Patent Description:
Magnetorheological (MR) fluid clutch apparatuses are used for transmitting motion/forces from a drive shaft with precision and accuracy, among other advantages. Accordingly, an increasing number of applications consider the use of MR fluid clutch apparatuses. In a common configuration, the MR fluid clutch apparatus has drums on both the input and the output, with MR fluid located in the annular gaps between the shear surfaces of drums of the input and output. To magnetize the MR fluid located in the annular gaps, a magnetic field passes through the drums, which are known to use materials with high permeability. Steel, for example, is commonly used as material for the drums of MR fluid clutch apparatuses.

There are fabrication constraints associated with steel drums, notably in terms of thickness in relation to cost. As such, drums of high permeability are relatively thick. The thickness of the drum walls results in non-negligible weight considering the mass of steel alloys. As a further consequence of the weight, inertia and momentum of high permeability materials may impact the bandwidth or natural frequency of MR fluid clutch apparatuses. In some of the application where high bandwidth is required, like in collaborative robotics where a robot needs to quickly react to human contact in order to be safe, the drum configuration of prior art MR fluid clutch apparatuses may hamper their performance.

Examples of background art can be found in <CIT>, <CIT> and <CIT> and <CIT>.

It is an aim of the present invention to provide magnetorheological (MR) fluid clutch apparatuses that addresses issues associated with the prior art.

Therefore, in accordance with a first embodiment of the present invention, there is provided a magnetorheological fluid clutch apparatus comprising: at least one input adapted to be coupled to a torque input, the input having at least one input shear surface; an output rotatably mounted about the input for rotating about a common axis with the input, the output having at least one output shear surface, the input shear surface and the output shear surface separated by at least one annular space; magnetorheological fluid in the at least one annular space, the magnetorheological fluid configured to generate a variable amount of torque transmission between the input rotor and output rotor when subjected to a magnetic field; and at least one electromagnet configured to deliver a magnetic field through the magnetorheological fluid, the electromagnet configured to vary the strength of the magnetic field; whereby actuation of the electromagnet results in torque transmission from the input to the output, wherein at least one member defining the at least one of the shear surfaces is made of a low-permeability material such that a circuit of the magnetic field passes through the low permeability material, the low permeability material having a permeability of at most <NUM>. 0x10-<NUM> H/m.

Further in accordance with the first embodiment, for example, the at least one output shear surface includes at least one output drum made with the low-permeability material.

Still further in accordance with the first embodiment, for example, the at least output drum has a thickness ranging <NUM> and <NUM>, inclusively.

Still further in accordance with the first embodiment, for example, a plurality of the output drum may be in a concentric arrangement about the common axis.

Still further in accordance with the first embodiment, for example, the output drums are defined by concentric tubular body portions connected to a common radial wall.

Still further in accordance with the first embodiment, for example, the common radial wall is made from a low-permeability material.

Still further in accordance with the first embodiment, for example, the concentric tubular body portions and the radial wall are a monolithic piece.

Still further in accordance with the first embodiment, for example, the output drums are cups inserted in one another.

Still further in accordance with the first embodiment, for example, the at least one output drum is cylindrical.

Still further in accordance with the first embodiment, for example, the at least one input shear surface includes at least one input drum made with the low-permeability material.

Still further in accordance with the first embodiment, for example, the at least input drum has a thickness ranging <NUM> and <NUM>, inclusively.

Still further in accordance with the first embodiment, for example, a plurality of the input drum may be in a concentric arrangement about the common axis.

Still further in accordance with the first embodiment, for example, the input drums are defined by concentric tubular body portions connected to a common radial wall.

Still further in accordance with the first embodiment, for example, the input drums are cups inserted in one another.

Still further in accordance with the first embodiment, for example, the annular space between the input shear surface and the output shear surface shear has a width of <NUM> +/- <NUM>.

Still further in accordance with the first embodiment, for example, the low-permeability material is a plastic or aluminum.

Still further in accordance with the first embodiment, for example, the plastic or aluminum is doped with metallic particles.

Still further in accordance with the first embodiment, for example, the input is rotatable.

Still further in accordance with the first embodiment, for example, the input is static, and the torque input is a brake torque.

