Patent Publication Number: US-2009218330-A1

Title: Sheathed-element glow plug unit and system for operating a plurality of sheathed-element glow plugs

Description:
FIELD OF THE INVENTION 
     The present invention relates to a sheathed-element glow plug unit having an input for connecting the sheathed-element glow plug unit to a control line, via which a sheathed-element glow plug of the sheathed-element glow plug unit is able to be controlled. 
     Furthermore, the present invention relates to a system for operating a plurality of sheathed-element glow plugs, including a central glow control device and at least two sheathed-element glow plug units having one sheathed-element glow plug in each case. 
     In addition, the present invention also relates to a method for operating a plurality of sheathed-element glow plug units, each sheathed-element glow-plug unit having one sheathed-element glow plug, and a central glow control device is provided for controlling the sheathed-element glow plug units. 
     BACKGROUND INFORMATION 
     Conventional sheathed-element glow plug units and corresponding systems require at least one electrical line for each sheathed-element glow plug for the supply of the individual sheathed-element glow plug, so that, in particular in the case of applications with a multitude of sheathed-element glow plugs, considerable wiring is required to connect a central glow control device to the various sheathed-element glow plugs. 
     Another disadvantage of conventional devices is that the central glow control device requires a large number of plug pins and correspondingly complex and. expensive plug connectors in order to enable a connection to each individual sheathed-element glow plug or sheathed-element glow plug unit. 
     SUMMARY 
     Example embodiments of the present invention provide a sheathed-element glow plug unit of the type mentioned in the introduction, and a corresponding system as well as an operating method such that the required wiring expenditure is low yet the functionality is not reduced in comparison to conventional systems. 
     According to example embodiments of the present invention, a sheathed-element glow plug unit of the type mentioned in the introduction includes an output, via which at least one additional sheathed-element glow plug unit is able to be connected to the control line. 
     In contrast to conventional systems, the arrangement of the sheathed-element glow plug unit according to example embodiments of the present invention, having an input and an output, allows a serial connection of a plurality of sheathed-element glow plug units and thus a lower wiring outlay than, for instance, in the case of sheathed-element glow plug units disposed about a central glow control unit in a star-shaped topology. This reduces the number of plug pins on the glow control unit. 
     Additional features and details of example embodiments of the present invention result from the following description, in which an exemplary embodiment of the present invention is explained in detail with reference to the drawing. In this context, the features mentioned may be provided alone or in any combination. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a block diagram of a system according to an example embodiment of the present invention; 
         FIG. 2  is a block diagram of a sheathed-element glow plug unit according to an example embodiment of the present invention; 
         FIG. 3   a  illustrates a position-evaluation unit according to an example embodiment of the present invention; 
         FIG. 3   b  illustrates a position-evaluation unit according to an example embodiment of the present invention; 
         FIG. 4  illustrates an additional example embodiment of the present invention; and 
         FIG. 5  is a flow chart of a method according to an example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION  
       FIG. 1  shows a simplified block diagram of a system  100  according to an example embodiment of the present invention, which includes a central glow control device  110  as well as a plurality of sheathed-element glow plug units  120   a,    120   b . System  100  is used, for example, in motor vehicles having self-igniting internal combustion engines in order to preheat the combustion chambers of various cylinders of the internal combustion engine with the aid of sheathed-element glow plugs provided in individual sheathed-element glow plug units  120   a ,  120   b.    
     According to example embodiments of the present invention, only the first of the plurality of sheathed-element glow plug units  120   a,    120   b  is directly connected to central glow control device  110 . As can be gathered from  FIG. 1 , additional sheathed-element glow plug units  120   b , . . . are connected in series to first sheathed-element glow plug unit  120   a.  This reduces the wiring expenditure in the region of central glow control device  110  in system  100 . Furthermore, central glow control device  110  requires only a single plug pin to connect a multitude of sheathed-element glow plug units  120   a,    120   b , etc. 
     Since the individual sheathed-element glow plug units  120   a ,  120   b  assigned to adjacent cylinders of an internal combustion engine are usually situated in close proximity to each other on account of the design of the internal combustion engine, the ohmic power losses in the additional sections  110   b ,  110   c  of control line  110 , each of which, by itself, is considerably shorter than a connection line between central glow control device  110  and a sheathed-element glow plug unit of the conventional type, are lower than in line connections of conventional systems. 
       FIG. 2  shows a block diagram of a sheathed-element glow plug  120  according to an example embodiment of the present invention. Sheathed-element glow plug units  120   a,    120   b,  for example, which are shown in  FIG. 1 , also have the same configuration. 
