GB2263939A

GB2263939A - Turbocharger system

Info

Publication number: GB2263939A
Application number: GB9202411A
Authority: GB
Inventors: Jake Walker
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1992-02-05
Filing date: 1992-02-05
Publication date: 1993-08-11
Anticipated expiration: 2012-02-05
Also published as: GB2263939B; GB9202411D0

Abstract

The actuator comprises a piston 50 which divides the actuator body 40 into two chambers. An actuating rod 38 connects the wastegate (28, Fig. 1) to the piston and a spring 62 lightly biases the wastegate closed. A modulating unit 80 has valves 96, 98 which are mechanically or electrically linked together, 97, to oscillate continuously between their extreme positions to alternately supply pressure from the inlet duct via line 102 to each chamber in turn, the remaining chamber being exposed to atmospheric pressure via lines 92, 94. By varying the proportion of time during which the inlet pressure is supplied to a particular side of the piston the force acting against the piston in either direction can be controlled and hence the opening of the wastegate can be controlled. The valves 96, 98 are controlled by signals from an engine speed sensor and a throttle angle sensor. <IMAGE>

Description

A TURBOCHARGER SYSTEM The present invention relates to turbocharger systems, and in particular to a turbocharger system for an internal combustion engine, the system comprising an exhaust duct leading from the engine, an inlet duct leading to the engine a turbine having its input connected to the exhaust duct and its output connected to the inlet duct and a wastegate in the exhaust duct operable to reduce the pressure in the exhaust duct. In such a system the boost produced by the turbo is controlled by opening or closing the wastegate to reduce or increase the pressure input to the turbine. The wastegate is conventionally controlled by a capsule comprising a chamber with a piston slidable therein and defining a pressure chamber on one side of the piston. The piston is linked to the wastegate by a pushrod and a pivoting actuator arm.An inlet port in the pressure chamber admits air under pressure to urge the piston in one direction to open the wastegate. A spring urges the piston in the opposite direction to close the wastegate. The pressure chamber inlet port is connected via a modulating control valve to the inlet duct of the engine which provides a source of pressurised air.

Under normal operation the boost provided by the turbine is modulated to a desired level by the modulating control valve and the capsule. As the boost increases above the desired level the pressure in the engine inlet duct increases. This pressure is fed via the modulating valve to the pressure chamber of the capsule which opens the wastegate against the action of the spring, thus reducing the pressure in the exhaust duct and decreasing the boost. The amount by which the wastegate can be opened therefore depends on the difference between the pressure in the engine inlet duct and the force of the spring, and the pressure difference across the turbine.

At low engine speeds the pressure drop across the turbine input in the exhaust duct is high, so if the spring is too weak the wastegate is forced open by the gas pressures acting directly on it and little boost is possible.

Such known systems therefore suffer from the problem that the spring urging the wastegate closed needs to be of a higher rating to provide more boost at low engine speeds, but needs to be of a lower rating to produce a greater range of boost through boost modulation at high engine speeds. The spring chosen is therefore a compromise between these demands.

The present invention provides a turbocharger -system for an internal combustion engine, the system comprising an exhaust duct leading from the engine, and an inlet duct leading to the engine, a turbine having its input connected to the exhaust duct and its output connected to the inlet duct. A wastegate in the exhaust duct operable to reduce the pressure in the exhaust duct, an actuating means connected to the wastegate, pressure supply means for supplying a variable pressure to the actuating means in each of two directions to urge the wastegate towards an open position and closed position respectively.

The present invention also provides a turbocharger wastegate control mechanism comprising a wastegate actuating means movable in two opposite directions and two chambers, each being partly defining by a respective part of the actuating means, each of the chambers having an inlet port for admitting pressurized fluid to urge the actuating means in a respective one of said two opposite directions.

Preferred embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a turbocharger system according to the invention; Figure 2 is a section through the wastegate control mechanism of the system of Figure 1; and Figures 3a and 3b show the operation of the modulation valve of the system of Figure 1.

An internal combustion engine 10 has an inlet manifold 11 connected to an air inlet duct 12, which in turn is connected to an air inlet 16 via the output side 18 of a turbine 20.

The engine also has an exhaust manifold 21 connected to an exhaust duct 22, which in turn is connected to an exhaust 24 via the input side 26 of the turbine 20. The exhaust duct 22 has an aperture 28 and a waste duct 30 leading from the aperture 28 connects the exhaust duct 22 to the exhaust 24 directly, bypassing the input side 26 of the turbine 20. A wastegate 32 is mounted on a pivoting actuator arm 34 which is rotatably mounted on a pivot 36 at one end. The wastegate 32 is movable between a closed position in which it covers the aperture 28 and an open position in which it is held away from the aperture. The other end of the actuator arm 34 is pivotally connected to an actuator rod 38.

A cylindrical capsule 40, shown in more detail in Figure 2, comprises a casing 42 formed in two halves 42a, 42b each of which has a lip 44 where the two halves are joined. The casing 42 has an aperture 46 formed in one end wall 47 which slidably receives the actuator rod 38. An airtight seal 48 is provided to seal the aperture 46 around the actuator rod 38. A piston 50 is mounted on the end 52 of the actuator rod 38 which is inside the casing 42. The piston 50 is in the form of a flat circular plate which is of a diameter slightly less than that of the capsule 42 and which has a lip 54 around its edge. A rolling diaphragm 56 has its inner edge attached to the lip 54 on the piston 50 and its outer edge secured between the lips 44 on the two casing halves 42a, 42b. The piston 50 and diaphragm 56 divide the capsule 40 into a front chamber 58 and a rear chamber 60.A coil spring 62 in the rear chamber 60 is under compression and acts between the end wall 47 and the piston 50 to bias the piston away from the end wall 47 to increase the volume of the rear chamber 60, decrease the volume of the front chamber 58, and move the wastegate 32 towards the closed position.

