Abstract:
A method for managing a torque applied to an output shaft of a combustion engine, the combustion engine including combustion chambers, in each of which there is mounted a piston connected to the output shaft in order to apply a torque to it, the output shaft being connected to a rotary machine associated with a management member. The method involves detecting conditions of deactivation of one combustion chamber and controlling the rotary machine so as to apply to the output shaft, prior to the deactivation of one combustion chamber, a compensating torque which tends to cause a resultant torque applied to the output shaft to tend towards a deactivation torque applied by the combustion engine to the output shaft after deactivation of the combustion chamber.

Description:
[0001]    The present invention relates to a method for managing a torque applied to an output shaft of a heat engine when a combustion chamber is deactivated, and a corresponding management system. 
       BACKGROUND OF THE INVENTION 
       [0002]    A heat engine of a motor vehicle usually comprises cylinders delimiting combustion chambers in each of which is mounted a piston connected to an output shaft (or crankshaft) in order to apply a torque thereto. The output shaft is itself connected, via the gearbox, to wheels of the vehicle in order to rotate the latter. The output shaft is also connected to one or more auxiliary rotating machines such as the alternator in order to produce the electricity consumed onboard the vehicle. 
         [0003]    There exist engines also comprising a member for managing a deactivation of one or more of the combustion chambers. Such engines with combustion chambers that can be deactivated usually comprise at least 8 combustion chambers. The deactivation of one or more combustion chambers makes it possible to limit fuel consumption when the engine load is constant. The deactivation of one or more combustion chambers however has the disadvantage of creating an imbalance of the output shaft that is likely to produce vibrations and relatively considerable operating noises. This imbalance is however less sensitive if the combustion chambers are numerous, so that the deactivation of the combustion chambers is used only in engines with large cubic capacity. 
         [0004]    It is also a practice known from document U.S. Pat. No. 6,382,163 to reduce the imbalance during the deactivation phase itself, that is to say between the moments of deactivation and reactivation, by controlling a rotating machine such as an alternator starter coupled to the output shaft. However, the results obtained are not very satisfactory. 
       SUBJECT OF THE INVENTION 
       [0005]    It would therefore be of value to have a method and a system making it possible to attenuate the consequences of an imbalance of the output shaft of a heat engine on the occasion of the deactivation and/or reactivation of one or more combustion chambers. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention proposes a method for managing a torque applied to an output shaft of a heat engine comprising combustion chambers in each of which is mounted a piston connected to the output shaft in order to apply a torque thereto, the output shaft also being connected to a rotating machine associated with a management member, the method comprising the steps of detecting conditions of deactivation of a combustion chamber and of controlling the rotating machine in order to apply to the output shaft, prior to the deactivation of a combustion chamber, a compensating torque tending to cause a resultant torque applied to the output shaft to change toward a deactivation torque applied by the heat engine to the output shaft after deactivation of the combustion chamber. 
         [0007]    It has been found that the management of the transitional phases by the anticipation of a change in the resultant torque applied to the output shaft prior to the deactivation reduces the jump in torque at the moment of deactivation and of reactivation, which minimizes the imbalance to which the output shaft is subjected according to a first-order compensation. 
         [0008]    According to an advantageous version of the invention, the compensating torque is also applied after the deactivation of the combustion chamber. This prevents any sudden variation in the torque applied to the output shaft at the moment of deactivation, which again minimizes the imbalance during the deactivation of the combustion chamber. 
         [0009]    According to another advantageous aspect of the invention, the method also comprises the step of applying to the output shaft a correction torque compensating for an imbalance of the output shaft. This therefore manages to dampen the imbalance according to a correction of second order so that the resultant torque becomes stable virtually throughout the combustion chamber deactivation phase. 
