Variable belt tensioner for an internal combustion engine

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.

Claims

1. A variable belt tensioner of an internal combustion engine for adjusting a belt tensioning comprising: an electric motor; a worm drive driven by the electric motor; a lever drive mechanically connected to the worm drive for transmitting a rotation thereto, said lever drive comprises a first lever, a second lever and a third lever which are mechanically interconnected, wherein a transmission ratio of the lever drive is derived from the quotient of a first angle () and a second angle (), wherein the first angle () is the angle of rotation for the first lever around a first fixed point and the second angle () is the angle of rotation for the third lever around its axis of rotation; and a belt tensioner roller mechanically connected to the lever drive for transmitting a translation thereto, wherein the belt tensioner roller is positionable to adjust a belt tensioning.

2. The variable belt tensioner according to claim 1, wherein said first lever rotates around a first pivot point located at a first end of the first lever, and a second end of the first lever moves in a groove formed in the second lever.

3. The variable belt tensioner according to claim 1, wherein said second lever rotates around a second pivot point and a first end of the second lever is guided through a groove in the third lever.

4. The variable belt tensioner according to claim 1, wherein said third lever rotates around an axis of rotation corresponding to a first end of said third lever and the belt tensioner roller is rotatably supported on a second end of the third lever.

5. The variable belt tensioner according to claim 1, wherein the transmission ratio of the lever drive is determined by the lengths of said first, second and third lever.

6. An internal combustion engine comprising a belt which transmits power to a plurality of engine components having a variable belt tensioner according to claim 1.

7. The variable belt tensioner according to claim 1 further comprising an electronic control unit and a non-transitory computer readable medium having a computer program stored thereon which when executed on the electronic control unit is configured to: receive an angle of rotation measurement for the first lever around a first pivot from a rotation sensor; compute an angular deviation based on a sum of a nominal angle and the angle of rotation, wherein the nominal angle is estimated on the basis of a nominal belt force; determine an actuation current on the basis of the angular deviation; and apply the actuation current to the electric motor for angularly adjusting the first lever around a first fixed point.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements.

(2) FIG. 1 is a view of the variable belt tensioner according to an embodiment of the present disclosure;

(3) FIG. 2 illustrates the geometry and the constructive implementation of the lever drive;

(4) FIG. 3 is a graph showing a characteristic diagram angle vs. force of the device in FIG. 3; and

(5) FIG. 4 illustrates the closed loop control of the device in FIG. 3.

DETAILED DESCRIPTION

(6) 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.

(7) 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'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'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.

(8) 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 is defined as the input value. This describes the rotation of the lever A about the point 1. The angle () 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 () 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.

(9) The transmission ratio is determined by the length of the levers in the starting position. The length l.sub.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.sub.B and l.sub.C. The value l.sub.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 and ().

(10) 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 . The angle describes the angle between the lever A and the engine bearer. The value of the angle 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 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.sub.R measured in Newton and the angle in degrees. This characteristic diagram can be calculated by modeling the variable belt tensioner or by experimental tests.

(11) FIG. 4 shows a closed loop control of the variable belt tensioner. The characteristic diagram 560 generates a nominal angle .sub.nom of a needed nominal belt force F.sub.R, nom. The current angle .sub.cur is measured by the rotation sensor 550. The angular deviation .sub.dev is calculated as the sum of the nominal angle .sub.nom and the current angle .sub.cur. The angular deviation .sub.dev is defined as the input parameter of the controller. As the actuation variable of the control loop, the current i.sub.act is defined by the controller 570. The current i.sub.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.sub.act and the disturbance variable i.sub.dist. The disturbance variable i.sub.dist can be affected by fluctuations in the on-board power supply. Because of the engine rotation, the current angle .sub.cur is changed and the control loop is closed.

(12) 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.

(13) 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.