In accordance with a second embodiment of the present invention, there is provided a magnetorheological fluid clutch apparatus comprising: at least one input adapted to be coupled to a torque input, the input having at least one input shear surface; an output rotatably mounted about the input for rotating about a common axis with the input, the output having at least one output shear surface, the input shear surface and the output shear surface separated by at least one annular space; magnetorheological fluid in the at least one annular space, the magnetorheological fluid configured to generate a variable amount of torque transmission between the input rotor and output rotor when subjected to a magnetic field; and at least one electromagnet configured to deliver a magnetic field through the magnetorheological fluid, the electromagnet configured to vary the strength of the magnetic field; whereby actuation of the electromagnet results in torque transmission from the input to the output, wherein at least one member defining the at least one of the shear surfaces is made of a plastic or of an aluminum.

Referring to the drawings and more particularly to <FIG>, there is illustrated a magnetorheological (MR) fluid clutch apparatus <NUM> configured to provide a mechanical output force based on a received input current. The MR fluid clutch apparatus <NUM> is shown as being of the type having collinear input and output shafts, <NUM> and <NUM>, respectively, with the rotational axis shown as CL, as an illustrative example. The concepts described herein may apply to other configurations of MR fluid clutch apparatuses <NUM>, for instance some with an input or output outer shell/casing for an output or input shaft, others with input and output shells, etc. The principles illustrated here will be explained with reference to a MR fluid clutch apparatus having drums but could also be applied to a plate type MR fluid clutch apparatus, i.e., a MR fluid clutch apparatus have disk(s) with the radial surfaces of the disk(s) being the main shear surfaces for torque transmission. Such a MR fluid clutch apparatus is shown in <FIG>.

The MR fluid clutch apparatus <NUM> may provide an output force in response to an input current received from a controller, to transmit an input force. The exemplary MR fluid clutch apparatus <NUM> of <FIG> may have a stator 10A by which the MR fluid clutch apparatus <NUM> is connected to a structure, in accordance with an embodiment. The fixed stator 10A may allow the MR fluid clutch apparatus <NUM> to provide a multiturn output (i.e., the output may rotate about more than <NUM> degrees relative to axis X). In some applications where multiturn is not required, a stator may not be present in the MR fluid clutch apparatus <NUM>. The MR fluid clutch apparatus <NUM> features driven member <NUM> (shown via its shaft <NUM>) and driving member <NUM> (also shown via its shaft <NUM>) separated by gaps filled with an MR fluid, as explained hereinafter. The driving member <NUM> may receive rotational energy (torque) from a power device, such as a motor or like source of torque, with or without a transmission, such as a reduction gear box, a belt, etc..

According to an embodiment, the driving member <NUM> may be in mechanical communication with a power input, and driven member <NUM> may be in mechanical communication with a power output (i.e., force output, torque output). As shown in <FIG>, the stator 10A, the driven member <NUM> and the driving member <NUM> may be interconnected by bearings 12A and 12B. Two bearings are shown, but more may be present. Moreover, as mentioned above, the MR fluid clutch apparatus <NUM> may be without a stator, with the driven member <NUM> and the driving member <NUM> being directly rotatably connected to one another, and with either one or both being mounted to a structure or the like. In the illustrated embodiment, the bearing 12A is between the stator 10A and the driving member <NUM>, whereas the bearing 12B is between the driven member <NUM> and the driving member <NUM>. Seals 12C, such as cup seals (shown, O-rings, etc), may also be provided at the interface between the driven member <NUM> and the driving member <NUM> and/or stator 10A, to preserve MR fluid between the members <NUM> and <NUM>. Moreover, the seals are provided to block MR fluid from reaching the bearing 12B or to leak out of the apparatus <NUM>.

