Abstract:
A lubricating oil supply system for internal combustion engine includes an oil reservoir and oil pump connected with a lubrication distribution network including a piloted pressure relief valve which selectively controls the pressure within the distribution network to at least one pressure value that is less than the maximum pressure produced by a primary pressure relief valve associated with the oil pump, while also protecting the lubrication distribution network from an unwanted overpressure condition.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    None. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an internal combustion engine lubrication system in which maximum pressure within the lubrication system is controlled by a dual mode pressure limiting valve. 
         [0004]    2. Related Art 
         [0005]    Pressure-lubrication has been used with automotive internal combustion engines for many years. Typically, a single pressure relief valve is used to limit the maximum pressure developed by an oil pump. The relief pressure is usually set at a fairly high value, in order to assure that the engine receives adequate lubrication in all operating regimes from idle to maximum speed-load operation. Unfortunately, this causes the lubrication pump&#39;s energy consumption to be higher than would otherwise be ideal, because in many operating regimes, only a reduced volume and pressure of oil is required by the engine. 
         [0006]    US Patent Publication 2002/0083915 discloses a system in which a minimum oil pressure is established by a mechanically operated valve, with an electrically operated valve positioned in the mechanical valve&#39;s relief port such that the system pressure may be increased through closure of the electronically operated valve. This system suffers from the drawback that the electrically operated valve does not have a fail-safe position. In the event that the electrically operated valve fails in an open position, only minimal oil pressure would be available to sustain the engine, and such minimal oil pressure would undoubtedly be inadequate to support the engine during high speed and load operation. On the other hand, if the electrically operated valve fails in a closed position, the resulting excessive oil pressure may damage or destroy the engine by causing the oil filter to rupture, with a consequent loss of all oil overboard. In other words, any failure of the electronic valve could lead to engine failure. In another vein, the reliability of the electrically operated valve is compromised because only unfiltered oil flowing from the oil pump passes through the valve, and foreign matter carried by the unfiltered oil may cause the valve to stick or wear excessively. 
         [0007]    It would be desirable to provide an internal combustion engine lubrication system in which an engine is reliably protected with a redundant high pressure mechanical relief valve, combined with the capability of reducing the oil pressure so as to promote fuel economy improvement during operating regimes in which maximum oil pressure and flow are unneeded. 
       SUMMARY OF THE INVENTION 
       [0008]    According to an aspect of the present invention, a lubricating oil supply system for an internal combustion engine includes an oil reservoir and an oil pump for pressurizing oil from the reservoir. A lubrication distribution network is connected with the oil pump. A primary pressure relief valve is connected to the distribution network downstream from the oil pump. The primary pressure relief valve limits oil pressure within the distribution system to a maximum permissible value. A pilot-controlled, dual mode pressure relief valve, operatively connected with said distribution network downstream from said primary pressure relief valve, selectively controls the pressure within said distribution network to a minimum pressure which is less than the highest pressure produced by the primary pressure relief valve. 
         [0009]    According to another aspect of the present invention, a dual-mode, piloted pressure relief valve, operatively connected with an oil distribution network downstream from a primary pressure relief valve, controls the pressure within the distribution network by returning oil from the distribution network to the oil reservoir, with the piloted pressure relief valve having a first operating mode, in which a pilot valve is energized, wherein the piloted pressure relief valve limits the pressure within the distribution network to a first pressure which is less than the highest pressure produced by a primary pressure relief valve, and a second operating mode, in which the pilot valve is not energized, wherein the piloted pressure relief valve limits the pressure within the distribution network to a second pressure value which is greater than the first relief pressure. 
         [0010]    It is an advantage of a lubricating oil supply system according to the present invention that engine fuel consumption may be reduced by minimizing parasitic losses associated with an engine driven lubricating oil pump, while at the same time safeguarding the engine&#39;s integrity, by using a piloted pressure relief valve having a normally closed pilot valve, such that if the pilot valve operating system fails, the engine oil pressure will be maintained at a safe level for all engine operating modes and regimes. 
