Abstract:
A method and a system for establishing and executing correct automatic relubrication for a number of bearings incorporated in a grease lubrication system. The system determines initial values for the relubrication interval t f  and/or lubricant volume utilizing data collected from the different bearing assemblies during operation. The data includes bearing load, bearing temperature and bearing rotational speed. A processor calculates a correct lubricant volume and a value for current lubrication interval t f  by comparing an initial value with a current value. The calculated correct lubricant volume and current lubrication interval t f  are supplying to an automatic lubricating apparatus, which functions in accordance with the determined values. The data collection and calculation procedures are repeated after each application of lubricant to the bearings.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is the US national stage of International Application No. PCT/SE2010/000210 filed on 26 Aug. 2010, which claims the benefit of Swedish Patent Application Serial No. 0901128-9, filed on 27 Aug. 2009, both of which are incorporated herein in their entireties. 
     FIELD OF THE INVENTION 
     The present invention refers to relubrication of a number of bearings, particularly for grease lubricated bearings relubricated by an automated lubrication system. 
     BACKGROUND OF THE INVENTION 
     Greases used for lubricating bearings often have a shorter service life than the expected service life for the bearings lubricated thereby. For that reason rolling bearings have to be relubricated, and relubrication shall take place at a time when the condition of the lubricant is still satisfactory. 
     The requirement for relubrication depends on many related factors, including bearing type and size, speed at which the bearings are running, operating temperature, type of grease, bearing environment, etcetera. 
     The common method for deciding the relubrication intervals t.sub.f for bearings is by using statistical rules, where for instance the SKF recommended relubrication intervals are defined as the time period, at the end of which 99% of the bearings are still reliably lubricated. 
     Diagrams have been created which are used for establishing the relubrication interval for a specific bearing, at a speed factor “A” multiplied by the relevant bearing factor “bf”, where the graphs represent the load ratio C/P. Such a relubrication interval chart can be seen in the accompanying  FIG. 1 . For a bearing having a value of Ab.sub.f&lt;&lt;475000 and a C/P ratio=8, it can be seen that the calculated t.sub.f value will be 1000 operating hours. 
     With this earlier and commonly used method, it is possible to decide before the operation of the bearing assembly or bearing assemblies shall be relubricated, and the method has proven itself to give a fairly satisfactory and reliable result. 
     However, some of the factors to be considered may change gradually during operation for the bearing assembly or bearing assemblies relubricated by the automated lubrication system. 
     Thus it is possible that the load acting on a bearing can change, the temperature, at which the bearing is operating, can vary for external reasons and the rotational speed can be altered. The previous method of setting the t.sub.f value described above, thus will only give a surely satisfactory result under the prerequisite, that all parameters or factors used at the original setting of the relubrication interval are maintained unchanged. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to propose a new efficient method and a new improved system for establishing correct relubrication intervals and executing correct relubrication for a number of bearings preferably relubricated by an automatic lubrication system, whereby changes are automatically effected at variations in such factors as load, temperature and rotational speed. 
     A first exemplary embodiment presents a method for establishing and executing correct automatic relubrication for a number of bearings incorporated in a grease lubrication system, wherein initial values for the relubrication interval t.sub.f and/or lubricant volume are calculated and established according to empirical methods, 
     data regarding bearing load, bearing temperature and bearing rotational speed are collected from the number of bearing assemblies during operation, 
     using the data for calculating a value for current lubrication interval t.sub.f, 
     comparing the initial value with the current value, and calculating a correct lubricant volume associated with a current relubrication interval t.sub.f independent of, if the current relubrication interval t.sub.f is equal to that initially established or not, supplying calculated current relubrication interval t.sub.f and lubricant volume to an automatic lubricating apparatus, and starting to calculate new initial values after performance of a lubrication sequence and inputting new current measured data regarding bearing load, bearing temperature and bearing rotational speed in an event of non-performance of a lubrication sequence. 
