Patent Description:
In-wheel electric motors are gaining popularity as both primary and secondary propulsion solutions for plug-in-hybrid vehicles (PHEVs) and electric vehicles (EVs). In-wheel electric motors mount inside the wheels of a vehicle and therefore permit better torque vectoring capabilities and offer packaging advantages because they do not take up additional space inside the vehicle body and allow for the elimination of traditional driveshafts.

<CIT> illustrates an example of such in-wheel electric motors.

An important factor when designing an in-wheel motor is magnetic gap deformation. Magnetic gap deformation is the relative displacement between the rotor and stator of the electric motor. High magnetic gap deformation worsens the high frequency vibrations experienced in the vehicle and can also be detrimental to the longevity and reliability of the in-wheel electric motor. It is therefore imperative to limit this magnetic gap deformation. When magnetic gap deformation is high, design tolerances require a larger gap between the rotor and the stator, which also decreases the efficiency of the in-wheel electric motor. In other words, in-wheel electric motors are most efficient when the gap between the rotor and stator is small, but magnetic gap deformation places design limits on the size of this gap, therefore necessitating the use of larger, less efficient electric motors. In addition to reduced efficiency, another drawback is that larger, less efficient in-wheel electric motors increase the unsprung mass of the vehicle because the electric motors are located inside the wheels. This can also worsen ride comfort and tire grip. As a result, there is a need for solutions that limit the negative effects magnetic gap deformation can have on vehicles that are equipped with in-wheel electric motors.

In particular, the description of the physical embodiments of the design are not intended to limit this disclosure to only the specific arrangements and design features of the particular examples shown and described herein.

The object of the disclosure is solved by the features of the independent claim <NUM>. Advantageous embodiments emerge from the dependent claims, the description and the figures.

In accordance with one aspect of the present disclosure, a wheel assembly is provided, which includes a wheel hub, a wheel rotatably mounted on the wheel hub, an in-wheel electric motor, and at least one wheel assembly bushing. The in-wheel electric motor includes a stator that is mounted on the wheel hub and a rotor that is coupled to the wheel. As such, the rotor and wheel rotate together relative to the stator and wheel hub. The wheel assembly bushing(s) include(s) an inner bushing member, an outer body, and a resilient sleeve. The outer body of the wheel assembly bushing(s) is concentrically arranged about and radially spaced from the inner bushing member and the resilient sleeve is positioned radially between the inner bushing member and the outer body.

The wheel assembly bushing(s) also include(s) a hydraulic chamber positioned within the resilient sleeve and a fluid channel that extends between first and second fluid channel ends, which are arranged in fluid communication with the hydraulic chamber. The resilient sleeve is made of a resilient material such that the resilient sleeve is configured to permit relative movement between the inner bushing member and the outer body. The fluid channel is configured to produce a phase delay between input forces that cause relative movement between the inner bushing member and the outer body and reaction forces that are produced by pressure pulses in the hydraulic chamber resulting from fluid flow through the fluid channel. The principle behind this phase delay between the input and reaction forces is known as inertance.

In accordance with another aspect of the present disclosure, a wheel assembly bushing is provided that includes an inner bushing member, an outer body, and a resilient sleeve. The inner bushing member of the wheel assembly bushing extends axially along a longitudinal axis. The resilient sleeve of the wheel assembly bushing extends annularly about the inner bushing and is made of a resilient material. The outer body of the wheel assembly bushing is concentrically arranged about and is radially spaced from the inner bushing member. The outer body of the wheel assembly bushing extends annularly about the resilient sleeve such that the resilient sleeve is positioned radially between the inner bushing member and the outer body.

