GB1570534A - Measurement of torsional vibration - Google Patents

Description

(54) IMPROVEMENTS IN AND RELATING TO THE MEASUREMENT OF TORSIONAL VIBRATION (71) We, WALLACE MURRAY CORPORATION, a corporation organized and existing under the laws of the State of Delaware, United States of America, having its principal place of business at, 299 Park Avenue, New York, State of New York, United States of America, (assignee of ROBERT CHARLES BREMER, JR., and HANS OTTO HAUPT), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a device for measuring torsional vibrations of a rotating shaft and more particularly to a device for measuring the performance of a torsional vibrational damper.

Many types of rotating machinery are subject to torsional vibrations. This is especially true of internal combustion engines wherein each cylinder contributes a discrete force (impulse) of short duration, thereby causing the crankshaft to rotate.

There is accordingly a - discontinuous application of force to the crankshaft and this, coupled with the mass and elasticity of the metal crankshaft, gives rise to torsional vibrations. Such vibrations may be considered as small amplitude back and forth twistings of the crankshaft, superimposed upon the main, unidirectional rotation of the crankshaft.

Unless controlled, torsional vibrations may attain relatively high amplitudes and lead to fatigue failure of the crankshaft, as well as various related problems in accessories driven by the crankshaft. This crankshaft behaviour has long been known to workers in the automotive art and a great number of constructions have evolttd for damping torsional vibrations. A common form of torsional vibration damper is defined by a hub member adapted to be attached to the end of an engine crankshaft. The hub carries an inertia member, the hub and inertia members usually coupled by elastomer or partially abutting frictional material. In a great number of torsional vibration dampers, the theory of operation is that the energy which causes the torsional vibrations is converted into heat in either the frictional material or the elastomer.

Thus, less energy is available to cause relatively high vibrational amplitudes than without the damper.

In the fabrication and design of torsional vibration dampers, it is often desirable to determine damper efficiency and damper performance, the efficiency and performance being to what degree vibration is controlled or altered and the frequency response of the damper itself, respectively.

A number of constructions are known which measure the torsional vibrations of a rotating shaft. Examples are afforded by, but not necessarily limited to, the following U.S. patents: Chilton, 1,568,544; Summers, 1,571,359; Schrater, 2,193,079; Dashefsky, 2,219,298; Zmuda, 2,491,240; Ciringione, 3,054,284; and Collette, 3,195,381.

According to the present invention there is provided a method of measuring the performance of a rotating torsional vibration damper, the damper having a hub adapted to be coupled to a rotating shaft, the shaft being subject to torsional vibrations while rotating, the hub carrying an annular inertia member with an annular elastomer band located therebetween, whereby the inertia member torsionally vibrates out by phase with the torsional vibrations of the hub, the method comprising the steps of measuring the entire angular motion of said hub to produce a first signal, measuring the entire angular motion of said inertia member to produce a second signal, processing said first and second signals to substantially remove portions thereof corresponding to unidirectional rotary motion of the shaft, whereby first and second signals corresponding to hub oscillating motion and inertia member oscillating motion along respectively, are obtained, and comparing said first and second processed signals, to thereby measure damper performance.

According to a further aspect of the present invention there is provided a system for measuring the performance of a rotating torsional vibration damper, the damper having a hub adapted to be coupled to a rotating shaft, the shaft being subject to torsional vibrations while rotating, the hub carrying an annular inertia member with an annular elastomer band located therebetween whereby the inertia member torsionally vibrates out of phase with the torsional vibrations of the hub, the system comprises means for measuring the entire angular motion of said hub to thus produce a first signal, means for measuring the entire angular motion of said inertia member to thus produce a second signal, means for processing said first and second signals to substantially remove portions thereof corresponding to unidirectional rotary motion of the shaft, whereby first and second signals corresponding to hub oscillating motion and inertia member oscillating motion alone respectively are obtained, and means for comparing said first and second processed signals, to thereby measure damper performance.

