CORRECT AUTOMATIC RELUBRICATION FOR A NUMBER OF BEARINGS

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 _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 b _f , 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 A b _f « 475000 and a C/P ratio = 8, it can be seen that the calculated t _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 _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 method for this purpose is characterized by the characterizing features of the accompanying claim 1 , whereas a system for effecting this is characterized by the features in the accompanying claim 7.

Brief summary of the drawings 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 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 _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 _f , which is depending on the bearing type and load conditions C/P.

In the example illustrated in Fig. 1 the A b _f -value of a bearing is expected to be « 475000 and the C/P ratio = 8, and when a vertical line is drawn from the Ab _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 Abf-value it is seen that the relubrication interval tf 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 _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 based on the just measured current values 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 _f is calculated and this new t _f value is compared in box 12 with the initial t _f value. If the new t _f value differs from the initial t _f value i.e. falling below the initial t _f value, the new tf value is introduced after calculation in box 13 as a new current t _f value. This new current t _f value then is supplied to box 14, where a correct amount of lubricant is calculated for the current t _f value.

In the event that the calculated tf value is not smaller than the initial or current t _f value, the initial or current t _f value is supplied directly to the box 14. The current relubrication interval t _f and the amount of lubricant required is output from box 15to a comparison box in 16 where the current time is compared to the value of the interval t _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 _f> 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 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, whuchh are introduced from box 20.

In box 21 , runtime calculations are performed to establish a new t _f value, and in box 22 this new t _f value is compared to actual t _f value. If the result of this calculation is that the new value is smaller than the actual, then the new t _f value is entered in box 23 as current actual t _f value, and if not the "old" actual t _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 _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" ate 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.