Abstract:
A belt drive is provided which includes a circulating belt ( 8 ) which is driven by at least one drive element ( 9 ) and which drives at least one driven element ( 10 ). At least one first tensioning device ( 20 ) acts upon the belt ( 8 ) in the slack strand and at least one second tensioning device acts in the tightened strand. To prevent or reduce jumps and/or transverse oscillations of the belt ( 8 ), the second device ( 21 ) guides the belt ( 8 ) and at least one third device ( 22 ) which is arranged radially inside the belt drive, which is suitable, optionally, limits deviations of the belt ( 8 ). The second device ( 30, 40, 50, 60, 70, 80, 90, 100 ) also tensions the belt ( 8 ) in such a manner that it is subjected to a force (F 1 ) which is smaller than the force (F 2 ) which is oriented counter thereto during the operation of the belt ( 8 ) on the second tensioning device ( 30, 40, 50, 60, 70, 80, 90, 100 ).

Description:
BACKGROUND 
       [0001]    The invention relates to a belt drive comprising a circulating belt means, which is driven by at least one drive element and which drives at least one driven element, as well as at least one first tensioning device acting on the belt means in a region of the belt drive, in which this belt means leaves the drive element in the circulating direction and reaches the closest driven element, and at least one second device in a region of the belt drive, in which the belt means reaches the drive element in its circulating direction and leaves the closest driven element. 
         [0002]    Such belt drives are used, for example, for timing and/or accessory drives in internal combustion engines. The traction means, for example, the timing belt, is here driven by a driving gear mounted on a crankshaft of the engine and drives driven gears, which are connected to timing shafts or camshafts of the engine. For limiting transverse vibrations in the timing belt, this belt is led over a guide on its tensioned side running into the driving gear and a force tensioning the belt is applied by a tensioning device to the slack side of the belt running out from the driving gear. 
         [0003]    EP 1 262 685 also shows a belt drive according to the class, in which for limiting transverse vibrations of a timing belt, a force is applied to this belt both on its tensioned side running into the driving gear and also on its slack side running out from the driving gear. The forces are set here by a rotating, adjustable ring body, to which guide rails are attached that act on the timing belt. The tensioning force acting on the timing belt increases or decreases with the degree of rotation of the ring body. The rotation of the ring body itself is generated by a combination of oil pressure and spring force. 
         [0004]    DE 196 16 081 C1 shows a belt drive comprised of belt disks and an endless belt with a device for steadying belt vibrations, in which a guide plate is arranged fixed at a close distance to the belt for reducing belt vibrations in a corresponding critical region. 
         [0005]    Limiting transverse vibrations in belt drives is of great importance with respect to their functionality, service life, and noise output. This applies independent of how many driving and driven gears are actually used for a belt drive. The belt means can involve, for example, a chain or a toothed belt of a timing drive, which synchronizes crankshafts and camshafts with each other, or, for example, also a driving belt, which connects a belt disk of a drive shaft to the belt disk of a driven shaft for some assembly in a driving manner. 
         [0006]    For transverse vibrations that become too large, adjacent components can be damaged, if a toothed belt or a chain temporarily loses positive-fit contact with a driving or also driven element due to transverse vibrations that are too large. Furthermore, unsuitably high mechanical loads for the belt means itself can occur due to excessive transverse vibrations, which lead to a shortened service life of the belt means. In addition, excessive transverse vibrations cause a comparatively high noise generation. 
         [0007]    Finally, synchronization errors between at least two camshafts and/or between these and the crankshaft of an internal combustion engine can occur, when the belt drive is lengthened due to wear and a tensioning device on a belt means strand compensates this by an increased tensioning path. Because this single tensioning device is typically activated by an actuator acted upon by the oil pressure of the internal combustion engine, in particular, at the start of the internal combustion engine, insufficient oil pressure is present in the actuator, so that disadvantageously, tooth jumping is hard to prevent in known belt drives. 
         [0008]    To be noted is also the increasing complexity of accessories for usually only limited space relationships in the region of the belt drive, as well as the necessary flexibility of the belt drive due to the increasing number of different accessories with respect to adaptability to different operating conditions. 
