WO2013186681A1

WO2013186681A1 - Acceleration attenuating seat assembly

Info

Publication number: WO2013186681A1
Application number: PCT/IB2013/054728
Authority: WO
Inventors: Dan Raz; Gregory Rinberg
Original assignee: Paltechnica Nitzanim A.C.S. Ltd.
Priority date: 2012-06-10
Filing date: 2013-06-10
Publication date: 2013-12-19

Abstract

A seat assembly includes a seat mounted on a support structure so as to be displaceable relative to the support structure between a normal position and a lowered position. An acceleration reducing arrangement, mechanically linking between the seat and the support structure, is configured to attenuate a vertical acceleration pulse experienced by the support structure so as to reduce an acceleration experienced by an occupant of the seat. The acceleration reducing arrangement includes a hydraulic damper having a piston displaceable within a cylinder, and a mechanical linkage deployed so as to define a non-linear relationship between displacement of the seat and displacement of the piston. Preferably, a derivative of piston displacement with respect to seat displacement has a first value at the beginning of motion from the normal position and increases with increasing seat displacement towards the lowered position.

Description

Acceleration Attenuating Seat Assembly

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to acceleration attenuating seat assemblies, particularly suitable for use in military vehicles of all types.

It is known to provide seating for military vehicles in which the seat mounting provides blast shock-absorbing properties, contributing to the safety of the occupant in the event that the vehicle is exposed to an explosive blast. The present invention relates particularly to attenuation of a vertical acceleration pulse such as may occur if a vehicle is subject to a blast from beneath. The invention may be employed to advantage in other contexts in which similar requirements exist, such as, for example, in a helicopter to improve chances of survivability of a crash.

Relevant background to the present invention may be found in US Pre-Grant Patent Application Publications Nos. 2010/0230988 and 2010/0230989 to Cantor et al. and 2010/0332079 to Wang et al., which discloses energy absorbing systems for seats which employ hydraulic dampers and return springs.

A major challenge for implementation of energy absorbing seating is the wide range of weights of personnel that must be accommodated by the same mechanism. A mechanism suited to a person of slight build is likely to "bottom out" under the load of a heavier person, while a mechanism suited to the heavier person may fail to be properly actuated to provide energy absorption when a light person is sitting in the seat.

To address this problem, Cantor et al. and Wang et al. both propose use of a variable damper which is set according to the passenger weight. However, this approach requires either manual adjustment for each user, which would be inconvenient and suffer from problems of compliance, or relies on automatic weighing of the occupant of the seat, which adds complexity and cost to the system, and reduces reliability.

There is therefore a need for an energy absorbing seat configuration which would be insensitive, or at least less sensitive, to variations in the weight of an occupant of the seat. SUMMARY OF THE INVENTION

The present invention is an acceleration attenuating seat assembly.

According to the teachings of an embodiment of the present invention there is provided, a seat assembly comprising: (a) a support structure; (b) a seat mounted on the support structure so as to be displaceable relative to the support structure between a normal position and a lowered position; and (c) an acceleration reducing arrangement mechanically linking between the seat and the support structure and configured to attenuate a vertical acceleration pulse experienced by the support structure so as to reduce an acceleration experienced by an occupant of the seat, wherein the acceleration reducing arrangement comprises: (i) a hydraulic damper including a piston displaceable within a cylinder, and (ii) a mechanical linkage linking between the support structure and the piston so as to define a non-linear relationship between displacement of the seat and displacement of the piston such that a derivative of piston displacement with respect to seat displacement has a first value at the beginning of motion from the normal position and increases with increasing seat displacement towards the lowered position.

According to a further feature of an embodiment of the present invention, the mechanical linkage comprises a cam-and-follower mechanism actuated by relative motion between the seat and the support structure.

According to a further feature of an embodiment of the present invention, the cam-and-follower mechanism includes a linear cam attached to a first of the seat and the support structure and a pivotally mounted follower pivotally mounted to the other of the seat and the support structure, the pivotally mounted cam follower supporting a part of the hydraulic damper.

According to a further feature of an embodiment of the present invention, the mechanical linkage comprises at least a first cable linking the piston to a first rotary element and at least a second cable linking the support structure to a second rotary element, the first and second rotary elements being mechanically linked for synchronous rotation, wherein at least one of the first and second rotary elements has a variable radius. According to a further feature of an embodiment of the present invention, the first and second rotary elements are mounted so as to rotate together with a common axle.

