WO2013112544A1 - Mécanisme de suspension à rigidité variable - Google Patents

Mécanisme de suspension à rigidité variable Download PDF

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Publication number
WO2013112544A1
WO2013112544A1 PCT/US2013/022691 US2013022691W WO2013112544A1 WO 2013112544 A1 WO2013112544 A1 WO 2013112544A1 US 2013022691 W US2013022691 W US 2013022691W WO 2013112544 A1 WO2013112544 A1 WO 2013112544A1
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WO
WIPO (PCT)
Prior art keywords
variable
strut
stiffness mechanism
cantilever arm
suspension system
Prior art date
Application number
PCT/US2013/022691
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English (en)
Inventor
Olugbenga Moses ANUBI
Carl David CRANE, III
Shannon C. RIDGEWAY
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University Of Florida Research Foundation, Inc.
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Application filed by University Of Florida Research Foundation, Inc. filed Critical University Of Florida Research Foundation, Inc.
Publication of WO2013112544A1 publication Critical patent/WO2013112544A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G3/00—Resilient suspensions for a single wheel
    • B60G3/18—Resilient suspensions for a single wheel with two or more pivoted arms, e.g. parallelogram
    • B60G3/20—Resilient suspensions for a single wheel with two or more pivoted arms, e.g. parallelogram all arms being rigid
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G11/00—Resilient suspensions characterised by arrangement, location or kind of springs
    • B60G11/14—Resilient suspensions characterised by arrangement, location or kind of springs having helical, spiral or coil springs only
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G11/00—Resilient suspensions characterised by arrangement, location or kind of springs
    • B60G11/14—Resilient suspensions characterised by arrangement, location or kind of springs having helical, spiral or coil springs only
    • B60G11/16—Resilient suspensions characterised by arrangement, location or kind of springs having helical, spiral or coil springs only characterised by means specially adapted for attaching the spring to axle or sprung part of the vehicle
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G17/00—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load
    • B60G17/02—Spring characteristics, e.g. mechanical springs and mechanical adjusting means
    • B60G17/021—Spring characteristics, e.g. mechanical springs and mechanical adjusting means the mechanical spring being a coil spring
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2204/00—Indexing codes related to suspensions per se or to auxiliary parts
    • B60G2204/10—Mounting of suspension elements
    • B60G2204/12—Mounting of springs or dampers
    • B60G2204/124—Mounting of coil springs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2204/00—Indexing codes related to suspensions per se or to auxiliary parts
    • B60G2204/10—Mounting of suspension elements
    • B60G2204/12—Mounting of springs or dampers
    • B60G2204/124—Mounting of coil springs
    • B60G2204/1244—Mounting of coil springs on a suspension arm
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2204/00—Indexing codes related to suspensions per se or to auxiliary parts
    • B60G2204/10—Mounting of suspension elements
    • B60G2204/12—Mounting of springs or dampers
    • B60G2204/127—Mounting of springs or dampers with the mounting of springs or dampers moving so that the direction of the related force vector can be changed, thus contributing to a variation of the loading of the wheel
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2204/00—Indexing codes related to suspensions per se or to auxiliary parts
    • B60G2204/10—Mounting of suspension elements
    • B60G2204/12—Mounting of springs or dampers
    • B60G2204/13—Mounting of springs or dampers with the spring, i.e. coil spring, or damper horizontally mounted
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2204/00—Indexing codes related to suspensions per se or to auxiliary parts
    • B60G2204/40—Auxiliary suspension parts; Adjustment of suspensions
    • B60G2204/421—Pivoted lever mechanisms for mounting suspension elements, e.g. Watt linkage
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2500/00—Indexing codes relating to the regulated action or device
    • B60G2500/20—Spring action or springs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2500/00—Indexing codes relating to the regulated action or device
    • B60G2500/20—Spring action or springs
    • B60G2500/22—Spring constant

Definitions

  • the present invention generally relates to the field of suspension systems, and more particularly relates to variable geometry suspension systems.
  • Springs are used in many common applications such as in automotive suspension systems.
  • a spring has an unchanging spring constant, which is a ratio of an applied external force to a resulting change in length of the spring.
  • An adaptive suspension utilizes a passive spring and an adjustable damper with slow response to improve the control of ride comfort and road holding.
  • a semi-active suspension is similar, except that an adjustable damper has a faster response and a damping force is controlled in real-time.
  • a fully active suspension replaces the adjustable damper with active elements, such as hydraulic, pneumatic and electromagnetic damper control, which can achieve optimum vehicle control, but at a high cost due to design complexity.
  • active elements such as hydraulic, pneumatic and electromagnetic damper control
  • a semi-active suspension systems may include one or both of a fast response magneto-rheological (MR) damper and a fast response electro-rheological (ER) damper.
  • MR and ER fluids are composed of a suspension of polarized solid particles dispersed in a non-conducting liquid.
  • MR and ER fluids are composed of a suspension of polarized solid particles dispersed in a non-conducting liquid.
  • both a viscous damping coefficient and a spring rate of suspension elements are usually used as optimization arguments.
  • a semi-active suspension system involves both damping modulation and stiffness modulation.
  • most practical implementations of semi-active suspension systems only control a viscous damping coefficient of a shock absorber while keeping stiffness constant. This is partly due to a relatively lower energy requirement for damping modulation. Another reason is due to unavailability of pragmatic low-power stiffness modulation methods.
