GB2466274A

GB2466274A - A lubrication system with a variable displacement oil pump and control method therefore

Info

Publication number: GB2466274A
Application number: GB0823108A
Authority: GB
Inventors: Andrea Almondo; Davide Donna
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2008-12-18
Filing date: 2008-12-18
Publication date: 2010-06-23
Anticipated expiration: 2028-12-18
Also published as: GB0823108D0; GB2466274B

Abstract

The lubrication system comprises: at least one piston cooling jet for cooling the pistons of the engine; an auxiliary gallery (18) connected to the at least one piston cooling jet; a main gallery (16) connected to the auxiliary gallery (18) through a line (46); a variable displacement oil pump (10) having an inlet (12) connected to a tank (T) and an outlet (14) connected to the main gallery (16), the pump (10) being provided with primary and secondary control chambers (36, 38) arranged to be fed with oil from at least the main gallery (16), whereby the displacement of the oil pump (10) is determined by the pressures in the primary and secondary control chambers (36, 38); first and second return lines (40, 42) connected to the primary and secondary control chambers (36, 38) of the pump (10), respectively, the first return line (40) connecting the primary control chamber (36) with the main gallery (16); and a first valve (44) placed along the line (46) connecting the main gallery (16) with the auxiliary gallery (18) to control oil flow from the main gallery (16) to the auxiliary gallery (18). The system is configured in such a manner that the pressure in the secondary control chamber (38) of the pump (10) depends not only on the pressure in the main gallery (16) but also on the pressure in the auxiliary gallery (18).

Description

A lubrication system for an internal combustion engine provided with a variable displacement oil pump and control method therefor The present invention relates to a lubrication system for an internal combustion engine, particularly although not necessarily for a motor vehicle, wherein the system includes a variable displacement oil pump, a main gallery supplied with oil by the pump, and an auxiliary gallery connected to the main gallery for supplying oil to at least one piston cooling jet for cooling the pistons of the engine.

According to another aspect, the present invention relates to a method for controlling the above-identified lubrication system.

The increased focus on fuel consumption reduction makes more and more interesting the application of variable displacement oil pumps to internal combustion engines. In these pumps the displacement, and hence the flow rate, is continuously adapted to the actual oil demand by the engine.

A variable displacement vane pump for use in the lubrication system of an internal combustion engine is known from German Patent Application No. DE 10 2008 007 491 Al. This known variable displacement oil pump includes pumping chambers defined by slide vanes carried by a rotor rotatable in a housing for pumping oil from an inlet to a pressurized outlet. The pump also has a displacement control device for controlling displacement of the pumping chambers. The displacement control device includes a cam ring or stator mounted between the rotor and the housing and pivotally connected to a wall of the housing by a pivot. The cam ring is engaged on its radially inner side by the vanes. A control chamber is defined by the cam ring and the housing wall.

Control oil in the control chamber exerts a force on the cam ring tending to move the cam ring towards a position at 0% eccentricity (zero displacement) . A resilient member biases the cam ring in a direction opposite to a direction of the force exerted by the control oil in the control chamber, i.e. towards a position at 100% eccentricity (maximum displacement).

A known example of a lubrication system for an internal combustion engine including a variable displacement oil pump of the type disclosed in the above-mentioned prior art document is schematically illustrated in Figure 1 of the accompanying drawings.

With reference to Figure 1, the lubrication system comprises an oil tank T, a variable displacement oil pump 10 having an inlet 12 (schematically depicted by an arrow) connected to the tank T and an outlet 14 (also schematically depicted by an arrow), a main gallery 16 connected to the outlet 14 of the pump 10 for supplying oil to lubricated components of the engine (such as in particular the main bearings of the crankshaft), and an auxiliary gallery 18 connected to the main gallery 16 for supplying oil to at least one piston cooling jet for cooling the pistons of the engine.

The pump 10 is a vane pump including a housing 20, a rotor 22 rotatably mounted about a fixed axis R, a plurality of vanes 24 carried by the rotor 22, and a cam ring or stator 26 radially interposed between the rotor 22 and the housing 20 and engaged on its radially inner side by the vanes 24.

Pumping chambers 28 are defined between the rotor 22, the stator 26 and pairs of adjacent vanes 24 for pumping oil from the inlet 12 to the outlet 14. The stator 26 is pivotally connected to a wall of the housing 20 by a pivot 30 in such a manner that it can be moved between a position at 0% eccentricity, in which the axis of the stator 26 (indicated S) coincides with the axis R of the rotor 22 and the pump 10 therefore operates at zero displacement, and a position at 100% eccentricity, in which the axis S of the stator 26 is at its maximum distance from the axis R of the rotor 22 and the pump 10 therefore operates at its maximum displacement. A resilient member 32, such as a spring, biases the stator 26 towards the maximum displacement position. Control oil fed to a control chamber defined between the stator 26 and the housing 20 exerts a force on the stator 26 opposite to the biasing force exerted by the resilient member 32, i.e. tending to move the stator 26 towards the zero displacement position. The control chamber is split by a sealing member 34 into a primary control chamber 36 and a secondary control chamber 38, which receive oil from the oil circuit of the engine through a first return line 40 and a second return line 42, respectively.