     As can be gathered from  FIG. 2 , sheathed-element glow plug unit  120  has an input  10  and an output  20 . Via input  10 , sheathed-element glow plug unit  120  is able to be directly connected to control line  110   a,  for example, which originates from central glow control device  110 , while output  20  of sheathed-element glow plug unit  120  is connected to an input  10  of an additional sheathed-element glow plug unit  120 , for instance via an additional section  110   b  ( FIG. 1 ) of control line  110   a,    110   b ,  110   c.    
     Via an electrical connection of input  10  to output  20  within first sheathed-element glow plug unit  120   a,  control line  110   a , which is connected to input  10  of first sheathed-element glow plug unit  120   a  ( FIG. 1 ), is able to be connected through to first sheathed-element glow plug unit  120   a  and can thereby be made available to following sheathed-element glow plug units  120   b,  . . . . The connection of input  10  to output  20  may be implemented by, for instance, corresponding switches, which are preferably embodied as low-impedance semiconductor switches. In the same manner, additional sheathed-element glow plug units  120   b,  . . . are able to determine whether control line  110   b ,  110   c , . . . is connected through to a following sheathed-element glow plug unit, which allows a corresponding forwarding of control signals that, for example, are transmitted from central glow control device  110 . 
     To coordinate local control processes such as the connection of an input  10  to an output  20 , and to implement diagnostic sequences and the like, sheathed-element glow plug unit  120  ( FIG. 2 ) has a local control unit  40 , which is preferably embodied as microcontroller or as application-specific, integrated circuit, ASIC. 
     Local control unit  40  is also used to evaluate control signals which central glow control device  110  outputs to sheathed-element glow plug units  120   a,    120   b , . . . via control line  110   a ,  110   b ,  110   c.    
     To receive such control signals, sheathed-element glow plug unit  120  has a communications unit, which, for instance, evaluates a voltage level between control line  110   a ,  110   b ,  110   c  and a reference potential, such as the ground potential, by which corresponding address signals and control signals from central glow control unit  110  are encoded. In the same manner, i.e. by ground sampling, the communications unit of sheathed-element glow plug unit  120  is also able to generate signals and transmit them via control line  110   a,    110   b ,  110   c.    
     For sheathed-element glow plug unit  120  to know its address code, it must be able to detect its position within a series connection of a plurality of sheathed-element glow plug units  120   a,    120   b,  . . . ( FIG. 1 ). To this end, it is equipped with a position-evaluation unit, which is denoted by reference numeral  30  in the block diagram according to  FIG. 2 . 
     Position-evaluation unit  30  has at least one resistive and/or inductive component, which is switchable between input  10  and output  20  during the position detection process. This results in a voltage-divider system between input  10  of first sheathed-element glow plug unit  120   a  and the output of the last sheathed-element glow plug unit, which is preferably connected to the ground potential during the position determination, the voltage-divider system being made up of the series connection of the resistive and inductive elements of the individual sheathed-element glow plug units  120 . 
     When an ohmic resistor is used as resistive element, this will therefore result in a simple ohmic voltage divider, and if all ohmic resistors are selected to have the same resistance value, then it is easily possible to infer the position of the particular sheathed-element glow plug unit  120  within the series connection by determining the voltage between input  10  and/or output  20  and the ground potential by applying the voltage-divider rule. 
       FIG. 3   a  shows a position-evaluation unit  30  by way of example; it has an ohmic resistor R, which is switchable between input  10  and output  20  of sheathed-element glow plug unit  120  ( FIG. 2 ) with the aid of switches  15   a,    15   b.  In the example embodiment shown, device V for a voltage measurement is provided as well, which measures a potential difference between the connection terminal of ohmic resistor R, shown on the left in  FIG. 3   a,  and a ground potential. After the position detection has been concluded, switches  15   a,    15   b  are opened and assume the state shown in  FIG. 3   a.  Switches  15   a ,  15   b  may advantageously be embodied as semiconductor switches, in particular as field-effect transistors. 
     In example embodiments of the present invention, instead of ohmic resistor R and switches  15   a,    15   b,  it is also possible to provide only a single semiconductor switch in position-evaluation unit  30 . In this case the semiconductor switch is preferably arranged as field-effect transistor and, by appropriate controlling at its gate electrode, for instance, allows the simulation of ohmic resistor R additionally provided in the exemplary embodiment according to  FIG. 3   a , by its own drain-source resistance, which comes about between its drain electrode and its source electrode. That is to say, in this case the field-effect transistor simultaneously realizes the functionality of switches  15   a,    15   b  ( FIG. 3   a ) to connect input  10  to output  20 , and the functionality of the serial resistor required for the position detection. The voltage measurement may be implemented analogously to the exemplary embodiment shown in  FIG. 3   a.    
       FIG. 3   b  shows a position-evaluation unit  30  according to an example embodiment of the present invention, which includes an inductive element L, such as a coil having a specifiable inductivity. Analogously to the above description, this produces an inductive voltage divider within the series connection of sheathed-element glow plug units  120   a,    120   b , . . . ( FIG. 1 ). 
