Abstract:
A method for adapting a preset value for a minimum valve stroke in an internal combustion engine, has the following steps: Replace the previous value for the minimum valve stroke with a new value; Determine an operating parameter of the internal combustion engine; Restore the previous value for the minimum valve stroke if the operating parameter is outside of a defined value range; otherwise retain the new value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German Patent Application No. 10 2008 003 834.2 filed Jan. 10, 2008, the contents of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The invention relates to a method and device for adapting a minimum valve stroke in an internal combustion engine. 
     BACKGROUND 
     Known internal combustion engines have cylinders in which a gaseous mixture of fuel and air is burnt in order to generate torque. The quantity of mixture admitted into a cylinder prior to ignition is decisive with regard to the torque delivered by said cylinder. To enable the torque delivered by the internal combustion engine to be adapted to different loads, known internal combustion engines have throttle valves which reduce the admission of mixture into the cylinders in a controllable way. However, the use of throttle valves is linked to throttle losses stemming from the resistance to flow which throttle valves cause. 
     To prevent throttle losses it is known for the quantity of gas flowing into a cylinder to be regulated by means of a valve stroke. Depending on the desired quantity of mixture to be admitted to the cylinder, one or more inlet valves on the cylinder are opened to a greater or lesser extent. This solution offers improved efficiency due to the reduction in throttle loss. The inlet valves can be opened mechanically, electromechanically or electrically. For example the inlet valves can be mechanically actuated by means of an adjustable intermediate mechanism that uses a camshaft. 
     In the prior art the valves of some or all of the cylinders are actuated by a common camshaft. Then the same valve stroke is set for each cylinder and consequently every cylinder receives an identical amount of mixture. In practice, though, tolerances arising during manufacture and in the components themselves lead to a variation in the resulting valve stroke and therefore also to a variation in the amount of mixture per cylinder. As a consequence the individual cylinders deliver different amounts of torque. When the valve strokes are small these differences have a particularly strong effect, since the percentage deviation is at its greatest in these conditions. Differences in the filling and torque amounts between the individual cylinders lead not only to increased rough running in the internal combustion engine but also to variations in the mixture attended by a worsening of exhaust gas quality together with increased engine wear. 
     Since the effects of manufacturing and component tolerances are particularly serious when the valve stroke settings are small, it is known in the prior art for a value to be established for a minimum valve stroke which guarantees an acceptable torque deviation in the different cylinders and which the valve stroke must not fall below. This value is empirically determined according to the prior art for a series of internal combustion engines and then permanently specified for every exemplar of the series. The chosen value is large enough to ensure that all exemplars in the series provide satisfactory running despite manufacturing and component tolerances. 
     However, due to this necessarily quite large minimum valve stroke value it is not possible to decrease the power of the internal combustion engine by reducing the valve stroke, and this effect must therefore be reproduced by using the throttle valve. This in turn gives rise to the throttle losses already described. 
     SUMMARY 
     According to various embodiments, a method and a device for adapting a minimum valve stroke in an internal combustion engine can be provided. 
     According to an embodiment, a method for adapting a preset value for a minimum valve stroke in an internal combustion engine, comprising the following steps: Replace the previous value for the minimum valve stroke with a new value; Determine an operating parameter of the internal combustion engine; Restore the previous value for the minimum valve stroke if the operating parameter is outside of a defined value range; otherwise retain the new value. 
     According to a further embodiment, a lambda signal can be determined as an operating parameter. According to a further embodiment, an acoustic signal of the internal combustion engine can be determined as an operating parameter. According to a further embodiment, a pressure can be determined as an operating parameter. According to a further embodiment, a rough running of the internal combustion engine can be determined as an operating parameter. 
     According to another embodiment, a control device may have a memory device that is provided in order to control a valve stroke in an internal combustion engine, wherein the control device holds a value for a minimum valve stroke in the memory device, and wherein the control device is provided in order to change the value for the minimum valve stroke. 
     According to yet another embodiment, the control device can be provided in order to execute the above described method. 