  • a combined variation of stiffness and damping achieves a better performance than a variation of damping or stiffness alone.
  • Variable damper semi-active suspension systems fall into a general class of variable damper, variable lever arm, and variable stiffness.
  • Variable damper semi-active suspension systems are capable of varying the damping coefficients across their terminals.
  • Initial practical implementations were achieved using a variable orifice viscous damper. By closing or opening the variable orifice, damping characteristics change from soft to hard and vice versa.
  • use of ER and MR fluids replaced the use of variable orifices.
  • an electric field or a magnetic field for MR
  • the polarized solid particles align along a direction of the electrical field. When this happens, a yield stress of the ER or MR fluid changes, hence a damping effect occurs.
  • Controllable rheological properties make ER and MR fluids suitable for use as smart materials for active devices, transforming electrical energy to mechanical energy.
  • Variable lever arm semi-active suspension systems conserve energy between the suspension and spring storage. Such suspension systems are characterized by controlled force variation which consumes minimal power.
  • the main idea behind their operation is a variation of a force transfer ratio, which is achieved by moving a point of force application. If the point of force application moves orthogonally to an acting force, then, theoretically, no mechanical work is involved in the control. This phenomenon is called reciprocal actuation.
  • variable stiffness feature of known semi-active suspension systems is achieved either by changing a free length of a spring or by a mechanism that changes a stiffness of the suspension system using one or more moving parts.
  • a hydro-pneumatic spring with a variable stiffness characteristic is used in one known variable stiffness semi-active suspension system.
  • a desired stiffness variation is achieved by augmenting a variable lever arm type system with a traditional, or conventional, passive suspension system.
  • the control of semi-active suspension systems has been a subject of much research. An initial aim of a controlled suspension was solely centered on ride comfort. One of the initial control concepts developed is a sky-hook damper.
  • the sky-hook damper is a fictitious damper between a sprung mass and an inertial frame (fixed in the sky). A damping force of the sky-hook damper reduces vibration of the sprung mass. A similar concept, called ground-hook, has also been developed for road-friendly suspension systems. These control concepts have also been applied to semi-active suspensions. Other control concepts that have been applied to semi-active and fully active suspension systems include: optimal control, robust control, and robust optimal control.
  • a known variable geometry actuator that reduces power consumption of active suspension elements is a 3D concept called a Delft Active Suspension (DAS).
  • the DAS concept includes a wishbone that can be rotated over an angle and is linked to a pretensioned spring at a variable length.
  • the spring pretension generates an effective actuator force at an end of the wishbone.
  • a force is controlled by varying a position of the pretensioned spring via an electric motor.
  • the DAS has inherent variation in stiffness, it is disadvantageous because it may be a source of discomfort to a passenger in a vehicle and/or may lead to instability in an absence of a secondary spring.
  • a modified fixed spring design with optimized geometry, called electromechanical low-power active suspension (eLPAS) may overcome some challenges posed by the DAS concept, in that a moving mass is reduced. Packaging and stiffness variation issues were overcome by optimized geometry. However, ensuring a good fail-safe behavior remains an open problem.
  • a "suspension system” is a collective term given to system of springs, damper and linkages that isolates a vehicle body (sprung mass) from a wheel assembly (unsprung mass).
  • independent suspension system is a suspension system that has no linkages between two hubs of a same axle.
  • variable stiffness mechanism comprises a cantilever arm having a first end rotatably attachable to a sprung mass, and having a second end attachable to an unsprung mass; a variable strut having a top slidably attached to a bracket and having a bottom slidably attached the cantilever arm.
  • the bracket is attachable to the sprung mass.
  • the variable stiffness mechanism also comprises a first device for relocating the top of the variable strut along a horizontal slot on the bracket, thereby causing a location of engagement of the variable strut with the bracket to relocate.
  • the variable stiffness mechanism also comprises a second device for relocating the bottom of the variable strut along a longitudinal slot on the cantilever arm, thereby causing a location of engagement of the variable strut with the cantilever arm to relocate.
  • the variable stiffness mechanism has an effective spring constant between the sprung mass and the unsprung mass. The effective spring constant depends at least on one or both of: the location of engagement of the variable strut with the bracket and the location of engagement of the variable strut with the cantilever arm.
  • a variable stiffness mechanism is disclosed.
  • the variable stiffness mechanism comprises a cantilever arm having a first end rotatably attachable to a sprung mass, and having a second end attachable to an unsprung mass; a variable strut having a top attachable to the sprung mass and having a bottom slidably attached the cantilever arm; and a device for relocating the bottom of the variable strut along a longitudinal slot on the cantilever arm, thereby causing a location of engagement of the variable strut with the cantilever arm to relocate.
  • the location of engagement of the variable strut with the cantilever arm depends on a frequency of excitation of the unsprung mass.
  • variable stiffness mechanism comprises a cantilever arm having a first end rotatably attachable to a sprung mass, and having a second end attachable to an unsprung mass; a variable strut having a top slidably attached to a bracket and having a bottom attached the cantilever arm.
  • the bracket is attachable to the sprung mass.
  • the variable stiffness mechanism also comprises a device for relocating the top of the variable strut along a horizontal slot on the bracket, thereby causing a location of engagement of the variable strut with the bracket to relocate.