According to a further feature of an embodiment of the present invention, the common axle is rotatably mounted so as to rotate about an axis which moves together with the seat.

According to a further feature of an embodiment of the present invention, the hydraulic damper includes a fully-hydraulic pressure-compensation arrangement configured to provide a substantially load-independent velocity-position profile for motion of the piston.

According to a further feature of an embodiment of the present invention, the piston displaces a hydraulic fluid through at least one flow restriction, and wherein the acceleration reducing arrangement further comprises a pneumatic spring integrated with the hydraulic damper so as to be compressed by hydraulic fluid that has passed through the at least one flow restriction.

There is also provided according to an embodiment of the present invention, a seat assembly comprising: (a) a support structure; (b) a seat mounted on the support structure so as to be displaceable relative to the support structure between a normal position and a lowered position; and (c) an acceleration reducing arrangement mechanically linking between the seat and the support structure and configured to attenuate a vertical acceleration pulse experienced by the support structure so as to reduce an acceleration experienced by an occupant of the seat, wherein the acceleration reducing arrangement comprises: (i) a hydraulic damper including a piston displaceable within a cylinder and a fully-hydraulic pressure-compensation arrangement configured to provide a substantially load-independent velocity-position profile for motion of the piston, and (ii) a mechanical linkage deployed so as to define a non-linear relationship between displacement of the seat and displacement of the piston.

There is also provided according to an embodiment of the present invention, seat assembly comprising: (a) a support structure; (b) a seat mounted on the support structure so as to be displaceable relative to the support structure between a normal position and a lowered position; and (c) an acceleration reducing arrangement mechanically linking between the seat and the support structure and configured to attenuate a vertical acceleration pulse experienced by the support structure so as to reduce an acceleration experienced by an occupant of the seat, wherein the acceleration reducing arrangement comprises: (i) a hydraulic damper including a piston displaceable within a cylinder, the cylinder being linked so as to move with the seat, and (ii) a mechanical linkage deployed so as to define a non-linear relationship between displacement of the seat and displacement of the piston.

According to a further feature of an embodiment of the present invention, the non-linear relation is such that a derivative of piston displacement with respect to seat displacement has a first value at the beginning of motion from the normal position and increases with increasing seat displacement towards the lowered position.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIGS. 1A and IB are front and rear isometric views, respectively, of an embodiment of an acceleration attenuating seat assembly, constructed and operative according to the teachings of the present invention;

FIG. 2 is an isometric view of the seat of FIG. 1 A separated into sub-assemblies;

FIG. 3A is a rear isometric view of the movable seat sub-assembly from the assembly of FIG. 1A;

FIG. 3B is a cross-sectional view taken through a hydraulic damper from the assembly of FIG. 1A;

FIG. 4A is a front isometric view of the assembly of FIG. 1A with the seat removed;

FIG. 4B is an enlarged view of the region of FIG. 4A designated I;

FIGS. 5 A and 5B are isometric views of a further embodiment of an acceleration attenuating seat assembly, constructed and operative according to the teachings of the present invention, with the seat shown in a normal state and lowered state, respectively;

FIG. 6 is a rear view of the seat of FIGS. 5A and 5B; FIGS. 7 A and 7B are isometric views similar to FIGS. 5A and 5B, respectively, with the movable seat removed;

FIGS. 8A and 8B are views similar to FIGS. 7A and 7B, respectively, showing an enlarged view of an acceleration attenuating mechanism;

FIG. 9 A is a schematic diagram of a hydraulic pressure compensation arrangement configured to render piston velocity substantially independent of applied load;

FIG. 9B is a schematic representation of piston velocity as a function of applied force in a system employing the pressure compensation arrangement of FIG. 9 A;

FIG. 10 is a schematic representation of a preferred non-linear linkage ratio between piston displacement and seat displacement according to an embodiment of the present invention;

FIG. 11 is a schematic representation of an exemplary "input" acceleration of a vehicle floor and the resulting "output" acceleration of a passenger within an acceleration attenuating seat assembly according to an embodiment of the present invention;

FIGS. 12A and 12B are front and rear isometric views, respectively, of a further embodiment of an acceleration attenuating seat assembly, constructed and operative according to the teachings of the present invention;

FIGS. 13A and 13B are isometric views similar to FIG. 12A but separately showing the vehicle-mounted components and the movable seat, respectively; and

FIGS. 14 A, 14B and I4C are rear views of the acceleration attenuating seat assembly of FIG. 12A showing the seat in a normal state, and intermediate state, and a lowered state, respectively. DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is an acceleration attenuating seat assembly.