The efficiency and performance of a torsional vibration damper are measured in accordance with the present invention, by sensing the motion of the hub member (rigidly coupled to the rotating crankshaft) and by simultaneously sensing the motion of the inertia member. The sensed motions are compared and the efficiency and performance calculated. In general, damper performance and efficiency include such parameters as the ratio of magnitudes of the inertia ring torsional vibration to the hub torsional vibration, at a given frequency; the phase relationship between the inertia ring and the hub; the ratio of the torsional vibration energy absorbed by the damper in a torsional system to the torsional vibration energy generated by the same system or in general the effect the damper has on the torsional system. The manner of sensing the motions is carried out by optical means.In general, it is known to optically sense the motion of a rotating member. Such optical sensing is illustrated by, but not necessarily limited to, the following U.S. patents: Aronoff, 1,878,658; Johnson, 3,146,432; Woods, 3,323,051; Gardner, 3,706,494. In the practice of the present invention, the optical sensing is preferably facilitated by a decalcomania placed upon one face of the damper. The decalcomania includes radial bands or sectors of alternating black and white, the sectors or both the hub member and the inertia member being initially angularly aligned. However, under the influence of torsional vibrations, the angular alignment changes as a result of the difference in vibration amplitude and general lagging phase relationship of the inertia ring relative to the hub inherent in a damped spring-mass system. This change is measured to make the calculations of performance.The calculations are carried out continuously by an electronic system.

Various parameters available in real time from the system include hub vibration amplitude, amplitude and phase of the inertia mass vibration relative to the hub, elastomer stress, engine rpm and various other derived parameters.

The invention is described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an elevational view of an optical sensor of this invention positioned at the end of a shaft carrying a torsional vibration damper.

Figure 2 is a view taken along section 22 of Figure 1, with some elements schematically shown.

Figure 3 is a vectorial representation of the torsional vibration of each of the hub and inertia members.

Figure 4 is a partially schematic view of an electro-optical system for continuously displaying damper performance by generating and processing certain electrical signals derived from the optical sensing of damper motion.

Referring now to Figures 1 and 2 of the drawings, the numeral 10 denotes an end of a rotating shaft subject to torsional vibration, the shaft 10 may be for example the crankshaft of an internal combustion engine. The numeral 12 denotes a torsional vibration damper of known construction and typically includes an outer inertia member 14 and an inner hub member 16, the latter rigidly coupled to shaft 10. The inertia and hub members are coupled by an elastomeric band 18.

The numeral 22 denotes a source of illumination and includes a length of an internally deflecting fiber optic bundle for projecting light on the left face of inertia member 14. Numeral 24 represents a source of illumination similar in construction to source 22, the former projecting light on the left face of hub 16. The numeral 26 denotes a cap on an end portion of shaft 10 and carries a printle bearing element 28, the member 28 extending through an arm 30 whose lower end carries a mass M. The arrangement of parts shown in Figure 1 is such that as shaft 10 rotates and also executes torsional vibrations, the hub member 16 rotates in exactly the same manner. Members 26 and 28 also rotate with shaft 10. By virtue of anti-friction elements (not illustrated) associated with pintle 28, the arm 30 remains in a substantially vertical position during shaft rotation.Accordingly, the light projection elements 22 and 24 do not significantly rotate with rotation of shaft 10.

The action of a vibration damper such as illustrated is known. Torsional vibrations of the shaft transmitted to hub 16 are not faithfully transmitted to inertia member 14.

The reason is that elastomer 18 does not define a rigid connection between the hub and inertia member and accordingly there is a lag or phase difference between the angular motion of ineria member 14 and that of hub 16. This difference in angular motion between the hub and the inertia member causes the elastomer to flex and ideally convert the torsional vibrational energy into heat within the elastomer material 18. That is to say, the radially innermost face of elastomer band or annulus 18 follows the torsional fibration of shaft 10, while the radially outermost annular face of the elastomer also twists back and forth, but lags because of the inertia of member 14.