A hydraulic chamber is positioned within the resilient sleeve. The hydraulic chamber extends annularly within the resilient sleeve and axially between a first hydraulic chamber end and a second hydraulic chamber end. A helical fluid channel extends helically about the inner bushing member between a first fluid channel end and a second fluid channel end. The wheel assembly bushing(s) also include(s) a divider body, within the resilient sleeve, that extends into the hydraulic chamber at a location that is positioned longitudinally between the first and second hydraulic chamber ends. The divider body divides the hydraulic chamber into first and second hydraulic chamber segments. The first fluid channel end of the helical fluid channel is arranged in fluid communication with the first hydraulic chamber segment and the second fluid channel end of the helical fluid channel is arranged in fluid communication with the second hydraulic chamber segment. In addition, a fluid passageway is provided in the resilient sleeve and/or the divider body, which permits fluid flow around or through the divider body such that fluid can pass between the first and second hydraulic chamber segments.

With typical in-wheel electric motors, the rotor is fixed to the wheel of the vehicle and the stator is fixed to the wheel hub mass. Such an arrangement does not allow the magnetic gap deformation to be adjusted independently. In order to reduce the ill-effects of magnetic gap deformation and improve the efficiency of in-wheel electric motors, the rotor and stator are isolated from the wheel and wheel hub using the wheel assembly bushings described herein. This effectively reduces magnetic gap deformation in the in-wheel electric motor without degrading ride comfort (often termed body vertical acceleration) and tire grip (often termed tire dynamic load).

Advantageously, the phase delay / inertance created by the fluid channel in the wheel assembly bushings described herein produces reaction forces proportional to the relative acceleration of fluid between the first and second fluid channel ends. Hence, these components of the wheel assembly bushings described herein act as a mechanical equivalent to an electrical capacitor, using the force-current relationship in an electrical capacitor as an analogy. The phase delay / inertance created by the fluid channel in the wheel assembly bushings (collectively forming a fluid-filled inertia track inside the wheel assembly bushing), combined with other damping and stiffness effects of the wheel assembly bushing, will provide phase and magnitude shifts between force and relative movement between the resilient sleeve and the outer body. Such effects significantly enhance the vibration suppression functionality of the wheel assembly bushings described herein.

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure.

Wherever possible, the same reference numbers will be used throughout the drawings to refer to same or like parts.

It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure, which is solely defined by the appended claims.

<FIG> and <FIG> illustrate an exemplary wheel assembly <NUM> for a vehicle (not shown). The wheel assembly <NUM> includes a wheel hub <NUM>, a wheel <NUM> that is rotatably mounted on the wheel hub <NUM>, and an in-wheel electric motor <NUM>. The wheel hub <NUM> includes a hub portion <NUM> and a shaft portion <NUM>. The shaft portion <NUM> of the wheel hub <NUM> has a smaller diameter than the hub portion <NUM> of the wheel hub <NUM> and is positioned outboard of the hub portion <NUM>, meaning that the shaft portion <NUM> of the wheel hub <NUM> is further from a centerline of the vehicle than the hub portion <NUM>. The shaft portion <NUM> of the wheel hub <NUM> extends out from the hub portion <NUM> to an outboard end <NUM> and a wheel bearing <NUM> is positioned on the outboard end <NUM> of the shaft portion <NUM> of the wheel hub <NUM>. The wheel <NUM> includes an attachment portion <NUM> that includes a central bore <NUM> and a plurality of bolt holes <NUM> that are circumferentially spaced about the central bore <NUM>. The wheel <NUM> also includes spokes <NUM> that extend radially outward from the attachment portion <NUM> to an outer rim <NUM> that supports a tire <NUM>. The wheel <NUM> is mounted over the wheel bearing <NUM> where the outboard end <NUM> of the shaft portion <NUM> of the wheel hub <NUM> and the wheel bearing <NUM> are received in the central bore <NUM> of the wheel <NUM>. In this way, the wheel <NUM> is supported on and can rotate relative to the shaft portion <NUM> of the wheel hub <NUM> about an axis of rotation <NUM>.

