GB2540348A

GB2540348A - Chain tensioner for an internal combustion engine

Info

Publication number: GB2540348A
Application number: GB1512003.3A
Authority: GB
Inventors: Conti Antonino; Pagliaro Pierluigi
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2015-07-08
Filing date: 2015-07-08
Publication date: 2017-01-18
Also published as: GB201512003D0

Abstract

A chain tensioner 500 comprising a plunger 510 for imparting tension to a timing chain (600 fig. 6) of an internal combustion engine (110 fig. 1), the chain tensioner comprising a hollow cylindrical housing 580 for guiding the plunger therein. In use the timing chain transmits forces to the plunger acting on a longitudinal plane B thereof, the chain tensioner being provided with a retaining hook 570 that engages with the grooves 535 of the knurled surface 530 on the plunger. The plunger further comprises a smooth surface 540 that is provided in the longitudinal plane B of action of the force transmitted to the plunger. The knurled or serrated surface may be provided on opposite sides of the plunger separated by two smooth surface portions. The plunger of the present invention may reduce wear on the housing by removing the grooved surface from the plane of force which acts on the plunger from the timing belt.

Description

CHAIN TENSIONER FOR AN INTERNAL COMBUSTION ENGINE TECHNICAL FIELD

The technical field relates to a chain tensioner for imparting tension to a chain adapted to transmit torque between two rotatable shafts of the internal combustion engine, e.g. from a crankshaft to a camshaft of an internal combustion engine. BACKGROUND

It is known that internal combustion engines are provided with a chain connecting a first rotatable shaft to a second rotatable shaft of the engine.

For example, it is known that internal combustion engines are provided with a timing chain (also known as drive chain) that synchronizes the rotation of the crankshaft and the camshaft(s) so that the engine's valves open and close at the proper times during each cylinder's intake and exhaust strokes.

The timing chain is typically a roller, bushing or inverted tooth IT chain connecting a crankshaft sprocket (i.e. a drive wheel), a camshaft sprocket (i.e. a driven wheel) and eventually other component like Fuel Injection Pump. The timing chain is guided by means of chain guides comprising a guide member arranged in contact with timing chain.

In particular, the chain guide can be coupled to the internal combustion engine in a fixed or in a movable manner. In other words, fixed chain guides are rigidly fixed to the engine with the aim of guide the timing chain in a path imposed by the guide, while mobile chain guide are hinged to the engine with the aim of guiding the timing chain, adjusting the timing chain tension during the engine functionality compensating dynamics and recover elongation of the chain occurring along engine life.

Chain tensioners for imparting tension to a timing chain adapted to transmit torque from a crankshaft to a camshaft of an internal combustion engine are known in the art.

The timing chain tensioning is adjusted by means of a chain tensioner which acts as a piston, using a spring and/or hydraulic pressure. The tensioner pushes the mobile chain guide that, rotating around a pivot, abuts against the timing chain to obtain a proper timing chain tensioning and to recover the chain elongation.

Known chain tensioners comprise a plunger that is sliding in a housing so as to be urged to protrude from the housing, wherein an end surface of the plunger imparts tension to the chain by interposition of a chain guide member (also known as tensioner shoe) or similar apparatus.

The plunger is driven by a compression spring and defines, in cooperation with the housing and a check valve, an oil chamber that provides a damping effect for the plunger by means of oil flowing across calibrated openings.

During engine start-up, the oil chamber may not have enough pressure and an undesired rattle noise may be produced by the system..

To prevent such occurrence, some known chain tensioners are provided with a ratchet system, namely a system that limits the plunger stroke to prevent rattle noise at engine start-up.

However, the chain tensioners of the prior art provided with a ratchet system may show some issues. A first issue is given by small oscillations that may be made by the ratchet around the working position of the plunger. A second issue is given by the fact that, in case a ratchet system is used, the plunger must be provided with a knurled or grooved external surface that may cause possible housing and/or plunger wear during the operations of the plunger, in particular as an effect of the sliding movement of the plunger inside the housing, a movement that may cause friction between the external knurled surface of the plunger and the internal surface of the housing.

