Patent Publication Number: US-2002000221-A1

Title: Device for preheating air in a diesel engine intake line

Description:
BACKGROUND OF THE INVENTION  
       [0001] The invention relates to a device for preheating air in a Diesel engine intake line with a heating flange which is arranged in the intake line and which is electrically energized as required for heating the air. The invention further relates to a method for testing the state of charge of a battery of a Diesel engine.  
       [0002] A device of the type referred to above is disclosed in DE 195 15 533 C2. Such a device with a heating flange is used to heat the air in the intake line leading to a Diesel internal combustion engine prior to, and during, the starting phase. This is particularly necessary for commercial Diesel engines, that is, for Diesel engines of commercial vehicles, since the glow plugs otherwise generally used in Diesel internal combustion engines may not be used in those engines.  
       [0003] Such known devices have proved superior to so-called flame starting systems in which the intake air is heated by means of an open flame for the cold starting of a Diesel internal combustion engine. However, with open flame starting systems, the combustion process taking place inside the Diesel engine is deprived of a large part of the required oxygen as a good part of the oxygen in the intake air is consumed by the preheating flame.  
       [0004] A disadvantage of the known device using a heating flange, however, is that, because of its operating principle wherein the relay switches the heating flange on and off, the known arrangement has a relatively short service life. For this reason, the heating flange for preheating the air in the intake line must only be switched on before starting the Diesel internal combustion engine and must be switched off again after a relatively short time, in order to prevent overheating of the heating element. In the known device, it is not possible to closely control the heat output of the heating flange. This means that in determining this output or the current fed to the heating flange a compromise must be reached between the high output initially required and the limited life of the heating element of the heating flange. This inevitably leads, however, to an inadequate heat output from such known heating flanges during adverse starting conditions.  
       [0005] It is the object of the present invention to provide a device for preheating air in an intake line of a Diesel engine by means of a heating flange, whereby it is possible to control the heat output of the heating flange without damaging or overloading any components.  
       SUMMARY OF THE INVENTION  
       [0006] In a device for preheating air in an air intake line leading to a Diesel engine in which a heating flange is arranged, the heating flange is switched off and on as required by means of a switching device comprising a semiconductor switching element. At the same time, the state of a battery can be determined by measuring the voltage drop of the battery during such energization of the heating flange.  
       [0007] Since the switching device is controlled by a semiconductor element, there is no wear so that the heating flange can be switched off and on as often as required and for virtually any periods. Switching may therefore occur at relatively high frequencies, thereby permitting a virtually continuous adjustment of the heat output of the heating flange and hence adaptations to the warm-up conditions of the Diesel engine. In this way, the heating flange need not be switched on continuously. The momentary current flow and hence the maximum heat output of the heating flange therefore can be multiplied many times, which permits a far more rapid temperature increase of the air fed to the Diesel engine, especially during the beginning of intake air preheating. This shortens the preheating time. The output of the heating flange can then easily be reduced by a corresponding control of the on and off switching period, while the current flow remains constant during the energizing periods.  
       [0008] The increased heat output possible according to the invention for example allows Diesel engines to be started at very low outdoor temperatures and at high altitudes, at which such starting was hitherto practically impossible. The fact that, according to the invention, the heating flange can be switched off and on as often as required means that preheating of the air also can be carried out over a longer period than was hitherto usual or possible, since energization of the heating flange can be controlled so as to prevent it from being damaged. In such a case, the on-times are steadily shortened so that they assume an ever-decreasing proportion of time compared to the off-times. This procedure is also highly advantageous in that it results in improved exhaust emission values for the Diesel engine.  
       [0009] In addition, the switching device, controllable by means of a semi-conductor element for switching the heating flange off and on, permits employment of an entirely new method for testing the state of charge of a battery of the Diesel engine, that is of a vehicle using such air preheating device.  
       [0010] According to the invention, the heating flange is switched on by means of the semi-conductor element for a specific period of time, wherein a relatively high current is drawn from the battery. From the drop in the battery voltage, it is then very easy to draw conclusions as to the state of charge of the battery.  
       [0011] Such a procedure was hitherto impossible because of the high load on the switching relay and because of the only very imprecisely defined switching points of a relay. Furthermore, there are no other devices in an internal combustion engine with which a sufficiently large current can be drawn from the battery without at the same time causing negative distortions of the measuring result. A sufficiently accurate measurement has therefore not been possible.  
       [0012] The high current flowing through the heating flange makes it possible to obtain precise determinations concerning the state of charge of the battery using the method according to the invention. Another reason why the state of charge of the battery can be measured by means of the procedure according to the invention is the switching accuracy of such a semiconductor element, which results in a precisely controllable, sometimes very brief, on-time of the heating flange. 
     
