FR2813098A1 - DEVICE FOR DETECTING MALFUNCTION OF THE ENGINE EXHAUST SYSTEM - Google Patents

Abstract

The diesel engine is provided with an EGR pipe (17) connecting an exhaust manifold (9) and a balance tank (2) to each other, and an EGR valve (18) arranged in the EGR conduit (17). The EGR valve (18) is feedback controlled to make the EGR ratio equal to a target EGR ratio, based on the detected EGR ratio, the target EGR ratio being predetermined based on the engine operating condition. An actual opening of the EGR valve is detected when the feedback control of the opening of the EGR valve is in progress. A reference opening is obtained beforehand, which is an opening of the EGR valve (18) necessary to make the EGR ratio equal to the target EGR ratio, the exhaust system being in a reference condition, the reference condition being a condition in which the DPF (12) is new. It is considered that a malfunction has occurred in the DPF (12) when the actual opening of the EGR valve (18) is greater than the reference opening.

Description

DEVICE FOR DETECTING MALFUNCTION

  OF THE ENGINE EXHAUST SYSTEM

  The present invention relates to a device intended to detect a malfunction of an engine exhaust system. More particularly, the present invention relates to a device intended to detect a malfunction in a filter with

particles or an EGR passage.

  A diesel engine is known which is equipped with a diesel particulate filter (DPF) disposed in an exhaust system thereof, for trapping particulate matter (PM), including soot or non-combustible fuel.

  burned, for example, in this one.

  However, the DPF undergoes vibrations due to the operation of the engine and receives a large amount of heat from the exhaust gases, as well as a cyclic thermal stress due to the engine being alternately and repeatedly put into operation and stopped. It follows that a malfunction, including rupture, cracking, tearing or the like may occur in the DPF. Specifically, in the case where the DPF comprises a filter element or a sheet of metal mesh wound in a cylindrical body, a central part of the filter element may protrude longitudinally from its ends, and therefore be broken. If the DPF includes a ceramic filter element, cracks can be formed in the filter. When the malfunction occurs in the DPF, particulate matter flows to

the atmosphere without being trapped.

  DPF malfunction does not cause significant deterioration in engine performance, such as

  as the engine power output and acceleration.

  Thus, the driver of the vehicle may not be aware of the malfunction in the DPF. As a result, the DPF continues to malfunction, and as a result the flow of particulate matter through

the atmosphere continues.

  In order to solve the problem, the unexamined Japanese patent publication No. 8-121150 describes a device intended to detect a malfunction of the DPF, in which a sound level sensor is placed in the exhaust system downstream from the DPF, and the DPF is judged to be deteriorated when the detected sound level is

above a threshold.

  However, the device mentioned above requires the sound level sensor and circuits for processing the signals coming from the sound level sensor only.

  for detection of a malfunction in the DPF.

  This complicates the structure of the device and increases the cost of the device. In addition, various kinds of sounds or noises are generated during engine operation, and so such noises can prevent detection

  correct malfunction.

  Furthermore, there is known a diesel engine provided with an EGR passage (exhaust gas recirculation) connecting the exhaust and intake systems of the engine to each other, and an EGR valve disposed in the passage EGR for controlling an amount of EGR gas flowing through the EGR passage, in which the EGR ratio is detected, and an opening of the EGR valve is feedback controlled to make the EGR ratio equal to a target EGR ratio based on the ratio EGR detected, the target EGR report being predetermined on the basis of a

  engine operating condition.

  An object of the invention is to provide a device intended to detect a malfunction in an engine exhaust system, which is capable of correctly and easily detecting the malfunction and without any particular equipment

such as a sound level sensor.

  According to one aspect of the present invention, there is provided a device for detecting a malfunction of the exhaust system of an engine, in which the engine is provided with an EGR passage connecting the exhaust system and a system. engine intake to each other, and an EGR valve disposed in the EGR passage for controlling an amount of EGR gas flowing through the EGR passage, and wherein the device comprises means for detecting a EGR ratio, and control means for retroactively controlling an opening of the EGR valve to make the EGR ratio equal to a target EGR ratio, based on the detected EGR ratio, the target EGR ratio being predetermined based on an operating condition of the engine, characterized in that the device further comprises a detection means intended to detect an actual opening of the EGR valve when the feedback control of the o EGR valve opening is in progress, a means of obtaining intended to obtain a reference opening, the reference opening being an opening of the EGR valve required to make the EGR ratio equal to the target EGR ratio, the system of exhaust being in a reference condition, the reference condition including at least one condition in which the exhaust system is normal, and judgment means for judging whether a malfunction has occurred in the exhaust system by comparing the opening of the

  EGR valve at the reference opening.

  According to another aspect of the present invention, there is provided a device for detecting a malfunction of a particulate filter disposed in an engine exhaust system, in which the engine is provided with a driven turbocharger. by exhaust gases comprising a turbine disposed in the exhaust system and a compressor disposed in an engine intake system, characterized in that the device comprises means for detecting an actual temperature of the intake gases when the turbocharger is in operation, a means of obtaining intended to obtain a reference temperature, the reference temperature being a temperature of the intake gases obtained with the filter in a reference position, the reference condition including at least one condition in which the filter is normal, and a judgment means for judging whether a malfunction has occurred in the filter by comparing the temperature

  actual intake gas at the reference temperature.

  The present invention can be better understood from

  from the description of the preferred embodiments

  of the invention as stated below read in conjunction

with the accompanying drawings.

