Abstract:
The present invention describes a filter screen for removing debris from the hydraulic actuating fluid in an internal combustion engine having a hydraulic pump for supplying hydraulic actuating fluid to hydraulically-actuated unit fuel injectors. An upper portion of a priming reservoir is mounted on a front cover of the engine. The front cover forms a lower reservoir portion. A screen assembly is positioned adjacent to an interface defining an entrance from the upper reservoir portion to the lower reservoir portion. The screen assembly includes a filter screen enclosing the entrance to force the actuating fluid to pass through the filter screen, thus retaining debris that exceed the mesh size of the filter screen.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of nonprovisional application Ser. No. 09/391,172, having a filing date of Sep. 7, 1999 which is related to Provisional Application Ser. No. 60/129,976 filed in Apr. 19, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to hydraulic systems for internal combustion engines. More particularly, this invention relates to hydraulic stems having a combination filter screen and gasket to remove debris from the hydraulic fluid in a fuel injection system with a high-pressure pump and a priming reservoir. 
     BACKGROUND OF THE INVENTION 
     In engine manufacturing, metal chips and other debris may remain in the engine even when engine parts are cleaned prior to assembly. By their nature, fittings with tapered thread connections create metal chips when assembled into a threaded hole. Machining also may leave metal chips. Casting processes may leave other debris in core passages and crevices. As a result, engines inevitably have some debris inside deep-drilled holes, cast-in core passages, and other places. During engine operation, the heating and cooling of the engine releases this debris into the hydraulic fluid. As the hydraulic fluid flows, the metal chips and other debris move throughout the hydraulic system. 
     The metal chips and other debris may interfere with proper operation of the engine. This interference is more problematic for engines with hydraulically actuated fuel injection systems. In these engines, a priming reservoir typically is disposed at a level higher than the inlet to the high-pressure pump. The priming reservoir includes a lower reservoir portion usually cast into the engine front cover. An upper reservoir portion is attached to the lower reservoir portion to increase the reservoir volume. A gasket seals the lower and upper reservoir portions. The priming reservoir provides gravity feed to the pump during engine start-up. Any debris in the hydraulic fluid tends to accumulate in the priming reservoir. On engine start-up, the pump drives accumulated debris throughout the hydraulic system. While the engine is running the pump continues to drive debris through the hydraulic system. 
     Debris in the hydraulic fluid may obstruct sensors, valves, and other parts of the hydraulic system and, especially, the hydraulic-actuating portion of the fuel injector system. Metal chips may clog injector pressure regulators, high-pressure pumps, injectors, and pressure control valves because these parts typically are manufactured to very close tolerances. Even though some parts (e.g., the pressure control valve) have internal filters (e.g., an edge filter), too much debris may clog and prevent proper function of these filters. 
     Accordingly, there is a need for a filter screen to remove debris from the hydraulic fluid of an internal combustion engine, especially those with hydraulically actuated fuel injection. 
     SUMMARY OF THE INVENTION 
     The present invention provides a hydraulic system with a filter screen for removing debris from hydraulic fluid in an internal combustion engine. The filter screen is disposed between the upper and lower reservoir portions which form a priming reservoir for the hydraulic system. In the engine, an upper reservoir structure may be mounted on a front cover at an interface. The front cover forms the lower reservoir and has a top edge with a depression. The upper reservoir structure forms the upper reservoir and has a bottom edge. The top and bottom edges form the interface. 
     The filter screen is located at the interface and may have a gasket and a screen assembly. The gasket is located along the interface inside the depression for sealing the upper reservoir structure to the front cover. The depression&#39;s depth and the gasket&#39;s thickness control the “squeeze” on the gasket. 
     The screen assembly has a plate member located at the interface for connecting with the gasket. The plate member forms an aperture having a cross-section area. A filter screen is connected to the plate member for enclosing the aperture. 
     In one embodiment, the plate member is integrally connected to the gasket. The plate member has bonding holes along its periphery. When the gasket is formed on the plate member, the gasket material fills the bonding holes to mechanically connect the gasket to the plate member. The edges of the plate member may be treated with a bonding agent to chemically bond the gasket to the plate member. 
     In another embodiment, the plate member is not integrally connected to the gasket. The loose gasket is placed in the depression at the top edge of the front cover. The plate member is positioned inside the gasket and between the upper reservoir structure and the front cover. The plate member is thinner than the depth of the depression, but extends to contact the gasket along its periphery. Once assembled, the gasket deforms to create a face seal between the upper reservoir structure and the front cover. The gasket also seals around the edges of the plate member. 
