Turbocharger with dual wastegate

A turbocharger wastegate valve assembly comprises a first bypass port communicating with a first portion of an exhaust inlet and a first valve member adapted for engaging and sealing a first valve seat surrounding the first bypass port. The valve assembly further comprises a second bypass port communicating with a second portion of an exhaust inlet and a second valve member adapted for engaging and sealing a second valve seat surrounding the second port. A shaft supports each valve member for rotation about a shaft axis to lift both the first and second valve members from sealing engagement with the first and second valve seats respectively. The first valve seat is inclined relative to the second valve seat and the shaft has freedom of movement in the axial direction.

BACKGROUND

The present invention relates to a wastegated turbocharger. In particular, the invention relates to a dual wastegate port and valve assembly for a turbocharger provided with a divided inlet turbine.

Turbochargers are well known devices for supplying air to the intake of an internal combustion engine at pressures above atmospheric pressure (boost pressures). A conventional turbocharger essentially comprises an exhaust gas driven turbine wheel mounted on a rotatable shaft within a turbine housing connected downstream of an engine outlet manifold. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft within a compressor housing. The compressor wheel delivers compressed air to the engine intake manifold. The turbocharger shaft is conventionally supported by journal and thrust bearings, including appropriate lubricating systems, located within a central bearing housing connected between the turbine and compressor wheel housings.

In known turbochargers, the turbine stage comprises a turbine chamber within which the turbine wheel is mounted. An annular inlet passageway is defined between facing radial walls arranged around the turbine chamber. An inlet volute is arranged around the inlet passageway and an outlet passageway extends from the turbine chamber. The passageways and chambers communicate such that pressurised exhaust gas admitted to the inlet chamber flows through the inlet passageway to the outlet passageway via the turbine and rotates the turbine wheel. It is also known to improve turbine performance by providing vanes, referred to as nozzle vanes, in the inlet passageway so as to deflect gas flowing through the inlet passageway toward the direction of rotation of the turbine wheel.

Turbines may be of a fixed or variable geometry type. Variable geometry turbines differ from fixed geometry turbines in that the size of the inlet passageway can be varied to optimise gas flow velocities over a range of mass flow rates so that the power output of the turbine can be varied to suite varying engine demands. For instance, when the volume of exhaust gas being delivered to the turbine is relatively low, the velocity of the gas reaching the turbine wheel is maintained at a level which ensures efficient turbine operation by reducing the size of the annular inlet passageway. Turbochargers provided with a variable geometry turbine are referred to as variable geometry turbochargers.

A turbocharger turbine may be provided with a valve controlled bypass port referred to as a wastegate, to enable control of the turbocharger boost pressure and/or shaft speed. A wastegate valve (typically a poppet type valve) is controlled to open the wastegate port when the pressure of the boost air increases toward a pre-determined level, thus allowing some of the exhaust gas to bypass the turbine wheel. Typically the wastegate port opens into a bypass passageway which diverts the bypass gas flow to the turbine outlet or vents it to atmosphere. The wastegate valve may be actuated by a variety of means, including electric actuators, but is more typically actuated by a pneumatic actuator operated by boost pressure delivered by the compressor wheel.

Turbochargers intended for installation on an engine with two banks of cylinders may be provided with a turbine which has a divided inlet volute. This provides separate parallel gas inlet flow paths to the turbine wheel from each of the engine cylinder banks so that separate impulses of the exhaust gases will be more effectively transmitted to the turbine wheel. Wastegating of such a divided inlet turbine requires two wastegate ports, one for each separate inlet path, controlled by a dual wastegate valve mechanism.

The provision of a dual wastegate valve mechanism which provides simultaneous opening and closing of dual wastegate ports whilst ensuring each valve seats correctly in a closed position is problematic. Early examples of dual wastegate valve mechanism comprising a pair of valve members mounted to a single support arm is disclosed in Japanese Patent Application laid-open publication no. 57-137619. This discloses a dual wastegate valve mechanism comprising two valve members secured directly to a linking support member so that movement of the support member moves both valve members together. However, even a relatively slight distortion of the support member can result in improper closing of one or both valves so that exhaust gas flow can leak through the respective wastegate port. An improvement on this mechanism is disclosed in Japanese utility model application laid-open publication no. 62-183033. In this mechanism, each valve member is loosely coupled to the support member by a pin which allows some movement of the valve member relative to the support member. This freedom of movement accommodates minor distortion in the support member. However, excessive freedom of movement between each valve member and the support member can result in premature opening of one or other valve member before the boost pressure reaches the predetermined level.