  In the drawings: Figure 1 shows a general view of a diesel engine; Figure 2 shows a flowchart for performing feedback control of an EGR valve; Figure 3 shows a flow chart for performing the detection of a DPF malfunction based on the comparison of an opening of an EGR valve; Figure 4 shows a flowchart for performing the detection of a malfunction of an EGR conduit based on the comparison of a valve opening

EGR;

  Figure 5 shows a flowchart for performing correction of a reference aperture; Figure 6 shows a flow chart for performing the detection of a malfunction of an EGR cooler based on the comparison of a cooling efficiency of the EGR cooler; Figure 7 shows a simplified view of a diesel engine to explain the parameters; and Figure 8 shows a flow chart for performing the detection of a malfunction in a DPF based on the comparison of a temperature of the intake gases. Figure 1 shows the present invention applied to a diesel engine for a vehicle, although the present invention can also be applied to a spark ignition type engine or to an engine for other use. Referring to Figure 1, the reference numeral 1 designates a diesel engine body having four cylinders la. Each cylinder 1a is connected to a balance tank 2 via a corresponding branch 3. The balance tank 2 is connected to an outlet orifice of a compressor 4a of a turbocharger driven by the exhaust gases (or a turbocharger) 4 via an intake duct 5 and a charge air cooler 6. The charge air cooler 6 is intended to cool the fresh air discharged from the compressor 4a and is, for example, of the cooling type by air or by water. An inlet port of compressor 4a is connected to an air filter (not

  shown) via an intake suction duct 7.

  An intake throttle valve 8 is disposed in the intake duct 5 in order to reduce the amount of fresh air circulating through the intake duct 5, and is driven by an actuator 8a of the type, for example, electromagnetic or unladen, in response to signals from an electronic engine control unit (ECU) 30. The opening of the intake throttle valve 8 is controlled to be equal to a target opening depending on the operating condition of the engine. In the present first embodiment, the intake throttle valve 8 is adapted to increase an amount of gas

  EGR when the engine speed is low, for example.

  Each cylinder 1a, moreover, is also connected to an inlet port of an exhaust turbine 4b of the turbocharger 4 to drive the compressor 4a, via an exhaust manifold 9. An outlet port of the turbine 4b is connected, via an exhaust duct 11, to an exhaust purification catalyst 10 of the type, for example, three-way catalyst. The catalyst is in turn connected to a diesel particulate filter (DPF) 12 comprising a filter element composed for example of a metallic mesh (metallic fabric) or of a porous material such as a ceramic intended to trap the particulate materials. (PM) contained in the exhaust gas. An additional catalyst can be provided

downstream of the DPF 12.

  An exhaust gas butterfly valve 13 is disposed in the exhaust pipe 11 to reduce the amount of exhaust gas flowing through the exhaust pipe 11, and is driven by an actuator 13a of the type, for example, electromagnetic. or unladen, in response to signals from the ECU 30. In the first embodiment, the exhaust throttle valve 13 is adapted to increase an exhaust gas temperature when the DPF 12 must be cooled or when engine

  is in a warming operation.

  Each cylinder 1a is provided with a fuel injector 14 intended to inject the fuel directly into the cylinder. The fuel injectors 14 are connected to a fuel pump 15 of a variable flow type, via a common rail 16 in order to store the

fuel under pressure.

  Referring again to Figure 1, the balance tank 2 and the exhaust manifold 9 are connected to each other via an EGR pipe (exhaust gas recirculation) 17. An EGR valve 18 is arranged in the EGR pipe 17 to control a quantity of EGR gas flowing through the EGR pipe 17, and is driven by an actuator of the type, for example, electromagnetic including a stepping motor, in response to the signals

from the ECU 30.

  The EGR duct 17 includes an EGR cooler 19 intended to cool the EGR gases. The EGR 19 and water-cooled type cooler, the cooling water of which is common to the engine cooling system. Alternatively, the EGR cooler 19 may be of the air-cooled type, or the cooling water may be for its own use. The EGR cooler 19 has an EGR pipe connected to the EGR pipe 17 through which the EGR gases circulate and around which the cooling water circulates. The EGR cooler 19 suppresses the deterioration of the efficiency per unit volume of the engine due to the EGR gases being at a high temperature, and allows a large amount of EGR gas to be delivered to the engine. Operation of the EGR cooler 19 is controlled in response to signals

from the ECU 30.

  When the turbocharger 4 is in operation, the fresh air sucked into the intake suction duct 7 is compressed by the compressor 4a, and is cooled by the charge air cooler 6. When the supply of EGR gas is in operation, the fresh air is then mixed with the EGR gases at the equilibrium tank 2, then is delivered to the engine together with the EGR gases. Thereafter, the mixture of gases including fresh air and EGR gases will be called gas

intake.

  The ECU 30 is composed of a digital computer including a ROM (read-only memory) 32, a RAM (random access memory) 33, a CPU (central processing unit) 34 and a B-RAM (random access memory) 35, an access inlet 36 and outlet access 37 interconnected to one another via a bidirectional bus 31. The air quantity sensor or flow meter 38, generating voltages representing the mass flow of fresh air, is arranged in the intake suction duct 7, and may be of the hot wire type. A temperature sensor 39, generating voltages representing a temperature of fresh air before entering the compressor 4a, is also arranged in the intake suction duct 7. A pressure sensor 40, generating voltages representing the pressure in the balance tank 2, is arranged in the balance tank 2, and a temperature sensor 41, generating voltages representing a temperature of the gases entering the balance tank 2, is also arranged in the balance tank 2. A temperature sensor 42 generating voltages representing a temperature of the exhaust gases discharged from the turbine 4b, is arranged in an exhaust pipe 20. The EGR valve 18 is provided with a sensor opening 43 generating voltages representing an opening thereof. A depression sensor 44 generating voltages representing a depression of the accelerator pedal (not shown) is attached to the accelerator pedal. The body of the engine 1 is provided with a temperature sensor 45 generating voltages representing a temperature of the cooling water of the engine or of the EGR cooler 19. The output voltages of the sensors 38 to 45 are supplied as input to the entrance access 36 via

A / D converters 46.

  An engine speed sensor 47 generating pulses representing a motor speed, and a vehicle speed sensor 48 generating pulses representing a vehicle speed are also

  connected to input port 36.

  The outlet access 37 is connected, via a corresponding drive circuit 50, to the actuators of the intake throttle valve 8, of the exhaust throttle valve 13, and of the EGR valve 18, to the fuel injectors 14 , to the fuel pump 15 and to the EGR cooler 19. The output access 37 is also connected to an alarm 49 via a corresponding drive circuit 50. The alarm 49 can be an electric lamp or an audible warning, and is intended to inform the driver of the vehicle of the appearance of a malfunction in the system

  exhaust when detected.