       SUMMARY 
       [0009]    The invention is based on the objective of creating a belt drive, in which tooth jumping caused by wear-related lengthening of the belt means between the belt means and the driving element or driven element can be prevented reliably and also at least the amplitude of transverse vibrations of the belt means can be reduced. 
         [0010]    The invention is based on the knowledge that through selective improvement of the belt drive layout or belt drive construction, transverse vibrations of the belt means can be reduced and also tooth jumping can be prevented. Here, the important feature is that a special means is provided and arranged on the belt drive for preventing loosening of the belt means due to decreasing force application by the actuator-controlled tensioning device, which would hold back the belt means before the drive element of the belt drive and would lift the belt means from this drive. 
         [0011]    The invention starts from a belt drive, comprising a circulating belt means, which is driven by at least one drive element and which drives at least one driven element, as well as at least one first tensioning device acting on the belt means in a region of the belt drive, in which the belt means leaves the drive element in its circulating direction and reaches the closest driven element, and at least one second device in a region of the belt drive, in which the belt means reaches the drive element in its circulating direction and leaves the closes driven element. 
         [0012]    In this belt drive, according to the invention it is also provided that the second device provided at least once in this drive is constructed for guiding the belt means and at least one third device arranged in the radial direction within the belt drive is provided, which is also suitable for limiting excursions of the belt means. 
         [0013]    Such a belt drive can be a timing drive of an internal combustion engine in the form of a toothed-belt drive or a chain drive, but it can also be constructed as a toothed-belt drive or chain drive for driving auxiliary accessories. 
         [0014]    Through this construction, it is advantageously achieved that a belt means lengthened due to wear past its original installed dimensions cannot lift from the drive element of the belt drive so that it jumps out of the teeth or it cannot be held back in front of this drive element, when the contact force of an allocated tensioning device that can be activated by a pressurized medium is not yet or no longer present due to operation. In addition, with a belt or chain drive built structurally according to the invention, the likelihood and the extent of the appearance of transverse vibrations of the belt means can be reduced. 
         [0015]    The third device arranged in the radial direction within the belt drive is suitable for this purpose and also provided to produce a steering effect on the inside of the belt means not reached by the other devices and, if necessary, is arranged where this appears most relevant to someone skilled in the art for fulfilling this purpose. 
         [0016]    Preferably, it is provided that the third device provided at least once in the belt drive is arranged in the region of the drive element, for example, a crankshaft drive wheel, by means of which, in this usually critical region, an additional avoidance or prevention of undesired vibrations and tooth jumping is advantageously enabled. 
         [0017]    If the third device present at least once in the belt drive is arranged in the region of the drive element, in which the belt means has reached the drive element in its circulating direction or is arranged in the region of the drive element, in which the belt means leaves the drive element in its circulating direction, then a positive effect on the vibrating behavior of the belt means, as well as a given run-in and run-out angle and a given advantageous contact length of the belt means on the drive element, can be realized on these sections of the belt means located in the direct area of the drive element, 
         [0018]    In this connection, it is especially useful if, in the construction of the invention, the third device present at least once in the belt drive is suitable for acting both in the region of the drive element, in which the belt means reaches the drive element in its circulating direction and also in the region of the drive element, in which the belt means leaves the drive element in its circulating direction. 
         [0019]    The third device present at least once in the belt drive here does not necessarily have to be constructed as guide means for the belt means. That is, it does not have to be in constant contact with the belt means, but instead it is absolutely advantageous when this is arranged at a defined distance from the inside of the belt means. In this way, this occurs only for actually appearing undesired transverse vibrations and/or holding back of the belt means in the slack belt strand, which leads, as a whole, to a reduction in friction on this third device. 
         [0020]    In addition, it can be advantageously provided that the third device present at least once in the belt drive is connected mechanically to the first tensioning device present at least once in the belt drive and/or to the second guide device present at least once in the belt drive. In this way, the devices connected to each other can be aligned in common and adjusted easily. 
         [0021]    If at least one of the mentioned devices is advantageously provided with a surface reducing the friction with the belt means, this can lead to further friction reduction and thus an increase in the service life of the belt means. 