A manner of measuring the phase difference between the hub and the inertia member will now be given by reference to figure 2. The numerial 40 denotes a circular decalcomania consisting of alternating black and white bands or sectors on one side thereof. The decalcomania 40 is adversely applied to the left face (see Figure 1 of damper 12. If there is a central recess in the damper, such as illustrated, the central portion of the decalcomania may be removed by cutting with a knife. By means of a knife or other suitable instrument the portion of the decalcomania which overlies the left edge of elastomer band 18 is removed. The result is a series of truncated, alternating black and white sectors around the left face of the damper. The sectors are radially divided by the radial width of elastomer 18.The white sectors attached to the inertia member are denoted by the numeral 42, while the white sectors attached to the hub are denoted by the numeral 48. The dark sectors attached to the inertia member are denoted by the numeral 44, while the dark sectors attached to the hub are denoted by the numeral 46.

The dashed lines at the left of center in Figure 2 illustrate the decalcomania prior to removal of its central portion. The decalcomania may be formed from paper or cardboard or the like, the paper carrying an adhesive on one face to facilitate attachment to damper 12.

As shown at Figure 1 and as schematically indicated in Figure 2, the fiber optic bundle in source 22 projects light onto the left face of inertia member 14 at the center of a white segment, the reflected light being directed into a photocell schematically denoted by the numeral 32. The photocell is also carried by arm 30. Similarly, the light emitted from the fiber optic bundle in illumination source 24 projects light onto the left face of hub 16 at the center of a black segment and this light is reflected into a photocell 34. As the damper rotates the two light beams will strike different regions, but the relative phase of the incident and reflected light of the respective light beams will be the same if there are no torsional vibrations. Photocells 32 and 34 are suitably connected to amplifiers.In practice, the transmitted and reflected light for each of the two optical paths is intermingled within a single fiber optic bundle. Thus, the fiber optic bundle of source 22 both projects and receives light, as does the bundle in source 24. The light reflected from the left face of hub 16 and inertia member 14 is converted in known manner into electrical signals by the photocells. Thus, when light is reflected from a white sector, the electrical output of the associated photocell will be relatively high (assuming a photovoltaic photocell).

When light is reflected from a dark sector, the photocell output will be relatively low.

Due to the different points of incidence between the two projected and reflected light beams, a phase shift of approximately 900 between the outputs of the two photocells is generated, and is independent of the rotational frequency.

The reader will now be in a position to recognize that if shaft 10 underwent no torsional vibration during its rotation, electrical signals generated by the two photocells would be 90" out of phase and of the same magnitude. However, in the presence of torsional vibration, the white sectors 42 and 48 will be at times out of their original angular alignment during rotation of shaft 10, as will dark sectors 44 and 46.

This angular misalignment will cause the phase of the electrical signals from the two photocell to change. Such change is detected and processed by an electrical circuit, to be described, to yield various dynamic performance parameters relative to the vibration.

If there is torsional vibration, the processed signals proportional to light reflected to the photocells will be periodic, and will vary in phase relative to each other proportional to the relative vibration of each member. In other words, the signals will be periodic but phase modulated, with the vibration amplitudes proportional to the amount of phase modulation. In addition, since the vibration damper is a dynamic system operating often near resonance, modulation will differ between these signals. A general shift in phase for each overall period of a given frequency will be present. The frequencies present in each signal will be the same.

Reference to Figure 3 illustrates one aspect of the behavior of the hub and inertia member rotating masses. The real component of vector pt represents the vibration of the hub relative to a circuit established reference. The real component of vector p2 represents the vibration of the inertia member relative to the same reference. The two vibrations are out of phase by an angle gamma and differ in magnitude by a factor M, where M is the ratio of magnitudes of the inertia ring torsional vibration to the hub torsional vibration, at a given frequency.

