METHOD FOR CONTROLLING A VIBRATION DAMPING DEVICE

Abstract: A vibration damping device includes first and second accelerometers (134, 136) which are used to determine the relative displacement between a body and a base between which the device is operatively connected. The output of one of the accelerometers (134, 136) is also monitored in a manner to determine the frequency of the vibration. This data is processed in a manner to ascertain the timing when the phases of a vertical spring input (produced by the compression of an elastomeric member (106) which defines the main spring of the damper) and an expansion spring input (produced by the displacement of rheopetic fluid between first (120) and second (122) variable volume chamber and the associated expansion characteristics of the members defining the same) are reversed. Using this data and the vibration frequency data the timing with which a voltage should be applied to electrodes (124a, 124b) disposed in an orifice (124) interposed between the first and second chambers (120, 122) to increase the viscousity of the rheopetic fluid and increase the flow resistance of the orifice (124). The device further includes a perforate suspended mass (126) which is tuned in a manner to act as a dynamic damper.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for controlling damping devices such as those including fluid filled elastomeric members and the like and more specifically to an improved arrangement which permits the damping characteristics to be controlled by sensing the parameters which vary with the vibration and producing a suitable control signal which can be applied to the member. Description of the Prior Art JP-A-60104828 discloses an arrangement wherein a damper is comprised of an annular rigid member on which a main elastomeric body and a flexible elastomeric diaphram are supported in a manner an enclosed space which is filled with a suitable working fluid which exhibits rheopectic properties. A partition member is disposed within the space to define first and second chambers. The partition is arranged to define an elongated rectangular cross-sectional communication passage therein. The partition includes electrodes which are disposed in the communication passage in a juxtaposed manner. These electrodes are connected with a control circuit which selectively applies a voltage thereacross. Fig. 1 is a model which depicts the arrangement of a device disclosed in JP-A-60104828 as a system having a single degree of freedom. In this model Fk denotes the applied vibration induced spring force which causes displacement while Fc denotes the damping force produced. Ftotal denotes the vibrational force which is transmitted through the device. As shown in Fig. 2, when Fk and Pc are in phase, the damping force is attenuated, and when the two are out of phase or in what shall be referred to as a reversed phase condition, the damping force is amplified. In this arrangement the fluid which is sealed in the elastomeric arrangement is arranged to flow through the orifice in a manner wherein the fluid within the orifice passage arrangement acts as a mass, and the accompanying fluid flow induces an expansion of the elastomeric body in a manner to define a spring effect. While the vibration frequency remains just below that at which resonance occurs the dynamic spring constant of the arrangement is effectively lowered and a dynamic damping effect is produced. However, in actual fact this device cannot be represented by a system having only a single degree of freedom in that the compressive spring component and the expansive spring component tend to develop a phase difference which varies between 0 and 18 degrees and as a result adequate attenuation of vibration transmission cannot be achieved under a wide range of operating conditions. A method for controlling damping device in accordance with the preamble of claim 1 was disclosed by DE-A-3433797. This document describes a hydraulically damped elastic bearing, having an annular spring element of elastic material, which encloses a fluid-filled working chamber. The working chamber is connected by a gap channel with a fluid-filled compensation chamber. The walls of said gap channel are electrically insulated from each other and can be connected to a power source. The fluid, filled into the working chamber and the compensation chamber exhibits rheopectic properties. The spring characteristic and the damping characteristic of the bearing can be changed by applying a voltage to the gap channel. Summary of the Invention The present invention has the objective to provide an improved method for controlling a damping device with a fluid having rheopectic properties. This object is solved by the subject matter of the main claim. Preferred embodiments of the method are subject-matter of the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a model showing the arrangement of the prior art device discussed in the opening paragraphs of the instant disclosure; Fig. 2 is a chart showing in terms of force and time the phasing of the spring force Fk and the damping force Fc; Fig. 3 is a schematic representation of the arrangement which characterizes an embodiment of the present invention; Fig. 4 is a sectional elevation showing the construction of the embodiment of the present invention; Fig. 5 is a flow chart-like diagram showing the steps which are executed by an algorithm which forms a vital part of the instant invention; Fig. 6 is a model showing the arrangement of the embodiment of the instant invention; and Fig. 7 is a graph showing in terms of applied