Abstract:
A recoil brake isolation system for the hydraulic recoil brake cylinder of a large caliber gun, includes two sets of hydraulic valves disposed respectively within the inlet valve block and return valve block of the hydraulic cylinder, an orchestrated combination of which together block the flow of hydraulic fluid to or from the hydraulic cylinder during the recoil/counterrecoil cycle or upon failure of the hydraulic circuit. A method of hydraulically isolating a recoil brake cylinder of a large caliber gun for survivability and improved weapon performance and a gun incorporating such a system are also included.

Description:
GOVERNMENT INTEREST  
       [0001] The invention described herein may be manufactured, used and licensed by or for the United States Government. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates to artillery. More particularly, the present invention relates to a valve system for improving the survivability of a large caliber gun by isolating the hydraulic recoil system from the hydraulic power components during the recoil/counterrecoil cycle and preserving the hydraulic fluid in the recoil system upon failure of any of the hydraulic supply or return components.  
         BACKGROUND OF THE INVENTION  
         [0003]    The current trend in the military is for deployable lightweight units which provide comparable lethality and effectiveness as provided by multiple traditional heavier units. This trend particularly applies to artillery which benefits from advances in munitions and automatic loading schemes. For example, currently used 155 mm self-propelled howitzers have a maximum rate of fire of four rounds a minute for up to three minutes. In order to reduce the total deployed units, there is a need then for a single weapon with a rate of fire two to three times that of current units. The drawback to this approach is that a single component failure on the weapon could shut down the equivalent of an entire artillery battery.  
           [0004]    There is a need then to ensure that the new artillery unit can withstand the increased operational demands. The weapon must be more reliable while maintaining high fire rates. In order to achieve the required firing rates, a number of subsystems within the weapon must evolve to withstand increased service demands. The sustained rate of fire creates extremely high temperatures within the barrel and the recoil system. Conventional large caliber guns utilize an integral sealed recoil brake in which a piston coupled to the barrel forces a fluid through a set of metering orifices during the recoil movement. As the firing rate increases so does the temperature of the fluid. Eventually the fluid reaches a thermal limit and the gun must stop firing.  
           [0005]    There is a need then for a survivable cooled recoil system. A typical cooling system, utilizing a combination of pumps, filters and a heat exchanger, increases the complexity of the recoil system. The gun must be able to continue operating should one of these systems fail due to mechanical or operational reasons. Furthermore, a recoil brake for a large caliber gun generates hydraulic pressures as high as 6500 psi, vacuum conditions, pressure spikes, and reversals of flow all induced by the action of the recoil piston. A hydraulic fluid cooling system subject to such extreme operating conditions would be cost and size prohibitive.  
           [0006]    There is a need then to provide a hydraulic recoil system for a large caliber gun that is capable of maintaining high rates of sustained fire. The recoil system should be cooled so as to maintain the high sustained fire volumes. The recoil system should be survivable so that the weapon does not become useless should a thermal control component fail or suffer damage. Further, the recoil system should not hinder deployability of the weapon by excessively increasing weight or size.  
         SUMMARY OF THE INVENTION  
         [0007]    The recoil brake isolation system of the present invention substantially meets the aforementioned needs. The system uses two sets of valves to control fluid flow for use with any piston style hydraulic recoil brake requiring active cooling due to high rates of fire. One set of valves is disposed along the hydraulic fluid supply line for the recoil system while the other set of valves is disposed on the return line. Valve activation occurs due to changes in hydraulic pressure as experienced by individual valves. The system does not require any wiring, software or electrical controls. The present invention relates to the arrangement, orchestration and functioning of the valves during the various modes of recoil, counterrecoil, and subsystem failure.  
           [0008]    During normal operations, the valves allow the fluid within the recoil brake to be circulated through the thermal dissipation system (TDS). Upon firing, the recoil/counterrecoil mode is automatically activated so that the valves protect the heat exchanger and fluid circulating equipment from pressure spikes, vacuum, high pressure conditions and reversal of flow. In the event of a subsystem failure, such as the loss of a supply line, the valves revert to a sealed mode system so as to minimize fluid loss and prevent ingestion of air by the recoil system. This allows continued operation of the weapon until thermal limits are reached. The system can return to operation after cooling below the thermal threshold.  
           [0009]    The present invention is a recoil brake isolation system, adaptable to any large caliber artillery piece using a piston style hydraulic recoil system, which incorporates an arrangement of valves to control fluid flow within the recoil system so as to maintain high rates of sustained fire under normal firing situations and an isolation mode which allows for continued use if the thermal system is damaged or fails. The present invention is further a method of configuring a valve system so as to minimize weight and maximize survivability of a large caliber artillery piece. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a perspective view of the gun with the turret area of a self-propelled howitzer in phantom with the gun mount system and thermal dissipation system highlighted.  