Referring now to Figure 4 of the drawings, an electrical system is schematically indicated for processing the photocell outputs to measure damper efficiency and performance. In Figure 4, the numeral 16 indicates the hub of Figure 1, while the numeral 14 indicates the corresponding inertia member. The illumination source 24 and the photocell associated with the hub are denoted by a box labeled 24, 34. The corresponding illumination source and photocell associated with the inertia member is denoted by a box labeled 22, 32. The unidirectional angular velocity of shaft 10 is denoted by W6, a typical value of which may represent an engine speed of 2100 rpm.The instantaneous angular displacement from the position defined only by w6 and time (t) of hub 16 due to torsional vibrations in the crankshaft 10 is denoted by ,B1 (t). Similarly, the instantaneous angular displacement from the position defined only by w8 and t of inertia member 14 due to torsional vibrations in the crankshaft 10 is denoted by p2 (t). Both such angular displacements will be alternatively in the same or in opposite directions with respect to the direction of rotation of the crankshaft at various times during engine operation.The instantaneous angular position of hub 16 as well as crankshaft 10 is denoted by Wet+/31(t), where We is the instantaneous unidirectional angular velocity of the hub and therefore Wet is the instantaneous position of the hub not considering vibration. Thus, the information received by amplifier A corresponds to Wet+P, (t).

This information is fed to a first phase feedback loop 01. The box denoted l is a phase feedback reference loop, known in the art. It has two input terminals denoted respectively 1 and 2, and an output terminal denoted by 3. Such a loop is described at, for example, page 355 of Reference Date For Radio Engineers, 1956, 4th Edition, published by International Telephone and Telegraph Co., the entire book being hereby incorporated by reference. The output of 01 is fed to a low pass filter and to a voltage controlled oscillator denoted by VCO.Then it passes to a divider denoted by K1 which generates an electrical signal corresponding to We but without the torsional vibration component p1t. A digital revolutions per minute indicator, denoted by RPM in Figure 4, will show exK, 60 The signal from amplifier A is also fed into another phase comparator denoted by the box 02 of construction similar to , with a signal corresponding to We impressed on its second input terminal.The output of 02 passes to a band pass filter or real time analyzer (a real time analyzer is analysis instrumentation designed to determine the magnitude of frequency components of a broad signal at the instant that the signal is being generated) or a variable frequency filter whose output corresponds to A,(t). The peak value thereof is indicated by meter M1. The signal from the band pass filter coupled to 02 is also amplified and fed to the Y axis terminal of a cathode ray tube denoted by CRT at the upper right-hand portibn ~ of Figure 4. The time base of X axis of this CRT is derived from the signal corresponding to We which is fed to divider K2 and its associated amplifier. A sawtooth generator (S.T.

GEN.) and frequency to voltage controller (F/V) feeds the automatic gain control (AGC). Here, the signal passes into meter M2 and thence to the X axis terminal of the CRT The signal fed to the input of amplifier B corresponds to We(t) and ,B2(t) where 2(t), as noted, corresponds to the instantaneous angular displacement of inertia member 14 from a position defined by Wet.The signal corresponding to We from divider K, is also fed into the second input terminal of a phase discriminator loop denoted by h (of construction similar to that of 0, and 12) and the output of 03 fed to a second band pass filter or real time analyzer or a variable filter, the output of the latter corresponding to 02(t). This is also amplified as indicated and fed to a cathode ray tube CRT and meter M.

The amplitude difference between A,(t) and j32(t) appears in the lower right summing amplifier F. The signals ,(t) and p2(t) are at the same time led to phase discriminator 04 which determines in its output the phase difference of the two input signals ,ss,(t) and ,B2(t). The discriminator 4i4 is of the same construction as . The reader will now be in a position to note that one function of the system shown at Figure 4 is to eliminate the effect of the uni-directional shaft rotational speed on the signals which are processed and utilized for display of damper performance.Thus, the system obtains ,Bl(t) and /32(t) substantially independent of speed. One performance parameter of the damper 12 can be denoted by 77 and is equal to the magnitude of /31(t) p1(t)+ss2(t) The meter M6 at the lower left of Figure 3 indicates this parameter and is fed from the indicated divider which performs the division.

