Damper assembly

Abstract

The present disclosure provides a damper assembly. The damper assembly includes an inner damper and an outer damper in a telescopic configuration. The inner damper includes a first tube, a rod disposed at least partially within the first tube and coaxial with the first tube, and a main piston connected to the rod and slidably disposed within the first tube. The main piston divides the interior of the first tube into a first chamber and a second chamber. The outer damper includes a second tube and a second piston. The second tube is disposed coaxially around the inner damper. The second piston is connected to an axial end of the first tube and divides the interior of the second tube into an upper oil chamber and a lower oil chamber. The second piston defines a second passage that provides fluid communication between the upper oil chamber and the lower oil chamber. A discharge fluid passage provides fluid communication between the first chamber and the upper oil chamber.

Description

Technical Field

[0001] The present invention generally relates to a damper assembly for a vehicle, and more particularly to a telescopic damper assembly. Background Art

[0002] Suspension systems are provided to filter or isolate the vehicle body (sprung portion) from the vehicle wheels and axles (unsprung portion) when the vehicle travels over vertical road irregularities and to control the movement of the body and wheels. Additionally, the suspension system is also used to maintain an average vehicle attitude to improve vehicle stability during maneuvers. A typical passive suspension system includes a spring located between the sprung and unsprung portions of the vehicle and a damping device in parallel with the spring.

[0003] Due to the increasing complexity of the vehicle body and suspension, the length of the shock absorber or damper assembly has become increasingly critical as it directly affects the vehicle body installation, placement (space), and cost. This is particularly true for electric vehicles, which face unique challenges in packaging suspension components.

[0004] One such damper assembly is disclosed in U.S. Patent No. 6,619,445. The damper assembly includes a main tube that extends along a central axis between a first end and a second end. The main tube defines a fluid chamber for containing a working fluid that extends between the first end and the second end. A main piston is slidably disposed in the fluid chamber and divides the fluid chamber into a compression chamber and a rebound chamber. A piston rod extends along the central axis and is connected to the main piston for moving the main piston between a compression stroke and a rebound stroke. An outer tube that is radially spaced from the main tube extends between a closed end and an open end around the main tube. The closed end is adjacent to the first end. The open end is adjacent to the second end. The outer tube and the main tube define a compensation chamber that extends between the outer tube and the main tube. Summary of the Invention

[0005] The present invention provides a damper assembly. The damper assembly includes an inner damper and an outer damper in a telescopic configuration. The inner damper includes a first tube, a rod that is at least partially disposed within the first tube and coaxial with the first tube, and a main piston that is connected to the rod and slidably disposed within the first tube. The main piston divides the interior of the first tube into a first chamber and a second chamber. The outer damper includes a second tube and a second piston. The second tube is disposed coaxially around the inner damper. The second piston is connected to an axial end of the first tube and divides the interior of the second tube into an upper oil chamber and a lower oil chamber. The second piston defines a second passage that provides fluid communication between the upper oil chamber and the lower oil chamber. The damper assembly further includes a displacement fluid passage that provides fluid communication between the first chamber and the upper oil chamber.

[0006] The present invention also provides a damper assembly. The damper assembly includes an inner damper and an outer damper in a telescopic configuration. The inner damper includes a first tube, a rod at least partially disposed within the first tube and coaxial with the first tube, and a main piston connected to the rod and slidably disposed within the first tube. The main piston divides the interior of the first tube into a first chamber and a second chamber. The outer damper includes a second tube and a second piston. The second tube is disposed coaxially around the inner damper. The second piston is connected to an axial end of the first tube and divides the interior of the second tube into an upper oil chamber and a lower oil chamber. The second piston defines a second passage that provides fluid communication between the upper oil chamber and the lower oil chamber. The outer damper is configured to move from a fully extended position toward a compressed position during a compression stroke after the main piston of the inner damper has moved substantially completely toward the second piston. The main piston of the inner damper is configured to move away from the second piston and toward an extended position during a rebound stroke after the outer damper has moved substantially completely to the fully extended position. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein:

