Patent Publication Number: US-7212390-B2

Title: Electronic control circuit for a starting switch of a motor vehicle

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates to an electronic control circuit for a starter contacter for a motor vehicle, the said contacter comprising a power contact for supplying power to the electric motor of the starter, and at least one excitation winding for actuating the power contact between an open position and a closed position, the said control circuit including a management unit having:
         first means for detecting the open or closed state of the power contact,   and second means for regulating the power supply to the winding during the starting cycle when the power contact is still open after a predetermined time after the commencement of the order for starting.       

     STATE OF THE ART 
     With reference to  FIG. 1 , a motor vehicle starter  10  comprises an electric motor  12  which is electrically connected to the positive terminal  14 A of a power supply battery, through an interposed power contacter  16 . The other terminal  14 B of the battery  14 , which is the negative terminal, is connected to earth. 
     The contacter  16  comprises at least one excitation winding  18  for actuating a moving contact  20 , which co-operates with fixed contacts  22 ,  24  in such a way that, in normal operation, it occupies either an open position when the winding  18  is not energised, or a closed position in the case where the latter is being excited during starting of the motor vehicle. The fixed contact  22  of the contacter  16  is connected to the terminal  14 A of the battery  14 , while the other fixed contact  24  is connected to the terminal  12 A of the motor  12 . The other terminal  12 B of the motor  12  is connected to earth. 
     Excitation of the winding  18  of the contacter  16  is governed by an electronic management unit  26 , in the form particularly of a microprocessor, which is automatically supplied with the battery voltage. The ignition key interrupter  28 , or ignition switch, is connected between the terminal  14 A of the battery  14  and the control unit  26 , for initiating the starting process when it is actuated. 
     The management unit  26  takes note of the voltage at the terminals of the fixed contacts  22 ,  24  so as to verify whether the contacter  16  is in the open or the closed state. The voltage is zero when the moving contact  20  is closed, and is not zero when the moving contact  20  is open. 
       FIG. 2  shows the pattern, or law, for the power supply to the contacter, which is described in the document FR-A-2 795 884, and it shows the development of a cyclic ratio of power supply voltage to the winding for normal operation of the contacter. 
     There may be many causes of failure of the moving contact  20  of the contacter  16  to close. Apart from mechanical causes they may be linked to the presence of non-conducting bodies at the surface of the contacts  22 ,  24 ,  20 , in particular dust, insulating particles, dirt, oxidation products, and so on. In that case, it is no longer possible to make electrical contact within the contacter  16 . The latter is faulty and the engine is unable to start because the electric starter motor  12  cannot be energised. 
     In the event of a malfunction of the contacter, holding the ignition key for too long a time in its starting position may give rise to over-heating of the contacter winding, or destruction of the power supply transistor. 
     Electronic control units for starters offer various functions, among which are the functions linked with:
         displacement of the moving core and moving contact of the contacter, and   operation of the contact of the contacter and of the associated electric motor.       

     According to the document FR-A-2 795 884, to which reference may be made for the structure of the starter, the management unit is capable of governing the pattern of the power supplied to the excitation winding of the contacter so as to optimise displacement of the moving core as a function of the displacement of the starter pinion. The cyclic ratio is applied to the power transistor which is in series with the winding, the value of the said cyclic ratio being regulated by the management unit in response to the power supply voltage across the terminals of the starter and the resistance of the winding, which is dependent on temperature. 
     In the document FR-A-2 746 449, the management unit is capable of detecting whether the moving contact of the contacter is really closed or not, during the control phase. The excitation current of the control winding of the contacter is automatically interrupted or reduced when the moving contact of the contacter is still open at the end of a predetermined period of time after the commencement of the demanded power supply. Such control of the excitation current of the contacter prevents damage to the control transistor or winding. 
     In the documents FR-A-2 760 891 and FR-A-2 760 910, the microprocessor management unit includes means for blocking the transistor which supplies power to the contacter winding, in response to the value of the drop in voltage supply after the contacter has been closed. 
     The system thus goes into protected mode. In this kind of situation, the operator will try again, and, because the pattern of power supply of the contacter is unchanged, the system runs the risk of again remaining with the contact open because of the presence of foreign bodies in the contact gap. 
     OBJECT OF THE INVENTION 
     The object of the invention consists in providing a solution to malfunctioning of the contacter of a motor vehicle starter, by automatically eliminating any fault consisting of unwanted insulation or pollution of the contact zone during the starting process, and by matching the energy supplied to the contacter. 
     According to the invention, the apparatus is characterised in that the second means are arranged to produce automatically, during a period of time, a series of pulses delivered to the winding, in such a way as to reiterate activation of the contacter so long as the order for starting is maintained, and for modifying the intensity of the power supplied to the winding during the said period of time, or when the operator repeats the demand for starting in the event of non-closure of the moving contact of the contacter. 
     The power supply pulses for the winding act on the displacement of the moving core of the contacter, causing the moving contact to be propelled rapidly towards the fixed contacts. The repeated impact of the moving contact on the fixed contacts generates mechanical shocks which are capable of destroying any possible foreign body (such as dirt, oxidation product or insulating particles), and clean the contact zone of the contacter. 
     According to a feature of the invention, the excitation pulses delivered by the management unit comprise peaks having an adjustable cyclic ratio. 
     The management unit preferably has means for determining the cyclic ratio of the power supplied to the winding as a function of various parameters, in particular the temperature in the vicinity of the winding, the number of commands for starting issued through the ignition switch, and the value of the voltage supplied to the terminals of the battery or of the contacter in the open state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and features will appear more clearly from the following description of one embodiment of the invention, which is given by way of non-limiting example and is shown in the attached drawings, in which: 
         FIG. 1  is an electronic power supply circuit diagram for a contacter, for a motor vehicle in accordance with the state of the art; 
         FIG. 2  shows a known power supply pattern for the contacter representing the development of a cyclic ratio of the power supply voltage for the winding in normal operation of the contacter; 
         FIG. 3  consists of diagrams of various parameters in the event of failure of the contact to close on the first try, with governing of the contacter in accordance with the invention; 
         FIG. 4  is a contacter control diagram in the event of failure to close on the first try; 
         FIG. 5  shows a contacter power supply pattern in the event of failure of the contact to close. 
     
