Wheel damping

Abstract: A wheel assembly (10) for a vehicle. The wheel assembly (10) includes a brake assembly (16,18) which defines the outer radius of an annular region about the axis of the wheel assembly (10) and a damping mass assembly (19) for damping vertical vibrations of the wheel assembly (10), located within the annular region.

Description: The invention relates to automobile suspensions and more particularly to assemblies for damping vertical vibrations of wheel assemblies. For background, reference is made to US-A-4,991,698 which represents prior art of which the applicant is aware. It is an important object of the invention to provide an improved automobile suspension. Document US-A-2854100 represents the features of the preamble of claim 1 and discloses a vibration damper suitable for installation on a convenient part of the unsprung mass of a motor vehicle suspension. According to the present invention there is provided a wheel assembly for a vehicle, comprising: a wheel; a wheel axle; a brake assembly, defining the outer radius of an annular region about said axle; a damping mass assembly including a damping mass for damping vertical vibrations of said wheel assembly, wherein said damping mass assembly is located generally within said annular region and further comprises a damping mass vertical positioning assembly for positioning said damping mass, said vertical positioning assembly comprising: a fluid-filled cylinder disposed within said damping mass, a first spring disposed in said fluid-filled cylinder, for opposing, in compression only, vertical motion of said damping mass in a first direction, second spring disposed in said fluid-filled cylinder, for opposing, in compression only, vertical motion of said damping mass in a second direction opposite said first direction, and a motion damper for damping vertical motion of said damping mass, comprising a shaft in said damping mass, and an orifice plate on said shaft in said fluid-filled cylinder between said first and second springs, through which orifice plate fluid is caused to flow on vertical movement of the wheel assembly to resist vertical motion of said damping mass caused by the vertical vibrations of the wheel assembly. Other features, objects, and advantages will become apparent from the following detailed description, which refers to the following drawings in which: FIG. 1 is a partially cutaway view of a wheel assembly and suspension system according to the invention; FIG. 2 is a cross sectional view of damping mass assembly according to the invention; FIG. 3 is a perspective view of an orifice plate according to the invention; FIG. 4 is a top elevational view of a flapper; FIG. 5 is the orifice plate of FIG. 3 with the flapper of FIG. 4 in position; and FIGS. 6a-6c are side cross sectional views of the orifice plate of FIG. 5, illustrating the operation of the flapper. With reference now to the drawings and more particularly to FIG. 1, there is shown an active suspension assembly according to the invention. Wheel assembly 10 includes an axis defined by axle 37, tire 12, hub 14, and brake elements including brake disk 16 and brake pad 18. Positioned within an annular region which has an outer radius generally defined by the outer extent of brake elements (brake pad 18 and brake disk 16), is mass damper assembly 19. Mass damper assembly 19 includes damping mass 20 and vertical positioning assembly 24 which includes central shaft 26 disposed in a hollow cylinder 27 in the damping mass 20, orifice plate 60, and vertical positioning springs 28 and 30. Actuator 36 couples wheel assembly 10 to the body subframe, both shown in this view. In this embodiment, mass damper assembly 19 includes a second vertical positioning assembly, not shown in this view. Elements of the mass damper assembly damp vertical vibration of the wheel assembly, and will be described in more detail below. Actuator 36, which may be a linear actuator such as described in U.S. Pat. 4,981,309, acts to oppose upward and downward motion of the wheel assembly, thereby isolating the body subframe and therefore the passenger compartment of the automobile from vertical motion caused by unevenness in the road. Additionally, actuator 36 may coact with similar actuators on other wheels to control the attitude of the passenger compartment. Referring now to FIG. 2, there is shown a diagrammatic view, partially in section of the mass damper assembly 19. Mass damper assembly 19 includes a damping mass 20 and two vertical positioning assemblies 24a, 24b, including central shafts 26a and 26b, vertical positioning springs 28a, 30a, 28b and 30b, orifice plates 60a and 60b, and fluid filled cylinders 27a and 27b. Slot 38 extends through damping mass 20 in a horizontal direction along an axis parallel to the axis of rotation of the tire to allow axle 37 to move vertically relative to damping mass 20. Hollow cylinders 27a, 27b extend vertically through damping mass 20. Shafts 26a, 26b, are rigidly attached at each end to the non-rotating portion of the wheel. Shafts 26a, 26b extend vertically through cylinders 27a, 27b. Orifice plates 60a, 60b are rigidly attached to the shaft at a