RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 60/686,159 filed June 1, 2005, the entire contents of which are hereby incorporated by reference.

BACKGROUND

[0002] The present invention relates to magnetorheological fluid clutches.

[0003] Magnetorheological fluid clutches are known, and include both stationary coil designs and rotating coil designs. Stationary coil designs can be advantageous in that they eliminate the need for a slip ring, which is required in a rotating coil design to transmit power to the rotating coil that is located in the rotor or the stator.

SUMMARY

[0004] Typically, the stationary coil of a magnetorheological fluid clutch is mounted independently of the two components of the magnetic circuit, and the clutch is configured to wrap around the stationary coil. The magnetorheological fluid clutch of the current invention includes an integrated stationary coil that is mounted substantially within the envelope of the clutch, and more specifically within the envelope defined by the two components of the magnetic circuit.

[0005] Tight control of the fluid gap between the two mating components of the magnetic circuit, and the air gap between the stationary coil and one of the magnetic circuit components, is important for proper performance of the clutch. Variations in the air gap or fluid gap can result in deficiencies in torque generation or power requirements. To control the air gap and the fluid gap, the magnetorheological fluid clutch of the invention includes bearings that precisely locate

the stationary coil and the two magnetic circuit components relative to one another. Additionally, the placement of the bearings provides a direct load path for the loads applied to a first component of the magnetic circuit to be passed to the shaft on which the clutch is mounted. Prior art stationary coil magnetorheological fluid clutch designs typically require the load path to travel around the non-integrated stationary coil to the shaft, which results in overhanging loads that may lead to premature bearing failure.

[0006] In one aspect, the invention provides a magnetorheological fluid clutch that includes three bearings to precisely locate the two magnetic circuit components and the integrated stationary coil relative to one another. The first bearing is positioned between the two magnetic circuit components. The second bearing is positioned between one of the magnetic circuit components and the stationary coil. The third bearing is positioned between the stationary coil and the other of the two magnetic circuit components. In one embodiment, the magnetorheological fluid clutch can be part of a power steering pump assembly.

[0007] The invention further provides a magnetorheological fluid clutch including a first magnetic circuit component and a second magnetic circuit component. The first and second magnetic circuit components define therebetween a fluid gap containing a fluid. A stationary coil assembly is operable to selectively magnetically lock the first and second magnetic circuit components together for co-rotation. A sensor is coupled with the stationary coil assembly and is operable to sense a rotational speed of the second magnetic circuit component. In one embodiment, a target wheel is coupled for rotation with the second magnetic circuit component, and the sensor is operable to sense a rotational speed of the target wheel.

[0008] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Fig. 1 is a perspective view, partially in section, illustrating a magnetorheological fluid clutch embodying the invention and being used in a power steering pump application.

[0010] Fig. 2 is a section view of the clutch of Fig. 1.

[0011] Fig. 3 is a magnetic flux diagram for the clutch of Fig. 1.

[0012] Fig. 4 is a perspective view illustrating a magnetorheological fluid clutch that is an alternative embodiment of the invention.

[0013] Fig. 5 is a section view of the clutch of Fig. 4.

[0014] Fig. 6 is a magnetic flux diagram for the clutch of Fig. 4.

DETAILED DESCRIPTION

[0015] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings.

[0016] Fig. 1 illustrates a power steering pump assembly 10 including a power steering pump 14 and a magnetorheological fluid clutch 18 (hereinafter referred to as "the MR clutch 18") embodying the invention. The MR clutch 18 enables the power steering to be deactivated when desirable to reduce horsepower loss. While the MR clutch 18 is shown and described for use in a power steering application, it should be understood that the MR clutch 18 can also be used in other applications, including but not limited to, transmission applications, engine cooling fan applications, and other applications requiring a clutch for torque responsive control.

[0017] The power steering pump 14 includes a housing 22 that contains the pump components (generally designated by the reference numeral 26). Additionally, the housing 22 includes an elongated storage chamber portion 30 that stores the power steering fluid. An input shaft 34 extends from the power steering pump 14 to receive a pulley 38 that is driven by the vehicle's engine via a belt 42 (see Fig. 2) coupled to the pulley 38. The MR clutch 18 is disposed on the input shaft 34 such that the pulley 38 forms a first component of the magnetic circuit. While the pulley 38 is illustrated schematically as being one piece, it would likely be formed as two or more pieces both for assembly purposes, and in order to have selective portions of the pulley 38 made of a magnetically conductive material (e.g. low carbon steel) and other portions of the pulley 38 made of non-magnetically conductive materials (e.g., aluminum or stainless steel).

