Abstract:
The present disclosure describes a variable belt tensioner of an internal combustion engine for adjusting a belt tensioning. The tensioner includes in a series configuration an electric motor, a worm drive, a lever drive and a belt tensioner roller. The worm drive is driven by the electric motor and is mechanically connected to the lever drive for transmitting a rotation thereto. The lever drive is mechanically connected to the belt tensioner roller for transmitting a translation thereto, thus allowing the belt tensioner roller to adjust the belt tensioning.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to British Patent Application No. 1319251.3 filed Oct. 31, 2013, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The technical field relates to a variable belt tensioner, which adjusts a belt tensioning of internal combustion engine belts. 
     BACKGROUND 
     Given the global demand to reduce the use of fossil fuels and to reduce the associated production of the greenhouse gas, carbon dioxide (CO 2 ), many new innovations and ideas have already emerged from the automotive industry to date, that minimize the fuel consumption of conventional internal combustion engines. However, to simultaneously meet the growing demand for more comfort and safety in automobiles, there must be an increase in auxiliary equipment. To supply the required energy to the extra components, mechanical power must be drawn from the internal combustion engine. The auxiliary units such as generator, air compressor, water pump and hydraulic steering pump, usually have a belt drive system for power. Among these known belts is the timing belt which is a part of an internal combustion engine that synchronizes the rotation of the crankshaft and the camshaft (or camshafts, if more than one are available) so that the engine valves open and close at the proper times during each cylinder intake and exhaust strokes. A timing belt is a belt that usually features teeth on the inside surface. 
     To make sure the belt can transmit power to the individual components in any situation, a defined pre-tensioning force must act on the belt. However, the friction caused by this mechanical belt drive leads to excess fuel consumption. 
     A belt tensioning device is disclosed in DE 101 18 277 A1 which includes a swinging lever mounted on a pivotal axis. A pre-tensioned spring acts on the lever. Spring tension is controlled by an electric motor with reverse motion prevention. The motor is controlled by an operational parameter associated with a stored engine characteristic diagram. However, such belt tensioner does not allow to adjust the belt tensioning in a flexible way, according to the engine operating conditions. 
     Therefore a need exists for a belt tensioner, which is designed to minimize the above inconveniences. 
     SUMMARY 
     The present disclosure provides a variable belt tensioner that acts under given technical and efficiency conditions during operation. This is intended to reduce the mechanical friction produced and consequently lower the total fuel consumption of the engine. Furthermore, a variable belt pre-tension controller lowers the average belt load and leads to a longer belt service life. 
     An embodiment of the disclosure provides a variable belt tensioner of an internal combustion engine for adjusting a belt tensioning including in a series configuration an electric motor, a worm drive, a lever drive and a belt tensioner roller. The worm drive is driven by the electric motor and is mechanically connected to the lever drive, to which the worm drive transmits a rotation. The lever drive is mechanically connected to the belt tensioner roller, to which the lever drive transmits a translation, thus allowing the belt tensioner roller to adjust the belt tensioning. 
     An advantage of this embodiment is that such variable belt tensioner is able to adjust the belt tension and fine tuning the transmission ratio between the electric motor and the belt tensioner roller, by using only a simple lever drive. In other words, the rotation imposed by the electric motor is transformed into a translation of the belt tensioner roller. The roller, according to the direction of the translation, increases or decreases pulling the belt, this increasing or decreasing the belt tensioning. 
     According to another embodiment, the lever drive includes a first lever, a second lever and a third lever, which are mechanically interconnected. An advantage of this embodiment is that the three levers provide the adjustment of the transmission ratio between the electric motor and the belt tensioner roller, only by means of the lever geometry and the interconnections among them. 
     According to a further embodiment the first lever rotates around a first fixed point, located at a first lever end, and a first lever second end moves in a groove of the second lever. An advantage of this embodiment is that the first lever has only a rotational degree of freedom, and the rotation of the lever can be determined by means of an angle value which is considered input angle of the lever drive, in other words, what is transmitted by the electric motor, via the worm drive, to the lever drive. 
     According to a still further embodiment, the second lever rotates around a second fixed point and a second lever first end is guided through a grove in the third lever. An advantage of this embodiment is the kinematics of such second lever allows to transform the input angle of the lever drive in an output angle of the lever drive. 