         [0011]    [0011]FIG. 2 is a front perspective view of the gun mount system for a self-propelled howitzer.  
         [0012]    [0012]FIG. 3 is a side perspective view of the components of the thermal dissipation system for the recoil modules and cannon cooling system.  
         [0013]    [0013]FIG. 4 is a schematic representation of the recoil brake isolation system including the recoil brake and hydraulic system.  
         [0014]    [0014]FIG. 5 is a perspective view of a recoil module with cut out section in which the return valve block and piston head are exposed.  
         [0015]    [0015]FIG. 6 is a block diagram representation of the gun cooling system and recoil cooling system for a self-propelled howitzer.  
         [0016]    [0016]FIG. 7 is a perspective view of the return valve block with the fluid circuit represented in phantom.  
         [0017]    [0017]FIG. 8 is a perspective view of the inlet valve block with a cutout which depicts the fluid circuit with excess flow valve and check valve. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    The recoil brake isolation system of the present invention is located within the recoil system  20  of a self-propelled howitzer. Any large caliber weapon, whether mounted on a vehicle platform such as a tank or self-propelled howitzer, or towed, in which sustained high rates of fire are planned, could utilize the present invention. Maintaining a high fire rate requires active cooling for the recoil system  20 . In a first embodiment, the present invention is included on a self-propelled howitzer.  
         [0019]    Referring now to FIG. 1, the liquid cooled cannon  14  and recoil system  20  are contained within the gun mount  40  and are fluidly connected to the thermal dissipation system (TDS)  30 . The TDS  30  operates to cool both the recoil system  20  and the cannon cooling system  15 . In order to reduce the weight of the vehicle, and allow access for servicing and removal, the TDS  30  is not afforded the same level of armor protection as the adjacent recoil system  20  and cannon  14 . Should the TDS  30  be damaged by enemy fire or fail due to a component malfunction, the recoil brake isolation system  10 , as is illustrated in FIG. 4, allows for continued firing.  
         [0020]    The gun mount  40 , depicted in greater detail in FIG. 2, is comprised of the cannon cooling system  15 , a pair of recoil modules  22 , and a pair of recuperator modules  24 , all installed within the gun cradle  25 . The recuperator module  24  is used to control the position of the gun after recoil in preparation for the next firing. The gun mount  40  is rotationally elevatable about trunion  28 . An armored shield assembly  26  is mounted above and below the cradle  25 . Note that the recoil module  22  and recuperator module  24  are mounted as pairs in alternating order on each side of cannon  14  so as to counteract the dynamic torque created during recoil/counterrecoil.  
         [0021]    The TDS  30 , as depicted in FIG. 6, contains two separate cooling circuits utilizing a common cooling fan  31  and heat exchanger  33 . The recoil system  20  is cooled through the circulation of a silicone brake fluid manufactured pursuant to Military Specification MIL-B-46176 or MIL-PRF-46176, although any comparable fluid would be acceptable. The cannon cooling system  15  dissipates heat through the circulation of an antifreeze solution, the composition of which is well known in the art.  
         [0022]    Referring to FIG. 3, hydraulic fluid leaving the recoil module  22  flows to heat exchanger  33  which is fluidly connected to the recoil reservoir  32 . Air inlet  34  is disposed proximate to the base of the TDS  30  along the slanting outer sidewall of the howitzer  12 , and provides the air required to cool the heat exchanger  33 . The hot exhaust from the heat exchanger  33  is blown by cooling fan  31  through an exhaust vent  42  mounted on top of the howitzer  12 . Pressurized hydraulic fluid from recoil coolant pump  35  is controllably directed to the recoil relief valve  39  which maintains a predetermined fluid compression. The pressurized fluid is then controllably directed through a filter  41  before reentering recoil module  22 . Likewise, the TDS  30  cooling circuit for the gun  14  utilizes the same heat exchanger  33  and cooling fan  31  and comparable pump  36  and reservoir  38  but provides thermal dissipation by circulating the antifreeze solution.  
         [0023]    The present invention isolates the entire TDS  30  during recoil and counterrecoil and, if any component of the TDS  30  fails, the present invention will maintain the isolated mode so as to conserve the hydraulic fluid within the recoil module  20 . The recoil brake isolation system  10  also prevents ingestion of air, potentially a catastrophic failure, should a return or supply line fail. In the event of component failure or damage by an enemy, the recoil brake isolation system allows for continued firing, at a reduced rate of fire comparable to that of a howitzer without active cooling.  
