Patent Description:
A typical automobile suspension system includes a shock absorber that dissipates energy associated with suspension motion. Shock absorbers typically include a shock housing with a piston positioned inside that is movable in both a compression stroke and an extension stroke. An orifice is positioned in the piston. The motion of the piston causes a high viscosity fluid to pass through the orifice as the piston moves in order to dampen suspension motion.

The applicants have appreciated that conventional shock absorbers, when providing dampening, waste a significant amount of energy as heat. This energy, if captured, could prove useful in providing energy for a vehicle. Related prior art may be found in <CIT> describing a regenerative suspension for a vehicle and in <CIT> describing an apparatus and method for hydraulic converting movement of a vehicle wheel to electricity for charging a vehicle battery.

The dependent claims define optional features and distinct embodiments.

Aspects of the invention relate to a regenerative shock absorber that captures energy associated with relative motion in the shock, while also providing ride performance that is comparable to or that exceeds that of conventional shock absorbers.

Aspects of the system relate to a regenerative shock absorber. Embodiments of the shock absorber may include a housing and a piston that moves at least partially through a compression stroke when the shock is compressed. The piston may additionally move at least partially through an extension stroke when the shock is extended (i.e., the piston may be double-acting). When the piston moves, hydraulic fluid is pressurized and moved to drive a hydraulic motor. The hydraulic motor, in turn, drives an electric generator that produces electric energy that may be provided to a vehicle.

According to one aspect, movement of the piston through the housing may always be associated with corresponding movement of the hydraulic motor. That is, fluid connections between the shock absorber and the hydraulic motor may be configured such that pressure of hydraulic fluid that is associated with movement of the piston through the compression volume always urges the hydraulic motor to move in a first direction. Similarly, pressure of the hydraulic fluid associated with movement of the piston through the extension volume may always urge the hydraulic motor to move in a second direction, opposite to the first direction. In this respect, the piston and hydraulic motor may always move in sync with one other (equivalently described herein as being in phase or lockstep). Freewheeling of the hydraulic motor, as occurs in some embodiments of regenerative shock absorber systems, is prevented. "Freewheeling", as that term is used herein, refers to rotation of a motor at a rate that drives more fluid than the fluid being displaced by piston movement. Freewheeling may occur if the damping force on the electric generator is less than the force presented from the rotational deceleration of a mass of the hydraulic motor.

According to another aspect, fluid connections between the housing of the shock absorber and the hydraulic motor may be made with few or no valves. Reducing or eliminating the number of valves, such as spool valves or check valves, between the shock absorber and hydraulic motor may reduce energy losses normally associated with the movement of hydraulic fluid through such valves (i.e., "valve-free"). This aspect may improve the energy efficiency of the regenerative shock absorber system.

According to another aspect, the system includes a reservoir that is sized to accommodate a change in the volume of the hydraulic system associated with movement of a piston rod into and out of the shock absorber housing. The reservoir is positioned on an outlet (i.e., low pressure side) of the hydraulic motor. Embodiments of the regenerative shock system with hydraulic motors that operate in different directions include one or more valves that operate to keep the reservoir positioned at the outlet of the hydraulic motor, since the fluid may move out of the hydraulic motor in different directions depending on the mode of operation.

The hydraulic motor is configured to be used as a hydraulic pump to apply a force to the piston. This may be accomplished by driving the electric generator as an electric motor. The electric motor, in turn, may drive the hydraulic motor as a hydraulic pump.

Additional aspects relate to changing damping of the electric generator to dynamically control a response of the shock absorber. A control may be used to control the direction and/or magnitude of force on the piston of the shock absorber to desired levels. By way of example, according to one embodiment a response can be controlled to mimic the force/velocity response (i.e., damping) of a conventional automotive shock absorber. According to other embodiments, the controller may alter the force/velocity response due to changes in driving conditions.