  • the variable stiffness mechanism has an effective spring constant between the sprung mass and the unsprung mass. The effective spring constant depends on at least the location of engagement of the variable strut with the bracket.
  • variable stiffness mechanism comprises a cantilever arm having a first end rotatably attachable to a sprung mass, and having a second end attachable to an unsprung mass; a variable strut having a top slidably attached to a bracket and having a bottom slidably attached the cantilever arm; and a device for relocating the variable strut along a horizontal slot on the bracket, thereby causing a location of engagement of the variable strut with the bracket to relocate and causing a location of engagement of the variable strut with the cantilever arm to relocate.
  • the bracket is attachable to the sprung mass.
  • a suspension system comprising a conventional strut having a top coupled to a sprung mass and having a bottom coupled to an unsprung mass.
  • the suspension system also comprises a variable stiffness mechanism that cooperates with the conventional strut.
  • the variable stiffness mechanism includes a cantilever arm with a first end rotatably attached to the sprung mass and with a second end coupled to the unsprung mass; a variable strut with an top slideably attached to the sprung mass and a bottom that engages the cantilever arm at a location of engagement; and a device for relocating the variable strut, thereby causing the location of engagement to relocate.
  • the stiffness of the variable stiffness mechanism between the sprung mass and the unsprung mass depends on at least a distance between the location of engagement and the first end of the cantilever arm. The distance between the location of engagement and the first end of the cantilever arm depends on a frequency of excitation of the unsprung mass.
  • FIG. 1 is a schematic of a lever arm.
  • FIG. 2 is a schematic of an idealized quarter car model of a suspension system.
  • FIG. 3 is a perspective view of a suspension system in accordance with one embodiment of the invention including a variable stiffness mechanism in accordance with the invention, and a conventional spring.
  • FIG. 4 is a front view of the suspension system of FIG. 3, with the variable stiffness mechanism at high stiffness.
  • FIG. 5 is a front view of the suspension system of FIG. 3, with the variable stiffness mechanism at low stiffness.
  • FIG. 6 is a side view of the suspension system of FIG. 3, showing cutline 7-7.
  • FIG. 7 is a cut view through cutline 7-7 of FIG. 6.
  • FIG. 8 is a perspective view of a suspension system in accordance with another embodiment of the invention including a variable stiffness mechanism in accordance with the invention, and a conventional spring.
  • FIG. 9 is a front view of the suspension system of FIG. 8, with the variable stiffness mechanism at high stiffness.
  • FIG. 10 is a front view of the suspension system of FIG. 8, with the variable stiffness mechanism at low stiffness.
  • FIG. 11 is a side view of the suspension system of FIG. 8, showing cutline 12-12.
  • FIG. 12 is a cut view through cutline 12-12 of FIG. 11.
  • FIG. 13 is a perspective view of a suspension system in accordance with yet another embodiment of the invention including a variable stiffness mechanism in accordance with the invention, and a conventional spring.
  • FIG. 14 is a front view of the suspension system of FIG. 13, with the variable stiffness mechanism at high stiffness.
  • FIG. 15 is a front view of the suspension system of FIG. 13, with the variable stiffness mechanism at low stiffness.
  • FIG. 16 is a side view of the suspension system of FIG. 13, showing cutline 17-17.
  • FIG. 17 is a cut view through cutline 17-17 of FIG. 16.
  • FIG. 18 is a perspective view of a suspension system in accordance with still another embodiment of the invention including a variable stiffness mechanism in accordance with the invention, and a conventional spring.
  • FIG. 19 is a front view of the suspension system of FIG. 18, with the variable stiffness mechanism at high stiffness.
  • FIG. 20 is a front view of the suspension system of FIG. 18, with the variable stiffness mechanism at low stiffness.
  • FIG. 21 is a side view of the suspension system of FIG. 18, showing cutline 22-22.
  • FIG. 22 is a cut view through cutline 22-22 of FIG. 21.
  • FIG. 23 is a graph of magnitude versus frequency illustrating car body acceleration.
  • FIG. 24 is a graph of magnitude versus frequency illustrating suspension deflection.
  • FIG. 25 is a graph of magnitude versus frequency illustrating dynamic tire force.
  • FIG. 26 is a graph of acceleration versus distance illustrating car body acceleration.
  • FIG. 27 is a graph of deflection versus distance illustrating suspension deflection.
  • FIG. 28 is a graph of force versus distance illustrating dynamic tire force.
  • variable stiffness suspension system in accordance with the invention improves suspension performance by modulating suspension force.
  • An variable stiffness suspension system comprises, in one embodiment, a conventional MacPherson-type passive suspension system augmented, in parallel, with a variable stiffness mechanism.
  • variable stiffness suspension system includes reciprocal actuation and has stiffness variation control that is orthogonal to gravity.
  • the variable stiffness suspension system uses spring and damper forces that are in linear regions of their operating ranges. Best performance may be achieved by optimally varying both the stiffness and damping (lower performance index) rather than by varying either the stiffness or damping alone. Therefore, a semi-active version of the variable stiffness suspension system varies both the stiffness and damping of the suspension element.
  • variable stiffness suspension system improves suspension performance by varying stiffness in response to road disturbance.
  • stiffness it is meant an effective stiffness between a sprung mass and an unsprung mass between which is coupled the variable stiffness suspension system.