[0008] Figure 1 is a cross-sectional view of a damper assembly according to an embodiment of the present invention;

[0009] Figures 2A to 2C shows the Figure 1 damper assembly in a nominal position, a fully compressed position, and a fully extended position, respectively;

[0010] Figure 3 shows Figure 1 the damper assembly during a compression stroke and moving from the fully extended position;

[0011] Figures 4A to 4E shows Figure 1 the damper assembly at various positions during a compression stroke;

[0012] Figure 5 shows Figure 1 the damper assembly during a rebound stroke and moving from the nominal position;

[0013] Figures 6A to 6E shows Figure 1 the damper assembly at various positions during a rebound stroke; and

[0014] Figure 7A graph showing the force in kilonewtons (kN) as a function of the stroke in meters (m) for each of a standard damper and the Sequential telescopic damper of the present disclosure is shown. Detailed Description

[0015] Referring to the drawings, in which like reference numerals represent corresponding parts in several views, a damper assembly 20 is provided. The damper assembly 20 may also be referred to as a shock absorber and may be used as part of a suspension system in a motor vehicle (such as a car or a truck). Compared with the design of a conventional damper, the damper assembly 20 of the present disclosure may provide a similar stroke and damping, but with a shorter body length. The damper assembly 20 may be referred to as a Sequential telescopic passive damper.

[0016] The damper assembly 20 is designed to have a relatively small body with a maximum stroke. When compared with a conventional damper, the damper assembly 20 may have a considerably shorter compression length while maintaining a similar or equal stroke. The damper assembly 20 of the present disclosure may provide many benefits at the vehicle level. It may provide a more compact rear suspension, thereby allowing passenger cars and light commercial vehicles to have additional space for a trunk and / or for a battery (for example, in an electric vehicle).

[0017] The damper assembly 20 of the present disclosure utilizes a two-piece (telescopic) rod that includes a damper rod and a second rod in the form of a moving single tube. The damper assembly 20 of the present disclosure may incorporate existing parts and existing component designs, as well as some additional components and design aspects. The damper assembly 20 of the present disclosure may incorporate the concept of a damper having separate operating ranges. The damper rod and the second rod may not move simultaneously, but rather move sequentially. The inner damper may provide damping and at the same time serve as the second rod of the outer damper, and the outer damper also provides a damping function.

[0018] By appropriately tuning the valves, the valve characteristics: single-tube piston valve, double-tube piston valve, and bottom valve, are appropriately selected to sequentially effect the movement of the damper rod and the second rod (single tube). There are two separate oil chambers - a single-tube oil chamber and a double-tube oil chamber.

[0019] The damper assembly 20 of the present disclosure can provide multiple advantages over conventional dampers. It can provide a compression length that is approximately 20% shorter compared to a conventional twin-tube damper with a similar extended length. The damper assembly 20 of the present disclosure includes design aspects and components based on proven solutions and techniques of single-tube dampers and twin-tube dampers. The damper assembly 20 of the present disclosure provides temperature compensation by combining two gas chambers connected via one or more gas channels. The damper assembly 20 of the present disclosure does not exhibit cavitation (caused by temperature-affected oil volume) on either side and does not have a multiplication of forces from the gas. It does not exhibit any high-pressure buildup with a rebound movement. The damper assembly 20 provided by the present disclosure is much simpler than other competing designs, with fewer seals and guiding components. Compared to alternative designs, the damper assembly 20 of the present disclosure can be more easily adjusted for a specific application.

[0020] Figure 1 is a cross-sectional view of a damper assembly 20 according to an embodiment of the present invention. The damper assembly 20 includes an inner damper 22 and an outer damper 24 in a telescopic configuration.