  It should be noted that the actual opening of the EGR valve 18 can be obtained by using a number of steps in the case where the EGR valve 18 comprises a stepping motor as an actuator, or a duty factor in the case where the EGR valve 18 is formed by a service control valve, or the power required to drive the EGR valve 18. Consequently, the sensor

  opening 43 could be omitted from these variants.

  In the motor shown in FIG. 1, the motor is controlled by feedback to make its idling speed equal to a predetermined speed, a speed

  target, based on the detected idle speed.

  In addition, the EGR valve 18 is feedback controlled to make the EGR ratio equal to a target EGR ratio which depends on the engine operating condition, when an EGR condition is established, where the EGR ratio is a ratio of one amount of EGR gas to that of

intake gas.

  The supply of EGR gases suppresses the generation of nitrogen oxides (NOx), and generally, an amount of NOx generated decreases as the amount of EGR gases delivered to the engine increases. However, if the amount of EGR gases becomes excessive, an amount of oxygen in the

  cylinder decreases and combustion may be deteriorated.

  This can increase the amount of particulate matter

  and / or generate smoke in a diesel engine.

  Consequently, the target EGR ratio is predetermined to maximize suppression of NOX generation, while avoiding deterioration of combustion and increase in the amount of particulate matter, and the EGR ratio

  is ordered to be equal to the target EGR ratio.

  Specifically, a volume of intake gases, that is,

  ie a sum of the volumes of fresh air and EGR gas delivered to the engine, is kept at a practically constant value which depends on the operating condition of the engine. Consequently, under a constant engine operating condition, increasing the amount of EGR gases by increasing the opening of the EGR valve 18 reduces the amount of fresh air and thus increases the EGR ratio, while reducing the quantity of EGR gases by reducing the opening of the EGR valve 18 increases the quantity of fresh air and thus reduces the EGR ratio. So the amount of fresh air represents the

EGR report.

  Consequently, in the first embodiment, a target quantity of fresh air, which is an quantity of fresh air necessary to make the EGR ratio equal to the target EGR ratio, is previously obtained, by experience, on

  the basis of the engine operating condition.

  Then, the operation of the EGR valve 18 is controlled by feedback to make the quantity of fresh air (mass flow) detected by the mass flow meter 38 equal to the target quantity of fresh air. As a result, the EGR report is made equal to the target EGR report. The target quantity of fresh air is stored in ROM 32 as a function of the quantity of fuel to be injected by the fuel injector 14 or the depressing of 11 the accelerator pedal which represents a load of the

engine and engine speed.

  FIG. 2 represents a subroutine intended for

  control the EGR valve 18 by feedback.

  program is executed by interruption at each interval

of predetermined time.

  Referring to Figure 2, in step 60, it is judged whether the EGR condition is established. In one example, the EGR condition is deemed to be established when the temperature of the engine cooling water is above a threshold, and when a period of time during which the engine is continuously in operation is above a threshold, and when depressing the accelerator pedal increased. If the EGR condition is not established, the EGR valve 18 is closed and the supply of EGR gases to the engine is stopped. When the EGR condition is not deemed to be established, the routine ends. Conversely, when the EGR condition is judged to be established, the subprogram advances to step 61, where the speed of the engine N, the quantity of fresh air Gn and the quantity of fuel Qf are read. The quantity of fuel Qf was calculated by another subroutine intended to obtain the

  amount of fuel (not shown).

  In the next step 62, the target quantity of fresh air TGn is calculated based on the speed of the engine N and the quantity of fuel Qf. In the next step 63, it is judged whether a deviation of the quantity of fresh air detected from the target quantity (Gn-TGn) is greater than a positive constant a. When the difference (Gn-TGn) is judged to be greater than the constant a, the subroutine goes to step 64, where a target opening TVEG of the EGR valve 18 is increased by a value dV. Then the subprogram goes to

step 67.

  Conversely, when the difference (Gn-TGn) is not greater than the constant a, the subroutine goes to step, where it is judged if the difference (Gn-TGn) is less than a negative constant -a. When the difference (Gn-TGn) is not less than the constant -a, the subroutine goes to step 67, maintaining the target opening TVEG. When the deviation (Gn-TGn) is less than the constant -a, the subroutine goes to step 66, where the target opening TVEG of the valve

  EGR 18 is reduced by the value dV. Then the sub-

  program goes to step 67. It should be noted that the value a is a relatively small value intended to avoid fluctuation in the opening of the EGR valve 18, and may be any value for this purpose. The dV value can

  be constant or variable depending on the difference (Gn-TGn).

  In step 67, the EGR valve 18 is driven to

  make its opening equal to the TVEG target opening.

  The first embodiment will be explained in more detail. Briefly, the first embodiment relates to the detection of a malfunction of the DPF

  12, with the feedback control of the EGR valve 18.

  The feedback control of the EGR valve 18 maintains the amount of fresh air at its target amount, and thus the EGR ratio to the target EGR ratio. At this time, the opening of the EGR valve 18 is maintained at a certain opening depending on the condition of

engine operation.

  However, if a malfunction occurs in the DPF 12, such as a rupture or a crack, the opening of the EGR valve 18 deviates from the certain opening. Specifically, the malfunction of the DPF 12 remarkably reduces a pressure drop at the DPF 12 and thus lowers the back pressure of the motor. This will reduce the pressure difference between the inlet and outlet of the EGR pipe 17, which in turn will reduce the amount of EGR gas flowing through the EGR pipe 17 and increase the amount of air

  fresh. Ultimately, this will reduce the EGR report.

  In this condition, the feedback control increases the opening of the EGR valve 18 to maintain the EGR ratio equal to the target EGR ratio. Consequently, when a malfunction occurs in the DPF 12, the opening of the EGR valve 18 necessarily becomes

  greater than an opening when the DPF 12 is normal.