[0018] While the pulley 38 forms a first component of the magnetic circuit, the MR clutch 18 includes a rotor 46 that forms a second component of the magnetic circuit. The rotor 46 is also made of a magnetically conductive material and is coupled to the shaft 34 for rotation therewith (e.g., by press-fit, keyed connection, etc.). The illustrated rotor 46 is housed completely within the envelope defined by the outer dimensions of the pulley 38. As best shown in Fig. 2, a fluid gap 50 is defined between an outer surface 54 of the rotor 46 and an inner surface 58 of the pulley 38, and contains magnetorheological fluid, as is understood by those skilled in the art. Seals 60 keep the magnetorheological fluid in the fluid gap 50. While the rotor 46 is illustrated schematically as being one piece, it would likely be formed as two or more pieces for assembly purposes.

[0019] Housed within the rotor 46 is a stationary coil assembly 62 including a stationary coil holder 64 made of a magnetically conductive material. The stationary coil holder 64 supports a stationary coil 66 (shown in Fig. 2, but removed in Fig. 1). Referring to Fig. 2, together the stationary coil holder 64 and the stationary coil 66 define a surface 70 spaced from an inner surface 74 of the rotor 46. The space between the surfaces 70 and 74 defines an air gap 78 between the stationary coil assembly 62 and the rotor 46.

[0020] The stationery coil holder 64 includes an extension portion 82 that extends toward the pump housing 22. The extension portion 82 is connected to the pump housing 22 such that the

stationary coil assembly 62 remains stationary during rotation of the shaft 34 and the rotor 46. By keeping the coil 66 and coil holder 64 stationary, it is easy to run power (e.g., by routing wires) to the coil 66 from the pump housing 22 through or along the stationary coil holder 64. Because of the ability to have a stationary wire attachment point, no slip rings or other electrical connections are required as is the case when a rotating coil design is used. While the stationary coil holder 64 is illustrated schematically as being one piece, it would likely be formed as two or more pieces for assembly purposes.

[0021] Except for the end of the extension portion 82 that connects to the pump housing 22, the entire stationary coil assembly 62 is housed completely within the envelope defined by the outer dimensions of the pulley 38, and is also housed completely within the envelope defined by the outer dimensions of the rotor 46. Integration of the stationary coil assembly 62 with and within the pulley 38 and the rotor 46 in this manner facilitates a more compact, efficient, and cost-effective design for an MR clutch 18 than was previously possible in designs that mounted the stationary coil separately from and independently of the components of the magnetic circuit.

[0022] Accurate control of the fluid gap 50 and the air gap 78 is important to the operation of the MR clutch 18, and requires precise positioning of the pulley 38, the rotor 46, and the stationary coil assembly 62 relative to one another. To maintain the precise positioning of these components, the MR clutch 18 includes a plurality of bearings arranged between the components. A first bearing 86 is positioned between the pulley 38 and the rotor 46 and helps accurately control the spacing of the fluid gap 50 by limiting the relative positioning between the pulley 38 and the rotor 46. The illustrated bearing 86 is a ball bearing, however, other rolling elements could be substituted for balls should space permit.

[0023] A second bearing 90 is positioned between the stationary coil assembly 62 and the rotor 46 and helps accurately control the spacing of the air gap 78 by limiting the relative positioning between the stationary coil assembly 62 and the rotor 46. The illustrated bearing 90 is a needle bearing, however, other types of roller bearings can also be substituted.

[0024] A third bearing 94 is positioned between the stationary coil assembly 62 and the pulley 38 and helps to accurately, at least partly, control the spacing of the fluid gap 50 by limiting the relative positioning between the stationary coil assembly 62 and the pulley 38. The

illustrated bearing 94 is a ball bearing, however, other rolling elements could be substituted for balls should space permit.