The principles and operation of seat assemblies according to the present invention may be better understood with reference to the drawings and the accompanying description. By way of introduction, the present invention will be described below with reference to three exemplary and non-limiting examples: a first with reference to FIGS. 1A-4B; a second with reference to FIGS. 5A-8B; and a third with reference to FIGS. 12A-14C. While each of the exemplary embodiments has its own distinctive structural features, they all implement a number of shared underlying principles which are believed to be of particular significance. Thus, for conciseness of presentation, we will first address the three embodiments generically, while referring to the reference numerals of the first exemplary embodiment. Corresponding features of the second exemplary embodiment are designated with the same reference numerals with the addition of 100 to the numeral, and of the third exemplary embodiment are designated with addition of 200 to the numeral. Embodiment-specific features will then be described separately for each embodiment.

Operating Principles

Generally speaking, the present invention provides a seat assembly with a support structure 10 (understood to refer also to 110 and 210, and likewise for other reference numerals throughout the description of the operating principles), typically mounted to the floor or wall of a vehicle (not shown), on which a seat 12 is mounted so as to be displaceable relative to the support structure between a normal position, as shown, and a lowered position. An acceleration reducing arrangement mechanically links between seat 12 and support structure 10. The acceleration reducing arrangement is configured to attenuate a vertical acceleration pulse experienced by support structure 10 so as to reduce an acceleration experienced by an occupant of seat 12.

Preferred implementations of the acceleration reducing arrangement of the present invention employ a combination of a hydraulic damper 14 including a piston 16 displaceable within a cylinder 18, together with a mechanical linkage 20. Mechanical linkage 20 preferably defines a non-linear relationship between displacement of the seat and displacement of the piston.

Preferred embodiments of the present invention provide one or more of a number of features which are helpful to reduce, and preferably substantially eliminate, dependence of the device's operation on the weight of a person using the seat. This preferably allows people of different weights to use the same seat, without requiring manual adjustment or even automated weighing. The features presented below are each believed to be of patentable significance in their own right, and are most preferably combined in synergy, as will be exemplified in the preferred exemplary embodiments.

Firstly, in certain preferred embodiments, cylinder 18 is linked so as to move together with the seat. This feature is particularly valuable in that it associates more of the mass of the system with the seat, thereby reducing the proportional variation of the total seat-plus-person inertial mass to which the system must cater. It should be noted, however, that the typical force-response curve of a hydraulic damper, and all the more so of the preferred damper implementation of the present invention (described below), does not provide an appropriate acceleration attenuation profile for implementing the present invention. It is therefore not possible to take a simplistic approach to implementing a seat-mounted damper cylinder by deploying the piston directly linked to the support structure. Instead, certain preferred embodiments of the present invention combine a seat-mounted damper cylinder 18 with a specially designed mechanical linkage 20 which transforms the overall effective response of the system. An example of a preferred form of the non-linear relationship between displacement of the seat and displacement of the piston is illustrated in FIG. 10. Addition details, as well as preferred implementations for achieving that relationship, will be discussed further below.

According to certain particularly preferred embodiments of the present invention, hydraulic damper 14 is implemented with a fully-hydraulic pressure- compensation arrangement configured to provide a substantially load-independent velocity-position profile for motion of the piston. In other words, the damper is implemented with a hydraulic feedback loop which varies the flow impedance as a function of the applied pressure so as to substantially eliminate dependence of the piston motion upon the input force. A hydraulic compensation mechanisms suitable for implementing the present invention is illustrated schematically in FIG. 9A. As illustrated here, force applied to piston 16 generates a pressure differential (Pj - P₂) between the two parts of cylinder 18. Motion is allowed by controlled flow of hydraulic fluid between the two parts of the cylinder via a flow restriction 22. Flow restriction 22 is provided with a diaphragm which is exposed to a proportion of the pressure differential (defined by additional flow restrictions Rl and R2) so as to vary the flow impedance as a function of the pressure differential. By suitable choice of parameters, the flow rate through flow restriction 22 can be made approximately constant, achieving a substantially constant output piston velocity substantially independent of the applied force. This output function is represented schematically in FIG. 9B. Although shown here as a constant velocity output, implementations which have output velocity varying as a function of piston position, but still substantially independent of applied force, also fall within the scope of this aspect of the present invention.