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     With reference to  FIGS. 3 to 5 , the invention is applicable to systems which make use of a unit for managing control of the commands to the contacter, comprising power supply patterns to the winding  18  of the contacter  16 , and detection that the contact  20  is open after it has been put into operation. During a malfunction of the starter in the event of non-closure of the moving contact  20  of the contacter  16 , due to the presence of foreign bodies (such as dirt or particles), the invention consists in:
         firstly, reiterating the actuation of the contacter  16  by repeated pulses, so long as the operator requires the starting function and so long as the contact  20  is considered to be open,   and secondly, modifying the power supply patterns of the contacter  16  during the operating mode described above, or when the operator is repeating his demand for starting in a predetermined period of time following failure of the contact  20  to close.       

     After activation of the control following closure of the interrupter  28  (diagram A,  FIG. 3 ), the control/command management unit  26  supplies power to the winding  18  of the contacter in accordance with a particular pattern which conforms with the development of the cyclic ratio of  FIG. 2 , as is described in the above mentioned document FR-A-2 795 884. 
     If the management unit  26  detects that the contact  20  has not closed (diagram B,  FIG. 3 ), and if the command made by the ignition key  28  is maintained, the system then automatically emits a salvo of pulses (diagram C,  FIG. 3 ) to the winding  18  of the contacter  16 , so long as the contact  20  does not close. A thermal protection function may be added to this mode of operation in the event that the contact  20  has not closed. 
     There corresponds, to each power supply pulse of the winding  18 , a displacement of the moving core of the contacter  16  which causes the moving contact to be propelled rapidly towards the fixed contacts  22 ,  24 . In this way, the repeated impact of the moving contact  20  on the contacts  22 ,  24  can destroy any foreign body (such as dirt, oxidation product or insulating particles), and to clean the contact zone of the contacter  16 . Thus, in diagram B, the contact closes and the winding  18  is supplied with power continuously (diagram C) for excitation of the motor  12 . Opening of the interrupter  28  and contact  20  occurs at a time Tn. 
     In  FIG. 3 , the width of a salvo of pulses (T 1 –T 0 ) corresponds, by way of example, to 200 ms. The gap between two successive pulses (T 2 , T 1 ) is 50 ms. The total time (Tn–T 0 ) between closure of the contact  20  and the initial instant at which control by the ignition switch  28  is activated, is less than 30 seconds before thermal protection occurs. 
     In this circuitry, it is proposed to match the power supply of the winding  18  as a function of parameters such as: temperature, the number of operations carried out, and supply voltage. The system is capable in certain cases of providing all the power from the battery  14 . 
     When the operator interrupts control of starting prematurely by opening the ignition switch  28  during malfunctioning of the contacter  16 , the power pulses have not had time to close the contact  20  correctly. Once the operator repeats his command within a predefined period of time, the management unit  26  matches the power supply of the winding  18  as a function of parameters such as: temperature, the number of operations carried out, and supply voltage. The power supply pattern, or law, is then modified in such a way that the system provides a sufficiently high level of energy to the moving core of the contacter  16  for the latter to transfer this energy to the moving contact  20 , which will then violently impact on the foreign bodies in the contact zone. 
     One example of a control law is to restore all of the power from the battery  14  in the winding  18  of the contacter  16 . In that case, the cyclic ratio of power supply voltage of  FIG. 5  will be used, the cyclic ratio being the ratio between the conduction time of the transistor (not shown) which is in series with the winding  18 , and the total duration of a cycle. The cyclic ratio R 4  between the instants t 5  and t 6  is constant, and enables high intensity current to flow in the winding  18 . The time interval t 5 –t 6  is greater than the time interval t 0 –t 1  of  FIG. 2 . The cyclic ratio R 5  beyond the instant t 6  substantially corresponds to the cyclic ratio R 3  in  FIG. 2 . 
     Such an operating cycle enables faults due to incidental contact insulation (such as oxidation products, insulating dusts, dirt and so on) to be automatically eliminated and controlled, the operator not having to try doing anything about it.