Exhaust purifying device and working vehicle

An exhaust purifying device mounted in a working vehicle includes: an exhaust passage through which an exhaust gas discharged from an engine flows; a throttle valve configured to change a passage area of the exhaust passage; an exhaust aftertreatment device disposed downstream of the throttle valve; and a valve controller configured to control an open degree of the throttle valve. The valve controller is configured to control the open degree of the throttle valve to be larger in a low load region below a predetermined load range and in a high load region exceeding the predetermined load range than in a medium load region that is the predetermined load range.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to International Application No. PCT/JP2017/004253 filed on Feb. 6, 2017, the contents of which are incorporated herein in their entirety.

TECHNICAL FIELD

The present invention relates to an exhaust purifying device and a working vehicle.

BACKGROUND ART

A working vehicle such as a wheel loader includes an exhaust aftertreatment device (e.g., a diesel oxidant catalyst (DOC) and a selective catalytic reduction (SCR)) provided in an exhaust passage of an engine, the exhaust aftertreatment device being configured to burn particulate matters (PM) existing in an exhaust gas and purify nitrogen oxides (NOx) existing in the exhaust gas (see, for instance, Patent Literature 1).

In order to burn PM and purify NOx, it is required to increase a temperature of the exhaust gas. Accordingly, an exhaust throttle valve is provided in the exhaust passage upstream of the exhaust aftertreatment device, and the temperature of the exhaust gas is controlled by controlling an open degree of the exhaust throttle valve, so that the exhaust aftertreatment device is functionally optimized.

However, a frequent control of the open degree by the exhaust throttle valve causes abrasion on sliding surfaces between a bearing member and a valve body in the exhaust throttle valve. When the abrasion progresses, the exhaust throttle valve interferes with a housing to shorten a working lifetime.

Accordingly, Patent Literature 2 discloses a technique of forming the bearing member using a heat-resistant alloy (e.g., Inconel (trade mark)) formed of a sintered metal.

CITATION LIST

Patent Literatures

Patent Literature 1: International Publication No WO02016/068347

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, in the technique disclosed in Patent Literature 2, the bearing member has to be made of an expensive heat-resistant alloy, which results in a considerable increase in a manufacture cost.

It is also conceivable to reduce a sliding speed of the exhaust throttle valve. However, since the reduction of the sliding speed delays starting rotation of the engine, the reduction of the sliding speed is only applicable for closing the exhaust throttle valve. Consequently, the sliding speed of the exhaust throttle valve is not sufficiently reducible.

An object of the invention is to provide an exhaust purifying device and a working vehicle which are capable of prolonging a working lifetime of an exhaust throttle valve affected by abrasion between a valve body and a bearing member without considerably increasing a manufacture cost.

Means for Solving the Problem(s)

According to an aspect of the invention, an exhaust purifying device mounted in a working vehicle includes: an exhaust passage through which an exhaust gas discharged from an engine flows; a throttle valve configured to change a passage area of the exhaust passage; an exhaust aftertreatment device disposed downstream of the throttle valve; and a valve controller configured to control an open degree of the throttle valve, in which the valve controller is configured to control the open degree of the throttle valve to be larger in a low load region below a predetermined load range and in a high load region exceeding the predetermined load range than in a medium load region that is the predetermined load range.

According to the above aspect of the invention, since the valve controller controls the open degree of the throttle valve to be larger in the low load region and the high load region than in the medium load region, the open degree of the throttle valve is kept large while the working vehicle is accelerated at the start and is brought into a deceleration state. Accordingly, an increase in a sliding distance of the throttle valve, which is to be caused by controlling the open degree of the throttle valve, can be inhibited to reduce abrasion of the valve body and the bearing member, so that the working lifetime of the throttle valve can be prolonged.

DESCRIPTION OF EMBODIMENT(S)

Exemplary embodiment(s) of the invention will be described below with reference to the attached drawings.