         [0024]    An added advantage produced by the recoil brake isolation system  10  is a reduction in the TDS  30  design requirements. The recoil brake isolation system  10  effectively blocks the flow of hydraulic fluid from the TDS  30  thereby eliminating the design requirements of operating with high pressures (on the order of 6500 psi), vacuum, pressure spikes and reversal of flow. In the preferred embodiment, the TDS  30  is sized to withstand pressures of 400 psi. The lower pressure requirements result in smaller components, less weight and less cost for the TDS  30 . Note that the internal valve components of the recoil module  22  must be sized for the higher pressure requirements.  
         [0025]    The recoil brake isolation system is comprised of the supply line isolation system  54  and the return line isolation system  59 . Referring to FIG. 6, the hydraulic power unit  47  of TDS  30 , which contains pump  35 , reservoir  32 , relief valve  39 , and filter  41  is fluidly connected to recoil module  22  by way of hydraulic fluid supply line  44  and hydraulic fluid return line  46 . Hydraulic fluid supply line  44  is fluidly connected to inlet supply valve block  50  in which the supply line isolation system  54  is disposed and hydraulic fluid return line  46  is fluidly connected to return valve block  52  in which the return line isolation system  59  is located. See FIG. 5.  
         [0026]    As depicted in FIGS. 4 and 5, the supply line isolation system  54 , disposed within inlet supply valve block  50 , is comprised of an excess flow valve  56  and a normally closed check valve  58 . A similar valve arrangement exists for the return line isolation system  59  disposed within the return valve block  52 , comprising a mechanically operated two position, two port control valve  66 , a normally closed pilot operated check valve  67  and a normally closed check valve  68 . The placement of the supply line isolation system  54  and return line isolation system  59  within the manifold blocks  50  and  52  advantageously removes unnecessary hydraulic lines from the fluid circuit thus reducing potential leakage points, reducing system size, and consolidating the system for repair/diagnostics.  
         [0027]    The valves  56 ,  58 ,  66 ,  67  and  68  themselves are readily available cartridge style valves which fit within cavities appropriately sized within the respective valve blocks  50  and  52 . See FIGS. 7 and 8. Mounting and retention of valves  56 ,  58 ,  66 ,  67  and  68  may be accomplished through the use of an expanding sleeve, external threads or with an external holding device. For this embodiment, the valves  56 ,  58 ,  66 ,  67  and  68  operate in a temperature regime of −51F to +400F. The entire recoil module  22  can be fluidly disconnected by way of quick disconnect couplings  69  and  69 ′ for servicing or replacement.  
         [0028]    In FIG. 5, inlet supply valve block  50  is an annular metal flange through which piston rod  61  extends and freely travels. Piston rod  61  is anchored on one end to the gun barrel  14  in a manner well known to those in the art so that the piston rod  61  moves with gun  14  during recoil. A piston head  62 , slidably arranged, disposed within and dimensioned closely to the inner diameter of the inner sleeve  65  of recoil chamber  63  is attached to the opposite end of piston rod  61 . Inlet supply valve block  50  seals recoil chamber  63  on one end while return valve block  52  provides the seal at the opposing end.  
         [0029]    In operation, firing of the howitzer results in a barrel  14  recoiling to the right (see FIG. 5) which forces the piston  61  to also travel to the right through recoil chamber  63 . The recoil chamber  63  contains a perforated orifice sleeve  65  closely dimensioned to the diameter of the piston head  62 . The inner sleeve  65  contains rows of perforations  70  which decrease in size from left to right. Therefore, the piston head  62  moves to the right with the recoil forcing hydraulic fluid within recoil chamber  63  through the perforations  70 . The piston  61  slows as resistance and pressure increases ahead of the piston head  62  due to the reduction in size and number of the perforations  70 . The hydraulic fluid forced through the perforations  70  travels between inner sleeve  65  and the inner face of recoil chamber  63  and is collected on the vacuum side of the piston head  62 . While the recoil module  20  halts the rearward progress of the barrel  14 , the recuperator  24 , upon completion of the recoil cycle, progressively moves the barrel  14  back to the firing position.  
         [0030]    The recoil brake isolation system  10  is activated under normal conditions by the operation of TDS pump  35 . Upon sensing a return to a static state, the recoil brake isolation system  10  allows circulation when pump  35  produces sufficient pressure in the system to open check valve  58 .  
