EP1969208B1

EP1969208B1 - Lubrication system and internal combustion engine comprising such a system

Info

Publication number: EP1969208B1
Application number: EP05849094A
Authority: EP
Inventors: Marc Miettaux
Original assignee: Renault Trucks SAS
Current assignee: Renault Trucks SAS
Priority date: 2005-12-27
Filing date: 2005-12-27
Publication date: 2009-11-25
Anticipated expiration: 2025-12-27
Also published as: EP1969208A1; ATE449903T1; WO2007073770A1; DE602005017953D1

Abstract

This lubrication system (2) comprises a main circuit (25), including a main pump (21) which draws oil from a sump (22) and feeds a main line (251) providing oil to an engine lubrication main system (11A, 14), and at least an auxiliary circuit (27) including an auxiliary pump (274) which feeds a hydraulic subsystem (18, 19). The auxiliary circuit (27) is fed from the main circuit (25) through a pressure regulating unit (28) whereas the auxiliary circuit (27) includes a dedicated filter (273) adapted to filter all oil coming from the pressure regulating unit (28).

Description

TECHNICAL FIELD OF THE INVENTION

This invention concerns a lubrication system for an internal combustion engine. It also concerns an internal combustion engine including such a system.

BACKGROUND OF THE INVENTION

It is known to use hydraulic subsystems on an internal combustion engine in order to drive some equipments providing specific functions. Such hydraulic subsystems might comprise a valve actuation equipment or an hydraulically powered fuel injection system. Oil circulating in such subsystems must be clean in order to guarantee correct working of the corresponding equipments.
In order to keep oil in such subsystems clean, it is known from US-A-2005/0011478 to provide a separate oil circuit for such an auxiliary equipment. This approach requires two dedicated sumps to collect oil, from the main lubrication system of the engine on the one side and from an auxiliary circuit on the other side. This increases engine weight and induces that maintenance is more complicated since two fluids have to be serviced separately.
It is also known from EP-A-0 811 765 to use a two-stage internal gear pump to feed different hydraulic circuits on an internal combustion engine. The flow rate in these circuits cannot be controlled independently.
Finally, US-A-4,721,185 discloses an oil container arrangement for vehicles where a lubricant- pump sucks oil from a sump and feeds transmission lubricating means, on the one side, and a container, on the other side. Another pump sucks oil from this reservoir in order to feed a hydraulic subsystem. Since the container is fed with oil coming from the main sump, oil in this container is not clean, so that there is a risk of malfunction of the hydraulic subsystem.

SUMMARY OF THE INVENTION

The invention aims at providing a lubrication system which is adapted to feed both an engine lubrication main system and a hydraulic subsystem, where the quality of the oil provided to the subsystem is optimized in order not to alter the working of the subsystem.
To this purpose, the invention concerns a lubrication system for an internal combustion engine which comprises a main circuit including a main pump which draws oil from a sump and feeds a main line providing oil to an engine lubrication main system and at least an auxiliary circuit including an auxiliary pump which feeds a hydraulic subsystem and including a dedicated oil filter as shown in JP-04228815 and US2004/112677 . According to the invention, this lubrication system is characterized in that said auxiliary circuit comprises a return line which redirects oil from the hydraulic subsystem towards the entry zone of the auxiliary circuit, the auxiliary circuit is fed from the main circuit through a pressure regulating unit and in that the dedicated filter is adapted to filter all oil coming from the pressure regulating unit.
The pressure and the flow rate of the oil provided to the hydraulic subsystem via the auxiliary circuit can be efficiently controlled thanks to the pressure regulating unit and the dedicated filter. Since the filter is adapted to filter oil coming from the pressure regulating unit, all oil entering the auxiliary circuit can be filtered, which guarantees that oil in this auxiliary circuit remains clean, even if oil in the main circuit is charged with soot or other pollutants.
According to further aspects of the invention, the lubrication system might incorporate one or several of the following features:

The dedicated filter is adapted to filter also oil coming from the return line of the auxiliary circuit,
The dedicated filter has a nominal filtration rating smaller than any filter in the main circuit,
The pressure regulation unit includes a one-way valve, adapted to allow oil circulation from the main circuit to the auxiliary circuit and to prevent oil circulation from the auxiliary circuit to the main circuit, and a Pressure limiter adapted to selectively establish a communication between the auxiliary circuit and a part of a return line which directs oil towards the sump.
The pressure limiter is a two-way pressure limiter mounted on the return line.
The pressure limiter can be piloted according to oil pressure in the auxiliary circuit.
The pressure limiter can also be piloted according to oil pressure in the main circuit. In such a case, the pressure regulation unit preferably includes a control line which connects the pressure limiter to the main circuit, on the upstream side of the one-way valve. This control line might include a check valve adapted to allow oil circulation from the pressure regulator to the main circuit, provided that there exists a pressure difference between the control port of the pressure regulator and the main circuit
According to another embodiment of the invention, the pressure regulation unit includes a three-way pressure regulator having two inlets/outlets respectively connected to the downstream side of the one-way valve and to part of the auxiliary circuit and another outlet connected to a line which allows to return oil to the sump. In such a case, the pressure regulation unit might include a set of two preset check valves mounted in opposed configuration between the pressure limiter and the auxiliary circuit.
The pressure regulation unit also includes an oil accumulator in fluid communication with the auxiliary circuit downstream of the one-way valve.

The invention also concerns an internal combustion engine which comprises at least the cylinder provided with a piston slidably movable in this cylinder and at least an hydraulic subsystem, this engine being characterized in that it includes a lubrication system as mentioned here-above.
Such an engine has a better workability than the engines of the prior art insofar as oil in the auxiliary circuit can be kept clean and at a relatively constant pressure, even if oil in the main circuit is polluted and has a varying pressure.
According to preferred embodiments of the invention, the hydraulic subsystem can be a camless valve driving system, an oil-driven fuel injection system or an oil driven braking system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on the basis of the following description, which is given in correspondence with the annexed figures and as an illustrative example, without restricting the object of the invention. In the annexed figures:

Figure 1 is a scheme of a lubrication system and an engine according to the invention,
Figure 2 is an enlarged view of detail II on figure 1,
Figure 3 is a scheme similar to figure 2 for a system according to a second embodiment of the invention,
Figure 4 is a scheme similar to figure 2 for a lubrication system according to a third embodiment of the invention,
Figure 5 is a view similar to figure 2 for a lubrication system according to a fourth embodiment of the invention,
Figure 6 is a view similar to figure 2 for a lubrication system according to a fifth embodiment of the invention, and
Figure 7 is a view similar to figure 2 for a lubrication system according to a sixth embodiment of the invention,