[0021] The inner damper 22 includes a damper rod 30 that extends along an axis A and is translatable along the axis A. The damper rod 30 includes a proximal end 32 and a distal end 34 spaced apart from the proximal end 32 along the axis A. The damper rod 30 includes a shoulder 36 that is spaced apart from the distal end 34 and is configured to be attached to an external structure, such as a suspension component or a chassis mounting bracket on a vehicle. In some embodiments, the damper rod 30 may include external threads (not shown) between the distal end 34 and the shoulder 36 for attachment to an external structure. The inner damper 22 further includes a first tube 40 having a tubular shape coaxial with the axis A and having a first end 42 and a second end 44 opposite the first end 42. An intermediate seal assembly 46 is disposed within the first tube 40 adjacent to the first end 42, thereby providing a fluid-tight seal. The intermediate seal assembly 46 defines a rod hole 48, and the damper rod 30 passes through the rod hole 48 in a fluid-tight seal and is configured to allow the damper rod 30 to translate relative to the first tube 40 along the axis A.

[0022] The main piston 50 is slidably disposed within the first tube 40 and is connected to the damper rod 30 adjacent the proximal end 32. The main piston 50 divides the interior of the first tube 40 into a first chamber 52 and a second chamber 54. The first chamber 52 extends between the intermediate seal assembly 46 and the main piston 50. The second chamber 54 is located on the side of the main piston 50 opposite the first chamber 52. During the compression stroke, the compression valves 56, 58 regulate the fluid flow between the first chamber 52 and the second chamber 54. The compression valves 56, 58 include one or more first piston passages 56 extending through the main piston 50 to provide fluid communication between the second chamber 54 and the first chamber. The compression valves 56, 58 further include one or more compression valve members 58, such as deflecting disks, which selectively cover the first piston passages 56 to control the fluid flow therethrough. As the main piston 50 moves through the first tube 40, fluid can be channeled through the first piston passages 56 to provide the damping function of the internal damper 22. A fastener 60, such as a retaining ring, holds the main piston 50 to the damper rod 30 adjacent the proximal end 32 of the damper rod 30.

[0023] The external damper 24 includes an outer tube 70 having a tubular shape, coaxial with the axis A and having an upper end 72 and a lower end 74 opposite the upper end 72. The outer tube 70 is closed at the lower end 74. The external damper 24 further includes a second tube 80 having a tubular shape, coaxial with the axis A and located inside the outer tube 70. The outer diameter of the second tube 80 is smaller than the inner diameter of the outer tube 70, thereby providing an annular chamber 102 between the outer tube 70 and the second tube 80. The second tube 80 is closed at one end adjacent its lower end 74. A main rod guide 76 is disposed within the second tube 80 adjacent the upper end 72, providing a fluid-tight seal with the first tube 40. The main rod guide 76 includes one or more seal rings 78, and the first tube 40 passes through the seal rings 78 in a fluid-tight seal to permit translation of the first tube 40 relative to the second tube 80 along the axis A. Thus, the first tube 40 of the internal damper 22 serves as a second rod in the external damper 24.

[0024] The external damper 24 also includes a second piston 84 connected to the second end 44 of the first tube 40. The second piston 84 is disposed within the second tube 80 and sealingly engages the inner surface of the second tube 80. The second piston 84 divides the interior of the second tube 80 into an upper oil chamber 86 and a lower oil chamber 88. The upper oil chamber 86 extends between the main rod guide 76 and the second piston 84. Rebound valves 90, 92 regulate the flow between the upper oil chamber 86 and the lower oil chamber 88 during the rebound stroke. The rebound valves 90, 92 include one or more second piston passages 90 that extend through the second piston 84 and provide fluid communication between the upper oil chamber 86 and the lower oil chamber 88. The rebound valves 90, 92 also include one or more rebound valve members 92, such as deflecting disks, that selectively cover the second piston passages 90 to control the fluid flow therethrough. When the second piston 84 moves through the second tube 80, fluid can be directed through the second piston passages 90 to provide the damping function of the external damper 24. The second piston 84 also includes a tubular portion 94 that has a tubular shape, is coaxial with the axis A, and defines an internal passage 95 that provides fluid communication between the lower oil chamber 88 and the second chamber 54 of the first tube 40.

