Abstract:
In an internal combustion engine having manifold injection, each cylinder is assigned at least one first injection device and one second injection device. The first injection device is at least intermittently actuated at a different crank angle than the second injection device.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method for operating an internal combustion engine having intake manifold injection. 
       BACKGROUND INFORMATION 
       [0002]    Already believed to be understood are four-stroke internal combustion engines, in which the fuel is injected into an intake manifold upstream from an intake valve of the internal combustion engine. Since most modern internal combustion engines are believed to have two intake valves per cylinder, it is also believed to be understood to provide two injection devices per cylinder. A separate injection device can be assigned to each intake valve. The injection devices are actuable at a crank angle that lies relatively far in advance of the particular crank angle at which the intake valves open. The actuation of the injection devices can take place simultaneously for each cylinder. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention has the objective of reducing an operating noise of the internal combustion engine. 
         [0004]    This objective may be achieved by a method having the features described herein. Further refinements of the present invention are indicated in the further descriptions herein. Features that are important for the present invention are furthermore to be found in the following description and the drawings. 
         [0005]    The present invention is based on the understanding that noise pulses that are spaced apart by less than approximately ten milliseconds are conceived as a single event by the human ear. 
         [0006]    Moreover, individually occurring noises pulses, i.e., such that occur at only a low pulse rate, are perceived as more annoying than more frequently occurring noise pulses. The subjective acoustic irritation potential thus drops with an increasing pulse rate and only a certain acoustic roughness still results. 
         [0007]    In the present invention, the injection devices of a cylinder are no longer actuated simultaneously but one after the other, i.e., at different crank angles. For one, this reduces the intensity of the sound pulse generated by the actuation of the injection devices, since the actuation of the injection devices per cylinder is resolved into two less intense and individually perceivable sound events. Furthermore, the acoustic frequency, i.e., the pulse rate, is increased, which reduces annoying noise subjectively perceived by the user. 
         [0008]    Because of the offset actuation of the injection devices, a noise is therefore generated that the user or listener perceives more as a pleasant “roughness” than the noise generated in the simultaneous actuation that was the rule until now. 
         [0009]    In a first further development of the method of the present invention, it is proposed that the injection devices of all cylinders are operated across two full crankshaft revolutions in an evenly distributed pattern. This leads to a uniform noise having twice the frequency and half the individual pulse intensity, which causes an especially marked reduction in the operating noise. Given two injection devices per cylinder, the crank angle at which the two injection devices must be operated at an offset per cylinder is able to be calculated by dividing the number 360 by the number of cylinders. In a four cylinder internal combustion engine, this crank angle thus amounts to 90 degrees, and in a six cylinder internal combustion engine it amounts to 60 degrees. 
         [0010]    It is furthermore proposed that the first injection device is actuated at a different crank angle than the second injection device only when the internal combustion engine is in a certain operating range, especially when a rotational speed of a crankshaft and/or a torque lie(s) below a limit value. This takes the fact into account that the method of the present invention is especially advantageous in an idling operation of the internal combustion engine, for instance, or at a low load. The other noises of the internal combustion engine are comparatively low in these operating ranges, so that the noise generated by the injection devices is then perceived as especially annoying. Furthermore, there are operating ranges of an internal combustion engine that lend themselves more readily than others to a division of the injections to different instants. 
         [0011]    It is also possible that the difference in the crank angles at which the two injection devices of a cylinder are actuated is a function of an actual operating parameter and/or an actual operating range of the internal combustion engine. When ascertaining the difference in the crank angles, for example, it is conceivable to also consider the influence of the temporally offset actuation on the exhaust gas values and the consumption values of the internal combustion engine as well as on a current operating temperature, an operating state of an auxiliary component, etc. It is also conceivable and especially advantageous if the difference is made dependent upon at least one current acoustic quantity. This quantity, for instance, could be a volume but also a frequency. If appropriate, even a type of regulation is conceivable in which the acoustic quantity is adjusted to a target value (frequency) or a minimum value (volume) by varying the difference of the crank angles. The acoustic quantity is able to be recorded by a structure-borne noise sensor disposed on the internal combustion engine, for instance, or by a microphone situated in the passenger compartment of the motor vehicle, for example. 
         [0012]    In the following text the present invention will be elucidated with reference to the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  shows a schematic plan view of an internal combustion engine. 
           [0014]      FIG. 2  shows four diagrams, in which a piston travel, an intake valve opening period and actuation periods of injection devices have been plotted over the individual crank angles for each cylinder of the internal combustion engine from  FIG. 1 . 
           [0015]      FIG. 3  shows a flow chart of a method for operating the internal combustion engine from  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    In  FIG. 1  an internal combustion engine is denoted by reference numeral  10  overall. It is a four cylinder, four stroke internal combustion engine. 
         [0017]    It includes an engine block  12  in which four cylinders  14 ,  16 ,  18  and  20  are provided. A respective first intake valve  22 ,  24 ,  26  or  28  and a second intake valve  30 ,  32 ,  34  or  36  is associated with each cylinder  14  through  20 . A separate intake duct  38  leads to each intake valve  22  through  36 , and a first injection device  40  through  46  and a second injection device  48  through  54  are assigned to each injection valve  22  through  36  in respective intake duct  38 . In addition, two outlet valves  56 , which lead to an exhaust gas pipe  58 , are part of each cylinder  14  through  20 . 
