Abstract:
Lubricating oil system for a combustion engine, in particular for industrial or commercial vehicles, the system comprising a bypass connection suitable to bypass an oil pump associated to an engine oil circuit, a controllable valve suitable to adjust an amount of oil to be bypassed through the bypass connection, control means controlling the controllable valve, programmed to control said controllable valve as a function of the combustion engine speed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to European Patent Application No. 14175218.8 filed Jul. 1, 2014, the entirety of the disclosures of which are expressly incorporated herein by reference. 
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not Applicable. 
     FIELD OF THE INVENTION 
     The present invention relates to a lubricating oil system for a combustion engine, in particular for industrial and commercial vehicles. Moreover, the present invention, relates to an engine braking system associated to said lubricating oil system, a method for adjusting an oil pressure in a lubricating oil system of a combustion engine, and commercial or industrial vehicles comprising a combustion engine implementing said oil lubricating system. 
     DESCRIPTION OF THE PRIOR ART 
     The lubricating oil system drains power from the combustion engine in order to execute its task to pump the oil through the several components of the combustion engine, in order to lubricate the components subjected to frictions and to cool the pistons. 
     The oil pumps usually are suitable to reach pressures of 4-6 bar, that could be high in comparison with normal operative conditions. In addition, the pressure within the oil circuit can change according to the oil temperature, that influences the oil viscosity. 
     For this reason a bypass path is usually provided coupled with a loaded spring valve in order to limit the oil pressure. 
     In order to limit the power drained by the combustion engine, it is known the possibility to implement variable displacement pumps, suitably to adapt the oil pressure according to the operative condition of the engine. 
     This task is usually reached by varying the pump geometry or by controlling its speed. 
     However, the variable pump have a really high cost in comparison with the traditional (non-controllable) pumps and, in addition, they show a high sensitivity to the impurity contained in the oil itself. Indeed, the variable oil pumps are much more sensitive to oil contamination and installation due to possible block/bedplate misalignments. In addition, their durability for 1.6 mio. km is not yet proven. 
     Therefore, the implementation of variable pump implies the increasing of the engine managing costs in spite of theoretical reduction of fuel consumption and pollutant emission. 
     SUMMARY OF THE INVENTION 
     Therefore it is the main object of the present invention to provide a lubricating oil system for a combustion engine, in particular for industrial and commercial vehicles, which overcomes the above problems/drawbacks. 
     In particular the system of the proposed invention is suitable to reduce the fuel consumption, by maintaining a high reliability of the combustion engine as a whole. 
     The main principle of the invention is the implementation of a bypass path through a controllable valve, whose state is controlled as a function of the engine speed and load. 
     Thanks to the present invention the pump can be a traditional oil pump, namely a non-controllable pump, associated with the engine lubricating oil circuit. 
     Nevertheless, a variable pump can be associated with the present invention in order to improve the responsiveness of a variable pump. 
     Preferably, such function implements a run-time engine model in order to calculate an expected oil pressure within the oil lubricating circuit or a map having as first input the engine speed, as second input the engine BMEP (brake mean effective pressure) and as output said expected oil pressure in the oil lubricating circuit. 
     The BMEP value to enter said map can be obtained in several known ways. 
     According to a preferred embodiment of the invention, the controllable valve state is adjusted according to a pressure feedback signal acquired in a point of the lubricating oil circuit. 
     Advantageously, the losses through the bypass path are small in comparison with the losses through the combustion engine, therefore, energy spent to circulate the oil through the bypass path is small too and the system shows nearly the same energy consumption behavior as a variable pump system, without its drawbacks. 
     These and further objects are achieved by means of the attached claims, which describe preferred embodiments of the invention, forming an integral part of the present description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will become fully clear from the following detailed description, given by way of a mere exemplifying and non limiting example, to be read with reference to the attached drawing figures, wherein: 
         FIGS. 1 and 2  show two preferred embodiment of the present invention, 
         FIG. 3  show an example of map for controlling the actuated valve of the  FIGS. 1 and 2 . 
     
    
    
     The same reference numerals and letters in the figures designate the same or functionally equivalent parts. 
     According to the present invention, the term “second element” does not implies the presence of a “first element”, first, second, etc. are used only for improving the clarity of the description and should not be interpreted in a limiting way. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  show preferred embodiments of the present invention. 
     A non-controllable pump P is connected to an engine oil circuit OC, preferably between the oil sump OS and the combustion engine to be lubricated/cooled, hence it pumps the engine lubricating oil from the oil sump OS towards the engine components E through a so called “main circuit”, then the oil falls within the oil sump OS to be circulated continuously. 
     A bypass path BP connects the output door of the pump P with its input door. A controllable valve CV is arranged on the bypass path BP. Therefore, this controllable valve is a 2-ways valve. 
