Hydraulically Damped Engine Mount Having Improved Throttle Ports

This invention relates to an engine mount having hydraulic damping.

A hydraulically damped engine comprises a working chamber which is defined by a bearing member, a bearing spring and a bearing wall and a compensation chamber which is defined by a resilient buffer wall with a partition wall disposed between the working chamber and the compensation chamber. A throttle port connects the working chamber and the compensation chamber in fluid communication. A hydraulic fluid fills the working chamber, the compensation chamber and the throttle port. German Patent Application No. 94 58 99 generally describes an engine mount of this type. The throttle ports of the engine mount of this reference have short identical lengths and the same cross section.

It is an object of the present invention to provide an improved hydraulically damped engine mount of the type hereinbefore described that achieves an improved damping effect and thus an improved insulation upon the simultaneous introduction of oscillations of small and large amplitude. Small amplitude oscillations are those of less than about 0.1 mm. These and other objects of the present invention will be apparent from the following description and claims in conjunction with the drawings.

In accordance with the present invention, a hydraulically damped engine mount is provided wherein the throttle ports connecting the working chamber and the compensating chamber are fashioned in the shape of channels and each has a length different from one another.

The effectiveness of the engine mount according invention utilizes the nonlinearity of the hydraulic damping force, the proportionality of which is determined to the square of the relative velocity of the fluid through the throttle, as well as its effect on the (equivalent) fluid mass.

The working chamber, the compensating chamber and the throttle port of the engine mount according to the invention are filled with a low-viscosity, incompresible fluid. The incompressible fluid is subject to acceleration forces upon introduction of the oscillations occurring under normal operating conditions which is accompanied by a change of the hydraulic pressure. This change is a function of the kind of the particular oscillations introduced and the shape and tuning of the throttle ports (length and/or diameter) relative to each other, which permits a lowering of the dynamic rigidity upon the introduction of high frequency oscillations above 30 Hertz. With the engine mount according to the present invention, excellent insulation of these oscillations is obtained. It is noteworthy that this insulating effect also occurs when simultaneously, low frequency oscillations below 20 Hertz are introduced into the engine mount. The mechanism of the operation of the engine mount according to the invention will be apparent from the physical equivalent diagram illustrated in FIG. 2. The listed values have the following means:

Force F(t) and the road response velocity Vo(t) are the interference parameters. Fd, Fr are the damping forces.

For the passive dampener:

M: Mass of the engine.

Mf: Equivalent mass of the fluid of the upper working chamber.

Mred: Mass of the reduced absorption system.

Co: Coupling spring rigidity of the upper working chamber.

Cu: Coupling spring rigidity of the lower working chamber.

Ro: Characteristic function of the channel system. It is a function determined by the throttle length, the diameter, the throttle shape, the kind of flow, the inertia of the fluid, and the ratio hydraulic compliance of the upper/lower working chamber.

.gamma.: Ratio (damping or effectiveness degree ratio) of the characteristic function of the compensating systems Rr, B Ru with respect to the characteristic function of the channel system Ro.

B: Ratio (damping or effectiveness ratio) of the characteristic function Ru, .gamma.Rr with respect to the characteristic function of the channel system Ro.

u: Ratio of the complex rigidity of the absorption system (Mred) and the coupling spring rigidity Co.

n: Ratio of the complex rigidity of the absorption system (Mred) and the coupling spring rigidity Cu.

Cr: Characteristic function of the absorption system Mred. It is a function which depends on the design of the reduced absorption system and the coupling spring rigidity Co.

The throttle port can be located in the rigidly affixed part of the partition wall, or in the relatively movable part of partitioning wall. Placing the throttle port in the rigidly fixed part of the partition wall is preferred.

Preferred embodiments of the present invention will be described in conjunction with the figures of the drawings.

FIG. 1 is a schematic cross-sectional view taken along the section I--I shown in FIG. 4 of one embodiment of an engine mount in accordance with the present invention.

