Actuator assembly for heavy machine

Abstract

To provide an actuator assembly involving three chambers for a heavy machine such as a drilling machine in order to reduce restriction loss in a control valve.SOLUTION: An actuator assembly 1000 includes a main cylinder assembly 1100 and a plunger cylinder assembly 1200 disposed in parallel with the main cylinder assembly. The main cylinder assembly is a double-acting type cylinder assembly, and the plunger cylinder assembly is a single-acting type cylinder assembly. The actuator assembly includes three chambers 1102A, 1102B, 1202A applied to be selectively coupled to at least one of a high pressure hydraulic pressure line, an intermediate pressure hydraulic pressure line and a low pressure hydraulic pressure line on the basis of a load requirement of the actuator assembly. The actuator assembly reduces restriction loss in a control valve and thus reduces entire power consumption of a heavy machine.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The following specification particularly describes the invention and the manner in which it should be practiced.

[0002] FIELD OF THE INVENTION Embodiments herein relate generally to heavy construction machines, and more particularly to actuator assemblies for heavy construction machines such as, but not limited to, excavators. [Background technology]

[0003] Generally, excavators are heavy machinery used in construction-related and civil engineering activities. For example, excavators are primarily used for mining purposes and for various lifting and transporting tasks in a variety of applications. Furthermore, specialized implements, such as hydraulic breakers, cutters, shears, grapples, and couplers, can be attached to the end of various boom and arm configurations, thereby enabling the excavator to perform a wider range of activities. Typically, an excavator includes a boom, arm, bucket, and cab atop a rotating superstructure atop a chassis with tracks or wheels. Each of the excavator's arm, boom, and bucket utilizes a hydraulic actuator. A hydraulic cylinder generates a force to move an object based on the hydraulic pressure in the cylinder and the effective area of ​​the piston moving within the cylinder, resulting in a load force. A typical cylinder uses two chambers, each with its own effective area, and such a configuration generates a force in each direction. The net force resulting from pressurized fluid acting on both areas of the cylinder is typically referred to as the cylinder load. Traditional applications typically affect the flow rate into / out of one chamber, while the remaining chambers are kept at the lowest possible pressure to reduce system losses. Various hydraulic control architectures have been developed over the years, particularly as the number of hydraulic actuators per machine has increased. These architectures typically use a shared hydraulic power supply, such as a hydrostatic pump, and dedicated control valves for each actuator. Challenges associated with these architectures include: first, controllability of multiple actuators with a single shared hydraulic power source; and second, energy efficiency. While various approaches have been successful in addressing the first challenge, most currently available circuits still have low efficiency when driving multiple actuators at once, primarily due to throttling losses in the control valves. When multiple hydraulic actuators share the same hydraulic supply, the pressure delivered must be slightly higher than the maximum pressure requirement of the system.Therefore, any other hydraulic actuator that requires lower pressure to achieve the desired load will require throttling control to reduce the supply pressure to the desired level, which incurs a power loss that can vary from 35% to 72% of the total energy consumption.

[0004] Therefore, there is a need for an actuator assembly that avoids the aforementioned drawbacks. Summary of the Invention [Problem to be solved by the invention]

[0005] The primary objective of the embodiments herein is to provide an actuator assembly with three chambers for heavy machinery (excavators) to reduce throttling losses in the control valve.

[0006] Another object of the embodiments herein is to reduce the energy power consumption of heavy machinery (excavators).

[0007] These and other objects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating embodiments and numerous specific details thereof, is given by way of illustration and not limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

[0008] Embodiments are illustrated in the accompanying drawings, in which like reference numerals designate corresponding parts in the various views throughout. The embodiments herein will be better understood from the following description which refers to the drawings. [Brief explanation of the drawings]