The lubrication system further comprises a first, ON/OFF solenoid valve 44, here a normally-closed valve, placed along a line 46 connecting the main gallery 16 with the auxiliary gallery 18, as well as a second, three-way two-position solenoid valve 48 placed along the second return line 42.

When energized, the first solenoid valve 44 puts the main gallery 16 into communication with the auxiliary gallery 18, thus allowing oil to be supplied to the pistons of the engines through the piston cooling jets. Accordingly, the piston cooling jets are normally not fed with oil, as the first solenoid valve 44 is kept in the closed position. When required, the first solenoid valve 44 is energized and opens the connection between the main gallery 16 and the auxiliary gallery 18, thereby supplying the piston cooling jets with oil. As far as the second solenoid valve 48 is concerned, it is normally kept in a first operating position in which it allows oil to flow towards the secondary control chamber 38 of the pump 10 through the second return line 42 and, upon energization, it is moved into a second operating position in which it closes the second return line 42 e puts the secondary control chamber 38 of the pump 10 into communication with the tank T. Accordingly, when the second solenoid valve 48 is not energized, both the primary and secondary control chambers 36 and 38 of the pump 10 are fed with control oil coming from the oil circuit of the engine and a higher force is thus applied on the stator 26, thereby reducing the displacement of the pump 10. On the other hand, when the second solenoid valve 48 is energized, only the primary control chamber 36 is fed with control oil and a lower force is thus applied on the stator 26, thereby increasing the displacement of the pump 10.

This known lubrication system makes it possible therefore to control the oil pressure in the main gallery by controlling energization of the second solenoid valve, i.e. the solenoid valve placed along the second return line leading to the secondary control chamber of the pump. More specifically, an ECU (not shown) controls energization of the second solenoid valve in order to shift between a high oil pressure profile and a low oil pressure profile, by decreasing and increasing respectively the control area on which the oil pressure acts.

On the other hand, by properly controlling energization of the first solenoid valve, it is also possible to deactivate the piston cooling jets when cooling is not necessary, thereby contributing to energy saving.

The known lubrication system described above is controlled on the base of a control strategy which provides for a first operational mode implemented at low engine load, according to which both the first and second solenoid valves are not energized to deactivate the piston cooling jets and to supply the secondary control chamber with oil, and a second operational mode implemented at high engine load, according to which both the first and second solenoid valves are energized to activate the piston cooling jets and to stop oil supply to the secondary control chamber.

The known lubrication system described above suffers however from the disadvantage of involving the provision of two solenoid valves, along with the respective electrical connections and ECU functions.

In view of the above, it is an object of the present invention to provide an improved lubrication system for an internal combustion engine having a variable displacement oil pump, as well as an improved method for controlling such a lubrication system, which allow to overcome the above-

mentioned disadvantages of the prior art.

This and other objects are fully achieved according to a first aspect of the present invention by a lubrication system for an internal combustion engine having the features defined in the enclosed independent claim 1, and according to another aspect of the present invention by a control method for a lubrication system for an internal combustion engine including the steps defined in the enclosed independent claim 9.

Advantageous embodiments of the lubrication system and modes of implementation of the control method according to the present invention are the subject of the dependent claims, whose contents are to be understood as integral or

integrating part of the following description.

The characteristics and advantages of the invention will become apparent from the following detailed description, given purely by way of a non-limiting example, with reference to the accompanying drawing, in which: Figure 1 is a schematic diagram of a lubrication system

according to the prior art;

Figure 2 is a schematic diagram of a lubrication system according to a first preferred embodiment of the present invention; Figure 3 is a schematic diagram of a lubrication system according to a second preferred embodiment of the present invention; and Figure 4 is a schematic diagram of a lubrication system according to a third preferred embodiment of the present invention.

Referring in general to Figures 2 to 4, where parts and elements identical or equivalent to those of Figure 1 have been given the same reference numerals, the lubrication system of the present invention comprises an oil tank T, a variable displacement oil pump 10 having an inlet 12 (schematically depicted by an arrow) connected to the tank T and an outlet 14 (also schematically depicted by an arrow), a main gallery 16 connected to the outlet 14 of the pump 10 for supplying oil to lubricated components of the engine (such as in particular the main bearings of the crankshaft), and an auxiliary gallery 18 connected to the main gallery 16 for supplying oil to at least one piston cooling jet (non shown) for cooling the pistons of the engine (also not shown).