FIG. 2 is a physical equivalent diagram illustrating the operation of one embodiment of an engine mount in accordance with the present invention.

FIGS. 3 to 5 illustrate various embodiments of throttle ports located in the rigidly fixed part of the partition wall of the engine mount of the present invention with FIGS. 3 and 5 being schematic cross-sectional views taken along the circular sections III--III and V--V, respectively. The circular sections have been extended to lie in plane of the view shown in FIG. 3 and FIG. 5, respectively, but have been shortened as indicated.

FIG. 4 is a cross-sectional plan view taken along line IV--IV of FIG. 3.

FIG. 4A is a view along line VI--VI of FIG. 4.

FIGS. 6 to 8 are schematic cross-sectional views of various embodiments of an inertial mass.

FIGS. 9 to 12 schematically illustrate various means of limiting the motion of the movable compensating part of a partition wall.

The engine mount shown in FIG. 1 contains a working chamber 12 delimited by a bearing member 1, a bearing spring 2, a bearing wall 9 and a partition wall 7. The bearing spring 2, which is an elastic material such as rubber, connects the bearing member 1 to the bearing wall 9. A compensating chamber 10 is defined by the partition wall 7 and a resilient buffer wall 3. The outer portion of the partition wall 7 is rigidly connected to the bearing wall 9. The working chamber 12 and the compensating chamber 10 are connected in fluid communication by two parallel throttle ports 4,4'. The throttle ports 4,4', located in the rigidly held part of the partition wall, are separated from each other by a radially extending annular wall 29 shown in FIGS. 1, 3 and 4A, and may differ from each other in length and diameter. Like the working and the compensating chamber, the throttle ports 4,4' are filled with a fluid of low viscosity, e.g., glycol and water. When the engine mount is installed in a motor vehicle, the bearing member 1 would be connected to the engine and the bottom plate below the resilient buffer wall 3 would be connected to the structural frame of the vehicle.

The partition wall 7 comprises in its central area a compensating part movable between the working chamber 12 and the compensating chamber 10. The compensating part is formed by two circular inertial masses 6 lying radially within each other. The inertial masses 6 are connected with each other and with the rigidly fixed part of the partition wall 7 by means of annular diaphragms 8. The annular diaphragms are suitably an elastomer material.

The range of motion of the inertial masses 6 is limited in the axial direction by stops 5. The stops 5 form a single piece component of the rigid part of the partition wall 7. Sounds of the inertial masses making contact with the stops are avoided by annular stop buffers 27, e.g. made of rubber, which are vulcanized in one piece to the inertial masses 6 lying on the inside.

The stop buffers have linear deformation. In the non-excited stated of the inertial masses, they may have, e.g., a distance on both sides from each of the associated stops of approximately 4 mm.

Mutual assignment and design of the individual ports forming the throttle ports 4, 4' are shown by way of example in FIGS. 3 and 4. In this case, both individual ports have identical cross sections which are rectangular. They are connected with each other through a transverse port 11 located at a distance from both ends of each port. The ratio of the cross-section of the transverse port 11 and the cross-section of each of the adjacent individual ports may suitably be from 1 to 3. The throttle ports 4,4' have a common inlet 25 shown in FIG. 3 and FIG. 4 which communicates with working chamber 12 and a common outlet 33 which communicates with compensating chamber 10.

FIG. 5 illustrates a developed view of a throttle port comprised of any number of individual ports which can all be located in the rigid part of the partition wall 7 of a design similar to FIG. 1 and which can, if necessary or desired, have cross sections different from each other and lengths L1, L2, . . . LN varying from each other. The individual ports have a common inlet 25' shown in FIG. 5 which, similar to the FIG. 3 embodiment, communicates with working chamber 12 and a common outlet 33' which communicates with compensating chamber 10. The ports are separated from each other by radially extending annular walls 29', 29". The volumes contained in the individual throttle ports, and thus the particular masses of liquid contained in each throttle port, are different. This leads to their resonating upon the introduction of frequencies different from each other and to a high degree of damping for each of the particular frequencies. This is technically still utilizable in frequency ranges that are not adjacent and thus in a frequency band of a certain width. This permits the compensation of the effect of the damping of one of the individual ports decreasing as the result of introduced oscillations of gradually changing frequencies through the newly starting damping effect of one of the other individual ports of slightly increased length. Given a sufficiently large number of individual ports with appropriate finely varied mutual gradations of the lengths, excellent damping effects in a broad spectrum of frequencies can be achieved.