The in-wheel electric motor <NUM> includes a stator <NUM> that is mounted on the wheel hub <NUM> and a rotor <NUM> that is coupled to the wheel <NUM> by a plurality of wheel bolts <NUM> that extend through the bolt holes <NUM> in the wheel <NUM> and thread into threaded bores <NUM> in a base portion <NUM> of the rotor <NUM>. In the illustrated example, the wheel <NUM> includes four bolt holes <NUM>, which receive four wheel bolts <NUM>. However, it should be appreciated that the number of wheel bolts <NUM> and bolt holes <NUM> may vary from vehicle to vehicle. Alternatively, the wheel <NUM> may be configured in a center-lock configuration where a single / central wheel bolt or fastener attaches the wheel <NUM> to the base portion <NUM> of the rotor <NUM>. Regardless of the configuration, the rotor <NUM> and wheel <NUM> rotate together relative to the stator <NUM> and wheel hub <NUM>. The stator <NUM> includes an inboard portion <NUM> and an outboard portion <NUM>. The inboard portion <NUM> of the stator <NUM> extends annularly about and is supported on the hub portion <NUM> of the wheel hub <NUM>, meanwhile the outboard portion <NUM> of the stator <NUM> extends annularly about and is support on the shaft portion <NUM> of the wheel hub <NUM>. The outboard portion <NUM> of the stator <NUM> includes a cylindrical base <NUM> that extends annularly about the shaft portion <NUM> of the wheel hub <NUM>, a disc portion <NUM> that extends radially outwardly from the cylindrical base <NUM> to an outer circumferential ring <NUM>. The base portion <NUM> of the rotor <NUM> includes a central cavity <NUM> that houses a rotor bearing assembly <NUM>. The rotor bearing assembly <NUM> extends annularly between the cylindrical base <NUM> of the stator <NUM> and the base portion <NUM> of the rotor <NUM>. The rotor <NUM> includes a transverse body <NUM> that extends radially outwardly from the base portion <NUM> of the rotor <NUM> to a circumferential housing <NUM> that extends about and encloses the outer circumferential ring <NUM> of the stator <NUM>. As such, a magnetic gap <NUM> is formed between the circumferential housing <NUM> of the rotor <NUM> and the outer circumferential ring <NUM> of the stator <NUM>.

Optionally, the wheel assembly <NUM> further includes a brake disc <NUM> and a brake caliper <NUM>. In the illustrated example, the brake caliper <NUM> is fixed to the inboard portion <NUM> of the stator <NUM> and the brake disc <NUM> is fixed to the rotor <NUM> and extends radially inwardly from the circumferential housing <NUM> such that the brake disc <NUM> and rotor <NUM> rotate together relative to the brake caliper <NUM>. However, it should be appreciated that alternative configurations are possible. For example, the brake caliper <NUM> may alternatively be mounted to the hub portion <NUM> of the wheel hub <NUM>.

The wheel assembly <NUM> illustrated in <FIG> and <FIG> also includes a number of wheel assembly bushings 84a, 84b, 84c. In particular, the wheel assembly <NUM> includes a first wheel assembly bushing 84a that is positioned between the hub portion <NUM> of the wheel hub <NUM> and the inboard portion <NUM> of the stator <NUM>. The wheel assembly <NUM> also includes a second wheel assembly bushing 84b that is positioned between the shaft portion <NUM> of the wheel hub <NUM> and the cylindrical base <NUM> of the outboard portion <NUM> of the stator <NUM>. As a result, the first and second wheel assembly bushings 84a, 84b are positioned radially between the wheel hub <NUM> and the stator <NUM> at longitudinally spaced locations. Finally, the wheel assembly <NUM> includes one or more third wheel assembly bushings 84c that are positioned in the bolt holes <NUM> between the wheel bolts <NUM> and the wheel <NUM>. While a total of four third wheel assembly bushings 84c are shown in the illustrated example, one for each wheel bolt <NUM>, it should be appreciated that the wheel assembly <NUM> may include a different number of third wheel assembly bushings 84c. For example, a single third wheel assembly bushing 84c may be used for center lock wheel configurations.