     A second exemplary embodiment presents a system for establishing and executing correct automatic relubrication for a number of bearings incorporated in a grease lubrication system, the system comprising: 
     a central processor unit; 
     a number of sensors provided in connection to bearing assemblies and adapted to measure temperature, load and rotational speed for the bearing assemblies; 
     a communication interface for transferring the values measured by the sensors to the central processing unit, wherein the values measured by the sensors includes bearing load, bearing temperature and bearing rotational speed are collected from the bearing assemblies during operation; and 
     an instruction set providing operational directions to the central processor unit, the instruction set including an instruction step of utilizing the data for calculating a value for current lubrication interval t.sub.f, and 
     an instruction step of comparing the initial value with the current value, and calculating a correct lubricant volume associated with a current relubrication interval t.sub.f; and 
     an automatic lubrication apparatus in communication with the central processing unit, the automatic lubrication apparatus arranged to feed out the correct lubricant volume to the bearing assemblies in accordance with the calculated correct relubrication interval t.sub.f calculated by the central processing unit in accordance with the instruction set based upon the current values measured by the sensors. 
    
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
       The invention will now be described with reference to the accompanying drawings which show a non-limiting example of embodiment thereof and in which: 
         FIG. 1  shows—as described hereabove—an example of a relubrication interval chart, used for establishing the correct initial relubrication intervals. 
         FIG. 2  is a flow chart showing the principle of the new system according to the invention, 
         FIG. 3  is a flow chart illustrating an embodiment of the method according to the invention, and 
         FIG. 4  is a flow chart illustrating a further embodiment of the method according to the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As described above, at the earlier common method of establishing appropriate relubrication intervals for grease lubrication, is used a relubrication interval chart of the type illustrated in  FIG. 1 . With aid of such an implement it is possible to find the estimated relubrication interval t.sub.f for a number of bearings connected to the system operating at an expected temperature, at a predetermined load and at a rotational speed, which is substantially constant. The speed factor A is multiplied with the bearing factor b.sub.f, which is depending on the bearing type and load conditions C/P. 
     In the example illustrated in  FIG. 1  the Ab.sub.f-value of a bearing is expected to be &lt;&lt;475000 and the C/P ratio=8, and when a vertical line is drawn from the Ab.sub.f-axis to meet the curve representing the C/P ratio and a horizontal line is then drawn from the intersection between the C/P value and the Ab.sub.f-value it is seen that the relubrication interval t.sub.f will be 1000 operating hours. As for instance a 15 degree increase in operating temperature above 70 degrees centigrade means that the relubrication interval should be half that obtained with the initial temperature, it is of course important that the temperature may not vary too much, and also that the other factors (load and rotational speed) during an operating period, as the t.sub.f-values estimated with the earlier method could be drastically reduced if the operating conditions are altered. 
     In  FIG. 2  is illustrated schematically a bearing assembly  1  equipped with a sensor  2  for measuring the bearing temperature in real time during the operation of the bearing assembly. Furthermore there is arranged a second sensor  3  arranged to detect the current load to which the bearing assembly is subjected, and finally, in the embodiment illustrated, there is also provided a third sensor  4  arranged to measure the rotational speed of the bearing assembly and to emit a signal representative for the speed. The values from all sensors  2 ,  3  and  4  are transmitted in appropriate manner by cable or by wireless transmission from the bearings to a processor unit  5 , arranged to calculate in real-time the required relubrication interval, also referenced as a current anticipated relubrication interval, based on the just measured current values, or last calculated preceding anticipated value for the relubrication interval, for the parameters temperature, rotational speed and load, and to emit continuously or intermittently signals to an automatic lubricating apparatus  6 , which is arranged to deliver to the individual bearings a dynamic volume of lubricant, thus calculated during operation. 
     In  FIG. 3  is schematically shown a flow chart illustrating a first embodiment of the method according to the invention, performed by the processor unit  5 . The method sequence is started at box  7  from where the sequence is transferred to box  8  where initial values are calculated, e.g., in the same manner as previously, i.e. with aid of a relubrication interval chart, as described and illustrated with reference to  FIG. 1 . 
     Data measured by the sensors  2 ,  3  and  4  in  FIG. 2  are supplied at  9  and are inputted at  10 , i.e. the current values for temperature, load and rotational speed to which the different portions of the bearing assemblies are subjected. 
     In box  11  a new interval t.sub.f is calculated and this new t.sub.f value is compared in box  12  with the initial t.sub.f value. If the new t.sub.f value differs from the initial t.sub.f value i.e. falling below the initial t.sub.f value, the new t.sub.f value is introduced after calculation in box  13  as a new current t.sub.f value. This new current t.sub.f value then is supplied to box  14 , where a correct amount of lubricant is calculated for the current t.sub.f value. 
