularly high so that the current has a ripple of notable amplitude.
If the duration of each fuel injection operation is controlled in an open loop, the time required for the injector to close completely depends on the instantaneous value reached by the current at the end of the electric injector activation time. In
The command signal CS, started at the initial instant ts, terminates at the final instant te. At the instant te in general the intensity of the current I may be between a minimum value IHMIN and a maximum value IHMAX. Correspondingly, complete closing again of the electric injector occurs at a instant variable within a time interval E which represents the error in determination of the actual injection time.
One object of the present invention is to provide a control circuit for driving an electric actuator, in which the current in the electric actuator is controlled in an open loop, which circuit allows the abovementioned drawback of the solutions according to the prior art to be overcome.
This object and other objects are achieved according to the invention with a control circuit, the main characteristic features of which are defined in the accompanying claim 1.
Further characteristic features and advantages of the invention will become clear from the detailed description which follows, provided solely by way of a non-limiting example, with reference to the accompanying drawings, in which:
The control circuit according to the invention has essentially the same architecture shown schematically in
Very succinctly, in a control circuit according to the invention the control unit 4 is designed to determine the last whole or complete switching period included within the activation time ti of the electric actuator 3 before the final instant te. This last complete switching period is indicated by P in the upper graph according to
In general, determination of the last complete switching period P included within the activation time ti is fairly straightforward since the control unit 4 knows the initial instant ts, the duration tr of the rise phase of the current I and the durations tp and th of the subsequent current intensity choppering phases. The duration p of the individual switching periods is also known. Therefore, whenever the electric actuator 3 must be activated (for opening in the case of an electric injector), the control unit 4 determines, on the basis of one or more external control parameters, the duration of activation ti and, since the values of the other abovementioned parameters are known, may easily determine the last complete switching period P included within the activation time ti.
In order to eliminate or at least substantially reduce the error E, the control unit 4 of a control circuit according to the invention is also designed to allocate in accordance with the duty cycle applied during the phase th the final interval of the activation time ti, indicated by tf in
The control unit 4 therefore drives the chopper circuit 2 during the final interval tf in a manner corresponding to allocation of this final interval performed in accordance with the abovementioned duty cycle, and hence with a command signal which during the final interval tf is “ON” for the interval indicated by t′on in
As a result of this control method, at the end of the activation period ti the intensity I of the current flowing in the electric actuator 3 assumes essentially the minimum value IHMIN defined above. The instant of actual deactivation of the electric actuator (actual complete closure of the electric injector) is thus determined with a high degree of accuracy and is no longer affected by the error typical of the control systems according to the art indicated by E in
The above is obviously applicable strictly speaking to conditions where the progression of the current I in the electric actuator may be reasonably represented by linear sections, i.e. by sections of straight lines. However, in less strict terms, but in conditions nevertheless suitable for evaluation from a quantitative point of view, the control system according to the invention is able to achieve a notable reduction in the error during the actual activation time (actual injection time) also with real, i.e. actual, progressions of the current I.
Obviously, without modifying the principle of the invention, the embodiments and the constructional details may be varied greatly with respect to that described and illustrated purely by way of a non-limiting example, without thereby departing from the scope of the invention, as defined in the accompanying claims.
Number | Date | Country | Kind |
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TO2003A000778 | Oct 2003 | IT | national |