GB2167806A - Turbocharger for an internal combustion engine - Google Patents

Abstract

A wastegate valve 32 or a variable geometry turbine housing system is controlled partly by a control signal related to the pressure in the intake manifold 10 and partly by a control signal related to the pressure in the exhaust manifold 14. The two signals act on the wastegate valve in opposite senses, with increasing intake manifold pressure tending to open the valve and increasing exhaust manifold pressure tending to close the valve. The arrangement is particularly useful for larger diesel engines where the exhaust manifold is split. The wastegate can be fitted in one exhaust manifold 12, while the control signal is taken from the other manifold 14. <IMAGE>

Description

SPECIFICATION Turbocharger for an internal combustion engine This invention relates to a turbocharger for an internal combustion engine, particularly a turbocharger for a diesel engine.

The use of a turbocharger on a diesel engine is a conventional method of increasing the power output. The natural turbocharger characteristic increases the boost pressure of the intake air more at high engine speeds and loads than at low engine speeds and loads (see curve a in Fig. 1). The result is that the boost pressure tends to be inadequate at low engine speeds, unless the turbocharger is rematched to provide low speed boost. In this case the boost pressure is too high at high engine speeds and this results in high cylinder pressures which may cause damage to the engine and which in any case reduce the engine durability (see curve b in Fig. 1).

It is known to fit a wastegate system to a turbocharger so as to allow exhaust gas flow to bypass a turbine of the turbocharger so that, above a certain level, a constant boost pressure is maintained by the action of a feedback control operated from the intake manifold which controls the opening and closing of the wastegate and leads to a boost pressure characteristic as shown by curve c in Fig. 1).

However the optimum boost pressure curve is approximately as shown by curve d in Fig.

1, where there is a higher pressure at high speed than at low speed. With this characteristic, the engine performance parameters of smoke cylinder pressure and exhaust temperature can be met, and a torque curve can be provided which gives high torque extending to low engine speeds.

According to the present invention, there is provided a turbocharger for an internal combustion engine where the turbine stage of the turbocharger is fed by the exhaust gases leaving the engine, and wherein means are provided for varying the force transmitted by the exhaust gases to the turbine, said means being controlled in the sense of decreasing the force transmitted by a pressure-related control signal from an intake manifold of the engine, and in the sense of increasing the force transmitted by a pressure-related control signal from the exhaust manifold.

Preferably the control signal is a pressure signal, and the means for varying the force transmitted by the exhaust gases is a pneumatic actuator.

The turbocharger may be used with an engine which has two exhaust manifolds leading into the turbine stage of the turbocharger. The control signal related to pressure in the exhaust manifold may be derived from one only of the two exhaust manifolds.

The means for varying the force transmitted by the exhaust gases may be variable geometry turbine housing system. Preferably however a wastegate is used which opens a bypass passage for the exhaust gases around the turbine. The wastegate may be fitted so as to provide a bypass for one exhaust manifold only, whilst the control signal related to the exhaust pressure is derived from the other exhaust manifold.

The wastegate valve may be pneumatically operated valve, using a piston moving in a cylinder to open and close the valve. The piston may be biassed on one side by pressure from the intake manifold, and on the other side by pressure from the exhaust manifold.

A balancing spring may be provided in the cylinder to assist the biassing force exerted on the piston by the exhaust gas pressure.

The valve is preferably a poppet valve, but other types of valve maybe used including, for example, a flap valve.

The cylinder may have a stepped cylindrical bore, with one piston working in the smaller diameter section of the bore and another piston working in the larger diameter section.

The pressure from the intake manifold may act on the larger piston, and the pressure from the exhaust manifold may act on the smaller piston. The space between the pistons would be vented.

The application of the exhaust gas pressure as a control signal to the wastegate valve allows the boost pressure to respond also to engine load as well as to speed. At low engine loading, the exhaust pressure is low and this causes the wastegate valve to open so that less boost pressure is produced, giving boost pressure only when it is requied so as to improve the overall fuel economy by optimising the use of exhaust energy.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a graph showing engine speed plotted against boost pressure; Figure 2 is a schematic view of a turbocharger arrangement in accordance with the invention; Figure 3 is a detailed view of the wastegate control arrangement in accordance with the invention; and Figure 4 shows an alternative form of wastegate control.

The curves shown in Fig. 1 have already been briefly described in the introduction to this specification. In the graph, the intake boost pressure is plotted against the engine speed. Curve a illustrates the linear change in boost pressure with rising engine speed which occurs in the absence of any provision for varying the turbocharger output. The disadvantage of this arrangement is that the boost pressure is inadequate at low engine speeds.

Curve b also shows a linear relationship between intake boost pressure and engine speed, but with the turbocharger rematched to give a higher boost at idle and a steeper rate of climb. The disadvantage of this however is that the boost rises too high at high engine speeds. Curve c shows the situation with a conventional wastegate, where the boost pressure initially rises at a set rate to a point where the wastegate opens. Thereafter the boost pressure remains flat irrespective of the engine speed. Curve d represents a more desirable characteristic which can be achieved by the turbocharger arrangement to be described.

Fig. 2 shows an intake manifold 10 and two exhaust manifolds 12 and 14. The manifolds are for connection to a six-cylinder engine, conveniently a six-cylinder diesel engine. The intake manifold is in a single piece, but the exhaust manifolds 12 and 14 are split and each receives exhaust gases from three out of the six cylinders. The manifolds are connected by separate pipes 16 and 18 to a turbine 20 of a turbocharger 22 which has a compressor stage 24. As is conventional, the turbine 20 is driven by the exhaust gases which finally exit through an exhaust pipe 26, and the rotation of the turbine drives the compressor 24 in order to compress intake air which enters the intake manifold 10 through a pipe 28.

