Engine having a high pressure hydraulic system and low pressure lubricating system

An engine includes a high pressure hydraulic system having a high pressure pump and at least one hydraulically-actuated device attached to an engine housing. A low pressure engine lubricating system is attached to the engine housing and includes a circulation conduit fluidly connected to an outlet from the high pressure pump.

TECHNICAL FIELD 
The present invention relates generally to engines that includes hydraulic 
devices, and more particularly to an engine that utilizes a low pressure 
oil lubricating system and a high pressure hydraulically-actuated device 
system. 
BACKGROUND ART 
Engines have long utilized a variety of devices that draw power directly or 
indirectly from the engine for their operation. Among these devices are 
fuel injectors, gas intake and exhaust valves, exhaust brakes, etc. In the 
past, these devices were typically actuated by a cam that is driven 
directly by the engine. In order to improve engine performance across its 
operating spectrum, there has been a trend in the industry toward the 
adoption of electronically controlled hydraulic devices. An example of 
this trend is the hydraulically-actuated electronically-controlled unit 
injector (HEUI) system utilized by Caterpillar, Inc., of Peoria, Ill., in 
their diesel engines. 
In a typically HEUI system, a high pressure pump maintains a common rail 
containing engine lubricating oil at a relatively high pressure that is 
sufficient to actuate the hydraulic fuel injectors. The high pressure pump 
draws oil from a reservoir that is filled by the engines' low pressure oil 
lubrication circulating pump. After the high pressure oil is utilized by 
the fuel injectors, it is circulated back to the oil pan. Thus, a portion 
of the oil moved by the low pressure oil lubrication pump is circulated 
through the engine for lubrication, and another portion is pumped into the 
reservoir that supplies the high pressure pump. 
In this current system, the high pressure pump is attached to the outside 
of the engine, and thus any noise emitted from the pump is easily 
detectable. In addition, the reservoir that supplies the high pressure 
pump is above the engine's oil pan. This can result in excessive engine 
cranking from a cold start while the low pressure pump provides enough oil 
to the reservoir for the high pressure hydraulic system to achieve the 
relatively high pressures necessary for its operation. Not only does the 
high pressure pump tend to emit noise, but its location on the outside of 
the engine creates a protrusion that undermines the ability to position 
the engine in a confined space. Finally, because the current system uses 
both a low and high pressure pump, there is generally a higher probability 
of failure than if the system could accomplish its tasks with a single 
pump. 
The present invention is directed to these and other problems associated 
with engines that utilize hydraulically actuated devices. 
DISCLOSURE OF THE INVENTION 
In one embodiment, an engine includes an engine housing. A high pressure 
hydraulic system has a high pressure pump, and at least one 
hydraulically-actuated device attached to the engine housing. A low 
pressure engine lubricating system is also attached to the engine housing 
and includes a circulation conduit fluidly connected to an outlet from the 
high pressure pump.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to FIG. 1, an engine 10 includes engine casing 11. An oil pan 
12, which is a portion of engine casing 11, is filled with an amount of 
lubricating oil up to a level therein. Engine 10 includes a low pressure 
lubricating system 19 and a high pressure hydraulic system 18 that both 
use lubricating oil originating from oil pan 12 as their respective 
working fluids. Unlike some previous engine systems, both high pressure 
hydraulic system 18 and low pressure lubricating system 19 share a common 
high pressure pump 30 that draws lubricating oil directly from oil pan 12. 
High pressure pump 30 includes a pump shaft 31 that is preferably driven 
directly by the drive shaft 16 of engine 10. In order to conserve the 
space occupied by engine 10 and reduce pump noise, the pump housing 34 is 
preferably at least partially submerged in oil 13 within oil pan 12. In 
this way, pump 30 preferably includes an inlet 32 that draws lubricating 
oil directly from oil pan 12. High pressure pump 30 is preferably an axial 
piston type pump having a plurality of reciprocating pistons 35, as known 
in the art. When lubricating oil leaves outlet 33 of high pressure pump 
30, a portion enters the lubricating oil system 19 by entering upstream 
circulation conduit 21, and another portion enters the high pressure 
hydraulic system 18 by branching into high pressure supply pipe 40. 
