Patent Description:
It is typical to provide an exhaust aftertreatment system (EATS) to handle emissions from diesel engines. An EATS will often include a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and a selective catalytic reduction catalyst (SCR). Urea is injected upstream of SCR to assist in reducing NOx generated by the engine to N2 and H2O.

When the engine is turned off, particularly in cold temperatures, a reversion process is ordinarily performed to remove urea from components including the lines leading from a reservoir of urea (i.e. a tank), the urea pump, and the urea injection valve. This is to avoid the potential for freezing of urea in the lines. The freezing point for aqueous urea is about -<NUM>. In some engine systems, a reversion process is performed if an ambient temperature at or below about -<NUM> is measured when the engine is turned off. In other systems, a reversion process is performed every time the engine is turned off, regardless what the ambient temperature is.

A drawback to performing a reversion process every time that the engine is shut down or every time that the engine is shut down at a low ambient temperature is that, if the engine is subsequently restarted before the urea in the lines would have been expected to have frozen, then the lines from the tank to the injection valve have to refill with urea before more urea can be injected. In addition to this process being a waste of energy, this process will result in there being a period of time during which urea will not be injected into the SCR to reduce NOx to N2 and H2O, and harmful emissions may be released to the atmosphere.

Further, the injection valve is more prone to becoming clogged when the system reverts immediately because the temperatures at the valve tend to be very hot from exhaust gases. The heat may cause micro-crystals to form inside the injector and externally on the tip of the injector that would not tend to form if urea is left in the valve while the system cools down.

According to its abstract, <CIT> relates to a metering device for introducing liquid reducing agent into an exhaust gas pipe. The metering device has a working tank with contents, a delivery unit which is connected to the working tank and the delivery direction of which can be reversed, and a metering valve which is connected to the delivery unit.

It is desirable to provide a method and apparatus that can minimize the performance of unnecessary reversions.

In accordance with an aspect of the present invention, a method for operating a urea dosing system in an exhaust aftertreatment system (EATS) of an engine is provided. The method includes steps of measuring an ambient temperature in an environment in which the EATS is disposed, monitoring one or more temperatures associated with the EATS to which there is a relationship to a temperature of urea in the urea dosing system, after turning off the engine, determining, based on the measured ambient temperature and the one or more monitored temperatures, whether urea in the urea dosing system is subject to freezing, and performing a reversion operation after turning off the engine with a delay until one or more events occur, the one or more events including determining that urea in the urea dosing system is subject to freezing.

In accordance with another aspect of the present invention, an engine system comprises an engine, an exhaust aftertreatment system (EATS), the EATS comprising a urea dosing system, means for measuring an ambient temperature in an environment in which the EATS is disposed, and means for monitoring one or more temperatures associated with the EATS to which there is a relationship to a temperature of urea in the urea dosing system, and a controller arranged to determine, after turning off the engine, whether urea in the urea dosing system is subject to freezing based on the measured ambient temperature and the one or more monitored temperatures, and to send an instruction to the urea dosing system to perform a reversion operation after turning off the engine with a delay until one or more events occur, the one or more events including determining that urea in the urea dosing system is subject to freezing.

The features and advantages of the present invention are well understood by reading the following detailed description in conjunction with the drawings in which like numerals indicate similar elements and in which:.

A vehicle <NUM> that includes an engine system <NUM> according to an aspect of the present invention is shown in <FIG>. The engine system <NUM> includes an engine <NUM> (typically a diesel engine) and an exhaust aftertreatment system (EATS) <NUM>. The EATS <NUM> comprises a dosing system <NUM> for a diesel exhaust fluid (typically but not necessarily urea, and the dosing system shall hereinafter be referred to as a urea dosing system for purposes of discussion), means <NUM> (<FIG> and <FIG>) for measuring an ambient temperature in an environment in which the EATS is disposed, and means <NUM> (<FIG> and <FIG>) for monitoring one or more temperatures associated with the EATS to which there is a relationship to a temperature of urea in the urea dosing system (except where otherwise indicated, hereinafter referred to as an EATS temperature monitoring means). The ambient temperature measuring means <NUM> typically includes devices such as a thermometer, thermocouple, thermistor, resistance temperature detector, or other device capable of performing the function of measuring temperature. Likewise, the EATS temperature monitoring means <NUM> typically includes devices that can be directly wired to a controller <NUM> such as a thermometer, thermocouple, thermistor, resistance temperature detector, or other device capable of performing the function of measuring temperature, such as a smart sensor of some type that communicates over a controller area network communication bus that need not be directly wired to a controller. It will be appreciated that the present invention has application in engine systems that are not associated with a vehicle <NUM>, however, it is presently anticipated that a particularly useful application for the engine system is in connection with a vehicle. The particular vehicle <NUM> illustrated is a truck, however, the vehicle may be any other form of vehicle or equipment that includes an engine system <NUM> of the type described herein, such as a marine vehicle, construction equipment, or a stationary engine.

