Particle filter overheating protection

Abstract

Engine exhaust system comprising a diesel particulate filter (6) and a thermal fuse (12) arranged in the exhaust path through or from the filter (6), wherein the thermal fuse comprises a body (24) made of an electrically conductive, fusible material into which extends a pair of electrical contacts (22) made of a material having a higher melting point than the fusible material, wherein the thermal fuse (12) comprises a housing (14) in which the body (24) made of fusible material is arranged, and characterized by the fact that the casing (14) is tubular and open at one end to allow the fusible material to flow out when it is molten.

Description

[0001] The present invention relates to the detection of overheating of a particulate filter and is concerned in particular, but not exclusively, with the detection of overheating in a diesel particulate filter (DPF) in a vehicle.

[0002] The installation of diesel particulate filters (DPFs) in the exhaust systems of diesel vehicles is a well-established measure to prevent the emission of soot particles from these vehicles. A DPF must undergo regular regeneration processes, during which the engine is operated in such a way as to ensure that an appropriate DPF temperature is maintained for a sufficient time to burn off accumulated soot deposits, for example, by introducing additional fuel into the exhaust stream.

[0003] The DPF filter elements are manufactured as monolithic bodies from various materials, such as cordierite, silicon carbide, and metals, and these can melt, burn, or be otherwise damaged if they overheat. Furthermore, the monolithic elements are housed in metal casings, which can also melt if overheated. Therefore, it is necessary to take measures to prevent overheating.

[0004] Typically, temperature sensors are placed in the exhaust stream downstream of the DPF. The output signal from these sensors is fed into a control device, such as an engine management system. If a sensor detects a high temperature indicating overheating or imminent overheating of the DPF, a warning signal is issued to the vehicle's driver, and the engine management system can intervene to restrict engine operation and thus reduce the temperature, or shut down the engine completely. An exemplary engine exhaust system with multiple temperature sensors is known from US 2009 / 0 097 528 A1.

[0005] Typical temperatures that occur when a DPF overheats are in the range of 900 to 950 °C, and thus beyond the tolerance limits of the materials used in current sensors. Consequently, the expensive temperature sensor must be replaced if overheating occurs.

[0006] According to a first aspect of the present invention, an engine exhaust system according to claim 1 is provided, comprising a diesel particulate filter and a thermal fuse arranged in the exhaust path through or from the filter, wherein the fuse comprises a body made of an electrically conductive, fusible material into which a pair of electrical contacts made of a material having a higher melting point than the fusible material extend. The thermal fuse comprises a housing in which the fusible body is arranged, the housing being tubular and open at one end to allow the fusible material to flow out when it has melted.

[0007] The other end of the tubular housing can accommodate an insulating material through which the electrical contacts extend.

[0008] The thermal fuse can be oriented so that, once the fusible material has melted, it flows out of the open end of the housing under gravity. This is achieved by orienting the thermal fuse so that the open end of the housing points downwards.

[0009] The thermal fuse can serve to prevent damage to the DPF system due to overheating. The thermal fuse can therefore be designed to provide an open circuit between the electrical contacts before such damage occurs. This is achieved by appropriately selecting the melting point and mass of the fuse body made of a fusible material.

[0010] The diesel particulate filter can have a monolithic filter element, in which case the melting point of the fusible material may be lower than the combustion temperature of the monolithic filter element.

[0011] The diesel particulate filter may have a metal housing, in which case the melting point of the fusible material may be lower than the melting point of the metal housing material.

[0012] In one embodiment according to the present invention, the melting point of the fusible material is not below 940 °C.

[0013] To prevent premature activation of the thermal fuse at a temporarily high temperature, it is desirable that a delay period follow the initial occurrence of a temperature above the melting point of the fusible material in the thermal fuse, before the fusible body melts and thus electrically separates the contacts. This can be achieved by selecting the mass of the fusible body such that it can withstand a temperature slightly above the melting point of the fusible material, for example, a temperature of 950 °C, for at least 10 seconds.

[0014] The electrical contacts can be connected to a control device, such as an engine control module, to provide an input signal to the control device when the fusible material melts and provides an open circuit between the contacts. The control device can be configured to provide an output signal when the fusible material melts. The output signal can generate an engine stop signal when the exhaust gas temperature exceeds a predefined value and can issue a fault signal when the temperature is below or at the predefined temperature.