  • the variable stiffness suspension system was analyzed using a quarter car model that incorporates kinematic details of the mechanical design.
  • a passive system shows superior performance over a conventional counterpart. Passive refers to a case where only pure mechanical elements such as springs and dampers are used. In other words, no active force generating element is used or any control algorithm implemented. As a result, the problem of ensuring a good fail-safe behavior is addressed.
  • the following is a basic forward analysis of the variable stiffness.
  • FIG. 1 illustrates a variable stiffness mechanism (hereinafter "mechanism") 100 that is a modification of the variable stiffness mechanism described in the aforesaid published paper.
  • Lever arm PAC is pinned to, and free to rotate about, a fixed point C.
  • Spring AB is constrained to remain vertical and can translate horizontally as indicated by the double-headed arrow.
  • Point A slides inside a lever arm while point B remains at ground level.
  • an external force F is assumed to act vertically downwards at point P on the lever which has a horizontal distance L from C.
  • ⁇ is a clockwise inclination of a lever arm from a horizontal plane.
  • H is a height of a fixed point C from the ground
  • d is a length of segment AC of the lever arm.
  • a goal is to vary an overall stiffness of the mechanism 100 by adjusting d accordingly. This is achieved through a control force u.
  • k and 1 0 be a spring constant and a free length, respectively, of the spring AB, and let ⁇ be vertical deflection of point P.
  • An overall free length ⁇ of the mechanism 100 is defined as vertical displacement of point P when no external force is acting on the mechanism. Summing moments about C and equating to zero yields
  • the whole system can be represented as a single spring whose spring constant is determined by d according to Equation (3).
  • spring AB When spring AB is on a left side of force F, a resultant spring is stiff er than the spring AB.
  • the resultant spring When the spring AB is on a right side of the force F, the resultant spring is softer. Softness or stiffness of the resultant spring depends on how far right/left of force F is the spring AB.
  • the overall stiffness of the mechanism 100 can be varied dynamically.
  • the stiffness characteristics of a variable stiffness suspension system (hereinafter “suspension system") 200 are examined, as follows.
  • the sprung and unsprung masses of the suspension system 200 are isolated by a parallel combination of a variable stiffness mechanism and a MacPherson strut.
  • An idealized quarter car model shown in FIG. 2 comprises a quarter car body (sprung mass), the MacPherson strut, a variable strut, a wishbone and a wheel assembly (unsprung mass).
  • strut means a combination of a spring and a damper or shock absorber.
  • the sprung mass is suspended from the unsprung mass by the MacPherson strut and the variable strut.
  • the wishbone is free to rotate about point O.
  • Points A and B are fixed on a vehicle, or car, body. Points D and F are such that line DF always remains perpendicular to line CE. Point D can slide along line CE.
  • Generalized coordinates are chosen as vertical displacement y s of the sprung mass, horizontal displacement d of the variable strut and rotation angle ⁇ of the wishbone. Assuming that the MacPherson strut is near vertical, the stiffness between the sprung and unsprung masses is approximately where k s and k are the spring constants of the MacPherson strut and the variable strut, respectively, and 1 is a length of the wishbone.
  • the following is an explanation of nonlinear dynamics modeling and linearization about an equilibrium configuration. A detailed dynamic modeling of the system using the Lagrange equation of motion was performed. The assumptions adopted in FIG. 2 are summarized as follows: (1) Horizontal movement of the sprung mass is neglected, i.e., only vertical displacement y s is considered. (2) Sprung and unsprung masses are lumped at some points, hence are assumed to be particles. (3) Coil spring deflection, tire deflection, deflection force and damping force are in linear regions of their operating ranges.
  • Position vectors, P B , P D , P F , and ⁇ ⁇ of the points B, D, F and X are given by:
  • Performance of a passive system was evaluated by comparing frequency response of the suspension system 200 with a conventional MacPherson counterpart.
  • the performance of suspension systems are usually evaluated using the following measures: ride comfort, suspension deflection, and road holding.
  • Ride comfort is the amount of vibration experienced by a passenger on a vehicle. It is quantified using the force transferred to a chassis. Because force is proportional to acceleration, ride comfort is given in terms of chassis acceleration,
  • Suspension deflection characterizes an amount of deflection undergone by the suspension element. Suspension deflection provides a metric to determine a tendency of the suspension element to exceed its physical deflection limit. Suspension deflection is given in terms of an angular displacement ⁇ of the wishbone.
  • Road holding is an extent to which the road-tire contact is maintained.
  • Road holding is characterized by deflection undergone by a tire.
  • road holding or dynamic tire force is given in terms of a deflection y u - r undergone by the tire.
  • the suspension system 200 shows improved performance in terms of ride comfort, suspension deflection and road holding.
  • FIGS. 23-25 show the frequency responses for the suspension system 200 and for a conventional MacPherson suspension system.
  • An L 2 -gain analysis-based feedback controller and a state feedback control were designed.
  • the L2-gain analysis-based feedback controller was designed using the concept of energy dissipation. Feedback control gains were obtained by solving a system of linear matrix inequalities which resulted from the L 2 -gain analysis.
  • An L 2 -gain analysis-based feedback controller further improves the performance of the system by compensating for unattainable stiffness and damping in a passive case of the suspension system 200.
  • the passive case of the suspension system 200 shows better performance over the conventional counterpart which implies a good fail-safe behavior.