In order to be able to control the boost pressure provided by the turbocharger 22, it is necessary to control the force transmitted by the hot exhaust gases to the turbine 20. A bypass passage 30 is provided between the pipe 16 and the exhaust pipe 26 so that some or all of the exhaust gases in the pipe 16 can be dumped directly to waste without acting on the turbine 20.

The bypass passage 30 can be opened or closed by means of a poppet valve 32. The valve is mounted on a stem 34 which is connected to a piston 36 working in a cylinder 38. The right-hand side of the cylinder 38 is fed with a control pressure from the intake pipe 28, through a port 40 and a control line 42. The left-hand side of the cylinder 38 is fed with control pressure from the exhaust manifold pipe 18 through a port 44 and a line 46.

In use, pressure from the intake manifold 10, through the line 42, tends to open the valve 32 and provides feed-back action to stabilise the boost pressure. In addition pressure from the exhaust manifold 18 is applied to the piston 36 in the sense that tends to close the valve 32. The pressure in the exhaust manifold 12, 14 rises with engine speed and load in a manner that gives the desirable boost pressure characteristic required and indicated by curve d in Fig. 1. A balancing spring 48 is also present in the wastegate control cylinder 38 and assists the exhaust pressure from the manifold 14.

Fig. 3 shows to a larger scale the construction of the poppet valve head 32 and the cylinder 38. Inlet ports 50 and 52 for intake and exhaust manifold pressures respectively are shown here. The poppet valve head 32 has a valve seat 54.

Fig. 4 shows an alternative control for the poppet valve 32. The working cylinder 56 has two coaxial bores 58 and 60 separated by a shoulder 62. A smaller diameter piston 64 works in the cylinder section 60, and a larger diameter piston 66 works in the cylinder section 58. The intake air pressure enters through port 50 and acts on the surface of the larger piston 66, whilst the exhaust pressure from the manifold 14 enters through the port 52 and acts on the smaller diameter piston 64 (assisted by a spring 48). The differential area of the pistons 64 and 66 allows a different weighting to be given to the exhaust and intake pressures, insofar as they control movement of the valve 32. The space between the pistons 64 and 66 is vented through a port 68.

The arrangement described has considerable flexibility and allows virtually any desired boost characteristic to be obtained, by suitable choice of the spring rate of the spring 48 and/or by a suitable choice of the relative areas of the pistons 64 and 66 if the Fig. 4 embodiment is being used.

The exhaust pressure through line 46 is fed via a length of metal pipe or similar conductive connection so that the gas entering the cylinder 38 is cooled sufficiently to prevent adverse effects on the operation of the piston 36. Only transient flow rates occur through this line, in addition to leakage, and the additional heat flow to the wastegate valve is not significant.

Claims (14)

1. A turbocharger for an internal combustion engine where the turbine stage of the turbocharger is fed by the exhaust gases leaving the engine, and wherein means are provided for varying the force transmitted by the exhaust gases to the turbine, said means being controlled in the sense of decreasing the force transmitted by a pressure-related control signal from an intake manifold of the engine, and in the sense of increasing the force transmitted by a pressure-related control signal from the exhaust manifold.

2. A turbocharger as claimed in Claim 1, wherein the control signal is a pressure signal, and the means for varying the force transmitted by the exhaust gases is a pnematic actuator.

3. A turbocharger as claimed in Claim 1 or Claim 2, adapted for use with an engine which has two exhaust manifolds leading into the turbine stage of the turbocharger.

4. A turbocharger as claimed in any preceding claim, wherein the control signal related to pressure in the exhaust manifold is derived from one only of the two exhaust manifolds.

5. A turbocharger as claimed in any preceding claim, wherein the means for varying the force transmitted by the exhaust gases is a variable geometry turbine housing system.

6. A turbocharger as claimed in any one of claims 1 to 4, wherein a wastegate is used which opens a bypass passage for the exhaust gases around the turbine.

7. A turbocharger as claimed in Claim 6, wherein the wastegate is fitted so as to provide a bypass for one exhaust manifold only, whilst the control signal related to the exhaust pressure is derived from the other exhaust manifold.

8. A turbocharger as claimed in Claim 6 or Claim 7, wherein the wastegate valve is a pneumatically operated valve, using a piston moving in a cylinder to open and close the valve.

9. A turbocharger as claimed in Claim 8, wherein the piston is biassed on one side by pressure from the intake manifold, and on the other side by pressure from the exhaust manifold.

10. A turbocharger as claimed in Claim 9, wherein a balancing spring is provided in the cylinder to assist the biassing force exerted on the piston by the exhaust gas pressure.

11. A turbocharger as claimed in any of claims 6 to 10, wherein the wastegage comprising a poppet valve.

12. A turbocharger as claimed in any one of claims 8 to 11, wherein the cylinder has a stepped cylindrical bore, with one piston working in the smaller diameter section of the bore and another piston working in the larger diameter section.

13. A turbocharger as claimed in Claim 12, wherein the pressure from the intake manifold acts on the larger piston, the pressure from the exhaust manifold acts on the smaller piston and the space between the pistons is vented.

14. A turbocharger substantially as herein described with reference to the accompanying drawings.