(54) MOTORCYCLE SUSPENSION (71) We, KAYABAKOGYOKABUSHIKIKAISHA, of Sekaiboeki-center-building, No. 4-1, 2-chome, Hamamatsu-cho, Minato-ku, Tokyo, Japan, a company organized under the Laws of Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a motorcycle front or rear wheel suspension.

In general, the motorcycle front or rear wheel suspension of the type comprising a pair of parallel suspension coil spring-shock absorber assemblies each having an inner tube which houses a coil spring and which is slidably and telescopically fitted into an outer tube, as well as other hydraulic shock absorbers, must be so constructed that the entrainment of air into a working hydraulic fluid or oil may be avoided so as to obtain stable damping effects. To this end, there have been proposed and demonstrated various devices, but no satisfactory results have been obtained in the suspension of the type described as will be explained below.

When a motorcycle suspension shortens or lengthens or when the inner tube is forced into or out of the outer tube, the volume of each suspension coil spring - shock absorber assembly varies depending upon the stroke of the inner tube. In order to compensate this variation in volume, the working hydraulic fluid or oil is forced to flow through a hollow rod or innermost tube between an upper reservoir within the inner tube and a lower reservoir or chamber within the outer tube. The inner diameter of the hollow rod is dependent upon the inner diameter of the inner tube and is in general 45 to 55% of the latter; in practice, the inner diameter of the hollow rod is in general 13 to 15mm. As a consequence, the working hydraulic fluid or oil is forced to flow through the hollow rod or innermost tube at a fast velocity when the inner tube is forced into the outer tube so that said fluid or oil jets or squirts into upper reservoir in the inner tube, impinging against and adhering to the coil spring fitted therein. As a result, the level of said fluid or oil in the upper reservoir becomes lower than normal because some of the working fluid or oil sticks to the coil spring. When the inner tube is forced out of the outer tube, the said fluid or oil is forced to flow through the innermost tube into the working chamber in the upper tube so that the air within an air chamber above the upper oil reservoir in the inner tube is entrained by the working oil. The prior art countermeasures were made without these fundamental problems or causes being taken into consideration so that they have all been unsuccessful.

The principal object of the present invention is therefore to provide an improved motorcycle suspension which substantially eliminates the entrainment of air into the working fluid or oil.

Accordingly, the present invention consists in a motorcycle suspension comprising a pair of suspension coil spring-shock absorber assemblies, wherein each assembly comprises an inner tube which houses a coil spring and which is telescopically fitted into an outer tube; a hollow rod secured at one end thereof to a wall of said outer tube, said wall extending transversely of said outer tube; a main piston carried by said inner tube and an auxiliary piston connected to said hollow rod, said piston and the outer wall surface of the hollow rod and the inner wall surface of the inner tube together defining a first chamber of annular cross-sectional shape; a second chamber of annular cross-sectional shape formed by said main piston, said transverse wall, the outer surface of the hollow rod and the inner wall surface of the outer tube; a third chamber; a reservoir in said inner tube on that side of said auxiliary piston which is remote from said first chamber; hydraulic fluid in each of said reservoir, said hollow rod, said first chamber, said second chamber and said third chamber; said reservoir also accommodating part of said coil spring; first and second air chambers of which the first is located in said inner tube above the level of the hydraulic fluid in said reservoir and of which the second is spaced from said second chamber by said third chamber; the ratio of the volume of the first air chamber to the volume of the second air chamber being made so close to the ratio of the cross-sectional area of the bore of said inner tube to the cross-sectional area of the material of which the inner tube is made that the entrainment of air into the hydraulic fluid in the second chamber and subsequently into the first chamber is prevented; relative axial movement in one direction between the outer tube and the inner tube causing the first chamber to increase in volume and the second chamber to decrease in volume simultaneously and simultaneously causing the air in the first and second air chambers to become compressed; relative axial movement in the opposite direction between the outer tube and the inner tube causing the first chamber to decrease in volume and the second chamber to increase in volume simultaneously and simultaneously permitting the air in the first and second air chambers to expand; said first, second and third chambers and said reservoir being hydraulically interconnected by passageways which restrict the rate of flow of said hydraulic fluid from one chamber to another, thereby damping relative movement between said inner and outer tubes; the volumes of oil in the third chamber and in the reservoir being simultaneously increased or decreased when the volume of said second chamber is decreased or increased, respectively.

