FR2660756A1 - DEVICE AND METHOD FOR IMPROVING THE EVALUATION OF THE PERFORMANCE OF A LUBRICANT. - Google Patents

Abstract

Device for improving the evaluation of the performance of a lubricant by loading a stationary part (11) on a mobile part (12), the two parts being in point, linear or surface contact, in the presence of the lubricant to be tested, characterized in that a jack (8) acts on one of the parts and a load sensor (9) continuously measures the applied force and transmits it to a regulation device which acts on the control fluid of the jack in such a manner that it is kept essentially equal to a programmable reference value, which is constant or variable with respect to time. Process for using the above-mentioned device by linking it to a computer.

Description

 The present invention relates to a device and a method for improving the evaluation of the performance of lubricants.

 Measuring the characteristics of lubricants and in particular evaluating their dynamic behavior when two surfaces rub against each other is very important both for manufacturers if they want to be able to improve their performance and for users if they want to properly appreciate the possibilities given the intended use.

 Currently, such an assessment is made using devices the principle of which is as follows: in the presence of the lubricant which it is desired to test, two parts are rubbed against each other for a given time. conditions as close as possible to reality.

 The devices are made in such a way that, at the start of the test, it is possible to manually adjust the characteristic parameters of the test, in particular the force exerted between the two parts, the relative speed between the friction surfaces and the temperature. lubricant.

 Such devices have several drawbacks.

First of all, the devices for applying the load between the two contact zones are not very precise and can be adjusted during operation, in particular due to the relative wear of the two friction surfaces. The reproducibility of one test compared to another is therefore poor. In addition, the force between the two contact zones is adjusted manually, so that the changes that can be made during a test require the intervention of an operator. The same applies to the other characteristic values which are generally set manually at the start of a test and are no longer modified until the end.

 Apparatuses known in the state of the art also have the drawback of not measuring the wear between the two contact zones during the entire test cycle.

 The object of the present invention is to overcome the above drawbacks, thus making it possible to subject the lubricants to be tested to predefined and perfectly reproducible test cycles.

 It is a device for evaluating the performance of lubricants by loading a fixed part on a moving part, said moving part being actuated by a motor, the two parts, surrounded by a tank intended for contain or collect the lubricant to be tested, being in punctual, linear or surface contact characterized in that a jack acts on one of the parts, a force sensor permanently measuring the applied force and transmitting it to a regulating device acting on the control fluid of said cylinder so that the force applied between the two parts is maintained substantially equal to a programmable set point. Said cylinder will be chosen from a type having very low friction, such as a membrane cylinder, so as to ensure good regulation precision.

 In order to follow precisely and continuously the behavior of the parts in friction, behavior reflecting the more or less good behavior of the lubricants ensuring the lubrication of the parts in contact, the present invention is characterized in that the depression is constantly measured progressive relative of a part compared to the other, depression equal to the wear between the two parts in contact, by means of a displacement sensor with great resolution. To do this, the measurement made by the sensor is memorized at the start of the test, this initial measurement then being permanently subtracted from the measurement made during the test. This continuously measures the wear between the two parts.

 The present invention also consists of a method intended to ensure the implementation of a test of the dynamic characteristics of a lubricant according to the above device. This process is characterized in that it comprises a series of elementary phases. Each of these phases fixes a value for the test parameters such as, in particular, contact pressure of the friction parts, oil temperature, speed of the moving part, one or more of these values being able to vary during the duration of the phase. It is indeed possible, for example, to fix the friction pressure and the speed of the moving part while determining a law of temperature progression between an initial value and a final value in a given time.

In the method, each of the elementary phases whose characteristic values and duration have been memorized are executed successively in accordance with a programmed sequence, the programmable control means ensuring throughout the duration of the test the measurement and storage of the quantities characteristic of the behavior of the lubricant, in particular the measurement of wear, coefficients of friction and electrical resistance of contact between parts.