  In other words, if a reference opening refers to an opening of the EGR valve 18 necessary to make the EGR ratio equal to the target EGR ratio with the DPF 12 being in a reference condition, the reference condition including a condition in which the DPF 12 is normal, the actual opening of the EGR valve 18 is maintained at the reference opening when the DPF 12 is normal, and becomes greater than the reference opening

  when a malfunction occurs in the DPF 12.

  In the first embodiment, the reference opening is obtained beforehand on the basis of the engine operating condition, such as the engine operating speed N and the quantity of fuel Qf, by experience, and is stored in ROM 32 in advance as a function of N and Qf. Then, the actual opening of the EGR valve 18 is detected and is compared with the reference opening, the engine operating condition of which is the same as that of

  engine operation, at the actual opening detected.

  When the actual opening of the EGR valve 18 is greater than the corresponding reference opening, it is judged that a malfunction has appeared in the

  DPF 12. Otherwise, DPF 12 is deemed to be normal.

  Although an opening of the EGR valve 18 necessary to make the EGR ratio equal to the target EGR ratio with DPF 12 being normal may vary depending on the amount of particulate matter trapped on the DPF 12, the reference opening can be any opening as long as it makes the EGR report equal to the EGR report

  target and be obtained with normal DPF 12.

  However, in the first embodiment, the reference opening is an opening with a new DPF 12, that is to say, the DPF 12 being normal and the quantity of particulate matter trapped being practically zero. In other words, the reference condition is a condition in which the DPF 12 is new. The reference opening with the new DPF 12 is maximum among those with the normal DPF 12, and thus delivers a

  correct judgment of a malfunction.

  Figure 3 shows a subroutine for a

  DPF 12 malfunction detected. This sub-

  program is run by interrupt every interval of

predetermined time.

  Referring to FIG. 3, in step 70, it is judged whether an indicator XF1, which represents the appearance of a malfunction of the DPF 12 and which has been initialized to be reset (XF1 = 0) , is reset. When the indicator XF1 is reset to zero, the subroutine goes to step 71, where it is judged whether the feedback control of the EGR valve 18 is in progress. If the feedback control is stopped, the routine ends. If the feedback control is in progress, the subroutine goes to step 72, where the engine speed N, the quantity of fuel Qf and the actual opening of the VEG EGR valve are read. In the next step 73, the reference opening RVEG is calculated on the basis of the speed of the motor N and

the quantity of fuel Qf.

  In the next step 74, it is judged whether a deviation of the actual opening of the EGR valve 18 from the reference opening (VEG-RVEG) is greater than a positive constant b. When the difference (VEG-RVEG) is judged to be greater than the constant b, the subroutine goes to step, where the indicator XF1 is established (XF1 = 1). When the XF1 indicator is set, alarm 49 is activated. It should be noted that the constant b is a relatively small value intended to avoid poor judgment due to the tolerances of the equipment such as sensors or valves, or to environmental conditions such as atmospheric temperature and pressure. Conversely, when the difference (VEG-RVEG) is not greater than the constant b, the subroutine ends and the indicator

  XF1 is kept to be reset.

  When the flag XF1 has been set in step 70, the routine ends. The XF1 flag will be returned for manual reset when the DPF 12 is

repaired or changed.

  It should be noted, in the first embodiment, that the actual opening of the EGR valve 18 is compared to the reference opening. Alternatively, the actual opening of the EGR valve 18 can be compared to an opening different from the reference opening mentioned above, but determined on the basis of

the reference opening.

  Next, the second embodiment according to the present invention will be explained. The second embodiment relates to a detection of a malfunction of the EGR duct 17, in particular of the EGR cooler 19, with the feedback control of

the EGR valve 18.

  In the diesel engine shown in Figure 1, the inlet port of the EGR conduit 17 is disposed upstream of the DPF 12, and thus the EGR gases flowing through the

  EGR 17 can contain particulate matter.

  Thus, the EGR pipe 17 can be clogged due to the particulate materials which adhere and accumulate on the internal surface of the EGR pipe 17. In particular, the EGR pipe of the EGR cooler 19 usually comprises

  cross section smaller than that of the EGR pipe 17.

  In addition, the carbon gas or the fuel contained in the EGR gases is cooled and liquefied while circulating in the EGR pipe of the EGR cooler 19. Consequently, the pipe

  EGR of the EGR 19 cooler can easily get dirty.

  The fouling of the EGR duct 17 including the EGR cooler 19 reduces the amount of EGR gas delivered to the engine and thus deteriorates the suppression of the generation of NOx by

EGR gases.

  Likewise, when the EGR pipe 17 deforms to reduce the cross section thereof, or when the EGR gases leak from the EGR pipe 17, the quantity of EGR gas

is reduced.

  Consequently, in the second embodiment, a malfunction of the EGR conduit 17 as mentioned above is detected. A detailed explanation

of this follows.

  When a malfunction occurs in the EGR pipe 17, the amount of EGR gas is reduced, which increases the amount of fresh air. At this time, as in the first embodiment, the feedback control of the EGR valve 18 increases the opening of the EGR valve 18 to avoid reduction of the EGR ratio. Consequently, when a malfunction occurs in the EGR pipe 17, the opening of the EGR valve 18 necessarily becomes larger than an opening with a pipe

EGR 17 normal.

  In other words, if a reference opening refers to an opening of the EGR valve 18 necessitating making the EGR ratio equal to the target EGR ratio with the normal EGR conduit 17, the actual opening of the EGR valve 18 is maintained at the reference opening when the EGR 17 conduit is normal, and becomes greater than the reference opening when a malfunction

occurs in the EGR duct 17.

  While the reference opening could be obtained beforehand for various engine operating conditions, only the reference opening, with the engine operating condition being in reference operating conditions, is obtained beforehand in the second embodiment. Then, the actual opening of the EGR valve 18 is detected when the engine operating condition is in the reference operating condition, and is compared to the reference opening. When the actual opening of the EGR valve 18 is greater than the corresponding reference opening, it is judged that a malfunction has occurred in the EGR conduit 17. Otherwise,

  the EGR 17 pipe is considered to be normal.