Referring now, in addition to FIG. 2, upstream circulation conduit 21 is 
connected to a pressure reducing valve 20 that reduces the pressure in the 
downstream circulation conduit 24 of lubricating system 19 to a pressure 
typical of low pressure oil lubricating systems. Preferably, pressure 
reducing valve 20 is a three-way valve that includes a valve member 29 
that is biased toward a position that opens upstream circulation conduit 
21 to downstream circulation conduit 24. However, valve member 29 is 
moveable to a lower position against biasing means 28 to channel a portion 
of the fluid in upstream circulation conduit 21 directly back to oil pan 
12 via over-pressure return line 22 when the pressure tap line 23 senses 
that pressure in downstream circulation conduit 24 has exceeded a 
predetermined maximum pressure. In general, the flow area through valve 20 
between upstream conduit 21 and downstream conduit 24 is preferably a 
function of pressure in downstream conduit 24. After leaving circulation 
conduit 24, the lubricating oil passes through a plurality of lubrication 
passages 25 that maintain the various moving parts within engine 10 
properly lubricated in a conventional manner. The oil then reconverges in 
a return conduit 26, and is routed back to oil pan 12 for recirculation. 
Operating in parallel to the engines lubricating system 18 is the high 
pressure hydraulic system 19 that utilizes the lubricating oil 13 as a 
hydraulic medium in actuating a plurality of hydraulic devices 44. 
Hydraulic devices 44 could include but are not limited to 
hydraulically-actuated fuel injectors, hydraulically-actuated intake and 
exhaust valves, hydraulically-actuated exhaust brakes, etc. Pressurized 
oil leaves pump 30 at outlet 33 and travels along high pressure supply 
pipe 40 to an inlet 41 of a high pressure common rail 42. High pressure 
rail 42 has a plurality of outlets 43, each of which is connected to a 
respective branch passage 48. The inlets 47 of hydraulic devices 44 are 
each connected to a separate branch passage 48. The drain ports 45 of the 
hydraulic devices empty the used oil into a common return pipe 46 that 
returns the oil to oil pan 12 for recirculation. 
INDUSTRIAL APPLICABILITY 
Those skilled in the art will appreciate that the present invention 
achieves noise reduction by at least partially submerging the high 
pressure pump 30 in an amount of oil so that the surrounding oil dampens 
the noise produced during the normal operation of the high pressure pump 
30. Additional noise attenuation is achieved by the enclosure of the high 
pressure pump in the oil pan 12. In many prior art hydraulic systems, the 
high pressure pump was typically attached to the outside of the engine, 
and thus it radiated undesirable noise away from the engine. 
By positioning the inlet of the high pressure pump near the bottom of the 
oil pan, the hydraulic system 18 is always exposed to a ready supply of 
oil, especially when the engine is undergoing a cold start condition. In 
the past, the inlet of the high pressure pump was exposed to a secondary 
reservoir located at a position well above the oil pan, was supplied by 
the same low pressure pump that circulated the lubricating oil through the 
engine. As a consequence, the engine could sometimes be required to crank 
excessively before the engine could start since the secondary reservoir 
would have to be substantially filled before the hydraulic system could 
have a sufficient amount of oil to draw upon for the necessary operation 
of the hydraulic fuel injectors. The present invention overcomes this 
perceived irritation by always exposing the inlet of the high pressure 
pump to oil in the oil pan. 
The present invention also aids in streamlining engine packaging since only 
one pump is utilized for both the hydraulic and oil lubricating systems. 
In addition, the present invention eliminates the need for a separate oil 
reservoir for the high pressure pump, by positioning the single high 
pressure pump within the engine casing as opposed to being attached to the 
outside surface of the engine as in some previous designs. Thus, the 
engine incorporating the present invention should not only perform better 
than their prior art counterparts, but should also have the ability to 
occupy less space and operate more quietly than their prior art 
counterparts. This combination of features permits engines according to 
the present invention to be positioned in more confined spaces than might 
be otherwise be possible with prior art engine systems. 
The above description is intended for illustrative purposes only, and is 
not intended to limit the scope of the present invention in any way. For 
instance, while the low and high pressure systems in the illustrated 
embodiment are shown to be completely parallel, those skilled in the art 
will appreciate that other variations might be possible. For instance, the 
medium pressure used oil leaving the hydraulic devices could be harnessed 
to push oil through the lubricating passages of the engine before being 
returned to the oil pan. Thus, various modifications could be made to the 
illustrated embodiment without departing from the intended spirit and 
scope of the present invention, which is defined in terms of the claims 
set forth below.