Said hollow rod may place said reservoir and said third chamber in direct communication with one another hydraulically, said third chamber disposed in said outer tube on that side of said transverse wall which is remote from said second chamber. In one embodiment which includes this feature, a first one of said passageways is provided in said hollow rod within the confines of said second chamber, a second one of said passageways is provided in said main piston, and a third one of said passageways is provided in said transverse wall, a one-way valve being associated with said third passageway in order to permit flow of hydraulic fluid through said third passageway as a result of relative movement in only one direction between said inner and outer tubes. In another embodiment which includes said feature, a first one of said passageways is provided in said hollow rod within the confines of said second chamber, a second one of said passageways is provided in said hollow rod within the confines of said first chamber, and a third one of said passageways is provided in said transverse wall, a one-way valve being associated with said third passageway in order to permit flow of hydraulic fluid through said third passageway as a result of relative movement in only one direction between said inner and outer tubes.

Preferably, the second air chamber is disposed in said outer tube adjacent to and coaxially with said third chamber. Said second air chamber may be separated from said third chamber by a floating piston or by an expansible bladder.

A motorcycle suspension according to the present invention may, on the other hand, comprise a cylinder fitted over said outer tube in such a manner as to be concentric with a lower portion of the length of said outer tube, the inner wall surface of said cylinder and the outer wall surface of said outer tube defining an annular space which is subdivided by an expansible bladder in order to create said third chamber radially inwardly of said bladder and in order to create said second air chamber radially outwardly of said bladder, said third chamber and said second chamber being in direct communication hydraulically by way of at least one of said passageways, the or each passageway being provided in said outer wall.

A motorcycle suspension according to the present invention may alternatively comprise a tank mounted on said outer tube and subdivided to form said third chamber and said second air chamber, said third chamber being in direct communication hydraulically with said second chamber by way of a connection which includes a first one of said passageways. Said second air chamber is separated from said third chamber by a floating piston or by an expansible bladder.

When the inner tube is forced into or out of the outer tube the pressures in the first and second air chambers which are compressed or expanded are balanced. When the inner tube is forced into or out of the outer tube. the volume in the inner and outer tubes varies as described above. The variation in volume which is dependent upon the cross sectional area of the bore of the inner tube is completely or nearly compensated by the variation in volume in the first air chamber while the variation in volume which is dependent upon the cross sectional area of the annulus or wall of the inner tube is completely or nearly compensated by the variation in volume in the second air chamber. As a result, the movement of the hydraulic fluid or oil through the hollow rod or the innermost tube will not occur or is negligible so that the jet or squirting of working oil into the upper oil reservoir in the inner tube, as well as the entrainment of air in the first air chamber by the working oil, are avoided.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments thereof in conjunction with the accompanying drawings. The preferred embodiments will be described in conjunction with a front fork of a motorcycle, but it will be understood that the present invention is not limited thereto and that the front fork may be easily modified as a rear wheel suspension based on the description of these embodiments as will be described hereinafter. In said drawings: Figure I is a front view partly in section of a first embodiment of a motorcycle front fork in accordance with the present invention; Figure 2 is a fragmentary sectional view, on enlarged scale, of one of the assemblies illustrated in Figure 1; Figure 3 is a fragmentary longitudinal sectional view thereof, on further enlarged scale, showing a main piston attached to an inner tube; Figure 4 is a fragmentary longitudinal sectional view of a second embodiment of the present invention; Figure 5 is a fragmentary longitudinal view thereof, on enlarged scale, showing a main piston; Figures 6 and 7 are fragmentary longitudinal sectional views, respectively, of a third embodiment and a modification thereof in accordance with the present invention; and Figures 8 and 9 are fragmentary longitudinal sectional views, respectively, of a fourth embodiment of the present invention and a modification thereof.