With additional reference to <FIG>, each of the wheel assembly bushings 84a-c includes an inner bushing member <NUM>, an outer body <NUM> that is concentrically arranged about and radially spaced from the inner bushing member <NUM>, and a resilient sleeve <NUM> that is positioned radially between the inner bushing member <NUM> and the outer body <NUM>. The inner bushing member <NUM> extends axially along a longitudinal axis <NUM> that is co-aligned with or parallel to the axis of rotation <NUM> of the wheel <NUM>. The resilient sleeve <NUM> extends annularly about the inner bushing member <NUM> and the outer body <NUM> extends annularly about the resilient sleeve <NUM> such that the resilient sleeve <NUM> is positioned radially between the inner bushing member <NUM> and the outer body <NUM>. The resilient sleeve <NUM> is made of a resilient material, such as rubber or another elastomeric material, for example, that is configured to permit relative movement between the inner bushing member <NUM> and the outer body <NUM> when input forces act on the inner bushing member <NUM> and/or the outer body <NUM> of the wheel assembly bushings 84a, 84b, 84c as the wheel <NUM> travels over bumps or potholes and/or during acceleration, braking, and cornering maneuvers.

A hydraulic chamber <NUM> is positioned within the resilient sleeve <NUM> of each wheel assembly bushing 84a-c. The hydraulic chamber <NUM> is filled with a fluid like oil or hydraulic fluid. The hydraulic chamber <NUM> extends annularly within the resilient sleeve <NUM> and axially between a first hydraulic chamber end <NUM> and a second hydraulic chamber end <NUM>. Each of the wheel assembly bushings 84a-c also has a helical fluid channel <NUM> that extends helically (i.e., in a spiral) about the inner bushing member <NUM>. In the illustrated example, the helical fluid channel <NUM> is formed by spiral grooves in both the inner bushing member <NUM> and the resilient sleeve <NUM>; however, it should be appreciated that the helical fluid channel <NUM> may alternatively be formed in just the resilient sleeve <NUM> or just the inner bushing member <NUM>. The helical fluid channel <NUM> has a first fluid channel end <NUM> that is open to and arranged in fluid communication with the first hydraulic chamber end <NUM> (i.e., the first fluid channel end <NUM> is provided as an opening in the first hydraulic chamber end <NUM>) and a second fluid channel end <NUM> that is open to and arranged in fluid communication with the second hydraulic chamber end <NUM> (i.e., the second fluid channel end <NUM> is provided as an opening in the second hydraulic chamber end <NUM>). A divider body <NUM>, within the resilient sleeve <NUM>, extends into the hydraulic chamber <NUM> at a location that is positioned longitudinally between the first and second hydraulic chamber ends <NUM>, <NUM>. For example, in the illustrated embodiment, the divider body <NUM> is an annular, radially extending wall that is integral with and made of the same material as the resilient sleeve <NUM>. However, it should be appreciated that the divider body <NUM> could alternatively be a separate or molded-in component of the wheel assembly bushings 84a-c. Regardless of the configuration, the divider body <NUM> divides the hydraulic chamber <NUM> into two hydraulic chamber segments <NUM>, <NUM> that are arranged in fluid communication with one another via a fluid passageway <NUM>, which is designed to provide a restriction to the fluid flow and thus result in a resistance/damping coefficient.