An object of an embodiment disclosed is to overcome the above mentioned issues by means of chain tensioner that combines the benefits of the chain tensioners that are not equipped with a ratchet system with the benefits of chain tensioners equipped with a ratchet system.This and other objects are achieved by the embodiments of the invention as defined in the independent claims. The dependent claims include preferred and/or advantageous aspects of said embodiments.

SUMMARY

An embodiment of the disclosure provides a chain tensioner comprising a plunger for imparting tension to a timing chain of an internal combustion engine, the chain tensioner comprising a hollow cylindrical housing for guiding the plunger therein, the timing chain transmitting to the plunger forces acting on a longitudinal plane thereof, the chain tensioner being provided with a retaining hook for the plunger, wherein an external surface of the plunger is provided with a knurled surface to engage with retaining portions of the retaining hook and with a smooth surface, the smooth surface being provided in the longitudinal plane of action of the forces transmitted to the plunger.

An advantage of this embodiment is that, by limiting the knurling of the plunger only on the two sides in contact with the retaining hook and leaving smooth the sides of the plunger that support forces due to the interaction of the plunger with the timing chain, the chain tensioner avoids wear on the plunger and on the internal surface of the cylindrical housing in which the plunger slides.

At the same time, since the chain tensioner is provided with a ratchet system, namely a retaining hook, rattle noise at engine start-up is still significantly reduced, without reducing the plunger guided length and/or without increasing the overall length of the tensioner.

According to an embodiment of the invention, smooth surfaces are provided on two mutually opposite regions of the external surface of the plunger.

An advantage of this embodiment is that the smooth surfaces are provided in the intersection of the plane of action of the forces transmitted to the plunger with the housing in such a way that these areas are not subjected to significant wear during operation of the chain tensioner.

According to another embodiment of the invention, knurled surfaces are provided on two mutually opposite regions of the external surface of the plunger, the knurled surfaces being separated by the smooth surfaces.

According to another embodiment of the invention, each of the knurled surfaces is provided on opposite regions of the external surface of the plunger.

An advantage of this embodiment is that the position of the knurled surfaces allow a symmetrical engagement of the retaining portions of the retaining hook.

According to another embodiment of the invention, the knurled surfaces are separated by the smooth surfaces.

An advantage of this embodiment is that knurled surfaces are provided only on the areas cut by a plane perpendicular to the plane of action of the forces acting on the plunger, the knurled surfaces allowing the engagement of the retaining hook and leading to the benefits of a ratchet system, but are not subject to significant wear action.

According to a further embodiment of the invention, each of the knurled surfaces comprises a plurality of grooves, each groove having a length smaller than half of a circle.

An advantage of this embodiment is that a portion of the plunger is provided with smooth surfaces that are in contact with the internal surface of the hollow cylindrical housing in the areas cut by the plane of action of the forces transmitted to the plunger.

Additionally, the knurled surfaces do not interfere with the areas cut by the plane of action of the forces acting on the plunger.

According to a further embodiment of the invention, each of the grooves of the knurled surfaces extends along the external surface of the plunger for less than 80° above and below a plane substantially perpendicular to the longitudinal plane of action of ' the forces transmitted to the plunger.

According to a further embodiment of the invention, each of the grooves of the knurled surfaces extends along the external surface of the plunger for less than 70° above and below the plane substantially perpendicular to the longitudinal plane of action of the forces transmitted to the plunger.

According to a further embodiment of the invention, each of the grooves of the knurled surfaces extends along the external surface of the plunger for less than 60° above and below the plane substantially perpendicular to the longitudinal plane of action of the forces transmitted to the plunger.

According to a further embodiment of the invention, each of the grooves of the knurled surfaces extends along the external surface of the plunger for less than 45° above and below the plane substantially perpendicular to the longitudinal plane of action of the forces transmitted to the plunger.

An advantage of these embodiments is that the length of the grooves of the knurled surfaces is limited in order to do not provide an extension on the regions of action of the forces on the plunger.

According to another embodiment of the invention, the length of each of the grooves of the knurled surfaces is equal to the length of each of the retaining portions of the retaining hook.

An advantage of this embodiment is that the machining action necessary to provide the grooves on the plunger is limited.

According to another embodiment of the invention, the minimum length of each groove of the knurled surfaces is at least equal to the length of the retaining portions of the retaining hook in contact with the surface of the plunger.