A dual wastegate valve mechanism proposed to further improve upon the mechanisms described above is disclosed in U.S. Pat. No. 5,046,317. In this mechanism, a pair of wastegate valve members (poppets) are loosely mounted to a linking support member and have limited freedom of movement relative to the support member. In addition, the support member is pivotally connected to a support arm at a mid point between the two valve members to allow a small degree of pivoting movement of the support member itself relative to the wastegate ports. The combined freedom of movement of the valve members on the support member, and the support member on the support arm is said to accommodate differences in the valve seat height whilst ensuring each valve member firmly sits properly on its valve seat when the wastegate ports are closed.

Another dual wastegate valve mechanism is disclosed in U.S. Pat. No. 5,996,348. This takes a different approach to the provision of a mechanism which allows the simultaneous opening and closing of the two valve members whilst permitting a limited freedom of movement between the two valve members. Each valve member (poppet) is mounted to a respective arm extending at an angle from a respective shaft so that rotation of the shaft raises or lowers the respective poppet to open and close the wastegate port. The two shafts are concentrically arranged and are welded together at their ends remote from the poppet valves, at which point they are connected to a common actuation lever, such that movement of the lever rotates both shafts together, to simultaneously open or close the wastegate ports. Although the shafts are welded together at one end, they are torsionally independent which is intended to allow the shafts to separately accommodate tolerance build up or deformation of the valve seats to enable each poppet to seat correctly when closed.

Whilst the more recent dual wastegate valve mechanisms proposed in U.S. Pat. Nos. 5,046,317 and 5,996,348 address shortcomings in earlier proposals, they are relatively complicated mechanisms and are prone to wear.

It is an object of the present invention to provide an improved dual wastegate valve mechanism that provides opening and closing of dual wastegate ports.

SUMMARY

According to the present invention there is provided a turbocharger wastegate valve assembly comprising:

a first bypass port communicating with a first portion of an exhaust inlet;

a first valve member adapted for engaging and sealing a first valve seat surrounding the first bypass port;

a second bypass port communicating with a second portion of an exhaust inlet;

a second valve member adapted for engaging and sealing a second valve seat surrounding the second port;

a shaft supporting each valve member for rotation about a shaft axis to lift both the first and second valve members from sealing engagement with the first and second valve seats respectively;

wherein the first valve seat is inclined relative to the second valve seat and the shaft has freedom of movement in an axial direction.

With the present invention, the reaction forces exerted on the valve members (preferably poppets) have a component in the axial direction of the shaft which by virtue of the freedom of movement of the shaft in the axial direction provides a centering action.

The valve seats may lie in planes which are inclined either toward one another (in a “V” shape) or away from one another (in an inverted “V” shape).

The valve seats preferably incline at an angle greater than 90° (included angle).

Each valve seat is preferably equidistant from a line of intersection of the respective valve seat planes, but alternatively one valve seat may be closer to said line of intersection than the other.

The axial direction of the shaft preferably extends in a direction parallel to a plane containing a line joining the centers of the two valve seats, and in the case of valve seats equidistant from the line of intersection of the respective planes it is preferably parallel to a line joining the centers of the two valve seats. Alternatively, the valve seats may be off set relative to the axis, so that one valve seat is closer to the axis than the other.

The valve members are preferably loosely secured to the support shaft to enable a certain degree of freedom of movement of each valve member to improve seating. However, the valve members may be rigidly secured to the shaft (or more preferably a support portion extending laterally from the shaft).

Other alternative, and preferred, features of the present invention will be apparent from the following description.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Referring toFIG. 1, this illustrates a turbocharger provided with a divide turbine inlet and twin wastegate valve assembly as disclosed in U.S. Pat. No. 5,046,317 referred to above. The illustrated turbocharger comprises a turbine1and a compressor2interconnected by a central bearing housing3. The turbine1comprises a turbine wheel4mounted on one end of a turbo shaft5within a turbine housing6. The compressor2comprises a compressor wheel7mounted on the other end of the turbo shaft5within a compressor housing8. The turbo shaft5rotates about the turbocharger axis on bearing assemblies (not shown) located within the bearing housing3.