frequency the changes in the dynamic spring constant Kd and the loss factor L which are produced in accordance with the instant invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figs. 3 to 7 disclose an embodiment of the present invention. As shown in Fig. 4, the embodiment comprises an upper plate 101 which can be detachably connected to a vibrating body such as an internal engine or the like, and a lower plate 103 which can be detachably connected to a base or body such as the chassis of an automotive vehicle 104. An essentially cylindrical hollow elastomeric body 106 is sealingly interconnected between the upper and lower plates 101, 103. In this arrangement, the upper plate 101 is arranged to close the upper end of the hollow formed in the elastomeric member 106 and define the top of a fluid chamber. A re-enforcing annular rib 108 is arranged about the external periphery of the elastomeric body 106 at a level approximately mid-way between the upper and lower ends thereof. An annular spacer member 110 is sealingly disposed against a peripheral radial flange 103a of the lower plate 103. A cap member 112 is secured to the lower face of the spacer 110. This cap member 112 sealingly clamps a flexible diaphram 114 against the spacer in a manner to define an air chamber 116 between it and the diaphragm. The diaphragm 114 in this position closes the lower end of the fluid chamber. An orifice plate 118 is supported on the upper face of the lower plate 103 and arranged to divide the fluid chamber into a working chamber 120 and an expansion chamber 122. The orifice plate 118 is provided with a multi-channel orifice member 124. This member includes electrically isolated electrodes which can be connected to the positive and negative terminals of a voltage source and which define positive and negative electrodes. In this case the electrodes are formed of platinum or are platinum coated. As will be noted from Fig. 4 the electrodes in this instance have the form of a coaxial rod 124a and an annular member 124b which is disposed coaxially thereabout. An essentially annular vibratable mass 126 is supported by a diaphragm-like arrangement 128, the peripheral edge of which is sandwiched between the spacer 110 and the lower plate 103. The circular aperture 126a defined in the center of the mass member is sufficiently large to provide relatively free communication between the upper and lower faces of the same. To prevent contamination and the like the mass member 126 is completely enclosed by the diaphram like member 128. The positive and negative electrodes are connected with the voltage source by way of lead lines which pass through the working chamber and which are sealingly clamped between the top of the cylindrical elastomeric member 106 and the upper plate 101. It will be noted at this point that the invention is not limited to this connection arrangement and that a number of changes in the electrode configuration and the lead line arrangement can be envisaged without departing from the spirit of the invention. A voltage source 130 is operatively connected to a control circuit 132 in a manner wherein the output of the voltage source is controlled by the output signal of the control circuit. The fluid chamber is filled with a fluid which exhibits rheopectic properties. Viz., the fluid in the fluid chamber is such as to exhibit an increase in viscousity when a voltage is applied thereto (Winslow effect). Accordingly, with the above disclosed arrangement when a voltage is applied across the positive and negative electrodes which define the multi-channel orifice arrangement the fluid which is contained within the annular electrode member 124b is induced to undergo an increase in viscousity. This of course has a marked influence on the manner in which fluid can be displaced between the working chamber 120 and the expansion chamber 122 and thus defines a variable damping control device. The embodiment further includes first and second sensors (accelerometers) 134, 136 which are arranged to sense acceleration in a predetermined direction. In this instance the acceleration is that which occurs normally to the essentially parallel upper and lower plates. This acceleration component will be referred to as vertical acceleration hereinafter. The first sensor 134 is disposed on the vibrating body (e.g. engine) while the second sensor 136 is disposed on the base or body (e.g. the vehicle chassis). The outputs of these sensors are applied to the control circuit 132. In this embodiment the control circuit includes a microprocessor which comprises a RAM, ROM, CPU and the like. An algorithm for processing the data input from the two sensors and for deciding the timing and level of the voltage to be applied to the positive and negative electrodes of the orifice, is included in the ROM of the device. The basic arrangement of the above disclosed arrangement is shown schematically in Fig. 3. The operation of the instant embodiment is such that when the engine is operating the output of the first and second sensors 134, 136 is fed to the control circuit 132. The inputs are read and, as shown in Fig. 5, the signals, indicative of acceleration, are each subject to two sequential integrations. The resulting signals are indicative of the displacement of the engine and the chassis. The two displacements are subtracted to obtain a relative displacement value. This value represents the power input from the elastomeric body and is indicative of the Fe component shown in Fig. 6. The output of the second sensor is also read in a manner which enables the frequency of