FIGS. 6 to 8 illustrate in cross section a variety of shapes for the design and the fastening of the inertial masses.

The inertial masses and the annular diaphragms supporting them are fashioned rotationally symmetrical.

In FIGS. 9 to 12, different stops are shown which limit the axial motion of the inertial mass. In the nonoperating engine mount, they have, e.g., a distance of approximately 0.5 to 5 mm from the closest adjacent place of the inertial mass whereby mutual contact can only occur during effective overloading. In this way, unintentional destruction of the diaphragms is avoided. Clapping sounds can be effectively suppressed by installing stop buffers.

In the embodiments according to FIGS. 9 to 11, the stops 5', 5", 5"' are located in front of the inertial masses in the direction of motion. As a rule, they are circular, but may in the manner shown in FIG. 11 comprise cams distributed uniformly on the circumference projecting radially inwardly and adapted to abut against stop buffer 27.

In FIG. 12, a stop is shown which encloses the inertial mass 6 and the annular diaphragm 8 radially at an axial distance. Depending on the deflection direction of the inertial mass 6, it can be contacted by one or the other of the two annular bulges 12 of the annular diaphragm 8, which leads to a limitation of the axial motion of the inertial mass 6. The stops in this embodiment do not in any way hinder the manner in which the pressure of the fluid contained in the working chamber acts upon the inertial mass 6. The effectiveness of the inertial mass 6 is thereby optimized and ensures that excellent uncoupling of high frequency oscillation is achieved.

Some general remarks will be made concerning the use of inertial masses. In view of the design of the engine mount according to the present invention for support of the engines of motor vehicles, it has proven to be of advantage if the ratio of the entire present absorption mass and the proportionate mass of the engine is maximally 0.1, and the ratio of the rigidity of each annular diaphragm to the rigidity of the bearing spring is maximally 1.0. If one of the two parameters is varied, the other parameter must always be changed in the same direction. The intial coarse tuning can take place using theoretical calculations of which further explanations are not necessary for one skilled in the art. The fine tuning is reserved for the practical trials of a motor driven vehicle equipped with the engine mount of the invention under normal operating conditions.

A further improvement of the effectiveness can be achieved if the ratio of the hydraulically effective piston area of the bearing wall affixed to the bearing spring and the corresponding hydraulically active area of the compensating part comprising the absorption mass lies in the range between 1 to 16, and preferably in the range between 2 to 8. The first mentioned piston area comprises approximately two thirds of that area which is obtained if the underside of the bearing wall and the bearing spring is projected onto an area transverse to its direction of motion. The last mentioned area comprises the corresponding projected image of each absorption mass enlarged by 50% of the area of the adjoining annular diaphragm projected in the same way.

The annular diaphragms used in the engine mount can be fashioned in such a way that they can be molded without significant dampening work. The absorption effect thereby becomes especially effective.

The absorption masses employed suitably have a weight of 10 to 200 grams for uses in motor driven vehicles, and for uses in passenger cars, usually a weight of 10 to 50 grams. A construction of the compensating mass and that of the associated annular diaphragm deviating from absolute circularity is possible. Oval or polygon-shaped designs are possible.

The use of inertial masses of this nature in certain cases can be omitted and represents only one embodiment of an engine mount in accorance with the present invention.

Although preferred embodiments of the present invention have been described in detail, it will be understood that modifications may be made by one skilled in the art all within the spirit and the scope of the present invention as defined in the claims.