         [0011]    It is another advantage of a system according to the present invention that the piloted pressure relief valve of the present invention may be mounted externally upon the engine, as opposed to the known conventional practice of mounting of relief valves deep inside an engine, such as in an engine oil pump, rendering such valves relatively inaccessible for service purposes. 
         [0012]    It is yet another advantage of a system according to the present invention that the piloted pressure relief valve of the present invention may be located downstream from an oil filter, thereby protecting the pressure controller from oil-borne contamination. 
         [0013]    It is yet another an advantage of a system according to the present invention that the inventive piloted pressure relief valve has a dual mode feature, whereby the piloted valve may be used to limit maximum lubrication system pressure in the event that a primary relief valve fails in a closed position. 
         [0014]    It is yet another an advantage of a system according to the present invention that flow of lubricating oil through an engine will not be diminished when the present dual mode valve is not operating in a pressure limiting mode. 
         [0015]    Other advantages, as well as features of the present invention, will become apparent to the reader of this specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic representation of an internal combustion engine having a lubricating oil supply system according to the present invention, in a normal operating condition. 
           [0017]      FIG. 2  is a partially schematic representation of a piloted pressure relief valve used in an engine lubrication supply system according to an aspect of the present invention, operating in a high pressure, redundant relief condition. 
           [0018]      FIG. 3  shows the valve of  FIG. 2  operating in a fail-safe pressure relief mode. 
           [0019]      FIG. 4  is similar to  FIG. 3  but shows the valve of  FIG. 3  operating in a low pressure, fuel saving condition, as opposed to the higher pressure operation shown in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    As shown in  FIG. 1 , an engine,  10 , has an oil reservoir,  14 , extending below a cylinder block,  28 , and a cylinder head,  26 . A lubrication distribution network,  22 , is connected with an oil pump,  18 . Those skilled in the art will appreciate in view of this disclosure that oil pump  18  could comprise either a gerotor type pump either driven concentrically by an engine crankshaft, or a gear pump or gerotor pump, typically mounted to the engine&#39;s cylinder block and driven by either a camshaft or another rotating component of the engine, or yet other types of pump arrangements. Such detail is committed to those wishing to employ the inventive oil supply system described and claimed herein. 
         [0021]    The present lubricating oil supply system includes not only oil reservoir  14 , oil pump  18 , and lubrication distribution network  22 , but also a primary pressure relief valve,  34 , employed to limit the oil pressure within distribution network  22  to a maximum permissible value. In other words, pressure relief valve  34  clips the oil pressure to a predetermined maximum value. This protects, for example, oil filter  38  from destruction were the oil pressure to be too high during cold operation at higher engine speeds. 
         [0022]    The present system also includes a pilot-controlled, dual mode pressure relief valve,  60 . Valve  60  is operatively connected with distribution network  22  downstream from primary relief valve  34  and preferably downstream from oil filter  38 . 
         [0023]    In the absence of any signal from controller  50 , valve  60  functions as a normally closed pressure relief valve having a pressure setting which approximates the setting of primary relief valve  34 . Thus, the lubrication system will function as shown in  FIG. 1 , with the normal pressure relief function being handled by primary relief valve  34 . Valve  60 , however functions as a backup maximum pressure valve as follows. Turning to  FIG. 2 , valve  60  is shown as having a body,  64 , with a normal, full-flow passage,  68 . When valve  60  is not energized, oil will continue to flow through valve  60  without any diminution because full-flow passage  68  offers no significant restriction to flow. 
         [0024]      FIG. 2  illustrates a condition in which controller  50  is not providing a signal voltage to opening coil  72  of valve  60 . Operating plunger  82  is urged in the direction of closing by the force of a resilient element, illustrated as spring  88 . Spring  88  is selected so that operating plunger  82  remains in its closed position unless the pressure differential acting upon plunger  82  exceeds a predetermined first pressure which is less than the pressure setting of primary relief valve  34 . When there is no opening force from opening coil  72 , control ball  100  is pushed to its closed position by the force of spring  96  acting through armature  92 . Spring  96  is selected to maintain ball  100  in its closed position unless the pressure acting upon ball  100  exceeds a predetermined second pressure which is preferably slightly above the relief pressure of primary relief valve  34 . Accordingly, valve  60  acts as a backup pressure relief valve to keep system pressure from increasing to an unwanted level. In a preferred embodiment, valve  60  will be set to relieve at a pressure slightly above the relief pressure of primary relief valve  34 . 
