The present invention relates to hybrid drive systems for vehicles, and more particularly to hybrid hydraulic drive systems for vehicles.
A typical vehicle hybrid hydraulic drive system uses a reversible pump/motor to absorb power from and add power to or assist a conventional vehicle drive system. The system absorbs power by pumping hydraulic fluid from a low pressure reservoir into a hydraulic energy storage system. This hydraulic energy storage system typically includes one or more nitrogen-charged hydraulic accumulators. Hybrid hydraulic drive systems typically add power to conventional vehicle drive systems by utilizing the hydraulic energy stored in the hydraulic accumulators to drive the reversible pump/motor as a motor.
The present invention provides, in one aspect, an expandable accumulator and reservoir assembly including a reservoir defining an interior chamber containing working fluid therein, and an expandable accumulator at least partially positioned in the reservoir and at least partially immersed in the working fluid contained within the interior chamber. The accumulator is configured to exchange working fluid with the reservoir.
The present invention provides, in another aspect, an energy storage system including a reservoir defining an interior chamber containing working fluid therein, a reversible pump/motor in fluid communication with the reservoir, and an expandable accumulator at least partially positioned in the reservoir and at least partially immersed in the working fluid contained within the interior chamber. The accumulator contains working fluid, and is in selective fluid communication with the reversible pump/motor to deliver pressurized working fluid to the reversible pump/motor when operating as a motor, and to receive pressurized working fluid discharged by the reversible pump/motor when operating as a pump.
The present invention provides, in yet another aspect, a method of operating an energy storage system. The method includes providing a reservoir defining an interior chamber containing working fluid therein, positioning an expandable accumulator at least partially within the interior chamber, immersing the expandable accumulator at least partially into the working fluid contained within the interior chamber, returning working fluid to the reservoir with a reversible pump/motor when operating as a motor, and drawing working fluid from the reservoir when the reversible pump/motor is operating as a pump.
The present invention provides, in another aspect, an expandable accumulator including a body having an inner layer defining an interior space and an outer layer at least partially surrounding the inner layer. The accumulator also includes an inlet/outlet port in fluid communication with the interior space. The inner layer includes a higher fracture strain than the outer layer.
The present invention provides, in yet another aspect, an expandable accumulator and reservoir assembly including a reservoir defining an interior chamber containing working fluid therein and an expandable accumulator. The expandable accumulator includes an inner layer and an outer layer at least partially surrounding the inner layer. The inner layer includes a higher fracture strain than the outer layer. The accumulator is at least partially positioned in the reservoir and at least partially immersed in the working fluid contained within the interior chamber. The accumulator is configured to exchange working fluid with the reservoir.
The present invention provides, in another aspect, an expandable accumulator and reservoir assembly including a reservoir defining a central axis and an interior chamber containing working fluid therein, and an expandable accumulator coaxial with the central axis, at least partially positioned in the reservoir, and at least partially immersed in the working fluid contained within the interior chamber. The accumulator is configured to exchange working fluid with the reservoir. The assembly also includes a support coaxial with the reservoir and extending for at least the length of the accumulator. The support is engageable with an outer periphery of the accumulator to limit expansion of the accumulator upon receipt of pressurized working fluid from the reservoir.
The present invention provides, in yet another aspect, an expandable accumulator and reservoir assembly including a reservoir defining an interior chamber containing working fluid therein and a single expandable accumulator at least partially positioned in the reservoir and at least partially immersed in the working fluid contained within the interior chamber. The accumulator is configured to exchange working fluid with the reservoir. The reservoir includes an internal volume, and the accumulator occupies between about 40% and about 70% of the internal volume of the reservoir depending upon the amount of working fluid in the accumulator.
Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
The assembly 14 includes a reservoir 22 and an accumulator 26 in selective fluid communication with the reservoir 22 via the pump/motor 18. The reversible pump/motor 18 is configured as a variable displacement, axial-piston, swashplate-design pump/motor 18, such as a Bosch Rexroth Model No. A4VSO variable displacement, axial piston reversible pump/motor 18. Alternatively, the reversible pump/motor 18 may be configured having a constant displacement rather than a variable displacement. The reversible pump/motor 18 is drivably coupled to a rotating shaft 30 (e.g., an output shaft of an engine, an accessory drive system of the engine, a drive shaft between a transmission and an axle assembly, a wheel or drive axle, etc.). As is described in more detail below, the pump/motor 18 transfers power to the rotating shaft 30 when operating as a motor, and the pump/motor 18 is driven by the rotating shaft 30 when operating as a pump.
