JPS6225893B2 - - Google Patents

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION The present invention relates to a shock mitigating suspension structure (ride strut, referred to herein as a "ride strut") for a load-hauling vehicle for rough terrain, and more specifically to a ride strut structure that uses a compressible liquid. This article concerns ride struts and how to maintain them. Load-hauling rough terrain vehicles are used in areas such as highway construction and mining. For many years, these vehicles were manufactured without spring suspension, except for the limited resiliency provided by the tires. These springless vehicles run at 10 miles per hour (approx.
It was operated at relatively low speeds (16 km/h) at which both driver and vehicle could endure the pain imposed by the stiff suspension. However, modern rough terrain tractors are no longer operated at such low speeds. For example, in mining operations, these rough terrain vehicles are driven along towpaths at speeds of up to 40 miles per hour. Conveying capacity, as well as operating speed, has been greatly increased, with payloads reaching 200 tons or more. At such speeds and payloads, the fatigue of both the driver and the vehicle itself is at its limit, making an elastic suspension a necessity. The first spring suspensions were similar in principle to those of road vehicles. For example, vehicles were manufactured with coil spring suspensions and shock absorbers to dampen the spring action. Recently, ride struts have been developed that are intended to perform both suspension and shock absorption functions. These struts use a variety of self-contained springs, including rubber, metal, and liquid. A number of different ride struts have been proposed and developed, but none have been fully satisfactory because the harshness caused by rough terrain load traction can cause excessive failure. Failures are due to (a) the high cost of the struts, (b) the extremely high yield from the lost vehicle, and (c) the high loading costs, especially if the failure occurs in a remote location with severe weather conditions. Repairs to tow vehicles are often difficult and therefore prohibitively expensive. Although so-called hydroelastic ride struts have been known for some years in some applications, they have exhibited deficiencies for rough terrain load traction. For these struts, a compressible liquid, such as liquid silicone, provides elastic suspension. A typical strut has a cylinder that defines a fluid-containing chamber. A ported piston is located within this chamber and is connected to the piston rod. A piston rod extends from one end of the cylinder. The weight of the vehicle forces the piston rod and fluid into the cylinder, compressing the fluid and creating a type of spring action. The ported piston has the function of mitigating this effect and thus acts as a shock absorber. One major advantage of liquid struts is that the liquid spring effectively lasts an infinite life unless the strut itself breaks. The reason the spring effectively has an infinite life is because the fluid strut can be filled with additional fluid to compensate for lost fluid. As long as there is a proper amount of fluid, proper spring capacity is maintained, and unlike metal and rubber springs,
Spring fatigue is excluded as a factor in suspension life. Another advantage of liquid ride struts is that, with a piston suitably ported to allow controlled fluid flow from one side of the piston to the other, liquid ride struts can also be used as spring suspensions. It also functions as a shock absorber that dampens the impact. However, although liquid struts have these advantages, conventional struts still have drawbacks. One drawback is the so-called “recoil”
The inability to adequately withstand forces imposed under (rebound) conditions. A recoil condition occurs when the vehicle bounces off the ground, or when a wheel falls into a pothole, causing the struts to extend, rather than being compressed to support the vehicle over the wheels and axle.