[0015] The thermal fuse can be located in the exhaust gas stream downstream of the diesel particulate filter.

[0016] The present invention also provides a motor vehicle having an engine exhaust system according to the first aspect of the present invention, as well as a thermal fuse for use in an engine exhaust system according to the first aspect of the present invention.

[0017] According to a second aspect of the present invention, a method for detecting overheating of a diesel particulate filter in an engine exhaust system is provided, wherein the method comprises arranging a thermal fuse in the exhaust gas flow through or from the filter and observing the resistance of the thermal fuse, wherein an increase in the resistance to a value above a predetermined resistance value causes the generation of an engine stop signal.

[0018] The exhaust gas temperature can be monitored, and an engine stop signal can be generated if the thermal fuse resistance exceeds a predefined resistance value and the exhaust gas temperature is above a predefined temperature. A fault signal can be generated if the thermal fuse resistance exceeds a predefined resistance value and the exhaust gas temperature is at or below a predefined temperature.

[0019] In the method according to the second aspect of the present invention, the thermal fuse can correspond to the first aspect.

[0020] For a better understanding of the present invention and for a better illustration of how it can be implemented, reference is now made by way of example to the attached drawings, in which: Fig. a schematic view of part of the exhaust system of a motor vehicle; Fig. A schematic view of a thermal fuse located in an exhaust pipe of the system of Fig. is arranged; Fig. an enlarged view of the thermal fuse; and Fig. A flowchart is a diagram that illustrates the operation of a control arrangement when receiving an input signal from the thermal fuse.

[0021] Fig. Figure 1 shows an exhaust manifold 2 of a motor vehicle engine, a diesel oxidation catalyst module 4, and a diesel particulate filter (DPF) 6 designed to filter particles from an engine exhaust stream. In the illustrated embodiment, the diesel oxidation catalyst module 4 and the DPF 6 are coupled together, with the DPF 6 being located downstream of the diesel oxidation catalyst module 4 and in communication with it. The illustrated embodiment also includes an exhaust pipe 8 located between the exhaust manifold 2 and the diesel oxidation catalyst module 4. In this configuration, exhaust gases from the engine can be fed directly or indirectly from the exhaust manifold 2 to the diesel oxidation catalyst module 4 and then to the DPF 6 and through an exhaust pipe 10 to other downstream elements of the exhaust system.

[0022] It is understood that the exhaust line 8 can direct the engine exhaust gases through one or more other devices on their way to the diesel oxidation catalyst module 4. For example, the exhaust line 8 can have one or more temperature sensor modules, lean NOx storage catalyst modules, and three-way catalyst modules, which are located downstream of the exhaust manifold 2 and upstream of the diesel oxidation catalyst module 4.

[0023] The DPF 6 can have a known general form and can, for example, comprise a monolithic, or one-piece, body made of a porous material, equipped with channels that communicate with each other through the porous material of the body. The porous material can be any suitable material that can withstand the high temperatures generated during operation in the DPF. Suitable materials include cordierite, silicon carbide, and some metallic materials. The monolith is housed in a casing, for example, made of steel.

[0024] The flow path through the DPF features regions of porous material where particulate matter in the exhaust stream is trapped. The exhaust stream leaving the DPF is therefore essentially free of particulate matter, and especially of soot.

[0025] The more soot material accumulates in the pores of the porous material, the more the efficiency of the DPF decreases. The DPF is regularly regenerated by raising the temperature of the exhaust gas flow to a level at which the soot deposits burn off. This is achieved, for example, by adding fuel to the exhaust system after combustion.

[0026] Under certain engine operating conditions, the DPF temperature can rise above the tolerance limits of the materials of either the monolith or the DPF housing, for example, to a temperature at which the monolith or the housing melts, burns, or is otherwise damaged. To prevent this, a thermal fuse 12 is installed in the exhaust pipe 10 downstream of the DPF 6, as shown in Fig. The function of thermal fuse 12 is to provide a signal that can be used to initiate a shutdown of the engine or another action to lower the temperature of the DPF before damage to the DPF occurs.