[1] Schematic Structure of Exhaust Purifying Device10

FIG. 1schematically shows a structure of a working vehicle1in which an exhaust purifying device10according to an exemplary embodiment of the invention is mounted.

Herein, the working vehicle1is a machine configured to work for excavation, ground leveling and the like and to deliver earth and sand and the like, for instance, in a mine and a construction site of a road and the like. Examples of the working vehicle1include: a construction machine such as a wheel loader and a wheel type backhoe; and a delivery vehicle such as a forklift.

The working vehicle1includes: a diesel engine2; a turbocharger3including a turbine and configured to rotate the turbine by an exhaust gas of the diesel engine2to compress air to be supplied to the diesel engine2; a controller8; a monitor9; and an exhaust purifying device10.

The diesel engine2includes: an engine speed detector6configured to detect an engine speed; and a fuel injector7configured to inject a fuel to the diesel engine2. Detection data of the engine speed detector6is outputted to the controller8. The controller8is configured to control the fuel injector7in response to an accelerator operation and the like.

The monitor9includes a display and an input unit. The display includes a liquid crystal display and the like.

The display is configured to display various information (e.g., a cooling water temperature and a fuel residual amount), a caution and the like. The monitor9of the exemplary embodiment includes a notification unit91configured to notify an operator to prompt an execution of a later-described stationary manual regeneration. The monitor9functions as a notifying device configured to notify the operator of various information.

The input unit includes a switch (a button) provided around the display. The display displays an icon and the like representing a function of the input unit. Accordingly, in executing the stationary manual regeneration, the operator can easily recognize which switch he should press. When a touch-panel type monitor9is used, the operator only needs to touch a switch displayed on a touch panel. The monitor9of the exemplary embodiment includes a switch92configured to instruct the execution of the stationary manual regeneration. The input unit is not limited to the switch integrally provided with the monitor9, but may be a switch provided in a casing and the like independent of the monitor9.

The exhaust purifying device10is configured to perform processes such as an oxidation and a reduction of a residual substance such as PM and NOx in an exhaust gas. The controller8is configured to control the exhaust purifying device10.

The exhaust purifying device10includes: an exhaust throttle valve20; and an exhaust aftertreatment device in a form of a DOC device30, a urea-aqueous-solution injection system40, and an SCR device50, sequentially from an upstream side of a flow direction of an exhaust gas discharged from the diesel engine2.

The DOC device30, the urea-aqueous-solution injection system40, and the SCR device50are disposed in a course of an exhaust passage11in which the exhaust gas flows from the diesel engine2. The exhaust passage11includes: an inlet pipe12configured to introduce the exhaust gas from the turbocharger3connected to the diesel engine2into the DOC device30; an outlet pipe13connecting the DOC device30to the SCR device50; and an outlet pipe14connected to an outlet of the SCR device50.

The exhaust throttle valve20includes a butterfly valve or the like disposed at the inlet pipe12and is configured to change a passage area of the exhaust passage11. A valve open degree of the exhaust throttle valve20is controlled by the controller8. As described later, a temperature of the exhaust gas is adjusted by adjusting the valve open degree.

When the valve open degree of the exhaust throttle valve20is decreased (i.e., an open area is decreased) to increase a pressure resistance, an internal pressure of the diesel engine2upstream of the exhaust throttle valve20is also increased. In order to maintain a torque outputted from the diesel engine2when the pressure resistance is thus increased, a fuel injection amount to be injected from the fuel injector needs to be increased, so that a burning temperature can be increased to increase the temperature of the exhaust gas. However, since the fuel injection amount is increased, a fuel efficiency is decreased.

At this time, although described in detail later, the controller8controls the valve open degree of the exhaust throttle valve20using map data for setting the valve open degree depending on the fuel injection amount and the engine speed.

Specifically, as shown inFIG. 2, the exhaust throttle valve20includes: a housing21connected with the inlet pipe12(seeFIG. 1); a motor22provided above the housing21; a valve body23rotatable by the motor22.

