The invention relates to a mounting arrangement with a shearing element for the dynamic support of forces between two parts of an assembly that can carry out vibration-type relative movements with respect to one another. The mounting arrangement of the invention is especially useful in supporting vehicle engines at a vehicle chassis.
A shearing element of the general type contemplated is disclosed in German Published Unexamined Application (DE-OS) No. 31 52 751. It is intended specifically for the vibration-insulating mounting of an engine at the body or at the chassis of a motor vehicle and comprises--in a mechanical parallel connection--a rubber-elastic buffer that provides an elastic coupling between the engine and the body, as well as a shearing unit that has the purpose of avoiding a resonance rise of the amplitudes of the vibrations that can occur in the buffer-mass system. Within a block that is firmly connected with the body, the shearing unit comprises a receiving space that is filled with a dilatant fluid, a plunger that is connected with the engine projecting into this receiving space and in a special development delimiting, in connection with the receiving space, an annular duct or gap in which the fluid is subjected to periodic flow movements that are forced by the immersion of the plunger. The fact is utilized that, in the case of an exceeding of critical values of the shearing .gamma. as well as of the shearing speed .gamma., a dilatant fluid experiences a drastic increase of viscosity that at the same time results in a jump of the rigidity of the mounting as a whole. The shearing unit is dimensioned in such a way that this jump in rigidity takes place approximately in the range of the natural-vibration frequency of the damping body/mass system, when it is considered separately. In addition, the known mounting is dimensioned in such a way that for vibration amplitudes that are smaller than about 60 .mu.m, the critical value of the shearing can no longer be exceeded and therefore, even if the shearing speed in the fluid were to be above the respective critical value .gamma..sub.S, which may occur in the case of acoustic vibrations of a higher frequency that, however, can be energized only with relatively small amplitudes, the jump in rigidity cannot occur and thus the vibration insulation characteristics toward higher frequencies are again determined only by the damping body which results in a favorable behavior of the mounting in the sense of a suppression of noise.
However, the known shearing unit has at least the following disadvantages:
The volume within which the dilatant fluid is subjected to the minimum shearing with an overcritical value of the shearing speed, is limited to an annular-gap-shaped space and therefore is relatively small. For a dimensioning of the shearing that is suitable for being able to absorb the dynamic loads that occur in practice and that range from 300 to 400 N, relatively large physical dimensioning of the plunger and of the block containing the receiving space are required that result in dimensions that are disadvantageous for an installation into a vehicle. Since the volume of fluid that is displaced by the plunger in the time unit is clearly larger than the speed of the relative movement of the plunger, that is multiplied with the area of the annular gap through which the dilatant fluid is forced, in relation to the block of the shearing unit, a multiplication of the flow speed of the dilatant fluid occurs in the shearing gap. This, on the one hand, has the result that the shearing unit responds very rapidly in the sense of an increase of its rigidity, i.e., it is sufficient, when the shearing has exceeded its minimum value .gamma..sub.min, to let even a slight change of the vibration frequency around the mounting "suddenly" harden, which can have the effect of an annoying impact to the body. In addition, the mentioned multiplication of the flow speed, even when the critical values of the shearing and/or the shearing speed in the dilatant fluid--in the range of acoustic vibrations of higher frequencies--are not longer exceeded, has the result that, because of the inertia of the fluid, an increasing dynamic rigidity of the shearing unit and thus of the mounting including of its damping body occurs, and its damping characteristics in the direction of higher frequencies of the excitable vibrations, deteriorate again.
In order to at least partially avoid the above-mentioned disadvantages of the known shearing element that arise from a multiplication of the flow speed of the dilatant fluid in a relatively narrow shearing gap that receives only a small volume of the dilatant fluid, it may be considered to modify a shearing element of the initially mentioned type to the extent that, as is known per se from West German (DE) No. 30 10 520 Al and East German (DD) 227 763 Al in connection with vibration damping arrangements in which, as the damping material, a highly viscous damping medium is used, tube-shaped immersion bodies are provided that also carry out the vibrations of the masses that can be moved with respect to one another, and that, with respect to an axis marking the vibrating direction, are arranged coaxially in such a way that the immersion bodies that go along in the vibrations of one mass dip into annular gaps that are delimited radially by the tube-shaped immersion bodies that go along in the vibrations of the other mass, these annular gaps then having to be filled with the dilatant fluid.