         [0010]    According to yet another aspect of the invention, provision is made for a system for managing a deactivation of at least one combustion chamber of a heat engine comprising several combustion chambers in each of which is mounted a piston connected to an output shaft in order to apply a torque thereto, the management system comprising a rotating machine connected to the output shaft and associated with a management member, the management member being configured so as to detect conditions of deactivation of a combustion chamber and to control the rotating machine in order to apply to the output shaft, prior to the deactivation of a combustion chamber, a compensating torque tending to cause a resultant torque applied to the output shaft to change toward a deactivation torque normally applied by the heat engine to the output shaft after deactivation of the combustion chamber. 
         [0011]    The rotating machine will then exert on the output shaft a force for compensation for the imbalance by accelerating or slowing the output shaft. 
         [0012]    According to one feature, the rotating machine is connected to the output shaft to draw off a share of the torque and is controlled by the management member in order to adapt the share of torque drawn off to the compensation of the imbalance. 
         [0013]    The share of torque drawn off by the rotating machine is then determined in order to compensate for the imbalance for example by drawing off a relatively greater torque when it is necessary to slow down the output shaft and a relatively lesser torque when it is necessary to accelerate the output shaft. 
         [0014]    According to another feature, the rotating machine is arranged to supply an additional torque to the output shaft and the management member is arranged to control the rotating machine so as to supply the additional torque as compensation for the imbalance. 
         [0015]    The rotating machine may then supply torque to the output shaft in order to accelerate the latter so as to compensate for the decelerations of the output shaft that are associated with the imbalance. 
         [0016]    According to an advantageous embodiment, the rotating machine is an alternator starter controlled by the management member in order to supply an additional torque to the output shaft or to draw off from the latter a share of torque in order to compensate for the imbalance. 
         [0017]    The alternator starter is then operated to draw off torque from the output shaft or to supply an additional torque to the output shaft making it possible to compensate for the imbalance. The alternator starter allows a particularly fast and effective compensation of the imbalances. 
         [0018]    Preferably, a detector is associated with the output shaft in order to measure the instantaneous speed of rotation of the output shaft, the management member being connected to the detector to control the rotating machine according to the instantaneous speed detected, and/or the management member comprises a memory containing laws for controlling the rotating machine according to the deactivated combustion chamber(s). 
         [0019]    The control of the rotating machine is then relatively simple. 
         [0020]    Other features and advantages of the invention will emerge on reading the following description of a particular, nonlimiting embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Reference will be made to the appended drawings, amongst which: 
           [0022]      FIG. 1  is a schematic view in perspective of a heat engine according to the invention, 
           [0023]      FIG. 2  is a partial schematic view in cross section of this engine, 
           [0024]      FIG. 3  is a schematic representation illustrating the resultant torque applied to the output shaft on a heat engine during a deactivation of a combustion chamber without application of a compensating torque, 
           [0025]      FIG. 4  is a schematic representation of the compensating torque applied according to a first aspect of the invention, 
           [0026]      FIG. 5  is a representation similar to that of  FIG. 1  of the theoretical resultant torque obtained during the application of a compensating torque according to  FIG. 4 , 
           [0027]      FIG. 6  is a representation similar to that of  FIG. 5  of the real resultant torque obtained, 
           [0028]      FIG. 7  is a schematic representation of a compensating torque according to the invention to which is added a correction torque compensating for an imbalance of the output shaft, 
           [0029]      FIG. 8  is a schematic representation of the resultant torque obtained by application of the torque represented in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    With reference to the figures, the heat engine according to the invention comprises a block  10  delimiting four in-line cylinders  1 ,  2 ,  3 ,  4 . Each cylinder  1 ,  2 ,  3 ,  4  defines a chamber  5  closed on one side by a cylinder head  6  and on the other side by a piston  7  that can be moved slidingly in the cylinder  1 ,  2 ,  3 ,  4  between two extreme positions (top dead center and bottom dead center) and connected via a connecting rod  8  to a crankshaft  9  mounted pivotingly in the block  10 . 