  The reference operating condition can be any operating condition. However, if the engine is at a high speed condition or at a high load operating condition, the return pressure becomes relatively high and thus a reduction in the amount of EGR gas may be small, even if a malfunction has occurred in the EGR duct 17. This prevents correct detection of the malfunction. Consequently, the reference operating condition is preferably a low speed operating condition where the motor speed is below a threshold, or a low operating condition.

  load o the engine load is below a threshold.

  It is also preferably a constant operating condition. Accordingly, in the second embodiment, the reference operating condition is a constant idle condition after the warming operation has been completed. In other words, the reference opening RVEGI is an opening of the EGR valve 18 necessary to make the EGR ratio equal to the target EGR ratio, the EGR conduit 17 being normal and the engine being in constant idle operation. This is obtained beforehand by experience and is memorized at

advance in ROM 32.

  FIG. 4 shows a subroutine for detecting a malfunction in the EGR conduit 17. This subroutine is executed by interruption each

predetermined time interval.

  Referring to FIG. 4, in step 80, it is judged whether an indicator XF2, which represents the appearance of a malfunction in the EGR conduit 17 and which has been initialized to be reset (XF2 = 0), has been delivered to

  zero. When the XF2 indicator has been established, the sub-

  program ends. When the indicator XF2 is reset to zero, the subprogram goes to step 81, where it is judged if the feedback control of the EGR valve 18 is in

  Classes. If the feedback control is stopped, the sub-

  program ends. If the feedback control is in progress, the subroutine goes to step 82, where it is judged if the engine is in constant idle operation. If the engine is not in constant idle operation, the routine ends. If the engine is in constant idle operation, the subroutine goes to step 83, o the actual opening of the VEG EGR valve and

  the RVEGI reference opening are read.

  In the next step 84, it is judged whether a deviation of the actual opening of the EGR valve 18 from the reference opening (VEG-RVEGI) is greater than a positive constant c. When the difference (VEG-RVEGI) is judged to be greater than the constant c, the subroutine goes to step o the indicator XF2 is established (XF2 = 1). When the XF2 indicator is set, alarm 49 is activated. It should be noted that the constant c is a relatively small value like the constant b of the second embodiment. Conversely, when the difference (VEG-RVEGI) is not greater than the constant c, the subroutine ends and the indicator XF2 is kept to be reset. As in step 82 in Figure 4, it is judged whether the engine operating condition is in the reference operating condition. In this case, the judgment can be executed on the basis of at least one of the speed of the engine, the depressing of the accelerator pedal, the amount of fuel, the temperature of the engine cooling water, the opening of the intake throttle valve 8, the opening of the exhaust throttle valve 13, a judgment if the DPF 12 is dirty and a judgment if the DPF 12 is not in cooling operation. In addition, it can be performed considering the conditions of auxiliary devices such as a compressor for an air conditioner and

  a pump for power steering.

  The third embodiment will then be explained in accordance with the present invention as a variant of the

second embodiment.

  In the second embodiment, the RVEGI reference opening is obtained and stored in ROM 32 in advance. However, the EGR device including the EGR conduit 17, the EGR valve 18 and the EGR cooler 19 may include irregularities, and thus the initial reference opening previously obtained may not be a correct value for a particular EGR device. Consequently, in the third embodiment, the initial reference opening is corrected on the basis of the actual opening of the EGR valve 18 obtained by the feedback control thereof, with the new

EGR device.

  Specifically, when the EGR device is new, that is to say that the vehicle itself is new or that the EGR device is replaced by a new one, a correction coefficient KC is calculated. The correction coefficient KC is an average value of a deviation of the actual opening of the EGR valve 18 from the initial reference opening (VEG-RVEGI) over predetermined periods of time. Then, the initial reference opening is corrected using the correction coefficient KC (RVEGI = RVEGI + KC). As a result, proper detection

  a malfunction is ensured.

  Figure 5 shows a subroutine for a

  correction of the RVEGI reference opening. This sub-

  program is run by interrupt every interval of

predetermined time.

  With reference to FIG. 5, in step 90, it is judged whether an indicator XC, which represents the completion of a correction of the reference opening RVEGI and which has been initialized to be reset (XC = 0), has been delivered to

  zero. When the XC indicator has been established, the sub-

  program ends. When the indicator XC is reset to zero, the subprogram goes to step 91, where it is judged if the feedback control of the EGR valve 18 is in

  Classes. If the feedback control is stopped, the sub-

  program ends. If the feedback control is in progress, the subroutine goes to step 92 where it is judged if the engine is in constant idle operation. If the engine is not in constant idle operation, the routine ends. If the engine is in constant idle operation, the subroutine goes to step 93, where a counter i, which represents the number of executions of the present subroutine, is incremented by one. In the next step 94, the actual detected opening VEG of the EGR valve 18 and the initial reference opening RVEGI are read. In the next step 95, the ith difference D (i) is calculated (D (i) = VEG-RVEGI). In the next step 96, it is judged if the counter i is equal to a constant n. If the

  counter i is not equal to the constant n, the sub-

  program ends. If i = n, the subroutine goes to step 97 where the correction coefficient KC is calculated (KC = (D (1) + ... + D (n)) / n). In the next step 98, the reference opening is corrected by KC (RVEGI = RVEGI + KC). In the next step 99, the corrected reference opening RVEGI is stored in RAM 33. A

  the next step 100, the indicator XC is established.

  After the completion of the correction, detection of a malfunction in the EGR conduit 17 is performed using the corrected reference opening RVEGI. XC indicator is reset manually

  when the EGR device is replaced by a new one.

  It should be noted that the corrected reference opening RVEGI is an average value of the actual opening of the EGR valve 18, and can thus be obtained even without the initial reference opening. However, the initial reference aperture is stored in advance in ROM 32 for detection of a malfunction before

the correction is not completed.