The hydraulic chamber segments <NUM>, <NUM> include a first hydraulic chamber segment <NUM> that is arranged in fluid communication with the first fluid channel end <NUM> and a second hydraulic chamber segment <NUM> that is arranged in fluid communication with the second fluid channel end <NUM>. The fluid passageway <NUM> permits fluid flow between the first and second hydraulic chamber segments <NUM>, <NUM> and is configured as an annular opening in the divider body <NUM> in the illustrated embodiment. However, it should be appreciated that other configurations are possible, and depending on the final identified network, the divider body <NUM> can be placed at other locations. For example, the fluid passageway <NUM> may be one or more holes or orifices in the divider body <NUM> or could alternatively be one or more fluid pathways provided in the resilient sleeve <NUM>. Regardless of the configuration, the fluid passageway <NUM> forms a pinch point in the hydraulic chamber <NUM> that limits fluid flow between the first and second hydraulic chamber segments <NUM>, <NUM> such that temporary pressure differentials between the first and second hydraulic chamber segments <NUM>, <NUM> can be generated by fluid flow through the helical fluid channel <NUM> in response to deflection of the resilient sleeve <NUM> for a period of time until the total fluid flow through both the fluid passageway <NUM> and the helical fluid channel <NUM> can equalize the pressures in the first and second hydraulic chamber segments <NUM>, <NUM>. As will be explained in greater detail below, the fluid passageway <NUM> and the helical fluid channel <NUM> cooperate to produce phase and magnitude shifts between the input forces causing relative movement between the inner bushing member <NUM> and the outer body <NUM> and deflection of the resilient sleeve <NUM>. This relative movement within the wheel assembly bushings 84a, 84b, 84c generates reaction forces that are caused by pressure pulses in the hydraulic chamber <NUM> resulting from fluid flow through the fluid passageway <NUM> and helical fluid channel <NUM> from one end of the hydraulic chamber <NUM> to the other.

With reference to <FIG>, it should be appreciated that the inner bushing member <NUM> and outer body <NUM> of the various wheel assembly bushings 84a, 84b, 84c can have different configurations and may be separate components or integrated into the components of the wheel assembly <NUM> described above. For example, the inner bushing member <NUM> of the first wheel assembly bushing 84a may be a cylindrical sleeve that extends annularly about and abuts the hub portion <NUM> of the wheel hub <NUM> while the outer body <NUM> of the first wheel assembly bushing 84a may be a cylindrical sleeve that is received within and abuts the inboard portion <NUM> of the stator <NUM>. Alternatively, the inner bushing member <NUM> of the first wheel assembly bushing 84a may be integral with the hub portion <NUM> of the wheel hub <NUM> and/or the outer body <NUM> of the first wheel assembly bushing 84a may be integral with the inboard portion <NUM> of the stator <NUM>. Regardless of the configuration, the resilient sleeve <NUM> of the first wheel assembly bushing 84a is positioned radially between the hub portion <NUM> of the wheel hub <NUM> and the inboard portion <NUM> of the stator <NUM>.

For the second wheel assembly bushing 84b, the inner bushing member <NUM> may be a cylindrical sleeve that extends annularly about and abuts the shaft portion <NUM> of the wheel hub <NUM> while the outer body <NUM> of the second wheel assembly bushing 84b may be a cylindrical sleeve that is received within and abuts the outboard portion <NUM> of the stator <NUM>. Alternatively, the inner bushing member <NUM> of the second wheel assembly bushing 84b may be integral with the shaft portion <NUM> of the wheel hub <NUM> and/or the outer body <NUM> of the second wheel assembly bushing 84b may be integral with the outboard portion <NUM> of the stator <NUM>. Regardless of the configuration, the resilient sleeve <NUM> of the second wheel assembly bushing 84b is positioned radially between the shaft portion <NUM> of the wheel hub <NUM> and the outboard portion <NUM> of the stator <NUM>.

The outer body <NUM> of the third wheel assembly bushings 84c may be provided in the form of cylindrical sleeves that are received within the bolt holes <NUM> in the wheel <NUM> while the inner bushing members <NUM> may be cylindrical sleeves in the third wheel assembly bushings 84c that receive the wheel bolts <NUM>. Alternatively, the inner bushing member <NUM> of the third wheel assembly bushings 84c may be integral with the wheel bolts <NUM> and/or the outer body <NUM> of the third wheel assembly bushings 84c may be integral with the wheel <NUM>. Regardless of the configuration, the resilient sleeve <NUM> of the third wheel assembly bushings 84c are positioned between the wheel bolts <NUM> and the wheel <NUM>.