According to additional aspects, the hydraulic motor, when used as a hydraulic pump, may allow the position of the piston in the shock absorber to be controlled. Controlling the position of the piston in a vehicle suspension system may, in turn, allow the height of a vehicle to be controlled. According to some embodiments, locks may additionally be incorporated into the system to hold the shocks and/or a vehicle at a desired height.

Additional aspects relate to determining whether the piston of a shock absorber is moving in a compression stroke or an extension stroke without the use of sensors. According to some embodiments, a voltage generated at the generator will change in polarity in response to a change in the direction of motion of the piston. In this respect, a controller may determine the direction of piston travel by identifying the polarity of electric generator output. According to some embodiments, such as automotive applications, the controller may employ information associated with the direction of piston motion to, in turn, control the damping rate for each direction.

Additional aspects relate to determining velocity of the piston in the shock absorber without the use of sensors. According to some embodiments, a voltage generated by the electric generator may change proportionally (linearly or otherwise) with respect to piston velocity. A controller may determine velocity of the piston travel by measuring the voltage of the electric generator output, along with information on the relationship between piston velocity and generator voltage.

According to yet another aspect, a regenerative shock absorber may be configured to provide damping when moved in only one of a compression or extension stroke. Valve(s) may be incorporated into the system that bypass the hydraulic motor when the system is moved in the opposite direction.

Other aspects relate to regenerative shock absorbers being assembled into the suspension system of a vehicle. The regenerative shock absorbers may provide a primary source of damping in the suspension system. Alternatively, however, the shock absorbers may be installed in parallel with conventional shock absorbers.

Other aspects relate to integrating the hydraulic motor and electric generator together to substantially reduce or eliminate frictional losses. The motor and generator may be at least partially integrated into a common motor/generator housing, which may eliminate the need to provide frictional shaft seal(s) on a shaft of the hydraulic motor.

Other aspects relate to a controller that sets an impedance on the electric generator to control a force/velocity response of the regenerative shock absorber.

Other aspects relate to a regenerative shock system having fluidic connections between the housing and the hydraulic motor that may be configured to allow the hydraulic motor to freewheel, at times. Freewheeling may reduce the apparent shock absorber inertia associated with a change in piston direction, as compared to systems in which freewheeling is prevented.

Turning now to the figures, and initially <FIG>, which shows a functional block diagram of a regenerative shock absorber system. The system includes a shock <NUM> that, when compressed or extended, pressurizes and moves hydraulic fluid to drive a hydraulic motor <NUM>. The hydraulic motor <NUM>, in turn, drives an electric generator <NUM> to produce electric energy. Hydraulic controls <NUM> control how and when the hydraulic fluid is passed to hydraulic motor <NUM>. Hydraulic controls ensure that fluid communication is maintained between reservoir <NUM> and an outlet of the hydraulic motor. The system may incorporate a controller <NUM> that controls a force/velocity relationship (i.e., damping) of the shock absorber, or other measured relationships such as force/frequency, to a desired constant value or to varying values.

As shown in <FIG>, various embodiments include a shock absorber <NUM> that has a housing <NUM> and a piston that moves in a compression stroke through at least a portion of a compression volume <NUM> of the housing <NUM> when the shock is compressed from a rest position. The piston <NUM> additionally moves in an extension stroke through an extension volume <NUM> of the housing <NUM> when the shock is extended from the rest position (i.e., the piston may be double-acting). It is to be appreciated that the piston <NUM> may only move partially through the compression volume <NUM> and/or extension volume <NUM> during typical operation. When the piston <NUM> does move, hydraulic fluid is pressurized in either the compression volume or the extension volume. The pressurized hydraulic fluid moves from the housing <NUM> to drive the hydraulic motor <NUM>. The hydraulic motor <NUM>, in turn, drives an electric generator <NUM> that produces electric energy.