[0025] It can therefore be seen that each of the three main components, i.e., the pulley 38, the rotor 46, and the stationary coil assembly 62 are integrated together, and are accurately positioned relative to one another via the three bearings 86, 90, and 94, as described above. This maintains the tight control needed for the fluid gap 50 and the air gap 78. Additionally, the three bearings 86, 90, 94 provide a direct load path for loads applied to the pulley 38 to be transmitted through the stationary coil assembly 62 and the rotor 46 to the shaft 34. At least two of the bearings 86, 90, 94, and as illustrated all three of the bearings 86, 90, 94, are located at least partially within the axial extents of the fluid gap 50, and radially between the fluid gap 50 and the shaft 34. Prior art stationary coil magnetorheological fluid clutch designs typically required the load path to travel around the stationary coil assembly, which was separate from and independent of the components of the magnetic circuit, before being transmitted to the shaft. This typically resulted in overhanging loads that could lead to premature bearing failure.

[0026] With reference to Figs. 1 and 2, the illustrated MR clutch 18 further includes a target wheel 98 coupled to the rotor 46 for rotation therewith. As best shown in Fig. 2, a sensor 102 is mounted on the stationary coil holder 64 opposite the target wheel 98 so that the speed of the pump shaft 34 can be sensed and monitored. In the illustrated embodiment, a Hall Effect sensor can be used for the sensor 102. In some embodiments, multiple Hall Effect sensors may be used to increase resolution. Other types of sensors that can also be used are magnetic speed pick-up sensors, optical sensors, and laser sensors.

[0027] Fig. 3 illustrates a model of the magnetic flux for the MR clutch 18 discussed above. The model of Fig. 3 illustrates that when the current is applied to the coil 66, a magnetic flux is created. Fluid in the fluid gap 50 is magnetized such that the conductive particles in the fluid align across the fluid gap 50 (as represented by the generally horizontal contour lines within the fluid gap 50) and magnetically lock the pulley 38 and the rotor 46 together for co-rotation to drive the input shaft 34 of the power steering pump 14.

[0028] Figs. 4-6 illustrate a second embodiment of a MR fluid clutch 118 of the invention. As with the clutch 18, the clutch 118 can be used with a power steering pump assembly 10 as

well as with other applications. The MR clutch 118 is a double-gap design, which can be more manufacturable than the single gap design illustrated in Figs. 1-3. Additionally, as those skilled in the art will understand, a double-gap design MR fluid clutch can reduce the axial envelope of the clutch while maintaining a sufficient surface area (i.e., the surface area for two gaps instead of just one) for the magnetic coupling.

[0029] A multi-piece pulley 138 forms a first component of the magnetic circuit. The multi- piece pulley includes a first portion 139 that is coupled to a drive belt (not shown). The first portion 139 can be an aluminum casting or other non-magnetically conductive material. A second portion 140 of the pulley 138, which is also an aluminum die-cast part in the illustrated embodiment, is rotationally fixed to the first portion 139 via toothed engagement 141. The second portion 140 includes first and second magnetically-conductive material portions 142, 143 (e.g., steel) that are adjacent the two fluid gaps, as will be discussed further below. In the illustrated embodiment, the first and second magnetically-conductive material portions 142, 143 are cast around/within the second portion 140 of the pulley 138, and can be formed by drawing or other suitable methods prior to being cast within the second portion 140 of the pulley 138. A non-magnetically conductive insert 144 (e.g., aluminum or stainless steel) is positioned within the first magnetically-conductive material portions 142 to facilitate the appropriate flux path. Finally, the pulley 138 includes an end cap 145 secured (e.g., by screws) to the second portion 140 of the pulley 138. The end cap 145 provides access to fill the clutch 118 with magnetorheological fluid.

[0030] A rotor 146 forms a second component of the magnetic circuit of the MR clutch 118. The rotor 146 is made of a magnetically conductive material and includes a rotor portion 147 coupled for rotation with a hub portion 148 configured to receive the input shaft 34 of the pump assembly 10. The rotor portion 147 extends between the first and second magnetically- conductive material portions 142, 143 of the pulley 138 to define first and second fluid gaps 150a, 150b. Seals 160 keep the magnetorheological fluid in the fluid gaps 150a, 150b.

[0031] A stationary coil assembly 162 includes a stationary coil holder 164 made of a magnetically conductive material. The coil holder 164 supports a stationary coil 166. Together, the stationary coil holder 164 and the coil 166 define a surface 170 spaced from an inner surface

174 of the pulley 138. The space between the surfaces 170 and 174 defines an air gap 178 between the stationary coil assenibly 162 and the pulley 138.