Same reference numerals are used to designate similar parts throughout the figures.

In Figures 1 and 2 there is shown a front fork 10 of a motorcycle in which is sprung at brackets 16 the front wheel of the motor cycle. The fork comprises in general a pair of parallel suspension spring- shock absorber assemblies 11 each of which includes a coiled suspension spring 12 and which are rigidly connected to each other with an upper bracket 17 and a lower bracket 18 which in turn are securely connected to a steering shaft 19. Since the suspension spring - shock absorber assemblies are substantially similar in construction, the description of one of them will suffice for the complete understanding of the present invention.

The suspension spring-shock absorber assembly 11 comprises in general an outer tube 20, an inner tube 21 and the suspension spring 12 fitted into the inner tube 21. As will be described in detail hereinafter, a first or upper air chamber 15 is defined in the inner tube 21 filled with a working oil. Thus the suspension springs 12 and the first or upper air chambers 15 of the front fork 10 damp the road shock transmitted to the motorcycle frame and the telescopic shock absorber prevent excessive movements of the suspension springs and the front wheel as well as spring oscillations.

As best shown in Figure 2, the inner tube 21 is telescopically inserted into the outer tube 20. An oil seal 23 which is securely retained at the upper end of the outer tube 20 by a snap ring 22 is interposed between the outer and inner tubes 20 and 21 and a dust cover 24 which is fitted over the upper end of the outer tube 20 is in sliding contact with the exterior peripheral surface of the inner tube 21 so that oil leakage and the instrusion of dust into the shock absorber may be prevented.

The outer tube 20 is divided into two chambers or sections by a partition wall 28 having apertures 54. A hollow rod or innermost tube 27 extends along the outer tube 20 and the inner tube 21 coaxially thereof and the lower end of this tube 27 is securely fitted into a locking tube 26 having a tapered or upwardly converging outer wall 25. A bolt 30 having a through-hole 29 is screwed through a central hole in the partition wall 28 into the lower end of the innermost tube 27 so that the locking tube 26 and the innermost tube 27 are securely held in position.

A spring retainer 31 is securely attached to the upper end of the innermost tube 27 with a lateral pin 33, and an auxiliary piston 32 is fitted over the innermost tube 27 immediately below the spring retainer 31 and is securely held against said retainer by a snap ring 36 and is intended to make sliding movements in the inner tube 21.

The upper end of the inner tube 21 is closed with a cap 13 having an air charge valve 14, said closure taking place after a spring retainer 35 and a spacer 34 have been inserted into the inner tube 21. The suspension coil spring 12 is therefore supported between the upper spring retainer 35 and the lower spring retainer 31 which is attached securely to the upper end of the innermost tube 27.

The auxiliary piston 32 at the top of the innermost tube 27 thus defines an oil reservoir 37 within the inner tube 21, and the upper air chamber 15 is defined between the surface of the oil and the cap 13.

Referring particularly to Figure 3, a main piston 38, a valve body 45, a valve seat disk 39 and a locking piston 41 having a bore 40 are fitted into the inner tube 21 in the order named from the lower end thereof and securely held in position between an annular step 42 formed in the interior peripheral surface of the inner tube 21 and a snap ring 43 fitted thereto. The main piston 38 is firmed with a plurality of equiangularly spaced oil holes 44, and the valve body 45 is fitted over the innermost tube 27 within the main piston 38 with freedom for movement relative to said piston 38. The valve seat disk 36 which is interposed between the main piston 38 and the locking piston 41 is also formed with a plurality of equiangularly spaced holes 46 which are opened or closed as the valve body 45 moves upwardly or downwardly with the main piston 38. Clearances between the valve seat disk 39 and the valve body 45 on the one hand and the innermost tube 27 on the other hand form an annular orifice 47.