     In either embodiment, the filter screen separates the upper and lower reservoirs, forcing the hydraulic fluid to pass through the filter screen. The filter screen retains any debris in the hydraulic fluid larger than the filter screen&#39;s mesh size. 
     The filter screen has an open area large enough to provide the desired pressure drop for operation of the pump. Consequently, the filter screen may have a surface area larger than the cross-section area of the aperture. If so, the filter screen has an open end and a closed end. As shown, the filter screen has a cylindrical shape. However, it may have other shapes including conic, rectangular, or flat. In addition, the filter screen has a mesh size to retain particles large enough to cause damage to the hydraulic system or other parts. The screen assembly may have a flange for connecting the filter screen to the plate member. A flange would facilitate producing a solid weld for joining the filter screen to the plate member. 
     In another embodiment, the plate member may have a basket assembly. The basket assembly mechanically supports and may be connected to the filter screen. The basket assembly, the plate member, and the filter screen may be a single part. While the screen assembly may be made from other materials and combinations of materials, the basket assembly is preferred when the screen assembly is made of plastic. 
     The following drawings and description set forth additional advantages and benefits of the invention. More advantages and benefits are obvious from the description and may be learned by practice of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be better understood when read in connection with the accompanying drawings, of which: 
     FIG. 1 is a front perspective view of an engine with a filter screen and gasket according to the present invention; 
     FIG. 2 is a top view a gasket and screen assembly disposed on a front cover according to the present invention; 
     FIG. 3 is a side view a filter screen and gasket disposed in a priming reservoir according to the present invention; 
     FIG. 4 is a top view of a gasket and screen assembly according to the present invention; 
     FIG. 5 is a top view of a screen assembly according to the present invention; 
     FIG. 6 is a side view of a screen assembly according to the present invention; 
     FIG. 7 is a cross-sectional view of the gasket at section B—B in FIG. 4 according to the present invention; 
     FIG. 8 is a perspective view of an alternate screen assembly according to the present invention; 
     FIG. 9 is a top view of a gasket according to another embodiment of the present invention; and 
     FIG. 10 is a top view of a screen assembly according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows an internal combustion engine  10  having a V-configuration. The engine  10  has a hydraulically actuated electronically controlled unit injection (HEUI) fuel system including a priming reservoir. The engine  10  has an upper reservoir structure  30  mounted on a front cover  14  at an interface  46 . As seen in FIG. 3, a high-pressure hydraulic pump  12  is mounted to the rear side of the engine front cover  14 . The high-pressure hydraulic pump  12  supplies hydraulic-actuating fluid, preferably lubricating oil, to the fuel injectors. The hydraulic pump is driven by a gear train (not shown) located within the front cover  14 . 
     In FIGS. 2 and 3, the front cover or lower portion  14  forms a lower reservoir  16  defined by a lower front wall  18 , lower side walls  19 , a lower rear wall  20 , and a bottom wall  22 . Preferably, the front cover  14  is made of cast iron. However, other suitable materials and forming methods may be used. The front cover  14  has a top edge forming a lower opening at interface  46 . The top edge has a depression  44 . 
     A lower reservoir supply passage  26  is cast as part of the front cover  14 . The lower reservoir supply passage  26  is even with the top edge of the front cover  14 . The depression  44  surrounds the lower reservoir supply passage  26  along the top edge. The lower reservoir supply passage  26  connects to the engine lubricating oil pump (not shown). The engine-lubricating pump supplies lubricating oil to the reservoir and hydraulic pump  12 . 
     The upper reservoir structure  30  is mounted on the front cover  14  at the interface  46 . The upper reservoir structure  30  forms an upper reservoir  35  defined by upper front wall  32 , upper sidewalls  33 , an upper rear wall  34 , and an access cover  36 . The upper reservoir  35  is larger than the lower reservoir  16 . Preferably, the upper reservoir structure  30  is made from cast iron. However, other materials and forming methods made be used. The upper reservoir structure  30  has a bottom edge forming an upper opening at interface  46 . 
     An upper reservoir supply passage  28  is cast as part of the upper reservoir structure  30 . The upper reservoir supply passage  28  is even with the bottom edge and terminates adjacent to the access cover  36 . The upper reservoir supply passage has an outlet  40 , which opens to the upper reservoir  35 . 