As shown inFIGS. 2 and 3, the valve body23includes: a shaft24rotatable by the rotation of a driving shaft (not shown) of the motor22; and a flap25provided to the shaft24and configured to rotate to adjust an open degree of the exhaust passage11.

As shown inFIG. 3, the housing21has a hole in which the shaft24is inserted. A spherical washer26is provided to an outer circumference of the shaft24to block the hole of the housing21.

A retainer27is integrally formed with an upper side of the shaft24and is pressed upward by a spring28. A bush29of the shaft24is attached in a recess21A of the housing21. An upper surface of the spherical washer26is slidably in contact with a lower surface of the bush29.

A pinion gear is provided to the driving shaft of the motor22. A gear (not shown) meshing with the pinion gear is provided at a base end of the shaft24of the valve body23. When the motor22is driven, the gear is rotated via the pinion gear, thereby rotating the valve body23.

When the valve body23is rotated by the motor22, a lower surface29A of the bush29and an upper surface26A of the spherical washer26are slid in a rotational direction of the valve body23. When a rotation frequency of the valve body23is increased, a sliding distance between the lower surface29A of the bush29and the upper surface26A of the spherical washer26is increased, so that the lower surface of the bush29is gradually worn. As the lower surface29A of the bush29is worn, the valve body23is drawn upward by the spring28, so that a top end25A of the flap25interferes with an inner surface21B of the housing21, thereby requiring a large force to rotate the valve body23. Accordingly, a working lifetime of the exhaust throttle valve20to adjust by rotation is shortened.

The DOC device30includes a casing in which a diesel oxidation catalyst is housed.

The DOC device30is a catalyst to oxidize a fuel (dosing fuel) supplied as needed into the exhaust gas to generate heat, thereby increasing the temperature of the exhaust gas to a predetermined high temperature region. With use of the exhaust gas whose temperature is increased, PM present in the exhaust gas is burned and a later-described urea deposit accumulated in the outlet pipe13and the like is burned to be removed, thereby purifying and regenerating the exhaust gas.

The urea-aqueous-solution injection system is configured to add a reductant aqueous solution in a form of a urea aqueous solution into the exhaust gas. The urea-aqueous-solution injection system40includes: an injection nozzle41attached to the outlet pipe13of the DOC device30and configured to inject the urea aqueous solution into the outlet pipe13; a urea water tank42configured to store the urea aqueous solution; and a pump unit43configured to supply the urea aqueous solution from the urea water tank42to the injection nozzle41.

The controller8is configured to control the injection nozzle41and the pump unit43to inject the urea aqueous solution from the injection nozzle41into the outlet pipe13. The urea aqueous solution injected into the outlet pipe13is hydrolyzed by the heat of the exhaust gas to become ammonia.

The SCR device50reduces and purifies nitrogen oxides present in the exhaust gas with ammonia (i.e., a reduction-causing agent) obtained by hydrolyzing the urea aqueous solution The ammonia is supplied to the SCR device50as a reduction-causing agent together with the exhaust gas.

An ammonia reduction catalyst may be provided downstream of the SCR device50. The ammonia reduction catalyst oxidizes ammonia unused in the SCR device50to make the ammonia harmless, thereby further reducing emissions in the exhaust gas.

The exhaust purifying device10is provided with various sensors for detecting conditions of the diesel engine2and the exhaust purifying device10.

Specifically, a NOx sensor32configured to detect a concentration of NOx contained in the exhaust gas is disposed to a side of the inlet pipe12downstream of the exhaust throttle valve20. To the DOC device30, an inlet temperature sensor31configured to measure an inlet temperature of the DOC device30, and an outlet temperature sensor45configured to measure an outlet temperature of the DOC device30are provided.

An SCR internal temperature sensor47and an SCR outlet temperature sensor51configured to measure an outlet temperature of the DOC device50are provided to the SCR device50.

An SCR outlet NOx sensor52configured to detect a concentration of NOx contained in the exhaust gas discharged from the SCR device50is disposed to the outlet pipe14connected to the SCR device50.