As seen in <FIG> and <FIG>, the engine system <NUM> also includes a controller <NUM> arranged to determine, after turning off the engine <NUM>, whether urea <NUM> in the urea dosing system <NUM> is subject to freezing based on the measured ambient temperature and the one or more monitored temperatures, and to send an instruction to the urea dosing system to perform a reversion operation after turning off the engine with a delay until one or more events occur, the one or more events including determining that urea in the urea dosing system is subject to freezing. The controller <NUM> may have a variety of suitable forms, such as a programmed computer, Engine Control Unit, or Aftertreatment Control Module. The delay that occurs before performing a reversion process will ordinarily be a function of the ambient temperature at shut down of the engine and the monitored temperature that is indicative of the temperature of the urea in the dosing system <NUM>. The delay may be permitted because, for example, residual heat in the components of and proximate the dosing system <NUM> may keep the urea in the dosing system from freezing for a period of time after turning the engine off. The length of the delay will vary depending upon the construction of the particular dosing system and other factors. Typically, an appropriate length of the delay for a particular system will be determined by testing and/or modeling of the system under consideration.

The ambient temperature measuring means <NUM> and the EATS temperature monitoring means <NUM> will ordinarily comprise temperature measuring equipment of the type that sends an electrical signal corresponding to the temperature measured/monitored. Ordinarily, the ambient temperature measuring means <NUM> will provide only a single signal corresponding to the ambient temperature, usually when the engine is turned off, and is therefore only a minimal drain on a battery <NUM>. By contrast, the EATS temperature monitoring means <NUM> will ordinarily continuously or periodically take temperature measurements and send signals to the controller <NUM>.

The precise nature of the reversion operation that is performed may vary depending upon the particular engine system structure. <FIG> and <FIG> schematically show a presently preferred engine system <NUM> comprising an injection (or urea dosage) valve <NUM> from which urea <NUM> is injected upstream of a selective catalytic reduction device (SCR) <NUM> to reduce NOx generated by the engine <NUM> to N2 and H2O. The injection valve <NUM> is connected via a pressure line <NUM> downstream from a pump unit <NUM> that typically includes a pump filter <NUM> connected downstream of a pump motor <NUM> that is connected via an inlet line <NUM> to a tank <NUM> for holding the urea <NUM>. A reverting valve <NUM> is provided in the inlet line <NUM> and is switchable between a first or injection position shown in <FIG> in which urea <NUM> pumped from the tank <NUM> to the injection valve <NUM> and a second or reversion position shown in <FIG> for reversing the direction of flow from the injection valve back to the tank so that urea is sucked from the injection valve and the pressure line <NUM> and pumped via the inlet line <NUM> back to the tank. The injection valve <NUM>, the pressure line <NUM>, the pump unit <NUM>, the inlet line <NUM>, and the tank <NUM> will typically be heated by one or more appropriate heating means, such as by an electric heater and/or a line <NUM> through which heated engine coolant flows. A backflow line <NUM> is typically provided to permit urea pumped by the pump unit <NUM> and that is in excess of the amount of urea that can be injected through the injection valve <NUM> at the particular pumping pressure to return to the tank <NUM>.

The EATS temperature monitoring means <NUM> monitors a temperature that, for the particular engine system <NUM>, is known to bear relationship to the temperature of urea in the engine system. By monitoring this temperature, the possibility of urea <NUM> in the engine system <NUM> freezing can be determined. When the temperatures measured by the ambient temperature measuring means <NUM> and monitored by the EATS temperature monitoring means <NUM> indicate that there is a possibility of freezing of the urea <NUM> in the engine system, the reversion operation can be performed. The controller <NUM> can assess the temperatures measured by the ambient temperature measuring means <NUM> and monitored by the EATS temperature monitoring means <NUM> and, even though there is a possibility of freezing, can be programmed to delay initiating the reversion operation for a period of time based on the measured and monitored temperatures until the risk of freezing exceeds a predetermined level. In this way, it is possible to avoid unnecessary reversion operations whenever an engine shut-down occurs, as it is possible that the engine will be restarted before freezing will actually occur, and exhaust of NOx during start-up can be minimized.