[0025] In operation, each of the first chamber 52 and the second chamber 54 of the first tube 40, as well as the upper oil chamber 86 and the lower oil chamber 88, can be filled with an incompressible fluid, such as oil.

[0026] A gas cup 96 is disposed within the second tube 80 and defines the lower surface of the lower oil chamber 88. The gas cup 96 separates the lower oil chamber 88 from a gas compartment 100 that extends from the lower surface of the gas cup 96 to the closed end of the second tube 80 adjacent the lower end 74 of the outer tube 70. The gas compartment 100 is in fluid communication with the annular chamber 102 via one or more gas passages 104 through the second tube 80 adjacent the lower end 74 of the outer tube 70. The gas cup 96 axially moves within the second tube 80, and the gas collected within the gas compartment 100 and the annular chamber 102 compensates for the volume changes of the portions inserted and withdrawn from the second tube 80 and the portions inserted and withdrawn from the first tube 40 (i.e., due to the inner damper 22 moving into and out of the external damper 24). The relatively large volume of gas within the gas compartment 100 and / or the annular chamber 102 compensates for the change in the amount of oil due to temperature variations.

[0027] The air cup 96 includes a concave upper surface 98 that can receive the tubular portion 94 of the second piston 84 when the damper assembly 20 is in a compressed state. The recessed upper surface 98 can also cause the air cup 96 to deform axially outward and increase the sealing pressure against the inner wall of the second tube 80 in response to the fluid pressure in the lower oil chamber 88. The air cup 96 includes an annular seal 99 that engages the inner wall of the second tube 80 and provides a fluid-tight seal to prevent oil from escaping into the gas chamber 100. A stop ring 106 is disposed in the inner wall of the second tube 80, adjacent to and just above one or more gas channels 104 to define a stroke end limit and prevent the air cup 96 from covering one or more gas channels 104.

[0028] The first tube 40 defines a displacement fluid passage 110 that extends annularly and axially between the second end 44 and the intermediate seal assembly 46 along the length of the first tube 40 and provides fluid communication between the first chamber 52 and the upper oil chamber 86. A plurality of first radial channels 112 are located near the second piston 84 and connect the displacement fluid passage 110 to the upper oil chamber 86 to provide fluid communication therebetween. A plurality of second radial channels 114 are positioned spaced apart from the second piston 84 and adjacent to the intermediate seal assembly 46 and connect the displacement fluid passage 110 to the first chamber 52 for providing fluid communication between the displacement fluid passage 110 and the first chamber 52.

[0029] The check valve 116 includes a valve body 117 disposed in the first tube 40 adjacent to the intermediate seal assembly 46. The check valve 116 is configured to allow fluid to flow out of the first chamber 52 and into the displacement fluid passage 110 while preventing fluid from flowing in the opposite direction.

[0030] The rebound coil spring 130 surrounds the second tube 80 and is disposed within the upper oil chamber 86 adjacent to the main rod guide 76. When the outer damper 24 is at or near the fully extended position and during the rebound stroke, the rebound coil spring 130 engages the top end of the second piston 84. A compression coil spring 132 is disposed in the second chamber 54 and adjacent to the second piston 84. When the inner damper 22 is at or near the fully compressed position during the compression stroke, the compression coil spring 132 engages the main piston 50 and biases the main piston 50.

[0031] Figure 2A The damper assembly 20 is shown in its nominal or design position, and Figure 2B and Figure 2CThe damper assembly 20 is shown in its fully compressed position and fully extended position, respectively. Importantly, the full stroke L1+L2 of the damper assembly 20 is provided by: the first stroke length L1 of the inner damper 22 generated by the main piston 50 moving axially with the damper rod 30 through the first tube 40; and the second stroke length L2 generated by the second piston 84 moving axially with the first tube 40 through the second tube 80.