[0027] The thermal fuse is described in more detail in Fig. The thermal fuse is shown in the figure. It comprises a tubular steel housing 14 with an external screw thread 16 and a head 18 at one end, which, for example, has a hexagonal profile to accommodate a tool such as a wrench for attaching the thermal fuse to the wall of the exhaust pipe 10. An insulator 20, for example made of ceramic material, is provided in the housing 14, through which a pair of electrical contacts in the form of pins 22 extend. The pins 22 protrude from the insulator at the end adjacent to the head 18 to allow connection of a control arrangement, as will be discussed further below. At their opposite ends, the pins 22 project into a space within the housing 14, which under normal circumstances is filled with a body of electrically conductive, fusible material 24.Any suitable material can be used, provided its melting point is below the temperature at which the DPF would be damaged due to overheating. In one exemplary embodiment, an alloy with a melting point of approximately 945 °C ± 5 °C is used, such as a brass alloy.

[0028] It can be seen that the body 24 provides an electrical connection between the pins 22, so that the measured resistance between the ends emerging from the head 18 is very low.

[0029] When the temperature of the exhaust gases flowing past the thermal fuse 12 reaches a value close to that at which damage to the DPF can occur, the body made of fusible material 24 begins to melt. This can be determined by Fig. It can be seen that the thermal fuse is located in the upper part of the wall of exhaust pipe 10, with the open end of the housing 14 (i.e., the end furthest from the head 18) pointing downwards. Accordingly, when the fusible material 24 melts, it flows from the housing 14 into the exhaust pipe 10. When this occurs, the pins 22, which were previously located in the body 24, are electrically separated from each other, and the resistance of the thermal fuse rises to a relatively high value. In this state, the thermal fuse 12 can be said to be "activated".

[0030] It is evident that when the temperature of the exhaust gases flowing in the exhaust pipe 10 reaches the melting point of the fusible material 24, there is a finite delay time before the material 24 melts to expose the ends of the pins 22. This delay time depends on several factors, including the mass of the fusible material 24. The delay time allows the thermal fuse to withstand temporary deviations slightly above the melting point of the fusible material 24 (for example, up to 5 °C above the melting point) without the thermal fuse interrupting the circuit. For example, the mass of the fusible material 24 can be chosen to achieve a delay time of at least 5 seconds, or more typically at least 10 seconds, at a temperature of 950 °C.

[0031] The thermal fuse 12 is connected via a series resistor to a control arrangement, which may be an engine control unit (ECU) or part thereof. Under normal operating conditions, the low resistance indicates that the thermal fuse 12 is intact, i.e., that the body 24 provides a continuous electrical connection between the pins 22, and consequently, that the thermal fuse has not been activated because it would have been exposed to a temperature corresponding to overheating of the DPF 6, for example, 950 °C.

[0032] An example of a process in which the thermal fuse 12 is used is shown in the flowchart in Fig.As shown, following step S1 "Ignition On", step S2 determines whether the exhaust gas flow temperatures upstream and downstream of an exhaust gas catalyst (i.e., the temperature before the catalyst, TPC, and the temperature after the catalyst, TAC) are below a predefined temperature representing the engine during the warm-up phase, for example, 150 °C. If TPC and TAC are at or below 150 °C, step S3 determines whether thermal fuse 12 is conducting. If so, the engine start diagnostic routine confirms that thermal fuse 12 is intact and generates a corresponding indication D1, such as by extinguishing a DPF overheat warning light.

[0033] If, in step S3, it is determined that the thermal fuse 12 has interrupted the circuit, this indicates a fault in the thermal fuse, since the thermal fuse should not normally have activated at a temperature of 150 °C or below. A corresponding fault warning indicator D2 is generated, alerting the driver that the thermal fuse 12 must be checked and / or replaced. The process then returns to step S1.

[0034] If step S2 determines that the engine has warmed up sufficiently, so that TPC and TAC are above 150 °C, the process continues with step S4, in which, as in step S3, it is determined whether the resistance signal from thermal fuse 12 is high or low. If it is low, indicating a continuous electrical connection between pins 22, the process returns to step S2, with a sampling rate determined by a clock signal generated by the ECU.

[0035] If in step S4 it is determined that the resistance signal is high, which means that the thermal fuse 12 has been activated and the pins 22 are electrically separated from each other, the ECU generates an indication D3 that the DPF is overheating, and in step S5 it generates an engine stop signal which causes the ECU and other vehicle systems to safely shut down the vehicle within a calibratable or programmable time.