As shown with reference to <FIG> below, drums are located circumferentially about the rotational axis CL. Drums may be defined as having a tubular body portion surrounding the rotational axis CL. The tubular body portion of a drum is shown as being cylindrical, but may have other shapes, such as frusto-conical. Some support must therefore extend generally radially to support the tubular body portion of the drums in their circumferential arrangement. In accordance with one embodiment of the claimed invention, referring to <FIG>, a low permeability input drum support <NUM> (a. , a radial wall or disk/disc) projects radially from a shaft of the driving member <NUM>. The input drum support <NUM> may be connected to an input rotor <NUM> defining the outer casing or shell of the MR fluid clutch apparatus <NUM>. The input rotor <NUM> may therefore be rotatably connected to the driven member <NUM> by the bearing 12B. In an embodiment, the input rotor <NUM> has an input rotor support 14A which forms a housing for the bearing 12B. According to an embodiment, the input rotor support 14A is an integral part of the input rotor <NUM>, and may be fabricated as a single piece. However, this is not necessary as the input rotor support 14A may be made from a low permeability material and the input rotor <NUM> may be made from a high permeability material, as a possibility among others. As another embodiment, as shown in <FIG>, the input rotor support 14A may be defined by an annular wall fabricated separately from a remainder of the input rotor <NUM>, though both are interconnected in any appropriate way for concurrent rotation. Therefore, in the illustrated embodiment, the shaft of the driving member <NUM>, the input drum support <NUM> and the input rotor <NUM> rotate concurrently. In an embodiment, it is contemplated to have the outer shell of the MR fluid clutch apparatus <NUM> be part of the stator 10A, or of the driven member <NUM>.

The input drum support <NUM> may support one or more concentric annular drums <NUM>, also known as input annular drums. The input annular drums <NUM> are secured to the input drum support <NUM>, being common to the annular drums <NUM>. In an embodiment, concentric annular channels are defined (e.g., machined, cast, molded, etc) in the input drum support <NUM> for insertion therein of the drums <NUM>. A tight fit (e.g., force fit), an adhesive and/or radial pins are among the numerous solutions that may be used to secure the drums <NUM> to the input drum support <NUM>. In an embodiment, the input drum support <NUM> is fixed to the shaft of the driving member <NUM> (e.g., monolithic construction, welded, spline, etc), whereby the various components of the driving member <NUM> rotate concurrently when receiving the drive from the power source.

The driven member <NUM> is represented by the output shaft, configured to rotate about axis CL as well. The output shaft may be coupled to various mechanical components that receive the transmitted power output when the MR fluid clutch apparatus <NUM> is actuated to transmit at least some of the rotational power input from the driving member <NUM>.

The driven member <NUM> also has one or more concentric annular drums <NUM>, also known as output drums, mounted to an output drum support <NUM>. The output drum support <NUM> may be an integral part of the output shaft, or may be mounted thereon for concurrent rotation. The annular drums <NUM> are spaced apart in such a way that the sets of output annular drums <NUM> fit within the annular spaces between the input annular drums <NUM>, in intertwined fashion. When either of both the driven member <NUM> and the driving member <NUM> rotate, there may be no direct contact between the annular drums <NUM> and <NUM>, due to the concentricity of the annular drums <NUM> and <NUM>, about axis CL.

In the embodiment of <FIG>, the input drums <NUM> may consist of a heavy high-permeability material (e.g., steel) or a light low-permeability material (e.g., plastic, plastic doped with metallic particle or aluminum) - permeability herein being magnetic permeability, for instance in H/m or N/A<NUM>. Low permeability can be defined as being at or below <NUM>×<NUM>-<NUM> H/m, i.e., at most <NUM>×<NUM>-<NUM> H/m. The output drums <NUM> may be made of a low-permeability material (e.g., plastic, plastic doped with metallic particles or aluminum). The plastic may be a polymer capable of withstanding the relatively high temperatures of operation in a MR fluid with friction. For instance, examples of polymers that may be used include polyetheretherketone (PEEK), or polyamide. Drums <NUM> and/or <NUM> being in the low-permeability material may be relatively thin, with a thickness ranging between <NUM> and <NUM>, inclusively.

According to an embodiment, the annular spaces have a width of <NUM> +/-<NUM>, between the facing surfaces of sets of drums <NUM> and <NUM>, i.e., in the radial direction. These surfaces may be known as the shear surfaces. The width range of the annular spaces is provided only as a non-exclusive example, as other annular space widths are considered as well, taking into account various factors such as overall torque, part sizes, viscous drag, etc..

An electromagnet unit <NUM> may be supported by the stator 10A in the embodiment with the stator 10A. The electromagnet unit <NUM> is used to activate and control the clutch function of the MR fluid clutch apparatus <NUM>. The electromagnetic unit <NUM> is shown schematically, but conventionally may have an annular coil and a core forming an electromagnet, and/or a permanent magnet, and all necessary wiring to create a variable magnetic field.