         [0022]    Alternatively, according to the invention a belt drive can be created, comprising a circulating belt means, which is driven by at least one drive element and which drives at least one driven element, as well as at least one first tensioning device acting on the belt means in a region of the belt drive, in which the belt means leaves the drive element in its circulating direction and reaches the closest driven element, and at least one second device in a region of the belt drive, in which the belt means reaches the drive element in its circulating direction and leaves the closest driven element. 
         [0023]    According to the invention, it is also provided that the second device present at least once in the belt drive is also constructed for tensioning the belt means, such that this means acts on the belt means with such a force F 1  that is smaller than an opposite force F 2  acting on the second tensioning device in the operation of the belt means. This opposite force F 2  acting on the second tensioning device is applied by the belt means tensioned by the first tensioning device. 
         [0024]    Through this construction, it is achieved that, especially in a standstill phase, in which the first tensioning device operated by pressurized medium does not exert a force tensioning the belt means on the belt means due to the lack of pressure in the pressurized medium, a wear-dependent lengthening of the belt means is compensated in the belt drive, in which this second tensioning device exerts an appropriate tensioning force on the belt means. 
         [0025]    Therefore, tooth jumping as well as associated rotational angle errors or synchronous running errors, for example, on a crankshaft disk or on the camshaft disks of an internal combustion engine, can be reliably prevented. In addition, the appearance likelihood and also the amplitude of transverse vibrations of the belt means are further reduced or even completely avoided. 
         [0026]    In addition, the second tensioning device can have a more compact construction in its structural design than the first tensioning device that can be activated by pressurized medium and is also suitable for guiding the belt means during its operation along its optimum belt path. Because the force F 1  of the second tensioning device acting on the belt means is less than the opposite force F 2  acting on the second tensioning device in the operation of the belt means, the force F 1  of the second tensioning device has no noticeable effect for the operation of the belt means. However, for the lack of pressurized medium supply to the actuator of the first tensioning device, it is in the position to strongly tension the belt means, so that lengthening of the belt means, for example, caused by wear or by counter rotation of the drive element, is compensated, especially when the belt drive is turned off or after the belt drive has been turned off. 
         [0027]    In addition, it can be provided that the force of the second tensioning device acting on the belt means is generated at least partially by a spring force, which allows a structurally simple construction of the device for high reliability. If the spring force is generated by at least one spiral, leaf, or torsion spring, costs can be saved tracing back to common structural elements. 
         [0028]    It is absolutely advantageous for the service life of the belt means if the second tensioning device, which is present at least once in the belt drive and which is acted upon by a spring force or which itself has a spring-elastic construction, is provided with a surface reducing the friction. In this way, the size of the spring can be kept smaller and thus space can be saved or the spring possibly could be completely eliminated. 
         [0029]    The second tensioning device present at least once in the belt drive can have, in an advantageous refinement of the concept of the invention, a guide body that can move in a direction toward the slack belt strand of the belt means or can have a guide body with a deformable construction. By moving the guide body, a very precise adjustment of this body on the belt drive is possible. The use of a deformable guide body leads to an additional force and supports the spring force of the second tensioning device acting on the belt means, by which a spring provided in the structure can be kept smaller. 
         [0030]    In an especially advantageous construction of the invention, it is provided that the first tensioning device present at least once in the belt drive can also be acted upon with a spring force acting on the belt means. In this way, a certain basic tensioning of the belt means on both sides of the drive element is guaranteed, independent of the operating situation of a tensioner of the first tensioning device that can be activated by pressurized medium. Changes in length in the belt means, for example, due to wear or due to counter rotation of the drive element, which can appear, e.g., when a motor is turned off or after the motor has been turned off, can be advantageously compensated. 
         [0031]    It is further advantageous when the first tensioning device that can be activated by pressurized medium and that is present at least once in the belt drive and the second tensioning device present at least once are connected to each other elastically by at least one spring. In this way, this spring generates a force acting on the belt means both on the tightened strand and also on the slack strand, so that too much slack in the belt drive is overcome when the drive machine is turned off or when the pressure supply is stopped for the tensioner of the first tensioning device that can be activated by pressurized medium. 
         [0032]    Similarly, however, it also offers advantages when the first tensioning device that can be activated by pressurized medium and that is present at least once in the belt drive and the second tensioning device present at least once in the belt drive are connected to each other by a linkage mechanism, wherein the linkage mechanism is connected to at least one spring, which generates a force acting constantly on the belt means. 