A first port 64 is formed in the side wall 65 of the front chamber 58, and a second chamber 66 is formed in the side wall 67 of the rear chamber 60.

A modulating valve 80 comprises two valves in a single unit. It has an input port 82, two output ports 84, 86 each connected by a respective connecting passage 88, 90 to the input port 82, and two vents 92, 94 each connected to one of the output ports. The output port 84 is connected via a switching valve 96 to either the input port 82 or to a vent 92 depending on the position of the switching valve 96. Similarly the output port 86 is connected via a switching valve 98 to either the input port 82 or to a vent 94. The two switching valves are linked by a mechanical link 97 such that when the output port 84 is connected to the input port 82 the other output port 86 is always connected to the vent 94. Conversely when the output port 86 is connected to the inlet port 82 the other output port 84 is always connected to the vent 92. As an alternative, the valves could be linked electrically.

The input port 82 of the modulating valve 80 is connected by a pipe 102 to a port 108 in the inlet duct 12 of the engine 10. The outlet ports 84, 86 of the modulating valve 80 are connected by pipes 104, 106 to the first and second ports 64, 66 on the capsule 40.

The modulating valve is controlled by signals from an engine speed sensor and a throttle angle sensor (not shown). The valves 96, 98 oscillate continually between their extreme positions, the period for which they remain in each extreme position determining what percentage of the time the valve outlet ports 84, 86 are connected to the inlet port 82 and what percentage of the time they are connected to a vent 92, 94. This determines how much of the pressure from the engine inlet duct 12 is fed to each of the front and rear chambers 58, 60 of the capsule 40.

Operation of the modulating valve can be seen more clearly with reference to Figures 3a, 3b in which the horizontal axis represents time and the vertical axis represents the position of the valves 96, 98. Position X corresponds to the position of the valves as shown in Figure 1 in which the modulating valve inlet port 82 is connected to the front chamber 58 of the capsule, the rear chamber 60 is connected to the vent 94 and the pressure from the engine inlet duct 12 urges the piston 50 towards the rear chamber 60 and hence the wastegate 32 towards the open position.

This reduces the boost provided by the turbine 20.

Position Y corresponds to the opposite position of the valves in which the modulating valve inlet port 82 is connected to the rear chamber 60 of the capsule, the front chamber 58 is connected to the vent 92, and pressure from the engine inlet duct 12 urges the piston 50 towards the front chamber 58, and the wastegate towards the closed position. This increases the boost provided by the turbine 20.

Figure 3a corresponds to a setting of the modulating valve 80 when the throttle is closed or only slightly open and the engine speed is high. Under such conditions no boost is required so the valves 96, 98 spend most of each cycle in position X so that pressure is supplied to the front chamber 58 and the wastegate 32 is kept open.

If the throttle is then opened the valve operates as shown in Figure 3b the reeds spending most of each cycle in position Y. The pressure from the engine inlet duct 12 and the spring 62 act together to urge the wastegate towards the closed position, overcoming the drop in pressure across the turbo input 26 which tends to lift the wastegate 32 towards the open position, and providing a high level of boost. Since the spring 62 is assisted in this situation it can be of a relatively low rating.

At low engine speeds, the pressure drop across the turbine input 26 is still fairly high because exhaust backpressure is very low and this pressure drop still tends to open the wastegate 32. However there is little pressure available from the inlet duct 12. Nevertheless, because the spring 62 is of a relatively low rating the pressure available in the engine inlet duct is still sufficient to open the wastegate 32 at low throttle. When the modulating valve operates as shown in Figure 3b, and when the throttle is open, the combined effort of the spring 62 and the pressure supplied to the rear chamber 60 is sufficient to close the wastegate.

Claims

1. A turbocharger system for an internal combustion engine, the system comprising an exhaust duct leading from the engine, and an inlet duct leading to the engine, a turbine having its input connected to the exhaust duct and its output connected to the inlet duct, a wastegate in the exhaust duct operable to reduce the pressure in the exhaust duct, an actuating means connected to the wastegate, pressure supply means for supplying a variable pressure to the actuating means in each of two directions to urge the wastegate towards an open position and a closed position respectively.

2. A turbocharger system according to claim 1 wherein the pressure supply means is adapted to supply fluid pressure.

3. A turbocharger system according to claim 1 or claim 2 wherein the actuating means includes a piston.

4. A turbocharger system according to claim 3 further comprising a housing, the piston dividing the housing into first and second chambers and the pressure supply means being arranged to supply pressure to either of the two chambers.

5. A turbocharger system according to any foregoing claim wherein the pressure supply means comprises a single pressure source and valve means for directing the pressure to act on the actuating means in either of said two directions.

6. A turbocharger systems according to claim 5 when dependant on claim 4 wherein the valve means comprises two valves, each for connecting one of the chambers to the pressure supply, and a vent.

7. A turbocharger system according to claim 6, the valve means comprising two vents each connectable by one of the valves to one of the chambers.

8. A turbocharger system according to claim 6 or claim 7 wherein the two valves are coupled together such that as one valve opens a vent to one of the chambers, the other valve opens the pressure source to the other chamber.

9. A turbocharger system according to any foregoing claim wherein the pressure supply means supplies pressure from the inlet duct.

10. A turbocharger wastegate control mechanism comprising a wastegate actuating means movable in two opposite directions and two chambers, each being partly defining by a respective part of the actuating means, each of the chambers having an inlet port for admitting pressurized fluid to urge the actuating means in a respective one of said two opposite directions.

11. A turbocharger system substantially as hereinbefore described with reference to the accompanying drawings.

12. A turbocharger wastegate control mechanism substantially as hereinbefore described with reference to the accompanying drawings.