  • a time domain simulation performance of a closed loop system of the passive case of the suspension system 200 and performance of a conventional MacPherson suspension were compared.
  • a vehicle traveling at a steady horizontal speed of 40mph was subjected to a road bump of height 10cm.
  • Responses were compared for the conventional MacPherson suspension, and for the passive and active cases of the suspension system 200.
  • FIGS. 26, 27 and 28 show car body acceleration, suspension deflection, and dynamic tire force responses, respectively.
  • the suspension system 200 provided globally better performance than the conventional MacPherson suspension in terms of ride comfort, suspension deflection and road holding.
  • FIG. 3 is a perspective view of a variable stiffness suspension system (hereinafter “suspension system”) 300 in accordance with one embodiment of the invention.
  • the suspension system 300 comprises a variable stiffness mechanism (hereinafter “mechanism”) 301 in accordance with the invention and a conventional MacPherson strut 302.
  • the suspension system 300 and the conventional MacPherson strut 302 act in cooperation with each other in that each is coupled to a same sprung mass and to a same unsprung mass.
  • the suspension system 300 and the conventional MacPherson strut 302 are arranged in a parallel configuration.
  • the mechanism 301 includes a cantilever arm, or wishbone, 310 having arms 311 and 312, and a control strut 352 disposed between the arms.
  • the wishbone 310 includes a longitudinal slot 317.
  • the wishbone 310 is coupled to a sprung mass by a revolute joint 315.
  • the sprung mass is not shown except for a small portion 304.
  • the sprung mass is an automobile.
  • a first end 313 of the wishbone 310 is coupled to the frame or the body of the automobile.
  • the unsprung mass 303 is a wheel assembly which may include a hub, hub extensions, a wheel, a tire, brake components, etc.
  • the mechanism 301 also includes a variable strut (hereinafter "strut") 320 having a top 321 and a bottom 322.
  • the strut 320 includes a spring 324 and a damper 326.
  • the spring 324 is a linear spring.
  • the spring 324 is a coil spring.
  • the spring 324 is another type of spring, such as a gas spring.
  • the spring 324 has a spring constant k and a free length 1.
  • the mechanism 301 has an effective spring constant, or stiffness, k eff that is advantageously variable.
  • k eff of the mechanism 301 is less or equal to k of the spring 324.
  • the damper 326 is a shock absorber.
  • the mechanism 301 further includes a bracket 330 attachable to the sprung mass by an attachment member 333 and by an attachment member 334. There is no relative movement between the bracket 330 and the sprung mass because of the attachment member 333 and the attachment member 334.
  • the bracket 330 includes a substantially horizontal slot 331.
  • the top 321 of the strut 320 is slidably attached to the bracket 330.
  • the bottom 322 of the strut 320 is slidably attached the wishbone 310.
  • the mechanism 301 includes a first device 340 that can relocate the top 321 of the strut 320 along the horizontal slot 331 on the bracket 330, thereby causing a location of engagement 345 of the strut with the bracket to relocate.
  • the first device 340 relocates the top 321 of the strut 320 along the horizontal slot 331 on the bracket 330, depending on a frequency of excitation of the unsprung mass.
  • a location of engagement 345 of the strut with the bracket relocates.
  • the first device 340 includes an upper control strut 342 having one end 341 coupled to the bracket 330 and having another end 343 coupled to the top 321 of the strut 320 by a revolute joint 327.
  • the upper control strut 342 comprises a linear coil spring 344 and a damper 346.
  • the linear coil spring 344 experiences some compression due the weight of the vehicle.
  • the mechanism includes a second device 350 that can relocate the bottom 322 of the strut 320 along the longitudinal slot 317 on the wishbone 310, thereby causing a location of engagement 355 of the strut with the wishbone 310 to relocate.
  • the second device 350 relocates the bottom 322 of the strut 320 along the longitudinal slot 317 on the wishbone 310, depending on a frequency of excitation of the unsprung mass. As result of the bottom 322 of the strut 320 being relocated along the longitudinal slot 317 on the wishbone 310, a location of engagement 355 of the strut with the wishbone relocates.
  • the second device 350 is disposed between the arms 311, 312 of the wishbone 310.
  • the second device 350 includes a lower control strut 352 having one end 351 coupled to the wishbone 310 and having another end 353 coupled to the bottom of the strut 320 by a revolute joint 328.
  • the lower control strut 352 comprises a linear coil spring 354 and a damper 356. The linear coil spring 354 experiences some compression due the weight of the vehicle.
  • FIG. 3 shows the mechanism 301 in an intermediate state of stiffness.
  • the mechanism 301 has an effective spring constant, or stiffness, between the sprung mass 304 and the unsprung mass that depends on an orientation of the strut 320 relative to the other portions of the mechanism. More specifically, the stiffness of the mechanism 301 between the sprung mass and the unsprung mass depends at least on one or both of: the location of engagement 345 of the strut 320 with the bracket 330, and the location of engagement 355 of the strut with the wishbone 310. The location of engagement 345 of the strut 320 with the bracket 330 and the location of engagement 355 of the strut with the wishbone 310 depend on a frequency of excitation of the unsprung mass.
  • FIG. 4 is a front view of the suspension system 300 with the mechanism 301 at high stiffness.