It should be noted that, in this context, the term "substantially constant" and

"substantially independent" are used to refer to levels of independence and constancy which are sufficient to ensure proper operation of the acceleration attenuation of the present invention. While in many cases, it is expected that constancy to within 5% can be achieved over the relevant range of applied forces, variations of up to 10%, or even 20%, may be acceptable within the working parameters of the system.

The aforementioned compensation mechanism is referred to as "fully hydraulic" in the sense that it is operated by fluid pressure alone, without requiring sensing systems or electronic control. This is believed to make the system lower maintenance and more reliable than systems relying upon electronic sensors, actuators and external controllers.

In particularly preferred implementations, rather than venting hydraulic fluid to the rear side of the piston, the output from the pressure-compensation arrangement is delivered to a pressure accumulator (e.g., a piston-driven pneumatic spring), which provides a biasing force to return the mechanism to its starting (normal) position after each operation. In the case of an explosion beneath a vehicle, this is important to prepare the seat for the secondary impact which occurs when the vehicle returns to the ground. The flow characteristics for the reverse flow can be defined independently from the forward flow characteristics by use of one-way flow valves, as will be clear to one ordinarily skilled in the art.

It will be appreciated that the use of a damper with constant velocity piston motion is highly effective to render the system of the present invention effective for people of different weights, since the output motion is inherently independent of the weight of the person using the seat. On the other hand, this approach poses a considerable challenge for achieving the desired motion profile for acceleration attenuation, which must accommodate the rapid initial upwards motion of the vehicle without delivering the full blow to the occupant of the seat, and then progressively accelerate the occupant in order to close the velocity differential. A typical "input" acceleration of the vehicle floor and the resulting acceleration of the passenger according to certain embodiments of the present invention are illustrated qualitatively in FIG. 11 as a function of time.

Mechanical linkage 20 bridges this gap between the constant velocity piston motion and the variable velocity seat motion by transforming a relatively large initial downward motion of the seat to a relatively small motion of piston 16, and then progressively increasing the ratio of piston motion to seat motion. In more technical terms, the non-linear relation defined by mechanical linkage 20 is preferably such that a derivative of piston displacement with respect to seat displacement has a first value at the beginning of motion from the normal position and increases with increasing seat displacement towards the lowered position. This relationship is illustrated schematically in FIG. 10, where the gradient of piston displacement to seat displacement is seen to increase with increasing displacement. It will be noted that this relationship refers to the relative magnitudes of the displacements of the piston relative to its cylinder, and of the seat relative to the support structure, independent of direction. In practice, the seat displacement is downwards displacement relative to the vehicle whereas piston displacement depends upon the orientation of the piston, as will become clear from the various examples discussed below.

In fact, even where a conventional (non-constant velocity) hydraulic damper is used, the use of a mechanical linkage with the aforementioned property of progressively increasing the derivative of piston displacement with respect to seat displacement has been found to provide highly advantageous results, in itself leading to more uniform performance of the system with passengers of greatly differing weights. Without in any way limiting the present invention, the following brief explanation may be helpful to the reader in understanding this insensitivity to variation in passenger weight qualitatively. Since the mechanical linkage defines a low initial ratio of piston displacement to seat displacement, the seat will start to move, and correspondingly absorb impact, even for a relatively light passenger. On the other hand, the progressively increasing ratio ensures that progressively more effective acceleration attenuation occurs as the motion continues, thereby catering also to the case of heavier passengers.

Parenthetically, when reference is made to various components being "attached to" or "mounted on" either the moving seat or the support structure, it should be noted that these terms encompass both direct and indirect connection between the recited components.

Particularly preferred practical examples for implementing mechanical linkage 20 with properties as described above will be presented below in the context of a more detailed description of the exemplary embodiments.