         [0031]    An inlet duct  11  and an exhaust duct  12  that are arranged in the cylinder head  6  lead into each combustion chamber  5 . The inlet duct  11  and the exhaust duct  12  are fitted respectively with an inlet valve  13  and an exhaust valve  14  moved between two positions, open and closed, by electromagnetic actuators  15 ,  16  respectively. 
         [0032]    A spark plug  17  is mounted on the cylinder head  6  in order to lead into the combustion chamber  5 . The spark plug  17  is connected to an ignition circuit known per se and not shown here. 
         [0033]    An injector  18  of a fuel supply device is also mounted on the cylinder head  6 . 
         [0034]    The engine also comprises an alternator starter  19  connected in a manner known per se to the crankshaft  9  by a belt  20 . The alternator starter  19  is a device that is known per se, connected to the battery and capable of operating like an electric motor or like an alternator. When it operates like an electric motor, the alternator starter  19  is supplied by the battery and supplies the crankshaft  9  with an additional torque in order to rotate the crankshaft  9 . The alternator starter  19  is therefore used for starting the heat engine. When it operates like an alternator, the alternator starter  19  is driven by the crankshaft  9  in order to recharge the battery. 
         [0035]    The engine also comprises a management member  21  connected notably to the injectors  18 , to the electromagnetic actuators  15 ,  16 , to the ignition circuit and to the alternator starter  19  in order to control the latter. The management member  21  comprises for example a microprocessor  22  associated with a memory  23  containing programs run by the micro-processor  22 . The management member  21  is in this instance arranged to detect in a manner known per se the conditions of a deactivation of a combustion chamber  5  at the moment td and the reactivation at the moment tr. 
         [0036]    A detector  24  is mounted on the block  10  in order to detect the instantaneous speed of the crankshaft  9 . The detector  24  is connected to the management member  21 . 
         [0037]    When the engine is subjected to a constant load (that is to say that the speed of the heat engine is constant and the crankshaft  9  rotates at a nominal speed), the engine control unit  21  commands the deactivation of one or two of the cylinders  1 ,  2 ,  3 ,  4 . The theoretical resultant torque obtained varies between a value CN corresponding to the nominal torque before the deactivation and a value CD during the deactivation of the combustion chamber as shown in solid line in  FIG. 3 . The nominal torque has for example a value of 200 N·m while the deactivation torque has a value of 194 N·m, namely a difference of 6 N·m. In reality, the deactivation of one or two of the cylinders  1 ,  2 ,  3 ,  4  causes an imbalance of the crankshaft  9  which results in a succession of accelerations or decelerations of the crankshaft  9  as illustrated in dashed line in  FIG. 3 . 
         [0038]    According to a first aspect of the invention, the management member  21  is configured to control the rotating machine in order to apply to the output shaft a correction torque CMT on the one hand during a period of time beginning before the moment of deactivation td and on the other hand for a period of time beginning before the moment of reactivation tr. The compensating torque is applied in a manner tending to cause, preferably in a continuous and linear manner, a resultant torque applied to the output shaft to change, including the imbalance torque, toward the deactivation torque CD until it reaches the latter. In the embodiment illustrated by  FIG. 4 , the compensating torque changes in a continuous manner in the direction of an increasing retardation from the moment t 0  from which it is applied up to the moment of deactivation td, then in the direction of a decreasing acceleration from the moment of deactivation td up to the end of the application of the compensation signal at the moment t 1 . For the numerical values given above relating to the nominal torque CN and the deactivation torque CD, the compensating torque CMT therefore varies in a continuous linear manner from 0 to −3 between t 0  and td and in a linear manner from +3 to 0 between td and t 1 . The negative values indicate a retardation torque applied to the output shaft while the positive values indicate an acceleration torque applied to the output shaft. Conversely, at the moment of reactivation of the combustion chamber, the compensating torque varies from 0 to +3 between a moment t 2  preceding the moment of reactivation tr and from −3 to 0 between the moment of reactivation tr and a moment t 3  when the compensating torque ceases to be applied. As an example, the periods t 0 , t 1  and t 2 , t 3  have a duration of approximately 100 ms. 