The pump 10 is preferably a vane pump including a housing 20, a rotor 22 rotatably mounted about a fixed axis R, a plurality of vanes 24 carried by the rotor 22, and a cam ring or stator 26 radially interposed between the rotor 22 and the housing 20 and engaged on its radially inner side by the vanes 24. Pumping chambers 28 are defined between the rotor 22, the stator 26 and pairs of adjacent vanes 24 for pumping oil from the inlet 12 to the outlet 14. The stator 26 is pivotally connected to a wall of the housing 20 by a pivot 30 in such a manner that it can be moved between a position at 0% eccentricity, in which the axis of the stator 26 (indicated S) coincides with the axis R of the rotor 22 and the pump 10 therefore operates at zero displacement, and a position at 100% eccentricity, in which the axis S of the stator 26 is at its maximum distance from the axis R of the S rotor 22 and the pump 10 therefore operates at its maximum displacement. A resilient member 32, such as a spring, biases the stator 26 towards the maximum displacement position.

A primary control chamber 36 and a secondary control chamber 38 are defined between the stator 26 and the housing 20 and receive oil from the oil circuit of the engine through a first return line 40 and a second return line 42, respectively. Control oil in the control chambers 36 and 38 exerts forces on the stator 26 which sum up to the force exerted by the resilient member 32, thereby determining the displacement of the pump 10. More specifically, in the embodiment of Figure 2 the two control chamber 36 and 38 are located on the same side with respect to the pivot 30 (the two control chambers being adjacent to each other and separated by a sealing member 34), whereby both the force exerted by the control oil in the primary control chamber 36 and the force exerted by the control oil in the secondary control chamber 38 oppose the force exerted by the resilient member 32, i.e. tend to move the stator 26 towards the zero displacement position. In both the embodiments of Figure 3 and Figure 4, on the other hand, the two control chambers 36 and 38 are located on opposite sides with respect to the pivot 30, whereby the force exerted by the control oil in the primary control chamber 36 opposes the force exerted by the resilient member 32, i.e. tends to move the stator 26 towards the zero displacement position, whereas the force exerted by the control oil in the secondary control chamber 38 supports the force exerted by the resilient member 32, i.e. tends to move the stator 26 towards the maximum displacement position.

The lubrication system further comprises an ON/OFF solenoid valve 44 placed along a line 46 connecting the main gallery 16 with the auxiliary gallery 18. In the illustrated embodiment, the solenoid valve 44 is a normally-closed valve.

In other words, when not energized, the solenoid valve 44 keeps the line 46 closed, whereas when energized, the solenoid valve 44 puts the main gallery 16 into communication with the auxiliary gallery 18 through the line 46, thereby allowing oil to be supplied to the pistons of the engines through the piston cooling jets. Accordingly, the piston cooling jets are normally not fed with oil, as the solenoid valve 44 is kept in the closed position. When required, the solenoid valve 44 is energized and opens the connection between the main gallery 16 and the auxiliary gallery 18, thereby supplying the piston cooling jets with oil. However, the solenoid valve 44 might also be a normally-open valve. In that case, the piston cooling jets would be normally fed with oil, as the solenoid valve 44 would normally keep the auxiliary gallery 18 into communication with the main gallery 16. When required, the solenoid valve 44 would be energized to close the connection between the main gallery 16 and the auxiliary gallery 18. The choice between these two options simply depends on the desired fail-safe strategy and in any case does not affect the principle of operation of the lubrication system according to the invention.

According to the embodiment of Figure 2, the lubrication system further comprises a three-way two-position pilot-operated valve 48 which is placed along the second return line 42 connecting the main gallery 16 with the secondary control chamber 38 of the pump 10 and is piloted by the pressure of a pilot line 50 connected to the auxiliary gallery 18. The pilot-operated valve 48 is normally kept by a spring in a first operating position in which it allows oil to flow from the main gallery 16 to the secondary control chamber 38 of the pump 10 through the second return line 42.

Pressure is thus applied to both the control chambers 36 and 38 of the pump 10, thereby reducing the displacement thereof.

When a pressure occurs in the pilot line 50 upon activation of the piston cooling jets by energization of the solenoid valve 44, which pressure is high enough to overcome the preload exerted by the spring, the pilot-operated valve 48 shifts continuously from the above-mentioned first operating position to a second operating position in which it closes the second return line 42 e puts the secondary control chamber 38 of the pump 10 into communication with the tank T. Therefore, only the primary control chamber 36 is fed with oil and the displacement of the pump 10 is increased accordingly.

