Pipes and tubular conduits – With pressure compensators – Variable capacity chambers
Reexamination Certificate
2001-12-04
2003-09-16
Hook, James (Department: 3752)
Pipes and tubular conduits
With pressure compensators
Variable capacity chambers
C138S026000, C137S495000, C251S082000, C251S083000
Reexamination Certificate
active
06619325
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The principal utility of the invention is to improve the efficiency of motor vehicles and thus reduce green house gas emissions. More specifically, the field of the invention is hybrid vehicular drivetrains combining at least one hydraulic motor with an internal combustion engine.
2. Prior Art
Hydraulic hybrid vehicles utilize accumulators to store mechanical energy which is recovered from braking the vehicle and/or excess energy generated by the engine. See U.S. Pat. No. 5,495,912 and U.S. patent application Ser. No. 09/479,844 (pending) for details of the use of accumulators in hydraulic hybrid vehicles. However, control of the flow of high pressure hydraulic fluid into and out of the accumulator represents a potential safety problem in the use of hydraulic hybrid drivetrains.
Conventional accumulators are made in several designs including: piston accumulators wherein the piston in a cylindrical accumulator vessel separates hydraulic fluid from a gas (usually nitrogen) which is compressed to store energy by liquid flowing into the vessel, bladder accumulators which use an elastic bladder to separate the hydraulic fluid from the gas, and diaphragm accumulators which use a diaphragm to separate the hydraulic fluid from the gas.
FIG. 1
shows a cross section of the liquid entrance and valve end of a conventional bladder accumulator
10
which is a cylindrical vessel with domed ends. Pressures up to 5,000 pounds per square inch (psi) are common for such a high pressure accumulator that would be used on a hydraulic hybrid vehicle. Hydraulic fluid is pumped into and discharged out of the accumulator through port
11
. The liquid flows around poppet valve
12
into the liquid chamber
13
of the accumulator. The accumulator walls
14
must be sufficiently strong to safely contain the high pressure liquid. A compressed gas (usually nitrogen) is contained within a sealed, elastic bladder
15
. Spring
16
keeps valve
12
open for normal operation. Valve assembly
17
can be removed from the accumulator if necessary. For a 5,000 psi accumulator, the gas in bladder
15
is usually pre-compressed to between 1,600 and 2,000 psi before any liquid is pumped into the accumulator, to maximize the energy which can be stored within the accumulator. When the bladder
15
is pressurized by admitting high pressure gas through a valve in the other end (not shown), the elastic bladder
15
expands against poppet valve
12
and compresses spring
16
to shut valve
12
. With valve
12
shut, bladder
15
is prevented from being extruded through fluid port
11
and rupturing the bladder. Hence the name commonly given to valve
12
is “anti-extrusion valve”, as this is its design function. When liquid is then pumped through port
11
at a pressure higher than the bladder pre-charge pressure, valve
12
is forced open and liquid flows into chamber
12
compressing bladder
15
and the gas contained therein. When sufficient liquid is pumped into chamber
13
to compress the gas in bladder
15
to 5,000 psi, the volume of the gas and bladder is reduced to approximately one third of its original volume, and substantial energy is stored in the compressed gas. When power is needed by the driver of the vehicle, liquid may be allowed to flow from the accumulator to a hydraulic motor to propel the vehicle. As liquid exits the accumulator, the bladder
15
expands. If liquid continues to be withdrawn down to the bladder
15
pre-charge pressure, the bladder will push against valve
12
, shutting valve
12
, stopping the further withdrawal of liquid and preventing extrusion of the bladder
15
. Spring
16
prevents the flow of liquid out of the accumulator from pre-maturely shutting valve
12
.
Anti-extrusion valve assembly
17
performs well in conventional applications of hydraulic accumulators. However, additional valve functions are necessary for the utilization of an accumulator in a hydraulic hybrid vehicle. In the prior art these additional valve functions can be provided only by utilizing separate valve assembles.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to improve safety of hydraulic hybrid drivetrains by improving control of high pressure hydraulic fluid into and out of an accumulator in the drivetrain by provision of an improved accumulator shut-off valve.
The present invention provides a unique means for providing the function of preventing the extrusion of the bladder when the liquid content approaches zero and the pre-charged gas in the bladder (at 2000 psi for a 5000 psi accumulator, for example) would otherwise force the bladder out of the accumulator.
More specifically, the present invention provides a shut-off valve for a hydraulic accumulator in a hybrid vehicular drive train which includes a valve body having a cylindrical hollow with a valve seat surrounding one end of the cylindrical hollow and, slidably mounted therein, a piston including a piston head having a central opening for receiving the stem of a poppet valve having a head which mates with the valve seat in a closed position. The central opening in the piston head which receives the valve stem serves to guide axial movement of the poppet valve relative to the piston. A spring is mounted between the head of the poppet valve and the piston head so as to urge the valve head away from the piston to an open position. The piston operating means, e.g., a control valve, serves to move the piston relative to the valve body between open and closed positions.
In the preferred embodiments, the spring between the head of the poppet valve and the piston head has a strength providing compression force equal to a pressure drop across the valve at a predetermined maximum flow rate, whereby the valve is closed by a flow rate exceeding the predetermined maximum flow rate, thus providing the so-called “flow fuse” feature of the present invention.
In one preferred embodiment, the piston and the valve body have defined therebetween an annular chamber wherein pressure is controlled by the piston operating means. The piston has at least one flange extending into and dividing the annular chamber and sealing against the inner wall of the valve body. The piston flange divides the annular chamber into a second chamber which is in constant communication with the low pressure reservoir and a first chamber which is in communication with the piston control means, e.g., control valve, for switching pressure in the first chamber between a high pressure source for moving the piston to an open position and a low pressure reservoir for allowing the piston to move to its closed position. Preferably, the control valve is a normally closed valve with the poppet valve being closed when the control valve is in its normally closed position. In one preferred embodiment, the piston has two flanges extending into the annular chamber to define first, second and third chambers wherein the third chamber is constantly open to the cylindrical hollow of the piston.
It is further preferred that the shut-off valve of the present invention be provided with at least one sensor for determining flow rate through the hollow interior of the piston (“cylindrical hollow”). Flow rate can be determined by use of two or more pressure sensors spaced along the flow path for the purpose of measuring pressure drop which can be used to calculate flow rate. An electronic control unit or computer receives signal from the sensor(s), computes the actual flow rate based on the signals and compares the actual flow rate against the commanded flow rate. If the actual flow rate exceeds the commanded flow rate, the electronic control unit issues a command signal to the control valve to close the poppet valve.
In a preferred embodiment the present invention also provides a new feature referred to herein as a “flow fuse.” If the accumulator outlet line is ever broken or mistakenly opened and the flow exceeds a pre-determined level that would otherwise be the maximum intended flow rate, the valve automatically shuts off.
Hook James
Lorusso, Loud & Kelly
The United States of America as represented by the Administrator
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