These sensors are connected to the controller8via Controller Area Network (CAN)18and are configured to output measurement data to the controller8.

The controller8serving as a valve controller is configured to control an open degree of the exhaust throttle valve20during a steady operation of the working vehicle1to control the temperature of the exhaust gas to around 300 degrees C., thereby enhancing a purifying efficiency of the SCR device50.

As shown inFIG. 4, the controller8includes an engine-speed acquisition unit81, a fuel-injection-amount acquisition unit82, and a valve open degree controller83.

The engine-speed acquisition unit81is configured to acquire an engine speed of the diesel engine2based on a detection value of the engine speed detector6.

A fuel injection amount injected by the fuel injector7is detected by a sensor (not shown) and is shown as a detection value. The fuel-injection-amount acquisition unit82is configured to acquire the detection value. The fuel injection amount is fluctuated mainly by an acceleration operation amount by an operator.

The valve open degree controller83is configured to control the open degree of the exhaust throttle valve20based on the engine speed acquired by the engine-speed acquisition unit81and the fuel injection amount acquired by the fuel-injection-amount acquisition unit82.

Specifically, the valve open degree controller83controls the open degree of the exhaust throttle valve20with reference to a data table TBL shown inFIG. 5. The data table TBL records the open degrees of the exhaust throttle valve20according to the engine speed of the diesel engine2and the fuel injection amount by the fuel injector7.

For instance, the data table TBL records an open degree OP1of the exhaust throttle valve20at an engine speed RP1and a fuel injection amount IN1. The valve open degree controller83outputs the open degree OP1as an open degree command to the exhaust throttle valve20, so that the motor22of the exhaust throttle valve20rotates the valve body23according to the open degree OP1.

In a map MAP of the exemplary embodiment, the open degree of the exhaust throttle valve20according to the fuel injection amount is set. The map MAP is sectioned into a low load region AR1, a medium load region AR2, and a high load region AR3.

The low load region AR1below a predetermined load range is a region in which the produced torque is equal to or less than a torque at which the working vehicle1is driven, specifically, a region in which the fuel injection amount is below approximately 10% of a fuel injection amount of the diesel engine2in a rated output. The open degree of the exhaust throttle valve20in the low load region AR1is set to be fully open (0%) in the exemplary embodiment. It should be noted that the open degree of the exhaust throttle valve20in the low load region AR1is not necessarily set to be fully open, but only needs to be set larger than an open degree of the exhaust throttle valve20in the later-described medium load region AR2.

The medium load region AR2that is a predetermined load range is a region in which the produced torque is equal to a torque that the working vehicle1requires for usual loading and unloading, specifically, a region in which the fuel injection amount is in a range from approximately 10% to less than approximately 40% of the fuel injection amount of the diesel engine2in a rated output. An open degree of the exhaust throttle valve20in the medium load region AR2is in a range from approximately 70% to approximately 90%. The open degree of the exhaust throttle valve20is changed according to the fluctuation of the fuel injection amount and the engine speed.

The high load region AR3exceeding the predetermined load range is a region in which the temperature of the exhaust gas is equal to or more than a regeneration temperature of the DOC device30and a purification temperature of the SCR device50, and which is a region of the torque that working vehicle1requires for traveling for loading. Specifically, the high load region AR3is a region in which the fuel injection amount is in a range from approximately 40% to 100% of the fuel injection amount of the diesel engine2in a rated output. The open degree of the exhaust throttle valve20in the high load region AR3is set to be fully open (0%).

In other words, the open degree of the exhaust throttle valve20in the medium load region is set smaller than those in other load regions.

Moreover, the medium load region AR2in the map MAP is sectioned into a low rotation region AR4and a high rotation region AR5of the engine speed.

The low rotation region AR4of the engine speed is a region in which the engine speed is equal to or less than the engine speed of the diesel engine2at which the working vehicle1can be driven, specifically, a region in which the engine speed is in a range from approximately 400 rpm to approximately 1100 rpm. The open degree of the exhaust throttle valve20in the low rotation region AR4is set to be fully open (0%).