An advantage of this embodiment is that the machining action is limited to the area that is actually providing a contact function with the retaining portions of the hook. A further embodiment of the disclosure provides for an internal combustion engine comprising a first rotatable shaft (e.g. a camshaft), a second rotatable shaft (e.g. a crankshaft) and a chain connecting said first rotatable shaft with said second rotatable shaft, at least one chain guide comprising a guide member configured to guide said chain. The internal combustion engine further comprises a chain tensioner comprising a plunger acting on said chain guide.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, wherein like numerals denote like elements, and in which:

Figure 1 shows an automotive system;

Figure 2 is a cross-section of an internal combustion engine belonging to the automotive system of figure 1;

Figure 3 is an isometric view of a chain tensioner according to an embodiment of the invention;

Figure 4 is a cross-section according to plane A of the chain tensioner of Figure 3, and

Figure 5 is a cross-section according to plane B of the chain tensioner of Figure 3;

Figure 6 is a schematic view of an internal combustion engine belonging to the automotive system of figure 1 in which a tensioner according to an embodiment of the invention is used.

DETAILED DESCRIPTION

Exemplary embodiments will now be described with reference to the enclosed drawings without intent to limit application and uses.

Some embodiments may include an automotive system 100, as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145. A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150. A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increases the pressure of the fuel received from a fuel source 190. Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145, for example by means of a timing chain 600. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200. An air intake duct 205 may provide air from the ambient environment to the intake manifold 200.

In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200.

In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust gases of the engine are directed into an exhaust system 270.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters. Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110 and with a memory system, or data carrier, and an interface bus.

The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, a Variable Geometry Turbine (VGT) actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

With reference to figures 3 - 5, a possible embodiment of a tensioner 500, according to an embodiment of the invention, will be now discussed. Figure 6 shows schematically an internal combustion engine in which a tensioner according to an embodiment of the invention is used.

More in details, the chain 600 connects the camshaft 135 and the crankshaft 145, as for example shown in figure 2. A camshaft sprocket 810 is attached to one end of the camshaft 135, and a crankshaft sprocket 820 is attached to one end of the crankshaft 145. A timing chain 600 connects the crankshaft sprocket 820 and the camshaft sprocket 810 so that the timing chain may transmit power from rotating crankshaft 145 to camshaft 135. In the shown embodiment, the timing chain 600 is guided by two chain guides 840a, 840b, respectively a fixed chain guide and a movable chain guide 840b associated to a tensioner 500.

In particular, chain guide 840b is a mobile chain guide comprising a guide member 845 (or tensioner shoe) arranged in contact with the timing chain 600.

The chain guide 840b, is provided with a guide bore 850 at which the guide member 845 is hinged to the engine 110 by a fastener, such as a screw or a bolt, acting as a pivot in order to provide a rotation point. By means of a tensioner 500, the chain guide 840b can be rotated in order to adjust the tensioning of the timing chain 600.

As it will be disclosed later in greater detail, forces are transmitted to the tensioner 500 and in particular to the plunger 510 of the tensioner along a plane B that is substantially corresponding to plane of movement of the timing chain 600, or a plane parallel to it. In figure 6 it is also visible a plane A perpendicular to the plane of action of the forces acting (transmitted) on the plunger 510 of the tensioner 500. A chain tensioner 500, according to an embodiment of the invention, is represented in more detail in Figure 3.

The chain tensioner 500 is used for imparting tension to a chain adapted to transmit torque from the crankshaft 145 to the camshaft 135 of the internal combustion engine 110 or, in general, for imparting tension to a chain or a belt or similar power transmission device.

The chain tensioner 500 is provided with a flange 595 equipped with holes 550,560 for attaching the chain tensioner 500 to the engine block 120.

The chain tensioner 500 comprises a hollow cylindrical housing 580 for accommodating a plunger 510 that may slide therein. A space internal to the hollow cylindrical housing 580 and closed by an end of the plunger 510 is filled with oil and forms an oil chamber 590.

The plunger 510 is pretensioned by means of a compression spring 520 in axial direction with respect to the hollow cylindrical housing 580, the compression spring 520 is adapted to push the plunger 510 against a flexible drive means, in particular a timing chain 600 of the internal combustion engine 110, eventually interposition of a tensioner shoe (e.g. a chain guide member) or similar apparatus, while oil in the oil chamber 590 operates as a damper for the plunger 510.