     When central glow control device  110  applies a jump-type control signal to control line  110 , the position of the corresponding sheathed-element glow plug unit  120  may be inferred based on the individual rise time of the voltage dropping across a coil L, since—depending on the position of sheathed-element glow plug unit  120 —a different resulting inductivity that influences the rise time is active on account of the series connection of the coils. The voltage across coil L may then be implemented locally using the already described means V for a voltage measurement, while appropriate monitoring of the rise time is preferably carried out by local control unit  40 . 
     Another position-evaluation unit  30  according to an example embodiment of the present invention provides a capacitive element instead of inductive element L, which allows a position determination analogously to the afore-described method, and is able to be realized even more easily and in a more cost-effective manner than inductive element L. 
     Following successful position determination, each sheathed-element glow plug unit  120   a,    120   b , . . . has appropriate information and stores it, preferably in a non-volatile memory, such as an EEPROM memory integrated in local control unit  40 , for example. The control of switches  15   a,    15   b  ( FIG. 3   a ) is preferably also implemented by local control unit  40 . 
       FIG. 4  shows a module  50 , which is likewise included in sheathed-element glow plug unit  120  and has a sheathed-element glow plug  51 . As can be gathered from  FIG. 4 , a grounded connection  51   b  of sheathed-element glow plug  51  is permanently connected to the ground potential, and an operating-voltage connection  51   a  of sheathed-element glow plug  51  is connectable to input  10  via switch  16 . For example, operating-voltage connection  51   a  of sheathed-element glow plug  51  is connected to input  10  via switch  16  whenever sheathed-element glow plug  51  is to be triggered. In this case, central glow control device  110  supplies sheathed-element glow plug  51  with electrical energy via input  10  and corresponding control lines  110   a ,  110   b , . . . . I.e., instead of the control signals otherwise exchanged via control lines  110   a,    110   b,  . . . , central glow control device  110  must then also supply an electrical output of sufficient size in order to ensure an adequate energy supply of sheathed-element glow plug  51 . 
     Sheathed-element glow plug units that are possibly situated upstream from the viewed sheathed-element glow plug unit in a series connection must configure their modules  50  accordingly in this case, such that their switch  16  connects input  10  directly to output  20 , so that the electrical energy will be conveyed to sheathed-element glow plug  51  to be triggered. 
     That is to say, in the case of a sheathed-element glow plug unit whose sheathed-element glow plug  51  is not to be triggered at the present time, switch  16  connects input  10  to output  20 . 
     A diagnosis of the operation of sheathed-element glow plug  51  is possible by device V, shown in  FIG. 4 , for a voltage measurement. To this end, device V could record a voltage characteristic coming about at sheathed-element glow plug  51 , for instance under the control of local control unit  40 ; in the event of a deviation from typical voltage values or voltage characteristics, a diagnosis report may possibly be transmitted from affected sheathed-element glow plug unit  120  to central glow control device  110 . 
     This makes it possible, for instance, to realize a short-circuit detection, which infers a short circuit in the region of sheathed-element glow plug  51  if a voltage applied to sheathed-element glow plug  51  is undershot during triggering of sheathed-element glow plug  51 . Aging of sheathed-element glow plug  51  is also detectable, by a change in the voltage characteristic coming about in the triggering of sheathed-element glow plug  51 . 
     Device V for a voltage measurement shown in  FIG. 4  may involve the same device shown in  FIG. 3   a  as well. In this case measuring device V may be directly and permanently connected to input  10  and activated either for position detection or for diagnostic purposes in an operation of sheathed-element glow plug  51  ( FIG. 4 ). 
     Device V for a voltage measurement may also be directly integrated in local control unit  40 , for instance in the form of at least one analog-to-digital converter channel of a local control unit  40  embodied as microcontroller. 
     The control of an electric power supplied to sheathed-element glow plug  51  may, for one, be implemented by central glow control device  110  via the selection of the voltage applied to control line  110   a,    110   b , . . . or, on the other, is able to be coordinated locally in a sheathed-element glow plug unit  120 , for instance by local control unit  40 . In a local control, local control unit  40  is able to open and close switch  16  according to a specified pattern, for instance, in order to thereby enable a pulse-width-modulated triggering of sheathed-element glow plug  51 . 
