BACKGROUND OF THE INVENTION

This application relates generally to turbochargers for internal combustion engines, and relates more particularly to turbochargers having a turbine bypass valve controllable to cause exhaust gases from the engine to bypass the turbine under certain operating conditions.

Some vehicles include a turbocharger system having one or more turbochargers. Typically, turbochargers include a turbine wheel and a compressor wheel mounted on a common shaft and carried within isolated turbine and compressor housings, respectively. The turbine wheel is rotatably driven by exhaust gas fed from the engine into an annular chamber of the turbine housing, from which the exhaust gas is directed to an annular nozzle radially inwardly to the turbine wheel. The turbine wheel in turn rotates the compressor wheel for compressing air that is fed to the combustion chambers of the engine. Accordingly, the turbocharger can provide a performance boost and increased efficiency to the engine.

Exhaust gas flow through the turbocharger system may change depending on the operating conditions of the engine. For example, in lower-load conditions, exhaust gas mass flow may be relatively low. In contrast, in higher-load conditions, exhaust gas mass flow may be relatively high. Also, exhaust gas flow may vary from engine startup to a fully warmed-up running condition. Other operating conditions may affect exhaust gas flow as well.

Accordingly, it is desirable to provide an improved turbocharger system that regulates the flow of exhaust gas in a variety of operating conditions. In a conventional turbocharger, the turbine housing defines a bypass conduit located generally to one side of the main bore through the housing, and the bypass conduit is connected to the exhaust gas inlet or the exhaust gas chamber of the housing via a bypass valve, also called a waste gate valve. The waste gate valve typically is a swing or poppet style valve comprising a circular valve member that is urged against a flat valve seat surrounding the bypass passage opening. The valve usually is arranged such that the exhaust gas pressure acts on the valve member in a direction tending to open the valve. One drawback associated with such an arrangement is that it is difficult to completely seal the valve in the closed position, since gas pressure tends to open the valve. Leakage past the closed waste gate valve is a cause of performance degradation of the turbine and, hence, the turbocharger and its associated engine. The typical solution to the leakage issue is to preload the waste gate valve member against the valve seat, but often this does not fully eliminate leakage, and in any event it causes additional problems such as an increase in the required actuation force for opening the valve.

Furthermore, swing or poppet valves tend to be poor in terms of controllability, especially at the crack-open point, and it is common for the bypass flow rate to be highly nonlinear with valve position, which makes it very difficult to properly regulate the bypass flow rate. This leads to problems such as poor transient response of the turbocharger and engine system.

One object of the development described herein is to provide improved controllability to the exhaust gas flow to and around the turbine in a turbocharger.

Another issue impacting exhaust gas flow regulation is engine emissions. New emission standards require significant reduction of cold-start emissions. A catalytic converter typically requires a minimum “light-off” temperature of approximately 300° C. to start the catalytic process. The period of time after a cold start during which the catalyst is being heated to this temperature is called the catalyst light-off period. Emissions of government-regulated exhaust gas components such as NOx are much higher during catalyst light-off than during normal engine running. Accordingly, significant work has gone into various schemes for reducing the level of emissions produced during catalyst light-off.

Because cold-start emissions can by reduced by faster heating of the catalytic converter, one potential scheme for reducing cold-start emissions would be to fully bypass the turbine and feed the exhaust gases directly to the catalyst, thereby avoiding the significant drop in temperature of the exhaust gases when they must first pass through the turbine. However, a standard waste gate system does not close the turbocharger inlet, and therefore is unable to completely bypass the turbine. Therefore, a secondary valve that closes the turbine inlet would be necessary, but double-valve systems mean high cost and packaging constraints.

SUMMARY OF THE DISCLOSURE

The present disclosure describes a single-valve system that is able to fully bypass the turbine for fast catalyst light-off, and is also able to regulate the flow through the turbine after the catalytic converter has reached its operational state. The described system requires only one valve and one actuator. At a peak torque condition, the turbine inlet can be open with no restriction, while the turbine bypass passage is fully closed. At full engine load, the turbine inlet can remain fully open while the bypass passage begins to open. In other operating conditions, the turbine inlet can be partially closed while the bypass passage is fully opened, so as to lead to a base boost benefit. For cold start, the turbine inlet can be fully closed while the bypass passage is fully open for rapid catalyst light-off.

A turbocharger in accordance with one embodiment of the invention comprises a compressor and a turbine, the turbine comprising a turbine housing having a turbine wheel disposed therein. The turbine housing defines an annular chamber surrounding the turbine wheel for receiving exhaust gases from an internal combustion engine, and an axial bore through which exhaust gases are discharged after passing through the turbine wheel. The turbocharger includes a three-way valve housing comprising an inlet, a first outlet, and a second outlet, the inlet and the first and second outlets being connected to a valve chamber defined by the three-way valve housing. The valve chamber defines a cylindrical inner surface surrounding a valve chamber axis. The first outlet has a first circumferential width and the second outlet has a second circumferential width.

The turbine housing further defines a turbine feed passage connected between the first outlet of the three-way valve housing and the annular chamber, and a bypass passage connected between the second outlet and the axial bore downstream of the turbine wheel. A rotary valve member is disposed in the valve chamber and is rotatable about the valve chamber axis between successive first, second, third, and fourth rotational positions. The rotary valve member comprises a hollow member having an outer wall defining a cylindrical outer surface confronting the cylindrical inner surface of the valve chamber. The outer wall of the valve member defines a valve member outlet comprising an opening through the outer wall, and the valve member outlet has a third circumferential width that is large enough to span across the entire first circumferential width of the first outlet plus a portion of the second circumferential width of the second outlet.

The first and second outlets in the valve housing and the valve member outlet are configured and positioned such that in the first rotational position of the rotary valve member, the valve member outlet circumferentially overlaps all of the first outlet while the outer wall closes the second outlet. Thus, in the first rotational position, the turbine feed passage is fully opened while the bypass passage is closed. In the second rotational position, the valve member outlet circumferentially overlaps all of the first outlet and overlaps partially with the second outlet, such that the turbine feed passage remains fully open and the bypass passage begins to open. In the third rotational position, the valve member outlet circumferentially overlaps partially with the first outlet and overlaps all of the second outlet, such that the turbine feed passage is partially open and the bypass passage is fully open. In the fourth rotational position, the valve member outlet circumferentially overlaps all of the second outlet while the outer wall closes the first outlet, such that the turbine feed passage is closed and the bypass passage is fully open.

In one embodiment, the first outlet defines a first outlet flow direction that makes an obtuse angle with the valve chamber axis, and the second outlet defines a second outlet flow direction that makes an obtuse angle with the valve chamber axis and makes an acute angle with the first outlet flow direction.

The first outlet can be rectangular and the second outlet can be triangular.

In one embodiment, one end of the rotary valve member adjacent the inlet to the three-way valve housing is open, and an opposite end of the rotary valve member is closed by a sloping end wall that makes an obtuse angle with the valve chamber axis.