position approximately vertically centered in the damping mass 20. Endcaps 44a, 44b, 46a, 46b are fixedly attached to damping mass 20 in the ends of cylinders 27a, 27b. Vertical positioning springs 28a, 30a, 28b and 30b urge damping mass 20 toward a vertically centered position relative to axle 37. In one embodiment, the outside diameter of springs 28a, 30a, 28b, and 30b, is approximately equal to the diameter of cylinders 27a and 27b. In the embodiment of the invention, vertical positioning springs 28a, 30a, 28b, and 30b are not attached at either end to an endplate, to an orifice plate, or to the shaft; that is, the positioning springs are "floating" and are not precompressed. Additionally, elements of vertical positioning assemblies 24a, 24b are dimensioned, constructed, and arranged so that only one of springs 28a, and 30b exert force at any one time. Furthermore, elements of vertical positioning assemblies 24a, 24b are dimensioned, constructed, and arranged so that vertical positioning springs 28a, 30a, 28b and 30b exert force only in compression. This is advantageous because it enables vertical positioning to be performed with shorter springs. Having shorter springs enables the mass damper assembly 19 to be smaller, which in turn allows both brakes and mass damper assembly 19 to be placed in the wheel. Sealed portions 70a and 70b of cylinders 27a, 27b between the endplates 44a, 46a and 44b, 46b contain a fluid, such as hydraulic oil. Bearings (not shown) in the endcaps permit damping mass 20 to move up and down relative to shafts 28a, 28b, while seals retain fluid in sealed portions 70a, and 70b. In the configuration of FIG. 2, force is exerted by a spring when the spring is compressed. If damping mass 20 moves downwards, upper spring 28a is compressed between endcap 44a and orifice plate 60a and upper spring 28b is compressed between endcap 44b and orifice 60b, causing upper springs 28a and 28b to exert upward force on endcaps 44a and 44b respectively, thereby urging damping mass 20 upwards toward a horizontally centered positioned. Similarly, an upward movement of damping mass 20 compresses springs 30a and 30b, which causes them to exert a downward force on endcaps 46a and 46b thereby urging damping mass 20 downwards toward a horizontally centered position. Since the springs are not attached at either end, springs 28a, 28b, 30a, 30b exert force in compression, but not in tension. Upper springs 28a and 28b do not oppose an upward motion of damping mass 20, and lower springs 30a and 30b do not oppose downward motion of damping mass 20. The fluid cylinders 27a and 27b acts as a part of damping mass 20 and also resist vertical motion of damping mass 20 relative to shafts 28a, 28b, to dissipate vertical vibrational energy. A vertical motion of damping mass 20 causes fluid to pass through orifices 72 in orifice plates 60a and 60b. The orifices are sized such that they resist the flow of the fluid, thereby damping the vertical motion of the damping mass. Orifice plates 60a and 60b are constructed and arranged so that they exert an appropriate resistive force at all motion velocities encountered by the mass damper assembly. The orifices will be discussed below in FIGS. 3-6c and the corresponding portions of the disclosure. In one embodiment of the invention, a damping mass assembly 19 has a damping mass 20 about one half the mass of the wheel assembly mass, a spring rate of 4.73x10 4 N/m (2701bs./inch) and a tire elasticity of 2.80x10 5 N/m (1600lbs./inch). A damping mass assembly according to the invention is advantageous because the size of the damping mass assembly may be made small enough, using conventional materials, to permit placing the brake elements in the wheel. Referring to FIG. 3, there is shown a more detailed perspective view of the orifice plate 60a. Orifice plate 60a has a generally round footprint to fit inside cylinder 27a. Orifice plate has two generally round faces, of which one face is shown in this view. Orifices 72 allow fluid to pass through orifice plate 60a. Two additional orifices are obscured in this view by flapper 80, which is mounted on face 79. Mounting hole 75 is for mounting a flapper (obscured in this view), similar to flapper 80, on the face opposite face 79. In operation, mounting hole 75 is occupied by a screw or other fastener (not shown), so there is no fluid flow through mounting hole 75. Low velocity holes 94, 96 will be explained below. Stop 100 (shown in dotted lines) may be mounted over flapper 80 and will be described below. Referring to FIG. 4, there is shown a top plan view of flapper 80. In one embodiment, flapper 80 is made of 0.559mm (0.022 inch) thick spring steel, and has a central section 84 with a mounting hole 82 which is aligned with orifice plate mounting hole 75 for accommodating a mounting screw or other fastener. Extending from central section 84 are arms 86, 88. At the distal ends of arms 86, 88 are flapping sections 90, 92, which may be circular with a radius of about 12.70mm (0.500 inches), slightly larger than orifices 72 of FIG. 3. Flapper 80 is positioned such that the central section is fixedly attached to the orifice plate and so that the flapping