     According to still another embodiment, the third lever rotates around an axis of rotation corresponding to a first end of the third lever and the belt tensioner roller is constrained to a second end of the third lever. An advantage of this embodiment is that the rotation of the third lever around the axis of rotation, which is located at one end of the lever implies that the other end of the lever will translate. The translation will be proportional to the angle of the lever rotation and to the lever length. Since the belt tensioner roller is constrained in the movable end of the lever, the roller will have the same translation, thus increasing or decreasing the belt tensioning. 
     According to another embodiment, a transmission ratio of the lever drive is derived from the quotient of a first angle and a second angle, being the first angle the rotation of the first lever around the first fixed point and the second angle the rotation of the third lever around the axis of rotation. An advantage of this embodiment is that the transmission ratio of the lever drive can be described only by means of two characteristic angles. 
     According to a further embodiment, the transmission ratio of the lever drive is determined by the length of the first, second and third lever. An advantage of this embodiment is that the transmission ratio of the lever drive can be easily adjusted, by varying the levers length. 
     According to another embodiment of the disclosure, an internal combustion engine is provided, including at least a belt, which transmits power to a plurality of engine components, having a variable belt tensioner according to any of the preceding claims. 
     According to a further embodiment of the disclosure, a method of controlling a variable belt tensioner is described. The variable belt tensioner is defined according to any of previous embodiments, and the method for controlling the first angle, which represents the rotation of the first lever around the first fixed point, by means of an actuated current determined by a controller on the basis of an angular deviation, which is calculated as the sum of a nominal angle and a current angle. The nominal angle is estimated on the basis of a required nominal belt force and the current angle is measured by a rotation sensor. 
     Consequently an apparatus is described for controlling the variable belt tensioner, the apparatus including a first angle controller, representing the rotation of the first lever around the first fixed point, by means of an actuated current determined by a controller on the basis of an angular deviation, which is calculated as the sum of a nominal angle and a current angle. The nominal angle is estimated on the basis of a required nominal belt force and the current angle is measured by a rotation sensor. An advantage of this embodiment is that the variable belt tensioner can be easily controlled in closed loop on the basis of the required belt force by controlling the input angle of the lever system by means of the current acting in the electric motor. 
     The method according to one of its aspects can be carried out with the help of a computer program including a program-code for carrying out all the steps of the method described above, and in the form of computer program product including the computer program. The computer program product can be embedded in a control apparatus for an internal combustion engine, including an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program all the steps of the method described above are carried out. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements. 
         FIG. 1  is a view of the variable belt tensioner according to an embodiment of the present disclosure; 
         FIG. 2  illustrates the geometry and the constructive implementation of the lever drive; 
         FIG. 3  is a graph showing a characteristic diagram angle vs. force of the device in  FIG. 3 ; and 
         FIG. 4  illustrates the closed loop control of the device in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses of the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
       FIG. 1  shows a variable belt tensioner  480  according to an embodiment of the present disclosure. As shown in view c) of  FIG. 1 , a belt  460 , for example a timing belt, transmits the power between the belt pulleys  470  from a driving component, for example the engine crankshaft to other engine components. A variable belt tensioner  480  has the function of tensioning the belt  460 . The tension to the belt  460  is applied by means of a belt tensioner roller  490 , which can be moved along the arrows A and B direction, respectively, increasing or decreasing the belt tension. As shown in view b) of  FIG. 1 , the power unit of the variable belt tensioner is an electric motor  500 , which is powered by the vehicle&#39;s electrical system. In order to keep energy consumption of the electric motor  500  and the required drive torque low, a combination of two different types of gear mechanisms are implemented. The mechanisms include a worm gear or worm drive  510  and a lever drive  520 , which is schematized in view a) of  FIG. 1 . The worm drive  510  is designed to be self-locking to keep the electric motor&#39;s energy use low. Through this, the flow of electricity can be cut off after a desired target value of the belt pre-tensioning force is achieved. The lever drive  520  is schematically represented by a combination of three individual levers that are mechanically interconnected. Consequently, the resulting variable belt tensioner includes a series configuration of an electric motor  500 , a worm drive  510 , and a lever drive  520 . The electric motor  500  is fixed by a clamping element  530  to a cross piece  540 . The worm drive  3  is driven by the electric motor  500  and is mechanically connected to the lever drive  520 . On its turn, the lever drive  520  is mechanically connected to the belt tensioner roller  490 . As will be explained hereafter, the lever drive  520  gets an input rotation, which is transmitted by the worm drive  510  to a first lever of the lever drive, and transmits an output rotation, which is transformed in a translation of the belt tensioner roller  490 , along the direction of the arrows A and B. 
