Abstract:
A traction-unit drive includes a continuous traction unit, e.g., a belt, which connects at least two belt pulleys connected to a drive element and a driven element. The traction-unit drive further includes an acoustic sampling device for sampling the surface of the continuous traction unit.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a traction-means drive and a method for detecting the wear of a continuous traction means of such a traction-means drive.  
       BACKGROUND INFORMATION  
       [0002]     In today&#39;s internal combustion engines, as well as in other drive systems, traction-means drives are now very frequently used. In this context, V-belt drives having V-belts made of plastic, rubber or similar materials are used for the transmission of power from the crankshaft to the camshaft, for example, or from a main shaft to an auxiliary shaft, in order to drive, e.g., a charger, a compressor or the like. The drive belts are subject to a high degree of wear and must therefore be replaced at regular maintenance intervals. In most cases, the wear pattern shows itself in a change of the elasticity of the drive belt, the formation or hairline cracks, an abrasion of the teeth in the case of toothed belts or in the loss of individual teeth and partly also in a change in thickness. Neglecting to adhere to the maintenance intervals can result in considerable malfunctions. Thus, when the valve operating mechanism in an internal combustion engine is controlled by a toothed belt, for example, a rupture of the toothed belt can result in the pistons striking the valves, thereby destroying the engine. As a consequence, a replacement of the engine is required, or at least complex and thus also expensive repairs.  
         [0003]     Therefore, there exists the need to monitor the current state of a continuous traction means, e.g., of a V-belt or a toothed belt, with respect to its reaching the wear limit in order to prevent such damage.  
         [0004]     A traction-means drive of this type is described in published German patent document DE 102 16 354, in which all components or components parts of the traction-means drive have an electrical conductivity irrespective of the material used. By determining the electrical conductivity, this makes it possible to continuously determine the state of wear of the traction means while the internal combustion engine is running. Since the resistance value of the traction means changes over its service life (in comparison to the resistance value at new condition), it is possible to replace the continuous traction means before it fails, by establishing a boundary value. For detecting the resistance value, sliding contacts that increase the friction, or complex contactless measuring devices that act inductively, are required in this context. In this context, it is problematic that, for example, contamination of the surface can change the resistance value, which can result in faulty conclusions regarding the wear.  
         [0005]     A method for detecting the wear of a continuous traction means by using an optical scanner represents an improvement over the method utilizing the detection of the resistance value, as described in the published German patent document DE 102 16 354. In many cases, however, optical scanning is not possible. In particular, this optical scanning may also be disturbed if there are substances between transmitter and receiver that are impervious to light beams or that strongly attenuate light beams.  
         [0006]     An object of the present invention is to provide an improved traction-means drive, as well as a method for detecting the wear of a traction means of such a traction-means drive, so as to make it possible to implement a contactless monitoring of the traction-means drive that is as independent of external influences as possible, and particularly enable a monitoring of the wear of the continuous traction means.  
         [0007]     Another object of the present invention is to provide an improved continuous traction means that may be implemented for use in the above-mentioned improved traction-means drive.  
       SUMMARY OF THE INVENTION  
       [0008]     In accordance with the present invention, the traction means is acoustically sampled using a sound signal at standstill, or permanently during operation, or only at specific time or angle intervals, and to infer the state of the continuous traction means, e.g., of a V-rib belt or toothed belt, on the basis of the sampled signal detected in this manner.  
         [0009]     For this purpose, stored reference signals of an unworn traction means may be compared with the sampled signal, and from this comparison the current state of the traction means, that is, of the drive belt, which is a toothed belt for example, is inferred. If a specified criterion is exceeded, then the replacement of the traction means is signaled to prevent damage to the engine in which the traction-means drive is used, for example, an internal combustion engine.  
         [0010]     For this purpose, the sampling may be performed by a transmitting device for sending the sound signal and by at least one receiving device for receiving the sound signal reflected on the traction means.  
         [0011]     The sound signal may be sent permanently by the transmitting device. One example embodiment provides for the transmitting device to send the sound signal in a pulsed manner.  
         [0012]     The pulsed transmission may be synchronized with the rotational speed of the drive element.  
         [0013]     For this purpose, the traction means has at least one coated surface that reflects sound signals.  
         [0014]     To improve the sampling of the traction means further, one advantageous example embodiment provides for a tensioning device situated opposite from the sampling device in such a way that in the area of the sampling device, the traction means is redirected by a tension roller in such a way that the coated side of the traction means is facing the sampling device. Possibly existing cracks are expanded by the tension roller to a particularly high degree, allowing for an improved sampling of the surface. The redirection via a tension roller occurs particularly on the side of the toothed belt or V-rib belt facing away from the teeth or V-ribs.  