[0032] Figures 4A to 4E A cross-sectional view of the damper assembly 20 is shown at various positions during the compression stroke.

[0033] During the compression movement, the damper rod 30 having the main piston 50 and the compression valves 56, 58 moves in the "-y" direction (i.e., in the compression direction). The check valve 116 prevents oil from flowing from the upper oil chamber 86 to the first chamber 52. Such a flow would cause the displacement of the first tube 40 in the "+y" direction (i.e., in the rebound direction) and would inhibit the generation of the damping force. The check valve 116 is configured to allow fluid to flow from the first chamber 52 through the fluid passage 110 to the oil chamber 86. In the initial stage of the compression movement, the damper rod 30 moves, and then the compression valves 56, 58 are responsible for generating an appropriate damping force. The first tube 40 does not move. When the inner damper 22 reaches its fully compressed position, the main piston 50 contacts and forces the first tube 40 to move in the compression direction via the compression coil spring 132 at the end of the first tube 40. The compression coil spring 132 can smoothly initiate the movement of the first tube 40.

[0034] In the initial stage of the compression stroke, only the main piston 50 moves axially with the damper rod 30 through the first tube 40. The main piston 50 moves within the inner damper 22. During this movement stage, the first tube 40 does not move. When the inner damper 22 is in the fully compressed position, the main piston 50 contacts the compression coil spring 132 and forces the first tube 40 to move, ensuring that the stroke continues - until the damper assembly 20 reaches the fully compressed position. In the initial stage of the rebound stroke, both the damper rod 30 and the first tube 40 move simultaneously. When the outer damper 24 reaches the fully extended position, with the second piston 84 contacting and compressing the rebound coil spring 130, the damper rod 30 having the main piston 50 continues its movement within the inner damper 22 until the damper assembly 20 reaches the fully extended position. In the nominal position, the force acting on the moving part will push the first tube 40 upward. The damper assembly 20 is designed to be asynchronous.

[0035] Figure 3A cross-sectional view of the damper assembly 20 during the compression stroke and moving from the fully extended position is shown. Starting from the fully extended position, during the compression stroke, a first level of movement is achieved by the movement of the damper rod 30 and the inner damper 22. After the inner damper 22 reaches the fully compressed position, with the main piston 50 contacting the compression coil spring 132, a second level of movement is engaged and then achieved by the first tube 40. Damping is provided by the compression valves 56, 58. In other words, the outer damper 24 is configured to move from the fully extended position towards the compressed position during the compression stroke after the main piston 50 of the inner damper 22 has substantially fully moved towards the second piston.

[0036] According to one aspect of the present disclosure, the first chamber 52 and the upper oil chamber 86 may have equal cross-sectional areas. Thus, the amount of oil forced through the compression valves 56, 58 will remain constant during the stroke of the outer damper 24. Therefore, whether the damper rod 30 or the first tube 40 remains in motion, the flow through the compression valves 56, 58 will not change (at a constant input speed). This means that the damping force will also not change. However, the force of the gas will increase with the change in speed.

[0037] During the compression movement, oil from the lower oil chamber 88 flows through the compression valves 56, 58 into the first chamber 52. Then, through the openings and channels of the first tube 40, this oil is forced into the upper oil chamber 86. The rebound valves 90, . To avoid cavitation in the first chamber 52 and / or the upper oil chamber 86, it may be necessary to ensure sufficient gas pressure in the gas chamber 100. The gas pressure can be adjusted based on the maximum assumed damping force of the compression movement.

[0038] Figures 6A to 6E Shows Figure 1 a cross-sectional view of the damper assembly at various positions during the rebound stroke.

[0039] Damping during the rebound stroke is provided by the rebound valves 90, 92. During the rebound movement, the first tube 40 and the damper rod 30 move in the “+y” direction together with the main piston 50. The compression valves 56, 58 are closed, and the oil is forced from the first chamber 52 through the check valve 116, then through the holes and channels in the first tube 40 and into the upper oil chamber 86. The oil then flows through the rebound valves 90, 92 into the lower oil chamber 88. The rebound coil spring 130 can be used to provide a smooth end stroke for the movement of the first tube 40 of the inner damper 22 during the rebound stroke.