     When the upper reservoir structure  30  is mounted on the front cover  14  at interface  46 , the upper front wall  32  meets lower front wall  18 . The upper sidewalls  33  meet the lower sidewalls  19 . The upper rear wall  34  meets the lower rear wall  20 . The upper reservoir supply passage  28  mates with the lower reservoir supply passage  26  to form one continuous reservoir supply passage. The upper opening meets the lower opening to form a priming reservoir along the inner periphery of the upper reservoir structure  30  and front cover  14 . The priming reservoir permits fluid communication between the upper and lower reservoirs. 
     Adjacent to the bottom wall  22 , a passage  24  intersects the reservoir portion  16 . The passage  24  connects to a fluid supply inlet (not shown) of the hydraulic pump  12 . In addition, an air bleed and overflow drain passage  27  extends between the upper reservoir structure  30  and the front cover  14  as partially shown FIG.  2 . The depression  44  surrounds the air bleed and overflow drain passage  27  along the top edge. 
     In FIGS. 2 and 3, a filter gasket  50  seals the interface  46  between the front cover  14  and the upper reservoir structure  30 . The filter gasket  50  includes a gasket  42  and a screen assembly  70 . The gasket  42  is preferably silicone rubber, but it may be made from another suitable sealant materials. The gasket  42  has an elongated circular cross section for disposing in the depression  44 . The gasket  42  surrounds the entire periphery of the interface  46 , the reservoir supply passage  26 ,  28 , and the air bleed and overflow drain passage  27 . As shown in FIG. 4, the gasket  42  has a reservoir gasket portion  54  surrounding the periphery of the reservoir. 
     As seen in FIGS. 4-6, the screen assembly  70  has a filter screen  76  connected to a plate member  56 . The filter screen  76  is cylindrical and has an open end  72  and a closed end  78 . The cylindrical shape has a large surface area for trapping debris. Filter screen  76  may be another shape including conic, rectangular, and flat. When filter screen  76  is cylindrical, the open end  72  preferably faces the direction of the fluid flow. When filter screen  76  is conic, closed end  78  preferably faces the direction of the fluid flow. The orientation of the screen reduces the adverse effects of debris build-up on the screen. For example, if the open end of a cone-shaped filter screen faces the direction of the fluid flow, the build-up of debris at the tip of the cone blocks the mesh on both sides of the screen. 
     Filter screen  76  has a mesh size based on the particle size to be excluded. The finer the mesh size, the more debris retained by the filter screen  76 . However, it is not necessary to retain all particles in the hydraulic fluid. Some particles are small enough to flow through the small orifices of the control valves and other engine parts without getting stuck. A screen with a 140 micron mesh size retains the larger, dangerous particles while permitting the smaller, inconsequential particles to pass. 
     In addition, the mesh size and the desired pressure drop across the screen determine the open area of filter screen  76 . At temperatures near −20° F., a pressure drop of less than 5 psi is desired for proper operation of the high pressure pump  12 . The desired pressure drop may require a screen with a large surface area, i.e. open area. Consequently, the filter screen  76  may need a cylindrical, conic, or some other non-flat shape in order to fit within the reservoir. The reservoir may be reconfigured so a flat screen with sufficient surface and open areas could be used to provide the desired pressure drop. 
     The plate member  56  has a solid, planar structure. It is configured to extend beyond the periphery of the reservoir and contact the reservoir gasket portion  54 . The plate member  56  forms an aperture  62 . While different shapes and dimensions may be used, aperture  62  has essentially the same shape and inside dimensions as the filter screen  76 . A flange  66  may be used to connect the filter screen  76  to the plate member  56 . If no flange is used, the filter screen  76  connects directly to the plate member  56 . If a flange is used, the plate member  56  preferably forms the flange  66  along the peripheral edge of aperture  62 . The flange  66  also may be a separate attachment to the plate member  56 . Flange  66  enables a solid weld or other connection between the filter screen  76  and plate member  56 . Accordingly, the plate member  56  forms a barrier between the lower reservoir  16  and the upper reservoir  35 , forcing fluid communication through the filter screen  76 . 
     Alternatively, the plate member  56  forms a basket assembly  80  for holding and supporting the filter screen  76  as shown in FIG.  8 . The basket assembly  80  has support arms  82  and a support ring  84 . The support arms  82  and the support ring  84  mechanically support the filter screen  76 . The filter screen  76  may be attached to the basket assembly  80 . 
     The plate member  56  and the filter screen  76  may be made from steel, aluminum, plastic, other materials, or a combination. In one embodiment, the plate member  56  is made from black-oxide coated, carbon steel plate. The filter screen  76  is made from stainless steel and is welded to the flange  66  formed on the plate member  56 . If used, the basket assembly  80  is made from the black-oxide coated, carbon steel plate. The stainless steel screen may be welded to the basket assembly  80 . 
