RECOVERY CONTROL SYSTEM

Abstract

A recovery control system that allows a dosing valve to recover from a malfunction to a normal state, or a liquid feed line through which urea solution is fed to recover from clogging to a normal state. An abnormality detector detects an abnormality of the dosing valve and a recovery controller controls a supply module to feed urea solution in the dosing valve back to an urea tank when the abnormality detector detects the abnormality.

Description

TECHNICAL FIELD

The present invention relates to a recovery control system that allows a dosing valve to recover from a malfunction to a normal state or a liquid feed line through which urea solution is fed to recover from clogging to a normal state.

BACKGROUND ART

A selective catalytic reduction (SCR) system incorporating an SCR device that has been developed is an exhaust gas purification system that purifies exhaust gas of a diesel engine of NO_X.

The SCR system is to purify exhaust gas of NO_X by supplying urea solution stored in a urea tank to an upstream part of the exhaust gas and reducing the NO_X on an SCR catalyst with ammonia derived from the urea solution by the heat of the exhaust gas (see Patent Literature 1, for example).

A process of deriving ammonia from urea solution will be described below with reference to FIG. 6.

As shown in FIG. 6, as the temperature of the urea solution rises beyond the boiling point, water starts evaporating, and the urea solution transforms into melt and then to gas. The resulting gas crystallizes into solid as the temperature further rises. The resulting solid then sublimates into ammonia. Part of the melt and gas are hydrolyzed with stream to form ammonia and carbonic acid gas.

The urea solution is injected through a dosing valve (a urea injection device or a dosing module) provided at the upstream side of the SCR device.

As shown in FIG. 7, a dosing valve 104 comprises a cylinder 127 having an injection orifice 128 and filled with urea solution at high pressure, a tubular plunger 130 having a slit 133, and a valving element 129 to close the injection orifice 128 that is attached to the plunger 130. A coil 131 is energized to pull up the plunger 130 to separate the valving element 129 from the injection orifice 128, thereby injecting the urea solution. Furthermore, a spring 132 is provided in the dosing valve 104 to bias the valving element 129 to be normally closed via the plunger 130. Therefore, when energization of the coil 131 is stopped, the plunger 130 is pushed down by the spring to make the valving element 129 close the injection orifice 128, thereby stopping injection of the urea solution.

The urea solution is supplied from the urea tank to the dosing valve 104 by a supply module, which comprises an SM pump, a urea solution pressure sensor and the like. More specifically, the urea tank and the supply module are connected to each other by a liquid feed line, and the urea solution sucked up from the urea tank through the liquid feed line is supplied to the dosing valve 104 through a pressure-feed line that connects the supply module and the dosing valve 104 to each other. In this process, the pressure of the urea solution in the dosing valve 104 (the measurement value of the urea solution pressure sensor of the supply module) is feedback-controlled to be constant, and injection of the urea solution starts when the pressure becomes constant.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent Laid-Open No. 2000-303826

SUMMARY OF INVENTION

Technical Problem

The dosing valve 104 is provided in the exhaust pipe, through which exhaust gas at high temperature flows. Therefore, as the temperature of the dosing valve 104 rises, the temperature of the urea solution in the dosing valve 104 also rises. As a result, the urea solution in the dosing valve 104 crystallizes and fixates to the valving element 129 as shown in FIG. 8(a), or the urea solution crystallizes into a solid 134, and the solid 134 gets caught between the valving element 129 and a valve seat on the cylinder 127 to make it impossible to stop injection of the urea solution as shown in FIG. 8(b), thereby leading to malfunction of the dosing valve 104 and failure of proper control of injection of the urea solution.

Furthermore, if the liquid feed line that connects the urea tank and the supply module to each other is clogged with a foreign matter, the pressure of the urea solution in the dosing valve 104 does not become constant or in other words does not rise, and there arises a problem that injection of urea solution does not start.

However, there has been proposed no recovery control to recover from such failures to a normal state.