<FIG> illustrate how the wheel assembly <NUM> described above may be modeled as a spring-mass system. The first and second wheel assembly bushings 84a, 84b combine to create a bushing interface between the stator <NUM> of the in-wheel electric motor <NUM> and the wheel hub <NUM>, while the third wheel assembly bushings 84c provide a bushing interface between the rotor <NUM> of the in-wheel electric motor <NUM> and the wheel <NUM>. It is important to note that the third wheel assembly bushings 84c may represent multiple bushings around the wheel <NUM>. The x<NUM> parameter represents the location of the road surface, the x<NUM> parameter represents the displacement of the wheel <NUM>, and the x<NUM> parameter represents the displacement of the vehicle body. The parameter labeled x<NUM> represents the displacement of the wheel hub <NUM>, the x<NUM> parameter represents the displacement of the stator <NUM>, and the x<NUM> parameter represents displacement of the rotor <NUM>. The mass of the wheel <NUM> is represented by the m<NUM> parameter, the sprung mass of the vehicle is represented by the m<NUM> parameter, the mass of the wheel hub <NUM> is represented by the m<NUM> parameter, the mass of the stator <NUM> is represented by the m<NUM> parameter, and the mass of the rotor <NUM> is represented by the m<NUM> parameter. The tire <NUM> itself acts as a spring and has a stiffness represented by the k<NUM> parameter, while the stiffness of the vehicle's suspension struts (e.g., coil-over springs) is represented by parameter k<NUM>. The damping coefficient of the vehicle's dampers are illustrated by parameter c<NUM>. The spring-mass sub-system labeled G(s) illustrates the combination of the first and second wheel assembly bushings 84a, 84b, while the spring-mass sub-system Y(s) illustrates the third wheel assembly bushings 84c. The combined static stiffness of the resilient sleeves <NUM> in both the first and second wheel assembly bushings 84a, 84b is represented by parameter k<NUM>. The combined static stiffness of the resilient sleeves <NUM> in the third wheel assembly bushings 84c is represented by parameter k<NUM>. The wheel bearing <NUM> and the rotor bearing assembly <NUM> also have spring constants, which are represented by parameters k<NUM> and k<NUM>, respectively.

The spring-mass sub-system G(s) shown in <FIG>, which models the combination of the first and second wheel assembly bushings 84a, 84b, has a stiffness k<NUM>, damping coefficient c<NUM>, and inertance b<NUM>. Similarly, the spring-mass sub-system Y(s) shown in <FIG>, which models the third wheel assembly bushings 84c, also has a stiffness k<NUM>, damping coefficient c<NUM>, and inertance b<NUM>. The values for these design parameters of spring-mass sub-systems G(s) and Y(s) can be determined using the optimization procedure describe below.

First, benchmark performance values for rubber bushings are calculated using the following equations: <MAT> <MAT> <MAT>.

In the above equations, J<NUM> , J<NUM> and JM represent the H<NUM> norm of the vertical body acceleration, dynamic tire load, and magnetic gap deformation under the random road input in the Laplace domain. The V parameter is vehicle speed, κ is a road roughness parameter, s is a Laplace operator, ∥-∥<NUM> represents the H<NUM> norm, and Xn is the Laplace transform of the mass displacements.

The spectral densities for the time varying displacement of the road surface traversed used in the above J<NUM>, J<NUM> and Jm relations can be described using the following equation: <MAT>.

In the equation above, f is frequency in Hz (cycles per second), V is the vehicle speed, n is the wave number in cycles per meter and f = nV. The parameters sx<NUM> and <MAT> represent the spectral density of the time varying displacement of the road surface traversed, and the corresponding spectral density of the road's time varying velocity, respectively.

The parameter values that were used throughout these calculations are listed in Table <NUM>, below:.

When the above values are used, the benchmark performance values are: <MAT> <MAT> <MAT>.