  • a distance from the sprung mass of the location of engagement of the strut 320 with the bracket 330 increases as the frequency of excitation of the unsprung mass decreases.
  • the orientation of the strut 320 becomes more nearly vertical.
  • the stiffness of the mechanism 301 increases as the strut 320 becomes more nearly vertical. Therefore, the stiffness of the mechanism 301 increases as the frequency of excitation of the unsprung mass decreases.
  • a smooth road tends to create lower frequency, rather than higher frequency, excitations.
  • the stiffness of the mechanism 301 advantageously increases when the vehicle is on a smooth road.
  • FIG. 5 is a front view of the suspension system 300 with the mechanism 301 at low stiffness.
  • a distance from the sprung mass of the location of engagement of the strut 320 with the bracket 330 decreases as the frequency of excitation of the unsprung mass increases.
  • the orientation of the strut 320 becomes farther from vertical.
  • the stiffness of the mechanism 301 decreases as the strut becomes farther from vertical. Therefore, the stiffness of the mechanism 301 decreases as the frequency of excitation of the unsprung mass increases.
  • a bumpy road tends to create higher frequency, rather than lower frequency, excitations.
  • FIG. 6 is a side view of the suspension system 300, showing cutline 7-7.
  • FIG. 7 is a cut view through cutline 7-7 of FIG. 6.
  • FIG. 7 shows the mechanism 301 at a high stiffness.
  • the suspension system 300 shown in FIGS. 3-7 is a suspension system for a land vehicle, and more specifically, a suspension system for a front wheel of an automobile.
  • the suspension system 300 shown in FIGS. 3-7 is configured as an independent suspension system. More specifically, the suspension system 300 shown in FIGS. 3-7 is configured as a single wishbone, independent suspension system. Other configurations of the suspension system 300 are foreseeable.
  • FIG. 8 is a perspective view of a suspension system 800 in accordance with another embodiment of the invention including a variable stiffness mechanism (hereinafter “mechanism”) 801 in accordance with the invention, and the conventional spring 302.
  • the mechanism 801 comprises the wishbone 310 having a first end 313 rotatably attachable to a sprung mass, and having a second end 314 attachable to an unsprung mass 303.
  • the strut 320 has a top 321 that is attachable to the sprung mass and has a bottom 322 that is slidably attached the wishbone.
  • the mechanism 801 also comprises a device 850 for relocating the bottom of the strut along a longitudinal slot 317 on the wishbone 310, thereby causing a location of engagement 855 of the strut 320 with the wishbone 310 to relocate.
  • the location of engagement 855 of the strut 320 with the wishbone 310 depends on a frequency of excitation of the unsprung mass.
  • the top of the strut 320 is coupled to a fixed location 848 on the sprung mass by a revolute joint 827. In one embodiment, such as shown in FIG. 8, the top of the strut 320 is coupled to a fixed location 848 on the bracket 330 by a revolute joint 827.
  • FIG. 9 is a front view of the suspension system 800 with the mechanism 801 at high stiffness.
  • the bottom 322 of the strut 320 is toward the left side of FIG. 10, which means that the location of engagement 855 of the strut with the wishbone 310 is nearer to the left side of FIG. 9.
  • FIG. 10 is a front view of the suspension system 800 with the mechanism 801 at low stiffness.
  • the bottom 322 of the strut 320 is toward the right side of FIG. 10, which means that the location of engagement 855 of the strut with the wishbone 310 is nearer to the right side of FIG. 9.
  • FIG. 11 is a side view of the suspension system 800, showing cutline 12-12.
  • FIG. 12 is a cut view through cutline 12-12 of FIG. 11.
  • FIG. 12 shows the mechanism 801 at a high stiffness.
  • the portions of the suspension system 800 shown in FIGS. 8-12 that also appear in the suspension system 300 shown in FIGS. 2-7 have analogous function, and, therefore, are not described in detail again.
  • FIG. 13 is a perspective view of a suspension system 1300 in accordance with yet another embodiment of the invention including a variable stiffness mechanism (hereinafter
  • the mechanism 1301 comprises the wishbone 310 having a first end 313 rotatably attachable to a sprung mass a second end 314 attachable to an unsprung mass 303.
  • the mechanism 1301 comprises the strut 320 having a top 321 slidably attached to the bracket 330 and having a bottom 322 attached the wishbone.
  • the bracket 330 is attachable to the sprung mass.
  • the mechanism 1301 also comprises a device 1340 for relocating the top of the strut 320 along the horizontal slot 331 on the bracket 330, thereby causing the location of engagement 345 of the strut with the bracket to relocate.
  • the bottom 322 of the strut 320 is coupled to a fixed location 1358 on the wishbone 310 by the revolute joint 328.
  • FIG. 14 is a front view of the suspension system 1300, with the mechanism 1301 at high stiffness.
  • the top 321 of the strut 320 is toward the left side of FIG. 14, which means that the location of engagement 345 of the strut with the bracket 330 is nearer to the left side of FIG. 14.
  • FIG. 15 is a front view of the suspension system 1300, with the mechanism 1301 at low stiffness.
  • the top 321 of the strut 320 is toward the right side of FIG. 14, which means that the location of engagement 345 of the strut with the bracket 330 is nearer to the right side of FIG. 14.
  • FIG. 16 is a side view of the suspension system 1300, showing cutline 17-17.
  • FIG. 17 is a cut view through cutline 17-17 of FIG. 16.
