Patent Application
20210340999
The present disclosure relates to an accumulator and a method of operating the accumulator.
A machine typically includes one or more accumulators, such as a piston type accumulator, associated with the machine. For example, the accumulator may be associated with lift/tilt cylinders of a machine linkage assembly or a machine braking system. As per application requirements, the accumulator may be used to smooth out pulsations/vibrations or to build-up pressure in the associated hydraulic system. The accumulator typically includes a housing and a piston that is slidably disposed within the housing. The piston divides a hollow space of the housing into a liquid chamber and a gaseous chamber. The liquid chamber is adapted to receive liquid flow from another hydraulic device, whereas the gaseous chamber is pre-charged with gases to a desired pressure.
Further, the piston includes a cavity such that the cavity faces the gaseous chamber. The cavity creates a trapped volume for the gas pre-charge in the gaseous chamber and also increases an overall volume of the gaseous chamber. When the accumulator is in operation and the piston moves towards the gaseous chamber due to fluid pressure from the incoming liquid flow, a pressure differential is created between the liquid and gaseous chambers. This pressure differential is created due to the increased volume of the gaseous chamber owing to the presence of the cavity. Due to the additional volume presented by cavity, the gas pre-charge gets trapped within the cavity. The trapped gases may not compress to a high level due to which a pressure in the gaseous chamber is lesser than a pressure in the liquid chamber. Such a pressure differential is highest when the piston is completely displaced towards the gaseous chamber causing liquid from the liquid chamber to flow past piston sealing rings towards the gaseous chamber. This leakage causes mixing of the liquid with the gas pre-charge which may cause loss of the gas pre-charge. The loss of gas pre-charge may in turn contribute to poor accumulator performance and reduce an efficiency of the hydraulic system, which is not desirable.
U.S. Pat. No. 7,108,016 describes a lightweight, low permeation, piston-in-sleeve high-pressure accumulator. The accumulator includes a cylindrical composite pressure vessel with two integral rounded ends. A piston slidably disposed in a thin nonpermeable internal sleeve in the accumulator separates two chambers, one adapted for containing a working fluid and the other adapted for containing gas under pressure. Working fluid is provided in a volume between the nonpermeable internal sleeve and the composite pressure vessel wall. Further means are provided for withstanding harmful effects of radial flexing of the composite vessel wall under high pressures, and from stresses present in use in mobile applications such as with a hydraulic power system for a hydraulic hybrid motor vehicle. A method for pre-charging the device is also presented.
In an aspect of the present disclosure, an accumulator is provided. The accumulator includes an accumulator housing defining a first end, a second end opposite to the first end, and a hollow chamber. The accumulator also includes a piston slidably disposed within the hollow chamber and adapted to displace between the first and second ends. The piston divides the hollow chamber into a gaseous chamber proximate to the first end of the accumulator housing and a hydraulic chamber proximate to the second end of the accumulator housing. Further, the piston defines a first side surface in communication with the gaseous chamber. The piston also defines a second side surface spaced apart from the first side surface such that a length of the piston is defined between the first and second side surfaces. The second side surface is in communication with the hydraulic chamber. Further, a cavity of the piston is in communication with the second side surface such that the cavity extends from the second side surface towards the first side surface along the length of the piston. The cavity is in fluid communication with the hydraulic chamber.
In another aspect of the present disclosure, a method of operating an accumulator is provided. The method includes communicating, fluidly, the accumulator with at least one hydraulic device. The accumulator includes an accumulator housing defining a first end, a second end opposite to the first end, and a hollow chamber. The accumulator also includes a piston that divides the hollow chamber into a gaseous chamber and a hydraulic chamber. The piston defines a first side surface in communication with the gaseous chamber, a second side surface in communication with the hydraulic chamber, and a cavity extending from the second side surface towards the first side surface along a length of the piston such that the cavity is in fluid communication with the hydraulic chamber. The method also includes receiving, from the at least one hydraulic device, a hydraulic fluid within the hydraulic chamber and the cavity. The method further includes displacing the piston towards the first end by a maximum displacement based on receipt of the hydraulic fluid within the hydraulic chamber and the cavity. Further, a first pressure within the gaseous chamber is greater than a second pressure within the hydraulic chamber and the cavity when the piston is displaced towards the first end by the maximum displacement.
Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Referring to
The machine 100 also includes a set of ground engaging members 110. The ground engaging members 110 are operably coupled to the frame 106. In the illustrated embodiment, the ground engaging members 110 include wheels. In other embodiments, the ground engaging members 110 may include tracks, or a combination of tracks and wheels, based on a type of the machine 100. The ground engaging members 110 support and provide mobility to the machine 100 on ground surfaces.
The machine 100 includes a machine operator station 112 mounted on the frame 106. The machine operator station 112 includes various input devices to control various functions associated with the machine 100. Further, a braking system (not shown) is associated with the machine 100 for reducing a speed of the machine 100 or to stop the machine 100. The braking system may be embodied as a hydraulic braking system that includes components (not shown) such as an accumulator, a pump assembly that is driven to maintain hydraulic pressure in the accumulator, a master cylinder assembly, a brake caliper assembly, a reservoir, and the like.
Further, a linkage assembly 114 is attached to the frame 106 of the machine 100. The linkage assembly 114 includes a pair of lift arms 116, 117. An implement 118, such as a bucket, is pivotally coupled to the lift arms 116, 117. During operation of the machine 100, the lift arms 116, 117 and the implement 118 may be moved to different positions to perform operations such as excavating, loading, and dumping, based on application requirements. It may be noted that the linkage assembly 114 and the implement 118 may vary based on the type of the machine 100 or a type of operation or task required to be carried out by the machine 100.
As shown in
Further, the second hydraulic actuator 124 is mounted between the frame 106 and a tilt lever 134 (shown in
Further, the machine 100 includes one or more accumulators 136, 138. The accumulators 136, 138 are in selective fluid communication with one or more hydraulic devices 120, 122. In the illustrated example, the one or more hydraulic devices 120, 122 are embodied as the first hydraulic actuators 120, 122. The hydraulic device 120, 122 may be hereinafter interchangeably referred to as the first hydraulic actuators 120, 122, without any limitations. Alternatively, the accumulator 136, 138 may be associated with the second hydraulic actuator 124, the braking system, or any other hydraulic system of the machine 100, without any limitations.
Further, the machine 100 includes a valve assembly 130. In some examples, the valve assembly 130 forms a part of the linkage assembly 114. The valve assembly 130, the accumulator 136, 138, the first hydraulic actuator 120, 122, and the second hydraulic actuator 134 may be connected via a number of fluid conduits. The valve assembly 130 may control an operation of the linkage assembly 114. The valve assembly 130 may be activated or deactivated based on control signals received from a machine control unit (not shown) present onboard the machine 100.
In addition to other functionalities, the valve assembly 130 provides fluid communication between the accumulator 136, 138 and the first hydraulic actuator 120, 122. The accumulator 136, 138 may be connected with the first hydraulic actuator 120, 122 via the valve assembly 130. More particularly, when the valve assembly 130 is activated, the valve assembly 130 provides fluid communication between the accumulator 136, 138 and the first hydraulic actuator 120, 122. Further, when the valve assembly 130 is deactivated, the valve assembly 130 restricts fluid communication between the accumulator 136, 138 and the first hydraulic actuator 120, 122. It should be noted that the valve assembly 130 may be activated or deactivated to allow or restrict fluid communication between the accumulator 136, 138 and the first hydraulic actuator 120, 122 based on activation of a ride control feature associated with the machine 100. When the ride control feature is activated, the accumulator 136, 138 absorbs any splashes or shocks during roading of the machine 100 so that the machine 100 is not exposed to sudden shocks or jumps.
Further, the accumulators 136, 138 are similar to each other in terms of design and functionalities. Thus, for explanatory purposes, the accumulator 136 associated with the first hydraulic actuator 120 will now be explained in detail. However, the description provided below is equally applicable to the accumulator 138. Further, the accumulator 136 includes an accumulator housing 140. The accumulator housing 140 is embodied as a hollow cylindrical member. The accumulator housing 140 is removably coupled with the frame 106 using a pair of straps 142 and mechanical fasteners 144.