[0032] The stationary coil assembly 162 further includes a stationary collar 180 fixed with the coil holder 164, and a mounting bracket 182 fixed to the stationary collar 180. The mounting bracket 182 secures the MR clutch 118 to the pump housing 22. Note that in the embodiment of Fig. 1, the mounting bracket is not shown, but would be fixed to the extension portion 82.

[0033] Just as with the MR clutch 18, accurate control of the fluid gaps 150a, 150b, and the air gap 178 is important to the operation of the MR clutch 118. To maintain precise positioning of the pulley 138, the rotor 146, and the stationary coil assembly 162 relative to one another, three bearings are provided. A first bearing 186 is positioned between the pulley 138 and the rotor 146. Specifically, the first bearing 186 is positioned between part of the second portion 140 of the pulley 138 and the hub portion 148 of the rotor 146. This bearing helps accurately control the spacing of the fluid gaps 150a, 150b by limiting the relative positioning between the pulley 138 and the rotor 146. The illustrated bearing 186 is a ball bearing, however other rolling elements (e.g., needles) could be substituted for balls should space permit.

[0034] A second bearing 190 is positioned between the stationary coil assembly 162 and the rotor 146, and more specifically between the mounting bracket 182 and the hub portion 148 of the rotor 146. The second bearing 190 helps accurately control the spacing of the fluid gaps 150a, 150b by limiting the relative positioning between the stationary coil assembly 162 and the rotor 146. The illustrated bearing 190 is a ball bearing, however, other types of roller bearings can also be substituted.

[0035] A third bearing 194 is positioned between the stationary coil assembly 162 and the pulley 138, and more specifically between the mounting bracket 182 and the first portion 139 of the pulley 140. The third bearing 194 helps to accurately, at least partly, control the spacing of the fluid gaps 150a, 150b and the air gap 178 by limiting the relative positioning between the stationary coil assembly 162 and the pulley 138. The illustrated bearing 194 is a ball bearing, however, other rolling elements could be substituted for balls should space permit.

[0036] As with the MR clutch 18 as described above, it can therefore be seen that each of the three main components of the MR clutch 118, i.e., the pulley 138, the rotor 146, and the stationary coil assembly 162 are integrated together, and are accurately positioned relative to one another via the three bearings 186, 190, and 194. This maintains the tight control needed for the fluid gaps 150a, 150b and the air gap 178. Additionally, the three bearings 186, 190, 194 provide a direct load path for loads applied to the pulley 138 to be transmitted through the stationary coil assembly 162 and the rotor 146 to the shaft 34. At least two of the bearings 186, 190, 194, and as illustrated all three of the bearings 186, 190, 194, are located at least partially within the axial extents of the fluid gaps 150a, 150b, and radially between the fluid gaps 150a, 150b and the shaft 34. Prior art stationary coil magnetorheological fluid clutch designs typically required the load path to travel around the stationary coil assembly, which was separate from and independent of the components of the magnetic circuit, before being transmitted to the shaft. This typically resulted in overhanging loads that could lead to premature bearing failure.

[0037] With reference to Fig. 5, the illustrated MR clutch 118 further includes a target wheel 198 coupled to the rotor 146 at the hub portion 148 for rotation therewith. A sensor 202 is mounted on the stationary collar 180 opposite the target wheel 198 so that the speed of the pump shaft 34 can be sensed and monitored. In the illustrated embodiment, a Hall Effect sensor can be used for the sensor 202. In some embodiments, multiple Hall Effect sensors may be used to increase resolution. Other types of sensors that can also be used are magnetic speed pick-up sensors, optical sensors, and laser sensors.

[0038] Fig. 6 illustrates a model of the magnetic flux for the MR clutch 118 discussed above. The model of Fig. 6 illustrates that when the current is applied to the coil 166, a magnetic flux is created. Fluid in the fluid gaps 150a, 150b is magnetized such that the conductive particles in the fluid align across the fluid gaps 150a, 150b (as represented by the generally horizontal contour lines within the fluid gaps 150a, 150b) and magnetically lock the pulley 138 and the rotor 146 together for co-rotation to drive the input shaft 34 of the power steering pump 14.

[0039] Various features of the invention are set forth in the following claims.