The invention will be better understood from the description below, which relates to a preferred embodiment, given by way of nonlimiting example, and explained with reference to the accompanying drawings - Figure 1: a schematic representation of a machine for testing lubricants in which the test pieces are subjected to a reciprocating movement - figure 2: a schematic representation of a machine for testing lubricants in which the test pieces are subjected to a rotational movement - figure 3: represents the force regulation loop applied between the two parts - figure 4: represents the lubricant temperature regulation loop - figure 5: represents the speed regulation loop of the two parts in relative movement - figure 6: represents the assembly of a displacement sensor intended to measure the wear between the two test specimens - figure 7: represents the device of acquisition of computer data
Figure 1 is a diagram showing a machine where the friction test pieces are subjected to each other in a reciprocating motion. It is a tribometer manufactured by the company PLINT / CAMERON. The operating principle of the machine is as follows. In a tank (1), intended to collect and contain the lubricant to be tested, is placed a test tube (11) representative of the parts which must, in real service, lubricate the oil which is being tested. The test piece (11) is in contact with another (12) itself carried by a support (2) which is actuated longitudinally by means of a motor (5) and a connecting rod-crank system (6 In the machine as proposed by the manufacturer, the loading device was reduced to a simple dial dynamometer. In the device according to the invention, the load is generated by a jack (8), the rod of which is connected to the chassis of the machine and the body to a thrust reversal piece (7) and transmitted to the support (2) by through a rod (6), a lever arm (5) acting on the stirrup (4) pressing on the support (2) via a bearing device (3). The cylinder, pneumatic or hydraulic, must have very low friction to ensure good regulation accuracy. To do this, we choose a diaphragm cylinder.

In order to ensure precise equality of the force and its setpoint, a force sensor (9) is placed between the thrust reversal piece (7) and the rod (6).

 The regulation loop is shown in FIG. 3. The force setpoint is delivered by a computer (20) transmitted to a regulator (21) via a communication interface (23). The regulator (21) ensures the value of the applied load via a force sensor (9) and an I / P converter (24) acting on the cylinder (8).

The regulation thus designed makes it possible to limit in all cases the relative difference between setpoint and measurement to 2 per 1000.

 FIG. 2 represents the application of the invention to another type of tribometer where the parts put in friction have a circular movement.

It is a device manufactured by the company
FALEX. The operating principle of the machine is as follows: an axis (32) made of material representative of those which oil or grease will have to lubricate in normal use, is driven in rotation by a motor. Two shoes (31), made of representative material, are applied to the axis (32) by the arms (33) and (34) articulated at (35). According to the invention at the other end of these arms, a cylinder (8) will be placed, acting by means of a part (37) carrying a force sensor (9).

 The regulation loop is identical to that of the machine shown in Figure 1. It is therefore shown in Figure 3. It should be noted however that in this case the force applied by the cylinder is amplified by the leverage due to the arms (33) and (34). The amplification ratio can reach ten.

 The temperature regulation of the lubricant is shown in FIG. 4. The temperature setpoint is delivered by the computer (20) to a regulator (42) via a communication interface (41). The measurement is carried out by a thermocouple (43). Heating is provided by a heating resistor (44) supplied by a power block (45). A contact (46), controlled by the computer (20), authorizes heating.

 The speed regulation of the two parts in relative motion, whether the alternating tribometer or the rotary tribometer, is shown in Figure 5. The motor is fitted with a speed variator as standard. The computer (20) drives a voltage generator (26) through an interface (25). This voltage is transmitted to the frequency converter (27) through an optical coupler (28) providing electrical insulation between the two systems, which prevents significant voltages which could appear at the frequency converter from damaging a part of the control electronics.

 The two test pieces rubbed by one or the other of the machines undergo wear. This wear is a function in particular of the greater or lesser efficiency of the lubricant, so it is advantageous to follow its progress continuously during a test. FIG. 6 represents the way in which the reciprocating tribometer has been equipped with a device making it possible to continuously monitor this wear. To do this, we measure the progressive sinking of the loading device, the vertical movement of which is directly linked to the wear between the two samples.

