Abstract:
A hydraulic accumulator is equipped with a novel shut-off valve. The shut off-valve includes a valve body having a cylindrical hollow with a valve seat surrounding one end. The main piston including a piston head has a central opening and is slidably mounted within the cylindrical hollow of the valve body. A poppet valve has a valve head which mates with the valve seat and a valve stem which extends through the central opening of the piston to guide axial movement of the poppet valve relative to the piston. A spring is mounted between the valve head and the main piston head for urging the valve head away from the piston head. A control valve moves the piston relative to the valve body between open and closed positions responsive to signals from a computer which signals valve closing upon determination that flow rate through the valve exceeds a maximum period. The spring between the poppet valve head and the piston head exerts a force approximately equal to that of a pressure drop across the poppet valve at a predetermined maximum flow rate.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    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.  
           [0003]    2. Prior Art  
           [0004]    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.  
           [0005]    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.  
           [0006]    [0006]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 .  
           [0007]    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  
         [0008]    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.  
           [0009]    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.  
           [0010]    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.  
           [0011]    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.  
           [0012]    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.  
           [0013]    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.  
           [0014]    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. In this preferred embodiment the spring holding the valve open is calibrated so that it allows the valve to close whenever the flow exceeds the predetermined maximum allowable rate.  
           [0015]    The present invention also provides for more rapid closing of the valve and opening of the valve. Very rapid closing of the valve (generally less than 50 milliseconds) is provided in response to an electronic command. The valve may be commanded to close if the computer senses that the outlet flow rate is higher than that expected for that instant, suggesting a leak in the system smaller than that which would trigger the emergency “flow fuse” shut off. The computer controls and therefore continually knows the outlet flow rate and by comparing the pressures at two locations in the outlet line (to determine a pressure drop which can be correlated to flow rate), or by other flow rate measurement means, and continuously compares the commanded flow rate to the measured flow rate. If the measured flow rate exceeds the commanded flow rate, the computer will command the valve to shut. The computer also commands the valve to shut when the system is turned off, e.g., when a key is turned off. The command to close (or shut) results in a very rapid closing since the pressure is essentially equal on both sides of the valve when it is open, and the closing force must only overcome valve friction and provide the desired acceleration.  
           [0016]    Opening the valve after a period of more than a few minutes (when the pressure downstream of the valve has dropped) requires a very large actuation force because it must not only overcome friction and accelerate the mass of the valve assembly, it must also overcome the force of the pressure in the accumulator acting on the accumulator side of the valve. In the extreme, when the downstream pressure reaches its lowest value (for example, 100 psi) and the accumulator pressure is at its highest value (for example, 5000 psi) a very large force is required to open the valve. For example, if the poppet valve face area is one square inch and the pressure difference is 4,900 psi, then the actuator would have to overcome an additional 4,900 pounds of force to rove the valve. Opening the valve of the present invention requires a much smaller actuation force since a small parallel line connects the accumulator to the downstream side of the main valve and contains a small on/off valve which is first commanded to open to equalize the pressure downstream of the main valve with the pressure in the accumulator. The only flow in the small parallel line is that required to pressurize the downstream volume, which is very small. When the pressure downstream of the main valve is the same as the accumulator pressure, the actuation force need be only just sufficient to overcome friction and to accelerate the mass of the valve assembly at the desired rate.  
           [0017]    The present invention utilizes a captive o-ring (or similar sealing material) in the poppet valve seat to provide for positive sealing with zero leakage. This prevents the accumulator from slowly losing pressure due to the seal slowly leaking as it would absent a positive seal.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a partial sectional view of a bladder-type accumulator equipped with the shut-off valve in accordance with the prior art;  
         [0019]    [0019]FIG. 2 is a partial cross-sectional view of a bladder type accumulator equipped with a shut-off valve, in accordance with a first embodiment of the present invention, in combination with an electric control unit and control valve;  
         [0020]    [0020]FIG. 3 is a partial sectional view of a bladder-type accumulator equipped with a shut-off valve, in accordance with a second embodiment of the present invention, in combination with an electric control unit and control valve;  
         [0021]    [0021]FIG. 4 is a cross-sectional view of a shut-off valve, in accordance with a third embodiment of the present invention, in combination with an electric control unit and control valve;  
         [0022]    [0022]FIG. 5 is a cross-sectional view of a shut-off valve, in accordance with a fourth embodiment of the present invention, in combination with an electric control unit and control valve; and  
         [0023]    [0023]FIG. 6 is a cross-sectional view of a bladder-type accumulator equipped with a shut-off valve, in accordance with a fifth embodiment of the present invention, in combination with an electric control unit and control valve.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    The present invention works well with all accumulator designs, but the preferred embodiment described below uses a bladder accumulator  10  to illustrate the invention. FIG. 2 shows an integrated valve assembly  21  as a first preferred embodiment of the present invention. Integrated valve assembly  21  replaces the conventional anti-extrusion valve assembly  17  of FIG. 1. Poppet valve  22  and spring  23  of FIG. 2 perform the same anti-extrusion function as poppet valve  12  and spring  16  of FIG. 1. However, the base of valve  22  is mounted in a slidable piston assembly  24 , in contrast to valve  12  of FIG. 1 which is fixed in an immovable base. More specifically, valve  22  includes a head portion  22   a  and a stem portion  22   b  which extends into a central opening  24   b  in the piston head  24   a  to guide valve  22  in axial movement relative to piston head  24   a.    