First Exemplary Embodiment

Turning now to FIGS. 1A-4B, these illustrate a first exemplary non-limiting embodiment of a seat assembly implementing the operating principles discussed above. In this case, support structure 10 is implemented as a single central support column which slidingly supports a carriage 24 on which seat 12 is mounted. Hydraulic damper 14 is here implemented as a vertically deployed cylinder 18 with a downward projecting piston 16 which terminates at a pulley 26. Cylinder 18 is mounted on carriage 24 so as to move together with seat 12, while the downwardly projecting piston 16 is pulled upwards relative to the seat as the seat is forced "downwards" (i.e., towards the floor of the vehicle).

The internal structure of this preferred but non-limiting implementation of hydraulic damper 14 is best seen in FIG. 3B. The upper end of piston 16 is sealingly received within the main chamber 36 of cylinder 18, which is filled with an incompressible hydraulic fluid. A flow limiting assembly 38, which may advantageously include a pressure-compensated constant velocity flow restrictor such as was described above with reference to FIG. 9A, is deployed in a fixed position within cylinder 18, for venting hydraulic fluid to a second chamber 40 where is acts upon a floating piston 42 to compress a volume of air or other compressible fluid in spring chamber 44. This acts as a pneumatic spring integrated with hydraulic damper 14 so as to be compressed by hydraulic fluid that has passed through the flow restriction, tending to return the piston towards its normal position after operation. The pneumatic spring is preferably provided with sufficient initial pressure, and/or supplemented by a mechanical spring, to ensure that the seat remains in its fully raised "normal" position under the load greater than the maximum expected load of a passenger and any load that he may be carrying.

As mentioned earlier, various embodiments of the present invention employ a mechanical linkage 20 to define a non-linear relationship between displacement of piston 16 and motion of seat 12. In certain particularly preferred implementations, it has been found advantageous to employ a mechanical linkage based on cables. It should be noted however that alternative implementations such as, for example, linkages based on scissor mechanisms or other mechanical linkages, also fall within the scope of the present invention.

In the example illustrated here, as best seen in FIGS. 2 and 4B, mechanical linkage 20 includes a first cable (or set of cables) 28 linking piston 16 to a first rotary element 30, and a second cable (or set of cables) 32 linking support structure 10 to a second rotary element 34. First and second rotary elements 30 and 34 are mechanically linked for synchronous rotation, and at least one of the rotary elements has a variable radius.

In the specific case illustrated here, a single elongated cable 28 passes around pulley 26 that is connected to the end of piston 16. The two ends of cable 28 are connected to two rotary elements 30, mounted so as to rotate as a unit on a common axle with rotary element 34. The use of a cable 28 passing around pulley 26 and wound onto two rotary elements 30 ensures that forces acting on the piston are applied symmetrically, and reduces the load on each rotary element and on the cable. Most preferably, rotary elements 30 and 34 are all mounted on a common axle rotatably mounted so as to rotate about an axis which moves together with seat 12.

In the arrangement as illustrated, cable 32 is anchored to support structure 10 and is initially wrapped around the circumference of rotary element 34, while cable 28 is mostly unwound from rotary elements 30. When seat 12 is forced downwards relative to the floor of the vehicle, cable 32 forces rotary element 34 to rotate as it unwinds, thereby forcing rotary elements 30 to turn so as to wind up a length of cable 28 on each side of the piston, thereby pulling up piston 16 relative to seat 12 to actuate the hydraulic damper 14.

The aforementioned non-linear ratio between piston motion and seat motion is defined by use of a variable radius of some or all of the rotary elements. In this case, rotary element 34 is implemented as a variable radius element with a generally spiral outer shape, such that the radius from the axle is at a maximum at the beginning of the motion and gradually reduces through the range of motion of the seat towards its fully lowered position. This translates into a relatively small angular motion of the axle per unit linear motion of the seat at the beginning of the motion which gradually increases as the motion progresses. This in turn results in a progressively increasing ratio of piston displacement to seat displacement, as described above. Clearly, similar results can be achieved using a variable radius (e.g., spiral form) for rotary elements 30 with circular elements 34, or by suitable choice of variable radius profiles for each of rotary element.

Second Exemplary Embodiment

Turning now to FIGS. 5A-8B, these illustrate a second exemplary non-limiting embodiment of a seat assembly implementing the operating principles discussed above. This embodiment is conceptually similar to the first embodiment, with analogous elements being labeled with like reference numerals, with the addition of 100 to each.