To measure the displacement of the stirrup, a capacitive sensor (62) is used in preference to sensors of the inductive type, the accuracy of which is less good. Indeed, no amplification of the wear being carried out, it is necessary that the sensor is at very high resolution because of the low wear involved, of the order of a few tens of microns.

 Said sensor is held above the stirrup by means of an adjustable arm bracket (63) on a fixed upright (64). A removable piece (61), of great hardness, is interposed between the caliper and the sensor in order to solve the problems of vibratory wear (fretting) due to possible vibrations.

 In order to follow the wear and not the position of the caliper and this with the greatest possible precision, the computer was used to memorize, at the start of the test, the position of the caliper and to permanently subtract this value from all subsequent positions. The wear value is therefore permanently obtained since the start of the test.

 The device described above for measuring wear will be applied in an equivalent manner for a rotary tribometer. In this case the capacitive displacement sensor will be placed at the end of the lever arms, so that the measurement obtained will be amplified by a ratio depending on the constructive characteristics of the machine.

 Machines sold commercially allow the measurement of the lubricant temperature, the contact resistance and the friction force between the two test pieces. This information will be entered by the computer implementing all of the operations.

 We have seen above that the computer coupled to the tribometer performs the functions of regulating the load, the temperature and the relative speed of the two friction parts. It will also ensure the start-up of the electric motor and the heating power.

 An example of data acquisition is shown in Figure 7. An ADFO card (71) from INFOTEK allows the acquisition over 12 bits of 16 normal channels at a frequency of 100 kHz.

Between this card (71) and the various signal sources (75) two voltage adaptation modules (72) and (73) are placed in order to respect the input voltage of the acquisition card. The modules allow you to adjust the gain and offset on the signal using potentiometers. The wear / displacement measurement (74) directly attacks the acquisition card (71).

 The software distinguishes two types of acquisition, a so-called fast for instantaneous friction and contact resistance signals and a so-called slow acquisition for the other measurements.

 The rapid acquisition can be viewed in real time, thus ensuring an oscilloscope function.

 The method for evaluating the characteristics of a lubricant is implemented according to the above device.

 Said method is characterized in that a series of elementary phases is executed, said phases being executed successively in accordance with a programmed sequence executed by a computer.

 Each elementary phase fixes the value of the various test characteristics for a given duration. They are carried out by the implementation by the computer of a common program into which the values of the various parameters are entered. The load applied between the two test pieces can be set interactively, from zero to the maximum admissible load by the tribometer, the speed of the moving part by fixing the motor speed between zero and the maximum admissible speed and the temperature of the lubricant between room temperature and four hundred degrees celtius.

If for any of these parameters no value is entered in the program it will be taken equal to a default value. Likewise, enter the total duration of the phase.

We will distinguish the case where all the parameters are fixed throughout the duration and the case where the phase allows for a parameter the passage from one value to another according to a ramp generated by the computer. If no duration is requested it is imposed by default.

 By way of nonlimiting example, in the case of a CAMERON PLINT machine, the adjustment ranges and the default values of the various parameters are from 2 to 50 hertz for the test frequencies the default value being 20 hertz , from 5 to 250 newtons for the load the default value being 40 newtons and from 20 to 400 "C for the temperature the default value being 20 C. For this same machine the duration of the phase can be chosen between 1 minute and 10 hours the default time being 1 hour. If one wishes to generate ramps, the phase durations must be chosen compatible with the possibilities of variation of the parameters. Thus for the CAMERON PLINT machine a charging ramp may last from 1 second to 5 minutes, the default time being 40 seconds, a temperature ramp can last from 1 minute to 2 hours, the default time being 20 minutes and a frequency ramp can last from 10 seconds to 1 minute the default time being 30 seconds.

 Each of the elementary phases will also be characterized by the possibility of acquiring, during its duration, one or more of the measurements accessible to the computer, in particular the measurement of wear, set to zero or not at the start of the phase, the electrical contact resistance and the friction force between the two test pieces.

 It will thus be possible to predetermine as many elementary phases as desired, these phases being stored by the computer. Their number will only depend on its capacity.

 All of these phases must then be performed in a predetermined order to perform a full test.