Referring back to Figure 2, the auxiliary piston 32 attached to the upper end of the innermost tube 27 and the main piston 38 attached to the lower end of the inner tube 21 define a pressure chamber 48 between the inner and innermost tubes 21 and 27. A lower oil chamber 49 is also defined within the outer tube 20 between the main piston 38 and the partition wall 28. The pressure chamber 48 and the lower oil chamber 49 are hydraulically intercommunicated through the annular orifice 47 and the bore 40 in the locking piston 41.

A free piston 50 is slidably fitted into the chamber below the partition wall 28 in the outer tube 20, and the lower end of the outer tube 20 is closed with a plug 51 which is equipped with an air charge valve 55 so that an oil chamber 52 and a second or lower air chamber 53 are defined above and below the free piston 50. The oil chamber 52 communicates not only with the lower working oil chamber 49 through the orifice 54 in the partition wall 28 and a check valve 69 disposed thereupon but also with the oil reservoir 37 in the inner tube 21 through the through-hole 29 of the bolt 30 and the innermost tube 27. The bore of the innermost tube 27 also communictes with the lower oil chamber 49 through an orifice 70 of a relatively large diameter formed through the wall of the innermost tube 27.

After the assembly of the front fork 10, air under a predetermined pressure is charged into the first and second air chambers 15 and 53 through the air charge valves 14 and 55.

Alternatively atmospheric air may be sealed within these air chambers in a suitable manner during the assembly.

When the front fork 10 shortens or when the inner tube 21 is forced into the outer tube 20, the overall variation in volume of the assembly 11 is the sum of the variation in volume above the auxiliary piston 32 due to the relative movement between the cap 13 and the auxiliary piston 32 and the variation in volume below the auxiliary piston 32 due to the downward stroke of the inner tube 21 in the outer tube 20. This volume variation V is given by V = 4 D22 5 + 4 . (D,2 - D22) . 5 where Dl = the outer diameter of the inner tube 21; D2 = the inner diameter of the inner tube 21; and S = the downward stroke of the inner tube 21.

Eq. (1) may be rewritten as follows: V = Al S +. A2 S = (Al + A2) S where A1 = the cross sectional area of the bore of the inner tube 21; and A2 = the cross sectional area of the annulus of the inner tube 21.

Let P0 and p0 denote the pressures, respectively, in the first and second air chambers 15 and 53 which have the volumes V0 and vO respectively, when the inner tube 21 is in the initial position thereof. Also let P, and p1 denote the pressures, respectively, in the first and second air chambers 15 and 53 which have now the volumes V, and v,, respectively, when the inner tube 21 is forced into the outer tube 20 by S. Then in the first air chamber 15, P V Vol = PI V1 Vli' (3) and in the second air chamber 53 p0 . v0 = p, . viz It is assumed that the variation in volume above the auxiliary piston 32 (that is, A, S) is compensated by the variation in volume in the first air chamber 15 while the variation in volume below the auxiliary piston 32 (that is, A2.S) is compensated by the variation in volume in the second air chamber 53. Then from Eq. (2), we have Vo - V1 = A1 S .. . (5) and vO - v1 = A2 S o e (6) From Eqs. (3) and (5) and Eqs. (4) and (6), we have

Since the first and second air chambers 15 and 53 are connected to each other through the intermediary of the oil reservoir 37 in the inner tube, the innermost tube 27 and the oil chamber 52 in the outer tube 20, the following relations are always held: Po p0 and P1 # p1 Therefore from Eqs. (7) and (8), we have

and

Rewritting Eqs. (9) and (10), we have

1 - A1 . S = 1 - A2 # S Vo Vo Vo/Vo = A1/A2 ...(11) and in like manner we have

V1 = A1 .. (12) v1 A2 And the same is true when the inner tube 21 is extended out of the outer tube 20.