         [0031]    Referring to FIG. 4, supply hydraulic fluid first passes through the excess flow valve  56  on its way to the recoil module  22 . In fluid communication with the excess flow valve  56  is check valve  58  which performs three functions. The check valve  58  is normally in a closed or blocked position. Check valve  58  is sized with a cracking pressure sufficiently high enough to close immediately if the supply pressure drops to atmospheric, as when the supply line is severed. The check valve  58  prevents fluid from leaving recoil chamber  63  and also prevents ingestion of air during counterrecoil. Check valve  58  opens due to the force exerted by pump  35  during normal cooling. When pump  35  turns off, line pressure decreases and check valve  58  reseats to a block position.  
         [0032]    Excess flow valve  56  is also commonly referred to as a velocity valve, a line rupture valve, or a flow fuse. Excess flow valve  56  closes during counterrecoil to prevent an in rush of fluid into the recoil module  22  since check valve  58  will be open. A vacuum condition downstream of valve  56  induces flow in excess of the valves operating requirements. This closure prevents excess fluid levels in the recoil chamber which would prevent the recoiling mass from regaining pre-fire positioning.  
         [0033]    The return valve block  52 , disposed proximate the end of recoil chamber  63 , contains a check valve  68 , a pilot operated check valve  67  and a mechanically operated two position, two port, cartridge style directional control valve  66 . Return valve block  52 , cylindrical in shape, forms a barrier between the recoil chamber  63  and the replenisher  75 . A counterrecoil buffer  72  extends axially from the center of return valve block  52  into the recoil chamber  63 . Piston head  62  contains a recessed central region sized so as to accommodate counterrecoil buffer  72  when the gun  14  is in battery.  
         [0034]    Check valve  68 , which acts as a relief valve, is normally in a closed position. It forms a bubble tight seal if return line  46  becomes severed, thus preventing loss of fluid or ingestion of air. The cracking pressure of check valve  68  is set above the maximum spring induced replenisher pressure. Check valve  68  is only open during normal cooling when the TDS pump  35  is operating. Check valve  68  reseats when pump  35  is turned off.  
         [0035]    Disposed upstream from check valve  68  is pilot operated check valve  67 . The main purpose of pilot operated check valve  67  is to close during the last few inches of the counterrecoil cycle when directional control valve  66  is activated but piston head  62  is still moving. The pilot port  64  is disposed approximately four inches from the piston head&#39;s  62  in battery position. During the end of counterrecoil the pressure at pilot port  64  will be at a vacuum thus closing valve  67 .  
         [0036]    When counterrecoil is complete, the piston head  62  will activate the mechanically operated two position, two-port directional control valve  66 . While in battery, valve  66  allows circulation for cooling. The two way, two-port directional control valve  66  is disposed immediately upstream from the pilot operated check valve  67 . Its mechanical plunger extends into the recoil chamber  63 . Due to the stroke distance of the plunger, which transitions valve  66  from open to closed, a time delay exists thus necessitating pilot operated check valve  67 .  
         [0037]    In the event that the supply line  44  is compromised due to TDS  30  failure or damage from an opposing force, the present invention must minimize the loss of hydraulic fluid and prevent the ingestion of air into the recoil module  22 . Upon loss of the supply line  44 , the inlet check valve  58  will immediately record the pressure drop which will allow the spring within the check valve  58  to block that line. Inlet check valve  58  will remain closed until repairs have been made. When the supply line  44  fails there is no longer any circulation during the static mode of the recoil cycle so outlet check valve  68  also remains closed.  
         [0038]    In the event of a return line  46  failure, commencement of the isolation mode is dependent on whether or not the recoil coolant pump  35  is circulating fluid through the recoil module  22  at the moment of failure. As described above, the return line isolation system  59  blocks fluid flow to the TDS  30  during recoil and counter recoil. However, circulation does occur for cooling during the static mode when the pump  35  is activated. In a worst case scenario, if return line  46  is compromised while in a static mode with pump  35  running, hydraulic fluid will be lost until pump  35  runs dry and a pressure drop occurs in recoil chamber  63  resulting in check valve  66  closing. It may require up to 30 seconds for pump  35  to run dry. Check valve  68  will then remain closed until replacement or repairs are effectuated to the system. If return line  46  is compromised when the pump  35  is off, check valve  68  will already be blocking hydraulic fluid flow.  
         [0039]    Although an embodiment of the invention has been illustrated in the accompanying drawings and described in the foregoing specification, it is especially understood that various changes such as in the relative dimensions of parts and materials used, modifications and adaptations, and the same are intended to be comprehended within the meaning and range of equivalent to the claims.