[0009] [Figure 1A]1 is a cross-sectional view of an actuator assembly for a heavy machine, the actuator assembly being in a retracted position, according to an embodiment disclosed herein. [Figure 1B] FIG. 1 is a cross-sectional view of an actuator assembly in an extended position according to an embodiment disclosed herein. [Figure 2A] FIG. 1 is a perspective view of a main cylinder assembly of an actuator assembly according to an embodiment disclosed herein. [Figure 2B] FIG. 1 is a cross-sectional view of a primary cylinder assembly according to an embodiment disclosed herein. [Figure 3A] FIG. 1 is a perspective view of a plunger-cylinder assembly of an actuator assembly according to an embodiment disclosed herein. [Figure 3B] FIG. 1 is a cross-sectional view of a plunger-cylinder assembly according to an embodiment disclosed herein. [Figure 4] FIG. 1 is a circuit diagram of an actuator assembly coupled to a high-pressure hydraulic line, a medium-pressure hydraulic line, and a low-pressure hydraulic line according to an embodiment disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0010] The embodiments herein and their various features and advantageous details will be more fully described with reference to the non-limiting embodiments illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as not to unnecessarily obscure the embodiments herein. The examples used herein are merely intended to aid in the understanding of the manner in which the embodiments herein can be implemented and to further enable those skilled in the art to implement the embodiments herein. Therefore, the examples should not be construed as limiting the scope of the embodiments herein.

[0011] 1-4, in which like reference numerals represent corresponding features consistently throughout the figures, an embodiment is shown that provides a three chamber actuator assembly for heavy machinery, such as, but not limited to, an excavator.

[0012] FIG. 1A depicts a cross-sectional view of an actuator assembly (1000) for heavy equipment, with the actuator assembly (1000) in a retracted position, according to an embodiment disclosed herein. In one embodiment, the actuator assembly (1000) includes a main cylinder assembly (1100) and a plunger-cylinder assembly (1200) disposed parallel to the main cylinder assembly (1100). The main cylinder assembly (1100) is a double-acting cylinder assembly, and the plunger-cylinder assembly (1200) is a single-acting cylinder assembly. For ease of understanding, the actuator assembly (1000) will be described herein below with reference to being provided in a heavy equipment, such as, but not limited to, an excavator. However, it is within the scope of the present invention to use / implement the actuator assembly (1000) in any other vehicle or in any other application without otherwise interfering with the intended function of the actuator assembly (1000) as can be inferred from the description and corresponding drawings.

[0013] Each of the boom, arm, and bucket of the heavy equipment utilizes an actuator assembly (1000). A common pressure rail (CPR) system is implemented to minimize the pressure difference between the supply system and the pressure requirements of each of the actuators (1000) sharing the same supply. To achieve this condition, it is possible to (1) increase the number of supply pressure rails so that multiple supply pressures are available, and (2) increase the number of cylinder chambers so that different combinations of connections between chambers and supply rails can be used to minimize throttling requirements and thereby reduce system losses. Having more options for combining different chamber areas and pressures allows the same load (effective cylinder force) to be achieved with a smaller difference between supply pressure and chamber pressure, thereby reducing throttling losses. As a result, the greater the number of available combinations (cylinder modes), the more efficient the actuator assembly (1000). To realize a discrete number of possible connections between pressure rails and cylinder chambers (modes) for various applications, the relationship between pressure rails and the number of chambers is determined by the following equation:

number

[0014] where n FL is the number of available force modes, and n PR is the number of pressure rails, and n CC is the number of cylinder chambers. Therefore, it is possible to increase the number of available static force modes by adding additional chambers to the actuator. In the embodiment, the number of cylinder chambers (n CC ) is three, and the number of pressure rails (n PR ) are three. Therefore, the actuator assembly (1000) is configured to have 27 force modes.

[0015] 2A and 2B illustrate a primary cylinder assembly (1100) of an actuator assembly (1000) according to an embodiment disclosed herein. In one embodiment, the primary cylinder assembly (1100) includes a primary cylinder (1102), a primary cylinder piston (1104), a primary cylinder cap end cover (1106), a primary cylinder head end cover (1108), a primary cylinder rod eye (1110), and a primary cylinder piston rod (1112). The primary cylinder (1102) defines a first chamber (1102A) and a second chamber (1102B) (as shown in FIG. 1A), and the primary cylinder piston (1104) separates the first chamber (1102A) from the second chamber (1102B). A main cylinder piston (1104) is slidably disposed within the main cylinder (1102). A main cylinder cap end cover (1106) is coupled to one end of the main cylinder (1102). For example, the main cylinder cap end cover (1106) is welded to one end of the main cylinder (1102). The main cylinder cap end cover (1106) defines a main cylinder cap end side port (1106P) adapted to facilitate the flow of hydraulic fluid into or out of the first chamber (1102A) of the main cylinder (1102). The main cylinder assembly (1100) includes a hydraulic fluid delivery tube (1109), one end of which is coupled to a main cylinder head end cover (1108), and the other end of which defines a main cylinder head end side port (1109P) adapted to facilitate the flow of hydraulic fluid into or out of the second chamber (1102B) of the main cylinder (1102). The main cylinder head end cover (1108) is coupled to the other end of the main cylinder (1102). For example, the main cylinder head end cover (1108) is removably coupled to a flange (1111) that is fixedly coupled (welded) to the other end of the main cylinder (1102). One end of the main cylinder piston rod (1112) is connected to the main cylinder piston (1104), and the other end of the main cylinder piston rod (1112) is connected to the main cylinder rod eye (1110).