     The layout of the lever drive  520  is specified in  FIG. 2 . View a) is a schematized front view of the lever drive  520 . View b) is a schematized top view of the mechanism  520 , with the levers represented as one-dimensional rods. View c) is an exploded view of the lever mechanism  520 . The first lever, lever A, rotates about the point  1 . Bolt  2  is located at the end of lever A, where it can move in a groove  6  formed in lever B. In turn, this is mounted at point  4 . Point  1  and point  4  are fixed to each other. The lever B contains a bolt at point  5 . In turn this is guided through a groove  7  in lever C (output lever) whose center of rotation is located in the axis of rotation  3 . Therefore, the distances between the points  1 ,  3 , and  4  are constant. The angle γ is defined as the input value. This describes the rotation of the lever A about the point  1 . The angle σ(γ) is stated as the output value, which indicates the rotation of the lever C about the point of rotation or rather the axis of rotation  3 , which is located at one end of lever C. As a consequence of the lever C rotation, the other end of lever C (point  5 ) will translate a length which is proportional to the output angle σ(γ) and to the length of lever C. Since the belt tensioner roller  490  is constrained at point  5 , the roller will have the same translation of point  5 , thus moving along the arrows A and B direction, increasing or decreasing the belt tension. 
     The transmission ratio is determined by the length of the levers in the starting position. The length l A  describes the distance between the points  1  and  2 . The distance between the points  2  and  3 , and the points  2  and  4  is respectively described by the lengths l B  and l C . The value l D  describes the distance from the point of rotation  4  to point of rotation  5 . The resulting transmission ratio is derived from the quotient of the angle γ and σ(γ). 
     The variable belt tensioner, as above described, can be controlled in closed loop. To this purpose, a relation between the belt force and a parameter of the system is needed. One possible parameter is the angle γ. The angle γ describes the angle between the lever A and the engine bearer. The value of the angle γ is measured by a rotation sensor  550 , which is arranged between the lever A and the engine bearer. To transform the belt force into the angle γ the characteristic diagram  560  is used, as shown in  FIG. 3 . The graph in the diagram  560  represents the relationship between the belt force F R  measured in Newton and the angle γ in degrees. This characteristic diagram can be calculated by modeling the variable belt tensioner or by experimental tests. 
       FIG. 4  shows a closed loop control of the variable belt tensioner. The characteristic diagram  560  generates a nominal angle γ nom  of a needed nominal belt force F R, nom . The current angle γ cur  is measured by the rotation sensor  550 . The angular deviation γ dev  is calculated as the sum of the nominal angle γ nom  and the current angle γ cur . The angular deviation γ dev  is defined as the input parameter of the controller. As the actuation variable of the control loop, the current i act  is defined by the controller  570 . The current i act  correlates with the required engine torque. The input of the control process (variable belt tensioner) is calculated as the sum of the current i act  and the disturbance variable i dist . The disturbance variable i dist  can be affected by fluctuations in the on-board power supply. Because of the engine rotation, the current angle γ cur  is changed and the control loop is closed. 
     Summarizing, it can be proven by measuring the fuel consumption for different static belt tension forces that, by reducing the belt pre-tensioning force, there is a definitive reduction in power drawn from the engine by drive the belt. This can be achieved by holding the allowable slip between the belt and the pulleys at its maximum. Furthermore, the fuel consumption results can only be achieved if the pre-tensioning force is combined with active force regulation. Because, if instead of a belt tension controller, a vibration-damping system is installed on the crankshaft pulley combined with reduced static pre-tensioning force, then, due to the increased mass moment of inertia, the gains in economy would be canceled out. Further advantages result from a need-based/controller-regulated belt pre-tensioning force, where a lower belt force can lead to a longer service live of the belt. 
     While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.