This occurs when the wheels and axles stretch to suspend the weight. Attempts have been made to solve the ride strut recoil problem, but none have been entirely satisfactory. For example, attempts have been made to use rubber discs as recoil cushions, but these are susceptible to deterioration at an excessive rate when exposed to liquid spring materials such as liquid silicone. Other approaches to recoil control are (a) high damping rates desired for recoil conditions that serve to deter and substantially prevent damage to the strut or other vehicle components; and (b) the ability of the strut to serve as a vehicle support. Both cannot achieve sufficient flow rates through the ported piston to allow the desired rate of piston movement when operative. SUMMARY OF THE INVENTION The present invention provides a vehicle equipped with a liquid ride strut that overcomes the aforementioned problems. By achieving a high recoil damping rate,
Provides excellent recoil characteristics. A ride strut constructed in accordance with the present invention has a piston disposed to reciprocate within a cylinder closed at one end. The other end of the cylinder supports a filler member in a sliding sealing relationship with a piston rod connected to the piston. The piston has a passageway for directing conditioned liquid therethrough and a seal member for engaging the inner cylinder surface in a sliding sealing relationship. The piston thus divides the interior of the cylinder into two parts. one between the piston and the closed end of the cylinder, and the other between the piston and the filling member. Both parts are filled with liquid, and because of the fluid flow through the piston passages, the strut internal pressure is equalized except for a short time after a sudden and significant change in load. The ride strut has a high velocity fluid flow through the piston during compression, an intermediate velocity fluid flow through the piston during extension through the normal operating range, and a very low fluid velocity during recoil extension. To provide normal range operation, a number of unobstructed passageways are provided within the piston, while other passageways within the piston include check valves. Valved passageways allow nearly unobstructed fluid flow during compression, but reduce flow during normal range extension. Extremely high recoil damping rates are achieved by further restricting flow through the piston passage through additional valving. This valving is provided by a pair of flanged collars supported by the piston rod, one of which is forced into engagement with the piston under recoil extension. Both collars are biased away from each other by a first spring, and the collar (valve member) closer to the piston is biased away from the piston by a second, weaker spring. When maximum extension of the strut is reached, the collar (cooperating member) remote from the piston encounters an obstruction and is forced back towards the piston. Then, the second
Since the spring is weak, the valve member is displaced into engagement with the piston and the orifice is covered. The valve member is provided with a large number of small holes so that liquid can flow through the valve member. An annular groove connects the outlets of these holes, and since the annular groove overlaps the orifice, only a very small amount of liquid will pass through the valve member and piston, no matter how maximal the strut extension. It can flow. By appropriately selecting the dimensions of the orifice, annular groove, and passage through the valve member, the flow of liquid under strut extension can be regulated very precisely. A portion of the piston rod also supports a resilient pad that engages a portion of the cylinder to prevent undue stress on the ride strut components in the event of extreme strut compression. do. Although such extreme strut compressions are rare, the elastic pads serve as a safety measure to protect the struts in such cases. The above-mentioned features result in a very robust and simple liquid ride strut, which can be adapted quite precisely to different requirements. Additional advantageous features of the invention will become apparent from the following description of preferred embodiments with reference to the drawings. DESCRIPTION OF THE PREFERRED EMBODIMENTS A combination ride strut 10 (hereinafter referred to as the "ride strut") is shown in FIG. The ride strut 10 is made up of several subassemblies: a body part (or housing structure) 12, a rod part 13 containing a piston rod 14, a piston part (or piston structure) 16, and a valve part (or valve means) 18. It is configured. This ride strut is used on large rough terrain vehicles carrying loads up to 200 tons or more. As an example, a ride strut used on a 170 ton vehicle, when extended, has an overall length of approximately 82 inches and a piston diameter of approximately 8 inches.
cm), the diameter of the piston rod is approximately 4.25 inches (approximately 11 cm)
It is. This ride strut has a stroke (or compression stroke) of approximately 4.50 inches (approximately 11 cm) from a quiet state of the vehicle, and a recoil extension (or extension stroke) of approximately 1.50 inches (approximately 3.8 cm) from a quiet state of the vehicle. and The body portion 12 is filled with a compressible silicone liquid that provides a spring action. Available fluids have compressibility range from 0.36% at 500psi to 11.6% at 30000psi
% silicone oil. Approximately 4.4 gallons (approximately 17) for a ride strut of the above dimensions
liquid is required. (1) Body part 12 The body part is a cylindrical housing structure consisting of an elongated cylinder 20, and the lower end (left end in FIG. 1) is closed with an end cap 22. An annular filling member 24 is screwed into the upper end (right end in FIG. 1) of the cylinder 20 in a sliding and sealing manner with the piston rod 14 to close the upper end of the cylinder. A rod eye 26 extends outwardly from the end cap and includes a hole 28 for attachment to a vehicle axle. Reinforcing members 30 are on either side of the rod eye 26. The end cap, rod eye and reinforcing member are permanently secured to each other by welding. The end cap is secured within the cylinder 20 by serrated screws 32 as shown in detail in FIG. Serrated threads are used because they better accommodate heavy loads in one direction, such as those caused by internal body pressure that tends to force the end cap away from the end of the cylinder. A seal 34 is interposed between the end cap and the cylinder to prevent fluid leakage from the housing. Fourth
Referring to the figures, seal 34 consists of an O-ring 36 disposed within a circumferential groove 38 formed in the end cap. A tapered ring 40 is also disposed within the groove 38 and compresses the O-ring as well as itself against the inner surface of the cylinder 20. Shock absorbing fluid is filled into the ride strut through the end cap (and can be withdrawn from the ride strut if necessary). A first passageway 44 extends from the exposed portion of the end cap toward its center.