     According to a further embodiment, the control device may hold at least two different minimum valve stroke values and these values are allocated to different valves or cylinders. According to a further embodiment, the control device can be designed to change a setting of a throttle valve in the internal combustion engine if a value for a valve stroke is below a defined limiting value. According to a further embodiment, the control device can be designed to change a setting of a camshaft in the internal combustion engine if a value for a valve stroke is below a defined limiting value. According to a further embodiment, the control device can be designed to change an ignition advance angle of a cylinder if a value for a valve stroke is below a defined limiting value. According to a further embodiment, the control device can be designed to change a mixture ratio of a cylinder if a value for a valve stroke is below a defined limiting value. According to a further embodiment, a value for a minimum valve stroke can be used as a defined limiting value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in greater detail below with the aid of the exemplary embodiments shown in the drawings. These show the following: 
         FIG. 1  A section of a cylinder from an internal combustion engine having an inlet valve with controllable valve stroke; 
         FIG. 2  A schematic diagram of an internal combustion engine having a control device according to an embodiment; 
         FIG. 3  A flowchart of a method for adapting a minimum valve stroke in an internal combustion engine according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A method according to various embodiments for adapting a preset value for a minimum valve stroke in an internal combustion engine involves replacing the previous value for the minimum valve stroke with a new value, determining an operating parameter of the internal combustion engine, restoring the previous value for the minimum valve stroke if the operating parameter is outside an established range, but otherwise retaining the new value. 
     Advantageously this method enables the value of a minimum valve stroke to be adapted individually to an actual internal combustion engine. In this method the value does not need to be set high enough to be usable in all exemplars of a series of internal combustion engines affected by manufacturing and component tolerances. Instead an individual and optimally adapted value for a minimum valve stroke can be used for each exemplar. 
     Consequently a wider power range can be produced in the internal combustion engine by changing the valve stroke. Advantageously this increases the efficiency of the internal combustion engine. 
     Preferred embodiments of the method use a lambda signal, an acoustic signal of the internal combustion engine, a pressure, a rough running of the internal combustion engine or a combination of these parameters as an operating parameter. 
     Advantageously, determining these operating parameters of the internal combustion engine makes it possible to establish the value for the minimum valve stroke below which a no longer acceptable torque inequality or a no longer acceptable mixture deviation between the cylinders of the internal combustion engine is set. 
     A control device according to various embodiments has a memory device and is provided in order to control a valve stroke in an internal combustion engine, wherein the memory device of the control device holds a value for a minimum valve stroke, and wherein the control device is provided in order to change the value of the minimum valve stroke. 
     Advantageously, the control device according to various embodiments permits the value for the minimum valve stroke to be individually adapted to a particular internal combustion engine. 
     In an embodiment the control device is designed to execute the method. 
     In a further embodiment the control device holds at least two different minimum valve stroke values which are allocated to different valves or cylinders in the internal combustion engine. 
     Advantageously this makes cylinder-specific or valve-specific adaptation of the minimum valve stroke possible. It also equalizes manufacturing and component tolerances between the individual valves or cylinders. This enables the internal combustion engine to deliver even lower power without the addition of a throttle valve. 
     In further embodiments the control device is designed to change a throttle valve setting of the internal combustion engine or a camshaft setting of the internal combustion engine if a value required for a valve stroke is below the minimum valve stroke value. 
     Advantageously this makes it possible to operate the internal combustion engine even in the lower load range without causing excessively strong torque and mixture deviations in the different cylinders together with the attendant negative characteristics due to the valve stroke being too low. 
     In further embodiments the control device is designed to change an ignition advance angle or a mixture ratio of a cylinder if the value of an actual valve stroke is below the minimum valve stroke value. 
     Advantageously this makes it possible to operate the internal combustion engine even in the lower load range simply by means of valve stroke control and to equalize the resulting torque deviations of the cylinders by other means. It is then possible to do away with the use of a throttle valve and the associated throttle losses even in the lower load range of the internal combustion engine. 