[0040] Because during the compression movement, the amount of oil forced through the rebound valves 90, 92 will not change, and thus the level of the damping force during the rebound movement will not depend on which element (the damper rod 30 or the first tube 40) is in motion.

[0041] Similar to the compression stroke, the gas force will vary during the velocity change in the rebound stroke.

[0042] The input velocity can be the result of the velocity of the first tube 40 and the velocity of the damper rod 30 relative to the first tube 40.

[0043] Figure 5 Is shown Figure 1 A cross-sectional view of the damper assembly moving during the rebound stroke and from the nominal position. Starting from the fully compressed position, during the rebound stroke, a first level of movement is achieved by the simultaneous movement of the first tube 40 and the damper rod 30. After the first tube 40 reaches the fully extended position, further damping is achieved by the movement of only the damper rod 30 within the inner damper 22. In other words, the main piston 50 of the inner damper 22 is configured to move away from the second piston 84 and towards the extended position after the outer damper 24 has moved substantially fully to the fully extended position during the rebound stroke.

[0044] The compression valves 56, 58 and the rebound valves 90, 92 can each have a typical construction, which means that the corresponding orifices are responsible for the force levels generated in the low velocity range, and the corresponding disk sets (such as the valve members 58, 92) are responsible for the force levels generated in the medium velocity range. The force generated in the high velocity range can be determined by the orifices in the corresponding one of the pistons 50, 84 (i.e., the first piston passage 56 and / or the second piston passage 90). The design provided can be used with one or more different types of valves.

[0045] During the full stroke of the damper assembly 20, the gas force due to the compression of the gas in the gas chamber 100 and the annular chamber 102 varies as a function of the linear stroke due to the change in the effective surface. In the sequential movement of the damper assembly 20 during compression, the damper rod 30 moves first, so the gas force acts on the cross-section of the main piston 50. When the first tube 40 starts to move, the gas force increases as the cross-section of the second piston 84 (which is larger than the cross-section of the main piston 50) becomes the effective cross-section.

[0046] Figure 7 A graph showing the force in kilonewtons (kN) as a function of the stroke in meters (m) is shown. Figure 7 Includes a first plot 200 showing the relationship between force and stroke for a standard damper, and a second plot 202 showing the relationship between force and stroke for the sequential telescopic damper of the present disclosure (such as the damper assembly 20). The slope of the second plot 202 at the transition is substantially due to the influence of the rebound helical spring 130 and / or the compression helical spring 132, which is caused by the length and characteristics of the helical springs 130, 132. The difference between the force levels is substantially due to the change in the gas force.

[0047] Obviously, many modifications and variations of the present disclosure are possible in accordance with the above teachings, and these modifications and variations can be implemented in a manner different from the specific description while remaining within the scope of the appended claims.

Claims

1. A damper assembly, the damper assembly comprising: An inner damper and an outer damper, the inner damper and the outer damper being in a telescopic configuration; The inner damper includes a first tube, a rod disposed at least partially within the first tube and coaxial with the first tube, and a main piston connected to the rod and slidably disposed within the first tube, the main piston dividing the interior of the first tube into a first chamber and a second chamber; The outer damper includes a second tube and a second piston, the second tube being disposed coaxially around the inner damper, the second piston being connected to an axial end of the first tube and dividing the interior of the second tube into an upper oil chamber and a lower oil chamber, the second piston defining a second passage that provides fluid communication between the upper oil chamber and the lower oil chamber; And A discharge fluid passage that provides fluid communication between the first chamber and the upper oil chamber.

2. The damper assembly according to claim 1, wherein, The outer damper is configured to move from a fully extended position toward a compressed position during a compression stroke after the main piston of the inner damper has moved substantially fully toward the second piston.