) extends radially inward. This passageway 44 communicates with a second axially extending passageway 46 which is a recess 48 formed in the inner end of the end cap.
It is familiar to With particular reference to FIG. 2, a charging valve 50 having a stopcock 52 is fitted into the exposed end of the first passageway 44. The charge valve and stopcock are protected by a U-shaped bracket 54 secured to the end cap with bolts 56. Once the bolt and U-bracket have been removed, the stopcock 52 and therefore the charging valve 50 are accessible. Another vent valve 58 (FIG. 2) is provided in the end cap. This vent valve is arranged angularly offset from the charging valve 50, and is arranged in the first and second passages 44, 4.
It communicates with the inside of the body via a passage (not shown) similar to 6. As liquid is charged inside the body, the internal pressure will eventually increase to the point where the ride strut is in an extended state. This is how the height of the vehicle and the internal preload of the ride struts are adjusted. Similarly, if the vehicle height and preload are too large,
Just let the liquid leak out from the charging valve. Referring to Figures 1, 8 and 9, filling member 2
4 has an inwardly extending collar 62 secured within the cylinder by serrated screws 64. Serrated screw 64
is the same as the serrated screw 32 shown in FIG.
The padding member 24 also has an end flange portion 65;
This overlaps and engages the end of the cylinder 20. The filler member provides a leak-tight closure for the piston rod 14 and provides centering of the piston rod. A rod seal 66 having an inner bore approximately the same diameter as the piston rod is supported by the collar portion 62.
Referring to FIGS. 8 and 9, the rod seal 66 is shown in (a)
(b) a pair of spaced apart lips 70a, 70b facing axially toward the lower end (left end in the figure) of the ride strut; have Rod Seal 66
is formed from polytetrafluoroethylene (TEFLON) for its anti-friction and sealing properties. An O-ring 72 is inserted between the lips 70a, 70b to maintain an appropriate radial spacing therebetween. Another O-ring 74 surrounds the outer lip 70a and engages the inner surface of the collar 62. An annular holding member 76 (hereinafter also referred to as recoil stopper 76) is fixed to the inner end of collar portion 62 by bolts 78 (only one is shown). Retention member 76 engages outer lip 70a of rod seal 66 to hold it in place. bolt 78
is further fitted into the hole 80 of the holding member.
The inner diameter of the retaining member 76 is larger than the outer diameter of the piston rod so that liquid can flow therebetween. The retaining member has a radially extending passageway 82 which intersects an axially extending passageway 84. An axial passage 86 extends through the collar 62 and is centered with the axial passage 84 . A bleed valve 88 having a plug 90 is fitted into the passageway 86 . This construction allows air to be forced out of the cylinder as liquid is filled into the cylinder during assembly. The bleed valve and plug are formed in the collar portion 62.
Since it is housed within the borehole 92, it will not be damaged when the ride strut is fully compressed. Collar portion 62 is provided with an outer seal 94 to minimize or prevent leakage of fluid toward serrated threads 64 . Referring to FIG. 5, seal 94 consists of an O-ring 96 located within a circumferential groove 98 formed in the collar. A tapered ring 100 is also received within the groove 98 and compresses the O-ring outwardly while also pressing itself against the inner surface of the cylinder 20. A split ring guide 102 is disposed between the collar portion 62 and the piston rod 14. (1st, 8th,
Figure 9). Guide 102 engages the upper end of rod seal 66. Guide 102 is held fixed by engagement with shoulder 104 of padding member 24, as best seen in FIG. To exclude dust and other contaminants from the guide 102 and the rod seal 66, a dust screen 106 is installed.
is provided at the boundary between the shoulder 104 and the piston rod 14. Referring to FIG. 6, the dust shield 106 consists of an annular ring 108 having axially facing lips 110a, 110b. Lip-shaped parts 110a, 11
An O-ring 112 is fitted between the holes 0b and inflates the lip portion to perform a sealing function. (2) Rod portion 13 The piston rod 14 has an elongated cylindrical portion (large diameter portion) 1
16, and a successively decreasing diameter portion 11 that follows.