On an external surface 515 of the plunger 510, knurled surfaces 530 are provided.

According to an embodiment, the knurled surfaces 530 on the external surface 515 of the plunger 510 are provided in two mutually opposite regions of the plunger 510 and are separated by two smooth surfaces 540.

In a preferred embodiment, each of the knurled surfaces 530 are provided on opposite regions of the external surface of the plunger 510.

Preferably, the knurled surfaces 530 are formed by a plurality of grooves 535, each groove 535 having a length smaller than half of a circle, so as to provide a portion of the plunger 510 with smooth surfaces 540 that are in contact with the internal surface of the hollow cylindrical housing 580 in the areas cut by the plane of action of the forces transmitted to the plunger 510 (plane B).

The chain tensioner 500 is further provided with a retaining hook 570 that has portions suitable for engaging in the grooves 535 of the knurled surfaces 530.

In particular, the retaining hook 570 is provided with arc-shaped retaining portions 575 to engage into the grooves 535 of the plunger 510.

In a preferred embodiment, the length of each of the grooves 535 of the knurled surfaces 530 may be substantially equal to the length of each of the retaining portions 575 of the retaining hook 570.

Furthermore, portions of the retaining hook 570 may be contacted by projections 610 when the plunger 510 is an extended position to block the plunger 510 therein.

Figure 4 is a cross-section according to plane A of the chain tensioner of Figure 3 where the knurled surfaces 530 are visible.

Since plane A is perpendicular to the plane B of action of the forces acting on the plunger 510, the areas of the plunger 510 that are in contact with the internal surface of the hollow cylindrical housing 580 may be knurled, or in other words, provided with the knurled surfaces 530 .

The knurled surfaces 530 are formed by a plurality of grooves 535, each groove 535 having a length of less than half a circle, preferably by extending of the same length below and above said plane A. More in detail, each groove 535 is extending of less than 90° above and below said plane A, so as to provide a length of less than half a circle. According to other possible embodiments, the knurled surfaces 530 are formed by a plurality of grooves 535, each groove 535 extending of less than 80°, preferably less than 70s, more preferably less than 60° and most preferably less than 45° above and below said plane A.

It has to be noted, that according to an aspect of the invention, the minimum length of each groove 535 of the knurled surfaces 530 is at least equal to the length of the retaining portions 575 of the retaining hook 570 in contact with the surface of the plunger 510.

As visible in Figure 5, the areas of the plunger 510 that are in contact with the internal surface of the hollow cylindrical housing 580 are smooth since plane B is the plane of action of the forces acting on the plunger 510.

In another embodiment, the knurled surfaces 530 are provided only on one region of one side of the external surface of the plunger 510 and do not intersect the longitudinal plane B of action of the forces transmitted to the plunger 510.

In operation, the chain tensioner 500 imparts tension to the timing chain 600 adapted to transmit torque from the crankshaft 145 to the camshaft 135 of the internal combustion engine 110. A force acting on a plane substantially perpendicular to the timing chain 600 is therefore transmitted by the plunger 510 to the timing chain 600, while at the same time the timing chain 600 reacts with a force acting on a longitudinal plane of the plunger 510, in particular acting along plane B in Figure 3.

Since the plunger 510 has smooth surfaces 540 that are in contact with the internal surface of the hollow cylindrical housing 580 in the areas cut by the plane of action of the forces transmitted to the plunger 510 (plane B), wear upon the internal surface of the hollow cylindrical housing 580 and on the external surface of the plunger 510 is reduced or eliminated.