         [0039]    The theoretical resultant torque is illustrated by  FIG. 5  but because of the imbalance created by the deactivation and reactivation, the imbalance which had been noted in  FIG. 3  is only reduced as illustrated by  FIG. 6 . 
         [0040]    According to a preferred embodiment illustrated by  FIG. 7 , a correction torque is superposed on the compensating torque in a direction tending to return the resultant torque to the theoretical value of the resultant torque as illustrated by  FIG. 5 . In practice, the compensation is made by measuring the variations of speed of rotation of the crankshaft by means of the detector  24  and by converting this variation of speed of rotation to a variation of resultant torque applied to the output shaft, the correction torque being computed by the management member  21  and applied by the alternator starter  19  in order to be in phase opposition with the variations of the resultant torque relative to the torque that is sought. 
         [0041]    Because of the lag between the detection and the computing of the correction torque, the resultant torque is not absolutely identical to the theoretical resultant torque but the imbalance is nevertheless minimized as illustrated by  FIG. 8  and the remaining imbalance is imperceptible to the occupants of the vehicle. 
         [0042]    In practice, the detector  24  transmits to the management member  21  a signal representative of the instantaneous speed of the crankshaft. The management member  21  then controls the alternator starter  19  so that the latter:
       draws off a greater share of torque from the crankshaft  9  when the crankshaft  9  accelerates to return the crankshaft  9  to its nominal speed,   draws off a lesser share of torque or supplies an additional torque when the crankshaft  9  decelerates to return the crankshaft  9  to its nominal speed.       
 
         [0045]    The share of torque drawn off and the additional torque to be supplied are in this instance determined by the engine control unit  21  according to the difference between the instantaneous speed of the output shaft  9  and the nominal rotation speed that the latter should have for the operating speed of the engine. 
         [0046]    The alternator starter  19  therefore makes it possible to compensate for the imbalance of the crankshaft  9  produced by the deactivation of one or more cylinders. 
         [0047]    The memory  23  in this instance also comprises laws for controlling the alternator starter  19  according to the deactivated cylinder(s). It is possible to control the alternator starter  19  either according to the speed detected by the detector  24 , or according to one of the control laws stored in the memory  23 . It is also possible to combine these two control modes for the purpose of optimizing the compensation for the imbalance. 
         [0048]    The management member  21 , the detector  24  and the alternator starter  19  therefore form components of a system for managing the deactivation of cylinders of the engine ensuring that the imbalance of the latter is compensated for. 
         [0049]    The engine may advantageously comprise an angular position sensor instead of the detector  24  or in association with the latter in order to allow a predictive control of the alternator starter (according to torque profiles for example) optionally associated with a closed-loop control according to the speed of rotation of the crankshaft. 
         [0050]    Naturally, the invention is not limited to the embodiment described and it is possible to apply variant embodiments thereto without departing from the context of the invention as defined by the claims. 
         [0051]    In particular, it is possible to use, instead of the alternator starter, any other rotating machine capable of drawing off a share of torque from the crankshaft and/or of supplying the crankshaft with an additional torque. The rotating machine used may therefore be a conventional alternator. The alternator starter may also be connected to the crankshaft via the gearbox. 
         [0052]    In addition, the invention is applicable to any type of engine and for example to a rotary engine of the WANKEL type or to an engine with uncontrolled ignition such as a diesel engine. The number of cylinders may be other than four. 
         [0053]    The members for actuating the valves may be cam shafts. 
         [0054]    Although the compensating torque has been illustrated according to an application divided into two periods of equal durations, the compensation may be performed according to another division relative to the moment of deactivation td, the division illustrated however being preferred in order to optimize the imbalance.