It consists of 8 (intermediate diameter part) and 120 (small diameter part). The intermediate diameter portion 118 and the small diameter portion 120 are the umbrella-shaped surface 1
However, the large diameter portion 116 and the intermediate diameter portion 118 are connected by a shoulder and umbrella 119 that extend in the radial direction. A valve portion 18 is provided in the intermediate diameter portion 118.
(described later) is supported, and the piston portion 16 (described later) is supported astride the intermediate diameter portion 118 and the small diameter portion 120. As clearly shown in FIG. 8, a threaded cylindrical portion 122 protrudes from the other end (right end) of the piston rod.
Nut 12 screwed into this threaded cylindrical portion 122
8, a disk 124 with an opening 126 is fixed to the piston rod. A two-part rod eye 130 (only one portion shown in FIG. 1) extends outwardly from disk 124 and has an opening 132 for attachment to a vehicle frame. The disk and rod eye are permanently secured together by welding. A rubber cylindrical shroud or boot 134 is secured to the outer periphery of the disk to shield the piston rod from dust and other contaminants. This boot is concentric with the outer surface of the cylinder 20 and surrounds the dust seal O-ring 114. wrap or boot 134
overlaps the body 12 by a convenient distance to make it difficult for dust to enter. The boot is recessed into the circumferential groove of disc 124 and secured thereto by circumferential clamp 136. A band 137 is attached to the outer circumference of the cylinder 20 in order to determine whether the amount of fluid in the ride strut is appropriate.
is fixed. The axial position of the band 137 is selected such that the lower edge of the boot 134 overlaps the band 137 when the vehicle is empty with a suitable amount of fluid in the ride strut. It is preferable for the band 137 to be made of tape of a color that is distinctly different from that of the cylinder and boot, so that they can be easily distinguished. A resilient pad 138 is secured to the inner surface of the disc 124 to cushion the end of the collar 62 during maximum compression of the ride strut. This pad is connected to the bolt 14 inserted into the hole 142.
It is fixed to the disk by 0. A gap is provided between the inner diameter of the pad and the large diameter portion of the piston rod 116, and a gap is similarly provided between the outer diameter of the pad and the boot 134. These gaps, along with the boreholes 142, allow the pad to flex during compression to reduce the possibility of component damage. (3) Piston part 16 The piston part is the inner end (lower end) of the piston rod 14.
A closely supported annular subassembly. The piston 143 included in this has a through hole, and the inner diameter shape is the same as that of the intermediate diameter portion 11 of the piston rod.
8. Curved to cooperate with the surface of the small diameter section 120 and away from the umbrella section 121.
A nut 144 is screwed onto the end of the small diameter portion 120. Relative movement between piston 143 and piston rod 14 is prevented since piston 143 is tightly fitted onto the end of the piston rod and pressed against a spacer sleeve 145 that surrounds intermediate diameter 118 and abuts shoulder 119. . (Figures 8 and 9). Piston portion 16 performs two primary functions.
(a) to maintain a concentric relationship between the cylinder and piston rod; and (b) to act as a dosspot during rapid piston strokes.
To accomplish this, the piston portion 16 engages the inner surface of the cylinder 20 in a sliding sealing relationship to separate chambers within the body between the first portion 146 and the second portion 148.
(Figure 8). It is clear that the volumes of these parts change relative to each other as the piston section moves up and down within the cylinder (although the first part 146 is always larger than the second part 148). The relationship between both volumes does not vary linearly, since the piston rod occupies a progressively larger portion within the second part upon compression of the piston rod. That is, the total volume of the chamber decreases as the piston rod enters the body and the liquid is compressed. Piston 143 has a through hole to allow liquid to pass from one chamber to the other as it moves. An orifice and check valve combination has been found to be effective in achieving the desired flow rates during compression and extension within the normal operating range of the piston. The seal and check valve structure are shown in detail in Figure 7. A split bearing ring 150 is disposed within a circumferential groove 152 on the outer periphery of the piston. Sealing action is also provided by a piston seal ring 154 in a circumferential groove 156 on the outer circumference of the piston. The bearing ring and seal ring together serve to establish an effective sliding sealing relationship with the inner surface of the cylinder 20. Two check valves are provided that are diametrically spaced from each other. In FIGS. 1, 8, and 9, only one check valve is shown at 158 because cross sections are taken in two planes to show both the passage leading to this valve and the restricting passage 174. Referring to FIG. 7, check valve 158
controls fluid flow through passage 160, which extends completely through the piston. The passage 160 has a punch hole 161. An annular valve seat 16 is provided at the lower end of this hollow hole.