These calculated values are then used as constraints when the wheel assembly bushings 84a-c are optimized to reduce the magnetic gap deformation JM so as to ensure that the improvement in magnetic gap deformation JM does not degrade the vertical body acceleration J<NUM> and dynamic tire load J<NUM> performance.

When the benchmark rubber bushings are replaced with the wheel assembly bushings 84a-c described herein, eight different topological combinations including one spring element, one damper element, and one inertance element are provided. These eight different layouts represent all of the possible combinations of these three elements. Using the above optimization procedure, the inventors identified that the particular layout of the inertance-integrated wheel assembly bushings 84a-c illustrated in <FIG> provide optimum performance values, where the values for vertical body acceleration J<NUM>, dynamic tire load J<NUM>, and magnetic gap deformation JM are as follows: <MAT> <MAT> <MAT>.

In other words, using the network configurations illustrated in <FIG>, the magnetic gap deformation JM is reduced by <NUM>% over a benchmark rubber bushing. At the same time, there is no degradation in the performance values for vertical body acceleration J<NUM> and dynamic tire load J<NUM> (in fact, the arrangement shown in <FIG> provided a <NUM>% improvement for vertical body acceleration J<NUM>).

Advantageously, by reducing the magnetic gap deformation JM without degrading the performance values for vertical body acceleration J<NUM> and dynamic tire load J<NUM>, the wheel assembly bushings 84a-c described herein allow for the use of in-wheel electric motors <NUM> that have a smaller gap between the rotor <NUM> and the stator <NUM>. Because in-wheel electric motors <NUM> are most efficient when the gap between the rotor <NUM> and stator <NUM> is small, the wheel assembly bushings 84a-c described herein allow for the use of smaller, more efficient in-wheel electric motors <NUM>. Advantageously, these smaller, more efficient in-wheel electric motors <NUM> decrease the unsprung mass of the vehicle, which improves performance, ride comfort, and tire grip.

The wheel assembly <NUM> and wheel assembly bushings 84a-c illustrated in <FIG> are physical examples of the topology shown in <FIG> and integrate inertance into the wheel assembly bushings 84a-c using fluid filled inertia-tracks provided by the hydraulic chamber <NUM> and helical fluid channel <NUM> to realize the inertance values b calculated above. In accordance with the wheel assembly bushings 84a-c design show in <FIG>, the relative motion between the outer body <NUM> and the inner bushing member <NUM> pushes fluid through the helical fluid channel <NUM>. The length and area of the helical fluid channel <NUM> and the density of the fluid contribute to the inertance effect experienced. This inertance b can be calculated using the following equation: <MAT>.

In the equation above, A<NUM> is the area of the hydraulic chamber <NUM>, A<NUM> is the area of the helical fluid channel <NUM>, ρ is the density of fluid, and the / parameter is the un-coiled length of the helical fluid channel <NUM>. By carefully designing the helical fluid channel <NUM> and selecting an appropriate fluid and resilient material for the resilient sleeve <NUM>, the stiffness, damping, and inertance of the wheel assembly bushings 84a-c can be optimized according the calculations described above. Any physical realization will need to be constructed according to the parameter values obtained through the optimization process. These parameter values can be seen in Table <NUM> below:.

The phase delay / inertance created by the helical fluid channel <NUM> of the wheel assembly bushings 84a-c described herein produces reaction forces proportional to the relative acceleration of fluid between the first and second fluid channel ends <NUM>, <NUM>. Hence, the helical fluid channel <NUM> of the wheel assembly bushings 84a-c described herein act as a mechanical equivalent to an electrical capacitor, using the force-current relationship in an electrical capacitor as an analogy. The phase delay / inertance created by helical fluid channel <NUM>, which forms a fluid-filled inertia track inside the wheel assembly bushings 84a-c, significantly enhances the vibration suppression functionality of the wheel assembly bushings 84a-c described herein. The results of this effect on the wheel assembly <NUM> is illustrated in <FIG>.