[0016] 3A and 3B illustrate a plunger-cylinder assembly 1200 of the actuator assembly 1000 according to an embodiment disclosed herein. In one embodiment, the plunger-cylinder assembly 1200 includes a plunger cylinder 1202, a plunger-cylinder piston 1204, a plunger-cylinder piston bearing 1205, a plunger-cylinder cap end cover 1206, a plunger-cylinder bimetallic bushing 1207, a plunger-cylinder head end cover 1208, at least one first sealing element 1209, a plurality of second sealing elements 1211, a plunger-cylinder piston rod 1212, and a linear position sensor 1222.

[0017] The plunger cylinder 1202 defines a third chamber 1202A therein (as shown in FIG. 1A). The plunger cylinder 1202 is provided with a vent port 1202P (as shown in FIG. 3A) adapted to facilitate removal of air trapped within the plunger cylinder 1202. Air is removed from the plunger cylinder 1202 prior to installation of the actuator assembly 1000 on heavy equipment. A plunger cylinder piston 1204 is slidably disposed within the plunger cylinder 1202. The plunger cylinder piston bearing (1205) is adapted to be attached to the plunger cylinder piston (1204), which does not have a piston seal, and a gap is defined between the plunger cylinder piston bearing (1205) and the plunger cylinder piston (1204) to allow hydraulic fluid to flow from one side of the plunger cylinder piston (1204) to the other side of the plunger cylinder piston (1204). The third chamber (1202A) of the plunger cylinder (1202) includes areas from both sides of the plunger cylinder piston (1204). The plunger cylinder cap end cover (1206) is coupled to one end of the plunger cylinder (1202). The plunger cylinder cap end cover (1206) defines a plunger cylinder cap end side port (1206P) adapted to facilitate the flow of hydraulic fluid into or out of the third chamber (1202A) of the plunger cylinder (1202). The plunger cylinder bimetallic bushing (1207) is adapted to be received by a bushing-receiving groove (not shown) defined in the plunger cylinder head end cover (1208) on its interior side. The plunger cylinder bimetallic bushing (1207) is adapted to guide the plunger cylinder piston rod (1212) during extension and retraction of the plunger cylinder piston rod (1212).The plunger-cylinder piston bearing (1205) and plunger-cylinder bimetallic bushing (1207) are adapted to improve the side load capacity of the plunger-cylinder assembly (1200). The plunger-cylinder head end cover (1208) is detachably coupled to the other end of the plunger cylinder (1202). The first sealing elements (1209) are adapted to be received by first sealing grooves (not shown) defined on the outer side of the plunger-cylinder head end cover (1208) and are engaged with the plunger cylinder (1202). The second sealing elements (1211) are adapted to be received by second sealing grooves (not shown) defined on the inner side of the plunger-cylinder head end cover (1208) and are engaged with the plunger-cylinder piston rod (1212). One end of the plunger-cylinder-piston rod 1212 is coupled to the plunger-cylinder-piston 1204, and the other end of the plunger-cylinder-piston rod 1212 defines a ball-and-socket joint 1212J that is coupled to the main cylinder rod eye 1110 of the main cylinder assembly 1100. The ball-and-socket joint 1212J is provided to improve the flexibility and freedom of the plunger-cylinder-piston rod 1212. In one embodiment, the actuator assembly 1000 includes a locating pin 1216 adapted to couple the plunger-cylinder-cap end cover 1206 with the main cylinder-cap end cover 1106, thereby positioning (aligning) the plunger-cylinder assembly 1200 relative to the main cylinder-cap end cover 1106.In one embodiment, the actuator assembly (1000) includes at least one first locking element (1210) adapted to lock the plunger cylinder cap end cover (1206) to the main cylinder cap end cover (1106), thereby locking the plunger cylinder assembly (1200) with the main cylinder cap end cover (1106). For ease of understanding, the first locking element (1210) is herein considered to be a bolt. In one embodiment, the actuator assembly (1000) includes a first retaining member (1214) adapted to hold the first locking element (1210) relative to the main cylinder cap end cover (1106). For ease of understanding, the first retaining member (1214) is herein considered to be at least a snap ring. In one embodiment, the actuator assembly (1000) includes a second retaining member (1218) adapted to retain the ball-and-socket joint (1212J) relative to the main cylinder rod eye (1110). Furthermore, in one embodiment, the actuator assembly (1000) includes a plurality of second locking elements (1220) adapted to lock the second retaining member (1218) relative to the main cylinder rod eye (1110). For ease of understanding, each of the second locking elements (1220) is referred to herein as at least a bolt. The linear position sensor (1222) is adapted to detect the position / stroke of the actuator assembly (1000) and sends an output signal to a heavy equipment controller. The linear position sensor (1222) is configured to utilize magnetostrictive properties to determine the position of the plunger cylinder piston rod (1212) and main cylinder piston rod (1112), providing velocity feedback to the control system which in turn estimates the required flow rate from the pressure rail.