         [0033]    In a preferred embodiment, it is provided that the guide body of the two tensioning devices are each supported at separate attachment points so that they can pivot, that these guide bodies are connected in articulated ways at other attachment points to a lever-like connection element, that these connection elements are connected to each other so that they can pivot at a connection point, and that at this connection point a spring attaches, such that a basic contact force acts on the belt means through the connection elements and the noted guide bodies. 
         [0034]    In addition, it has been judged to be advantageous when the connection elements and the spring of this belt drive are arranged in the radial direction inside of this drive. 
         [0035]    Through the above structural features, an equal distribution or different distribution of the basic contact force F 1  acting on the belt  8  due to different lever-arm lengths of the connection elements can be achieved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    The invention will be explained in more detail below with reference to the enclosed drawing using a few embodiments. Shown therein are 
           [0037]      FIG. 1  a block diagram of a belt drive according to a first solution according to the invention and 
           [0038]      FIGS. 2 to 9  different schematic diagrams for embodiments of a belt drive according to a second solution according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0039]    The belt drive shown schematically in  FIG. 1  can be used in a motor-vehicle engine and features at the bottom a belt disk  9 , which is connected to a not-shown crankshaft and which drives a circulating belt  8  in the counterclockwise direction. The belt  8  also drives two belt disks  10 , which are arranged at the top and which are connected to not-shown camshafts. 
         [0040]    The region of the belt drive, in which the belt  8  leaves the driving belt disk  9  in its circulating direction and reaches the closest belt disk  10 , it designated in general as the slack strand. The region of the belt drive, in which the belt  8  reaches the driving belt disk  9  in its circulating direction and leaves the closest belt disk  10 , is designated in general as the tightened strand. 
         [0041]    As  FIG. 1  shows, in the slack strand a first tensioning device  20  is provided, which is comprised of a tensioner  1  that can be activated by pressurized medium in the form of a piston-cylinder arrangement, a guide body  2  hinged to an attachment point  4  so that it can pivot, and a friction-reducing sliding coating  3  deposited on the guide body  2  on the belt side. The tensioner  1  applies a force on the guide body  2  of the first tensioning device  20  with a force that presses and thus tensions the belt  8  running over the sliding coating  3  in this diagram to the right in the radial direction approximately in the direction of the center of the belt drive. 
         [0042]    In the tightened strand, an additional device  21  is provided for guiding the traction means, which is constructed as a belt  8 , and which has a guide body  5  that is mounted at two attachment points  4  and a friction-reducing sliding coating  7  is deposited on this guide body on the belt side. Furthermore, below in the direct area of the belt disk  9 , a guide device  22 , which is suitable for guiding the belt  8 , is provided in the radial direction within the belt drive and above the belt disk  9 . 
         [0043]    This guide device  22  has a guide body  13 , which carries two guide rails that are each provided, in turn, with a sliding coating  14 . Of the two guide rails, one guide rail faces the inside of the slack strand and the other guide rail faces the inside of the belt  8  located in the tightened strand. 
         [0044]    The guide rails are arranged with their sliding coating  14  at a slight distance from the belt  8 , such that an approximately funnel-shaped guide channel  23 ,  24  for the belt  8  is formed between the sliding coating  7  of the guide body  5  of the additional device  21  and the sliding coating  14  of the guide body  13  or between the sliding coating  3  of the guide body  2  of the first tensioning device  20  and the sliding coating  14  of the guide body  13 . 
         [0045]    The guide channel  23  prevents, for example, on the slack strand side that a lengthened belt  8  caused by wear can lift so far from the belt disk  9  that the belt jumps from the teeth when tension on the belt  8  falls due to decreasing application of force by the first tensioning device  20 . The other guide channel  24  generates the same effect on the tightened strand side of the driving belt disk  9 , where tooth jumping caused by the belt  8  being held back is prevented. In addition, in this way the production of transverse vibrations in the belt  8  is advantageously prevented or at least advantageously reduced. 
         [0046]    However, the guide rails of the guide device  22  can also be arranged with the sliding coatings  14  such that they are located in constant contact with the belt  8 . It is also possible that the additional guide device  22  located in the radial direction inside the belt drive is arranged at a different position in the radial direction inside of the belt drive, or other guide devices are provided in the radial direction inside the belt drive. 