[0036] Although the thermal fuse 12 has been described as being installed downstream of the DPF 6 in the exhaust pipe 10, it can be seen that the thermal fuse 12 can instead be attached to the housing of the DPF 6, so that it is directly exposed to the exhaust gases flowing through the DPF.

[0037] Furthermore, although the activation of thermal fuse 12 has been described as causing the vehicle to shut down, it may instead, or as an initial procedure, cause a limitation of engine power or some other action that lowers the temperature of the DPF 6 without stopping the engine. As another possible initial procedure, the shutdown of the vehicle may be preceded by an urgent instruction to the driver to stop the vehicle immediately and switch off the engine.

Claims

[1] Engine exhaust system comprising a diesel particulate filter (6) and a thermal fuse (12) arranged in the exhaust path through or from the filter (6), the thermal fuse comprising a body (24) made of an electrically conductive, fusible material into which extends a pair of electrical contacts (22) made of a material having a higher melting point than the fusible material, wherein the thermal fuse (12) comprises a housing (14) in which the body (24) made of fusible material is arranged, and characterized by , that the casing (14) is tubular and open at one end to allow the fusible material to flow out when it is molten. [2] Engine exhaust system according to claim 1, wherein the other end of the tubular housing (14) accommodates an insulating material (20) through which the electrical contacts (22) extend. [3] Engine exhaust system according to claim 1 or 2, wherein the thermal fuse (12) is oriented such that when the fusible material has melted, it can flow out of the open end of the housing (14) under gravity. [4] Engine exhaust system according to claim 3, wherein the open end of the housing (14) opens downwards. [5] Engine exhaust system according to one of the preceding claims, wherein the melting point of the fusible material is below the temperature at which damage to the diesel particulate filter (6) occurs. [6] Engine exhaust system according to claim 5, wherein the diesel particulate filter (6) has a monolithic filter element and the melting point of the fusible material is lower than the combustion temperature of the monolithic filter element. [7] Engine exhaust system according to claim 5 or 6, wherein the diesel particulate filter (6) has a metal housing and the melting point of the fusible material is lower than the melting point of the material of the metal housing. [8] Engine exhaust system according to one of the preceding claims, wherein the melting point of the fusible material is not below 940 °C. [9] Engine exhaust system according to one of the preceding claims, wherein the mass of the body (24) is made of fusible material such that it can withstand a temperature slightly above the melting point of the fusible material for not less than 10 seconds. [10] Engine exhaust system according to one of the preceding claims, wherein the electrical contacts (22) are connected to a control arrangement to provide an input signal to the control arrangement when the fusible material melts to provide an open circuit between the contacts. [11] Engine exhaust system according to claim 10, wherein the control arrangement is designed to provide an output signal when the fusible material melts. [12] Engine exhaust system according to claim 11, wherein the output signal generates an engine stop signal when the temperature of the exhaust gas flow is above a predetermined value, and generates a fault message signal when the temperature of the exhaust gas flow is below or at the predetermined temperature. [13] Engine exhaust system according to one of the preceding claims, wherein the thermal fuse (12) is arranged in the exhaust stream downstream of the diesel particulate filter (6). [14] Motor vehicle with an engine exhaust system according to any of the preceding claims. [15] Thermal fuse (12) for use in an engine exhaust system according to any one of claims 1 to 13. [16] Method for detecting overheating of a diesel particulate filter (6) in an engine exhaust system, wherein the method comprises arranging a thermal fuse (12) in the exhaust gas flow through or from the filter (6) in an engine exhaust system according to any one of claims 1 to 13 and monitoring the resistance of the thermal fuse (12), wherein an increase in resistance to a value above a predetermined resistance value causes the generation of an engine stop signal. [17] Method according to claim 16, wherein the temperature of the exhaust gas flow is monitored and wherein the engine stop signal is generated when the resistance of the thermal fuse (12) is above the predetermined resistance value and the temperature of the exhaust gas flow is above a predetermined temperature. [18] Method according to claim 17, wherein a fault message signal is generated when the resistance of the thermal fuse (12) is above the predetermined resistance value and the temperature of the exhaust gas flow is at or below the predetermined temperature.

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