Thus, an object of the present invention is to provide a recovery control system that allows a dosing valve to recover from a malfunction to a normal state or a liquid feed line through which urea solution is fed to recover from clogging to a normal state.

Solution to Problem

The present invention has been devised to attain the object described above. The invention according to claim 1 is a recovery control system for allowing a dosing valve through which urea solution is injected into an exhaust pipe to recover from a malfunction to a normal state, comprising the dosing valve and a supply module that sucks up urea solution in a urea tank and supplies the urea solution to the dosing valve and feeds the urea solution in the dosing valve back to the urea tank, the dosing valve having a cylinder charged with the urea solution, a plunger that opens and closes a normally closed valving element of the cylinder and a coil that operates the plunger, wherein the recovery control system further comprises: abnormality detection means of monitoring the dosing valve and detecting an abnormality of the dosing valve; and recovery control means of controlling the supply module to feed the urea solution in the dosing valve back to the urea tank when the abnormality detection means detects an abnormality of the dosing valve.

The invention according to claim 2 is a recovery control system for allowing a liquid feed line to recover from clogging to a normal state, comprising a dosing valve through which urea solution is injected into an exhaust pipe and a supply module that sucks up urea solution in a urea tank and supplies the urea solution to the dosing valve and feeds the urea solution in the dosing valve back to the urea tank, the urea tank and the supply module being connected to each other by the liquid feed line, wherein the recovery control system further comprises: pressure abnormality detection means of detecting an abnormality in a urea solution pressure based on a measurement value of a urea solution pressure sensor that measures a pressure of the urea solution supplied to the dosing valve; and recovery control means of controlling the supply module to feed the urea solution in the liquid feed line back to the urea tank when the pressure abnormality detection means detects an abnormality in the urea solution pressure.

Advantageous Effects of Invention

According to the present invention, a dosing valve can recover from a malfunction to a normal state, and a liquid feed line through which urea solution is fed can recover from clogging to a normal state.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing an SCR system according to the present invention.

FIG. 2 is a diagram showing an input/output configuration of a DCU.

FIG. 3 is a graph showing a waveform of a coil current when a dosing valve is activated.

FIG. 4 is a flowchart illustrating an operation of a recovery control system according to the present invention.

FIG. 5 is a flowchart illustrating an operation of the recovery control system according to the present invention.

FIG. 6 is a diagram showing a change of state of urea solution with temperature.

FIG. 7 is a cross-sectional perspective view of a dosing valve.

FIGS. 8( a) and 8(b) are cross-sectional views for illustrating failures of the dosing valve.

DESCRIPTION OF EMBODIMENT

In the following, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

First, an SCR system installed on a vehicle will be described.

As shown in FIG. 1, an SCR system 100 primarily comprises an SCR device 103 provided on an exhaust pipe 102 of an engine E, a dosing valve (a urea injection device or a dosing module) 104 that injects urea solution on the upstream side of the SCR device 103 (in an upstream part of exhaust gas), a urea tank 105 that stores the urea solution, a supply module 106 that supplies the urea solution stored in the urea tank 105 to the dosing valve 104, and a dosing control unit (DCU) 126 that controls the dosing valve 104, the supply module 106 and other components.

In order from upstream to downstream of the exhaust gas, the exhaust pipe 102 of the engine E is provided with a diesel oxidation catalyst (DOC) 107, a diesel particulate filter (DPF) 108 and the SCR device 103. The DOC 107 is intended to oxidize NO in the exhaust gas discharged from the engine E to produce NO₂ to adjust the ratio between NO to NO₂ in the exhaust gas in order to improve the denitration efficiency of the SCR device 103. The DPF 108 is intended to collect a particular matter (PM) in the exhaust gas.