The turbine housing defines a divided inlet volute having parallel exhaust gas inlet paths9and10which deliver exhaust gas to the turbine wheel4via an annular inlet passage11and exits the turbine housing via an axial outlet passage12.

The compressor housing2defines an axial inlet13and an outlet volute14.

Exhaust gas flow through the turbine1causes rotation of the turbine wheel4which in turn rotates the compressor wheel7mounted to the opposite end of the turbo shaft5. As the compressor wheel7rotates, air is drawn in through the axial inlet13, and delivered to cylinders of a combustion engine (not shown) via outlet volute14at a boosted pressure.

The turbine1is a wastegated turbine and as such each exhaust gas inlet path9and10is provided with a respective wastegate port15and16which communicate with a bypass gas passage17via a dual wastegate valve assembly. The dual wastegate valve assembly comprises a pair of wastegate valve members, i.e. poppets18and19loosely mounted to opposite ends of a linking support member20. Each poppet has a limited freedom of movement allowing the precise position of each poppet to shift slightly to accommodate small variations in the height of the respective valve seats defined around the opening of each outlet bypass port9,10.

The support member20is mounted to one end of the support arm21which extends through a wall22of the turbine housing and is connected at its opposite end to an actuator arm23. A bushing24is provided in the turbine housing wall22to accommodate rotation of the support arm21.

The end of the support arm21which is fixed to the support member20is bent at right angles to the axis of rotation of the support arm21. The opposite end of the support arm21is linked to the actuator arm25so that reciprocal movement of the actuator arm (as indicated by arrow25) causes rotation of the support arm21which in turn moves the linking support member20and the poppets18,19to simultaneously open or close the wastegate ports9,10. The tip of the support arm21is secured to the support member20so as to allow limited angular movement between the two. In particular, the pivotal connection between the tip of the support arm21and the support member20is intended to provide a centering action to improve accurate seating of the poppets.

The wastegate valve assembly is controlled to open as boost pressure produced by the compressor2reaches a predetermined level to permit a portion of exhaust gas flowing through the turbine inlet paths9and10to bypass the turbine wheel4and thus limit any further increase in boost pressure produced by the compressor. The bypass gas passage17may communicate to atmosphere (as suggested in U.S. Pat. No. 5,046,317) or may for instance communicate with the turbine outlet passage12so that the bypass gas flow merges with the main exhaust gas flow downstream of the turbine wheel4.

Referring now toFIGS. 2 and 3, these illustrate a dual wastegate port and valve assembly according to the present invention. Only those details relevant to the invention are described. For instance, other details of the turbocharger, such as the construction of the turbine housing and the parallel exhaust gas inlet paths, and the manner in which the wastegate ports communicate with the inlet paths, may be entirely conventional and could for instance have the general structure illustrated inFIG. 1.

FIG. 2is a perspective section through part of a turbocharger turbine housing illustrating dual wastegate ports30and31extending through a housing wall32and a dual wastegate valve assembly33according to the present invention.FIG. 3is a view in the direction of arrow A inFIG. 2. It will be understood that the wastegate ports30and31communicate with respective exhaust gas flow paths (not shown) of a divided turbine inlet (not shown) which may for instance have substantially the same structure as that shown inFIG. 1.

The wastegate port30opens at a first surface34of the turbine wall32and the wastegate port31opens at a second surface35of a turbine wall32. The second wall surface35is inclined toward the first surface34forming a shallow V shape. Accordingly, respective valve seats defined on surfaces34and35around the opening of each wastegate port30,31are preferably similarly inclined toward each other so that the plane of one valve seat meets the plane of the other valve seat at a line substantially equispaced between the centers of the openings of the wastegate ports31,32.