  In the above-mentioned embodiments, the EGR report is controlled by controlling the EGR valve 18 only. In this case, when the EGR valve 18 is fully open, the amount of EGR gas or the EGR ratio cannot be increased. This can prevent the

  actual EGR report to be equal to the target EGR report.

  Consequently, when the EGR valve 18 is fully open, the intake throttle valve 8 can be feedback controlled to make the actual EGR ratio equal to the target EGR ratio. In this case, a second reference opening, which is an opening necessary for the inlet throttle valve 8 to make the actual EGR ratio equal to the target EGR ratio with the DPF 12 or the normal EGR conduit 17, is predetermined. Then, the actual opening of the intake throttle valve 8 is detected, and it is compared with the second reference opening. If the actual opening of the intake throttle valve 8 is less than the second reference opening, it may be judged that a malfunction

  occurred in the DPF 12 or the EGR 17 conduit.

  The lower opening of the intake throttle valve 8 reduces the amount of fresh air and increases the amount of

EGR gas.

  Next, the fourth embodiment will be explained in accordance with the present invention. The fourth embodiment relates to the detection of a malfunction of the EGR cooler 19, without the control

  by feedback from the EGR valve 18.

  In the above-mentioned embodiments, the feedback control of the EGR valve 18 is

  necessary for the detection of a malfunction.

  Thus, there may be a case where the detection cannot be executed during the stopping of the feedback control, such as the operation under high load of the motor. Accordingly, in the fourth embodiment, the detection of the malfunction is performed on the basis of the cooling efficiency of the

EGR cooler 19.

  Specifically, when the EGR cooler 19 is normal or is not fouled, a cooling efficiency of the EGR cooler 19 is maintained at a certain efficiency depending on the operating condition of the engine. However, when particulate matter adheres to the internal surface of the EGR pipe of the EGR cooler 19 and thus when the EGR cooler 19 is fouled, the contact surface area between the EGR gases flowing through the EGR pipe and the cooling water is reduced. This lowers the heat exchange efficiency of the EGR cooler 19 and thereby lowers the cooling efficiency of the EGR cooler 19. In addition, fouling of the EGR cooler 19 can increase the pressure in the EGR pipe and thus, can

  increase the temperature of the EGR gases.

  In other words, if a reference efficiency refers to an efficiency of the EGR cooler 19 obtained when the EGR cooler 19 is normal, the actual efficiency of the EGR cooler 19 is maintained at the reference efficiency when the EGR cooler 19 is normal, and becomes lower than the reference efficiency when a malfunction occurs in the EGR cooler 19. In the fourth embodiment, the reference efficiency with the normal EGR cooler 19 and the operating condition of the engine in the reference operating condition is obtained beforehand and it is stored in advance in ROM 32. Then, the actual cooling efficiency of the EGR cooler 19 is detected when the engine operating condition is in the condition of reference operation and it is compared to the reference efficiency. When the actual cooling efficiency of the EGR cooler 19 is lower than the reference efficiency, it is judged that a malfunction has occurred in the EGR cooler 19. Otherwise, the EGR cooler 19 is

considered normal.

  Figure 6 shows a subroutine for detection

  fouling of the EGR cooler 19. This sub-

  program is run by interrupt every interval of

predetermined time.

  Referring to FIG. 6, in step 110, it is judged whether an indicator XF3, which represents the appearance of fouling of the EGR cooler 19 and which has been initialized to be reset (XF3 = 0) , has been delivered to

  zero. When the XF3 indicator has been established, the sub-

  program ends. When the indicator XF3 is reset to zero, the subprogram goes to step 111, where it is judged if the EGR cooler 19 is in operation. The EGR cooler 19 is in operation when the temperature of the engine cooling water is greater than a threshold, the engine speed is greater than a threshold, the depressing of the accelerator pedal is greater than a threshold and the exhaust gas temperature detected by the temperature sensor 42 is greater than a threshold, for example. When the

  EGR 19 chiller is not operating, the sub-

  program ends. When the EGR cooler 19 is in operation, the subroutine goes to step 112, where it is judged if the engine is in the reference operating condition which is predetermined. If the motor is not in the reference operating condition, the subroutine ends. If the engine is

  in the reference operating condition, the sub-

  program goes to step 113, o the actual cooling efficiency of the EGR EFFCL chiller is calculated. In the next step 114, the reference efficiency

REFF is read.

  In the next step 115, it is judged whether a deviation of the actual cooling efficiency of the EGR cooler 19 from the reference efficiency (REFF-EFFCL) is greater than a positive constant d. When the difference (REFF-EFFCL) is judged to be greater than the constant d, the subroutine goes to step 116, where the indicator XF3 is established (XF3 = 1). When the XF3 flag is set,

  alarm 49 is activated. Conversely, when the difference (REFF-

  EFFCL) is not greater than the constant d, the sub-

  program ends and the XF3 flag is kept for

be reset.

  Next, the calculation of the actual cooling efficiency EFFCL of the EGR cooler 19 is explained in

referring to figure 7.

  The EFFCL cooling efficiency is calculated using the following equation:

  EFFCL = (TEGI-TEGO) / (TEGI-THW) ... (1)

  Here, TEGI represents a temperature of the EGR gases circulating in the EGR cooler 19 or before being cooled by the EGR cooler 19, or of the exhaust gases circulating in the exhaust turbine 4b or before being expanded by the turbine exhaust 4b. TEGO represents a temperature of the EGR gases discharged from the EGR cooler 19 or after being cooled by the EGR cooler 19. THW represents a temperature of the cooling water circulating in the EGR cooler and which is detected by

the sensor 45.

  The temperature of the incoming EGR gases TEGI is calculated or estimated on the basis of the temperature of the exhaust gases discharged from the exhaust turbine 4b and the thermal energy consumed in the exhaust turbine 4b. Specifically, TEGI is calculated using the following theoretical equation for the exhaust turbine 4b. ETB = (TEGITEXA) / (TEGI (1-l / (PEXB / PIG) 0.248) ... (2) Here, ETB represents an efficiency of the exhaust turbine 4b. TEXA represents a temperature of the circulating exhaust gases through the exhaust pipe 20

  or after being expanded by the exhaust turbine 4b.