A primary difference between the embodiment of FIGS. 1A-4B and that of FIGS. 5A-8B is that the latter is implemented with a seat 112 having an open-back frame to facilitate use of the seat by a person loaded with a backpack and/or other body-mounted loads. Most preferably, this feature is implemented according to the teachings of PCT Patent Application Publication No. WO 2012/035537, co-assigned with the present invention, according to which the load-supporting garment is anchored to the seat to become part of a back support and/or seat restraint.

In order to accommodate the open-back structure, support structure 110 is here implemented as a pair of upright supports based one two feet on either side of the seat. Support structure 110 slidingly supports seat 112. Hydraulic damper 114 is here implemented as a horizontally deployed cylinder 118 and piston 116 (inside housing) to avoid obstructing the opening in the seat back. Here too, cylinder 118 is mounted so as to move together with seat 112, while piston 116 is here pulled sideways relative to the seat as the seat is forced "downwards" (i.e., towards the floor of the vehicle).

The mechanical linkage 120 differs somewhat in layout from mechanical linkage 20 described above, but is conceptually analogous. In this case, two cables 132 are anchored to support structure 110, one on each side of the support structure, and they pass around pulleys 132« to corresponding spiral rotating elements 134, arranged in 180 degrees out-of-phase relation. Rotating elements 134 are mounted so as to rotate together on a common axle with rotatable elements 130 deployed on each side of hydraulic damper 114, to which there are attached cables 128 which link to a cross-bar 128Λ mounted at the end of piston 116. When sudden upward acceleration is applied to the floor of the vehicle, seat 112 moves downwards, with cables 132 causing rotation of rotary elements 134, and hence also of rotary elements 130 which wind in cables 128, thereby driving piston 116 along cylinder 118 to generate the required hydraulic damping. As in the first embodiment, the hydraulic fluid is preferably routed into a pneumatic spring 144, here provided in parallel to cylinder 118 in order to fit within the width limitations of the assembly.

All of the details regarding preferred implementations of the hydraulic damper and mechanical linkage properties discussed above are equally applicable here, but for brevity, will not be discussed again in detail.

Third Exemplary Embodiment

Turning now to FIGS. 12A-14C, these illustrate a third exemplary non-limiting embodiment of a seat assembly implementing the operating principles discussed above. This embodiment is conceptually similar to the first embodiment, with analogous elements being labeled with like reference numerals, with the addition of 200 to each.

The embodiment of FIGS. 12A-14C differs from the previously described embodiments primarily in that it illustrates an alternative implementation of mechanical linkage 220 without use of cables. Instead, mechanical linkage 220 is here implemented using a linear cam with a pivotally-mounted cam-follower, as will be detailed below. Referring to the features of this embodiment in more detail, as already described in the generic description of operating principles above, this non-limiting exemplary embodiment of the present invention provides a seat assembly with support structure 210, in this case illustrated configured for mounting to a wall of a vehicle, but may equally stand on a vehicle floor, on which seat 212 is mounted so as to be displaceable relative to the support structure between a normal position (FIG. 14 A) and a lowered position (FIG. 14C). An acceleration reducing arrangement mechanically links between seat 212 and support structure 210.

Here too, the preferred implementations of the acceleration reducing arrangement employs a combination of hydraulic damper 214, including piston 216 displaceable within cylinder 218, together with mechanical linkage 220 that defines a non-linear relationship between displacement of the seat and displacement of the piston.

Preferred implementations of hydraulic damper 214 are as discussed above in the context of the first embodiment with reference to FIGS. 9 A and 9B. For conciseness of presentation, the details are not be repeated here.

As in the previous embodiments, mechanical linkage 220 preferably plays a critical role in defining the overall effective response of the system by transforming a relatively large initial downward motion of the seat to a relatively small motion of piston 216, and then progressively increasing the ratio of piston motion to seat motion (i.e., such that a derivative of piston displacement with respect to seat displacement has a first value at the beginning of motion from the normal position and increases with increasing seat displacement towards the lowered position), as described above with reference to FIG. 10.