The exhaust pipe 102 is provided with the dosing valve 104 on the upstream side of the SCR device 103. As described above with reference to FIG. 7, the dosing valve 104 comprises a cylinder 127 having an injection orifice 128 and filled with urea solution at high pressure, a tubular plunger 130 having a slit 133, and a valving element 129 to close the injection orifice 128 that is attached to the plunger 130, and a coil 131 is energized to pull up the plunger 130 to separate the valving element 129 from the injection orifice 128, thereby injecting the urea solution. Furthermore, a spring 132 is provided in the dosing valve 104 to bias the valving element 129 to be normally closed via the plunger 130. Therefore, when energization of the coil 131 is stopped, the plunger 130 is pushed down by the spring to make the valving element 129 close the injection orifice 128, thereby stopping injection of the urea solution.

On the upstream side of the dosing valve 104, the exhaust pipe 102 is provided with an exhaust gas temperature sensor 109 that measures the temperature (SCR inlet temperature) of the exhaust gas at an inlet of the SCR device 103. Furthermore, an upstream-side NO_X sensor 110 that detects the NO_X concentration on the upstream side of the SCR device 103 is provided on the upstream side of the SCR device 103 (on the upstream side of the exhaust gas temperature sensor 109 in this example), and a downstream-side NO_X sensor 111 that detects the NO_X concentration on the downstream side of the SCR device 103 is provided on the downstream side of the SCR device 103.

The supply module 106 comprises an SM pump 112 that pressure-feeds the urea solution, an SM temperature sensor 113 that measures the temperature of the supply module 106 (the temperature of the urea solution flowing through the supply module 106), a urea solution pressure sensor 114 that measures the pressure of the urea solution in the supply module 106 (the pressure on the outlet side of the SM pump 112), and a reverting valve 115 that switches between urea solution flow channels to selectively supply the urea solution in the urea tank 105 to the dosing valve 104 or feed the urea solution in the dosing valve 104 back to the urea tank 105. In this example, the urea solution in the urea tank 105 is supplied to the dosing valve 104 when the reverting valve 115 is turned off, and the urea solution in the dosing valve 104 is fed back to the urea tank 105 when the reverting valve 115 is turned on.

When the reverting valve 115 is set to supply urea solution to the dosing valve 104, the SM pump 112 of the supply module 106 sucks up the urea solution in the urea tank 105 through a liquid feed line (suction line) 116, supplies the urea solution to the dosing valve 104 through a pressure-feed line (pressure line) 117, and feeds any excessive urea solution back to the urea tank 105 through a collection line (back line) 118.

In the key off state (ignition off state or vehicle stop state), the reverting valve 115 is switched to feed the urea solution in the dosing valve 104 back to the urea tank 105, thereby preventing crystallization of urea solution, which causes occurrence of malfunction of the dosing valve 104. The control to feed the urea solution in the dosing valve 104 back to the urea tank 105 is referred to as emptying in this specification.

In emptying, the dosing valve 104 is previously opened, and then the urea solution in the dosing valve 104 is fed back to the urea tank 105, so that the exhaust gas (air) in the exhaust pipe 102 is also sucked into the urea tank 105 via the dosing valve 104.

The urea tank 105 is provided with an SCR sensor 119. The SCR sensor 119 comprises a level sensor 120 that measures the liquid level of the urea solution in the urea tank 105, a temperature sensor 121 that measures the temperature of the urea solution in the urea tank 105 and a quality sensor 122 that measures the quality of the urea solution in the urea tank 105. The quality sensor 122 determines the quality of the urea solution in the urea tank 105 by detecting the concentration of the urea solution or whether or not a foreign matter is mixed into the urea solution from the propagation velocity of an ultrasonic wave or the electrical conductivity.

A cooling line 123 through which cooling water for cooling the engine E circulates is connected to the urea tank 105 and the supply module 106. The cooling line 123 passes through the urea tank 105 so that heat exchange occurs between the cooling water flowing through the cooling line 123 and the urea solution in the urea tank 105. The cooling line 123 also passes through the supply module 106 so that heat exchange occurs between the cooling water flowing through the cooling line 123 and the urea solution in the supply module 106.