3. The damper assembly according to claim 1, wherein, The main piston of the inner damper is configured to move away from the second piston and toward an extended position during a rebound stroke after the outer damper has moved substantially fully to the fully extended position.

4. The damper assembly according to claim 1, wherein, The outer damper is configured as a twin-tube damper, the twin-tube damper including an outer tube that is disposed coaxially around the second tube and defines an annular chamber between the second tube and the outer tube.

5. The damper assembly according to claim 1, wherein, The discharge fluid passage extends axially and along the length of the first tube through the wall of the first tube.

6. The damper assembly according to claim 5, wherein, The wall of the first tube further defines a first radial passage that is positioned adjacent to the second piston and connects the discharge fluid passage to the upper oil chamber to provide fluid communication between the discharge fluid passage and the upper oil chamber.

7. The damper assembly according to claim 5, wherein, The wall of the first tube further defines a second radial passage that is spaced from the second piston and connects the discharge fluid passage to the first chamber.

8. The damper assembly according to claim 1, the damper assembly further comprising a check valve configured to allow fluid to flow out of the first chamber and into the discharge fluid passage while preventing fluid from flowing in the opposite direction.

9. The damper assembly according to claim 1, the damper assembly further comprising an air cup disposed in the second tube and separating the lower oil chamber from a gas compartment, wherein the gas compartment extends from the lower surface of the air cup to the closed lower end of the second tube.

10. The damper assembly according to claim 1, wherein, The first chamber and the upper oil chamber have equal cross-sectional areas.

11. A damper assembly, the damper assembly comprising: An inner damper and an outer damper, the inner damper and the outer damper being in a telescopic configuration; The inner damper includes a first tube, a rod disposed at least partially within the first tube and coaxial with the first tube, and a main piston connected to the rod and slidably disposed within the first tube, the main piston dividing an interior of the first tube into a first chamber and a second chamber; The outer damper includes a second tube and a second piston, the second tube being disposed coaxially around the inner damper, the second piston being connected to an axial end of the first tube and dividing an interior of the second tube into an upper oil chamber and a lower oil chamber, the second piston defining a second passage providing fluid communication between the upper oil chamber and the lower oil chamber; wherein the outer damper is configured to move from a fully extended position toward a compressed position during a compression stroke after the main piston of the inner damper has moved substantially fully toward the second piston; and wherein the main piston of the inner damper is configured to move away from the second piston and toward an extended position during a rebound stroke after the outer damper has moved substantially fully to the fully extended position, wherein the damper assembly further includes a check valve configured to allow fluid to flow out of the first chamber and into the upper oil chamber while preventing fluid from flowing in the opposite direction.

12. The damper assembly according to claim 11, wherein, The outer damper is configured as a twin-tube damper including an outer tube disposed coaxially around the second tube and defining an annular chamber between the second tube and the outer tube.

13. The damper assembly according to claim 11, the damper assembly further including a discharge fluid passage providing fluid communication between the first chamber and the upper oil chamber.

14. The damper assembly according to claim 13, wherein, The discharge fluid passage extends axially and along a length of the first tube through a wall of the first tube.

15. The damper assembly according to claim 14, wherein, The wall of the first tube further defines a first radial passage positioned adjacent to the second piston and connecting the discharge fluid passage to the upper oil chamber to provide fluid communication between the discharge fluid passage and the upper oil chamber.

16. The damper assembly according to claim 14, wherein, The wall of the first tube further defines a second radial passage spaced from the second piston and connecting the discharge fluid passage to the first chamber.

17. The damper assembly according to claim 11, the damper assembly further including an air cup disposed in the second tube and separating the lower oil chamber from a gas chamber, wherein the gas chamber extends from a lower surface of the air cup to a closed lower end of the second tube.

18. The damper assembly according to claim 11, wherein, The first chamber and the upper oil chamber have equal cross-sectional areas.

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