In the embodiment of <FIG>, the compression volume <NUM> and the extension volume <NUM> are in direct fluid communication with first <NUM> and second ports <NUM>, respectively, of the hydraulic motor <NUM>. That is, the fluid connections between the compression <NUM> and extension volumes <NUM> and ports <NUM>, <NUM> of the hydraulic motor <NUM> lack valves that provide a restriction to flow, such as check valves and the like (i.e., they are "valve-free"). Valves are often configured in a manner that restricts the flow of fluid therethrough, even when fully open. Elimination of valves, in this respect, may eliminate restriction points that might otherwise cause energy losses in the system, particularly between the shock housing <NUM> and hydraulic motor <NUM>, where flow rates may be the greatest. It is to be appreciated, however, that other embodiments may include one or more valves between the compression and/or extension volumes and the hydraulic motor.

The hydraulic controls <NUM> in the embodiment of <FIG> run in parallel to the hydraulic motor <NUM> such that flow through the hydraulic controls <NUM> is separate from flow through the hydraulic motor <NUM>. The hydraulic controls <NUM> in the embodiment of <FIG>, include a valve that selectively controls fluid communication between a reservoir <NUM> and the first and second ports of the hydraulic motor. Valve(s) in the hydraulic controls may be configured to sense pressure at the first <NUM> and second ports <NUM> of the hydraulic motor <NUM>, and to maintain fluid communication between the low pressure side, or outlet side, of the hydraulic motor and the reservoir <NUM>. By way of example, when pressure is higher at the first port <NUM>, such as during a compression stroke, the valve(s) <NUM> may open fluid communication between the second port <NUM> and the reservoir <NUM> while closing fluid communication between the first port <NUM> and reservoir <NUM>. Conversely, when pressure is higher at the second port <NUM>, fluid communication may be opened between the first port <NUM> and reservoir <NUM>, and closed between the second port <NUM> and reservoir <NUM>. In this respect, flow through the valve(s) <NUM> may be minimized to, in turn, minimize losses in the system since flow to and from the reservoir <NUM> is substantially less than flow through the hydraulic motor <NUM>.

The hydraulic controls <NUM> in the embodiment of <FIG> may include various valve arrangements. Some examples include spool valves <NUM> as represented schematically in <FIG>, which are pilot operated hydraulic spool valves. The spool valve shown in <FIG> may be acquired from Parker Hannifin Corporation. Pilot connections <NUM> of the spool valves react to a pressure differential across the first <NUM> and second ports <NUM> of the hydraulic motor <NUM>, and move the spool <NUM> of the valve <NUM> accordingly to direct hydraulic flow, as discussed above. The spool of <FIG> is a two position valve that either places the reservoir <NUM> in fluid communication with the hydraulic motor at only one of the first port <NUM> or the second port <NUM>. The spool of <FIG> includes a third position where fluid communication with the reservoir is closed altogether. <FIG> is a cross-sectional view of one embodiment of a valve represented by the schematic of <FIG>. It is to be appreciated that <FIG> merely show a few embodiments of valve(s) that may be used to control fluid communication to a reservoir <NUM> in a system like that of <FIG>, and that other arrangements are also possible.

<FIG> show alternative embodiments of hydraulic controls <NUM> that may be implemented into the system of <FIG> to control fluid communication to the reservoir <NUM>. In the embodiment of <FIG>, a first pilot operated valve <NUM> is positioned between the first port <NUM> of the hydraulic motor <NUM> and the reservoir <NUM>. Additionally, a second pilot operated valve <NUM> is positioned between the second port <NUM> of the hydraulic motor and the reservoir <NUM>. Each of the valves <NUM>, in this embodiment, individually closes or opens fluid communication between the reservoir <NUM> and the corresponding port of the hydraulic motor <NUM>, depending on the direction of motion of the piston <NUM>. In the embodiment of <FIG>, one of the pilot operated valves <NUM> is replaced with a check valve <NUM>. Although <FIG> show two different embodiments of valve(s) that may be used to control fluid communication to the reservoir, it is to be appreciated that others may also exist.

