5.1 Overview
• The diesel particulate filter regeneration control system burns and removes the particulate matter (PM) in the ceramic filter using high temperature exhaust gas to prevent excessive accumulation of particulate matter in the ceramic filter. Thus the diesel particulate filter is regenerated.
• The regeneration is divided into two types. One is the continuous regeneration utilizing high temperature exhaust gas during high-speed or high-load operations. The other is the automatic or parked regeneration which uses high
temperature exhaust gas created by the regeneration control by the engine electronic control unit.
• For automatic or parked regeneration, the engine electronic control unit estimates the accumulated amount of particulate matter from the vehicle operating hours, driving distance and the engine condition during driving, and the regeneration is performed by controlling the fuel injection (amount and timing), turbocharger, exhaust shutter and intake throttle to make high temperature exhaust gas.
5.2 Structure
5.3 Diesel particulate filter, rear oxidation catalyst
• Diesel particulate filter unit consists of the front oxidation catalyst, ceramic filter, and rear oxidation catalyst attached at the rear end.
(1) Front oxidation catalyst
• In normal driving condition, unburnt fuel and part of the particulate matter in the exhaust gas from the engine is purified by this catalyst.
• During filter regeneration, the unburnt fuel supplied by the post injection is oxidized by the front oxidation catalyst, and the oxidation heat raises exhaust gas temperature.
(2) Ceramic filter
• The ceramic filter is an aggregate of thin tubes, and these tubes are closed at either end alternatively. During normal operation, particulate matter is trapped when the exhaust gas enters a tube and passes through the wall of the tube (filter section) to the adjacent tube.
• During regeneration, the particulate matter accumulated in the filter is cleared by burning at high temperature. This, however, cannot remove the calcium (ash) contained in the engine oil and the ash will accumulate in the filter. The excessively accumulated ash may cause early clogging of the ceramic filter. Therefore, the ceramic filter must be cleaned periodically.
(3) Rear oxidation catalyst
• The rear oxidation catalyst oxidize and remove the components (HC and CO) which remain untreated through the diesel particulate filter.
5.4 Electronic control system
(1) System block diagram
(2) Diesel particulate filter regeneration control
• The above diagram shows the relations between the driving distance or hours and the particulate matter accumulation amount, and the range of each diesel particulate filter regeneration operation.
• The particulate matter accumulation amount increases as the driving distance or hours increase. However, by conducting the regeneration operation that matches the vehicle operating condition and the particulate matter accumulation amount, the particulate matter accumulation amount is reduced to keep the performance of the diesel particulate filter.
• The regeneration is divided into two types – the continuous regeneration utilizing exhaust gas during normal driving operation and the automatic or parked regeneration which uses exhaust gas created by the regeneration control.
Continuous regeneration
When exhaust gas temperature is high during high-speed or high-load operation, NO2 created by the action of the front oxidation catalyst continuously burns the particulate matter accumulated in the ceramic filter.
Regeneration control
• Automatic regeneration
When the particulate matter accumulation level is between A and B on the diagram, the engine electronic control unit decides the regeneration period and the automatic regeneration will be performed at an appropriate period.
During regeneration, the unburnt fuel (HC) supplied by the post injection is oxidized by the front oxidation catalyst, and the oxidation heat from that reaction burns the particulate matter accumulated in the ceramic filter.
• Parked regeneration
– If the particulate matter (PM) deposit exceeds the level B, it becomes impossible to cease the combustion removal of particulate matters by means of automatic regeneration. The diesel particulate filter indicator lamp will blink if such a condition is encountered to alert the driver of the need to perform the parked regeneration. The parked regeneration is performed when the diesel particulate filter cleaning switch is turned on with all of the following requirements satisfied.
• Engine has warmed up (coolant temperature: 70°C or higher)
On vehicles with idling speed adjusting potentiometer, its knob must be set to “AUTO” position.
• Accelerator pedal released (accelerator pedal position sensor: 0%)
• Parking brake applied (parking brake switch: ON)
• Gearshift lever placed in N position.
• Power take-off inactive (power take-off switch: OFF)
– During regeneration, the diesel particulate filter indicator lamp blinks in two intervals (slow and fast) in accordance with the particulate matter accumulation amount.
– The exhaust gas temperature increase procedure and the particulate matter burning procedure are the same as that for the automatic regeneration.
• Restriction on drive conditions
– When the particulate matter accumulation level exceeds C on the diagram, the engine warning lamp illuminates and some restrictions are applied to the driving conditions.
– Under this restriction, parked regeneration will not take place even if the diesel particulate filter cleaning switch is turned on.
(3) Resetting the DPF-related information (ECU reset function)
• Resetting the DPF-related information is performed to make the particulate matter (PM) deposit recognized by the engine electronic control unit coincide with the actual particulate matter (PM) deposit accumulated in diesel particulate filter after replacing or cleaning diesel particulate filter.
• The DPF-related information is memorized by the engine electronic control unit as historical records for alerting the driver of the need to make the diesel particulate filter regeneration. (For the method for resetting the DPF-related information, see “ON-VEHICLE INSPECTION AND ADJUSTMENT”.)
(4) Particulate matter (PM) deposit verification function
• The particulate matter (PM) deposit verification function allows the driver to recognize the current particulate matter (PM) deposit through the number of flashing times of diesel particulate filter indicator. This function is activated while the diesel particulate filter cleaning switch is kept pressed with the starter switch placed in the “ON” position (without starting the engine).
• Periodical use of this function will give the operator a yardstick for the parked regeneration of the diesel particulate filter, which is helpful for preventing system failures caused by clogged or broken diesel particulate filter resulting from excessive particulate matter (PM) deposit.
• The relationship between the diesel particulate filter indicator flashing pattern and the particulate matter (PM) deposit is as shown below:
(5) Fault diagnosis function
• The engine electronic control unit continuously monitors the electronic drive units and sensors for faults. In the event that the engine electronic control unit finds a component faulty, it causes an indication to be made in the meter cluster to alert the driver. At the same time, it memorizes the fault location in the form of a diagnosis code and starts a control during fault.
• While control necessitated by a fault is taking place, the system’s functionality is limited to ensure vehicle and driver safety. It is possible to read the memorized diagnosis code using a Multi-Use Tester or from flashing of the warning lamp.
5.5 Electronic control unit wiring diagram