The EATS temperature monitoring means <NUM> may be in the form of means for measuring a temperature of the urea dosing pump unit <NUM> of the urea dosing system <NUM>. The EATS temperature monitoring means <NUM> is in the form of means for measuring a temperature of an EATS component proximate the injection valve <NUM> of the urea dosing system. An EATS component that is proximate the injection valve <NUM> and that has a temperature that bears a direct relationship to the temperature of urea <NUM> in the engine system <NUM> is a diesel particulate filter (DPF) <NUM> that is typically disposed immediately upstream of injection valve <NUM> and the SCR <NUM>.

In accordance with a further aspect of the invention, the engine system <NUM> comprises means <NUM> for monitoring voltage of the battery <NUM> of the engine <NUM> where the battery is arranged to start the engine and also to power the EATS temperature monitoring means <NUM>. The controller <NUM> can be arranged to determine, in response to a signal from the voltage monitoring means <NUM>, after turning off the engine <NUM>, whether voltage of the battery <NUM> has fallen below a predetermined voltage, and the one or more events that must occur in order for the controller to send the instruction to the urea dosing system <NUM> to perform a reversion operation after turning off the engine with a delay can include determining that voltage of the battery has fallen below a predetermined voltage. In this way, it can be assured that operation of power draining devices such as the EATS temperature monitoring means <NUM> (and other battery powered equipment, if provided) will not continue past a point at which the battery <NUM> no longer has sufficient charge to start the engine <NUM>. The voltage monitoring means <NUM> can be any suitable device for sending a signal to the controller <NUM> upon detection of a voltage below a particular value, such as a voltage monitoring relay. In a presently preferred embodiment, the controller <NUM> reads the voltage directly, however, other alternatives are possible, such as smart sensors that relay voltage level measurements over a controller area network bus. It is presently preferred that battery voltage not fall below a value of <NUM> Volts DC, however, the particular voltage at which the controller <NUM> will control the engine system <NUM> to perform a reversion operation may be different in different engine systems and with different factors of safety.

In accordance with a further aspect of the invention, the engine system <NUM> comprises means <NUM> for measuring an elapsed time from turning off the engine <NUM>. The controller <NUM> can be arranged to determine, in response to a signal from the elapsed time measuring means <NUM>, after turning off the engine <NUM>, whether the elapsed time from turning off the engine has exceeded a predetermined length of time, and the one or more events that must occur in order for the controller to send the instruction to the urea dosing system <NUM> to perform a reversion operation after turning off the engine with a delay can include determining that the elapsed time from turning off the engine exceeds a predetermined length of time. Performing a reversion operation after a predetermined elapsed time provides an additional or alternative measure of safety in addition to or as an alternative to measuring battery voltage to ensure that the battery <NUM> will not be drained beyond the point where it will not be able to start the engine <NUM> while monitoring temperature with the EATS temperature monitoring means (or while operating other battery powered components). The predetermined length of elapsed time can, for example, be a function of an expected battery voltage after turning off the engine <NUM> and monitoring the one or more temperatures associated with the EATS. The elapsed time measuring means <NUM> can be in any suitable form, such as a clock that is adapted to send a signal to the controller <NUM> (or is part of a controller, such as an after-treatment control module) after the engine is turned off.

