GB2437985A

GB2437985A - Diesel Engine control

Info

Publication number: GB2437985A
Application number: GB0609038A
Authority: GB
Inventors: Khizer Tufail
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2006-05-09
Filing date: 2006-05-09
Publication date: 2007-11-14
Anticipated expiration: 2026-05-09
Also published as: GB2437985B; GB0609038D0

Abstract

A diesel engine 10 is fitted with a diesel particulate filter 24, and a variable geometry turbocharger 16 having a turbine 18 arranged in the exhaust system of the engine upstream of the diesel particulate filter 24. A control system 30 generates an intake manifold pressure demand signal in dependence upon the prevailing engine speed and load and varies the geometry of the turbocharger 16 to achieve an intake manifold pressure corresponding to the demand signal. In the invention, a sensor 28 is provided for determining the drop in pressure across the diesel particulate filter 24 and the demand signal generated by the control system 30 is reduced in dependence upon the drop in pressure across the diesel particulate filter 24 in order to avoid overloading the turbocharger 16.

Description

DIESEL ENGINE CONTROL

Field of the invention

The present invention relates to the control of a diesel engine fitted with a turbocharger and a diesel particulate filter (DPF)

Background of the invention

It is currently common to fit diesel engines with a turbocharger to boost the pressure in the intake manifold in order to increase the mass of air in the cylinders and thereby increase the peak output power of the engine. It is also common for diesel engines to be fitted with particulate filter traps in order to prevent soot particles from being discharged by way of the exhaust system into the ambient atmosphere.

The pressure in the engine intake manifold is set by means of a control system in dependence upon the prevailing operating conditions of the engine, in particular the engine speed and load. Turbochargers are known that have a variable geometry to allow the degree of boost to be regulated. Such turbochargers can be used in a closed loop feedback system to maintain the pressure in the intake manifold at the value dictated by the engine control system.

A disadvantage of existing control systems is that they take no account of the condition of the DPF. As soot builds up within the DPF, it becomes progressively more difficult for the turbine of the turbocharger to pump air through it.

If the closed loop feedback system sets the geometry of the turbocharger to yield the intake manifold pressure demanded by the control system, without taking into account the blockage in the DPF, then the turbocharger can be overloaded, resulting in possible damage.

Summary of the invention

With a view to mitigating the foregoing disadvantage of the prior art, the present invention provides a diesel engine having a diesel particulate filter, a variable geometry turbocharger having a turbine arranged in the exhaust system of the engine upstream of the diesel particulate filter, and a control system for generating a demand signal in dependence upon the prevailing engine speed and load and varying the geometry of the turbocharger to achieve an intake manifold pressure corresponding to the demand signal, characterised in that a sensor is provided for determining the drop in pressure across the diesel particulate filter and in that the demand signal generated by the control system is reduced in dependence upon the drop in pressure across the diesel particulate filter in order to avoid overloading the turbocharger.

In the present invention, the control system takes the state of the DPF into consideration when setting the demand signal for the intake manifold pressure and essentially reduces peak engine output power by limiting the degree of boost when the engine is operating at full load so that the turbocharger is not overloaded and damaged. This loss of power will, if severe, be noticed by the operator and will serve as a warning that the DPF is blocked and in need of attention.

The demand signal for setting the intake manifold pressure is normally derived in the control system from a look-up table that is populated during initial engine calibration. Conventionally, the look-up table is two dimensional, allowing the correct demand pressure to be looked up using two input parameters, namely engine speed and load.

In one embodiment of the present invention, use is made of a three dimensional look-up table where the third input parameter is the pressure drop caused by the DFF.

It is alternatively possible to use a modification algorithm to vary the value of the demand pressure looked up from a two dimensional table. The algorithm may for example reduce the intake manifold demand pressure by a factor and/or by an offset that varies with the severity of the blockage of the DPF.

Engines having an DPF can, in addition to their normal mode of operation, be operated in a mode designed to generate high exhaust temperature and surplus exhaust oxygen for the purpose of regenerating the DPF when it is blocked, by burning off the soot that has accumulated within it. The limitation of the boost pressure proposed by the present invention to avoid damage to the turbocharger is applicable not only when the engine is operating normally but also when it is operating in a DPF regenerating mode.

Brief description of the drawings

The invention will now be described further, by way of example, with reference to the accompanying which is a schematic diagram showing a diesel engine of the present invention together with its control system.

Detailed description of the preferred embodiment

The drawing shows a diesel engine 10 having an intake manifold 12 and an exhaust manifold 14. A turbocharger, generally designated 16, is connected to the intake and exhaust systems of the engine 10. The turbocharger comprises a turbine 18 driven by the engine exhaust gases and a compressor 20 which is mechanically driven by the turbine and serves to compress ambient air drawn in through an intake pipe 22 before it enters the intake manifold 12.