     In the event that the calculated t.sub.f value is not smaller than the initial or current t.sub.f value, the initial or current t.sub.f value is supplied directly to the box  14 . 
     The current relubrication interval t.sub.f and the amount of lubricant required is output from box  15  to a comparison box in  16  where the current time is compared to the value of the interval t.sub.f received from box  15 . 
     If the actual time and the preset relubrication interval time coincide, information is outputted to the box  17 , from which is delivered a lubrication impulse to the automatic lubrication apparatus  6  shown in  FIG. 2 , and from this position the sequence is restarted after an impulse is issued to box  8 . 
     If there is a difference between the actual time and the calculated relubrication interval t.sub.f&gt;the comparison box emits a signal to box  10  for inputting load, temperature and speed values representing the instantaneous conditions, delivered by the box  9 . After such a signal has been sent out and the current data has been inputted, the sequence is repeated via the boxes  11 - 16 . The sequence includes the steps of collecting data, using the current data, and comparing the current anticipated value until the automatic lubrication apparatus provides lubricant to the bearing. 
     The input data required can be read continuously or intermittently and the signals emitted by the box  15  are preferably delivered to an electromagnetic valve of any appropriate type. 
       FIG. 4  illustrates a flow chart of a further embodiment of a method according to the invention. 
     After start of the system in this case there is made a calculation of initial values in box  18 , whereupon load, speed and temperature variables are inputted in  19 , together with details of current running condition, which are introduced from box  20 . 
     In box  21 , runtime calculations are performed to establish a new t.sub.f value, and in box  22  this new t.sub.f value is compared to actual t.sub.f value. If the result of this calculation is that the new value is smaller than the actual, then the new t.sub.f value is entered in box  23  as current actual t.sub.f value, and if not the “old” actual t.sub.f value is inserted in box  24 , where the grease amount required is calculated and set. In the event the comparison in box  22  results in a “Yes”, the new actual t.sub.f value as obtained in box  23  is used for the grease amount calculation in box  24 . The current values from box  24  are displayed in box  25 , and in box  26  it is considered if it is time to relubricate or not. If the comparison results in a “No”, a new calculating process is initiated in box  19 . If the comparison in box  26  results in a “Yes” in box  27  it is established if the last set grease amount is bigger than the minimum amount that the system can deliver in a relubrication cycle. In such case the relubrication is performed at  28  and the amount is returned to box  29  in which it is established whether the maximum grease amount is reached or not. If this comparison is positive in box  30  is displayed message regarding removing grease and requiring reset, whereas at a negative result, i.e. if the maximum grease amount has not been reached. The sequence is again returned to box  19  for start of a new relubrication cycle. If the result of the comparison in box  27  is negative, i.e. the last set lubricant amount is not bigger than the minimum amount the system can deliver, it is first established in box  31  if the maximum cycles of withhold lubrication has been reached. If the result from this comparison is “Yes” at  32  a relubrication is forced and the amount is returned to box  29 . In case of a “No” at this location in box  33  is initiated that the relubrication should not be executed and the number of hold the relubrication cycles is incremented. The sequence thereupon is continued in box  29 . 
     In this embodiment thus the system will check if the last set amount of grease is larger than the minimum amount the system can deliver in a relubrication cycle. If the last set amount is greater than the minimum amount, the system will trigger a relubrication sequence and add the amount of grease to a “grease amount variable” (box  29 ). 
     If the last set amount of grease is lower than the minimum amount, the system will hold the lubrication cycle for the next time, but this can only be effected for a preset number of times. 
     If the maximum number of hold cycles is reached, the system will act for enforcing a relubrication and add the amount to the “grease amount variable”. 
     Before returning to the main loop, the system will check the total amount of lubricant, which has been supplied to the bearing, “grease amount variable” against a “maximum grease amount variable”. 
     When the maximum amount has been reached, the system will enter a never ending loop, telling the operator to stop, clean and reset. 
     With methods and systems as described hereinabove, the problem associated with incorrect input data regarding load, temperature and rotational speed at determination of lubrication interval is eliminated. 
     The method and system further makes it possible to apply a dynamically adjustable lubrication interval and/or an adjustable lubricant quantity during operation of the bearing assemblies associated with the system.