<FIG> shows steps in a method for operating a urea dosing system <NUM> in an EATS <NUM> of an engine <NUM>. After the engine <NUM> is turned off at step S1, an ambient temperature is measured at step S2, via suitable ambient temperature measuring means <NUM>, in an environment in which the EATS <NUM> is disposed, usually at least a single time after the engine is turned off. While the ambient temperature may be measured only a single time, it may alternatively be intermittently or continuously monitored, however, such intermittent or continuous monitoring may draw more power from the battery <NUM> than is desirable. Also after the engine <NUM> is turned off at step S1, one or more temperatures associated with the EATS <NUM> to which there is a relationship to a temperature of urea <NUM> in the urea dosing system <NUM> are monitored at step S3, the monitoring occurring continuously or periodically. After turning off the engine <NUM> at step S1, a determination is made at step S4A, based on the measured ambient temperature and the one or more monitored temperatures, whether urea <NUM> in the urea dosing system <NUM> is subject to freezing. At step S5, a reversion operation is performed after turning off the engine, with a delay based on when freezing of the urea can be expected to occur calculated as a function of the measured ambient temperature and the temperature monitored that is indicative of the temperature of the urea in the dosing system, until one or more events occur, the one or more events including determining at step S4A that urea <NUM> in the urea dosing system <NUM> is subject to freezing after the delay.

The one or more monitored temperatures monitored at step S3 includes monitoring of temperature of a DPF <NUM>.

The method can further include, at step S4B, monitoring voltage of the battery <NUM> of the engine <NUM>, the battery being arranged to start the engine and to power the EATS temperature monitoring means. At step S5, a reversion operation is performed after turning off the engine with a delay until one or more events occur, the one or more events including determining at step S4B that voltage of the battery has fallen below a predetermined voltage.

The method can further include, at step S4C, measuring an elapsed time from turning off the engine <NUM>. At step S5, a reversion operation is performed after turning off the engine with a delay until one or more events occur, the one or more events including determining at step S4C that the elapsed time from turning off the engine exceeds a predetermined length of time. The predetermined length of time is ordinarily a function of an expected battery voltage after turning off the engine <NUM> and monitoring the one or more temperatures associated with the EATS with the EATS temperature monitoring means <NUM>.

The method can be performed with only one of steps S4A, S4B, or S4C being performed. For example, the engine system <NUM> may only comprise ambient temperature measuring means <NUM> and EATS temperature monitoring means <NUM> and a controller <NUM> for performing step S4A, i.e. determining whether urea is subject to freezing and delaying reversion until it is determined that urea is subject to freezing, and may not include voltage monitoring means <NUM> or time monitoring means <NUM> for performing steps S4B or S4C (shown in phantom in <FIG> to reflect that they can be omitted). Alternatively, the engine system <NUM> may only comprise voltage monitoring means <NUM> and/or time monitoring means <NUM> for performing steps S4B and/or S4C and may not include ambient temperature measuring means <NUM> and EATS temperature monitoring means <NUM> and a controller <NUM> for performing step S4A. It is, however, presently preferred that all of the steps be performed. As soon as the conditions of any one of steps S4A, S4B, or S4C that the engine system <NUM> is able to perform are satisfied, a reversion operation will automatically be performed, without necessarily also performing any of the other steps. If fewer than all of the steps S4A, S4B, and S4C are performed, it is presently preferred that at least step S4A be performed using ambient temperature measuring means <NUM>, EATS temperature monitoring means <NUM>, and the controller <NUM> for determining whether urea is subject to freezing and delaying reversion until it is determined that urea is subject to freezing.

After a reversion operation is performed, equipment associated with the engine system <NUM> that causes a drain on the battery <NUM>, such as the EATS temperature monitoring means <NUM>, the voltage monitoring means <NUM>, the time measuring means <NUM>, and the controller <NUM> will ordinarily be shut down so that no unnecessary drain on the battery will occur.

In the present application, the use of terms such as "including" is open-ended and is intended to have the same meaning as terms such as "comprising" and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as "can" or "may" is intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such.

Claim 1:
A method for operating a urea dosing system (<NUM>) in an exhaust aftertreatment system (EATS) (<NUM>) of an engine (<NUM>), comprising:
measuring an ambient temperature in an environment in which the EATS is disposed;
monitoring, with a temperature monitoring means (<NUM>), one or more temperatures associated with the EATS to which there is a relationship to a temperature of urea in the urea dosing system;
after turning off the engine, determining, based on the measured ambient temperature and the one or more monitored temperatures, whether urea in the urea dosing system is subject to freezing; and
performing a reversion operation to remove urea from components of the urea dosing system after turning off the engine with a delay until one or more events occur, the one or more events including determining that urea in the urea dosing system is subject to freezing,
wherein the one or more monitored temperatures includes a temperature of a diesel particulate filter (<NUM>) of the EATS.