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The lubrication system represented on figures 1 and 2 is adapted to be mounted onto an internal combustion engine 1 of a vehicle, e.g. a truck. Engine 1 comprises a crankshaft 11 and several cylinders 12, only two cylinders being represented on figure 1. A piston 13 is slidably movable within each cylinder 12, between a top dead center position and a bottom dead center position. A piston cooling jet 14 is provided for each cylinder 12 and adapted to direct a flow of oil towards its piston 13 as shown by arrows A₁, in particular when this piston is near its bottom dead center position.
Each cylinder 12 is provided with an intake valve 15 and an exhaust valve 16, these valves being loaded towards their respective seats by springs 17 and hydraulically driven by hydraulic actuators 18. These actuators 18 are fed from a common ramp or reservoir 19.
The lubrication system 2 of engine 1 includes a main pump 21 which draws oil from a sump 22 via a strainer 23. Pump 21 supplies oil under pressure via a filter 24 to a main circuit 25 which includes a main line 251 which divides itself into two feeding lines 252 and 253. The first feeding line 252 provides oil to the interface between crankshaft 11 and the corresponding bearings, one of which is represented on figure 1 with reference 11A. Second feeding line 253 feeds the piston cooling jet 14. Return lines 254 and 255 convey oil, respectively from the interface between crankshaft 11 and bearing 11A and from the bottom of the cylinders 12, back to the sump 22.
This interface 11/11A and the cooling jets 14 form a main lubrication system for engine 1.
During its travel in the main circuit 25, oil is polluted with soot coming from deposits resulting resulting from fuel combustion. Oil may also be polluted with particles or debris coming from mechanical components wear. Therefore, oil redirected to sump 22 cannot be considered as clean.
A two-way pressure limiter 26 is provided on the downstream side of pump 21 and allows to re-direct a part of the oil coming out of pump 21 to sump 22 in case the pressure in an upstream line 256 of circuit 25 is above a predetermined value, namely P_1.
An auxiliary circuit 27 is used to feed ramp 19 and the associated actuators 18. This circuit 27 is formed of a first line 271 which feeds ramp 19 and a return line 272 which re-direct oil from ramp 19 towards the entry zone of circuit 27. A dedicated filter 273 is provided on line 271, upstream of a dedicated auxiliary pump 274 which feeds ramp 19.
Circuit 27 is fed with oil from a branch line 257 of circuit 25 via a pressure regulating unit 28 which is represented in more detail on figure 2. Unit 28 is connected, on its inlet or upstream side, to branch line 257 and, on its outlet or downstream side, to line 271. Unit 28 comprises a one-way valve 281 and a two-way pressure limiter 282. A connection line 283 connects the downstream side of valve 281 to the outlet of unit 28, that is to line 271. A return line 284 branches off from line 283 and allows to re-direct some oil from circuit 27 to sump 22. Pressure limiter 282 is mounted on return line 284.
Oil pressure level P₂ downstream of valve 281 and in the upstream part of line 284 is set via pressure limiter 282. This pressure level P₂ is set at a value higher than the value of P₁.
The function of unit 28 is to control the pressure of the oil supplied to ramp 19 through filter 273 with the constraint of limiting the quantity of oil drawn from sump 22 in order to avoid a fast clogging of filter 273 by excessive use of engine oil coming from main sump 22. Unit 28 allows to compensate the variations of oil flow rate needed to feed ramp 19, these variations being dependent on the actual working conditions of actuators 18. When the camless valve driving system made of parts 18 and 19 is operating, oil circulates in a closed loop within auxiliary circuit 27. In particular, oil flowing in return line 272 is recycled towards line 271 in order to supply again tank 19, through filter 273 and pump 274.
In order to guarantee that oil sent to ramp 19 and actuators 18 is clean, the nominal filtration rating of filter 273 can be chosen small enough in order to stop particles of soot and other particles of the same size. The mesh size of filter 273 is chosen to provide a filtration efficiency of 95% or more with particles of a size in the range from 3 to 5 µm. In fact, the nominal filtration rating of filter 273 is smaller than the nominal filtration rating of filter 24 and any other filter in the main circuit 25. These filters in circuit 25 have an efficiency of about 80% with particles of a size of 20 µm since soot particles, of a size smaller than 20 µm, might circulate in circuit 25 and since, if one were to use very fine filters in this circuit, these filters would rapidly clog. On the contrary, since most of the oil flowing through filter 273, which is dedicated to circuit 27, comes from return line 272, this oil is not polluted so that clogging of filter 273 is unlikely.
When there is a difference between the flow rate of oil required at an entry point P₂₇₁ of line 271 and the flow rate coming from line 272 at an exit point P₂₇₂ of this line, a flow of oil to or from circuit 27 is provided via unit 28. If more oil is needed in line 271 than the quantity coming from line 272, oil pressure in line 283 drops below the pressure level P₁ of oil branch line 257, this pressure level P₁ being set via pressure limiter 26. In such a case, since pressure in line 257 is higher than pressure in line 283, oil flows from circuit 25 to circuit 27 via one-way valve 281.
In a case where more oil comes in line 272 than needed in line 271, pressure in connection line 283 rises to a level greater than P₂ which induces that pressure limiter 282 opens and oil in excess returns to sump 222 via line 284. This happens as long as pressure in line 283 is above pressure level P₂.
In other words, unit 28 allows to control that pressure of oil provided to the first line 271 of circuit 27 is regulated at a value of about P₂.
In the embodiment of figure 3, the same elements as in the first embodiment have the same references. Unit 28 of this embodiment also include a one-way valve 281 1 and a pressure limiter 282, whereas a connection line 283 connects the downstream side of valve 281 to the first line of auxiliary circuit 27. The pressure level P₂ set by pressure limiter 282 is higher than the pressure level set by the pressure limiter used to control the feeding pressure of the main circuit 25. Unit 28 incudes an oil accumulator 285 connected to line 283 and where oil can be stored at a pressure substantially equal to P_2.
