Controlling engine operation during diesel particulate filter regeneration to avoid runaway

Abstract

A motor vehicle diesel engine (10) has an exhaust system (16) having a diesel particulate filter (18) that traps particulate matter in engine exhaust gases passing through the exhaust system. A control system (22) processes certain data to control engine and diesel particulate filter operation. In response to driver release of the accelerator, the engine decelerates toward idling at a lower low idle speed that has been predetermined appropriate for low idling when the diesel particulate filter is not being regenerated but inappropriate when the diesel particulate filter is being regenerated because of the potential for causing on-going regeneration to become uncontrolled. When the diesel particulate filter is being regenerated, a higher low idle speed sufficiently higher than the lower low idle speed is substituted as the low idle speed set-point essentially eliminating the potential for continuation of on-going diesel particulate filter regeneration becoming uncontrolled as the engine idles.

Description

FIELD OF THE INVENTION [0001] This invention relates generally to emission control systems of internal combustion engines, more particularly diesel engines that have certain exhaust gas treatment devices for treating exhaust gases passing through their exhaust systems. The invention more especially also relates to a system and method for controlling engine operation in ways that avoid on-going controlled regeneration of a diesel particulate filter (DPF) from becoming uncontrolled when the engine is decelerated to low idle speed. BACKGROUND OF THE INVENTION [0002] A known system for treating exhaust gas passing through an exhaust system of a diesel engine comprises a diesel oxidation catalyst (DOC) associated with a diesel particulate filter (DPF). The combination of these two exhaust gas treatment devices promotes chemical reactions in exhaust gas and traps diesel particulate matter (DPM) as exhaust flows through the exhaust system from the engine, thereby preventing significant amo...

AI Technical Summary

Benefits of technology

[0011] For example, when a truck stops at a stop light and engine speed drops to low idle speed, the exhaust gas flow through the exhaust system, including the DPF, will significantly decrease and the concentration of oxygen inside the DPF will increase. Because the regeneration that is in progress has already elevated substrate temperature to that required for burning off trapped soot, the combination of decreasing flow rate and increasing oxygen concentration can start a self-propagating (uncontrolled) reaction that elevates the substrate temperature even higher.

[0015] An aftertreatment strategy that provides a software solution for avoiding runaway regeneration as a consequence of a drop-to-idle event is especially advantageous because the need for additional hardware, except for possibly the necessary computing capability to incorporate a small amount of additional software, is obviated.

[0022] In response to release of the accelerator the control system causes the engine to idle at a lower low idle speed that has been predetermined appropriate for low idling when the diesel particulate filter is not being regenerated but inappropriate when the diesel particulate filter is being regenerated because of the potential for causing on-going regeneration to become uncontrolled, and when the diesel particulate filter is being regenerated, to idle at a higher low idle speed sufficiently higher than the lower low idle speed to essentially eliminate the potential for continued diesel particulate filter regeneration becoming uncontrolled as the engine idles

Problems solved by technology

Such a high temperature shock increases stresses in the internal materials.

Even a single drop-to-idle event can create a shock that cracks a substrate.

Repeated shocks have a cumulative effect that can eventually lead to even more cracking of the material and resulting DPF failure, because a DPF will progressively lose soot trapping effectiveness as cracks propagate.

DPF failure within an applicable warranty period imposes a warranty cost on the manufacturer.

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