The annular spaces between the annular drums <NUM> of the driving member <NUM>, and the annular drums <NUM> of the driven member <NUM> are filled with the MR fluid <NUM>. The MR fluid <NUM> used to transmit force between the driven member <NUM> and the driving member <NUM> is a type of smart fluid that is composed of magnetisable particles disposed in a carrier fluid, usually a type of oil. When subjected to a magnetic field, the fluid may increase its apparent viscosity, potentially to the point of becoming a viscoplastic solid. The apparent viscosity is defined by the ratio between the operating shear stress and the operating shear rate of the MR fluid comprised between opposite shear surfaces. The magnetic field intensity mainly affects the yield shear stress of the MR fluid. The yield shear stress of the fluid when in its active ("on") state may be controlled by varying the magnetic field intensity produced by electromagnets and/or permanent magnets, i.e., the input current, via the use of a controller. Accordingly, the MR fluid's ability to transmit force can be controlled with the electromagnet unit <NUM>, thereby acting as a clutch between the members <NUM> and <NUM>. The electromagnet unit <NUM> is configured to vary the strength of the magnetic field via a controller such that the friction between the members <NUM> and <NUM> is low enough to allow the driving member <NUM> to freely rotate relative to the driven member <NUM> and vice versa. Consequently, the MR fluid clutch apparatus <NUM> may vary the amount of force provided in response to a received input by changing the amount of magnetic flux to which is exposed the MR fluid. In particular, the MR fluid clutch apparatus <NUM> may provide an output force based on the input force by changing the amount of magnetic flux based on the input force.

The annular spaces between each set of drum <NUM> and <NUM> are part of a MR fluid chamber sealed off by a seal or seals. The MR fluid chamber include the annular spaces between the set of drums <NUM> and <NUM>, and may include space at the end of drum tips, and space between the drums <NUM> and <NUM> and shear surfaces that are part of the shaft of the driving member <NUM> and input rotor <NUM>. The MR fluid chamber may also include the annular space <NUM>, located opposite the output drum support <NUM>. According to an embodiment, a flow of the MR fluid is as follows. When the driving member <NUM> rotates, some pumping action may be created by the input drums <NUM>, by which the MR fluid <NUM> moves in a radial outward direction after reaching ends of drums <NUM> and <NUM>. Upon going beyond the outermost drum <NUM>, the MR fluid <NUM> may be directed to pass the radial edge of the output drum support <NUM> and into the annular space <NUM>. The MR fluid <NUM> will move radially inward, to return to the other side of the output drum support <NUM> to cycle between the drums <NUM> and <NUM>, via holes in the output drum support <NUM>.

The movement of the MR fluid in the manner described above allows the MR fluid to cycle in the MR fluid chamber. The movement may be achieved via the presence of helical channels on the surface of the drums <NUM>. Other surface depressions or local variations of permeability could also be used on either one of the drum sets <NUM> or <NUM> to induce a pumping action in the MR fluid chamber, i.e., some form of cavity, protrusion or channel in an otherwise smooth cylindrical surface.

In the embodiment of the claimed invention of <FIG>, the MR fluid clutch apparatus <NUM> is similar to the one of <FIG>, whereby like reference numerals represent like elements. In the embodiment of <FIG>, as shown as assembly <NUM>, the input drum support <NUM> and the input drum(s) <NUM> are one integral piece, such as a monolithic piece. As shown as assembly <NUM>, the output drum(s) <NUM> and output drum supports <NUM> may also be made of one integral piece, such as a monolithic piece. For example, the assembly <NUM> of input drum support <NUM> and input drum(s) <NUM> may consist of a relatively heavy high-permeability material (e.g., steel) or a light low-permeability material (e.g., plastic, plastic doped with metallic particle or aluminum). The assembly <NUM> is made of a low-permeability material (e.g., plastic, plastic doped with metallic particle, aluminum or aluminum doped with metallic particle, among other possibilities). In accordance with an embodiment, the assembly <NUM> and/or the assembly <NUM> is(are) integrally molded into a single piece(s). For example, the assembly <NUM> and/or <NUM> may be injection-molded from plastic.