         [0047]    It is also possible that only one guide device  22  or several guide devices each with only one guiding surface allocated to the belt  8  are arranged in the radial direction inside the belt drive. 
         [0048]    The guide body  13  of the guide device  22  can be connected mechanically in another variation to one of the two other guide bodies  2  or  5  or also to both guide bodies  2  and  5  in a suitable way. 
         [0049]      FIG. 2  likewise shows a belt drive of an internal combustion engine with a circulating traction means constructed as a belt  8  and connecting a driven wheel and at least one drive wheel. In the present case, the drive of the belt disk  9  is transmitted by the belt  8  to the two belt disks  10 . In the slack strand, in turn, a first tensioning device  20  composed of a tensioner  1  that can be activated by pressurized medium and a guide body  2  with a sliding coating  3  is arranged. 
         [0050]    On the tightened strand, there is a second tensioning device  30  with a guide body  35  featuring a sliding coating  7 . The guide body  35  is acted upon by a spring  6  with a force, wherein the spring attachment  11  can be realized on a stationary part, for example, on the housing of the internal combustion engine. In addition, a piston-cylinder arrangement  31  is connected to the guide body  35  and to the housing of the internal combustion engine, such that the guide body  35  of this second tensioning device  30  can be moved away from the belt  8  against the contact force of the spring  6 . 
         [0051]    To enable the movement of the guide body  35  of this second tensioning device  30 , this also features two elongated recesses  51  and  52 , which are aligned in the direction toward the tightened strand of the belt  8  and which are intersected by two attachment points  4  constructed as stay bolts, so that the guide body  35  is arranged so that it can move in the direction toward the belt  8 . 
         [0052]    During operation of the internal combustion engine, a sufficiently large pressurized medium pressure is generated, which is led to the tensioner  1  of the first tensioning device  20  and to the piston-cylinder arrangement  31  of the second tensioning device  30 . Therefore, the first tensioning device  20  presses against the belt  8  in order to tension the belt, while the piston-cylinder arrangement  31  of the second tensioning device  30  is acted upon with oil pressure  12 , such that the guide body  35  lifts from the belt  8  in a friction-reducing way against the force of the spring  6  or contacts the belt  8  at least with low force in a guiding manner on this belt strand. 
         [0053]    If the internal combustion engine is turned off and thus there is no more pressurized medium available for the tensioner  1  or for the piston-cylinder arrangement  31 , then the tensioner  1  of the first tensioning device  20  also cannot tension the belt  8 . Now if the belt  8  becomes longer than its installed dimension due to wear, this leads to a belt  8  suspended in the belt drive that is overall only relatively looser without additional means. Now if the internal combustion engine is started again, undesired tooth jumping can occur on the drive disk  9  and/or on the driven disks  10 , which would lead to phase or rotational angle errors of the shafts in this belt drive. 
         [0054]    Because the piston-cylinder arrangement  31  of the second tensioning device  30  for a deactivated drive motor or for no or insufficient pressurized medium pressure does not generate a counter force overcoming the force of the spring  6 , the spring  6  presses the guide body  35  against the belt  8  just with this spring force F 1 , so that the belt is also tensioned in this operating position and tooth jumping is reliably prevented. 
         [0055]    In contrast, for an activated drive motor, that is, during operation of the belt  8 , sufficient oil pressure  12  for the tensioner  1  that can be activated by pressurized medium is generated, which acts against the spring force F 1  of the spring  6  with a force F 2  on the belt  8  or the second tensioning device  30  arranged in the slack strand, which is greater than the spring force F 1 . Therefore, the guide body  35  is pressed outward until, as  FIG. 2  shows, the attachment points  4  constructed as stay bolts are located at the left stop of the recesses  51 ,  52  in the guide body  35  of the second tensioning device  30 . 