The reservoir <NUM> may be sized to accommodate changes in the volume of the hydraulic system that are associated with movement of the piston rod <NUM> into and/or out of the housing <NUM>. The piston rod <NUM>, when moved into the housing <NUM> of the shock absorber <NUM>, occupies a volume of space internal to the housing <NUM> that was previously available for hydraulic fluid. The reduction in volume associated with the introduction of the piston rod <NUM> into the hydraulic system is accommodated by the reservoir <NUM>, which may increase in volume by at least the same volume occupied by the piston rod <NUM> when fully compressed. It is to be appreciated that the volume occupied by the piston rod <NUM> in the housing <NUM> is equivalent to the difference in the maximum volume associated with the compression volume <NUM> (i.e., when the shock is in a fully compressed state) and the maximum volume associated with the extension volume <NUM> of the shock <NUM> (i.e., when the shock is in a fully extended state). As used herein, the term "extension volume" refers to the volume available for hydraulic fluid in the housing <NUM>, on the same side of the piston as the piston rod. As used herein, the term "compression volume" refers to the volume available for hydraulic fluid in the housing <NUM>, on the opposite side of the piston as the piston rod.

The hydraulic system is pressurized to maintain a minimum system pressure. Pressuring the system to some minimum level, such as206843 Pa (<NUM> psi) , may help prevent cavitation from occurring, particularly when the piston <NUM> rapidly changes direction. According to some embodiments, the reservoir <NUM> may include a spring loaded piston or a gas-pressurized bladder to maintain a minimum pressure in the hydraulic system. The reservoir <NUM> is positioned at the outlet of the hydraulic pump, where pressures may be lowest in the system, to be most effective. As is to be appreciated, the outlet of the hydraulic motor <NUM> in the embodiments of <FIG>, <FIG> changes between the first port <NUM> and the second port <NUM> depending on whether the piston <NUM> is moving in a compression stroke or an extension stroke. The hydraulic controls <NUM> of these embodiments are arranged to maintain fluid communication between the hydraulic motor outlet and the reservoir <NUM> regardless of the direction in which the piston is moving.

According to some embodiments, including those of <FIG>, <FIG>, the hydraulic motor <NUM> may move in phase or in sync with the motion of the piston <NUM>. In such embodiments, freewheeling of the hydraulic motor <NUM> may be prevented. Embodiments that prevent freewheeling may allow greater control of the force/velocity response of a shock absorber <NUM> and in this respect, may improve shock performance.

Embodiments that are configured to have the piston <NUM> move in sync with the hydraulic motor <NUM> may allow the hydraulic motor <NUM> to drive the piston <NUM>, when the motor <NUM> is operated as a pump. According to some embodiments the electric generator <NUM>, which may include a brushless permanent magnet motor, may be operated as an electric motor <NUM> to drive the hydraulic pump <NUM>. This may allow the electric motor <NUM> to control the position and/or force at the piston <NUM>, such that the shock absorber may be actively controlled. In such embodiments, valve(s) and the reservoir may operate similarly, even though the piston <NUM> may be providing an active force as opposed to a force that is merely resistive to movement of the shock <NUM> that originates from external sources. According to one embodiment, the hydraulic motor <NUM> may include a positive displacement motor, such as a gerotor, that may operate as a motor and a pump. It is to be appreciated that the term "hydraulic motor" as used herein, refers to an apparatus that converts hydraulic power to mechanical power.

The electric generator and/or the hydraulic motor, when operated as an electric motor and hydraulic pump, may be used to alter the position of the piston within the housing. In this respect the system may be used to control the overall height of a vehicle in which an embodiment of the shock absorber has been installed. This may prove particularly useful for military vehicle transportation, among other applications.