According to the embodiment of Figure 3, the lubrication system further comprises a three-way two-position pilot-operated valve 48 which is placed along the second return line 42 connecting the main gallery 16 with the secondary control chamber 38 of the pump 10 and is piloted by the pressure of a pilot line 50 connected to the auxiliary gallery 18. The pilot-operated valve 48 is normally kept by a spring in a first operating position in which it closes the second return line 42 e puts the secondary control chamber 38 of the pump 10 into communication with the tank T. Therefore, only the primary control chamber 36 is fed with oil and the displacement of the pump 10 is reduced accordingly. When a pressure occurs in the pilot line 50 upon activation of the piston cooling jets by energization of the solenoid valve 44, which pressure is high enough to overcome the preload exerted by the spring, the pilot-operated valve 48 shifts from the above-mentioned first operating position to a second operating position in which it allows oil to flow from the main gallery 16 to the secondary control chamber 38 of the pump 10 through the second return line 42. Pressure is thus applied to both the control chambers 36 and 38 of the pump 10, thereby increasing the displacement thereof.

According to the embodiment of Figure 4, no valve is provided along the second return line 42 connecting the main gallery 16 with the secondary control chamber 38 of the pump 10.

Therefore, when the solenoid valve 44 is not energized and the auxiliary gallery 18 is not fed with oil from the main gallery 16, only the primary control chamber 36 of the pump is fed with oil and the displacement of the pump is kept at a low level. On the other hand, when the solenoid valve 44 is energized and the auxiliary gallery 18 is fed with oil from the main gallery 16 to activate the piston cooling jets, both the primary and secondary control chambers 36 and 38 of the pump 10 are fed with oil and the displacement of the pump is thereby increased.

The lubrication systems according to the three preferred embodiments described above are controlled each on the base of a control strategy which provides for a first operational mode implemented at low engine load, according to which the solenoid valve 44 is not energized to stop oil supply to the auxiliary gallery 18 and hence to deactivate the piston cooling jets, and a second operational mode implemented at high engine load, according to which the solenoid valve 44 is energized to feed the auxiliary gallery 18 with oil and hence to activate the piston cooling jets.

In the first operational mode, the displacement of the pump is set to a lower level depending on the equilibrium between the forces exerted on the stator 26 by the oil pressure in the control chambers 36 and 38 on the one hand, and by the resilient member 32 on the other hand. More specifically, this is obtained in the embodiment of Figure 2 by the fact that the pilot-operated valve 48 is kept by its spring in a position in which it allows oil to flow from the main gallery 16 to the secondary control chamber 38 through the second return line 42, in the embodiment of Figure 3 by the fact that the pilot-operated valve 48 is kept by its spring in a position in which it prevents oil from flowing from the main gallery 16 to the secondary control chamber 38 through the second return line 42, and in the embodiment of Figure 4 by the fact the auxiliary gallery 18, the second return line 42 and the secondary control chamber 38 are not fed with pressurized oil.

In the second operational mode, the displacement of the pump 10 is set to a higher level depending on the equilibrium between the forces exerted on the stator 26 by the oil pressure in the control chambers 36 and 38 on the one hand, and by the resilient member 32 on the other hand. More specifically, this is obtained in the embodiment of Figure 2 by the fact that the pilot-operated valve 48 is shifted by the pressure acting in the pilot line 50 into a position in which it prevents oil from flowing from the main gallery 16 to the secondary control chamber 38 through the second return line 42, in the embodiment of Figure 3 by the fact that the pilot-operated valve 48 is shifted by the pressure acting in the pilot line 50 into a position in which it allows oil to flow from the main gallery 16 to the secondary control chamber 38 through the second return line 42, and in the embodiment of Figure 4 by the fact the auxiliary gallery 18, the second return line 42 and the secondary control chamber 38 are all fed with pressurized oil.

To summarize, all the embodiments of the lubrication system according to the invention described above with reference to Figures 2 to 4 share the idea of controlling the displacement of the oil pump by means of the pressure in the auxiliary gallery, i.e. in the gallery which supplies the piston cooling jets with oil. This is obtained in the embodiments of Figures 2 and 3 by the fact that the pressure in the auxiliary gallery is used as pilot pressure for a pilot-operated pressure placed along the second return line to control the connection between the secondary control chamber of the pump and the main gallery, and in the embodiment of Figure 4 by the fact that the auxiliary gallery directly supplies the secondary control chamber with oil. Since it does not make use of a second solenoid valve in addition to the one controlling the oil supply from the main gallery to the auxiliary gallery, the lubrication system according to the invention is simpler, less expensive and more reliable than the lubrication system of the prior art discussed in the introductory part of the description with reference to Figure 1.

Naturally, the principle of the invention remaining unchanged, the embodiments and the constructional details may be varied widely from those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the present invention as defined in the attached claims.