Thus, as shown in Eqs. (11) and (12), the ratio in volume of the first air chamber to the second air chamber is made equal to the ratio of the cross sectional area of the bore of the inner tube 21 to the cross sectional area of the annulus thereof. As a consequence, when the front fork 10 shortens or lengthens, the pressures in the first and second air chambers 15 and 53 are always maintained equal, and the variation in volume above the auxiliary piston 32 is compensated by the variation in volume in the first air chamber 15 while the variation in volume below the auxiliary piston 32 is compensated by the variation in volume in the second air chamber 53. Furthermore, no movement of the working oil through the innermost tube 27 occurs so that the squirting of working oil into the oil reservoir 37 and the entrainment of air into the oil chamber 52 is avoided.

The mode of operation of the front fork 10 with the above construction will be described hereinbelow:- When the front fork 10 shortends or when the inner tube 21 is forced into the outer tube 20, the lower oil chamber 49 decreases in volume so that part of the working oil therein is forced to flow through the orifices in the valve seat disk 39 into the pressure chamber 48 which increases in volume. The remaining oil in the chamber 49 is forced to flow through the orifice 70 into the innermost tube 27 and then into the oil chamber 52 while forcing the check valve 69 to close. While a relatively gentle damping effect is produced by the working oil forced to flow through the orifices 46, 70, the first and second air chambers 15 and 53 are both compressed so that the decrease in volume of the chamber 49 in the outer tube 20 due to the advance of the inner tube 21 into the outer tube 20 is compensated.

As the inner tube 21 is further forced into the outer tube, the locking tube 26 having the outwardly converging outer wall 25 is inserted into the bore 40 in the locking piston 41 which is attached to the lower end of the inner tube 21, with the result that the working oil which is forced to flow through the clearance between the locking tube 26 and the locking piston 41 offers resistance to the downward stroke of the inner tube 21 and, consequently, the lower end of the inner tube 21 may be prevented from striking against the partition wall 28 with strong impact.

When the inner tube 21 is moved upwardly (as viewed in Figure 2) relatively to the outer tube 20 or when the front fork 10 lengthens, the pressure chamber 48 decreases in volume so that the working oil therein is forced to flow through the clearances 47 and the bore 40 in the locking piston 41 into the lower oil chamber 49 which increases in volume; the result is that damping is produced by the resistance which is encountered by the working oil being forced to flow through the clearances 47. Concurrently, the first and second air chambers 15 and 53 increase in volume because of oil being drawn into the chamber 49 from the chamber 52, whereby the increase in volume of the outer tube 20 due to the retraction of the inner tube 21 is compensated. The working oil in the oil chamber 52 is forced to flow into the lower oil chamber 49 through the check valve 69, As best shown in Figure 2, the innermost tube 27 may have the outer wall diverged upwardly as indicated by the chain lines so that the effective area of the clearances 47 will vary depending upon the stroke of the inner tube 21 relative to the outer tube 20; such an arrangement would ensure that the front fork 10 possesses optimum damping characteristics. Furthermore, by this means, the main piston 38 attached to the lower end of the inner tube 21 would be prevented from striking with strong impact against the auxiliary piston 32 which is attached to the upper end of the innermost tube 27.

As described above, as the front fork 10 shortens or lengthens, both of the first and second air chambers 15 and 53 are either compressed or exanded, respectively. One of the important features of the present invention is that the ratio in volume of the first chamber 15 to the second or lower air chamber 53 is determined in the manner described in detail above.

So far, the present invention has been described as setting the ratio of the volume in the first air chamber 15 to the volume in the second air chamber 53 equal to the ratio of the cross sectional area of the bore of the inner tube 21 to the cross sectional area of the annulus thereof so that no movement of working oil through the innermost tube 27 occurs, but it will be understood that it is not necessary to do so; that is, the volume ratio can be suitably varied to permit the movement of working oil within the innermost tube 27 without excessive squirting of working oil into the oil reservoir 37 and excessive entrainment of air into the oil chamber 52 occurring. and this will now be described with reference to Figures 4 and 5.