         [0025]    In the condition illustrated in  FIG. 2 , spring  88  is able to maintain operating plunger  82  in its closed position during normal lubrication system operating pressures because bleed orifice  84  causes the pressure of oil acting within distribution network  22  act equally on both the active side of plunger  82 , which is exposed to the pressure within passage  68 , and the control side, which is exposed to hydraulic control pressure and the pressure of spring  88 . If, however, the pressure within lubrication network  22  increases above the second pressure setting, control ball  100  will be forced off its seat against the force of spring  96 , which acts upon control armature  92 . In essence, control ball  100  and spring  96  function as a secondary maximum pressure relief valve, providing redundant protection against system overpressure. 
         [0026]    Once control ball  100  has been displaced from its seat due to an overpressure episode, the pressure at the control side of operating plunger  82  decreases and operating plunger  82  opens to allow oil to flow into outlet passage  80 . This condition is shown in  FIG. 3 . When valve  60  is operating in this mode, the pressure within lubrication distribution network  22  is determined by the sizing of spring  88  and outlet passage  80 , as well as by the sizing of control orifice  104  and spring  96 . While operating in the emergency pressure limiting mode, ball  100  will be unseated from orifice  104  by only a small amount, as shown in  FIG. 3 . 
         [0027]    The operating mode depicted in  FIG. 4  is achievable through electronic control of opening coil  72 , which is connected with controller  50 . Energization of coil  72  displaces armature  92  in a direction away from control orifice  104 , allowing control ball  100  to permit flow through passage  106  and into reservoir  14 . Because orifice  104  and passage  106  are much larger than bleed orifice  84 , the control pressure within bore  86  will be much less than the pressure within passage  76 , thereby allowing operating plunger  84  to be pushed open against the force of spring  88 , bypassing oil and reducing the oil pressure to the first pressure setting. Those skilled in the art will appreciate in view of this disclosure that the pilot function of the present device is implementable not only with the illustrated spring-loaded ball and plunger, but alternatively by a fluidically or electronically controlled spool valve. 
         [0028]    As shown in  FIG. 1 , valve  60  is placed downstream from primary relief valve  34 . When valve  60  is operating in the condition of  FIG. 4 , oil pump  18  is required to do less work because oil is pumped against a lower head. Because valve  60  is normally closed, a loss of signal from controller  50  will merely cause the lubrication system to revert to a maximum pressure system controlled by not only by primary pressure relief valve  34 , but also by the previously described pressure relief function of valve  60 . This protects the integrity of engine  10 . 
         [0029]    Although oil is bypassed at a lower pressure by valve  60 , adequate oil pressure is provided to cylinder head  26  and to crankshaft bearings  30  because valve  60  is opened by controller  50  only during the several operating regimes in which it is not necessary to provide maximum oil pressure to sustain appropriate engine life. In fact, in many operating regimes such as those characterized, for example, by operation at less than half of the engine&#39;s maximum load, oil pressure may be significantly reduced while still providing adequate lubrication to the engine. 
         [0030]    Valve  60  is preferably mounted to an external surface of engine  10 , such as an outer surface of cylinder block  28 . Such external mounting is shown in  FIG. 1 . This will permit relatively easy access to valve  60  for the purposes of repair or adjustment, without the necessity of removing engine hardware such as the oil pan or front cover. In a preferred embodiment, valve  60  is mounted upstream of any of crankshaft bearings  30 . 
         [0031]    The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and fall within the scope of the invention. Accordingly the scope of legal protection afforded this invention can only be determined by studying the following claims.