[0018] 4 depicts a circuit diagram of an actuator assembly (1000) coupled to a high-pressure (HP), medium-pressure (MP), and low-pressure (LP) hydraulic line according to an embodiment disclosed herein. Each of a first chamber (1102A), a second chamber (1102B), and a third chamber (1202A) is selectively disposed in fluid communication with one of the high-pressure (HP), medium-pressure (MP), and low-pressure (LP) hydraulic lines based on the load requirements of the actuator assembly (1000). When the sum of the forces generated in the first chamber (1102A) of the main cylinder (1102) and the third chamber (1202A) of the plunger cylinder (1202) exceeds the force generated in the second chamber (1102B) of the main cylinder (1102), the main cylinder piston rod (1112) and the plunger cylinder piston rod (1212) move to the extended position (as shown in Figure 1B). For example, the first chamber (1102A) of the main cylinder (1102) and the third chamber (1202A) of the plunger cylinder (1202) are configured to selectively receive hydraulic fluid from any one of the high-pressure hydraulic line, the medium-pressure hydraulic line, and the low-pressure hydraulic line through the main cylinder cap end side port (1106P) and the plunger cylinder cap end side port (1206P), respectively, and the hydraulic fluid exits from the second chamber (1102B) of the main cylinder (1102) to the corresponding pressure hydraulic line to which the second chamber (1102B) is connected to facilitate extension of the main cylinder piston rod (1112) and the plunger cylinder piston rod (1212) based on the load requirements of the actuator assembly (1000). Conversely, if the force generated in the second chamber (1102B) of the main cylinder (1102) exceeds the resultant force in the first chamber (1102A) of the main cylinder (1102) and the third chamber (1202A) of the plunger cylinder (1202), the main cylinder piston rod (1112) and the plunger cylinder piston rod (1212) will move to their retracted positions (as shown in Figure 1A).For example, the second chamber (1102B) of the main cylinder (1102) is configured to selectively receive hydraulic fluid from either a high pressure hydraulic line or a medium pressure hydraulic line through the main cylinder head end side port (1109P), and hydraulic fluid exits from the first chamber (1102A) of the main cylinder (1102) and the third chamber (1202A) of the plunger cylinder (1202) to the respective pressure hydraulic lines to which the first chamber (1102A) and the third chamber (1202A) are connected to facilitate retraction of the main cylinder piston rod (1112) and the plunger cylinder piston rod (1212) based on the load requirements of the actuator assembly (1000). The stroke of the plunger-cylinder assembly (1200) is slightly greater than the stroke of the main cylinder assembly (1100), so that the plunger-cylinder piston (1204) does not come into contact with the plunger-cylinder cap end cover (1206) and the plunger-cylinder head end cover (1208) during the entire operation of the actuator assembly (1000).

[0019] Technical advantages of the actuator assembly (1000) include: The actuator assembly (1000) is configured to reduce throttling losses in the control valve, thereby reducing the overall power consumption of the heavy equipment.