         [0056]    In contrast to  FIG. 2 ,  FIG. 3  shows a belt drive, in which the guide body  45  of a second tensioning device  40  provided in the slack strand has a deformable construction. For this purpose, in this embodiment the guide body  45  has a two-part construction, wherein this is fixed so that it can pivot on attachment points  4  at the ends of its longitudinal extent. The two individual parts  41  and  42  of the multiple-part guide body  45  are connected to each other so that they can pivot in a middle region of this body at an attachment point  4 ′. A spring  6 , which is fixed in position on the motor housing, for example, with its other end, also engages to this attachment point  4 ′. For this embodiment, the spring force F 1  generated by the spring  6  and acting in the direction toward the belt  8  is also smaller than the force F 2  generated by the first tensioning device  20  and acting on the guide body  45  via the belt  8  in the activated drive motor. 
         [0057]    The belt drive shown in  FIG. 4  has, in contrast to the variant according to  FIG. 2 , in the tightened strand a second tensioning device  50 , in which the one-part guide body  55  is fixed to two end-side attachment points  4  and in which a spring  6 ′ is arranged between the sliding coating  7  and the guide body  55 . The term sliding coating is understood in this connection not as a coating of a body but instead the body itself, which is in contact with the belt  8  in a spring-loaded manner. 
         [0058]    However, this so-called sliding coating  7  itself (as shown in  FIG. 5 ) can also have a spring-elastic, for example, leaf spring-shaped construction, which is supported on the end on a guide body  65  according to the second tensioning device  60  shown there. This guide body  65  is here fixed to the housing also at two attachment points  4 . For the belt drives shown in  FIG. 4  or  FIG. 5 , the spring force F 1  generated by the spring  6 ′ or the spring-elastic sliding coating  7  itself in the direction toward the belt  8  is also smaller than the force F 2  generated by the tensioner  1  of the first tensioning device  20  that can be activated by pressurized medium and guided by the belt  8  to the guide body  55  or  65 . 
         [0059]    In contrast to the embodiment according to  FIG. 2 ,  FIG. 6  shows a belt drive with a second tensioning device  70 , in which a guide body  75  of this second tensioning device  70  provided on the tightened strand is hinged so that it can pivot via an attachment point  4  only in a lower region pointing toward the drive element  9 . In addition, the two tensioning devices  20 ,  70  arranged in the slack strand and tightened strand, respectively, are connected elastically to each other via a spring  6 . Therefore, it is achieved that the belt  8  is acted upon with a basic tension that overcomes belt slack that is too much independent of the pressure supply for the tensioner  1  that can be activated by pressurized medium both in the slack strand and also in the tightened strand. 
         [0060]    For an internal combustion engine during operation, pressurized medium under sufficient operating pressure is generated for the tensioner  1 , so that this tensions a belt  8  compensating for belt slack caused by wear. The spring  6  between the first tensioning device  20  and the second tensioning device  70  also generates in this operating phase a contact force, with which the guide body  75  is pressed against the belt  8 . 
         [0061]    If the pressure supply for the tensioner  1  that can be activated by pressurized medium is interrupted, this definitely leads to a restoring motion of the guide body  2  of the first tensioning device  20  away from the belt  8 , because the spring  6  is pulled along for this restoring movement but with its end fixed to this guide body  2 , the force at least of the guide body  75  of the second tensioning device  70  on the belt  8  remains at least the same size. An undesired large belt slack, as well as tooth jumping in the belt drive, is reliably prevented. 
         [0062]    In  FIG. 7 , in a modification to the embodiment according to  FIG. 6 , a belt drive is shown, in which a lever-like connection element  15  or  16  is hinged to a corresponding attachment point  4 ″ on the guide bodies  2  and  85  of the two tensioning devices  20  and  80  arranged on the slack strand or tightened strand in their region pointing away from the drive element  9 . These connection elements  15  or  16  are connected to each other in an articulated manner with their other end at a connection point  48 . In turn, a spring  6 , whose spring force acts on the guide body  2  or  5  through the use of the lever-like connection elements  15  or  16  for approximately the same parts, engages at this connection point  48 . This happens in that the belt  8  is acted upon with a basic tensioning force that tensions a slack belt  8  for no compressed-means supply for the tensioner  1  independent of the tensioner  1  that can be activated by pressurized medium both in the slack strand and also in the tightened strand. In the operating behavior, that is, for an activated or deactivated pressure supply for the tensioner  1 , these two tensioning devices  20  and  80  according to  FIG. 7  act like the two tensioning devices  20  and  70  according to  FIG. 6 . 