    
    
     [0013] Advantageous embodiments and further developments of the invention are apparent from the following description of an exemplary embodiment of the invention on the basis of the accompanying drawings.  
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014]FIG. 1 shows schematically a Diesel engine with a device according to the invention for preheating air in an intake line;  
     [0015]FIG. 2 is a sectional view of a heating flange according to the invention; and  
     [0016]FIG. 3 shows a control circuit for the heating flange shown in FIG. 2. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT  
     [0017] A Diesel internal combustion engine  1  represented in FIG. 1 in extremely schematic form is provided with an intake line  2 , which carries fresh air, drawn in by an exhaust turbocharger  3  and conducted through an intercooler  4  to the Diesel engine  1 . From the exhaust turbocharger  3 , exhaust gas produced by the Diesel engine  1  is discharged by way of an exhaust pipe  5 .  
     [0018] The Diesel engine  1  is primarily intended for use in commercial vehicles. It therefore is necessary to heat the air drawn in by way of the intake line  2  before starting of the Diesel engine  1  during difficult outdoor conditions. To facilitate starting, a device  6  is provided, which has a heating flange  7  projecting into the intake line  2 , which flange is arranged immediately upstream of the Diesel engine  1 . For measuring the air intake temperature, a temperature sensor  8  is provided between the heating flange  7  and an intake manifold, which is not shown but which is directly connected to the Diesel engine  1 .  
     [0019] The heating flange  7  is shown in greater detail in FIG. 2.  
     [0020] In a manner known in the art, it has a canister-shaped housing  9  with a cover  10  fitted thereto. The cover  10  is provided with bores  11  for mounting the heating flange  7  to the intake line  2 . In addition, there are two electrical connections on the cover  10  leading to the inside of the housing  9 , that is a control connection  12  and a electrical power supply connection  13 . Electrical current is supplied by way of the power connection  13  serving as a supply lead to an electrical heating element  14 . The heating element  14  is arranged inside the housing  9  in a manner known in the art. The heating element  14 , in this case, is designed as helical heating filament generating the heat for heating the intake air. The control connection  12  serves to control the on/off switching of the heating flange  7 , which is described in greater detail below.  
     [0021] A switching device  15  is provided for switching the heating flange  7  off and on, which device includes the control connection  12  and a semiconductor element  16 . When a corresponding pulse is applied to the semiconductor element  16  by way of the control connection  12 , the semiconductor element  16  switches the heating element  14  on or off, that is current flow is controlled via the power connection  13 . The control connection  12  may, at the same time, be coupled to the temperature sensor  8 .  
     [0022] Since the semiconductor element  16  is not subjected to wear of any kind, the heating element  14  of the heating flange  7  can be switched off and on as often as required by means of the switching device  15 . In order to regulate the output of the heating element  14 , the switching device  15  switches the heating element  14  off and on with a certain frequency. If the on-time is longer than the off-time, this results in a higher output of the heating element  14  over time, so that the air in the intake line  2  can be heated more rapidly, thereby facilitating starting of the Diesel engine  1 . It is to be noted that the current flow applied to the heating element  14  remains constant and the heating output is determined solely by the length of time the heating element  14  is switched on. When starting the Diesel engine  1 , the heating flange  7  is briefly switched off, in order to make sufficient power available to a starter (not shown). The starting procedure for preheating and starting the Diesel internal combustion engine  1  may be recorded in a characteristic performance graph.  
     [0023] By using a fuse element (not shown) on the input side of the power connection  13 , it is possible to prevent overloading of the heating element  14 . Since the power supply can be accurately controlled, the heating element  14  can be supplied by way of the power connection  13  with far higher momentary currents than hitherto possible, thereby also generating increased heat output.  
     [0024]FIG. 3 represents a circuit diagram for the heating flange  7 , in which a diagnostics input  17  is arranged between the semiconductor element  16  and the two heating elements  14  provided in this case. In addition, a control module  18  known in the art and connected to the temperature sensor  8  is connected to the semiconductor element  16 . In FIG. 3, the power connection  13  is represented by a positive pole  19  and a negative pole  20 , to which the battery voltage is applied in order to permit a flow of current for heating the heating element  14 . In FIG. 3, the direction of flow of the intake air is indicated by the arrow A.  
     [0025] The diagnostics input  17  permits a fault diagnosis for the device  6 , that is, for the heating flange  7  and the semiconductor element  16 , which diagnosis assigns the following error messages to the signals on the diagnostics input  17  specified below and to the control module  18 .  
     [0026] The signals  0  on the diagnostics input  17  and on the control module  18  indicate that no voltage is present; the semiconductor element  16  is defective and/or there is a short-circuit to ground.  
     [0027] A signal  1  on the diagnostics input  17  indicating a voltage is present and the signal  0  on the control module  18  indicate that there is no fault and that the heating flange  7  is switched off.  
     [0028] The signal  0  on the diagnostics input  17  and the signal  1  on the control module  18  indicates that there is no fault, the heating flange  7  is switched on.  
     [0029] The signals  1  on the diagnostics input  17  and on the control module  18  indicate that there is an interruption in the power connection  13  and/or the semiconductor element  16  is defective.  
     [0030] With the arrangement shown in the figures, a new method for testing the state of charge of a battery  21  of the Diesel engine is also available. For testing the battery, it is necessary to switch the heating flange  7  on for a certain period of time by means of the semiconductor element  16  of the switching device  15 . Depending on its fixed internal resistance, the heating flange  7  then draws a certain current from the battery  21  and the state of charge of the battery  21  can then be determined by measuring the voltage drop of the battery  21 . The method described is very suited for example for use with a vehicle on-board diagnostics system.  
     [0031] The method can be performed because the heating flange  7  or the heating element  14  draws a large current of up to 400 amps and more from the battery  21  that is required for such a measurement and for drawing conclusions from such a measurement. Since, during the operation of the heating element  14 , there are no electrical conductors moving in a magnetic field, as is the case for example with a starter, no current is induced that can influence the measuring result.