In said Figures. instead of generating the damping effect by the resistance encountered by the working fluid which is forced to flow through the clearances 47 between the disk 39 and the valve body 45 on the one hand and the innermost tube 27 on the other hand when the front fork 10 is lengthened, an orifice 47a is formed through the wall of the innermost tube 27 at the upper portion thereof as shown in Figure 4, with the result that the damping effect is produced, when the front fork 10 is extended by the working oil being forced to flow from the pressure chamber 48 through the orifice 47a into the innermost tube 27. The volume of working oil forced out of the pressure chamber 48 through the orifice 47a is given by Q = s/4 (D22 - D32) S where D3 = the outer diameter of the innermost tube 27.

This volume Q is relatively small, and furthermore the working oil forced out of the pressure chamber 48 into the innermost tube 27 will not cause the working oil therein to squirt into the oil reservoir 37. The working oil flows through the innermost tube 27, the through-hole 29 in the bolt 30, the oil chamber 52 and the orifice 54 in the partition wall 28 into the lower oil chamber 49 so that entrainment of the air in the first air chamber 15 by the working oil is prevented. With this arrangement the innermost tube 27 is not needed to be formed with the outwardly diverging wall. When the front fork 10 is extended, the working oil trapped in the space between the main and auxiliary pistons 38 and 32 after the main piston 38 has passed beyond the orifice 47a prevents the main piston 38 from striking against the auxiliary piston 32 with strong impact.

In the first embodiment described above in conjunction with Figures 1-5, the space below the partition wall 28 in the outer tube 20 is divided into the oil chamber 52 and the second or lower air chamber 53 by the free piston, but as shown in Figure 6 this space may be divided by a bladder 57 made of rubber or the like. The peripheral edge of the bladder 57 is securely sandwiched between the plug 51 and a stepped portion at the lower end of the outer tube 20.

The front forks shown in Figures 1 - 6 have a common disadvantage in that their lengths are relatively great because the oil chamber 52 and the second air chamber 53 are defined within the outer tube 20 below the partition wall 28. This problem however may be overcome by the arrangement shown in Figure 7 in which a cylinder 61, having a diameter greater than the outer diameter of the outer tube 20b, is fitted over the lower portion thereof and is securely attached thereto, coaxially thereof, between an annular step 62 formed in the outer peripheral surface of the outer tube 20b and a snap ring 63 which is supported on another annular step which is similar to the step 63. A cylindrical bladder 57b is fitted over and radially spaced apart by a suitable distance from the outer tube 20b within the cylinder 61 and has its upper and lower edges firmly held between the outer tube 20b and upper and lower annular plugs or caps 59 and 60 fitted into the space between the outer tube 20b and the cylinder 61 at the upper and lower ends thereof. The cylindrical bladder 57b therefore defines an oil chamber 52b, and a second air chamber 53b within the cylinder 61. The oil chamber 52b is in communication hydraulically with the lower oil chamber 49 through a plurality of orifices 70b formed through the wall of the outer tube 20b and vertically spaced apart from each other by a suitable distance so that when the front fork 10 is compressed or shortened, the damping effect may be suitably varied depending upon the downward stroke of the inner tube 21.

The outer tube 20b has a bottom wall 28b, and the locking tube 26 and the innermost tube 27 are securely held in position on the bottom wall 28b with a bolt 30b in a manner substantially similar to that described above.

The overall length of the front fork 10 may be also shortened by the arrangements shown in Figures 8 and 9. Referring firstly to Figure 8, a radially outwardly extending boss 64 is formed integrally with the outer tube 20c at a lower portion thereof, and a bolt 65 having a blind hole is screwed into the boss 64. A tank 66, which has the air charge valve 55 at the top thereof and which is divided into an oil chamber 52c and a second or lower air chamber 53c by a free piston 50c slidably fitted therein, is mounted on the bolt 65 in parallel with the outer tube 20c, and the oil chamber 52c is in communication through an orifice 70c formed through the wall of the bolt 65 and through the blind bore in said bolt with the lower working oil chamber 49 within the outer tube 20c.

In the arrangement shown in Figure 9, the bolt 65d with the orifice 70d i

So far the present invention has been described in conjunction with the front fork of the motorcycle, but it will be apparent to those skilled in the art that the front forks described above with reference to Figures 1 - 9 may be easily modified into the rear wheel suspensions of the motor cycles; that is, the suspension spring - shock absorber assemblies which are essentially similar in construction to those described above may be reduced in length and provided with suitable means for connection with the motorcycle frame. Further description will be redundant.