In the embodiment of the claimed invention of <FIG>, the MR fluid clutch apparatus <NUM> is similar to the one of <FIG>, whereby like reference numerals represent like elements. In <FIG>, the input drums <NUM> and/or the output drums <NUM> are stamped in a light low-permeability material (e.g., plastic, plastic doped with metallic particle, aluminum or aluminum doped with metallic particle, among other possibilities). In the embodiment of <FIG>, the input drums <NUM> and/or the output drums <NUM> may be regarded as a plurality of cylindrical cups inserted into one another, from larger to smaller. This is shown for example in greater detail in <FIG>, with lines of annularity removed to emphasize the cups. Such lines are present in <FIG> as vertical lines at the open end of cups.

<FIG> is a close-up view of the input drums <NUM> and/or the output drums <NUM> of MR fluid clutch apparatus <NUM> of <FIG>. The close-up shows the plurality of cylindrical cups inserted into one another, from larger to smaller. The cups may be attached one to another by any appropriate way, including spot welding, bonding, press-fit or any other type of mechanical attachment method.

In one or more of the embodiments of <FIG>, the space <NUM>, if present, may be in fluid communication with an expansion system <NUM>. The expansion system <NUM> may be in a cavity inside shafts of the driven member <NUM> and driving member <NUM> and the cavity may be filled with a compliant material, like closed cell neoprene, or a diaphragm or like compliant membrane. This is one example among others of MR fluid circulation.

In one or more of the embodiments of <FIG>, when a current passes through the annular coil, a magnetic field is produced in the core of the electromagnetic unit <NUM> and through the intertwined arrangement of drums <NUM> and <NUM> and shear surfaces of the shaft <NUM> and input rotor <NUM>, with MR fluid <NUM> therebetween. The magnetic field therefore increase the apparent viscosity of the MR fluid <NUM>, to seize the drums <NUM> and <NUM>, to cause a transmission of the rotational motion from the input drums <NUM> to the output drums <NUM>. The intertwined arrangement of drums <NUM> and <NUM>, allows the increase of the total clutch contact surface and of the clutch contact surface per volume of MR fluid <NUM>. In another embodiment, the electromagnetic unit <NUM> is used to reduce a magnetic field on the arrangement of drums <NUM> and <NUM>, as caused by a permanent magnet. This is for instance as described in <CIT>, entitled Magnetorheological Fluid Clutch Apparatus with Cylindrical Air Gap.

In one possible configuration, during operation, a power source (not shown) causes the driving member <NUM> to rotate. MR fluid <NUM> transmits at least some rotational energy (torque) to the driven member <NUM> by the application of a magnetic field by the electromagnet unit <NUM>, thereby causing driven member <NUM> to rotate. The electromagnet unit <NUM> subjects MR fluid <NUM> to a magnetic field that, if varied, may change the apparent viscosity of MR fluid <NUM>. Changing the apparent viscosity of MR fluid <NUM>, in turn, may change the amount of rotational energy transferred from driving member <NUM> to driven member <NUM>. Accordingly, in the example of the MR fluid clutch apparatus <NUM>, the amount of rotational energy transferred to driven member <NUM> may be regulated by controlling the amount of magnetic field generated by the electromagnet unit <NUM>, for instance via a controller.

The use of low-permeability materials for the drums <NUM> and/or <NUM> may result in a lighter MR fluid clutch apparatus <NUM> in comparison to high-permeability drums <NUM> and/or <NUM> of the same diameter. In some conditions, it may be possible to reduce the inertia of the output drum <NUM> more than four times by using a light low-permeability material (i.e., plastic). This may have the effect of doubling the bandwidth of the MR fluid clutch apparatus <NUM>, in a particular set up. Consequently, the performance of the MR fluid clutch apparatus <NUM> of the present disclosure may be improved in terms of bandwidth (i.e., response frequency) via a reduced inertia over MR fluid clutch apparatuses <NUM> without low-permeability materials for the drums or discs. Moreover, with lower inertial and momentum forces due to the weight reduction in the drums <NUM> and/or <NUM>, the durability of the MR fluid <NUM> may be increased, as there may result reduced slippage. There may also be an advantage (e.g., increase torque, increase MRF durability and decrease drum wear) of having a boundary layer of MR fluid <NUM> "stick" or adhere to the drum surfaces. Increased adhesion may limit the slip between the fluid boundary layer and the adjacent drum surface. Having a limited slip may distribute the shearing motion in the MR fluid <NUM> itself, between MR fluid particles, and not between the drum surface and the MR fluid particles. The boundary layer speed in relation to the drum <NUM>/<NUM> may also be decreased. The surface of the drums <NUM>/<NUM> may be irregular or with a high roughness, due to liberties from manufacturing, and this may be used to increase the adhesion of the MR fluid <NUM> on the drum surface. The surface of the low-permeability material may also be coated with a thin film of high-permeability material in order to increase the propensity of the MR fluid <NUM> to stick to the drum material.