The computer will ensure the implementation of the method according to the invention. The stages will be as follows - Choice of the test to be carried out: either it exists in memory and it will be enough to call it or it does not yet exist and it will be necessary to create it before by linking in a program the elementary phases previously memorized.

- Creation of a file intended to receive the values measured during all the test and preparation of the visualization console associated with the computer.

- Printer initialization.

- Launch of phase 1 and execution of setpoints and ramps with data acquisition if planned by the program.

The acquired data are stored as and when they are entered on the file created for this purpose at the start of the test.

- When phase 1 is completed, automatic launch of phase 2 provided for by the program corresponding to the chosen test.

- Successive launching of the phases until the last.

- Launch of an automatic edition of the data collected during the test in the form of a test report.

- End of test.

 The various process steps are carried out according to a program. If this program exists, it will be called by the computer. If it does not exist, it will be created before test by the operator who, as and when the requests appearing on the console screen, will successively enter the elementary phases which he wishes to appear there with, if necessary, creation of those that have not yet been created. As this program is created, the computer checks the compatibility of the various phases with each other and at the end of creation checks the overall compatibility of the program with respect to the test envisaged.

 The implementation of the method therefore makes it possible to carry out on fully commercial machines modified according to the invention fully automatic tests, perfectly reproducible and implemented very easily thanks to the storage of the elementary phases and of the sequences of the phases in question in the memory d 'a calculator.

 It goes without saying that numerous modifications can be made to the device and to the process without departing from the scope of the invention.

Claims (11)

1 - Device intended for the evaluation of the performances of  lubricants by loading a fixed part (11)  (31) on a moving part (12) (32), the two parts,  surrounded by an oil tank (1) being in contact  point, linear or surface, characterized in  that a cylinder (8) acts on one of the parts, a sensor  effort (9) continuously measuring the applied force  and transmitting it to a regulator  acting on the control fluid of said cylinder so  that the force applied between the two parts is  maintained substantially equal to a setpoint  programmable, fixed or variable in time. 2 - Device according to claim 1 characterized in that  that the cylinder (8) is of a low friction type, such  than a diaphragm cylinder. 3 - Device according to claim 1 characterized in that  that the temperature of the friction parts is  maintained equal to a programmable setpoint by  regulating the temperature of the oil bathing or  spraying said parts. 4 - Device according to claim 1 characterized in that  that the relative movement of the pieces is a movement  alternative 5 - Device according to claim 4 characterized in that  that the frequency of the movement kept equal to one  programmable setpoint by speed regulation of a  motor (5) driving a rod type system  crank (6). 6 - Device according to claim 1 characterized in that  that the relative movement of the pieces is a movement of  rotation. 7 - Device according to claim 6 characterized in that  that the speed of rotation is kept equal to one  programmable setpoint by speed regulation of a  engine. 8 - Device according to one of claims 4 or 7  characterized in that the coupling between the dimmer  speed (27) of the motor and the controls is a  optical coupling (28). 9 - Device according to claim 1 characterized in that  that we continuously measure the progressive sinking  relative from one part to the other, sinking  equal to the wear between the two parts by means of a  high resolution proximity sensor (62). 10- Device according to claim 9 characterized in that  that we memorize at the start of the test the measurement made by  the sensor (62), this initial measurement being in  permanently cut off from the measurement under test on  result of this operation continuously giving the  wear value at the contact between the two  rooms. 11- Device according to any one of claims  previous characterized in that the tribometer is  coupled to a computer (20) by an acquisition system  of data. 12- Application of the above device, according to one of  claims 1 to 11, to the implementation of a test of  dynamic characteristics of a characterized lubricant  in that it comprises a series of elementary phases  consisting of each of them imposing  values programmed to the different test parameters at  namely, in particular, contact pressure, oil temperature, frequency of the moving part, one or more of these values which can be variable during the duration of said phase, each of these elementary phases of predetermined duration being executed successively in accordance with a programmed sequence, the programmable control means ensuring, throughout the duration of the test, the measurement and storage of the values of wear, friction, contact resistances and controlled variables.