<FIG> is a plot comparing the frequency domain response of benchmark rubber bushings and the optimized wheel assembly bushings 84a-c described herein to random road inputs. In <FIG>, the x-axis of the plot is the frequency of the domain response to road inputs, which is measured in Hertz (Hz). The y-axis of the plot is the absolute magnitude of the domain response to road inputs, which is shown on a scale with a x10-<NUM> multiplier (i.e., where the y-axis values listed are multiplied by <NUM>-<NUM>). For example, the absolute value listed on the y-axis as "<NUM>" represents an absolute value of <NUM>. The domain response curve illustrated as a solid line in <FIG> provides a benchmark showing the magnitude of the response to road inputs in a wheel assembly <NUM> where the rotor <NUM> of the in-wheel electric motor <NUM> is mounted to the wheel <NUM> of the vehicle and the stator <NUM> of the in-wheel electric motor <NUM> is mounted to the wheel hub <NUM> with rubber bushings before any optimization has been undertaken. The domain response curve illustrated as a solid line with broken line segments in <FIG> shows the magnitude of the response to road inputs in a wheel assembly <NUM> equipped with rubber bushings between the rotor <NUM> and the wheel <NUM> and between the stator <NUM> and the wheel hub <NUM>, where these rubber bushings have gone through the same optimization process discussed in this patent. The domain response curve illustrated as a dashed line in <FIG> shows the magnitude of the response to road inputs in a wheel assembly <NUM> equipped with the wheel assembly bushings 84a-c described herein.

As <FIG> illustrates, the overall magnitude of the system response is reduced extensively in the frequency domain for the wheel assembly <NUM> equipped with the wheel assembly bushings 84a-c described herein. In particular, the peaks of the system response are drastically reduced at the natural frequencies (at approximately <NUM> and <NUM>) for the wheel assembly <NUM> equipped with the wheel assembly bushings 84a-c described herein.

Claim 1:
A wheel assembly, comprising:
a wheel hub (<NUM>);
a wheel (<NUM>) rotatably mounted on the wheel hub;
an in-wheel electric motor (<NUM>) including a stator (<NUM>) mounted on the wheel hub and a rotor (<NUM>) coupled to the wheel such that the rotor and wheel rotate together relative to the stator and wheel hub; and
at least one wheel assembly bushing (84a-c) comprising a radially inner bushing member, a radially outer body that is concentrically arranged about and radially spaced from the inner bushing member, and a resilient sleeve (<NUM>) positioned radially between the inner bushing member and the outer body,
wherein the at least one wheel assembly bushing includes a hydraulic chamber (<NUM>) positioned within the resilient sleeve and a fluid channel (<NUM>) extending between first and second fluid channel ends that are arranged in fluid communication with the hydraulic chamber,
wherein the fluid channel (<NUM>) is configured as an inertia-track where fluid flow through the fluid channel produces inertance within the at least one wheel assembly bushing that operates to reduce magnetic gap deformation between the stator and the rotor of the in-wheel electric motor,
wherein the at least one wheel assembly bushing includes a divider body (<NUM>) within the resilient sleeve that extends into the hydraulic chamber to divide the hydraulic chamber into first and second hydraulic chamber segments (<NUM>, <NUM>) and a fluid passageway (<NUM>) that causes hydraulic resistance and damping when the fluid flows between the first and second hydraulic chamber segments through the fluid passageway,
wherein the fluid passageway (<NUM>) is an annular opening that forms a pinch point in the hydraulic chamber that limits fluid flow between the first and second hydraulic chamber segments such that the fluid passageway (<NUM>) in the hydraulic chamber and the fluid channel (<NUM>) cooperate to produce a phase delay between input forces causing relative movement between the inner bushing member and the outer body and reaction forces caused by pressure pulses in the hydraulic chamber resulting from the fluid flow through the fluid passageway and the fluid channel.