At the same time, the knurled surfaces 530 are provided only on the areas cut by a plane (plane A) perpendicular to the plane of action of the forces acting (transmitted) on the plunger 510, the knurled surfaces 530 allowing the engagement of the retaining hook 570 and therefore leading to the benefits of a ratchet system.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS 100 automotive system 110 internal combustion engine (ICE) 120 engine block 125 cylinder 130 cylinder head 135 camshaft 140 piston 145 crankshaft 150 combustion chamber 155 cam phaser 160 fuel injector 170 fuel rail 180 fuel pump 190 fuel source 200 intake manifold 205 air intake duct 210 intake air port 215 valves of the cylinder 220 exhaust gas port 225 exhaust manifold 230 turbocharger 240 compressor 250 turbine 260 cooling system 270 exhaust system 275 exhaust pipe 280 exhaust aftertreatment device 290 VGT actuator 300 EGR system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant and oil temperature and level sensors 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensor 445 accelerator pedal position sensor 450 electronic control unit (ECU) 500 chain tensioner 510 plunger 515 external surface of plunger 520 compression spring 530 knurled surface 535 grooves 540 smooth surface 550 hole 560 hole 570 retaining hook 575 retaining portion of hook 580 hollow housing for plunger 590 oil chamber 595 flange 600 timing chain 610 projection 810 camshaft sprocket 820 crankshaft sprocket 840a chain guide 840b chain guide 845 guide member of the chain guide 850 guide bore B plane of action of the forces transmitted to the plunger A plane perpendicular to the plane of action of the forces transmitted to the plunger

Claims

1. A chain tensioner (500) comprising a plunger (510) for imparting tension to.a timing chain (600) of an internal combustion engine (110), the chain tensioner (500) comprising a hollow cylindrical housing (580) for guiding the plunger (510) therein, the timing chain (600) transmitting to the plunger (510) forces acting on a longitudinal plane thereof (B), the chain tensioner (500) being provided with a retaining hook (570) for the plunger (510), wherein an external surface of the plunger (510) is provided with a knurled surface (530) to engage with retaining portions (575) of the retaining hook (570) and with a smooth surface (540), the smooth surface (540) being provided in the longitudinal plane (B) of action of the forces transmitted to the plunger (510).

2. The chain tensioner (500) according to claim 1, wherein smooth surfaces (540) are provided on two mutually opposite regions of the external surface (515) of the plunger (510).

3. The chain tensioner (500) according to claim 1, wherein the knurled surfaces (530) are provided on two mutually opposite regions of the external surface of the plunger (510).

4. The chain tensioner (500) according to claim 2 and 3, wherein the knurled surfaces are separated by the smooth surfaces (540).

5. The chain tensioner (500) according to claim 1, wherein each of the knurled surfaces (530) comprises a plurality of grooves (535), each groove (535) having a length smaller than half of a circle.

6. The chain tensioner (500) according to claim 5, wherein each of the grooves (535) of the knurled surfaces (530) extends along the external surface of the plunger (510) for less than 80° above and below a plane (A) substantially perpendicular to the longitudinal plane (B) of action of the forces transmitted to the plunger (510).

7. The chain tensioner (500) according to claim 6, wherein each of the grooves (535) of the knurled surfaces (530) extends along the external surface of the plunger (510) for less than 70° above and below the plane (A) substantially perpendicular to the longitudinal plane (B) of action of the forces transmitted to the plunger (510).

8. The chain tensioner (500) according to claim 7, wherein each of the grooves (535) of the knurled surfaces (530) extends along the external surface of the plunger (510) for less than 60° above and below the plane (A) substantially perpendicular to the longitudinal plane (B) of action of the forces transmitted to the plunger (510).

9. The chain tensioner (500) according to claim 8, wherein each of the grooves (535) of the knurled surfaces (530) extends along the external surface of the plunger (510) for less than 45° above and below the plane (A) substantially perpendicular to the longitudinal plane (B) of action of the forces transmitted to the plunger (510).

10. The chain tensioner (500) according to claim 5, wherein the length of each of the grooves (535) of the knurled surfaces (530) is equal to the length of each of the retaining portions (575) of the retaining hook (570).

11. The chain tensioner (500) according to claim 5, wherein the minimum length of each groove (535) of the knurled surfaces (530) is at least equal to the length of the retaining portions (575) of the retaining hook (570) in contact with the surface of the plunger (510).

12. An internal combustion engine (110) comprising a first rotatable shaft (135), a second rotatable shaft (145) and a chain (600) connecting said first rotatable shaft (135) with said second rotatable shaft (145), at least one chain guide (840b) comprising a guide member (845) and a chain tensioner (500) comprising a plunger (510) according to any of the preceding claims.