In comparison to MR fluid clutch apparatuses with drums made solely of high-permeability materials, the MR fluid clutch apparatus <NUM> of the present disclosure may have an increased torque to inertia ratio resulting from the lighter drums. A higher torque to inertia ratio may improve controllability (higher bandwidth). However, using a low-permeability material for the drums will decrease the ability of the drums to support and transmit the magnetic flux and therefore, for a given design and coil current, the amount of magnetic flux in the MR fluid <NUM> may be reduced. If the magnetic circuit of the MR fluid clutch apparatus <NUM> reaches saturation, this may result in a decrease in the torque to weight ratio with the MR fluid clutch apparatus <NUM>. The torque to weight ratio may be maintained high, notably by keeping the thickness of the low-permeability material relative low. The torque to volume ratio of the MR fluid clutch apparatus <NUM> may also be decreased in comparison to conventional MR fluid clutch apparatuses because a larger coil for the electromagnet unit <NUM> may be required to saturate the MR fluid <NUM>. This ratio may also be controlled by keeping the thickness of the low-permeability material as small as possible.

As shown in the embodiments of <FIG>, by making some or all of the drums <NUM> and/or <NUM> in a low-permeability material, parts may be combined together, such as the input drum support <NUM> with input drums <NUM>, and/or the output drum support <NUM> with output drums <NUM>. Combining parts may reduce the parts counts and the cost.

In the embodiment of <FIG>, the MR fluid brake apparatus <NUM> is similar to the MR fluid clutch apparatus <NUM> of <FIG>, whereby like reference numerals represent like elements. The MR fluid brake apparatus <NUM> may also be referred to as a MR fluid clutch apparatus, with a static member. In <FIG>, the driving member <NUM> and the stator 10A are now represented as a non-moving part in order to act as a brake when stator 10A is mounted on a chassis (not illustrated) or like structure. Stated differently, there is no stator 10A or no driving member <NUM> in <FIG>. Torque generation of the MR fluid brake apparatus <NUM> is similar to the one of MR fluid clutch apparatus <NUM> of <FIG>, with the driven member <NUM> rotating because of an output it may receive via its shaft, and exteriorly from the MR fluid clutch apparatus <NUM>. The electromagnet unit <NUM> is actuated to cause a braking effect on the driven member <NUM>, by the static driving member <NUM>/stator 10A. The MR fluid brake apparatus <NUM> may have the cup configuration shown in <FIG> and <FIG>, or the configurations shown in <FIG> and <FIG>.

Claim 1:
A magnetorheological fluid clutch apparatus (<NUM>) comprising:
at least one input (<NUM>) adapted to be coupled to a torque input, the input having at least one input shear surface;
an output (<NUM>) rotatably mounted about the input (<NUM>) for rotating about a common axis with the input (<NUM>), the output having at least one output shear surface, the input shear surface and the output shear surface separated by at least one annular space;
magnetorheological fluid (<NUM>) in the at least one annular space, the magnetorheological fluid (<NUM>) configured to generate a variable amount of torque transmission between the at least one input (<NUM>) and the output (<NUM>) when subjected to a magnetic field; and
at least one electromagnet (<NUM>) configured to deliver a magnetic field through the magnetorheological fluid (<NUM>), the electromagnet configured to vary the strength of the magnetic field;
whereby actuation of the electromagnet (<NUM>) results in torque transmission from the input (<NUM>) to the output (<NUM>),
characterized in that:
at least one member defining the at least one of the shear surfaces is made of a low-permeability material such that a circuit of the magnetic field passes through the low-permeability material,
wherein the low-permeability material has a permeability of at most <NUM>×<NUM>-<NUM> H/m.