With continued reference to
The reversible pump/motor 18 is in fluid communication with the accumulator 26 via a fluid passageway 42 to deliver pressurized working fluid (in the direction of arrow A in
With continued reference to
With continued reference to
In the illustrated construction of the system 10, the reservoir 22 is substantially air-tight (i.e., “closed”) and is capable of maintaining air within the reservoir 22 at atmospheric pressure (e.g., 0 psi gauge) or at a pressure higher than atmospheric pressure. Alternatively, the reservoir 22 may be open to the atmosphere and include a breather to permit an exchange of air with the atmosphere. The interior chamber 50 of the reservoir 22 includes an air space 66 surrounding the accumulator 26, above the working fluid. As previously mentioned, the air space 66 may include air at atmospheric pressure or at a pressure higher than atmospheric pressure. Pressurization of the reservoir 22 (i.e., providing air in the air space 66 at a pressure higher than atmospheric pressure) substantially ensures that the pressure of the working fluid at the inlet of the pump/motor 18 (and the inlet/outlet port 58 of the reservoir 22) is maintained at a level sufficient to substantially prevent cavitation of the pump/motor 18 when operating as a pump.
In the illustrated construction of the system 10, the reservoir 22 is schematically illustrated as having a generally cylindrical shape. However, the reservoir 22 may be configured having any of a number of different shapes to conform with the structure of a hybrid vehicle within which the reservoir 22 is located. In addition, the reservoir 22 may be made from any of the number of different materials (e.g., metals, plastics, composite materials, etc.). Also, in the illustrated construction of the system 10, the reservoir 22 is schematically illustrated in a vertical orientation. However, the reservoir 22 may be positioned in any of a number of different orientations in the hybrid vehicle incorporating the system 10. For example, the reservoir 22 may be oriented upright (i.e., vertical) in the vehicle, laid flat (i.e., horizontal), or positioned at an incline at any angle between a horizontal orientation of the reservoir 22 and a vertical orientation of the reservoir 22.
With continued reference to
With reference to
With continued reference to
The expandable tube 70 or bladder is made from an elastomeric material (e.g., polyurethane, natural rubber, polyisoprene, fluoropolymer elastomers, nitriles, etc.) to facilitate deformation of the tube 70 in response to pressurized working fluid being pumped into the accumulator 26 when the reversible pump/motor 18 is operating as a pump. Specifically, as shown in
Applicants have discovered through testing that when the interior of a homogeneous tube 70 (i.e., a tube 70 having only a single layer, without reinforcing fibers) is pressurized, most of the strain energy stored in the tube 70 is concentrated near the inner surface of the tube 70. Applicants have also discovered that the concentration of strain energy stored in the tube 70 decreases with an increasing radial position along the thickness of the tube 70. In other words, the material proximate the outer surface of the tube 70 contributes less to the storage of strain energy than the material proximate the inner surface of the tube 70. To increase the uniformity of distribution of strain energy along the thickness of the tube 70, a multi-layer construction may be used in which an innermost layer of the tube includes a higher fracture strain (i.e., the strain at which fracture occurs during a tensile test) than an outermost layer, and in which the outermost layer includes a higher stiffness than the innermost layer. Because such a multi-layer tube can more efficiently store strain energy along its thickness, the maximum internal pressure that the tube is capable of handling would also be increased compared to the single-layer tube 70.
As shown in
In addition to providing the performance characteristics discussed above, the materials comprising the inner and outer layers 122, 130 of the bladder 118 may be selected such that each of the layers 122, 130 may be resistant to the working fluid such that deterioration of either of the layers 122, 130 after prolonged contact with the working fluid is substantially inhibited. For example, the inner and outer layers 122, 130 of the bladder 118 may be made from an elastomer including a nitrile butadiene rubber (NBR), a fluoropolymer elastomer (e.g., VITON), a polyurethane polymer, an elastic hydrocarbon polymer (e.g., natural rubber), and so forth. Each of the inner and outer layers 122, 130 may be made from different grades of material within the same material family. Alternatively, the inner and outer layers 122, 130 may be made from materials having distinctly different chemistry.