2 is secured by a snap spring 164. A valve body 166 is positioned within the borehole 161 for limited axial movement. Valve body 1
66 has a tapered end 168 that selectively engages the valve seat to create a substantially liquid-tight seal. The valve body 166 also has a number of radially extending passageways 170 that communicate with an axially extending body bore 172. The inner hole 172 communicates with a narrow diameter throttle passage 173 that extends in the axial direction. When the ride strut of the present invention is compressed, the piston is advanced to the left in FIG.
6 is pushed to the right by the action of the liquid impinging on it to the position shown in FIG. The tapered end of the valve body 166 thus separates from the valve seat and liquid flows into the valve body bore 172 through both the passage 170 and the throttle passage 173. During extension of the ride strut, the piston is moved to the right in FIG. 1, and the impinging fluid forces the tapered end of the valve body against its seat, and the fluid is only directed back through the throttle passage 173. It can pass through the stop valve and not through the radial passage 170. Two-pass flow of liquid through the piston is also provided by two diametrically spaced restriction passages (only one shown at 174 as they are identical). Although the illustrated throttle passage 174 is shown as being 180 degrees offset from the valved passage 160 for illustrative purposes, it is actually in a 90 degree relationship. The throttle passage is formed by threading a throttle orifice body 178 into a through hole 176 passing through the piston (FIGS. 8 and 9). By selecting an orifice body and a check valve body with appropriately sized through holes, the damping characteristics of the ride strut can be set very precisely. Orifice bodies and check valve discs are relatively inexpensive, provide precise flow control, and once the desired dimensions are empirically selected, ride struts with consistent damping characteristics can be quickly and easily constructed. Can be manufactured at favorable labor costs. (4) Valve Section 18 The valve section has spaced annular cooperating valve members or valve spools 180, 182 which are capable of limited axial movement under spring bias. These are slidably supported on the spacer sleeve 145. The cooperating valve members are held together by a number of shoulder bolts 186. The head of the bolt is normally positioned within a counterbore 188 formed in the cooperating member 182, while the shank of the bolt is slidable within the connecting hole 189. A helical spring 190 is disposed between the flange portions 191a, 191b of the cooperating valve member to bias them away from each other to the extent permitted by the bolts 186. A helical spring 192 with a small diameter is connected to the piston 14.
3 and the valve member 180. This small spring 192 acts on the valve member 180 to bias the valve portion 18 to the right as shown in FIG. This spring action maintains the cooperating member in engagement with the shoulder 119 and maintains the valve portion 18 away from the piston passageway except under recoil conditions. Referring to FIGS. 10 and 11, the valve members and cooperating members 180, 182 have various apertures to permit passage of liquid. Valve member 180 has four through holes 194 extending therethrough. Annular groove 1
96 is formed on the side of the valve member 180 facing the piston 143 and communicates with the through hole 194, so that liquid can still flow through the valve and the piston when the valve member is pressed against the piston. The limiting effect of the through holes 194 results in a greatly reduced proportion. The flow path during reaction is through hole 1 of the valve member.
94, an annular groove 196, and throttle passages 172, 174 of the piston portion 16. Cooperative member 182 has multiple through holes 198 that extend completely through the valve spool. The vents 198 provide effective and complete venting when the strut is initially filled with liquid. [Operation] The relationship of the ride strut components under unloaded vehicle conditions is not shown in the drawings. FIG. 1 shows the relationship between parts removed from the vehicle when sufficient fluid has been filled in the body 12. In an empty vehicle, the rod portion 13 and the piston portion 16 are
Until the bottom of the boot 134 overlaps the band 137,
The body portion 12 is moved to the left in FIG. Under this condition, the valve portion 18 is separated from both the piston and the retaining member, as shown in FIG. 8 (which shows the fully compressed strut).