  • FIG. 17 shows the mechanism 1301 at a high stiffness.
  • the portions of the suspension system 1300 shown in FIGS. 13-17 that also appear in the suspension system 300 shown in FIGS. 2-7 have analogous function, and, therefore, are not described in detail again.
  • FIG. 18 is a perspective view of a suspension system 1800 in accordance with still another embodiment of the invention including a variable stiffness mechanism (hereinafter
  • the mechanism 1801 in accordance with the invention, and a conventional spring.
  • the mechanism 1801 comprises the wishbone 310 having a first end 313 rotatably attachable to a sprung mass and a second end 314 attachable to an unsprung mass 303.
  • the mechanism 1801 also comprises the strut 320 having a top 321 slidably attached to the bracket 330 and having a bottom 322 slidably attached the wishbone 310, wherein the bracket is attachable to the sprung mass.
  • the mechanism 1801 further comprises a device 1840 for relocating the strut 320 along the horizontal slot 331 on the bracket 330, thereby causing the location of engagement 1845 of the strut with the bracket to relocate and causing the location of engagement 1855 of the strut with the wishbone to relocate.
  • the location of engagement 1845 of the strut 320 with the bracket 330 and the location of engagement 1855 of the strut with the wishbone 310 depend on a frequency of excitation of the unsprung mass.
  • FIG. 19 is a front view of the suspension system 1800, with the mechanism 1801 at high stiffness.
  • the strut 320 is toward the left side of FIG. 19, which means that the location of engagement 345 of the strut with the bracket 330 and the location of engagement 1855 of the strut with the wishbone 310 are nearer to the left side of FIG. 14.
  • FIG. 20 is a front view of the suspension system 1800, with the mechanism 1801 at low stiffness.
  • the strut 320 is toward the right side of FIG. 19, which means that the location of engagement 345 of the strut with the bracket 330 and the location of engagement 1855 of the strut with the wishbone 310 are nearer to the right side of FIG. 14.
  • FIG. 21 is a side view of the suspension system 1800, showing cutline 22-22.
  • FIG. 22 is a cut view through cutline 22-22 of FIG. 21.
  • FIG. 21 shows the mechanism 1801 at a high stiffness.
  • the portions of the suspension system 1800 shown in FIGS. 18-22 that also appear in the suspension system 300 shown in FIGS. 2-7 have analogous function, and, therefore, are not described in detail again.
  • FIG. 23 is a graph of magnitude versus frequency illustrating car body acceleration.
  • FIG. 24 is a graph of magnitude versus frequency illustrating suspension deflection.
  • FIG. 25 is a graph of magnitude versus frequency illustrating dynamic tire force.
  • FIG. 26 is a graph of acceleration versus distance illustrating car body acceleration.
  • FIG. 27 is a graph of deflection versus distance illustrating suspension deflection.
  • FIG. 28 is a graph of force versus distance illustrating dynamic tire force.
  • An advantage of the mechanism 301 is power saving.
  • the direction of travel of the control struts is advantageously not against gravity.
  • a type of active actuator can be used, such as hydraulic or pneumatic.
  • a semi-active (MR, ER, etc.) system can be used instead of the control struts.
  • the mechanism 301 is, in one embodiment, a passive system in which no sensors, actuators, or computer control elements are needed or used.
  • variable stiffness mechanism 301 has an effective spring constant between the sprung mass and the unsprung mass that depends on orientation of the strut 320.
  • Low frequency excitation occurs when a vehicle is traveling on a smooth road or when road height changes slowly. Typically, low frequency means 4-10MHz. At lower frequency excitation, there is minimal transfer of energy from the near- vertical strut 320 to the horizontal control struts 342, 352. High frequency excitation occurs when a vehicle goes over a bump, or when the road height changes rapidly. Typically, high frequency means higher than 10MHz. At higher frequency excitation, there is maximum transfer of energy from the near- vertical strut 320 to the horizontal control strut 342, 352. Referring now to FIG. 5, this transfer of energy causes the top 321 of the strut 320 to move to the right, which causes the control struts 342, 352 to become more compressed.
  • the top 321 of the strut 320 moves to the right, as shown in FIG. 5.
  • the stiffness becomes less because the strut 320 moves farther from the near- vertical position.
  • the farther that the top 321 of the strut 320 moves to the left the less stiff is the suspension because the strut moves farther from a vertical position.
  • the spring in the strut 320 responds faster than the road excitation. As a result, all the input energy gets transferred through the strut 320 to the car body, then to a passenger. Because this energy is low, the resultant vibration felt by the passenger is low. Also, because all the input energy is absorbed by the spring in the strut 320, the bottom 322 of the strut does not move much, thereby causing the deflection of the control strut, from the near- vertical position, to be minimal.
  • the spring 324 in the strut 320 responds slower than the road excitation. As a result, only part of the input energy is transferred through the strut. The rest of the input energy is transferred to the control strut 342, 352. This causes the strut 320 to deflect farther from the near- vertical position. The sprung mass and the unsprung mass vibrate at different frequencies because road input energy is partially absorbed by the suspension system 300. The frequency of vibration of the unsprung mass is closer to the road excitation frequency which determines (and advantageously varies) the stiffness of the suspension system 300. It is the control strut(s) 342, 352 of the suspension system 300 that partial absorbs the road input energy.