WHAT WE CLAIM IS: 1. A motorcycle suspension comprising a pair of suspension coil spring-shock absorber assemblies, wherein each assembly comprises an inner tube which houses a coil spring and which is telescopically fitted into an outer tube; a hollow rod secured at one end thereof to a wall of said outer tube, said wall extending transversely of said outer tube; a main piston carried by said inner tube and an auxiliary piston connected to said hollow rod, said pistons and the outer wall surface of the hollow rod and the inner wall surface of the inner tube together defining a first chamber of annular cross-sectional shape; a second chamber of annular cross-sectional shape formed by said main piston, said transverse wall, the outer wall surface of the hollow rod and the inner wall surface of the outer tube; a third chamber; a reservoir in said inner tube on that side of said auxiliary piston which is remote from said first chamber; a hydraulic fluid in each of said reservoir, said hollow rod, said first chamber, said second chamber and said third chamber; said reservoir also accommodating part of said coil spring, first and second air chambers of which the first is located in said inner tube above the level of the hydraulic fluid in said reservoir and of which the second is spaced from said second chamber by said third chamber; the ratio of the volume of the first air chamber to the volume of the second air chamber being made so close to the ratio of the cross-sectional area of the bore of said inner tube to the cross-sectional area of the material of which the inner tube is made that the entrainment of air into the hydraulic fluid in the second chamber and subsequently into the first chamber is prevented; relative axial movement in one direction between the outer tube and the inner tube causing the first chamber to increase in volume and the second chamber to decrease in volume simultaneously and simultaneously causing the air in the first and second air chambers to become compressed; relative axial movement in the opposite direction between the outer tube and the inner tube causing the first chamber to decrease in volume and the second chamber to increase in volume simultaneously and simultaneously permitting the air in the first and second air chambers to expand; said first, second and third chambers and said reservoir being hydraulically interconnected by passageways which restrict the rate of flow of said hydraulic fluid from one chamber to another, thereby damping relative movement between said inner and outer tubes; the volumes of oil in the third chamber and in the reservoir being simultaneously increased or decreased when the volume of said second chamber is decreased or increased respectively.

2. A motorcycle suspension as claimed in Claim 1, wherein said hollow rod places said reservoir and said third chamber in direct communication with one another hydraulically, said third chamber being disposed in said outer tube on that side of said transverse wall which is remote from said second chamber.

3. A motorcycle suspension as claimed in Claim 2, wherein a first one of said passageways is provided in said hollow rod within the confines of said second chamber, a second one of said passageways is provided in said main piston, and a third one of said passageways is provided in said transverse wall, a one-way valve being associated with said third passageway in order to permit flow of hydraulic fluid through said third passageway as a result of relative movement in only one direction between said inner and outer tubes.

4. A motorcycle suspension as claimed in Claim 2, wherein a first one of said passageways is provided in said hollow rod within the confines of said second chamber, a second one of said passageways is provided in said hollow rod within the confines of said first chamber. and a third one of said passageways is provided in said transverse wall, a one-way valve being associated with said third passageway in order to permit flow of hydraulic fluid through said third passageway as a result of relative movement in only one direction between said inner and outer tubes.

5. A motorcycle suspension as claimed in any one of the preceding Claims, wherein the second air chamber is disposed in said outer tube adjacent to and coaxially with said third chamber.

6. A motorcycle suspension as claimed in Claim 5, wherein said second air chamber is separated from said third chamber by a floating piston.

7. A motorcycle suspension as claimed in Claim 5, wherein said second air chamber is separated from said third chamber by an expansible bladder.

8. A motorcycle suspension as claimed in Claim 1, wherein a cylinder is fitted over said outer tube in such a manner as to be concentric with a lower portion of the length of said

**WARNING** end of DESC field may overlap start of CLMS **.