  PEXB represents an exhaust gas pressure at the exhaust manifold 9 or before being expanded by the exhaust turbine 4b. PIG represents a pressure of the inlet gases or of the mixture of air gases

  and EGR gases at the balance tank 2.

  The efficiency of the ETB turbine which is a specific value for the exhaust turbine 4b is obtained at

  prior, by experience, and is stored in ROM 32.

  The pressure PIG and the temperature TEXA are detected by the corresponding sensors 40, 42. The pressure PEXB is calculated on the basis of the pressure PIG and the quantity of fresh air Gn. As a result, the temperature of the EGR gases

  TEGI inbound is calculated using equation (2).

  Furthermore, the temperature of the TEGR exhaust gases TEGO is calculated or estimated on the basis of the EGR report, the temperature of the fresh air exhausted from the air cooler of

  supercharging 6 and the intake gas temperature.

  Specifically, TEGO is calculated using the following equation.

  TIG = REPORT TEGO + (1-REPORT) TFAO ... (3)

  Here, TIG represents an inlet gas temperature at the equilibrium tank 2. REPORT represents an EGR report. TFAO represents a temperature of the fresh air exhausted from the charge air cooler 6 or after being cooled by the charge air cooler 6, or before being mixed with the EGR gases. The temperature of the intake gases TIG is detected by the sensor 41. The report EGR REPORT is calculated on the basis of GALL representing a total quantity of the intake gases supplied to the engine, and the quantity of fresh air Gn (REPORT = (GALL-Gn) / GALL). The total quantity GALL is calculated on the basis of the intake gas pressure PIG and the filling efficiency of the engine, which is calculated on the basis of the engine speed N. The quantity of fresh air Gn is detected by sensor 38. The filling efficiency can be obtained beforehand and stored

in ROM 32.

  The temperature TFAO of the fresh air after being cooled by the charge air cooler 6 is calculated on the basis of the cooling efficiency EIC of the charge air cooler 6, and the temperature TFAI of the fresh air before or after being cooled by charge air cooler 6

  have been compressed by compressor 4a.

  The efficiency of the charge air cooling EIC is calculated on the basis of the speed of the vehicle V detected by the sensor 48, and of the quantity

fresh air Gn.

  The temperature TFAI of fresh air before cooling is calculated using the equation

  next theoretical for compressor 4a.

  ECMP = TF ((PFAI / PIG) 0.286-1) / (TFAI-TF) ... (4)

  Here, ECMP represents an efficiency of compressor 4a. TF represents a temperature of the fresh air circulating in the compressor 4a or before being compressed by the compressor 4a. PFAI represents a pressure of the fresh air circulating in the charge air cooler 6 or before being cooled by the charge air cooler 6 or after being compressed by the

compressor 4a.

  The efficiency of the ECMP compressor, which is a specific value for the compressor 4a, is calculated on the basis of the quantity of fresh air Gn and the fresh air pressure PFAI. The fresh air temperature TF and the inlet gas pressure PIG are detected by the corresponding sensors 39, 40. The fresh air pressure PFAI is calculated by subtracting a pressure loss from the charge air cooler 6 from PIG inlet gas pressure. Consequently, the temperature TFAI of fresh air before cooling is calculated using

* equation (4).

  Consequently, the temperature TFAO of the fresh air after cooling is calculated on the basis of the efficiency of the charge air cooler EIC and the temperature TFAI of the fresh air before cooling. As a result, the temperature of the EGR gases

  TEGO evacuees is calculated using equation (2).

  Consequently, the actual EFFCL efficiency of the EGR cooler 19 is calculated using equation (1). Alternatively, one or more sensors may be provided to detect the pressures and temperatures mentioned above PFAI, PEXB, TFAI, TFAO, TEGI and TEGO. In addition, the temperature of TEGI incoming EGR gases can be estimated based on the amount of fresh air, the temperature of the cooling water, the amount of fuel and the cyclic efficiency of the engine. The temperature of the TEGR exhausted EGR gases can be estimated as follows. First, the TIG temperature is assumed. Then, an assumed TEGO is calculated using the TIG pressure, the filling efficiency, the TFAO temperature and the assumed TIG, and the

  TIG temperature is calculated using the assumed TEGO.

  The calculation is repeated until TIG calculated using

  the assumed TEGO is equal to the assumed TIG.

  Next, the fifth embodiment will be explained in accordance with the present invention. The fifth embodiment relates to the detection of a malfunction of the DPF without the feedback control of

the EGR valve 18.

  As previously indicated, if the DPF 12 is broken, the pressure at the outlet of the exhaust turbine 4b drops. This increases the exhaust energy given to the turbine 4b, and thus increases the

  pressure at the compressor outlet 4.

  This, in turn, increases the temperature of the fresh air at the outlet of the compressor 4a, and the temperature of the TIG inlet gases. Consequently, when a malfunction occurs in the DPF 12, the temperature of the TIG inlet gases necessarily becomes higher than a temperature with the normal DPF 12. At this time, the temperature of the TIG intake gases will become higher, even considering the cooling of the charge air cooler 6

  and / or mixing with the EGR gases at high temperature.

  In other words, if a reference temperature refers to an intake gas temperature obtained with the DPF 12 under a reference condition, the reference condition including at least one condition in which the filter is normal, the temperature actual intake gas is maintained at the reference temperature when the DPF 12 is normal, and becomes higher than the reference temperature when a malfunction

occurs in DPF 12.

  It should be noted that in the case where the DPF 12 is disposed upstream of the exhaust turbine 4b, the temperature of the intake gases also increases when the DPF 12 is ruptured since the pressure at

  the inlet of the turbine 4b increases at this time.