  • control strut advantageously becomes maximally compressed when subjected to high frequencies excitations and becomes minimally compressed when subjected to low frequencies excitations. It is a combination of the mechanism design
  • a conventional suspension lacks a control strut.
  • the bottom of its suspension strut is fixed which means that the conventional suspension lacks any means for facilitating partial absorption of the road input energy by the suspension strut.
  • all the input energy is transferred to the passenger through the suspension strut. Only the energy dump by the shock absorber is available. This is a reason that the variable stiffness suspension system achieves a significant improvement in performance over the conventional system at high frequencies.
  • dampers shock absorbers
  • the energy absorbed by them over a half-cycle is dissipated and are not available to the system over the next half-cycle. In this way, the input energy is attenuated. Effect of amplitude of excitations on the stiffness is only significant at high frequencies.
  • the amplitudes at high frequencies are assumed to be within stability margins of the system.
  • High frequency amplitudes correspond to the depths of pot-holes, speed humps, bumps and the general roughness of the road. Unnecessarily high amplitude at high frequencies will result in instability, the effect of which can cause the vehicle to overturn, for example.
  • control strut moves left or right depends on several factors such as the frequency of excitation, the stiffness of all the springs, the values of the damping coefficient of the shock absorbers, and the masses and the inertias of the rigid bodies.
  • the drawings show the arrangement of the mechanical elements, not the actual behavior.
  • the mechanism 301, 801, 1301 and 1801 does not include the unsprung mass 303 or the sprung mass. Rather, the variable suspension mechanism 301, 801, 1301 and 1801 can be attached to the unsprung mass 303 and/or to the sprung mass (or the unsprung mass 303 and/or the sprung mass can be attached to the mechanism 301, 801, 1301 and 1801).

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Vehicle Body Suspensions (AREA)

Abstract

La présente invention décrit un mécanisme à rigidité variable (301, 801, 1301, 1801) comprenant un bras en porte-à-faux (310) ayant une première extrémité (313) pouvant être fixée de manière rotative à une masse suspendue (304), et ayant une seconde extrémité (314) pouvant être fixée à une masse non suspendue (303) ; une entretoise variable (320) ayant une partie supérieure (321) fixée de manière coulissante à une patte de fixation (330) et ayant un fond (322) fixé de manière coulissante au bras en porte-à-faux, dans lequel la patte de fixation peut être fixée à la masse suspendue ; et au moins un dispositif (340) pour relocaliser l'orientation de l'entretoise variable. Le mécanisme à rigidité variable a une constante de ressort effective entre la masse suspendue et la masse non suspendue, et dans lequel la constante de ressort effective dépend d'une fréquence d'excitation de la masse non suspendue. Un système de suspension (300, 800, 1300, 1800) comprend le mécanisme à rigidité variable dans un agencement coopératif avec un ressort conventionnel (302).
PCT/US2013/022691 2012-01-23 2013-01-23 Mécanisme de suspension à rigidité variable WO2013112544A1 (fr)

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US61/589,624 2012-01-23

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108891219A (zh) * 2018-07-13 2018-11-27 太原科技大学 一种mr仿袋鼠腿悬架
CN113370733A (zh) * 2021-07-29 2021-09-10 广东电网有限责任公司 一种车辆避震调节装置及车辆
CN114635946A (zh) * 2022-03-31 2022-06-17 盐城工学院 一种交通公路设备转向减震装置

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Publication number Priority date Publication date Assignee Title
EP0370217A2 (fr) * 1988-11-23 1990-05-30 Bayerische Motoren Werke Aktiengesellschaft, Patentabteilung AJ-3 Suspension pour roue directrice de véhicule
US6161844A (en) * 1997-05-16 2000-12-19 Conception Et Developpement Michelin S.A. Suspension device comprising a spring corrector
US20050258614A1 (en) * 2004-05-18 2005-11-24 Dove Jason L Linear suspension spring
RU2412067C2 (ru) * 2007-12-21 2011-02-20 Др. Инж. х.к. Ф. Порше АГ Подвеска колеса для передней оси автомобиля

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0370217A2 (fr) * 1988-11-23 1990-05-30 Bayerische Motoren Werke Aktiengesellschaft, Patentabteilung AJ-3 Suspension pour roue directrice de véhicule
US6161844A (en) * 1997-05-16 2000-12-19 Conception Et Developpement Michelin S.A. Suspension device comprising a spring corrector
US20050258614A1 (en) * 2004-05-18 2005-11-24 Dove Jason L Linear suspension spring
RU2412067C2 (ru) * 2007-12-21 2011-02-20 Др. Инж. х.к. Ф. Порше АГ Подвеска колеса для передней оси автомобиля

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108891219A (zh) * 2018-07-13 2018-11-27 太原科技大学 一种mr仿袋鼠腿悬架
CN113370733A (zh) * 2021-07-29 2021-09-10 广东电网有限责任公司 一种车辆避震调节装置及车辆
CN113370733B (zh) * 2021-07-29 2023-06-16 广东电网有限责任公司 一种车辆避震调节装置及车辆
CN114635946A (zh) * 2022-03-31 2022-06-17 盐城工学院 一种交通公路设备转向减震装置
CN114635946B (zh) * 2022-03-31 2024-01-19 盐城工学院 一种交通公路设备转向减震装置

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