Before they are discharged into the ambient atmosphere, the engine exhaust gases pass through the diesel particulate filter 24 which acts as a trap for any soot particles.

Downstream of the DPF 24, the exhaust system 26 may include a catalytic converter and a silencer (muffler) but these are not shown as they are not relevant within the present context.

The turbocharger 16 is one that has a variable geometry. Such turbochargers are well known in the art and have adjustable vanes or nozzles which allow the degree of boost to be varied.

The control of the engine 10 and the turbocharger 16 is effected by a control system 30. The control system 30 receivers various input signals over input lines 40 of which only two are shown in the drawing to represent engine speed and engine load. From these two input parameters, the control system 30 looks up, or otherwise calculates, the amount of fuel that needs to be injected into the engine 10 and the pressure that is required in the intake manifold 12.

The intake manifold pressure is controlled to the level demanded by the control system 30 by means of a closed feedback loop that incorporates an intake pressure sensor 38. The sensor 38 provides the control system 30 over a line 36 with a signal indicative of the actual pressure in the intake manifold 12. If this actual pressure differs from the demand pressure determined by the control system 30, then a signal is sent over a line 34 to vary the geometry of the turbocharger 16 in the correct sense to reduce the error between the actual and desired values of the intake manifold pressure.

As so far described the construction and operation of the engine 10, the turbocharger 16 and the control system 30 are conventional, the control system 30 taking no account of the state of the DPF 24. Because of this, when operating under high engine speed and load, the control system 30 will set a high intake manifold demand pressure, requiring a high degree of boost by the turbocharger 16, even if the DFF 24 is blocked. Attempting to force a large volume of exhaust gases at high temperature and pressure through a blocked DPF 24 can cause damage to the turbocharger 16 and it is this problem that the invention seeks to mitigate.

To determine the state of the DPF 24, a differential pressure sensor 28 is connected upstream of the DPF 24. The differential pressure sensor 28 may simply measure the difference between the pressure in the exhaust system upstream of the DPF and the ambient atmospheric pressure.

Alternatively, as represented by a second collection shown in dotted lines, the differential pressure sensor 28 may be connected both upstream and downstream of the DPF 24. The output of the differential pressure sensor 28, which is indicative of the state of the DPF 24 is applied by way of a line 32 to the control system 30. The control system 30 is designed in the present invention to take the signal from line 32 into consideration when setting the demand pressure for the intake manifold 12. The signal from line 32 may either be used as a further parameter to address a three-dimensional lookup table or it may be used in an algorithm to modify the demand pressure value looked up from a two-dimensional table, to reduce it appropriately as the backpressure in the exhaust system increases.

As a result, when the DPF 24 in the present invention is blocked, the control system 30 does not attempt to operate the engine and the turbine at full power thereby reducing the risk of damage to the turbocharger. The reduction in the maximum engine output power, if sufficiently severe, will alert the engine operator to the fact that the DPF 24 is in need of attention.

The limiting of the demands placed on the turbocharger 16 will apply regardless of the mode of operation of the engine and will safeguard the turbocharger 16 from damage both when the engine is operating normally and when it is operating in a DPF regenerating mode.

Claims

CLAIMS

1. A diesel engine having a diesel particulate filter, a variable geometry turbocharger having a turbine arranged in the exhaust system of the engine upstream of the diesel particulate filter, and a control system for generating a demand signal in dependence upon the prevailing engine speed and load and varying the geometry of the turbocharger to achieve an intake manifold pressure corresponding to the demand signal, characterised in that a sensor is provided for determining the drop in pressure across the diesel particulate filter and in that the demand signal generated by the control system is reduced in dependence upon the drop in pressure across the diesel particulate filter in order to avoid overloading the turbocharger.

2. A diesel engine as claimed in claim 1, wherein the demand signal is looked-up in the control system from a three-dimensional look- up table.

3. A diesel engine as claimed in claim 1, wherein the demand signal is looked-up in the control system from a two-dimensional look-up table in dependence upon engine speed and load and is modified by an algorithm to take into account the drop in pressure across the diesel particulate filter.

4. A diesel engine as claimed in any preceding claim, in which pressure sensor is operative to measure the difference between two points in the exhaust system that are upstream and downstream, respectively, of the diesel particulate filter.

5. A diesel engine as claimed in any of claims 1 to 3, wherein the pressure sensor is operative to measure the difference in pressure between a point in the exhaust system upstream of the diesel particulate filter and the ambient atmospheric pressure.

6. A diesel engine constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawing.