IMPROVEMENTS IN AND RELATING TO VEHICLE SEATS

Abstract: This invention relates to vehicle seats. The vehicle seat comprises a back rest (11) mounted for substantially vertical movement relative to a base part (1), and a seat rest (10) movable simultaneously with the back rest but also arranged to tilt relative to the back rest as the seat rest rises and falls. Such tilting is about horizontal transverse axes such that the seat occupant's ankles remain stationary where­ as his knees swing about an axis through his ankles. The invention is applicable to heavy duty vehicles and more particularly to vehicles designed to move over rough ter­ rain.

Description: IMPROVEMENTS IN AND RELATING TO VEHICLE SEATS This invention relates to vehicle seats of the type in which a seat part, normally comprising a seat rest and a back rest, is supported and guided for upward and downward movement relative to a base part by means of a spring suspension. The suspension includes spring means capable of counterbalancing the load of the seat part and its occupant so that the seat part, under static conditions, is located at a mid-ride position substantially midway between UP-stop and DO#iN-stop positions. Said spring means can comprise any means of taking up, storing. and giving out energy so that the seat and its occupant can oscillate between the UP-stop and DOWN-stop positions when subjected to external forces. Such a vehicle seat assists in isolating the occupant from vibrations transmitted from the vehicle wheels, particularly as the vehicle passes over rough terrain. However, the necessary freedom of the seat part to move up and down carries with it the danger, in the case of a driver's seat, of the driver's feet losing correct contact with the control pedals. Previous attempts to overcome this difficulty have largely been based on the concept that the seat part of a suspension seat should move pivotally about a horizontal axis through the knee-hinges of the driver, since if such a knee-hinge axis (sometimes referred to herein as the K axis) is fixed relative to the base part of the seat, the lower leg, and hence the ankles, of the driver can remain stationary irrespective of the movements of the seat. However, if the seat rest and back rest of a seat part move in this way, the driver's back inclination will vary with rise and fall of the seat. This difficulty can be overcome by incorporating a linkage to change the inclination of the back rest with changes in the inclination of the seat rest. An example of a suspension seat designed in this way is found in British Patent Specification No. 1,156,942. Such suspension seats have the disadvantage of a relatively large fore and aft movement of the entire part of the driver's body above his hip (H axis), since the knee hinge axis is the axis about which the seat rest and the hip region of his body is arranged to swin#. The present invention is based on the realisation that if a suspension seat can be designed to move in such a way that the seat occupant's lower leg will move about a horizontal transverse axis through the occupant's ankle hinges (A axis), with very little, if any, fore and aft movement of the occupant's hips the knee hinge axis accordingly being free to swing about the ankle hinge axis, such a seat will afford the driver a high degree of control over the vehicle over a wide range of seat movement. Moreover, it is found that a seat movable in this way affords a high degree of comfort to the driver. In our copending British patent application no. 79.08539 filed 12th March 1979 we have discussed a method of locating the instantaneous centres of rotation of the thigh of a seat occupant in relation to those parts of a seat suspension, including the base part, which move relatively to the thigh of the seat occupant as the seat rises and falls. In such a method, the thigh and lower leg of the seat occupant are considered as links in a mechanism in which the ankle hinges of the seat occupant are located on a fixed transverse axis at A. Accordingly if a seat rest for supporting the thighs of the seat occupant is pivotally supported on parallelspaced horizontal transverse axes through such centres, the movement of the seat rest will not cause any displacement of the ankle-hinge axis at A. Such instantaneous centres are not however always practical locations at which to support the seat rest, and a close approximation to an ideal arrangement can be achieved by mounting the seat rest for pivotal movement about at least two horizontal transverse axes at least one of which can be other than at a said instantaneous centre of rotation. According to one aspect of the invention there is provided a method of supporting the seat rest for pivotal movement approximately about one or more instantaneous centres which comprises arranging for at least the seat rest support point to rotate about a point lying on the line joining the seat rest support point and the corresponding instantaneous centre, such that the instantaneous direction of motion of the seat rest support point is the same as it would have been in the ideal situation with the seat rest support rotating about the said instantaneous centre. According to another aspect, the present invention provides a vehicle seat comprising a seat part, which includes a seat rest and a back rest, and a base part, and means connecting the seat part to the base part, said means comprising a spring suspension by which the back rest is supported on the base part and which is effective to restrict movement of the back rest to a substantially vertical direction, and supporting means for effecting movement of the seat rest relative to the back rest about at least two horizontal transverse axes, the supporting means pivotally connecting the seat rest to two parts of the seat which move relatively to each other during the rise and fall of the seat part, said axes being so located that the instantaneous directions of motion of the pivot connections between the seat rest and the supporting means at the mid-ride position of the seat are the same as if the said transverse axes were located at the instantaneous centres of rotation of the thigh of a seat occupant relative to said two parts of the seat, at least one of the transverse axes being spaced from the corresponding instantaneous centre, the arrangement being such that the seat occupant's lower leg is caused to move pivotally about his hinge axis during rise and fall of the seat. The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic side elevation, part sectioned, of a vehicle seat in accordance with the invention; Figure 2 is a diagrammatic representation in skeletal form of the means for supporting the seat rest of the seat of Figure 1 in combination with another type of suspension for supporting the back rest of the seat, and Figure 3 is a diagrammatic representation of a modification of the seat supporting means of Figure 2. Figures 4 and 5 are views similar to that of Figure 1, of two alternative embodiments of a vehicle seat according to the invention. The seat shown in Figure 1 includes an X type suspension of a well known type described for example in British Patent Specification No. 957,332 to which attention is directed for a detailed explanation of its construction and operation. Briefly the seat comprises a base part 1, and two pairs of scissor links spaced transversely of the seat, only one being visible, this pair consisting of first and second links 2, 3. Link 3 is connected at its forward end by a roller or slider 4 to the base part 1 and by a fixed pivot P1 at its rearward end to a seat frame 6. Link 2 is connected at its forward end by a roller or slider 5 to the seat frame 6 and by a fixed pivot P2 at its rearward end to the base part 1. Links 2 and 3 have a pivotal interconnection P3 at their intersection. The upper leg or thigh of the seat occupant will be looked upon as a link 7 and the lower leg as a link 8 pivoted at the ankle hinge point A to the floor, and hence to the base part 1. It is considered, in this connection, that the thigh of the seat occupant extends between the knee-hinge point K and a point H which is either at the centre of the hip joint or preferably at a "preferred pivot point" which is somewhat behind the true hip joint. This is the point about which the thigh effectively rotates relative to seat frame 6. The seat part is seen to consist of the seat frame 6 together with the seat rest 10 and back rest 11 supported on frame 6. The seat rest 10 consists of a seat pan 12 covered by a seat cushion 13, and back rest 11 consists of a back pan 14 and back cushion 15. The spring means for supporting the seat part 6, 10, 11 on the base part 1 is a torsion bar 17 extending within a tube 18 to which the upper rearward end of each link 3 is secured. The tube 18 is journalled at its ends in the seat frame 6. One end of bar 17 is secured to one end of tube 18 and the opposite end of bar 17 is connected to the frame 6 via a preload adjustment mechanism (not shown) t Manual operation of this mechanism by the seat occupant enables the preload in the torsion bar 17 to be varied. It has been shown in our copending application of even date that if the seat rest is pivoted about horizontal transverse axes through selected instantaneous centres of rotation of the thigh 7 of the seat occupant about parts of the seat on which the seat rest is supported, the seat rest will tilt forwardly or backwardly with rise and fall of the seat. This tilting will occur in such a way that although the knee hinge axis at K will swing about the ankle hinge axis at A, displacement of the ankle hinge axis will not occur. Two such instantaneous centres are 17.1 and I7 6 so that by pivotally supporting the seat rest on base 1 at point 17.1, (i.e. by extending the base 1 up to the point I. and pivotally connecting a rigid link from 17.1 to the seat rest), the ideal movement of the seat rest can be achieved for small deflections away from the mid-ride position. The pivotal support at 17.1 is inconvenient but can be approximated to by the provision of a rigid link 20 connected at its rearward lower end to a pivotal connection P4 on the base 1 and at its forward upper end by a pivotal connection P5 on the seat pan 12 of the seat rest 10. Since P5 is located on the straight line connecting 17.1 and P4 the movement of the front of the seat rest 10 will closely approach that which would occur if link 20 were pivoted at points 17.1 and P5 instead, base 1 having been extended upwardly to point I7 1 The mounting of the seat rest 10 for pivotal movement about point I7 6 is effected by providing a side member 21 of any convenient shape mounted on each side of frame 6 and so located as to be intersected by the transverse horizontal axis through I7 6. An arm 22 rigidly secured to each side of the seat pan 12 extends upwardly therefrom to a--pivotal connection P6 on the corresponding side member 21 at I7 6. Thus, in operation of the seat, the seat frame 6 and back rest 11 will rise and fall vertically under the guidance of links 2 and 3. Since the only connection between the seat rest 10 and the frame 6 is at P6, although the part of the seat rest 10 adjacent P6 will rise and fall with the frame 6, the movement of the front of the seat rest 10 will be dictated by the link 20 connected between base 1 and. seat pan 12 at P4 and P5. Thus as the frame 6 rises thereby tilting the thigh 7 in an anti-clockwise direction about I the front of the seat 10 will fall relative to frame 6. The knee hinge K will therefore be permitted to swing in a clockwise direction about ankle hinge A as indicated by arrows, if 17.6 is above K. In the description which follows, the references used in Fig. 1 will be retained so far as possible to represent the same type of parts as shown in Fig. 1 in spite of minor variations in the shape and function of the parts, in order to avoid confusion by adopting different references. References 2 and 3 will denote any two links by means of which the seat part is mounted on the base part. Fig. 2 shows a seat frame 6 which supports a back rest 11, the frame 6 itself being supported on a base part 1 by parallel links 2, 3 pivoted at their ends respectively to base part 1 and frame 6. Thus the links 2 and 3 guide the frame 6 for substantially vertical movement. Seat part 10 is supported, as in the embodiment of Figure 1, by a link 20 pivoted at its ends to base part 1 and seat part 10. To the rear of seat part 10, arm 22 rigidly connected thereto is pivoted by pivotal connection P6 at point 17.6 to side member 21 of the frame 6. The inconvenience of the side members 21 and arm 22 of Fig. 2 can be avoided by the modification of Figure 3. In Figure 3, the seat part 10 is provided with a roller or slider 23 which engages a surface 24 which is fixed to the frame 6 and is arcuate about the point I7 6. Thus roller or slider 23 moves as though it were suspended from I7 6. In order to restrain the forward movement of roller 23, a link 25 rigidly connected to seat part 10 connects the rearward part of seat rest 10 to a roller or slider 26 which rides on a guide surface 27 fixed to the frame 6 and arcuate about 17.6 at a location sufficiently spaced from roller 23 to provide stability. Thus in each of the embodiments of Figs. 1, 2 and 3, the seat rest pivots about a first horizontal transverse axis through the instantaneous centre 17.6 and about a second horizontal transverse axis through the point P4 which closely approximates in effect to rotation about the instantaneous centre 17.1. Other constructions which permit approximation to the ideal motion of the seat rest about instantaneous centres of rotation are illustrated in Figs. 4 and 5. In Fig. 4, the front of the seat rest 10 is supported for rotation about the instantaneous centre 17.2 by a pivotal connection 30 between the seat pan 12 and the link 2. At the rear, the seat rest 10 is supported by a roller 32 rolling on a flat guide track 31 supported on tube 18. The guide track has its centre of curvature at infinity on a line passing through the centre 32a of roller 32 and instantaneous centre I7 3. Consequently as roller 32 rolls on flat guide track 31 its motion will approximate to the movement of a roller 32 moving about point I7 3, its instantaneous direction of movement being perpendicular to the straight line connecting the centre of roller 32 to point I7 3. Although, in theory, the best result would be achieved by making guide track 31 arcuate about point I7 3, the radius of curvature is so large that a flat plate provides an economically justifiable approximation to an arcuate plate. In Fig. 5, the arrangement of Fig. 4 is modified in that a rigid link 40 is connected from a pivot connection 41 on the rearward end of the seat rest 10 to a pivot connection 42 on the torsion bar tube 18, the pivot connection 42 lying on a straight line connecting pivot connection 41 to the instantaneous centre I7 3. Thus as the seat rises and falls from the mid-ride position as shown, the instantaneous direction of movement of pivot connection 41 will be perpendicular to the straight line connecting pivot connection 42 to point I7 3 and hence the movement of pivot connection 41 will approximate to that which would occur if connection 41 were coupled to point 17,3 by a rigid link. Although Figs. 1 to 5 illustrate five different embodiments of the invention, further embodiments can be formed by different combinations of the features shown in the drawings. For example, in the embodiment of Fig. 1, the rearward pivot connection for the seat part at P6 could be replaced by the rearward pivot connection shown in Fig. 3. Similarly the forward pivot connection at 30 in Fig. 4 could be combined in another embodiment- with a rearward pivot connection employing merely a roller or slider(23)on a surface (24) as in Fig. 3.

Claims: CLAIMS 1. A vehicle seat comprising a seat part, which includes a seat rest (10) and a back rest (11), a base part (1), and means connecting the seat part to the base part, said means comprising a spring suspension by which the back rest is supported on the base part and which is effective to restrict movement of the back rest to a substantially vertical direction, characterised in that the suspension comprises supporting means for effecting movement of the seat rest relative to the back rest about at least two horizontal transverse axes, the supporting means including pivot connections between the seat rest and two parts (e.g. 1, 6 or 2, 6) of the seat which move relatively to each other during the rise and fall of the seat part, said axes being so located that the instantaneous directions of motion of the said pivot connections at the mid-ride position of the seat are the same as if the said transverse axes were located at the instantaneous centres (e.g. 17.1, 17.6 or I7 2 17.6) of rotation of the thigh (7) of a seat occupant relative to said two parts of the seat, at least one of the transverse axes being spaced from the corresponding instantaneous centre, the arrangement being such that the seat occupant's lower leg is caused to move pivotally about his ankle hinge axis (A). 2. A vehicle seat according to claim 1 characterised in that one of said pivot connections is provided by a rigid coupling (20) located at the front of the seat and pivoted at its lower end to the base part and at its upper end to the front of said seat part (Figs. 1, 2, 3). 3. A vehicle seat according to claim 1 characterised in that the means connecting the seat part to the base part comprise a link (2) having a pivot connection between its forward upper end and the frame (6) and a pivot connection (P2) between its rearward lower end and the base part (1), said link (2) having a fixed pivot connection (30) adjacent its forward upper end to the seat rest (10) adjacent the front thereof, said connection (30) being located on a first of said horizontal axes. (Figs. 4, 5). 4. A vehicle seat according to claim 2 or claim 3 characteris#ed in that said pivot connections comprise pivots (P6) located on a second said horizontal transverse axis and supported on said frame (6), and pivot arms (22) rigidly secured to the seat rest and suspended from said pivots (partly shown in Figs. 1, 2). 5. A vehicle seat according to claim 2 or claim 3 characterised in that said supporting means comprise rollers or sliders (23 and 26) mounted on said seat rest (10) and arranged to move in contact with surfaces (24 and 27) fixed to said frame (6) and part-cylindrical about a horizontal transverse axis through 17.6, to constrain the movement of seat part (10) about said axis through .17.6 relative to frame 6. (Partly shown in-Fig. 3). 6. A vehicle seat according to claim 2 or claim 3 characterised in that said means connecting the seat part to the base part comprise a link (3) having a lower forward end connected by a pivot connection to the base part, and a rearward upper end connected by a pivot connection to said frame (6), the seat part having a pivot connection with said rearward upper end of the link (3) formed by a roller member in rolling contact with a flat plate member, one of said members being secured to the seat part and the other to said link (3). (Partly shown in Fig. 4). 7. A vehicle seat according to claim 2 or claim 3 characterised in that said means connecting the seat part to the base part comprise a link (3) having a lower forward end connected by a pivot connection to the base part, and a rearward upper end connected by a pivot connection to said frame (6), the seat part having a pivot connection with said rearward upper end of the link (3) formed by a rigid coupling (40) having pivots ('it, 42) at its opposite ends respectively to the seat pan (12) and to the link (3), the pivot (41) between the seat pan (12) and the coupling (z;0) being instantaneously movable, in response to movement of the link (3), along a line perpendicular to the line connecting the pivot (42) to the point 17,3 (partly shown in Fig. 5). 8. A vehicle seat comprising a seat part, which includes a seat rest (10) and a back rest (11), a base part (1) and means connecting the seat part to the base part, said means comprising a spring suspension by which the back rest is supported on the base part and which is effective to restrict movement of the back rest to a substantially-vertical direction, characterised in that the suspension includes support means for constraining pivotal movement of the seat rest relative to the back rest to take place about at least two horizontal axes, the supporting means connecting the seat rest to two parts of the seat which move relative to one another during rise and fall of the seat, one supporting means comprising a coupling member having a first pivot connection at a support point on the seat rest and a second pivot connection to a mounting point on one of said two parts of the seat, the mounting point being spaced from the instantaneous centre of rotation of the thigh of the seat occupant relative to said one part of the seat, the support point being located on, and instantaneously movable perpendicular to, a straight line connecting said instantaneous centre of rotation to said mounting point, the other supporting means pivotally connecting the seat rest to the other of said parts of the seat at the instantaneous centre of rotation of the thigh of the occupant relative to said other part of the seat, whereby the seat occupant's lower leg is caused to move pivotally about his ankle hing axis (A) during rise and fall of the seat part. 9. A vehicle seat comprising a seat part, which includes a seat rest (land a back rest (11), a base part (1) and means connecting the seat part to the base part, said means comprising a spring suspension by which the back rest is supported on the base part and which is effective to restrict movement of the back rest to a substantially vertical direction, the suspension including suspension means supporting the seat rest for upward and downward movement with the back rest characterised in that said suspension means support the seat rest for pivotal movement about at least two horizontal traverse axes one of which is spaced from a selected centre of rotation and another of which passes through or is spaced from a different selected centre of rotation (said centres of rotation being selected from the instantaneous centres of rotation of the thigh of a seat occupant relative to any two parts of the seat which move relative to one another during upward and downward movement of the seat part relative to the base part), the or each said axis which is spaced from a said centre of rotation extending perpendicularly through the straight line which connects said centre of rotation to the point on the seat rest, related to said centre, at which the coupling means is supported, whereby the seat occupant's lower leg is caused to move pivotally about his ankle hinge axis (A) during rise and fall of the seat part. 10. A vehicle seat comprising a seat part, which includes a seat rest (10) and a back rest (11), a base part (1) and means connecting the seat part to the base part, said means comprising a'spring suspension by which the back rest is supported on the base part and which is effective to restrict movement of the back rest to a substantially vertical direction, characterised in that the suspension includes coupling means including a first coupling (such as 20) connecting a first pivotal support point (P5) on the seat rest to a mounting point (P4) on a first part (1) of the seat which moves relative to the seat rest (10), and a second coupling (such as 21) connecting a second pivot support point (P6) on the seat rest to a mounting point on a second part (6) of the seat (said first and second parts (1, 6) of the seat being movable relative to each other as the seat part rises and falls), said pivot support points permitting rotation of the seat rest relative to the back rest about horizontal transverse axes, and each coupling being such that if the mounting point is not located at the instantaneous centre of rotation of the thigh of a seat occupant relative to the part of the seat to which said coupling is connected, the support point is located on, and instantaneously movable perpendicular to, the straight line connecting the mounting point of the coupling with said instantaneous centre of rotation, at least one of said mounting points being spaced from the corresponding instantaneous centre of rotation, and the arrangement being such that the seat occupant's lower leg is caused to move pivotally about his ankle hinge axis (A) during rise and fall of the seat part.

Inventors: BARLEY, GEOFFREY WILFRED
Applicants: UOP INC.
Application year: 1980
Main classification: B60N1
IPC codes: A47C3, B60N2