     Instead of the configuration of module  50  illustrated in  FIG. 4 , for the purpose of triggering one sheathed-element glow plug  51  it is also possible to connect input  10  ( FIG. 2 ) to output  20  in all sheathed-element glow plug units  120 , and to optionally connect operating-voltage connection  51   a  of corresponding sheathed-element glow plug  51  to input  10  or output  20 , or disconnect it therefrom, by a switch provided in module SO. In an especially advantageous manner, a parallel triggering of sheathed-element glow plugs  51  of a plurality of sheathed-element glow plug units  120  is possible simultaneously since all sheathed-element glow plug units  120  or modules  50  are supplied with electrical energy via respective input  10 . In this case it must be ensured that central glow control device  110  ( FIG. 1 ) is able to provide sufficient electrical power via control line  110   a,    110   b,    110   c , . . . , and that switches provided locally in sheathed-element glow plug units  120  for the connection of input  10  to the respective output  20  are configured for the currents that arise. 
     In a very advantageous manner, sheathed-element glow plug unit  120  has an energy-supply unit, which stores electrical energy supplied to sheathed-element glow plug unit  120  via control line  110   a,    110   b,    110   c,  and/or makes it available to the components of sheathed-element glow plug unit  120 , in particular to local control unit  40 . For this purpose the energy-supply unit may, for instance, be equipped with a voltage converter, protective diodes or also with a local charge-coupled store in a manner known per se. 
     A method of an example embodiment of the present invention is described in the following text with the aid of the flow chart shown in  FIG. 5 . 
     In step  200 , central glow control device  110  ( FIG. 1 ) first applies a specifiable voltage to control line  110   a,  and individual switches  15   a,    15   b  of position-evaluation units  30  of the various sheathed-element glow plug units  120   a ,  120   b , . . . are closed, so that a position is able to be evaluated. 
     Subsequently, in step  210 , the determined position of each sheathed-element glow plug unit  120   a,    120   b,  . . . is stored locally, for example in a non-volatile memory of local control unit  40 . If applicable, status feedback of individual sheathed-element glow plug units  120  to central glow control device  110  may occur, in which a corresponding item of position information of the individual sheathed-element glow plug unit  120  is advantageously transmitted as well. 
     In step  220 , a specific sheathed-element glow plug unit  120   b  is triggered. The triggering may, for example, be implemented in such a manner that central glow control device  110  first outputs the address or position of sheathed-element glow plug unit  120   b  to be triggered, possibly together with trigger parameters such as, for example, a trigger duration or a power profile or the like, using control lines  110   a ,  110   b, . . . .    
     Following successful address or position comparison, the communications unit of corresponding sheathed-element glow plug unit  120   b  forwards the information received via control line  110   a,    110   b , . . . to local control unit  40  of sheathed-element glow plug unit  120   b , and sheathed-element glow plug  51  of sheathed-element glow plug unit  120   b  will then be triggered accordingly. 
     A special advantage of system  100  is that all sheathed-element glow plug units  120  may have the same design and are quasi able to initialize themselves via the described position detection, so that no special sequence or the like need to be observed when sheathed-element glow plug units  120  are installed. Furthermore, the absolute number of sheathed-element glow plug units  120  connected to a central glow control device  110  is able to be determined in an uncomplicated manner. 
     In addition, the series connection allows a particularly uncomplicated and low-cost wiring with power losses that are lower than in conventional systems. In a particularly advantageous manner, first section  110   a  of the control line may have an especially large diameter, since a reduction in the power losses in this section  110   a  has an effect on all triggering processes as a result of the series connection. 
     The fact that only a single plug pin must be provided on central glow control device  110  in system  100  is to be considered an additional advantage, the plug pin being utilized to connect control line  110   a.    
     Furthermore, measuring device V ( FIGS. 3   a,    4 ) integrated into the corresponding sheathed-element glow plug unit  120  makes it possible to perform a diagnosis of each individual sheathed-element glow plug  51 . 
     A conventional protocol suitable for single-wire transmission is able to be used for the communication of components  110 ,  120  via control line  110   a,    110   b,    110   c , . . . . In an advantageous manner, an interference-resistant and self-synchronizing Manchester coding is also employable for the encoding of data to be transmitted. 
     Furthermore, it is possible to use a low-pass frequency range for the energy transmission via control line  110   a,    110   b ,  110   c , . . . , in particular also for the supply of sheathed-element glow plugs  51 , and to transmit control signal in a band-pass frequency range so that the control signals may, for instance, be separated from an equisignal provided for energy transmission, with the aid of corresponding filters in, e.g., a conventional manner. 
     In general, sheathed-element glow plug unit  120  or system  100  allows the use of sheathed-element glow plugs configured for an operating voltage of 11 Volt as well as low-voltage sheathed-element glow plugs. 
     To ensure reliable communication between central glow control device  110  and sheathed-element glow plug units  120   a,    120   b , it may be provided as standard state that input  10  is connected to output  20  in each sheathed-element glow plug unit  120 , via a corresponding switch, for instance, and that the particular communications unit is activated in order to be able to evaluate trigger signals that may arise.