However, a shearing element of this type would then have the disadvantage that, in the case of relative movements of the masses that can vibrate with respect to one another that take place at a right angle with respect to the axis or direction marking the "main vibrating direction", within the receiving space that is filled with the dilatant fluid, at least in areas, drastic changes of the shearing gap widths would occur and thus of the shearing speeds within the dilatant fluid, with the disadvantageous result that, also in the case of a shearing element that is modified in this way, the vibrating characteristics would change in an uncontrolled way. Also, at least in areas, high shearing speeds would occur that are multiplied by the narrowing of the shearing gap, with the above-mentioned disadvantageous consequences for the dynamic behavior of a shearing element of this type. In order to reliably exclude damage to the immersion bodies, it would have to be ensured by means of guiding and/or stop elements that the masses that can vibrate with respect to one another can carry out vibrating movement only in such a way that a change of the shearing gap widths is largely excluded. The application possibilities of a shearing element of this type would therefore be limited to the few cases in which a vibration insulation is required only for one vibrating direction. It would therefore not be suitable for use as a vibration-insulating shearing element, the vibration-insulating characteristics must not be impaired when an overlapping of vibrations is be expected in all coordinate directions, as, for example, in the case of an engine mounting of a motor vehicle.
It is therefore an objective of the invention to provide a shearing element of the initially mentioned type that, in the case of a design for a predetermined dynamic maximum load, results in a softer rise of the viscosity of the dilatant fluid in the natural vibration range of the mounting-mass system when critical values of the shearing and of the shearing speed are exceeded, but in the direction of higher frequencies, develops less dynamic rigidity, that without any impairment of its vibration insulating characteristics, can also still be used when it is subjected to an overlapping of vibrating movements in different coordinate directions, and in this case can still be implemented as a simple and space-saving construction.
According to the invention, this objective is achieved by constructing the shear element as respective sets of plate shaped lamellae immersed in viscous fluid and connected to the engine and body side respectively. Preferably the plates are mounted pivotally and configured so they can move relatively to one another in multiple space coordinate directions.
By means of the accordingly provided development of the immersion bodies that can be moved with respect to one another within the dilatant fluid, as "lamellar combs" that, with their swivelling lamellae, engage between two lamellae respectively of the lamellar comb that can be moved in opposite direction, a highly effective utilization is achieved of the space that is available for generating a shearing in the dilatant fluid, in such a way that, when the increase of viscosity occurs in the dilatant fluid, a massive "fixed" column occurs between the masses that vibrate against one another that permits the absorption of high dynamic loads. Since the shearing and the shearing speed, in the case of the shearing element according to the invention in each case corresponds to the amplitudes of the relative movements of the masses that are supported with respect to one another and their time-related change, these parameters change correspondingly "slowly" so that the viscosity rise of the dilatant fluid occurs within an expanded variation range of the change of the shearing and of its speed, and the connected increase of the rigidity of the shearing element does not occur in steps but softly in a "ramp shape". Since within the space that is filled by the dilatant fluid, compensating movements of the dilatant fluid occur as a result of the speed of the relative movements of the masses that vibrate against one another, and this taking place with a very small volume of the lamellae, the dynamic stiffening of the shearing element according to the invention that is caused by the inertia of the fluid is also advantageously low.
As a result of the pivotable mounting of the shearing lamellae, these shearing lamellae, also when the masses that can vibrate with respect to one another carry out relative movements in one vibration form that correspond to an overlapping of vibrations in all--three--coordinate directions, can carry out compensating movements that, within the vibrating amplitudes occurring in practice, lead to no more than an insignificant change of the shearing gap widths which does not impair the vibration insulating characteristics of the shearing element according to the invention.
In especially preferred embodiments the lamella plates at the engine side and body side are pivotably supported about respective pivot axes that are parallel with one another, providing the desired movement direction Possibilities. This provides for a constructively uncomplicated development of the shearing unit that is suitable for relative movements in all coordinate directions of the masses that can vibrate with respect to one another.
In especially preferred embodiments of the invention the receiving space for the dilatant fluid and the shearing lamellae plates is bounded in a radial direction with respect to a central longitudinal axis by flexible bellows. A head plate is connected for movement with one mass (e.g. an engine) and a base plate is connected for movement with the other mass (e.g., a vehicle body support part). The bellows and the head and base plate form a fluid tight receiving space for the dilatant fluid and the shearing lamellae plates.