The reader will note that a single source of illumination may be employed in lieu of the separate sources 22, 24. It will also be apparent that the bands 42, 44 and 46, 48 may alternate in magnetic qualities, radioactive qualities, etc., instead of alternating in optical absorption of light, provided a suitable change is made in the sensors 32, 34. Calibration may be carried out by known methods. For example, calibration can be achieved by shifting the fibe optic device 22 or 24 in an angular direction a certain amount so as to measure a specific displacement in terms of the width of one of the sectors. The amount of shift would have to be limited so as to measure a distance equal to or less than equivalent to one-half of one of the block sectors.The system may also be calibrated by removing 22 and 24 from 30 and placing them in a fixture for measuring the system response to a calibration disc where the width of the sectors 42-48 thereon is made to yield a synthetic calibration signal. The disc rotating without vibration will synthesize magnitude signals and phase shift by the nature of its uneven and offset sectors.

The signals corresponding to A1(t) and A2(t) may be suitably processed to yield any desired performance parameter of the damper, such as its dynamic characteristics or transfer function. For example, referring to Fig. 4, the several meters M1Me show the parameters indicated. The system of Fig. 4 permits measurement of several performance parameters of a torsional vibration damper no matter how fast the engine is turning. The frequency of the torsional vibrations will normally be higher than the rotation frequency of the shaft, a fact utilized by the system of Fig. 4. Further, the system effectively generates a smooth signal corresponding to engine speed if the engine speed is rapidly changing.

Additionally, prior art systems employing teeth on the periphery of rotating disc or hub elements have often employed, typically, sixty teeth. The number of black and white sectors employed with the present invention is much smaller and hence measurement of higher torsional vibration amplitudes is usually possible.

WHAT WE CLAIM IS: 1. A method of measuring the performance of a rotating torsional vibration damper, the damper having a hub adapted to be coupled to a rotating shaft, the shaft being subjected to torsional vibrations while rotating, the hub carrying an annular inertia member with an annular elastomer band located therebetween, whereby the inertia member torsionally vibrates out of phase with the torsional vibrations of the hub, the method comprising the steps of measuring the entire angular motion of said hub to produce a first signal, measuring the entire angular motion of said inertia member to produce a second signal, processing said first and second signals to substantially remove portions thereof corresponding to unidirectional rotary motion of the shaft, whereby first and second signals corresponding to hub oscillating motion and inertia member oscillating motion alone respectively, are obtained, and comparing said first and second processed signals, to thereby measure damper performance.

2. A method as claimed in claim 1 in which the entire angular motions of the said hub and the said inertia member are obtained by sensing light reflected from alternate black and white sectors attached to each of the hub and the inertia member.