According to some embodiments, a lock may be incorporated into the system to hold the piston <NUM> at a particular position relative to the housing <NUM>. In the embodiment of <FIG>, the lock includes a pair of valves <NUM> and <NUM>. A first valve <NUM> is positioned to close fluid communication to the compression volume <NUM> and the second valve <NUM> is positioned to close fluid communication to the extension volume <NUM>, thereby preventing the piston <NUM> from moving in either a compression or an extension stroke. In other embodiments, only a single valve may be used to prevent the piston from moving in one of a compression or extension directions. Additionally or alternatively, mechanical locks may be used to hold the piston at a given position relative to the housing.

According to some embodiments, the shock absorber <NUM> may provide damping only during one of the compression or extension strokes (i.e., the shock absorber may have "uni-direction damping"). By way of example, <FIG> shows one embodiment which is not part of the claimed invention, configured to provide damping only during an extension stroke. In this embodiment, as the piston moves in an extension stroke, a higher fluid pressure in the compression volume <NUM> opens a check valve <NUM> and allows hydraulic fluid to bypass the hydraulic motor <NUM> and to move toward the extension volume <NUM> through a bypass <NUM>. As with the embodiment of <FIG>, the volume of hydraulic fluid that is displaced by entry of the piston rod <NUM> into the system is accounted for by the volume available for hydraulic fluid in the pressurized fluid reservoir <NUM>. When the piston reverses direction and begins an extension stroke, the check valve <NUM> closes. Pressure builds in the extension volume <NUM> and fluid then begins to fluid flows through the hydraulic motor <NUM> to capture energy from movement of the piston <NUM>. Fluid exits the reservoir <NUM> to compensate for the volume of hydraulic fluid that the piston rod <NUM> had displaced. It is to be appreciated, that although the illustrated embodiment captures energy from the shock only when the piston is moved in an extension stroke, that other embodiments may be configured to capture energy only during a compression stroke.

According to some embodiments, a bypass (not shown) may be included to bypass the hydraulic motor <NUM> at particular operating points, such as when hydraulic fluid pressure or piston velocity exceed pre-set threshold values. By way of example, a pressure-relief valve may be included in the system to allow fluid to pass from the inlet side to the outlet side of the motor without flowing through the motor. Such a bypass may protect the hydraulic motor <NUM> and/or generator <NUM> from over spinning, which might otherwise occur during a pressure spike. According to some embodiments, a bypass may include a valve connected in parallel with the hydraulic motor <NUM>. For embodiments that include hydraulic motors that operate in both directions, a pair of bypass valves may be installed in parallel to the hydraulic motor such that one of the pair of valves opens in each direction. Bypass valve(s) may be incorporated directly into the piston <NUM> or connected by fluid circuit that runs parallel to the motor. Although unidirectional and bidirectional configurations are described here, it is to be appreciated that other configurations of bypass valves may also exist.

According to some embodiments, an orifice may be placed in the piston <NUM> to allow fluid to directly communicate between the extension volume <NUM> and the compression volume <NUM>. This may be desirable so that there is minimal damping at low velocities and so that the piston may move even if the hydraulic motor is locked in place, as may be the occur at times due to static friction of the hydraulic motor <NUM> and/or the electric generator <NUM>. Energy loses associated with movement of hydraulic fluid through the orifice during shock operation may be minimized by ensuring the orifice is sufficiently small.

The applicants have appreciated that seals <NUM> found on output shafts <NUM> of many hydraulic motors, as shown in <FIG>, may cause frictional losses. These frictional losses may be substantial when the hydraulic motor is operated in an oscillating manner as the motor in the embodiments of <FIG>, <FIG>. As is to be appreciated, output shaft seal friction may be associated with a roughly constant resistive force, regardless of output shaft velocity. The hydraulic motor <NUM> found in these embodiments may operate at relatively low velocities. Additionally, velocity will reach zero at least at times when the piston and hydraulic motor change directions, according to some embodiments. During low velocities, the constant resistive force associated with shaft seals may be substantially greater when compared to the net torque on the output shaft.