Referring to
As shown in
Further, the piston 156 includes a wear band 168 disposed within a first groove 176. The first groove 176 is defined proximate to the first side surface 164. The first groove 176 extends circumferentially along the outer surface 162 of the piston 156. Moreover, the piston 156 includes one or more sealing rings 170. In the illustrated example, the piston 156 includes the single sealing ring 170 disposed within a second groove 178. The second groove 178 is defined proximate to the second side surface 166. The second groove 178 extends circumferentially along the outer surface 162 of the piston 156. Alternatively, the piston 156 may include multiple second grooves 178 to accommodate multiple sealing rings 170 therein.
Further, the piston 156 defines a cavity 172 in communication with the second side surface 166 such that the cavity 172 extends from the second side surface 166 towards the first side surface 164 along the length “L1” of the piston 156. The cavity 172 is in fluid communication with the hydraulic chamber 160. The cavity 172 is spaced apart from the second side surface 166. The cavity 172 is centrally disposed within the piston 156. The cavity 172 is circular in shape such that a diameter “D2” of the cavity 172 is concentric with the diameter “D1” of the piston 156. In some examples, the diameter “D2” of the cavity 172 is more than half of the diameter “D1” of the piston 156. Further, the cavity 172 extends along more than half of the length “L1” of the piston 156. More particularly, a length “L2” defined by the cavity 172 is more than half of the length “L1” of the piston 156.
Further, the gaseous chamber 158 is adapted to contain a pre-charged quantity of gas therein. In an example, the gas is nitrogen. The pre-charged quantity of gas is introduced in the gaseous chamber 158 through the first port 152 (see
Further, the pre-charged quantity of gas is compressed based on the displacement of the piston 156 towards the first end 146. A first pressure “P1” within the gaseous chamber 158 increases based on the displacement of the piston 156 towards the first end 146. The increase in the first pressure “P1” is a result of the compression of the pre-charged quantity of gas. Moreover, the first pressure “P1” within the gaseous chamber 158 decreases based on the displacement of the piston 156 towards the second end 148 and expansion of the pre-charged quantity of gas.
Further, the hydraulic chamber 160 and the cavity 172 contain a hydraulic fluid therein. In an example, the hydraulic fluid is oil. When the valve assembly 130 (see
Further, the hydraulic chamber 160 and the cavity 172 of the piston 156 define a second volume “V2” that varies based on the displacement of the piston 156. The second volume “V2” is isolated from the first volume “V1”. More particularly, the second volume “V2” is isolated from the first volume “V1” by the sealing ring 170 associated with the piston 156. The second volume “V2” increases as the piston 156 displaces towards the first end 146 and the second volume “V2” decreases as the piston 156 displaces towards the second end 148.
Further, the second volume “V2” is greater than the first volume “V1” when the piston 156 is displaced towards the first end 146 by a maximum displacement. The term “maximum displacement” as referred to herein may be indicative of a maximum allowable travel of the piston 156 towards the first end 146 along the direction 174. As the gaseous chamber 158 is filled with the pre-charged quantity of gas, the piston 156 may not fully displace towards the first end 146. The displacement of the piston 156 may be dependent on a type, pressure, and amount of the pre-charged quantity of gas. Accordingly, the maximum displacement of the piston 156 may vary based on the type, pressure, and amount of the pre-charged quantity of gas.
When the valve assembly 130 is activated, the hydraulic chamber 160 and the cavity 172 receive the hydraulic fluid from the head end 126 of the first hydraulic actuator 120. The hydraulic fluid entering the accumulator housing 140 pressurizes the hydraulic chamber 160 and the cavity 172 to a second pressure “P2”. As the second pressure “P2” within the hydraulic chamber 160 and the cavity 172 increases, the piston 156 starts displacing towards the first end 146. The displacement of the piston 156 towards the first end 146 causes the second volume “V2” to increase. Moreover, the displacement of the piston 156 towards the first end 146 causes the first volume “V1” to decrease and the first pressure “P1” in the gaseous chamber 158 to increase.