3. A system for measuring the performance of a rotating torsional vibration damper, the damper having a hub adapted to be coupled to a rotating shaft, the shaft being subject to torsional vibrations while rotating, the hub carrying an annular inertia member with an annular elastomer band located therebetween whereby the inertia member tortionally vibrates out of phase with the torsional vibrations of the hub, the system comprising means for measuring the entire angular motion of said hub to thus produce a first signal, means for measuring the entire angular motion of said inertia member to thus produce a second signal, means for processing said first and second signals to substantially remove portions thereof corresponding to unidirectional rotary motion of the shaft, whereby first and second signals corresponding to hub oscillating motion and inertia member oscillating motion alone respectively are obtained, and means for comparing said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. is of the same construction as . The reader will now be in a position to note that one function of the system shown at Figure 4 is to eliminate the effect of the uni-directional shaft rotational speed on the signals which are processed and utilized for display of damper performance. Thus, the system obtains ,Bl(t) and /32(t) substantially independent of speed. One performance parameter of the damper 12 can be denoted by 77 and is equal to the magnitude of /31(t) p1(t)+ss2(t) The meter M6 at the lower left of Figure 3 indicates this parameter and is fed from the indicated divider which performs the division. The reader will note that a single source of illumination may be employed in lieu of the separate sources 22, 24. It will also be apparent that the bands 42, 44 and 46, 48 may alternate in magnetic qualities, radioactive qualities, etc., instead of alternating in optical absorption of light, provided a suitable change is made in the sensors 32, 34. Calibration may be carried out by known methods. For example, calibration can be achieved by shifting the fibe optic device 22 or 24 in an angular direction a certain amount so as to measure a specific displacement in terms of the width of one of the sectors. The amount of shift would have to be limited so as to measure a distance equal to or less than equivalent to one-half of one of the block sectors.The system may also be calibrated by removing 22 and 24 from 30 and placing them in a fixture for measuring the system response to a calibration disc where the width of the sectors 42-48 thereon is made to yield a synthetic calibration signal. The disc rotating without vibration will synthesize magnitude signals and phase shift by the nature of its uneven and offset sectors. The signals corresponding to A1(t) and A2(t) may be suitably processed to yield any desired performance parameter of the damper, such as its dynamic characteristics or transfer function. For example, referring to Fig. 4, the several meters M1Me show the parameters indicated. The system of Fig. 4 permits measurement of several performance parameters of a torsional vibration damper no matter how fast the engine is turning. The frequency of the torsional vibrations will normally be higher than the rotation frequency of the shaft, a fact utilized by the system of Fig. 4. Further, the system effectively generates a smooth signal corresponding to engine speed if the engine speed is rapidly changing. Additionally, prior art systems employing teeth on the periphery of rotating disc or hub elements have often employed, typically, sixty teeth. The number of black and white sectors employed with the present invention is much smaller and hence measurement of higher torsional vibration amplitudes is usually possible. WHAT WE CLAIM IS:

1. A method of measuring the performance of a rotating torsional vibration damper, the damper having a hub adapted to be coupled to a rotating shaft, the shaft being subjected to torsional vibrations while rotating, the hub carrying an annular inertia member with an annular elastomer band located therebetween, whereby the inertia member torsionally vibrates out of phase with the torsional vibrations of the hub, the method comprising the steps of measuring the entire angular motion of said hub to produce a first signal, measuring the entire angular motion of said inertia member to produce a second signal, processing said first and second signals to substantially remove portions thereof corresponding to unidirectional rotary motion of the shaft, whereby first and second signals corresponding to hub oscillating motion and inertia member oscillating motion alone respectively, are obtained, and comparing said first and second processed signals, to thereby measure damper performance.

2. A method as claimed in claim 1 in which the entire angular motions of the said hub and the said inertia member are obtained by sensing light reflected from alternate black and white sectors attached to each of the hub and the inertia member.

3. A system for measuring the performance of a rotating torsional vibration damper, the damper having a hub adapted to be coupled to a rotating shaft, the shaft being subject to torsional vibrations while rotating, the hub carrying an annular inertia member with an annular elastomer band located therebetween whereby the inertia member tortionally vibrates out of phase with the torsional vibrations of the hub, the system comprising means for measuring the entire angular motion of said hub to thus produce a first signal, means for measuring the entire angular motion of said inertia member to thus produce a second signal, means for processing said first and second signals to substantially remove portions thereof corresponding to unidirectional rotary motion of the shaft, whereby first and second signals corresponding to hub oscillating motion and inertia member oscillating motion alone respectively are obtained, and means for comparing said

first and second processed signals, to thereby measure damper performance.

4. A system as claimed in claim 3, in which said means for measuring the entire angular motion of said hub and of said inertia member includes alternate black and white sectors attached to each of the hub and the inertia member, said measuring means also including a light source and a light senser for each of the hub and the inertia member.

5. A system as claimed in claim 3, in which said processing means includes a cathode ray tube for yielding a visual display of damper performance.

6. A system as claimed in claim 4, in which said sectors are located on an axial face of the hub and an axial face of the inertia member.

7. A system as claimed in claim 3, in which a magnetic sensing arrangement forms said means for measuring the entire angular motion of said hub and of said inertia member.

8. A method substantially as herein described with reference to the accompanying drawings.

9. A system substantially as hereinbefore particularly described with reference to and as illustrated in the accompanying drawings.