         [0025]    Slidable piston assembly  24  is slidably mounted in the cylindrical hollow  30  (hereinafter “chamber  30 ”) of valve body  20 . Slidable piston assembly  24  can be moved to the left and thereby close valve  22  on command by reducing the pressure at port  25  and within chamber  26 , from system high pressure at ports  31  and  32 , to system low pressure at reservoir  33 . When CPU  8  issues a command to close valve  22 , electric power to control valve  27  (generally referred to as a normally closed valve) is terminated. The choice of a normally closed valve for control valve  27  insures that the accumulator will shut off in the event of loss of electric power, a fail-safe design feature. Since the pressure on the right and left faces of valve  22  are equal or approximately equal when the valve  22  is open (only difference is due to a small pressure drop from the one face to the other face caused by any fluid flow into or out of the accumulator), assembly  24  will rapidly move to the left to shut off valve  22 . Chamber  38  is always open to low pressure reservoir  33  through port  28 . Chamber  29  is always open to accumulator downstream pressure in chamber  30  through port  34 . Accumulator downstream pressure in chamber  30  is prevented from causing flow through port  35  to either port  25  or low pressure reservoir  33  (after command to close valve  22 ) by check valve  36 .  
         [0026]    An elastomer seal  37  is provided as a seat for poppet valve  22  to assure zero leakage from the accumulator when valve  22  has been commanded shut. A zero leakage accumulator shut off valve is critical for a hydraulic hybrid vehicle since the accumulator downstream pressure in chamber  30  is exposed to several valves (not shown) that are likely to experience slow leakage, and the accumulator must retain pressure after several weeks of vehicle non-use since the energy stored in the accumulator is used to start the vehicle&#39;s engine and to assist in the initial vehicle acceleration.  
         [0027]    Spring  23  is calibrated to allow valve  22  to “slam shut” when the flow from the accumulator exceeds the maximum flow ever needed by the vehicle. Once the pressure drop from the right face of valve  22  to the left side of valve  22  reaches the pressure drop at the maximum allowable flow, the force of this pressure drop acting on the right face of valve  22  will overcome the force of spring  23  and begin to close valve  22 . When valve  22  begins to close, the pressure drop increases due to flow velocity increases, and the valve  22  sees an increase force to close which causes the valve  22  to close extremely fast. This “fuse valve” function is an extremely important safety feature for hydraulic hybrid vehicles since the accumulator stored energy is shut off in the event of an accumulator downstream system rupture.  
         [0028]    Another important safety feature included in the present invention is the ability to compare the pressure at port  35  to the pressure at port  32 . This pressure difference is correlated to flow rate of liquid leaving the accumulator. This calculated flow rate is compared to the flow rate being commanded by the vehicle&#39;s computer to drive the vehicle at each instant. If the calculated flow rate exceeds the commanded flow rate by a specified safety margin, the computer will command valve  22  to shut by movement of slidable piston assembly  24  to the left. This feature will detect a small system leak (which can still be dangerous) that has not yet reached the maximum allowable flow necessary to trigger the “fuse valve” function previously described. This mode of closing wherein the entire slidable piston assembly  24  moves to the left relative to valve body  20  is different from the “fuse valve” function wherein only poppet valve  22  moves to the left relative to valve body  20 .  