         [0018]    Internal combustion engine  10  also includes a crankshaft  60  (only indicated symbolically), whose rotational speed and position are detected by a crankshaft sensor  62 . In addition, a control and regulation device  64 , which controls and regulates the operation of internal combustion engine  10 , is part of internal combustion engine  10 . For this purpose, control and regulation device  64  receives the signals from various sensors that record current operating quantities of internal combustion engine  10  such as the signal from crankshaft sensor  62 , for example. Control and regulation device  64  controls various actuating devices of internal combustion engine  10 , such as injection devices  40  through  54 . 
         [0019]    Additional components of internal combustion engine  10 , e.g., spark plugs, throttle valves, exhaust-gas purification devices, the fuel system including fuel pump, etc., are not shown in  FIG. 1  for reasons of clarity. 
         [0020]    As mentioned previously, internal combustion engine  10  has a first intake valve  22  through  28  and a first injection device  40  through  46  as well as a second intake valve  30  through  36  and a second injection device  48  through  54  per cylinder  14  through  20 . The control or actuation of injection devices  40  through  54  will now be explained with reference to  FIG. 2 . 
         [0021]    In  FIG. 2 , four diagrams have been plotted, whose abscissa corresponds to a crank angle KW in each case. The top upper diagram in  FIG. 1  applies to first cylinder  14 , the second diagram from the top to third cylinder  18 , the third diagram from the top to fourth cylinder  20 , and the diagram all the way at the bottom, to second cylinder  16 . A sinusoidal curve denoted by K i  (i-14 through 20) in each diagram supplies information about the position of the particular piston of cylinder  14  through  20 . At 0° or minus 720° ZW, the piston is at top dead center ignition (ZOT), at a crank angle KW of −180°, the piston is at a lower dead center UT between intake and compression stroke. At a crank angle KW of −360°, the piston is at a top dead center OT between exhaust stroke and intake stroke. At a crank angle KW of −540°, the piston is at a lower dead center UT between working stroke and exhaust stroke. 
         [0022]    Also plotted in  FIG. 1  are the opening periods of intake valves  22  through  36  of each cylinder  14  through  20 . They are denoted by EV i  there, i=22 through 36 for intake valves  22  through  36 . It is clear that intake valves  22  through  36  open for each cylinder  14  through  20  shortly after the start of the aspiration phase and that they close shortly after the start of the compression phase. 
         [0023]    Finally, the actuating periods of injection devices  40  through  54  for each cylinder  14  through  20  have been plotted in  FIG. 2 . The actuating periods have been designated by the letter B, which is indexed by the reference numeral of the particular injection device  40  through  54 . It is obvious that first injection devices  40 ,  42 ,  44  and  46  are actuated during actuating periods B 40 , B 42 ,  42  B 44 , and B 46 , which begin at a crank angle KW of −770° in this example and end at a crank angle KW of −720°. 
         [0024]    Second injection devices  48  through  54  are actuated during actuating periods B 48 , B 50 , B 52 , and B 54 , respectively, which begin at a crank angle KW of −680° (for example) and end at a crank angle KW of −630°. That is to say, first injection devices  40  through  46  are actuated at a different crank angle (in this instance, −770° to −720° KW by way of example) than second injection devices  48  through  54  (in this instance, at −680° to −630° KW by way of example). It can also be seen that a crank angle difference of 90° lies between the start of actuating period B 40  and the start of actuating period B 48 , and another crank angle difference of 90° lies between the start of actuating period B 48  and the start of actuating period B 44 , etc. In other words, actuating periods B i  of injection devices i (i=40 through 54) are completely evenly distributed across two full crankshaft revolutions, which corresponds to a crank angle of 720° KW. The difference between crank angle KW at which first injection device  40  through  46  is actuated, and the crank angle at which second injection device  48  through  54  is actuated, therefore corresponds, as already mentioned, to a crank angle of 90° KW, which is calculated by dividing the number 360 by the number (in this instance 4) of cylinders  14  through  20  of internal combustion engine  10 . 
         [0025]    In an actuation of injection devices  40  through  44 , a method elucidated in the following text with reference to  FIG. 3  will be used. Following a start block  66 , in block  68  it is checked in which operating state internal combustion engine  10  happens to be just then. To do so, for example, the signal from crankshaft sensor  62  is compared to a limit value. If the rotational speed of crankshaft  60  is below a predefined limit value, branching to a block  70  takes place, whereas a switch to block  72  takes place in the other case. According to block  72 , first injection devices  40  through  46  and second injection devices  48  through  54  are operated simultaneously; in other words, it is precisely not the case that the actuation discussed in  FIG. 2 , which is offset at 90° there, takes place. 
         [0026]    In block  70 , the differential crank angle between the respective first actuations B 40  through B 46  and the respective second actuations B 48  through B 54  is ascertained, i.e., as a function of the actual operating variables of the internal combustion engine such as an actual operating temperature, an actual torque requested by the user of internal combustion engine  10 , an operating state of an exhaust purification system, etc. These operating variables are sketched by block  74 . In a block  76 , second injection devices  48  through  54  are then actuated at an offset in relation to first injection devices  40  through  46 , i.e., using the differential crank angle ascertained in block  70  (in the example of  FIG. 2 , it is 90°). The method ends in a block  78 . 
         [0027]    The method shown in  FIG. 3  is stored as a computer program in a memory of control and regulation device  64 .