         [0015]     The received sound signals are processed and evaluated in a circuit device that is advantageously part of an existing engine control unit.  
         [0016]     In the process, the sampled signal is compared to a stored sampled signal of an unworn traction means. The wear is inferred from this comparison if a specified wear threshold value is exceeded. In this case, the circuit device generates and emits an optical and/or acoustic wear signal such that for example the driver of a vehicle is alerted to an imminent failure of the traction means. Moreover, the wear signal may also be stored in a fault storage and may be read out, for example, during maintenance work so that the traction means is replaced before the traction-means drive experiences failures and this results, for example, in a significant defect of an internal combustion engine.  
         [0017]     The continuous traction means used in such a traction-means drive, that is, for example a V-rib belt or toothed belt, has at least on at least one of its surfaces at least one layer that reflects sound signals particularly well. For example, this layer is situated on the V-rib or tooth side of the V-rib belt or toothed belt. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  shows a schematic illustration of the front view of an internal combustion engine having an acoustic sampling device for detecting the wear of a continuous traction means.  
         [0019]      FIG. 2   a  shows a schematic representation of an acoustic sampling device for detecting the wear of the traction means and sampled signals according to a first exemplary embodiment of the present invention.  
         [0020]      FIG. 2   b  shows a graph illustrating the sound intensity plotted against the frequency of a worn continuous traction means.  
         [0021]      FIG. 2   c  shows a graph illustrating the sound intensity plotted against the frequency of a new, unworn traction means.  
         [0022]      FIG. 3   a  shows a schematic representation of an acoustic sampling device for detecting the wear of the traction means and sampled signals according to a second exemplary embodiment and a third exemplary embodiment of the present invention.  
         [0023]      FIG. 3   b  shows the sound intensity plotted against the frequency of a worn continuous traction means.  
         [0024]      FIG. 3   c  shows the sound intensity plotted against the frequency of a new, unworn traction means. 
     
    
     DETAILED DESCRIPTION  
       [0025]      FIG. 1  schematically shows an engine  100 , for example an internal combustion engine of a motor vehicle, the crankshaft  110  of which engine drives a belt pulley  115 . Across the belt pulley  115  runs, for example, a V-rib belt  120 , which additionally runs across belt pulleys  130 ,  140 ,  150  on the drive shafts, for example, of a water pump  135 , a servo pump  145  and an alternator  155 , respectively. A tensioning device is provided for tightening V-rib belt  120 , which has a tension roller  180 , across which V-rib belt  120  is laid and which exerts a tensional force on V-rib belt  120 .  
         [0026]     The entire assemblage made up of belt pulleys  115 ,  130 ,  140 ,  150  and tension roller  180  represents a traction-means drive, the traction means being formed by V-rib belt  120 . In addition to V-rib belt  120 , toothed belts are also often used as traction means, which like V-rib belt  120  also allow for a form-fitting traction means drive and thus also allow for driving a plurality of aggregates such as, for example, generators, ventilators, water pumps, air-conditioning compressors, power-steering pumps and the like.  
         [0027]     An acoustic sampling device  170  is situated at the front side of engine  100  in the area of the traction-means drive, which emits a sound signal  172  and receives it again. The sampled signals are supplied via an electric signal line  210  to an evaluation electronics, for example, to a control unit  200 , in which the sampled signals are evaluated in the manner described below.  
         [0028]     In accordance with the present invention, the V-rib drive belt  120  is now used, the bottom side of which is coated with at least one surface  122  that reflects sound signals particularly well, as shown in  FIG. 2   a.  Sound signal  172  emitted by sampling device  170  is thus reflected on this coating  122  and is received by a sensor (not shown in  FIG. 2   a ) situated in the sampling device.  
         [0029]     An ultrasonic source or also an infrasonic source may be used as sound source. The reflected sound waves are detected or evaluated. For this purpose, the current state of wear of drive belt  120  is ascertained using an evaluation algorithm that is part of control unit  200  on the basis of propagation delay differences, intensity fluctuations or decreases in intensity, the excitation of harmonic oscillations, interference frequencies and the like. The evaluation is performed with the aid of an evaluation algorithm, a neural network, a fuzzy logic and the like. It should be pointed out that sampling device  170  may be situated at any location of the engine  100  along which drive belt  120  is running.  