Therefore, in the normal operating range of motion, the valve part has no effect on the flow of liquid. When the ride strut is loaded, the components are moved to the position shown in FIG. Since the valve body 166 has been separated from its seat by the impinging liquid experienced during the compression stroke, liquid is flowing through the piston from the lower chamber to the upper chamber at maximum flow rate. In the situation of FIG. 8, since the collar 62, including its flange 65, is against the resilient pad 138, the energy from the force applied to the ride strut is being absorbed by the pad. When the piston and rod portions rise from the position shown in FIG. 8, the valve body 166 seats against the valve seat 162 to restrict flow. This flow restriction provides a shock absorbing effect that dampens the spring action of the compressible liquid. This situation continues during strut extension until the strutted vehicle is cleared. When the strut is unloaded under extreme recoil conditions, the cooperating member 182 engages the annular retainer 76 (FIG. 9). After a slight further extension, the relatively light spring 192 is compressed until the valve member 180 contacts the piston as shown in FIG. Opposing the valve member to the piston greatly enhances the damping characteristics of the ride strut. Liquid flow through the piston is greatly reduced because all passage holes through the piston are covered by the valve member. Valve member passage 17 via annular groove 196
2 and the small valve member passage hole 194 which communicates with the restrictor orifice 174, downward flow of liquid from the upper chamber portion is no longer possible. Under normal conditions, the present ride strut is actuated between the positions shown in FIGS. 8 and 9. Under these circumstances, springs 190, 192 and pad 138
Since it is not compressed, the compression characteristics of the fluid and the dartpot characteristics of the piston determine the damping capacity of the ride strut.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional side view of a hydraulic ride strut according to the present invention, FIG. 2 is an end view of the ride strut as seen from the plane indicated by line 2-2 in FIG.
Figure 3 shows the details of the structure of the screw, circle 3 in Figure 1.
Enlarged cross-sectional views of three parts, Figures 4, 5 and 6 show details of the structure of the seal and dust guard, respectively.
FIG. 7 is an enlarged sectional view of the circle 7-7 in FIG. 9 is an enlarged partial sectional view showing the relationship between the ride strut components under full compression; FIG. 9 is an enlarged partial sectional view showing the relationship between the ride strut components under recoil range extension; FIG. 11 is an end view of the valve components as viewed from the plane shown by lines 10-10 and 11-11 in FIG. 8, respectively. 10... Impact mitigation suspension structure (ride strut), 12... Body part (housing structure), 13
... Rod part, 14 ... Piston rod, 16 ... Piston part (piston structure), 18 ... Valve part, 20
... Cylinder, 24 ... Filling member, 36,9
6,112...O-ring, 143...piston,
146, 148...first part, second part of cylinder chamber, 158...check valve, 160...passage, 1
72... Inner hole, 173... Throttle passage, 174...
Throttle passage, 176... Through hole, 180, 182...
Valve member (cooperative member; valve spool), 190,
192...Spring, 196...Annular groove, 194,
198...through hole.

Claims (1)

[Scope of Claims] 1. A housing structure defining a fluid chamber and a piston rod insertion port, and a piston structure installed in the housing structure and dividing the chamber into two parts;
at least one through hole in the piston arrangement for forming a fluid flow path between the two parts; a piston rod connected to the piston structure and projecting through the insertion opening; a compressible fluid substantially filling the opening, and a fluid seal disposed between the piston rod and the housing structure to form a seal at the opening, the housing structure and the piston structure having a range of motion. a first condition for restricting flow through the through hole when the piston rod and the housing structure move relative to each other in the compression direction in the range of motion; a second condition that further restricts the flow through the through hole when the piston rod and the housing structure move relative to each other in the elongation direction, and the piston rod and the housing structure move relative to each other in the elongation direction in the reaction range; a fluid ride strut for a rough terrain vehicle including valve means for establishing a third condition that sometimes further restricts flow through the through hole, the means comprising: (i) a first valve spool; (ii) a first valve spool; ) a first spring positioned between the valve spool and the piston structure to bias the valve spool away from the piston structure; and (iii) a first spring positioned between the first valve spool and the piston structure. (iv) a second spring disposed between the first and second valve spools so as to bias the first and second valve spools away from each other; . 2 The second spring is stronger than the first spring, so that when the second valve spool is displaced towards the piston structure, the first
2. The ride strut of claim 1, wherein the spring is compressed until the first valve spool engages the piston, and only then is the second spring compressed. 3. The ride strut of claim 1, wherein the first valve spool completely overlaps the through hole of the piston structure when the valve spool is in its overlapping position. 4. The ride strut of claim 3, wherein the valve spool includes a through hole that allows fluid flow through both the valve spool and the piston structure when the first valve spool is in its overlapping position. .