Embodiments of the hydraulic motor and electric generator may be configured to improve power transmission efficiency. As shown in the embodiments of <FIG>, the hydraulic motor <NUM> and electric generator <NUM> may be incorporated into a common motor/generator housing <NUM>. In these embodiments, rotational frictional is reduced substantially by eliminating the need for shaft seals that may cause friction. This may additionally allow the rotational element <NUM> of the electric generator <NUM> to be immersed in the hydraulic fluid of the hydraulic motor <NUM>. In the embodiments of <FIG> coils <NUM> of the electric generator <NUM> are also positioned in the hydraulic fluid. In this respect, the additional hydraulic fluid may provide a greater overall thermal mass to the system. Smaller coils may also be used in the electric generator without an associated risk of over-heating, which may reduce the inertia of the system and allow for more compact packaging. The greater thermal mass may assist in cooling the electric generator through thermal and mechanical commutation with the overall system. Additionally, placing the rotational elements <NUM>, <NUM> of the hydraulic motor <NUM> and the electric generator <NUM> on a common shaft may reduce the overall rotational mass, which may be beneficial.

Portions of an electric motor <NUM> in a combined hydraulic motor/electric generator may alternatively be positioned outside of a motor/generator housing <NUM>. In the embodiment of <FIG>, coils of the electrical motor are positioned outside of the motor/generator housing <NUM>. In such embodiments, the motor/generator housing <NUM> may be made of plastic or other materials that allow magnetic flux to pass therethrough to prevent interference with power generation by the electric generator <NUM>. Additionally, placement of coils outside of the housing may eliminate the need to provide an electrical connection through the motor/generator housing.

According to some embodiments, the electric generator <NUM> or portions thereof may be integrated directly into the hydraulic motor <NUM> itself. The rotating components <NUM> of the electric motor in the embodiment of <FIG> are positioned at an outer edge of the rotor <NUM> on a positive displacement motor, according to one embodiment. This may further reduce rotational inertia of the hydraulic motor / electric generator. Additionally or alternatively, the construction shown in <FIG> may provide a more compact hydraulic motor / electric generator.

<FIG> shows yet another embodiment which is not part of the claimed invention, in which compression <NUM> and extension volumes <NUM> of a shock <NUM> may be placed in fluid communication with a hydraulic motor <NUM>, similar to that described in <CIT>. In this embodiment, each of the compression volume <NUM> and the extension volume <NUM> are in fluid communication with a pair of check valves. One valve <NUM>, <NUM>' of each the pair of check valves is configured to open fluid communication between the hydraulic motor inlet <NUM> and hydraulic fluid that is pressurized by the shock <NUM>. The other valve <NUM>, <NUM>' of each of the pair of check valves closes fluid communication to motor outlet <NUM> and the hydraulic fluid that is pressurized by the shock <NUM>. The reservoir <NUM> in the illustrative embodiment of <FIG> remains in fluid communication with the hydraulic motor outlet <NUM> or, equivalently, the low pressure side of the hydraulic motor <NUM>.

In the embodiment of <FIG>, check valve <NUM>' closes as the piston begins moving in a compression stroke and check valve <NUM>' opens, providing fluid communication to the hydraulic motor inlet <NUM> for pressurized hydraulic fluid. As the piston rod <NUM> enters the shock housing <NUM>, upon compression, the volume displaced by the piston rod <NUM> is accommodated by hydraulic fluid entering the reservoir <NUM>. As the piston <NUM> reverses direction and begins the extension stroke, check valve <NUM> closes and check valve <NUM> opens, allowing fluid to flow through the hydraulic motor in the same direction as during the compression stroke. In this manner, the bi-directional movement of the piston <NUM> and shock <NUM> is converted into uni-directional rotational movement of the hydraulic motor <NUM>.