The cooling line 123 is provided with a tank heater valve (coolant valve) 124 that selectively supplies or does not supply the cooling water to the urea tank 105 and the supply module 106. The cooling line 123 is also connected to the dosing valve 104. However, the dosing valve 104 is configured to be supplied with the cooling water whether the tank heater valve 124 is open or closed. Although not shown in the simplified configuration shown in FIG. 1, the cooling line 123 is arranged along the liquid feed line 116, the pressure-feed line 117 and the collection line 118 through which the urea solution flows.

FIG. 2 is a diagram showing an input/output configuration of the DCU 126.

As shown in FIG. 2, input signals lines from the upstream-side NO_X sensor 110, the downstream-side NO_X sensor 111, the SCR sensor 119 (the level sensor 120, the temperature sensor 121 and the quality sensor 122), the exhaust gas temperature sensor 109, the SM temperature sensor 113 and the urea solution pressure sensor 114 of the supply module 106, and an engine control module (ECM) 125 that controls the engine E are connected to the DCU 126. Signals indicative of the outside air temperature and engine parameters (including the engine rotation speed) are input from the ECM 125.

Furthermore, output signal lines to the tank heater valve 124, the SM pump 112 and the reverting valve 115 of the supply module 106, the dosing valve 104, a heater of the upstream-side NO_X sensor 110 and a heater of the downstream-side NO_X sensor 111 are connected to the DCU 126. Signal exchange between the DCU 126 and each component can occur through the individual signal line or via a controller area network (CAN).

The DCU 126 is configured to estimate the amount of NO_X in the exhaust gas based on a signal indicative of an engine parameter from the ECM 125 and the exhaust gas temperature from the exhaust gas temperature sensor 109 and determine the amount of urea solution to be injected through the dosing valve 104 based on the estimated amount of NO_X in the exhaust gas. Furthermore, when the determined amount of urea solution is injected through the dosing valve 104, the DCU 126 is configured to control the dosing valve 104 based on the detection value from the upstream-side NO_X sensor 110 to adjust the amount of urea solution injected through the dosing valve 104.

As shown in FIG. 3, the dosing valve 104 is energized to inject urea solution for a period of t₁ at (fixed) intervals of t₀. The length of t₁ varies with the amount of injected urea solution. In emptying, the energization is maintained for a predetermined time. The predetermined time is a length of time required to return the urea solution in the piping to the urea tank 105.

The SCR system 100 according to the present invention is provided with a recovery control system that allows urea solution in the dosing valve 104 that is heated by the exhaust gas at high temperature and crystallizes and fixates to the interior of the dosing valve 104 to recover from a malfunction to a normal state. The recovery control system is provided in the DCU 126 and comprises abnormality detection means of detecting an abnormality of the dosing valve 104 and recovery control means.

The abnormality detection means is configured to detect an abnormality based on whether or not the open/close operation of the dosing valve 104 is normal.

The recovery control means is configured to control the supply module 106 to feed the urea solution in the dosing valve 104 back to the urea tank 105 when the abnormality detection means detects an abnormality of the dosing valve 104. More specifically, the recovery control means is configured to open the dosing valve 104, switch the reverting valve 115 of the supply module 106, activate the SM pump 112 of the supply module 106 and forcedly perform emptying (forced emptying).

An operation of the recovery control system will be described with reference to FIG. 4.

The recovery control system is configured to repeatedly perform the following operation.

The abnormality detection means detects whether or not the dosing valve 104 is normal (S401).

If an abnormality of the dosing valve 104 is detected in S401, the recovery control means opens the dosing valve 104, switches the reverting valve 115 of the supply module 106, activates the SM pump 112 of the supply module 106 and perform forced emptying (S402).

Then, it is determined whether the forced emptying is completed (S403). If the forced emptying is completed, urea solution is supplied to the dosing valve 104 (S404).

