GB2421983A

GB2421983A - Hydraulic control of a turbocharger

Info

Publication number: GB2421983A
Application number: GB0500132A
Authority: GB
Inventors: Brian Eves; Andrew David Scarisbrick; Derek Eade
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2005-01-06
Filing date: 2005-01-06
Publication date: 2006-07-12
Anticipated expiration: 2025-01-06
Also published as: GB0500132D0; GB2421983B

Abstract

A turbocharger has a hydraulic actuator 26 which is operable to vary the output of the turbocharger at a given exhaust gas flow rate. The hydraulic actuator 26 may be supplied with oil from an oil supply line 30 which also supplies lubricating oil to bearings which support a shaft of the turbocharger. The hydraulic actuator 26 may have a working chamber 28 connected to the oil supply line 30, and to an oil reservoir via a return line 22, 24, the return of oil being regulated by an electrically controlled valve 20. The valve 20 may be a solenoid valve operated by a pulse width modulated signal. The hydraulic actuator 26 may operate a waste gate, a dump valve or a variable intake geometry of the turbocharger.

Description

TURBOCHAIGER CONTROL

Field of the invention

The present invention relates to the control of turbochargers.

Background of the invention

As is well known, a turbocharger is a device that increases the pressure in the intake system of an engine Using power derived from the exhaust gases. A turbine wheel arranged in the exhaust stream is mounted on the same shaft as a compressor wheel that boosts the pressure in the intake system. The shaft is mounted on bearings which are normally oil lubricated.

It 5 desirable in an engine with a turbocharger to be able to vary the boost pressure in the intake system at any given exhaust gas flow rate in dependence upon other operating conditions For this purpose, turbochargers are known which have a variable intake geometry while other known turbochargers have a so-called wastegate to allow a proportion of the exhaust gases to bypass the turbine wheel.

It is also known to provide a turbocharger with a dump valve arranged in a passage that short circuits the compressor wheel. when the throttle plate is rapidly closed, e.g. during gearshjft5, the airflow momentarily ceases and the pressure between the compressor and the throttle plate increases. This slows the turbocharger, meaning that it would need to be accelerated once again when the throttle is re-opened, causing an undesirable delay in engine torque output. By opening a dump valve, the compressed air is allowed to flow back to the low pressure air inlet side of the compressor mitigating the foregoing problem. Opening of a dump valve also avoids other undesirable effects such as excessive loads on the compressor which cause wear and noise as the compressor blades stall. The dump valve is normally Operated by vacuum from the engine intake manifold or via a vacuum reservoir fed from the intake manifold.

In all three of the above described turbocharger controls, an external actuator is required, whether it is for varying the intake geometry, for opening and Closing the wastegate or for operating the dump valve. Hitherto such io actuators have been Pneumatically operated (i.e. by air or vacuum) but the present invention is predicated on the realisation that this is disadvantageous because an undesirable closed control loop is created. In particular, the control pressure for the actuator 5 normally derived from the intake manifold while the movements effected by the actuator themselves affect the pressure in the intake manifold.

Aside from the above disadvantage, the use of a vacuum to control a turbocharger requires the use of a large accumulator, that it difficult to accornmodate within a crowded engine compartment while the use of electrical actuators 15 unduly costly and complex.

Summary of the invention

To mitigate the foregoing disadvantages the present invention provides a turbocharger having an actuator for varying the output of the turbocharger at any given exhaust gas flow rate, characterised in that the actuator is a hydraulic actuator.

Preferably, a shaft of the turbocharger connecting the turbine and the compressor of the turbocharger is supported in an oil lubricated bearing, the bearing and the actuator being connected to a common oil supply.

The preferred embodiment of the invention recognises that the oil supply to the turbocharger bearing offers a conveniently located alternative Source of power for driving the actuator.

A further advantage of using a hydraulic actuator is that it requires considerably less space than a pneumatic actuator, space being often at a premium in the engine compartment of modern engines.

To permit control of the pressure in the hydraulic working charner of the actuator, the working chamber may have a supply line Connected to the line supplying oil to the shaft bearing and a return line leading to a reservoir under ambient pressure by way of an electrically Controlled valve.

The electrically controlled valve may be variable throttle valve (controlled for example by a tapering needle) or a pulse width modulated solenoid valve.