The wastegate valve assembly33comprises a pair of wastegate valve members, in this case poppets36and37, fixed to a valve member support38mounted on one end of a valve shaft39for rotation therewith. The valve shaft39extends along an axis40which is preferably parallel to, but laterally offset from, a line joining the centers of the openings of each valve port30and31. The shaft39is supported for rotation about the axis40by a bushing41fitted in a bore through a housing wall portion42. A radially extending lever arm43is secured to the end of the shaft39opposite the valve member support38.

The valve member support38comprises a sleeve portion44securely fixed to the shaft39and a flag portion45extending laterally from the sleeve44. Each valve member36,37is secured to the support member flag portion45so that its sealing surface36a,37alies in a plane parallel to the plane of the respective wastegate port valve seat. The valve members36and37are preferably “loosely” secured to the support member38, to allow a limited freedom of movement about an axis perpendicular to the plane of the respective valve seat, for instance to accommodate minor distortions in the valve member support38relative to the surfaces34and35of the housing wall32. In the illustrated embodiment this is achieved by loosely riveting each valve member to the support member38in a conventional manner.

In accordance with the invention, the shaft39is axially slidable within the bushing41, and has a freedom of movement in the axial direction limited by the abutment of the sleeve44and bushing41on one side of the wall member42, and the lever arm43and the bushing41on the opposite side of the wall member42.

In use, a wastegate valve actuator (not shown) is linked to the lever arm43in order to reciprocate the lever arm43through a small angle to rotate the shaft39sufficiently to open and close the wastegate ports30and31. For instance, the actuator may be a conventional pneumatic actuator linked to the lever arm43by an actuating arm (not shown) which reciprocates in response to pressure in the turbine compressor. There are many examples of such actuators in the art. Typically, the actuator will be spring biased to maintain the wastegate valve in a closed position unless the spring bias is overcome by boost pressure transmitted to the actuator thus causing the wastegate valve to open. However, other forms of actuator, such as electric actuators controlled in accordance with monitored boost pressure, could also be used. Rotations of the lever arm43through a small angle in a clockwise direction as shown inFIG. 2will rotate the shaft39, which will in turn rotate the valve member support38about the shaft axis40to lift the valve members36and37to open the wastegate ports30and31.

Actuating force applied to the lever arm in a anti-clockwise direction as shown inFIG. 2will close the wastegate ports30and31by seating the valve members36and37on respective housing surfaces34and35. The loose connection of the valve members36and37to the valve member support38will allow each valve member to shift slightly to accommodate minor deformation or wear in the valve or support38seats. In addition, the combination of the inclined valve seats and the freedom of the shaft to move along its axis will tend to center the valve members on their valve seats as force is applied to maintain the valve members in a closed position.

The present invention therefore provides a dual wastegate port and valve assembly which provides for accurate seating of each valve member using a mechanically simple and robust mechanism.

FIGS. 4 and 5illustrate a second embodiment of the present invention.FIG. 4is a perspective view from above andFIG. 5is a sectional view, of a part of the turbine housing50defining dual wastegate ports51and52communicating between respective exchange gas inlet paths53and54and a bypass passage55. A dual wastegate valve assembly comprising valve members56and57seated on inclined wastegate port valves seats58,59defined by bosses60and61. As shown in the cross sectional view ofFIG. 5, the valve seats58and59defined by the bosses60and61, respectively, lie in preferably mutually inclined planes. Similarly, the valve members56and57are mounted to a valve member support62so that their sealing surfaces63and64lie (with some limited freedom and movement) in mutually inclined planes parallel to the valve seat planes.

The valve member support62is mounted for rotation on one end of a shaft69and operates in the manner described in relation to the embodiment ofFIGS. 3 and 4.

In the above described embodiments of the invention, the valve member support links the two valve members and has angled portions to which each valve member is mounted. However, in other embodiments each valve member could be mounted to a respective support arm extending from the sleeve portion rather than being directly linked.

With the above described embodiments of the invention the valve seats defined at the opening of each wastegate port are inclined toward one another. In alternative embodiments of the invention the valve seats may be inclined away from one another in an inverted V shape. In addition, the orientation of the wastegate ports in the illustrated examples is perpendicular to each of the valve seats. This need not necessarily be the case, rather the wastegate ports may be angled with respect to the respective valve seats. Other modifications will be apparent to the appropriately skilled person.