       FIG. 1  shows a section of a cylinder  110  of an internal combustion engine  100  known per se. The cylinder has a combustion chamber  111  in which a mixture of air and fuel can be burnt in order to transfer force via a piston (not shown) to a crank shaft (not shown). The combustion chamber  111  is connected to an inlet manifold  113  via a valve  112  through which air or an air-fuel mixture can be drawn in. The inlet manifold  113  can be provided with a throttle valve  114  designed to control the amount of air drawn in by the combustion chamber  111  and/or the amount of air-fuel mixture drawn in by the combustion chamber  111 . One throttle valve  114  can be provided per cylinder  110  of the internal combustion engine  100 , or a common throttle valve  114  can be provided for all cylinders  110  of the internal combustion engine  100 . In another embodiment the throttle valve  114  can be done away with entirely. 
     The valve  112  must be open in order to permit air or an air-fuel mixture to be drawn from the inlet manifold  113  into the combustion chamber  111 . For this purpose the valve  112  has a lifter  118 . A camshaft  115  which rotates about its long axis is provided with a cam  119  that can exert force on the lifter  118  of the valve  112  via an intermediate lever  116  and a cam follower  117  in order to open the valve  112 . A spring (not shown) is provided in order to close the valve  112  again after an opening action. 
     The position of the intermediate lever  116  relative to the cam follower  117  and the camshaft  115  can be changed by means of a stepper motor (not shown) and a spring element (not shown). Depending on the position of the intermediate lever  116 , a rotation of the camshaft  115  causes the valve  112  to open with different valve strokes. The amount of gas drawn into the combustion chamber  111  when the valve  112  is opened depends on the valve stroke concerned. Regulating the valve stroke makes it possible to regulate the amount of mixture admitted into a cylinder  110  of the internal combustion engine  100 . Said regulation is performed by a control device  101  (not shown in  FIG. 1 ) which is designed to drive the stepper motor. 
     The camshaft  115 , cam  119 , intermediate lever  116 , cam follower  117 , valve  112  and lifter  118  must be manufactured with greater precision in order to enable an accurate and reproducible valve stroke setting. Nonetheless manufacturing and component tolerances lead to some variation in the valve stroke that actually results, and therefore also to deviations in the amount of mixture admitted into the cylinder. The percentage deviation is at its greatest in the small valve stroke range. 
     Differences in filling quantities between individual cylinders  110  of the internal combustion engine  100  cause the different cylinders  110  to provide different contributions to the torque delivered by the internal combustion engine  100 . The consequence of this is increased rough running of the internal combustion engine  100 , causing greater wear of the mechanical components in the internal combustion engine  100 . Inaccuracies in the valve stroke and consequent inaccuracies in the filling quantity of a cylinder  110  also cause a deviation in the mixture, leading to an increase in harmful emissions. 
     To avoid an excessive deviation in the valve strokes of the different cylinders  110  in an internal combustion engine  100 , the prior art establishes a minimum valve stroke value below which the valve stroke must not fall. 
     In other embodiments the valve  112  of the internal combustion engine  100  can be opened in another way. For example the valve  112  can be actuated by an electrical or electromechanical adjustment mechanism such as a piezoelectric actuator driven by the control device  101 . 
       FIG. 2  shows a control device  101  of an internal combustion engine  100  according to an embodiment. The control device  101  is designed to control the internal combustion engine  100  in accordance with various nominal values and operating parameters. The internal combustion engine is equipped with one or more throttle valves  114  and one or more camshafts  115 , for example. The control device  101  is designed to change settings of the throttle valve  114  and camshaft  115 . The control device  101  is linked to a series of sensors which the control device  101  can use to determine various operating parameters of the internal combustion engine  100 . For example the control device  101  can be linked to an acoustic sensor  121  which delivers information about an operating noise in the internal combustion engine  100 . The control device  101  can also be equipped with a pressure sensor  122  which delivers information about a pressure at a location inside or outside of the internal combustion engine  100 . The control device  101  can also be connected to a lambda probe  123  which delivers information about the composition of an exhaust gas of the internal combustion engine  100 . The control device  101  can also be connected to a sensor for rough running of the internal combustion engine  100 , delivering information about mechanical rough running of the internal combustion engine  100 . 