sections are free to deflect away from the orifice plate as will be further explained below. Flapper 80 may include a low velocity hole 94, 96 in each flapping section 90, 92 which may be concentric with the circular flapper section. In one embodiment, the low velocity hole has a radius of approximately 4.242mm (0.167 inches). Referring to FIG. 5, there is shown a top plan view of one of the orifice plates 60a with a flapper 80 in position. Central hole 95 accommodates shafts 26a or 26b. Four orifices 72 approximately 11.862mm (0.467 inches) in diameter allow fluid to pass through orifice plate 60a. Flapper 80 is positioned such that sections 90, 92 cover orifices 72. A second flapper 80 (not shown in this view) may be positioned on the opposing face of orifice plate 60a. Referring to FIGS. 6a-6c, there are shown partial cross sectional views of orifice plate 60a illustrating the operation of the flappers 80. During low speed fluid motion in the direction indicated by arrow 97, fluid flows through low velocity holes 94 as shown in FIG. 6a, so that the effective area of each orifice 72 is the area of the hole 94. At higher speed fluid flow, force against flapping section 90 is sufficient to deflect flapping section 90 away from orifice plate upward as shown in FIG.6b, so that the fluid flows not only through low velocity hole 94, but also through region 98 in which the flapper has been deflected away from orifice plate 60a, thereby making the effective area of orifice 72 larger. At still higher speed fluid flow as shown in FIG. 6c, force against flapping section 90 is sufficient to deflect flapping section 90 sufficiently away from orifice plate 60a so that the flow is not restricted by flapping section 90 but rather by orifice 72 and the effective area of orifice 72 is essentially equal to the area of the orifice. Additional deflection of flapping section 90 does not increase the effective area of orifice 72, but may deform flapping section 90. To prevent excessive deflection of flapping section 90, stop 100 may be included.

Claims: A wheel assembly (10) for a vehicle, comprising: a wheel; a wheel axle (37); a brake assembly (16, 18), defining the outer radius of an annular region about said axle (37); a damping mass assembly (19) including a damping mass (20) for damping vertical vibrations of said wheel assembly, wherein said damping mass assembly is located generally within said annular region and further comprises a damping mass vertical positioning assembly (24a,24b) for positioning said damping mass (20), characterised in that said vertical positioning assembly comprises: a fluid-filled cylinder (27a, 27b) disposed within said damping mass (20), a first spring (28a, 28b) disposed in said fluid-filled cylinder, for opposing, in compression only, vertical motion of said damping mass (20) in a first direction, a second spring (30a,30b) disposed in said fluid-filled cylinder, for opposing, in compression only, vertical motion of said damping mass (20) in a second direction opposite said first direction, and a motion damper for damping vertical motion of said damping mass, comprising a shaft (26a,26b) in said damping mass, and an orifice plate (60a,60b) on said shaft in said fluid-filled cylinder between said first and second springs, through which orifice plate fluid is caused to flow on vertical movement of the wheel assembly to resist vertical motion of said damping mass caused by the vertical vibrations of the wheel assembly. A wheel assembly (10) in accordance with claim 1, the motion damper further comprising: a size adjuster (90,92) for varying said effective size of said orifice responsive to said flow velocity. A wheel damping assembly (10) in accordance with claim 2, said size adjuster comprising a flap (80) covering said orifice (72), constructed and arranged so that said flap is deflectable away from said orifice. A wheel damping assembly (10) in accordance with claim 3, said flap (80) having a hole (94,96) therethrough. A wheel damping assembly according to any of claims 1 to 4, further including a second fluid-filled cylinder (27b) disposed within said damping mass, said second cylinder including a first spring (28b) disposed in said fluid-filled cylinder, for opposing, in compression only, vertical motion of said damping mass (20) in a first direction, a second spring (30b) disposed in said fluid-filled cylinder, for opposing, in compression only, vertical motion of said damping mass (20) in a second direction opposite said first direction, and a motion damper for damping vertical motion of said damping mass, comprising a shaft (26a,26b) in said damping mass, and an orifice plate (60a,60b) on said shaft in said fluid-filled cylinder between said first and second springs, through which orifice plate fluid is caused to flow on vertical movement of the wheel assembly to resist vertical motion of said damping mass caused by the vertical vibrations of the wheel assembly.

Inventors: KNOX LAWRENCE D, PARISON JAMES A, KNOX, LAWRENCE D., PARISON, JAMES A.
Applicants: BOSE CORP, BOSE CORPORATION
Application year: 1999
Main classification: B60G13
IPC codes: F16F15, B60B37, B60G3, F16F9, B60G13, F16F7