Accumulator 285 allows to limit the volume of oil sucked from main circuit 25 when more oil is needed in line 271 than available from line 272. In such a case, oil present in accumulator 285 flows in line 283 before valve 281 opens. If the quantity of oil in accumulator 285 is sufficient, valve 281 does not open and no polluted oil flows from circuit 25 to the dedicated filter of circuit 27, similar to filter 273 of the first embodiment. If the quantity of oil needed is greater than what is available from accumulator 285, pressure in line 283 drops below P₁ and valve 281 opens, as explained here-above for the first embodiment.
On the contrary, when oil pressure in connection line 283 increases because excess oil comes from return line 272, a part of this oil is stored in accumulator 285 before oil pressure reaches level P₂, so that pressure limiter 282 does not open and no clean oil is wasted to sump 22 if all oil in excess can be stored in accumulator 285. If accumulator 285 is filled with oil in excess and pressure in line 283 increases above value P₂, pressure regulator 282 opens to allow oil to flow to sump 22 via line 284.
In the embodiment of figure 4, the same elements as in the first embodiment have the same references. Unit 28 of this embodiment includes a one-way valve 281 and a pressure limiter 282 mounted on a return line 284 which branches off a connection line 283 connecting the downstream side of valve 281 to the outlet of unit 28 which is connected to the first line of the auxiliary circuit 27. The operational pressure of pressure limiter 282 is controlled by the actual pressure of oil in branch line 257. To this end, a pilot line 286 connects branch line 257 to pressure limiter 282. In fact, the operational pressure of pressure limiter 282 is slightly offset with respect to the pressure in branch line 257, which results from the internal design of pressure limiter 282 and the pressure drop induced by the differential pressure provided by a preset check valve 287 placed in pilot line 286.
Check valve 287 is optional and placed in pilot line 286 in such a way that the check valve pressure drop occurs when pilot oil flows from the control port of regulator 282 in the direction of branch line 257.
In the embodiment of figure 5, the same elements as in figure 2 have the same references. Unit 28 of this embodiment also includes the one-way valve 281 and a three-way pressure limiter 282 mounted on connecting line 283 which connects the downstream side of valve 281 to the first line of auxiliary circuit 27.
Pressure limiter 282 is in the form of a three-way regulator valve which is connected by a first inlet/outlet to valve 281 and by a second inlet/outlet to circuit 27. The overflow line of pressure limiter 282 is connected to a return line 284 similar to the one of the previous embodiments. Pressure limiter 282 is designed to keep oil pressures in the part of line 283 comprised between pressure limiter 282 and circuit 27, at a predetermined level P₂ which is almost constant, whatever the flow going through unit 28.
According to some embodiments of the invention which are not represented, units 28 of figures 4 and 5 can also be provided with an oil accumulator similar to the one of unit 28 of figure 3.
In the fifth embodiment of the invention represented of figure 6, the same elements as in the previous embodiments have the same reference numbers. The pressure regulating unit 28 of this embodiment also includes a one-way valve 281 and a pressure limiter 282 in the form of a three-way regulator valve installed, in the same way as in the fourth embodiment, on a connection line 283 which connects valve 281 to the outlet of unit 28 and circuit 27. In this embodiment, two check valves 288A and 288B are mounted on the downstream part of line 283, between pressure limiter 282 and circuit 27. These valves allow flow of oil in both directions, that is from pressure limiter 282 to circuit 27 and return, but the pressure drop in these check valves allows to increase the hysteresis of the opening of valve 281 on one side and pressure limiter 282 on the other side.
More precisely, the pressure drop ΔP_A in check valve 288A adds itself to the value of oil pressure at the outlet of unit 28 so that, even if pressure in a point similar to point P₂₇₁ of the first embodiment is at a level below P₁, valve 281 will not systematically open. On the other hand, if pressure at a point similar to P₂₇₂ of the first embodiment exceeds pressure level P₂ set by pressure limiter 282, oil pressure sensed by pressure limiter 282 will be lower by an amount of ΔP_B corresponding to the pressure drop in check valve 288B, so that pressure limiter 282 will not immediately open. Therefore, check valves 288A and 288B increase pressure variations hysteresis, which allows to minimize the quantity of oil flowing through unit 28.
The embodiment of figure 7 is similar to the one of figure 6 but for the addition of an oil accumulator 285. The other parts of the pressure regulating unit 28 of this embodiment bear the same references as in the embodiment of figure 6.
In the embodiments of figures 1 to 3 and 5 to 7, the pressure limiter is piloted according to oil pressure in the downstream part of line 283, that is according to oil pressure in circuit 27.
In all its embodiments, the invention allows to guarantee that oil provided to the hydraulic subsystems formed by ramp 19 and actuators 18 is kept clean by dedicated filter 273 which filters both all oil coming from return line 272 and all oil coming from circuit 25 via unit 28. Oil is provided to unit 27 with a pressure which varies by a limited amount and remains next to value P₂ set by pressure regulator 282.
This is particularly advantageous for an engine 1 whose valves are hydraulically driven.
The invention could also apply to en engine provided with other types of hydraulic subsystems, such as an oil driven fuel injection system or an oil driven braking system.
The invention is also applicable to an engine equipped with several hydraulic subsystems. In such a case, one or several auxiliary circuits are provided to feed these subsystems, together with a corresponding number of pressure regulating units. It might also prove advantageous to use a single pressure regulating unit 28 and a single filter 273 in order to feed several subsystems which each include an auxiliary pump similar to pump 274. In such a case, the return lines of these subsystems are connected together.