     The control device  101  is designed to change the valve stroke of the valves  112  on the cylinder  110  of the internal combustion engine  100  in accordance with the power required from the internal combustion engine  100 . In the event of an increase in the required power, the control device increases the valve stroke of the valves  112  of the cylinders  110  in the internal combustion engine  100 . In the case of a reduction in the required power, the control device  101  reduces the valve stroke of the valves  112  in the internal combustion engine  100 . The control device  101  can change the valve stroke of the valves  112  by, for example, manipulating the intermediate lever  116  of the cylinders  110  in the internal combustion engine  100 . The control device  101  has a memory device  120  that stores a value for a minimum valve stroke. 
       FIG. 3  shows the flowchart of a method for adapting the minimum valve stroke of the internal combustion engine  100 , using as an example the way in which it can be executed by the control device  101 . 
     In a first method step  201  a copy of the previous minimum valve stroke value is stored. 
     In a second step  202  a new value for a minimum valve stroke is computed. This can be done for example by changing the previous value for the minimum valve stroke by a predetermined or random amount in a predetermined or random direction. In the further sequence of the method the newly computed value is used as the value for the minimum valve stroke of the internal combustion engine. 
     In a third method step  203  an operating parameter of the internal combustion engine  100  is determined. The operating parameter can be for example a signal from a lambda probe  123 . The operating parameter can also be a signal from an acoustic sensor  121 , a signal from a pressure sensor  122  or a signal from a sensor for rough running  124  of the internal combustion engine  100 . The operating parameter can also be another measured variable which delivers information about whether a desired property of the internal combustion engine is present. 
     The next method step  204  checks whether the operating parameter determined in step  203  is within a specified range. If the operating parameter is a signal from an acoustic sensor  121 , the check can determine whether for example the operating noise emitted by the internal combustion engine  100  is below a defined limiting value. If the operating parameter is a signal from a lambda probe  123 , the check can determine whether the composition of the exhaust gas from the internal combustion engine  100  is within a specified value range. 
     If the comparison in step  204  gives the result that the operating parameter determined is within the specified value range, the new value computed in method step  202  can be retained for the minimum valve stroke of the internal combustion engine  100 , at which point the method ends. If the operating parameter determined in step  203  is found to be outside of the specified value range when a comparison is made in step  204 , the value for the minimum valve stroke is replaced in method step  205  by the copy of the previous minimum valve stroke value that was stored in step  201 . The method then ends. 
     In a further embodiment of the method, a plurality of operating parameters of the internal combustion engine  100  can be determined in step  203  and compared with specified value ranges in step  204 . In a first embodiment the new minimum valve stroke value is only retained when all the determined operating parameters are within the value ranges assigned to them. In other embodiments the new minimum valve stroke value is also retained when only a defined number of operating parameters are within the value ranges assigned to them. In further embodiments the plurality of operating parameters can be differently weighted in order to decide whether the new minimum valve stroke value needs to be retained. In these embodiments it is possible to increase the accuracy of the described method and reduce its proneness to error. 
     In one embodiment the control device  101  is designed to execute the method shown in  FIG. 3  at defined times during the operation of the internal combustion engine  100 . This is always possible when the power required from the internal combustion engine  100  is so low that the valves  112  can be opened with the minimum valve stroke. In this embodiment an optimum value for the minimum valve stroke of an internal combustion engine  100  can be determined by the control device  101  making repeated use of the described method. It is also possible to compensate for changes in the accuracy of the valve stroke settings of the different valves  112  in the internal combustion engine  100  due to ageing characteristics by executing the described method over again. 
     In another embodiment the method shown in  FIG. 3  is executed once only after the assembly of an internal combustion engine and stored in the memory device  120 . In this embodiment it is also possible to determine an optimum value for the minimum valve stroke of the internal combustion engine  100  that is independent of manufacturing and component tolerances. 
     In this embodiment the method is executed by a control device  101 , or by some other equipment such as a diagnostic device, or by a person. 