     In another embodiment, the plate member  56  and the filter screen  76  are made of plastic. When plastic is used, it is preferable to have the basket assembly  80  as part of the plate member  56 . The plastic screen may be integrally formed with the plate member  56  and basket assembly  80  when they are molded from the plastic. The plate member  56  and the basket assembly  80  may be a single part. 
     Preferably, the plate member  56  is integrally incorporated into the reservoir gasket portion  54  as shown in FIG.  4 . As shown in FIG. 5, a plurality of bonding holes  58  are disposed adjacent to and along the periphery of plate member  56 . When gasket  42  is made, plate member  56  is positioned inside an injection mold so the gasket material forms the reservoir gasket portion  54  along the periphery of plate member  56 . Upon injection, the material used to make gasket  42 , essentially fills the bonding holes  58 . Once set, the material in the bonding holes  58  remains in contact with and is part of the gasket  42 . As a result, the gasket  42  is mechanically bonded to the plate member  56 . To assist the plastic forming process, the plate member has a locating bump  60  for positioning the plate member  56  in the injection mold. The edges of plate member  56  may be coated with a bonding agent to chemically bond the reservoir gasket portion  54  to the plate member  56 . 
     Without the plate member  56 , it is very difficult to attach gasket  42  directly to the filter screen  76 . The gasket material bleeds through the screen openings upon injection into the mold. Other methods do not provide a suitable connection. A solid plate attached to both sides of the screen shuts-off the material flow. A leak path could develop between the plates and the screen when the screen is held in the mold by the edges. A hole or bump in the screen or the plate allows the gasket material to bleed through the plates and onto the screen. 
     In contrast, the plate member  56  avoids these problems. It enables the filter gasket  50  to be a single part having the filter screen  76  integrally-connected to the gasket  42 . The plate member  56  also separates the upper and lower portions  16 ,  35 . Consequently, it forces the hydraulic fluid to flow through the filter screen  76 . 
     In an alternate embodiment, the plate member  56  is not integrally formed with the reservoir gasket portion  54  as shown in FIGS. 9-10. The screen assembly  70  and the gasket  42  are separate pieces. Consequently, there is no need for the bonding holes  58  and the locating bump  60  on the plate member  56 . When the upper reservoir structure  30  is mounted on the front cover  14 , the screen assembly is placed into the opening for the lower reservoir  16 . The periphery of the plate member  56  extends beyond the periphery of the lower reservoir  16  and rests on the top edge of the front cover  14 . The loose gasket  42  is positioned in the depression  44 . The upper reservoir structure  30  is mounted on the front cover  14  sealing the gasket  42  against the plate member  56 . The plate member  56  forms a barrier between the lower reservoir  16  and the upper reservoir  35 , thus forcing fluid communication through the filter screen  76 . 
     While the screen assembly  70  and the gasket  42  may be separate pieces, the filter gasket  50  provides a further advantage when the plate member  56  is integrally-attached to the reservoir gasket portion  54 . The integrally-attached filter gasket makes it impossible to build the engine or system without the filter screen and pass a leak check test. If the filter screen  76  is omitted, there will be a noticeable leak from the missing gasket  42 . 
     In these embodiments, the location of the filter gasket  50  takes advantage of the natural break between the upper reservoir structure  30  and the front cover  14 . However, the filter gasket  50  could be applied in other locations. These locations include other natural breaks between parts forming the reservoir, other natural breaks between parts forming the hydraulic system, and even places where there are no natural breaks between the parts. 
     For example, the filter gasket may be placed between the top of the reservoir and its cover. In this case, the supply to the reservoir needs to enter through the cover. Alternately, the supply could enter an outlet located in the space between the filter gasket and the cover. 
     In addition, the filter gasket  50  may be positioned in places where there is not a natural break between the parts. In these locations, the filter gasket will need some means to hold it in position. The gasket  42  may not be necessary in these locations depending on the means used to hold the filter screen in place. However, the filter still must separate the reservoir or hydraulic section to force the hydraulic fluid through the screen. 
     While the invention has been described and illustrated, this description is by way of example only. Additional advantages will readily occur to those skilled in the art, who may make numerous changes without departing from the true spirit and scope of the invention. 
     Therefore, the invention is not limited to the specific details, representative devices, and illustrated examples in this description. Accordingly, the scope of the invention is to be limited only as necessitated by the accompanying claims.