In the course of repetition of the above operation, urea crystals can be removed along with the urea solution by the force of feeding the urea solution in the dosing valve 104 back to the urea tank 105. If urea crystals cannot be removed (and thus the dosing valve 104 does not move and is kept closed), the urea solution cannot be fed back nor supplied and therefore remains in the dosing valve 104. However, if the forced emptying and the supply of urea solution are still repeated to change the pressure applied to the urea solution in the dosing valve 104, the urea solution can be fed to the site of the urea crystal, and the urea crystal can be resolved and removed. In this way, if the cause of the malfunction of the dosing valve 104 is fixation of the urea crystal, the malfunction of the dosing valve 104 can be eliminated. If the malfunction of the dosing valve 104 cannot be eliminated by repeating the Steps S401 to S404 to repeat the forced emptying and the supply of urea solution a predetermined number of times, it can be determined that the dosing valve 104 has failed. In this case, it can be determined whether recovery from the malfunction is possible or not, so that it is possible to avoid warning the driver or the like of a failure when recovery from the malfunction is possible.

As described above, the recovery control system according to the present invention can allow the dosing valve to recover from a malfunction to a normal state.

In emptying, as described above, the dosing valve 104 is opened in advance, and the exhaust gas (air) in the exhaust pipe 102 is sucked into the urea tank 105 from the dosing valve 104. That is, if emptying occurs, the exhaust gas is sucked through the liquid feed line 116, the pressure-feed line 117 and other lines. Therefore, foreign matters or the like in the liquid feed line 116 and the pressure-feed line 117 can also be removed.

In view of this, according to a modification of the present invention, the recovery control system may be provided with pressure abnormality detection means that detects an abnormality in the urea solution pressure based on the measurement value of the urea solution pressure sensor 114 that measures the pressure of the urea solution supplied to the dosing valve 104, the recovery control means may perform forced emptying when the pressure abnormality detection means detects an abnormality in the pressure of the urea solution. Specifically, as shown in FIG. 5, the pressure abnormality detection means may detect whether the pressure of the urea solution supplied to the dosing valve 104 is abnormal or not (becomes constant or not) (S501), and the recovery control means may perform forced emptying (S502) when a pressure abnormality is detected in S501.

In this case, it is possible to detect clogging of the liquid feed line 116 and remove a foreign matter that causes the clogging by forced emptying.

Furthermore, in forced emptying, the reverting valve 115 may not be activated, and the SM pump 112 may simply be turned off.

REFERENCE SIGNS LIST

• 102 exhaust pipe
• 104 dosing valve
• 105 urea tank
• 106 supply module
• 127 cylinder
• 129 valving element
• 130 plunger
• 131 coil

Claims

1. A recovery control system for allowing a dosing valve through which urea solution is injected into an exhaust pipe to recover from a malfunction to a normal state, comprising the dosing valve and a supply module that sucks up urea solution in a urea tank and supplies the urea solution to the dosing valve and feeds the urea solution in the dosing valve back to the urea tank, the dosing valve having a cylinder charged with the urea solution, a plunger that opens and closes a normally closed valving element of the cylinder and a coil that operates the plunger, wherein the recovery control system further comprises:abnormality detection means of monitoring the dosing valve and detecting an abnormality of the dosing valve; andrecovery control means of controlling the supply module to feed the urea solution in the dosing valve back to the urea tank when the abnormality detection means detects an abnormality of the dosing valve.

2. A recovery control system for allowing a liquid feed line to recover from clogging to a normal state, comprising a dosing valve through which urea solution is injected into an exhaust pipe and a supply module that sucks up urea solution in a urea tank and supplies the urea solution to the dosing valve and feeds the urea solution in the dosing valve back to the urea tank, the urea tank and the supply module being connected to each other by the liquid feed line, wherein the recovery control system further comprises:pressure abnormality detection means of detecting an abnormality in a urea solution pressure based on a measurement value of a urea solution pressure sensor that measures a pressure of the urea solution supplied to the dosing valve; andrecovery control means of controlling the supply module to feed the urea solution in the liquid feed line back to the urea tank when the pressure abnormality detection means detects an abnormality in the urea solution pressure.