     In a further embodiment, the described method is executed once only for a series of an internal combustion engine  100 . The value determined for the minimum valve stroke is then stored in the memory devices  120  of all the internal combustion engines  100  in the series. The operating parameters determined in method step  203  shown in  FIG. 3  can be a signal from a lambda probe  123  for example. However, the operating parameter determined can also be for example an assessment of the rough running of the internal combustion engine  100  determined in a vehicle test carried out by a person. 
     In this embodiment also, the method is executed by a control device  101 , or by some other device, or by a person. 
     In another embodiment the control device  101  stores a value table in which minimum valve stroke values are held as a function of values for a mileage reading of the internal combustion engine  100 . The control device  101  can infer a suitable minimum valve stroke value from said table in accordance with the distance which the vehicle driven by the internal combustion engine  100  has covered. In this way it is likewise possible to compensate for ageing characteristics of the internal combustion engine  100 . 
     In a further embodiment, different components of the internal combustion engine  100 , such as the intermediate lever  116 , cam follower  117  or valve  112 , are calibrated before the internal combustion engine  100  is assembled and divided into different quality groups according to their degree of deviation from a nominal state. After the internal combustion engine  100  has been assembled a value is determined for the minimum valve stroke in accordance with the quality groups from which the built-in components have been taken. This value can be inferred from, for example, an empirically determined table that contains a suitable value for the minimum valve stroke for each possible combination of component qualities. 
     If during the operation of the internal combustion engine  100  there is a demand for power which is so small that in order to achieve it the valves  112  in the internal combustion engine  100  would have to be actuated at a valve stroke that is below the minimum valve stroke, different procedures are possible depending on the embodiment. 
     In a first embodiment a control device  101  reduces the actual valve stroke only as far as the minimum valve stroke value stored in the memory device  120 . If the power delivered by the internal combustion engine  100  needs to be reduced further, the control device  101  reduces the power of the internal combustion engine by adjusting the camshaft  115 . The control device  101  offsets the rotation of the camshaft  115  for this purpose. This has the effect of shifting the instant in time at which a valve  112  of a cylinder  110  is opened. Since different pressure ratios predominate at different times in the combustion chamber  111  of a cylinder  110  in the internal combustion engine  100 , a change in the time at which a valve  112  opens also causes a change in the resulting amount of mixture admitted to the cylinder and thus changes the power delivered by the internal combustion engine  100 . Alternatively the control device  101  can change the angle of aperture of a throttle valve  114  in order to reduce the amount of mixture admitted to the cylinder  110  of the internal combustion engine. 
     In another embodiment of the control device  101 , the control device  101  reduces the valve stroke of the valves  112  in the internal combustion engine  100  to values that are even lower than the minimum valve stroke value stored in the memory device  120 . The differences occasioned by manufacturing and component tolerances in the individual valves  112  and cylinders  110  in the internal combustion engine  100  give rise to differences in the extent to which the individual cylinders  110  are filled with mixture. As already remarked, these differences in filling lead to different contributions from the individual cylinders  110  to the torque delivered by the internal combustion engine  100 , bringing about an increase in rough running, harmful emissions and engine wear. In order to counteract this, the control device  101  can equalize the torque of the cylinders  110 . For this purpose the control device  101  can adjust an ignition advance angle or ignition timing of one or more cylinders  110 , or change a mixture ratio of an air-fuel mixture admitted to a cylinder. 
     In this embodiment the control device  101  must be designed to detect which cylinder  110  in the internal combustion engine  100  needs an increase or reduction in delivered torque. This is possible since the individual cylinders  100  in an internal combustion engine  100  are ignited in chronological sequence. If one or more of the previously mentioned or other operating parameters of the internal combustion engine  100  can be determined quickly enough, the control device  101  can use this information to adjust the respective torque contributions of the different cylinders  110  independently of one another. The control device  101  can then equalize differences in the torque contributions of the individual cylinders  110  by direct intervention on the ignition advance angle or mixture. In this embodiment therefore it is possible in certain circumstances to do away with using the throttle valve  114  or offsetting the rotation of the camshaft  115 .