the vibration to be counted. The relative displacement and the frequency counts are used in connection with a look-up map (map B) in a manner which permits the timing of the reverse phase to be determined. Viz., the map is logged in terms of Fe and Fo and in a manner which enables the timing at which the Fo plot and the Fe plot are going in opposite directions (reverse phase) and proceeding in the same direction (in phase) to be obtained based on the knowledge of the Fe plot which is derived using the two previously mentioned values (the relative displacement value and the frequency count). The frequency count is used alone to look-up the most appropriate voltage application timing from map A which is recorded in terms of voltage application time and frequency. Finally, the voltage application time and the timing of the reverse phase are used to induce the voltage source 130 to generate an ON - OFF type signal. At this point it should be noted that the arrangement shown in Fig. 4 can be depicted (as shown in Fig. 6) as a model which exhibits multiple degrees of freedom and which includes a dynamic damper mechanism. In the disclosed arrangement the fluid contained in the electronically controlled orifice 124 acts as a mass while the flow of the fluid between the two chambers together with the expansive characteristics of the elastomeric members 106, 114 cooperate in a manner to define a spring. As shown in Fig. 7 the dynamic spring constant Kd characteristics are such as to be lower at resonance frequency A than at resonance frequency B and to exhibit a reduction at frequency A. On the other hand, the loss factor L characteristics are such as to exhibit a dynamic damping effect at resonance frequency B. Accordingly, it will be understood that the vibration damping device or mounting device according to the present invention cannot be expressed as a model having only one degree of freeedom. Prior to resonance the phase difference between the vertical spring input power Fe and the expansion spring input power Fo is close to 0 degrees. That is to say, the phase difference is limited to deviating within a range of 0 to 180 degrees. In other words, under these conditions, the damping coefficient varies as a function of the changes in Fe and Fo between an inphase relationship and a reverse phase relationship. During the inphase relationship Fe and Fo are such that the value of |Ftotal| = |Fe + Fo| increases and the system assumes an undesired condition. That is to say, at this time the damping constant C is reduced and the fluid mass which is transferred through the orifice 124 is subject to ready movement. On the other hand, when the inphase changes to the reverse phase |Ftotal| reduces and during this period the damping coefficient C increases and the system assumes a condition wherein the energy damping effect takes place in a desired manner. However, if we consider the previously mentioned phase difference problem and the effect of the expansive spring input power Fo produced by the orifice damping, the vertical spring input force Fe and the expansive spring input force Fo are such that during the reverse phase the effective increase in the orifice damping effect tends to be lost. In accordance with the present invention it is at this time that the control timing produced by the control algorithm takes effect. That is to say, with the instant embodiment, during modes of operation wherein large amplitude low frequency vibration is produced (viz., during engine idling) no voltage is applied to the orifice electrodes 124a, 124b. Under these conditions the resonance frequency of the mass of fluid defined in the orifice 124 is tuned so that the dynamic spring constant Kd is minimized for a predetermined vibration frequency which is applied at that idling engine speed. That is to say, tuned in a manner to induce the resonance frequency to correspond to frequency A of Fig. 7. With this arrangement during engine idling, the dynamic spring constant is minimized and is possible to attenuate vibration under such conditions. When the engine is operated at normal rotational speeds, an extremely high voltage is applied to the orifice electrodes 124a, 124b (in an ON-OFF manner) and during the application of the voltage the fluid body defined therein tends to become almost solid. Accordingly, the orifice passage defined within the outer cylindrical electrode becomes blocked. With the orifice so restricted and with the resulting expansion spring value, the resonance frequency is tuned to a second predetermined value at which the lost factor L is maximized and which corresponds to the applied frequency produced by shaking of the engine. That is to say, at the engine speed at which engine shake is generated, the resonance is tuned to correspond to the frequency of the applied vibration which occurs at B of Fig. 7. Therefore, during running of the engine the engine shake vibration is attenuated by the effect of the dynamic damper mechanism. Further, the previously described algorithm provides ON-OFF control of the voltage which is applied to the orifice electrodes 124a, 124b and allows the expansion spring input power Fo to be selectively reduced in a manner which permits the force which is applied from the chassis to be reduced and effective damping of the engine vibration can be achieved. During modes of operation when small amplitude high frequency vibration is produced, the vibratable mass 126 which is suspended by the diaphragm-like arrangement 128 and which defines the dynamic damper mass, can be tuned so that its resonance frequency is located in