  In the fifth embodiment, the reference temperature is first obtained on the basis of the operating condition of the engine, such as the engine speed N, the quantity of fuel Qf, and the quantity of fresh air Gn, by experience, and is stored in advance in ROM 32 as a function of N, Qf and Gn. Then, the actual temperature of the intake gases is detected, and is compared with the reference temperature, an engine operating condition of which is the same as an engine operating condition at the actual sensed temperature. When the actual temperature of the intake gases is higher than the corresponding reference temperature, it is considered that a malfunction has occurred in the DPF 12. Otherwise, the DPF 12 is considered to be normal. The change in the quantity of fresh air Gn due, for example, to the change in the opening of the intake throttle valve 8 will change the work of the compressor 4a, and thus change the temperature of the intake gases. Accordingly, the reference temperature in the fifth embodiment is predetermined as a function of the amount of fresh air Gn. However, it should be noted that during the feedback control of the EGR valve 18, the quantity of fresh air Gn depends on the speed of the engine N and on the quantity of fuel Qf, as has been

previously mentioned.

  Figure 8 shows a subroutine for detection

  a malfunction in the DPF 12. This sub-

  program is run by interrupt every interval of

predetermined time.

  Referring to Figure 8, in step 120, it is judged whether an indicator XF1 is reset. If the XF1 flag is set, the routine ends. When the indicator XF1 is reset to zero, the subroutine goes to step 121 where it is judged if the operating condition of the engine is constant. When any one of the engine speed N, the amount of fuel Qf and the amount of fresh air Gn changes by a predetermined value compared to that of the last treatment cycle, the engine operating condition is not not deemed to be constant and the routine ends. Otherwise, the engine operating condition is judged to be constant and the subroutine goes to step 122, o the engine speed N, the amount of fuel Qf, the amount of fresh air Gn and the actual temperature of the gases. TIG admissions are read. In the next step 123, the reference temperature RTIG is calculated on the basis of the engine speed N, the quantity of fuel Qf and

the amount of fresh air Gn.

  In the next step 124, it is judged whether a deviation of the actual temperature of the intake gases from the reference temperature (TIG-RTIG) is greater than a constant e. When the deviation (TIG-RTIG) is less than the

  reference temperature, the subroutine ends.

  When the difference (TIG-RTIG) is greater than the reference temperature, the subroutine goes to step 125 where the indicator XF1 is established. It should be noted that the constant e is a relatively small value like the constant b in the second embodiment. The temperature of the TIG inlet gases and the reference temperature may vary depending on the atmospheric temperature. Consequently, they should

  be corrected based on atmospheric temperature.

  When the DPF 12 is broken, the turbine speed of the exhaust turbine 4b and / or the pressure of the intake gases will also increase. Thus, a detection of a malfunction in the DPF 12 can be performed by comparing the turbine speed or the pressure of the intake gases to the corresponding reference value with the normal DPF 12. In addition, the turbocharger 4 is typically provided with a relief valve which is usually closed and opens to communicate upstream and downstream of the exhaust turbine 4b to each other when the air pressure charge compressed by compressor 4a increases to a threshold. The relief valve should open when the DPF 12 is broken and thus, detection of a malfunction in the DPF 12 can be performed depending on whether the relief valve

opens.

  Alternatively, when the DPF 12 is clogged, the amount of exhaust gas flowing to the exhaust turbine 4b is reduced. This reduces the speed of the exhaust turbine and lowers the temperature of the intake gases. Thus, it can be judged that the DPF 12 is fouled when the temperature of the intake gases is below a reference temperature. In this case, the reference temperature can be an intake gas temperature obtained with normal DPF 12 and the quantity of particulate matter trapped being the maximum possible quantity. The maximum possible quantity can be a threshold

  to start the DPF 12 recovery operation.

  In accordance with the present invention, it is possible to provide a device for detecting a malfunction in an exhaust system of an engine which is capable of correctly and easily detecting the

malfunctionning.

Claims (7)

  1. Device intended to detect a malfunction in a particulate filter (12) disposed in an exhaust system (9) of an engine, in which the engine is provided with a turbocharger (4) driven by the gases of exhaust comprising a turbine (4b) disposed in the exhaust system and a compressor (4a) disposed in an engine intake system, characterized in that the device comprises means (42) for detecting an actual temperature of the intake gas when the turbocharger (4) is in operation, obtaining means (36) for obtaining a reference temperature, the reference temperature being a temperature of the intake gases obtained with the filter in a condition of reference, the reference condition including at least one condition in which the filter is normal, and judgment means (30) for judging whether a malfunction has occurred in the filter (12) in comparison nt the actual temperature of the inlet gases to the reference temperature.   2. Device according to claim 1, characterized in that the judgment means (30) judges that a malfunction has occurred in the filter (12) when the actual temperature of the intake gases is higher or   below the reference temperature.   3. Device according to claim 1, characterized in that the reference condition is a condition in   which the filter (12) is new.   4. Device according to claim 1, characterized in that the reference temperature is predetermined on the basis of the operating condition of the engine, and in that the actual temperature -of the intake gases is compared to the reference temperature whose the operating condition of the engine is the same as that of the   actual intake gas temperature detected.   5. Device according to claim 1, characterized in that the obtaining means (36) obtains the actual temperature of the intake gases when the engine operating condition is in a reference operating condition, and in that the judgment means (30) judges if a malfunction has occurred in the filter (12) by comparing the actual temperature of the intake gases with the reference temperature, the reference temperature being an intake gas temperature obtained with the filter (12) in the reference condition and the engine operating condition   in the reference operating condition.   6. Device according to claim 5, characterized in that the reference operating condition is a condition in which the engine is in an operating condition at low speed or at low load. 7. Device according to claim 1, in which an EGR cooler (19) is arranged in the EGR passage (17) to cool the EGR gases flowing through it, characterized in that the device further comprises means (45 ) intended to obtain an actual cooling efficiency of the EGR cooler, a means intended to obtain a reference efficiency, which is a cooling efficiency of the EGR cooler obtained with the EGR cooler in the reference condition, the reference condition including at least a condition in which the EGR cooler (19) is normal, and means for judging whether a malfunction has occurred in the EGR cooler (19) by comparing the actual cooling efficiency to benchmark efficiency.