LIST OF REFERENCES

1: engine
11 crankshaft
11A bearing
12 cylinders
13 piston
14 piston cooling jet
15 intake valve
16 exhaust valve
17 spring
18 hydraulic actuators
19 common ramp
2: lubrication system
21 main pump
22 sump
23 strainer
24 filter
25 main circuit
251 main line
252 first feeding line
253 second feeding line
254 return line
255 return line
256 upstream line
257 branch line
26 pressure limiter
27 auxiliary circuit
271 first line
272 return line
273 dedicated filter
274 auxiliary pump
28 pressure regulating unit
281 one-way valve
282 pressure limiter
283 connection line
284 return line
285 oil accumulator
286 pilot line
287 check valve
288A check valve
288B check valve
A₁: arrows
P₂₇₁: entry point
P₂₇₂: exit point
P₁: pressure level in line 256 and branch 257
P₂: pressure level in downstream part of unit 28
ΔP_A: pressure drop in 288A
ΔP_B: pressure drop in 288B

Claims

A lubrication system (2) for an internal combustion engine (1) said system comprising:
- a main circuit (25) including a main pump (21) which draws oil from a sump (22) and feeds a main line (251) providing oil to an engine lubrication main system (11/11 A, 14),

- at least an auxiliary circuit (27) including an auxiliary pump (274) which feeds an hydraulic subsystem (18, 19) and a dedicated filter (273);
characterized in that:
- said auxiliary circuit (27) comprises a return line (272) which redirects oil from the hydraulic subsystem towards the entry zone of the auxiliary circuit (27),

- said auxiliary circuit (27) is fed from said main circuit (25) through a pressure regulating unit (28), and

- said dedicated filter (273) is adapted to filter all oil coming from said pressure regulating unit.
Lubrication system according to claim 1, characterized in that said dedicated filter (273) is adapted to filter also oil coming from said return line (272) of said auxiliary circuit (27).
Lubrication system according to one of the previous claims, characterized in that said dedicated filter (273) has a nominal filtration rating smaller than any filter (23, 24) of the main circuit (25).
Lubrication system according to any one of the previous claims, characterized in that said pressure regulation unit (28) includes a one-way valve (281), adapted to allow oil circulation from said main circuit (25) to said auxiliary circuit (27) and to prevent oil circulation from said auxiliary circuit to said main circuit, and a pressure limiter (282) adapted to selectively establish a communication between said auxiliary circuit and a part of a return line (284) which directs oil towards said sump (22).
Lubrication system according to claim 4, characterized in that said pressure limiter is a two-way pressure limiter (282) mounted on said return line (284).
Lubrication system according to one of claims 4 or 5, characterized in that said pressure limiter (282) is piloted according to oil pressure in said auxiliary circuit (27).
Lubrication system according to one of claims 4 or 5, characterized in that said pressure limiter (282) is piloted according to oil pressure in said main circuit (25).
Lubrication system according to claim 7, characterized in that said pressure regulation (28) unit includes a control line (286) connecting said pressure limiter to said main circuit (25), on the upstream side (257) of said one-way valve (281).
Lubrication system according to claim 8; characterized in that said control line includes a check valve (287) adapted to allow oil circulation from said pressure regulator (282) to said main circuit (25), providing that there exists a pressure difference between the control port of said regulator and said main circuit.
Lubrication system according to claim 4, characterized in that said pressure regulation unit (28) includes a three-way pressure regulator (282) having two inlets/outlets respectively connected to the downstream side of said one-way valve (281) and to a part of said auxiliary circuit (27) and another outlet connected to a line (284) which allows to return oil to said sump (22).
Lubrication system according to claim 10, characterized in that said pressure regulation unit (28) also includes a set of two preset check-valves (288A, 288B) mounted in opposed configuration, between said pressure limiter (282) and said auxiliary circuit (27).
Lubrication system according to one of claims 4 to 11, characterized in that said pressure regulation unit (28) also includes an oil accumulator (285) in fluid communication with said auxiliary circuit (27) downstream of said one-way valve (281).
An internal combustion engine (1) comprising at least a cylinder (12), provided with a piston (13) slidably movable in said cylinder, and at least a hydraulic subsystem (18, 19), characterized in that it includes a lubrication system (2) according to one of the previous claims.
Internal combustion engine according to claim 13, characterized in that said hydraulic subsystem is a camless valve driving system (18, 19).
Internal combustion engine according to claim 13, characterized in that said hydraulic subsystem is an oil driven fuel injection system.
Internal combustion engine according to claim 13, characterized in that said hydraulic subsystem is an oil driven braking system.