         [0029]    After valve  22  has been shut, the downstream pressure in chamber  30  will begin to drop, and the difference between the accumulator pressure at port  31  and the downstream pressure in chamber  30  will increase. To reopen valve  22  and overcome the force associated with the pressure difference across the valve  22 , a very large force must be applied to the left side of valve  22  (with associated structural and other problems), or as is the case with the present invention, the pressure is first equalized across valve  22  so that a much smaller force can quickly open the valve  22 . When a command to open valve  22  is issued, control valve  27  is opened to connect accumulator high pressure from port  32  to the lower pressures of port  25  and  35 . The high pressure liquid pressurizes chamber  26  and flows through chamber  29  and port  34  to increase the accumulator downstream pressure in chamber  30 . The high pressure within chamber  26  acts on slidable piston assembly  24  and moves it to the right. As pressure in chamber  30  equalizes with pressure at  31 , spring  23  opens valve  22 .  
         [0030]    Integrated valve assembly  21  can also be used to allow the hydraulic hybrid vehicle to operate in a hydrostatic mode (when the engine can produce a higher downstream pressure in chamber  30  than is instantly available in the accumulator at  31 ). When hydrostatic operation is desired, valve  22  is commanded to shut as described above. When downstream pressure in chamber  30  rises above accumulator pressure  31  a net force will act on the left face of valve  22  urging valve  22  toward its open position. It is only necessary to size the area of the piston within chamber  29  to overcome this force, and valve assembly  21  will perform well to control hydrostatic mode operation. When normal, accumulator assisted operation is again desired, the downstream pressure in chamber  30  will be reduced to near accumulator pressure and valve  22  will be opened as previously described.  
         [0031]    [0031]FIG. 3 shows a second preferred embodiment of the present invention. Integrated valve assembly  41  replaces the anti-extrusion valve assembly  17  of FIG. 1. Poppet valve  42  and spring  43  of FIG. 3 perform the same anti-extrusion function as poppet valve  12  and spring  16  of FIG. 1. However, the base of valve  42  is mounted in a slidable piston assembly  44 , in contrast to valve  12  of FIG. 1 which is fixed to a base.  
         [0032]    Slidable assembly  44  can be moved to the left and thereby close valve  42  on command by reducing the pressure at port  45  and within chamber  46 , from system high pressure at ports  51  and  52 , to system low pressure at reservoir  53 . Control valve  47  moves to the position shown in FIG. 3 when a command to close valve  42  is given. Since the pressure on the right and left faces of valve  42  are equal or nearly equal when valve  42  is open, assembly  44  will rapidly move to the left to shut off valve  42 . Chamber  58  is always open to low pressure reservoir  53  through port  48 . Chamber  58  contains spring  59  which applies force on assembly  44  to rapidly move assembly  44  to the left to shut off valve  42 . Check valve  56  prevents accumulator downstream pressure in chamber  50  from causing liquid flow through port  55  to either port  45  or low pressure reservoir  53 . An elastomer seal  57  serves as a seat for poppet valve  42  to assure zero leakage from the accumulator when valve  42  has been commanded shut.  
         [0033]    Spring  43  is calibrated to allow valve  42  to “slam shut” when the flow from the accumulator exceeds the maximum flow ever needed by the vehicle.  
         [0034]    After valve  42  has been shut, the downstream pressure in chamber  50  will begin to drop, and the difference between the accumulator pressure  51  and the downstream pressure in chamber  50  will increase. To re-open valve  42 , the pressure across valve  42  is equalized so a relatively small force can quickly open valve  42 . When a command to open valve  42  is given, control valve  47  is opened connecting accumulator high pressure from port  52  to the lower pressures of ports  45  and  55 . The high pressure fluid pressurizes chamber  46  and flows through port  54  to increase accumulator downstream pressure in chamber  50 . The high pressure within chamber  46  acts on slidable piston  60 , which is rigidly attached to and is therefore a portion of slidable assembly  44 , and moves it to the right. As pressure in chamber  50  equalizes with pressure at port  51  spring  43  opens valve  42 .  
         [0035]    [0035]FIG. 4 shows an integrated valve assembly  61  as a third preferred embodiment of the present invention. Poppet valve  62  and spring  63  perform the same anti-extrusion function as poppet valve  12  and spring  16  of FIG. 1. However, the base of valve  62  is mounted in a slidable piston assembly  64 , in contrast to valve  12  of FIG. 1 which is fixed in an immovable base. More specifically, valve  62  includes a head portion  62   a  and a stem portion  62   b  which extends into a central opening  64   b  in the piston head  64   a  to guide valve  62  in axial movement relative to piston head  64   a.    