With continued reference to
With reference to
The layers 138, 146, 150, 142 may be made from the same materials discussed above with respect to the bladder 118 of
The individual layers 138, 146, 150, 142 may be separately formed and assembled such that the mating surfaces of the layers 138, 146, 150, 142 conform to each other. The layers 138, 146, 150, 142 may or may not be bonded together. Alternatively, the layers 138, 146, 150, 142 may be co-molded such that subsequent assembly of the layers 138, 146, 150, 142 is not required. For example, when configured as a tube 134, the layers 138, 146, 150, 142 may be co-extruded layer by layer.
With reference to
In operation, when the system 10 recovers kinetic energy from the rotating shaft 30, the pump/motor 18 operates as a pump to draw working fluid from the reservoir 22 (via the inlet/outlet port 58) in the direction of arrow A (see
As working fluid exits the reservoir 22, the volume of the air space 66 above the working fluid is substantially unchanged because the working fluid is merely transferred from outside the tube 70 (as shown in
Consequently, the total volume of working fluid maintained within the accumulator 26 and the reservoir 22 at any given time during operation of the system 10 is substantially constant. In addition, because the volume of the air space 66 is maintained substantially constant during operation of the system 10, working fluid may be drawn from the reservoir 22 and returned to the reservoir 22 without an exchange of gas or air with the atmosphere (i.e., drawing replacement air from the atmosphere or venting air to the atmosphere). After the kinetic energy of the rotating shaft 30 is recovered, the isolation valve 46 is actuated to a closed configuration, and the tube 70 exerts a compressive force on the working fluid to maintain the working fluid at a high pressure within the accumulator 26.
When the hybrid vehicle requires propulsion assistance, the isolation valve 46 is actuated to an open configuration to permit the flow of pressurized working fluid in the direction of arrow B (see
With reference to
With reference to
As discussed above, the cage 202 is spaced from the outer periphery of the bladder 178 by a particular distance corresponding with the desired extent to which the bladder 178 may expand. The end of the cage 202 proximate the low-pressure inlet/outlet port 58a is also spaced from the end of the reservoir 22a a sufficient distance to permit free-flow of working fluid between locations in the interior chamber 50a inside the cage 202 and outside the cage 202. With reference to
With reference to
With reference to
In one construction, the assembly 14a occupies only about 3.6 cubic feet of space. Such a relatively small package is possible as a result of positioning the bladder 178 within the reservoir 22a, and by permitting the bladder 178 to occupy up to about 70% of the internal volume of the reservoir 22a when the bladder 178 is fully charged with pressurized working fluid. With the available energy storage capabilities of the assembly 14a when operating between system pressures of 2,000 psi and 6,000 psi, the energy density (i.e., the stored energy divided by the occupied space of the storage device) of the assembly 14a may range between about 41,500 ft-lbs/cubic foot and about 208,500 ft-lbs/cubic foot. In comparison, the energy density of a conventional hybrid hydraulic system including a gas-charged accumulator and a separate low-pressure reservoir is about one-third to about one-fifth the energy density of the assembly 14a. Because the energy density of the assembly 14a is much higher than that of a conventional hybrid hydraulic system including a gas-charged accumulator and a separate low-pressure reservoir, the assembly 14a may be packaged much more efficiently within a vehicle or other machinery with which the assembly 14a is used.
In one construction of the multi-layer bladder 190 which Applicants have tested, the inner layer 226 includes an inner diameter D1 of about 2.25 inches and an outer diameter D2 of about 10.25 inches, and the outer layer 230 includes an inner diameter D3 of about 10.25 inches and an outer diameter D4 of about 13.25 inches. Therefore, the wall thickness T1 of the inner layer 226 is about 4 inches, while the wall thickness T2 of the outer layer 230 is about 1.5 inches. The values of these dimensions D1-D4, T1, T2 correspond with the unexpanded state of the bladder 190, as shown in
Operation of either of the assemblies 14a, 14b is substantially similar to the operation of the assembly 14 as described above.
Various features of the invention are set forth in the following claims.
This application claims priority to co-pending U.S. Provisional Patent Application No. 61/369,214 filed on Jul. 30, 2010, and co-pending U.S. Provisional Patent Application No. 61/248,573 filed on Oct. 5, 2009, the entire contents of both of which are incorporated herein by reference.
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