In the implementation illustrated here, the desired properties are achieved using a linear cam 240 which is mounted so as to move together with the seat, and a pivotally-mounted cam follower (or "rocker") 242 which is pivotally anchored to a bracket 244 fixed to support structure 210. The free end of cam follower 242 is pivotally linked so as to support hydraulic cylinder 218 so that rocking of the cam follower moves hydraulic cylinder 218 vertically relative to the vehicle. The operation of this structure will be best understood with reference to FIGS. 14A-14C. In the initial fully-raised "normal" position of FIG. 14A, cam follower 242 sits on the thick lowest extreme of linear cam 240, thereby maintaining hydraulic cylinder 218 in a fully-raised initial position. On occurrence of a sudden upward motion of the vehicle, seat 212 starts to move downwards relative to the vehicle and support structure 210, and cam follower 242 correspondingly follows the inward curve of linear cam 240. The resulting rotation of cam follower 242 (anticlockwise as viewed in FIGS. 14A-14B) moves hydraulic cylinder 218 downwards, thereby reducing the initial relative motion between piston 216 and cylinder 218. As a result, the ratio between the displacement of the hydraulic damper and the displacement of the seat is initially less than 1.

Near the middle of the range of vertical motion of the seat (FIG. 14B), cam follower 242 reaches the most recessed region (i.e., a "minimum" of the cam profile) such that hydraulic cylinder 218 reaches its lowest position and momentarily stops. At this point in the motion, there is a 1:1 instantaneous ratio between the displacement of the hydraulic damper and the displacement of the seat.

As the downward motion of the seat relative to the vehicle continues, cam follower 242 follows the increasingly thick profile of linear cam 240 so that cam follower 242 rotates back in the clockwise direction as shown, towards the final position of FIG. 14C. This motion drives the hydraulic cylinder 218 upwards, thereby increasing the rate of travel of piston 216 relative to the cylinder so that the ratio between the displacement of the hydraulic damper and the displacement of the seat is greater than 1.

The overall result of this structure is thus variation of the derivative of piston displacement with respect to seat displacement that increases with increasing seat displacement towards the lowered position, as described above with reference to FIG. 10.

In the case illustrated here, additional mechanical springs 250 are preferably deployed to return seat 212 to its normal position after operation of its acceleration attenuating function. Springs 250 are visible projecting downwards from the rear of the fixed part of the support frame in FIGS. 12B and 13 A. Additionally, or alternatively, hydraulic damper 214 may include an integrated pneumatic spring, as described above. As mentioned above, the flow characteristics of the hydraulic damper for the reverse flow can be defined independently from the forward flow characteristics by use of oneway flow valves, as will be clear to one ordinarily skilled in the art, thereby providing a suitable rate of return to the raised position, ready for repeat operation if needed in a secondary impact.

It should be noted that the linear cam structure illustrated here is one preferred example from among many possible implementations of a similar non-cable-based mechanical linkage providing the desired properties described herein. For example, a reverse configuration in which a linear cam is attached to the support structure, and the part of the hydraulic damper linked to the seat is mounted via a pivotally mounted cam follower, also falls within the scope of the present invention. Furthermore, a similar effect may be achieved using a rack-and-pinion driving a rotary cam which displaces part of the hydraulic damper, as will be clear to a person having ordinary skill in the art.

It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A seat assembly comprising:

(a) a support structure;

(b) a seat mounted on said support structure so as to be displaceable relative to said support structure between a normal position and a lowered position; and

(c) an acceleration reducing arrangement mechanically linking between said seat and said support structure and configured to attenuate a vertical acceleration pulse experienced by said support structure so as to reduce an acceleration experienced by an occupant of said seat, wherein said acceleration reducing arrangement comprises:

(i) a hydraulic damper including a piston displaceable within a cylinder, and

(ii) a mechanical linkage deployed so as to define a non-linear relationship between displacement of said seat and displacement of said piston such that a derivative of piston displacement with respect to seat displacement has a first value at the beginning of motion from said normal position and increases with increasing seat displacement towards said lowered position.

2. The seat assembly of claim 1_? wherein said mechanical linkage comprises a cam-and-follower mechanism actuated by relative motion between said seat and said support structure.

3. The seat assembly of claim 2, wherein said cam-and-follower mechanism includes a linear cam attached to a first of said seat and said support structure and a pivotally mounted follower pivotally mounted to the other of said seat and said support structure, said pivotally mounted cam follower supporting a part of said hydraulic damper.

4. The seat assembly of claim 1, wherein said mechanical linkage comprises at least a first cable linking said piston to a first rotary element and at least a second cable linking said support structure to a second rotary element, said first and second rotary elements being mechanically linked for synchronous rotation, wherein at least one of said first and second rotary elements has a variable radius.