         [0036]    Spring  66  biases slidable piston assembly  64  to the right against the pressure within the accumulator. Slidable piston assembly  64  can be moved to the left relative to valve body  65  and thereby close valve  62  on command by reducing the pressure at port  67  and within chamber  67   a , from system high pressure at ports  69  and  70 , to system low pressure at reservoir  71 . When CPU  72  issues a command to close valve  62 , electric power to control valve  73  (generally referred to as a normally closed valve) is terminated. As in the previously described embodiments, the choice of a normally closed valve for control valve  73  insures that the accumulator will shut off in the event of loss of electric power, a fail-safe design feature. Accumulator downstream pressure in chamber  68  is prevented from causing flow through port  74  to port  67  by check valve  75 . An elastomer seal  76  is provided as a seat for poppet valve  62 .  
         [0037]    Spring  63  is calibrated to allow valve  62  to “slam shut” when the flow from the accumulator exceeds the maximum flow predetermined to be the maximum ever needed by the vehicle.  
         [0038]    This third embodiment also has the capability to compare the pressure at port  74  to the pressure at port  70 . This pressure difference is correlated to flow rate of fluid leaving the accumulator. This calculated flow rate is compared to the flow rate being commanded by the vehicle&#39;s computer to drive the vehicle at each instant. If the calculated flow rate exceeds the commanded flow rate by a specified safety margin, the computer  72  will command valve  62  to shut by movement of slidable piston assembly  64  to the left.  
         [0039]    When a command to open valve  62  is issued, control valve  73  is opened to connect accumulator high pressure from port  69  to the lower pressures of port  67  and port  74 . The high pressure fluid pressurizes chamber  67   a  and flows through port  74  to increase the accumulator downstream pressure in chamber  68 . The high pressure within chamber  67   a  acts on slidable piston assembly  64  along with spring  66  to move it to the right. As pressure in chamber  68  equalizes with pressure at  70 , spring  63  opens valve  62 .  
         [0040]    Unlike the above-described embodiments wherein the poppet valve seals to the right of slidable piston assembly  84  against a seat at  97 , the fourth embodiment depicted in FIG. 5 has a poppet valve head  82   c  sealing against an internal seat  111  to the left of slidable piston assembly  84 . This configuration allows the slidable piston assembly  84  to be more easily moved to the left (relative to the embodiments of FIGS. 2, 3 and  4 ) and outside of the portion of chamber  90  that is located within the structure of the accumulator. The portion of chamber  90  within the accumulator needs to be of the smallest diameter possible and still allow a maximum liquid flow rate without unacceptably high flow losses (pressure drop) to minimize impact on the design of the accumulator structure (i.e., a large opening requires a stronger structure around the opening). Placing the slidable piston assembly  84  outside the accumulator portion of chamber  90  allows the diameter of chamber  90  which extends into the accumulator to be smaller, in comparison to similar structure in the embodiments of FIGS. 2, 3 and  4 . However, the basic function and features are similar to the previous embodiments. To open the valve  82 , pressure equalization valve  87   a  (normally closed valve) opens and the pressure in chamber  89   a  downstream of the seal at  111  is made equal to the pressure within chamber  90 . Valve  87   b  moves to the energized position connecting chamber  86  through port  85  with lower pressure reservoir  93 . Slidable piston assembly  84  moves to the right (position shown in FIG. 5) allowing spring  83  to open valve  82  as pressures equalize between chambers  89   a  and  90 . To shut valve  82 , valve  87   b  is unenergized (normally “off” position), which shutting serves to connect chamber  86  through port  85  with pressurized chamber  92   b  through port  91   b.  High pressure within chamber  86  acts on piston assembly  84  and moves it to the left shutting valve  82  as the face of valve head  82   c  seals against seal  111 . The pressure in chamber  98  is always at the pressure of low pressure reservoir  93 .  
         [0041]    [0041]FIG. 6 shows a fifth embodiment which emphasizes the pressure equalization function. A conventional ball valve  121  is attached to anti-extrusion valve assembly  122 , with the flow-fuse calibrated spring  123 , the anti-extrusion flow-fuse poppet valve  124 , positive seal  125  and accumulator (high pressure) access port  126  modifications as described in the previous embodiments. To open the accumulator shut-off valve  121  (in this case a ball valve), control valve  127  (normally closed as shown) is opened and high pressure from the accumulator at port  126  is provided to downstream port  128  to equalize pressure across the ball  129 , and to ball valve actuator  130  to provide torque to rotate ball shaft  131  and ball  129  against the closing torque of spring  132  (or other closing torque means) to open the valve  121 . To close valve  121 , control valve  127  is closed (as shown) and without high pressure to actuator  130 , spring  132  closes valve  121 .  
         [0042]    The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.