According to some embodiments, the controller <NUM> may provide a varying impedance to the electric generator <NUM> to control the force response of shock <NUM>, based in various parameters such as velocity, while simultaneously capturing energy associated with movement in the shock. The force response may follow a present equation or a lookup table based on such parameters. For example, the force response may be linear based on shock velocity, according to one embodiment. The applicants have appreciated that an output load associated with the electrical system of a vehicle may vary according to electrical demands on the system and/or other factors, such as battery charge state. To capture energy associated with movement of the shock and provide a desired force response, the controller may mix the output load with either a low resistance element to decrease impedance on the electric generator or with a high resistance element to increase impedance on the electric generator. Such mixing may be accomplished, in one embodiment, by pulse-width-modulation (PWM) switching.

A controller, such as that represented by <FIG>, may allow the system to achieve various objectives. First, the controller may provide isolation between electric generators <NUM> associated with different shocks in a vehicle suspension system. This may insure that each shock operates independently of the output load <NUM>, such as that of a vehicle battery. Second, the controller <NUM> may provide variable damping. The damping may be controlled by the user or automatically via sensors such as a strain gauge sensor that adjusts performance based on vehicle weight or a sensor that directly measures shock position or vehicle height. Such sensors may change the reference resistance that the resistance feedback controller executes. The controller <NUM> may also enable operation with multiple shock absorbers by matching voltage between multiple shock absorbers by adjusting for the effects of each unit on an electrical bus of a vehicle by feedback control. Additionally or alternatively, the controller may provide battery-safe charging by regulating output voltage and current to safe levels.

<FIG> shows, schematically, how the output load <NUM> being mixed with either a low resistance element or a high resistance element may provide a desired impedance to an electric generator <NUM>. As shown, the output <NUM> of the electric generator <NUM> is connected to a feedback controller <NUM> that switches the output <NUM> from the electric generator <NUM> among a low resistance element <NUM>, an output converter <NUM> such as a voltage-controlled buck/boost converter, and a high resistance element <NUM>, such as an open circuit. The output <NUM> of the output converter <NUM> is always connected to an output load <NUM> of the vehicle, such as the vehicle battery.

Electric energy transfer to the output load <NUM> may be controlled by different types of output converters <NUM>. One type of voltage controlled output converter <NUM> that may be used is a buck/boost converter, as shown in <FIG>. The output converter, through a voltage-feedback circuit, may use a reference voltage to maintain a given output voltage level on the output <NUM>. This allows several regenerative shock absorbers, as may be found on a vehicle, to be wired in parallel. A diode (not shown) in the converter <NUM> may also insure that power can only flow out from the generator. A filtering capacitor (not shown) on the input <NUM> of the converter <NUM> may maintain voltage to the input of the converter even while the time-averaged resistance feedback controller <NUM> switches the generator <NUM> between multiple elements <NUM>, <NUM>, <NUM>. The filtering capacitor on the output <NUM> of the converter may average voltage and current to the output load <NUM>.

To control the rate of damping, or force/velocity response, the impedance at the electric generator output <NUM> may be switched between the low resistance element <NUM>, the load <NUM> (preferably through the voltage controlled output converter), and the high resistance element <NUM>. Pulse-width-modulation (PWM) may however be used to switch between combinations of these states to create an averaged damping rate and to allow more selective control over damping. Since output power is only captured when the electric generator <NUM> is connected to the output load <NUM>, the controller may be biased to maintain this connection over switching between the low resistance element <NUM> or the high resistance element <NUM>. A microcontroller with appropriate sensors may be used to determine the resistance seen by the generator <NUM>.

The controller <NUM> may modify the electrical impedance across the generator terminals, thus affecting the damping characteristics of the shock absorber. As discussed herein, resistance across the generator winding may be adjusted by switching the output <NUM> of the electric generator <NUM> between the three sources including the low resistance element <NUM>, the converter <NUM>, and the high resistance element <NUM>. The low resistance element <NUM> (such as a closed-circuit connection (a wire)) creates high damping force. The high resistance element <NUM>, such as an open circuit, provides very low damping. Depending on the load connected to the output of the converter <NUM>, the converter provides differing damping force. The controller preferably uses feedback to achieve a given effective resistance across the generator <NUM>. This feedback may come from sensors such as a voltage and current sensor placed across the terminals of the electric generator. This resistance may be set to a particular value by the manufacturer, the driver (to dynamically adjust the suspension dynamics based on road conditions, driving, or cargo), or by sensors such as strain gauges that adjust damping based on cargo weight.