         [0063]    In contrast to the embodiment according to  FIG. 6 , in the belt drive shown in  FIG. 8 , the guide body  2 ,  95  of the two tensioning devices  20  and  90  are each acted upon by a spring  6  with a spring force. In this way, it is also achieved that the belt  8  is acted upon with a spring-generated basic tensioning force independent of an activation force of the tensioner  1  that can be activated by pressurized medium both in the slack strand and also in the tightened strand. Here, for a stopped pressurized medium supply for the tensioner  1 , the guide bodies  2  and  95  each press onto the belt  8  via an associated spring  6 , so that tooth jumping of the belt means  8  is prevented, compensating for too much undesired belt slack. 
         [0064]    Deviating from the embodiment according to  FIG. 6 , in the belt drive shown in  FIG. 9 , the guide bodies  2  and  105  supported so that they can pivot on one side at the attachment points  4  in the two tensioning devices  20  and  100  each act with a spring force on their lower end close to the drive wheel through torsion springs  6 ′ constructed as leg springs. The torsion springs  6 ′ are here supported against stationary spring attachment points  11 ′. In this way, it is also achieved that the belt  8  is acted upon with a basic tensioning force independent of the tensioner  1  that can be activated by pressurized medium both in the slack strand and also in the tightened strand. Belt lengthening caused by wear is compensated in this way and also, finally, rotational angle errors between the shafts rotating in the belt drive are prevented. 
         [0065]    As the embodiments according to  FIGS. 6 to 9  make clear, also for these embodiments, during operation of the belt means or when pressure is applied to the tensioner  1  that can be activated by pressurized medium, a force F 1  acts via the second tensioning device  30 ,  40 ,  50 ,  60 ,  70 ,  80 ,  90 ,  100  on the belt means  8 , with this force being smaller than the force F 2  that the belt means  8  itself exerts during operation on these second tensioning devices  30 ,  40 ,  50 ,  60 ,  70 ,  80 ,  90 ,  100 . 
         [0066]    The second tensioning devices  40 ,  50 ,  60 ,  70 ,  80 ,  90 , and  100  according to  FIGS. 3 to 9  can also be equipped with a piston-cylinder arrangement  31  according to  FIG. 2 , which presses such a second tensioning device away from the belt  8 , reducing friction, when during operation of the drive motor, a sufficiently high pressurized medium pressure is provided for the tensioner  1  that can be activated by pressurized medium in the first tensioning device  20 , so that this can reliably tension a non-tensioned belt means  8  that becomes too loose in the belt drive (not shown). 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
           1  Tensioner that can be activated by pressurized medium 
           2  Guide body of slack strand 
           3  Sliding coating of guide of slack strand 
           4  Attachment point 
           4 ′ Attachment point, hinge point 
           4 ″ Attachment point 
           5  Guide body on guide body 
           6  Spring 
           6 ′ Torsion spring 
           7  Sliding coating or surface of guide body 
           8  Belt, belt means 
           9  Drive element, belt disk on crankshaft 
           10  Drive element, belt disk on camshaft 
           11  Spring attachment 
           11 ′ Spring attachment 
           12  Oil pressure 
           13  Guide body of inner guide device 
           14  Sliding coating of guide of inner guide device 
           15  Connection element 
           16  Connection element 
           20  First tensioning device 
           21  Second device, second tensioning device 
           22  Guide device 
           23  Guide channel 
           24  Guide channel 
           30  Second tensioning device 
           31  Piston-cylinder arrangement 
           35  Guide body 
           40  Second tensioning device 
           41  Individual part of guide body  40   
           42  Individual part of guide body  40   
           45  Guide body 
           48  Connection point 
           50  Second tensioning device 
           51  Recess of guide body 
           52  Recess of guide body 
           55  Guide body 
           60  Second tensioning device 
           65  Guide body 
           70  Second tensioning device 
           75  Guide body 
           80  Second tensioning device 
           85  Guide body 
           90  Second tensioning device 
           95  Guide body 
           100  Second tensioning device 
           105  Guide body 
         F 1  Force of second tensioning device on belt means 
         F 2  Force of belt means during its operation on second tensioning device