     According to a preferred embodiment of the invention, the valve is a spring loaded valve, controllable by an actuator, for example, the pre-load of the spring is controllable by the actuator. 
     According to another embodiment of the invention, a fixed-load-spring valve is coupled with a controllable valve. 
     A control unit ECU, preferably defining the same control unit controlling the combustion engine, acquires as inputs the engine speed and controls the state of the controllable valve CV in order to adapt the oil pressure, within the combustion engine, as a function of said engine speed. 
     According to a preferred embodiment of the present invention, the control unit acquires also the current BMEP and through a model base calculation or a map, calculates/extracts a reference oil pressure to be maintained within the lubricating oil circuit.  FIG. 3  shows an example of map where the X-axis refers to the engine speed revolutions, the Y-axis, the BMEP and according to each of couple of values is found a curve or the closest curve indicating the optimal oil pressure. In the example curves P 1  is 1 bar, P 2  is 1.5 bar, P 3  is 2 bar and P 4  is 2.5 bar. 
     According to another preferred embodiment of the invention, also the oil temperature is accounted for, by the control unit, in order to calculate/extract a reference oil pressure to be maintained within the lubricating oil circuit. Therefore, the sensor S indicated in  FIGS. 1 and 2  could be implemented a pressure sensor or an oil flow and eventually also a temperature sensor in order to implement closed loop control schemes. 
     In any case, the control unit controls the state of the controllable valve CV in order to control the engine oil pressure, namely the oil pressure in at least one point of the engine. 
     Preferably,  FIG. 3  refers to the reference pressures measured at the main circuit of the engine, namely the duct downstream the pump P, before its subdivision into several channels. However, the map of  FIG. 3  can be redrawn according to a specific measurement point within the oil circuit. 
     In any engine operating point, at any actual oil temperature, the oil pressure can be controlled or steered. This allows to adapt the oil pressure in general and especially to reduce the energy absorbed by the pump in order to save fuel consumption, without mandatorily introducing a variable pump that is prone to frequent failures. 
     As alternative to the pressure sensor, an oil flow sensor can be implemented. In such a case the  FIG. 3  can be modified in order to express the oil flow curves instead of the oil pressures ones. 
     The figures herewith attached refer to one single non-controllable oil pump. However, the present invention can be equally implemented by using two or more separate oil circuits with at least one of them arranged according to the present invention. 
     According to a preferred implementation of the present invention, the present scheme is adopted at least for supplying the engine brake actuation. 
     The actuation of the hydraulic engine brake needs really short times, typically less than 0.8 seconds with high pressure, namely in the order of 4 bars. 
     If the highest pressure value of the map of  FIG. 3  is compared with this value of 4 bar, it is immediately clear that the reaction of oil system pressure should be really fast. 
     According to the present invention, it is possible to obtain such pressure variation in less than 0.2 seconds, much quicker than it can be reached with a variable pump. 
     Therefore, the present invention can be advantageously implemented in connection with a variable pump. 
     Another advantage of the present invention is the fact that the pressure can be controlled in a so refined way, that it can be possible to reduce the impact of clearances or machining tolerances without compromising the bearings wear. 
     This advantage can be favorably exploited for added WHR-systems and/or power turbines, that are really sensible to lubricating issues. 
     The opening of the bypass path induces to reduce oil pressure in the main circuit, hence less pressure losses in oil filter and oil cooler, because the bypassed oil does not flow through this components. 
     Eventually, the fixed pump flow is not changed, however the superfluous oil flow is bypassed. 
     The difference, in terms of fuel consumption (BSFC gain) between the present solution and the implementation of a variable pump alone is negligible, but the cost of the variable pump is considerably higher and its reliability is a strong issue. 
     The controllable valve CV, according to the example on  FIG. 1 , is realized through a rotary sleeve valve V 1  commanded, preferably, through a rotatable electric actuator A 1 , e.g. a stepped drive. 
     The controllable valve CV, according to the example on  FIG. 2 , is realized through an axial sleeve valve V 2  commanded, preferably, by a linear actuator A 2 . 
     It should be clear that several kind of actuators, either pneumatic or hydraulic ones, can be implemented. 
     Furthermore, it should be clear that it is preferred to implement a controllable valve CV suitably to manage several opening intermediate states, or continuously variable states, rather than an ON/OFF valve. 
     This invention can be implemented advantageously in a computer program comprising program code means for performing one or more steps of such method, when such program is run on a computer. For this reason, the patent shall also cover such computer program and the computer-readable medium that comprises a recorded message, such computer-readable medium comprising the program code means for performing one or more steps of such method, when such program is run on a computer. 
     Many changes, modifications, variations and other uses and applications of the subject invention will become apparent to those skilled in the art after considering the specification and the accompanying drawings which disclose preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by this invention. 
     Further implementation details will not be described, as the man skilled in the art is able to carry out the invention starting from the teaching of the above description.