In certain preferred embodiments the bellows is surrounded by a cup-shaped upwardly open part that is fixed to the base plate of the shearing element. An elastic damping body connected to the engine is supported at the top of the outer rim of the cup-shaped part, the head plate of the shearing unit being fixed at a rigid mounting piece that penetrates centrally through the damping body and is firmly connected with the engine and the damping body. This arrangement of the shearing unit and of the damping body of a shearing element is particularly suited for an integrated method of construction with small outer dimensions.
In especially preferred embodiments the lamellae plates are provided with rod shaped edges which form a pivot connection at the respective head and base plate. Such a contructionally simple and operationally reliable arrangement is particularly suited for a design of the shearing element for moderate dynamic loads. Especially preferred are one piece stamped parts, preferably aluminum, with a plate thickness of 1 mm and a rod shaped round rod edge with a diameter of 2 mm.
Certain preferred embodiments provide a shearing element with swivelling shearing lamellae connected via t-grooves in a head plate movable with the engine and a base plate movable with an engine. Anchoring pieces with roll off edges are provided to permit pivoting. Such a design is especially suited for higher dynamic loads. Advantageous ways are provided for implementing the shearing lamellae and their arrangement with respect to one another that permit a particularly effective utilization of the volume range within which the dilatant fluid can be subjected to the required shearing.
By means of an equidistant arrangement of the shearing lamellae within the receiving space containing the dilatant fluid, in which case, an advantageous range of possible values of the lamella distances is indicated and it is achieved that the whole volume range within which the dilatant fluid can be subjected to the shearing, contributes uniformly to the increase of rigidity of the shearing element in the case of a resonance.
Spacers that are provided for maintaining the desired lamella distances can be implemented in a simple way by means of dome shaped arched out areas in the lamella plates.
In especially preferred arrangements the shearing element is suitable for use in an engine mount for a motor vehicle with the swivel axes of the lamellae extending at right angle to the vehicle longitudinal direction. This minimizes bothersome noise development expected which is mainly caused by the vertical relative movements of the engine and the body, and possibly also by tilting-swinging movements of the engine around the longitudinal axis of the vehicle.
In a special development of the shearing element according to the invention, two shearing lamellae respectively of the shearing lamellae on the side of the base plate are, in a U-shape, combined to a double shearing lamella into which the shearing lamallae on the side of the head plate immerse that are held at the distance of the width of a shearing gap by means of spacers. As a result, although the utilizable shearing volume is reduced slightly, the maintaining is ensured of shearing gap widths that are Predetermined in a defined way and thus a defined response behavior of the shearing element is also ensured.
The shearing element units constructed according to the invention, in varied ways, can be adapted to the respective occurring requirements, by means of the composition of the used dilatant fluid as well as by means of the number of the shearing lamellae and their design and arrangement with respect to one another, whereby the amplitude and the frequency of the vibrations can be predetermined, at which the shearing element responds in the sense of an increase of rigidity. If it is important that the shearing element, in the frequency scale of the possible vibrations within a frequency interval that is as narrow as possible, develops its full rigidity, an equidistant arrangement of the shearing lamellae is most advantageous. If, on the other hand, it is desired that the shearing element develops its stiffness within a wider frequency interval "gradually", this type of spreading of the response range, in a simple way can be achieved by means of an arrangement that deviates from an equidistant arrangement of the shearing lamellae. A--contemplated--design of a shearing element according to the invention that is advantageous for use as an engine mount at a motor vehicle may, for example, consist of the fact that this shearing element experiences its jump in rigidity, seen in the frequency scale of the possible vibrations, between the so-called cancelling frequency and the resonance frequency of the spring-mass system that is formed by the mass m.sub.1 of the engine and the mass m.sub.2 of the body and the damping body or bodies coupling these two masses with one another. The shearing element then, at the cancelling frequency .nu..sub.T, with which that form of vibration is connected at which the engine alone carries out vibratory movements with respect to the body that is stationary--seen in vibratory direction--will still be sufficiently flexible in order to accommodate this moving condition of minimal sound transmission to the body, at the resonance frequency .nu..sub.R that is by the factor .sqroot.(m.sub.1 +m.sub.2 /m.sub.2 larger and that corresponds to the natural vibration form, at which the engine and the body with approximately the same amplitudes experience phase-opposed deviations, but in its condition of maximum rigidity that is most advantageous for the suppression of the resonance rise of the vibration amplitudes.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
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