[0020] The foregoing description of specific embodiments fully reveals the general nature of the embodiments herein such that others, by applying their current knowledge, may readily modify and / or adapt such specific embodiments for various applications without departing from the general concept; therefore, such adaptations and modifications should, and are intended to, be grasped within the meaning and range of equivalents of the disclosed embodiments. It will be understood that the terminology employed herein is for purposes of description and not of limitation. Thus, while the embodiments herein are described in terms of embodiments, those skilled in the art will recognize that the embodiments herein may be practiced with modifications within the spirit and scope of the embodiments as described herein.

Claims

1. An actuator assembly (1000) for heavy machinery, said actuator assembly (1000) comprising: a main cylinder assembly (1100) having a main cylinder (1102) and a main cylinder piston (1104) slidably disposed within the main cylinder (1102); a plunger cylinder assembly (1200) disposed in parallel with the main cylinder assembly (1100), the plunger cylinder assembly (1200) including a plunger cylinder (1202) and a plunger cylinder piston (1204) slidably disposed within the plunger cylinder (1202); Equipped with the main cylinder assembly (1100) is a double-acting cylinder assembly, the main cylinder (1102) defines a first chamber (1102A) and a second chamber (1102B), the main cylinder piston (1104) separates the first chamber (1102A) from the second chamber (1102B); the plunger cylinder assembly (1200) is a single-acting cylinder assembly, the plunger cylinder (1202) defining a third chamber (1202A) therein; each of the first chamber (1102A), the second chamber (1102B), and the third chamber (1202A) being selectively provided in fluid communication with one of a high pressure (HP) hydraulic line, a medium pressure (MP) hydraulic line, and a low pressure (LP) hydraulic line based on load requirements of the actuator assembly (1000); Actuator assembly (1000).

2. The main cylinder assembly (1100) a main cylinder cap end cover (1106) connected to one end of the main cylinder (1102); a main cylinder head end cover (1108) connected to the other end of the main cylinder (1102) through a flange (1111); a main cylinder rod eye (1110); and a main cylinder piston rod (1112), one end of the main cylinder piston rod (1112) connected to the main cylinder piston (1104) and the other end of the main cylinder piston rod (1112) connected to the main cylinder rod eye (1110).

3. The plunger cylinder assembly (1200) a plunger cylinder cap end cover (1206) connected to one end of the plunger cylinder (1202); a plunger cylinder head end cover (1208) detachably connected to the other end of the plunger cylinder (1202); and a plunger cylinder piston rod (1212) defining a ball-and-socket joint (1212J), one end of the plunger cylinder piston rod (1212) coupled to the plunger cylinder piston (1204) and the other end of the plunger cylinder piston rod (1212) coupled to the main cylinder rod eye (1110) of the main cylinder assembly (1100).

4. The actuator assembly (1000) a locating pin (1216) adapted to connect the plunger cylinder cap end cover (1206) with the main cylinder cap end cover (1106), thereby locating (aligning) the plunger cylinder assembly (1200) relative to the main cylinder cap end cover (1106); at least one first locking element (1210) adapted to lock the plunger cylinder cap end cover (1206) to the main cylinder cap end cover (1106), thereby locking the plunger cylinder assembly (1200) with the main cylinder cap end cover (1106), wherein the first locking element (1210) is at least a bolt; and a first retaining member adapted to retain the first locking element against the main cylinder cap end cover, the first retaining member being at least a snap ring.

5. The actuator assembly (1000) a second retaining member (1218) adapted to retain the ball-and-socket joint (1212J) relative to the main cylinder rod eye (1110); and a plurality of second locking elements (1220) adapted to lock the second retaining member (1218) to the main cylinder rod eye (1110), each of the second locking elements (1220) being at least a bolt.

6. the plunger-cylinder assembly (1200) includes a linear position sensor (1222) adapted to detect the position / stroke of the actuator assembly (1000); the linear position sensor (1222) is configured to utilize magnetostrictive properties to determine the position of the plunger cylinder piston rod (1212) and the main cylinder piston rod (1112), and provides velocity feedback to a control system which in turn estimates the required flow rate from the pressure rail; the plunger cylinder cap end cover (1206) defines a plunger cylinder cap end side port (1206P) adapted to facilitate the flow of hydraulic fluid into or out of the third chamber (1202A) of the plunger cylinder (1202); the main cylinder cap end cover (1106) defines a main cylinder cap end side port (1106P) adapted to facilitate the flow of hydraulic fluid into or out of the first chamber (1102A) of the main cylinder (1102); 4. The actuator assembly (1000) of claim 3, wherein the main cylinder assembly (1100) includes a hydraulic fluid delivery tube (1109), one end of the tube (1109) connected to the main cylinder head end cover (1108), and the other end of the tube (1109) defining a main cylinder head end side port (1109P) adapted to facilitate the flow of hydraulic fluid into or out of the second chamber (1102B) of the main cylinder (1102).