         [0030]     A new, unworn drive belt, which has no hairline cracks  125  (shown in  FIG. 2   a ), produces a signal pattern shown in  FIG. 2C  and marked by “N” having a characteristic frequency pattern of the reflected sound waves. With increasing wear, i.e., if for example hairline cracks  125  (shown in  FIG. 2   a ) between teeth  124  due to the strong flexing motions when drive belt  120  revolves over the different belt pulleys  115 ,  130 ,  140 ,  150  as well as over tension roller  180 , this signal pattern changes in that, for example, the number of different peaks at different frequencies, the signal intensity and the like changes. Thus, in a new unworn drive belt  120 , for example, signal N (shown in  FIG. 2   c ) contains characteristic frequency peaks  220 ,  221 ,  222 ,  223 . In the signal pattern A ( FIG. 2   b ) of a worn V-belt that has a plurality of hairline cracks  125 , interference frequencies  227 ,  228  are detected in addition to these frequency peaks  220 ,  221 ,  222  and  223 . The state of wear of drive belt  120  is inferred from the changes in the frequency spectrum. Changes in the frequency spectrum that lead to an inference of a worn state of drive belt  120  may also include, in addition to the occurrence of interference frequencies  227 ,  228 , the excitation of harmonic waves of a fundamental wave/frequency, and/or phase shifts between sent and reflected frequencies, and/or wavelength changes between sent and reflected frequencies, and/or propagation delay differences between sent and reflected frequencies. Pattern comparisons, signal level comparisons, frequency comparisons, rate of repetition comparisons, difference comparisons and the like can be used as comparison methods.  
         [0031]     In the evaluation electronics, which is part of control unit  200  and which may be implemented, for example, as a program or take the form of a neural network, detected signal “A” of worn drive belt  120  is now compared to signal “N” of unworn drive belt  120 , and from this comparison an inference is made to the wear of drive belt  120 .  
         [0032]      FIG. 2   a  schematically show the assemblage of sampling device  170  on the bottom side, that is, the “toothed side,” of a drive belt  120  that runs essentially uncurved. The sampling precision may be increased further by situating sampling device  170  opposite tension roller  180 , which redirects drive belt  120  in such a way that its bottom side is facing sampling device  170  ( FIG. 1 ). Tension roller  180  stretches the bottom side of drive belt  120  to a particularly high degree, which results in a widening of possibly present hairline cracks, which allows sampling device  170  to detect them better.  
         [0033]     Following the comparison of signal pattern “N” of a new, unworn drive belt and signal pattern “A” of sampled drive belt  120 , the wear is indicated, for example, by the fact that an acoustic or optical warning sign is issued, for example, to a driver of a vehicle in which the above-described traction-means drive is situated, thereby indicating that a specified wear threshold value has been reached. Furthermore, an error message may also be stored in a memory and be read out, e.g., during a later maintenance work.  
         [0034]     The sampling may occur during a standstill of engine  100 , occur continuously during engine operation, or only at certain time or angle intervals.  
         [0035]     The sound signal  172  used may be permanent, pulsed or be switched on and off in synchronization with the rotational speed of crankshaft  110 , for example.  
         [0036]     In an exemplary embodiment of the sampling implementation of a drive belt  120  and the signals obtained thereby shown in  FIGS. 3   a  through  3   c,  identical elements are indicated by identical reference symbols as in the exemplary embodiment shown in  FIGS. 2   a - 2   c.    
         [0037]     In contrast to the exemplary embodiment shown in  FIGS. 2   a  through  2   c,  in the exemplary embodiment shown in  FIG. 3   a  the upper side of teeth  124  is sampled. In addition to the upper side of teeth  124 , it is also possible to additionally or alternatively sample their slopes. With increasing wear, the tooth/slope width decreases such that the sampled square-wave signal A ( FIG. 3   b ) with increasing wear changes significantly in comparison to the signal N of a new, unworn drive belt  120  ( FIG. 3   c ). Thus the width t n  of the square-wave flange of signal N of an unworn, new drive belt  120  decreases with increasing wear in that the teeth are ground down, such that the width t a  of square-wave pulses  265  of a worn drive belt  120  becomes smaller, as shown schematically in  FIG. 3   b  illustrating the signal pattern A. This change is evaluated in control unit  200 . In this case, the tooth time correlates with the rotational speed of the drive. Depending on the rotational speed, specific tooth times are produced which can be stored in a characteristics map or a value table or in a corresponding manner. With increasing wear, the tooth times become significantly shorter than the reference values at the same rotational speed. The differences of the tooth times may thus be used for the diagnosis.  
         [0038]     If manufacturing-related tolerances of the tooth width cannot be avoided, averaged tooth times may also be used as a diagnostic signal.  
         [0039]     In addition, a gap is created on drive belt  120  when a tooth falls out, for example, and as a consequence a pause in the sequence of the tooth times occurs, which is also detected.  
         [0040]      FIG. 3   a  furthermore shows another, third exemplary embodiment having a sampling device  170 ′, which does not lie opposite of the bottom surface of the drive belt  120 , but is situated in such a way that the sound strikes at an angle from below and is reflected, for example, on a slope of a tooth and is received in a receiving unit (not shown).