Brief description of the drawing

The invention will now be described further, by way of example, with reference to the accompanying drawing which is a schematic diagram of a turbocharger control system.

Detailed description of the drawings

It is assumed that the skilled person in the art will already be familiar with the construction and principle of operation of turbochargers, both of the wastegate and variable geometry variety, as well as turbochargers having a dump valve. For this reason, the construction of the turbocharger is not shown in the drawing and will not be described in detail and the reader is instead to referred to prior art references such as US Patents 4,630,445 and 6,203,272. For the present purposes, it Suffices to know that a turbocharger comprises a shaft mounted on an oil lubricated bearing which is connected at one end to a turbine wheel arranged to be driven by the engine exhaust gases and at the other end to a compressor wheel which boosts the pressure in the intake manifold The turbocharger also has a control lever connected to a wastegate, to a dump valve or to a movable vane to change the boost pressure at any given rate of flow of the engine exhaust gases.

The accompanying drawing shows an engine inlet manifold in which the pressure is boosted by being connected to the compressor side of a turbocharger of which only the wastegate 36 is shown in the drawing. The boost pressure is measured by a sensor 12 which sends a signal over a line 14 to an engine control unit 16. The ECU 16 forms part of a closed control loop, now to be described that maintains the boost pressure at a desired level by acting on the control lever of the turbocharger. In the drawing and the following description it is assumed that the turbocharger has a wastegate but it will be clear from what has been Stated above that the invention may be applied to turbochargers of the variable geometry type.

The wastegate 36 of the turbocharger has a control linkage 34 connected to the piston 32 of a hydraulic actuator 26. The actuator 26 has a working chamber connected to an oil supply line 30 that also supplies oil to lubricate the bearings of the shaft of the turbocharger. The working chaer 28 is further connected by way of a line 22 and a solenoid valve 20 to a return line 24 leading to the engine oil sump, which is at ambient pressure. The Solenoid valve 20 is controlled by a signal received Over a line 18 from the engine control unit 16.

The signal sent to the solenoid valve 20 is a PM (pulse width modulated) signal and its operation is to connect the working chamber 28 to the ambient pressure of the return line 24 intermittently. The mark to space ratio of the signal regulates the flow of oil through the valve 20 and therefore its effective flow resistance. it will be appreciated that if the valve 20 is Permanently shut, the working chamber will be at the same pressure as the oil supply line 30 and if it is Permanently open the working chamber 28 will be under ambient pressure. Accordingly, by varying the mark to space ratio of the PWM signal on the line 18, the ECU can vary the pressure in the working chamber 28 between these two limits and thereby determine the position of the wastegate valve 36.

If the boost pressure sensed by the sensor 12 is above the desired boost pressure determined by the engine control unit 16, the latter send a PM signal over the line 18 to increase the opening of the wastegate 36. This will have the effect of lowering the boost pressure because a greater proportion of the exhaust gases will be diverted to bypass the turbine wheel of the turbocharger. Conversely, if the boost pressure is lower than desired, the wastegate 36 will be closed.

It will be clear that in place of a solenoid valve 20 operated by a digital PWM signal, one may use a electrically variable throttle valve Operated by an analogue signal. All that is required is that the engine control unit Should be able to regulate the pressure in the working chamber 28 so as to control the boost pressure.

The hydraulic actuator 26 and, if desired, the solenoid valve 20 may be integrated into the turbocharger so that the oil supply line 30 may be formed by a gallery in the body of the turbocharger. This makes for a very compact construction which reduces the number of pipes leading to the actuator.

Claims

1. A turbocharger having an actuator for varying the output of the turbocharger at any given exhaust gas flow rate, characterised in that the actuator is a hydraulic actuator.

2. A turbocharger as claimed in claim 1, wherein a shaft of the turbocharger connecting the turbine and the compressor of the turbocharger is Supported in an oil lubricated bearing, the bearing and the actuator being connected to a common oil supply.

3. A turbocharger as claimed in claim 2, wherein the hydrauj actuator has a working chamber having a supply line connected to the line supplying oil to the shaft bearing and a return line leading to a reservoir under ambient pressure by way of an electrically controlled valve.

4. A turbocharger as claimed in claim 3, wherein the electrically controlled valve is a solenoid valve adapted to be Operated by a pulse width modulated signal.