7. The plunger cylinder assembly (1200) a plunger cylinder piston bearing (1205) adapted to be attached to the plunger cylinder piston (1204), wherein a gap is defined between the plunger cylinder piston bearing (1205) and the plunger cylinder piston (1204) to allow hydraulic fluid to flow from one side of the plunger cylinder piston (1204) to the other side of the plunger cylinder piston (1204), and the third chamber (1202A) of the plunger cylinder (1202) includes areas from both sides of the plunger cylinder piston (1204); a plunger cylinder bimetallic bushing (1207) adapted to be received by a bushing receiving groove defined in an interior of the plunger cylinder head end cover (1208); the plunger-cylinder piston bearing (1205) and the plunger-cylinder bimetallic bushing (1207) are adapted to improve the side load capacity of the plunger-cylinder assembly (1200); 2. The actuator assembly (1000) of claim 1, wherein the plunger cylinder bimetallic bushing (1207) is adapted to guide the plunger cylinder piston rod (1212) during extension and retraction of the plunger cylinder piston rod (1212).

8. The plunger cylinder assembly (1200) at least one first sealing element (1209) adapted to be received by a first sealing portion receiving groove defined on an outer surface of the plunger cylinder head end cover (1208) and engaged with the plunger cylinder (1202); 4. The actuator assembly (1000) of claim 3, comprising: a plurality of second sealing elements (1211), each of the second sealing elements (1211) adapted to be received by a second seal receiving groove defined in an inner portion of the plunger cylinder head end cover (1208), and the plurality of second sealing elements (1211) engaged with the plunger cylinder piston rod (1212).

9. the first chamber (1102A) of the main cylinder (1102) and the third chamber (1202A) of the plunger cylinder (1202) are configured to selectively receive hydraulic fluid from any one of the high-pressure hydraulic line, the medium-pressure hydraulic line, and the low-pressure hydraulic line through the main cylinder cap end side port (1106P) and the plunger cylinder cap end side port (1206P), respectively, and the hydraulic fluid exits from the second chamber (1102B) of the main cylinder (1102) to the corresponding pressure hydraulic line to which the second chamber (1102B) is connected to facilitate extension of the main cylinder piston rod (1112) and the plunger cylinder piston rod (1212) based on load requirements of the actuator assembly (1000); 2. The actuator assembly of claim 1, wherein the second chamber (1102B) of the main cylinder (1102) is configured to selectively receive hydraulic fluid from either the high-pressure hydraulic line or the medium-pressure hydraulic line through the main cylinder head-end side port (1109P), and the hydraulic fluid exits from the first chamber (1102A) of the main cylinder (1102) and the third chamber (1202A) of the plunger cylinder (1202) to respective pressure hydraulic lines to which the first chamber (1102A) and the third chamber (1202A) are connected to facilitate contraction of the main cylinder piston rod (1112) and the plunger cylinder piston rod (1212) based on load requirements of the actuator assembly (1000).

10. when the sum of the forces generated in the first chamber (1102A) of the main cylinder (1102) and the third chamber (1202A) of the plunger cylinder (1202) exceeds the force generated in the second chamber (1102B) of the main cylinder (1102), the main cylinder piston rod (1112) and the plunger cylinder piston rod (1212) move to the extended position; when the force generated in the second chamber (1102B) of the main cylinder (1102) exceeds the resultant force in the first chamber (1102A) of the main cylinder (1102) and the third chamber (1202A) of the plunger cylinder (1202), the main cylinder piston rod (1112) and the plunger cylinder piston rod (1212) move to the retracted position; 10. The actuator assembly (1000) of claim 9, wherein the stroke of the plunger cylinder assembly (1200) is greater than the stroke of the main cylinder assembly (1100), such that the plunger cylinder piston (1204) does not contact the plunger cylinder cap end cover (1206) and the plunger cylinder head end cover (1208) during the entire operation of the actuator assembly (1000).

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