Adjustment of output voltage <NUM> is achieved by the converter <NUM>. The converter <NUM> may include a feedback loop that maintains a substantially constant voltage output <NUM> when powered. Since input power <NUM> from the suspension varies, the converter <NUM> holds the voltage substantially steady while allowing current to fluctuate. The converter circuitry may be similar to that of a buck/boost converter with negative feedback based on output voltage. Capacitors (not shown) smooth the output voltage. It is to be appreciated that any type of efficient converter that is able to output a desired voltage, ensure one-way current flow, and have sufficient input filtering to accommodate a PWM input, may alternatively be used. The buck/boost converter is merely one such example.

Depending on a switching duty cycle, this circuitry has the effect of either reducing the output voltage or increasing output voltage. Duty cycle is controlled via a feedback loop that maintains a given output voltage high enough to be utilized to, for example, charge a vehicle battery or displace vehicle alternator load to increase fuel economy. Neglecting parasitics, the converter <NUM> operation may be perfectly efficient. Thus for the regenerative shock absorber disclosed herein connected to a conventional <NUM> volt car battery, the converter may convert <NUM>. 2v at 1A from the generator into <NUM>. 4v at <NUM>. Likewise it will convert <NUM>. 6v at 1A into <NUM>. Voltage stays relatively constant, regardless of the input, as compared to the amount by which current typically varies. There may be some increase in voltage when higher power is provided to an electrical system of a vehicle (subject to voltage limits of the electrical system). Energy is conserved and energy from the generator, minus heat losses, may be harvested for use.

The low resistance element <NUM> may dissipate energy from the shock absorber <NUM> as heat if, for example, no additional energy may safely go to the output load <NUM>, such as when the battery of a vehicle is fully charged and no energy consuming devices are in use. In this respect, damping may be provided to the shock absorber <NUM> even when the output load <NUM> may not receive electric power from the regenerative shock absorber <NUM>.

The generator may be connected to the high resistance element <NUM>, such that the electric generator winding is disconnected from the load <NUM>. In this mode, the generator output is effectively an open-circuit and very little back-EMF is produced. No energy is captured for use in this mode and close to zero damping is provided from the electrical system.

Claim 1:
A regenerative shock absorber (<NUM>) comprising:
a housing (<NUM>) that includes a compression volume (<NUM>) and an extension volume (<NUM>);
a piston (<NUM>) disposed in the housing and that in a first mode moves through at least a portion of a compression stroke to pressurize hydraulic fluid in the compression volume (<NUM>) and that in a second mode moves at least partially through an extension stroke to pressurize hydraulic fluid in the extension volume (<NUM>);
a hydraulic motor (<NUM>) including a first port (<NUM>) in fluid communication with the compression volume and a second port (<NUM>) in fluid communication with the extension volume (<NUM>);
a pressurized reservoir (<NUM>); and
one or more valves (<NUM>) configured to selectively control fluid communication between the pressurized reservoir (<NUM>) and a low pressure side of the hydraulic motor (<NUM>),
wherein the hydraulic motor (<NUM>) is configured and arranged to be operated as a hydraulic pump in at least one mode of operation of the regenerative shock absorber (<NUM>); characterized in that
the fluid communication includes flow to and from the pressurized reservoir (<NUM>), and in that the one or more valves (<NUM>) are arranged in parallel to the hydraulic motor (<NUM>) such that the flow through the one or more valves (<NUM>) is separate from flow through the hydraulic motor (<NUM>).