the range of 50 - 60 Hz (by way of example only). Under these circumstances, the power which is inputted from the engine and the vibration of the dynamic damper mass are such as to cancel each other and thus block the transmission of the vibration component having a frequency of 80 Hz and above and which tends to produce cabin reverberation noise. Further, as the dynamic damper mass is provided with the central opening 17a the flow of fluid which passes through the orifice is not restricted and engine shake and cabin reverberation which tend occur at the same time can be effectively reduced due to the attentuation of a compouned vibration input containing 10 Hz and 80Hz components. The merits which are obtained with the instant embodiment are deemed to be that: 1. The reverse phase timing of the vertical spring input force Fe and the expansive spring input force Fo can be calculated and this timing used in combination with the vibration frequency to establish a predetermined timing with which a voltage should be applied across the terminals 124a, 124b of the orifice and increase the orifice damping effect. This permits the expansive spring force produced during the reverse phase to be attenuated due to the effective reduction in dynamic spring constant and the establishment of a dynamic damper effect; 2. The dynamic damper mass 126 is suspended by an elastomeric diaphram like member which enables the resonance frequency of the arrangement to be tuned in a manner wherein cancellation of predetermined vibrations is possible; and 3. The dynamic damper mass is provided with a relatively large central opening 126a which permits engine shake and cabin reverberation noise to be simultaneously attenuated. It will be of course noted that the instant invention is not limited to the construction disclosed in Fig. 4 and that the concept on which the instant invention is based can be applied to arrangements such as shock absorbers wherein the springs take the form of actual coil springs and the like and which shock absorbers are utilized in automotive suspensions and the like.

Claims: A method for controlling a damping device interposed between a vibrating body and a base, this damping device comprising means defining a spring (106, 114), said spring being operatively interconnected between said body and said base, said spring undergoing distortion when said body moves relative to said base; means defining first (120) and second (122) variable volume chambers, said first and second chambers being filled with a fluid which exhibits rheopectic properties, the chamber defining means being operatively connected between said body and said base in a manner wherein displacement of said body with respect to said base induces fluid to be displaced between said first and second chambers; an orifice (124) operatively interposed between said first and second fluid chambers; first and second electrodes (124a, 124b) defined in said orifice (124), said first and second electrodes being arranged to define a multi-passage arrangement in said orifice in a manner wherein when a voltage is applied to said first and second electrodes, the viscosity of said rheopectic fluid between said electrodes increases and the restriction to fluid flow through said orifice increases; first sensor means (134) for detecting the relative displacement between said body and said base; second sensor means (136) for detecting the frequency of the vibration being applied to said device; a control circuit (132) which is responsive to said relative displacement sensing means and said frequency sensing means; characterized in that said control device (132) calculates, on the basis of the detected relative displacement of the input force (produced by the compression of an elastomeric member which defines the main spring of the damper), acting on the damping device and on the basis of the relative displacement and the detected frequency of the expansive spring input force (produced by the displacement of rheopectic fluid between first and second variable volume chamber and the associated expansion characteristics of the members defining the same), the timing in which the phase of the input force, acting on said damping device and the expansive spring input force are reversed; and said control circuit (132) determines on the basis of this calculation the timing with which a voltage should be applied to said first and second electrodes. A method in accordance with claim 1, characterized in that the values, detected by said first and second sensor means (134, 136) are acceleration values and that said control circuit (132) subjects the outputs of these sensors to two sequential integrations and then subtracts the results to derive said relative displacement. A method as claimed in claim 1 or 2 characterized in that said control circuit (132) is responsive to the output of said second sensor means (136) in a manner to develop a count which corresponds to the frequency of the vibration at the location of said second sensor means and which further includes data which are recorded in a manner to define first and second maps, said second map being arranged to enable the timing wherein the phases of said spring input force and said expansive spring input force are reversed while said first map is arranged to enable the timing with which the voltage which is to be applied to said first and second electrodes (124a, 124b) to be ascertained based on the frequency count.

Inventors: DOI, KAZUHIRO
Applicants: NISSAN MOTOR CO., LTD.
Application year: 1988
Main classification: F16F9
IPC codes: B60K5, F16F13