Based on receipt of continual hydraulic fluid within the hydraulic chamber 160 and the cavity 172, the piston 156 is displaced towards the first end 146 by the maximum displacement. When the piston 156 is displaced towards the first end 146 by the maximum displacement, the second volume “V2” is greater than the first volume “V1”. Thus, based on reduction in the first volume “V1”, the pre-charged quantity of gas are compressed to the maximum allowable pressure which in turn increases the first pressure “P1” in the gaseous chamber 158. Further, the first pressure “P1” is greater than the second pressure “P2” within the hydraulic chamber 160 and the cavity 172 when the piston 156 is displaced towards the first end 146 by the maximum displacement.
It is to be understood that individual features shown or described for one embodiment may be combined with individual features shown or described for another embodiment. The above described implementation does not in any way limit the scope of the present disclosure. Therefore, it is to be understood although some features are shown or described to illustrate the use of the present disclosure in the context of functional segments, such features may be omitted from the scope of the present disclosure without departing from the spirit of the present disclosure as defined in the appended claims.
This section will now be explained in relation to the accumulator 136 associated with the first hydraulic actuator 120. However, it should be noted that the details provided in this section is equally applicable to the accumulator 138, without any limitations.
The accumulator 136 also includes the piston 156 that divides the hollow chamber 150 into the gaseous chamber 158 and the hydraulic chamber 160. Further, the piston 156 defines the first side surface 164 in communication with the gaseous chamber 158, the second side surface 166 in communication with the hydraulic chamber 160, and the cavity 172 extending from the second side surface 166 towards the first side surface 164 along the length “L1” of the piston 156 such that the cavity 172 is in fluid communication with the hydraulic chamber 160.
At step 504, the hydraulic fluid is received within the hydraulic chamber 160 and the cavity 172 from the hydraulic device 120. More particularly, the hydraulic fluid is received based on the fluid communication of the hydraulic chamber 160 and the cavity 172 with the hydraulic device 120. At step 506, the piston 156 is displaced towards the first end 146 by the maximum displacement based on receipt of the hydraulic fluid within the hydraulic chamber 160 and the cavity 172. Further, the first pressure “P1” within the gaseous chamber 158 is greater than the second pressure “P2” within the hydraulic chamber 160 and the cavity 172 when the piston 156 is displaced towards the first end 146 by the maximum displacement. The first pressure “P1” within the gaseous chamber 158 increases based on the compression of the pre-charged quantity of gas within the gaseous chamber 158.
Moreover, the first volume “V1” defined by the gaseous chamber 158 decreases based on the displacement of the piston 156 towards the first end 146. Simultaneously, the second volume “V2” defined by the hydraulic chamber 160 and the cavity 172 increases based on the displacement of the piston 156 towards the first end 146. Further, the second volume “V2” is greater than the first volume “V1” when the piston 156 is displaced towards the first end 146 by the maximum displacement.
The accumulator 136 of the present disclosure can be used in a variety of hydraulic applications, including but not limited to, the hydraulic system of the linkage assembly 114 and the braking system associated with the machine 100. The accumulator 136 includes the piston 156 having the cavity 172. The piston 156 is disposed within the accumulator housing 140 such that the cavity 172 is in fluid communication with the hydraulic chamber 160.
When the piston 156 is displaced towards the first end 146 by the maximum displacement, the presence of the cavity 172 in fluid communication with the hydraulic chamber 160 causes the second volume “V2” to be greater than the first volume “V1”. Due to the decreased first volume “V1”, the gaseous chamber 158 attains the first pressure “P1” that is greater than the second pressure “P2” within the hydraulic chamber 160 and the cavity 172. This phenomenon in turn reduces a condition of a high pressure differential between the hydraulic chamber 160 and the gaseous chamber 158. Accordingly, a leakage of the hydraulic fluid from the hydraulic chamber 160 towards the gaseous chamber 158 is prevented. Thus, the accumulator 136 may operate with improved efficiency and eliminate a possibility of loss of pre-charged quantity of gas. Further, due to improved isolation of the gaseous and hydraulic chambers 158, 160, a frequency of servicing/replacement of the accumulator 136 may reduce which may in turn reduce a downtime associated with the machine 100.
While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of the disclosure. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.