5. The seat assembly of claim 4, wherein said first and second rotary elements are mounted so as to rotate together with a common axle.

6. The seat assembly of claim 5, wherein said common axle is rotatably mounted so as to rotate about an axis which moves together with said seat.

7. The seat assembly of claim 1, wherein said hydraulic damper includes a fully-hydraulic pressure-compensation arrangement configured to provide a substantially load-independent velocity-position profile for motion of said piston.

8. The seat assembly of claim 1, wherein said piston displaces a hydraulic fluid through at least one flow restriction, and wherein said acceleration reducing arrangement further comprises a pneumatic spring integrated with said hydraulic damper so as to be compressed by hydraulic fluid that has passed through said at least one flow restriction.

9. A seat assembly comprising:

(a) a support structure;

(c) an acceleration reducing arrangement mechanically linking between said seat and said support structure and configured to attenuate a vertical acceleration pulse experienced by said support structure so as to reduce an acceleration experienced by an occupant of said seat, wherein said acceleration reducing arrangement comprises: (i) a hydraulic damper including a piston displaceable within a cylinder and a fully-hydraulic pressure-compensation arrangement configured to provide a substantially load-independent velocity- position profile for motion of said piston, and

(ii) a mechanical linkage deployed so as to define a non-linear relationship between displacement of said seat and displacement of said piston.

10. The seat assembly of claim 9, wherein said mechanical linkage comprises a cam-and-follower mechanism actuated by relative motion between said seat and said support structure.

11. The seat assembly of claim 10, wherein said cam-and-follower mechanism includes a linear cam attached to a first of said seat and said support structure and a pivotally mounted follower pivotally mounted to the other of said seat and said support structure, said pivotally mounted cam follower supporting a part of said hydraulic damper.

12. The seat assembly of claim 9, wherein said mechanical linkage comprises at least a first cable linking said piston to a first rotary element and at least a second cable linking said support structure to a second rotary element, said first and second rotary elements being mechanically linked for synchronous rotation, wherein at least one of said first and second rotary elements has a variable radius.

13. The seat assembly of claim 12, wherein said first and second rotary elements are mounted so as to rotate together with a common axle.

14. The seat assembly of claim 13, wherein said common axle is rotatably mounted so as to rotate about an axis which moves together with said seat.

15. The seat assembly of claim 9, wherein said non-linear relation is such that a derivative of piston displacement with respect to seat displacement has a first value at the beginning of motion from said normal position and increases with increasing seat displacement towards said lowered position.

16. The seat assembly of claim 9, wherein said piston displaces a hydraulic fluid through at least one flow restriction, and wherein said acceleration reducing arrangement further comprises a pneumatic spring integrated with said hydraulic damper so as to be compressed by hydraulic fluid that has passed through said at least one flow restriction.

17. A seat assembly comprising:

(a) a support structure;

(i) a hydraulic damper including a piston displaceable within a cylinder, said cylinder being linked so as to move with said seat, and

(ii) a mechanical linkage linking between said support structure and said piston so as to define a non-linear relationship between displacement of said seat and displacement of said piston.

18. The seat assembly of claim 17, wherein said mechanical linkage comprises at least a first cable linking said piston to a first rotary element and at least a second cable linking said support structure to a second rotary element, said first and second rotary elements being mechanically linked for synchronous rotation, wherein at least one of said first and second rotary elements has a variable radius.

19. The seat assembly of claim 18, wherein said first and second rotary elements are mounted so as to rotate together with a common axle.

20. The seat assembly of claim 19, wherein said common axle is rotatably mounted so as to rotate about an axis which moves together with said seat.

21. The seat assembly of claim 17, wherein said non-linear relation is such that a derivative of piston displacement with respect to seat displacement has a first value at the beginning of motion from said normal position and increases with increasing seat displacement towards said lowered position.

22. The seat assembly of claim 17, wherein said hydraulic damper includes a fully-hydraulic pressure-compensation arrangement configured to provide a substantially load-independent velocity-position profile for motion of said piston.

23. The seat assembly of claim 17, wherein said piston displaces a hydraulic fluid through at least one flow restriction, and wherein said acceleration reducing arrangement further comprises a pneumatic spring integrated with said hydraulic damper so as to be compressed by hydraulic fluid that has passed through said at least one flow restriction.