The high rotation region AR5of the engine speed is a region in which the engine speed falls within the engine speed of the diesel engine2at which the working vehicle1can be driven, specifically, a region in which the engine speed exceeds approximately 1100 rpm. The open degree of the exhaust throttle valve20in the high rotation region AR5is set in a range from approximately 70% to approximately 90% as described above.

The open degree of the exhaust throttle valve20in the low rotation region AR4is set to be fully open, because an engine oil and a lubricating oil for a driving system become highly viscous to increase agitation resistance and slide resistance of an accelerator, the engine, a pump and the like when the working vehicle1is kept in a low idling state at low temperatures in winter and the like. For this reason, a driving torque is increased to increase the fuel injection amount of the diesel engine2. When the open degree of the exhaust throttle valve20is controlled in this state, the fuel injection amount approaches the region AR2of a large fuel injection amount and repeats entering and exiting the region AR2and the region AR1, so that the exhaust throttle valve20moves tremblingly to increase a sliding distance of the exhaust throttle valve20.

Accordingly, the open degree of the exhaust throttle valve20is set to be fully open in the idling state of the working vehicle1irrespective of temperatures (low or high), whereby the exhaust throttle valve20is not moved, so that the sliding distance of the exhaust throttle valve20is decreased.

[10] Regeneration Process of SCR Device50

When the urea aqueous solution is injected from the injection nozzle41as shown inFIG. 2in a regeneration process, urea is sometimes crystallized to be deposited in the outlet pipe13. For this reason, it is necessary to perform a purification process for increasing the temperature of the exhaust gas to decompose a substance (urea deposit) deposited in the outlet pipe13. The purification process includes: an temperature-increasing control that is automatically performed when the working vehicle1is activated and kept being operated; and a stationary manual regeneration that is performed when an operator operates the switch92on the monitor9after the working vehicle1is stopped. The increasing-temperature control and the stationary manual regeneration are selectively switched to be controlled by the controller8.

The controller8measures the temperature of the exhaust gas at the inlet of the DOC device30using the inlet temperature sensor31, controls the open degree of the exhaust throttle valve20according to the measured temperature to adjust the temperature of the exhaust gas.

The controller8acquires the engine speed from the engine speed detector6, acquires the temperature of the exhaust gas at the inlet of the DOC device30from the inlet temperature sensor31, and acquires a NOx concentration at the inlet of the DOC device30from the NOx sensor32. Moreover, the controller8acquires the temperature of the exhaust gas at the outlet of the DOC device30from the outlet temperature sensor45, acquires the temperature of the SCR catalyst from the SCR internal temperature sensor47, acquires the SCR outlet temperature from the SCR outlet temperature sensor51, and acquires the NOx concentration at the outlet of the SCR device50from the SCR outlet NOx sensor52.

The controller8controls the operations of the fuel injector7, the exhaust throttle valve20, the injection nozzle41, and the pump unit43based on the acquired data and information (e.g., acceleration operation by an operator).

[11] Operation and Effects in Exemplary Embodiment(s)

Next, operation of the working vehicle1in a form of a wheel loader in the exemplary embodiment will be described with reference toFIGS. 5 and 6. Output torque of the working vehicle1transitions within a torque curve TRQ shown inFIG. 5.

As a typical V-shape loading operation of the working vehicle1(e.g., a wheel loader) as shown inFIG. 6, firstly, an operator starts the diesel engine2and starts operating the working vehicle1in an idling state ST1.

Until reaching a loading site, the operator operates the working vehicle1in an accelerator full open state ST2in which an accelerator is fully open.

When the working vehicle1approaches the loading site, the operator turns off the accelerator and puts on a brake to enter a deceleration state ST3.

Controlling the open degree of the exhaust throttle valve20accompanying the typical operation of the wheel loader will be described with reference toFIG. 5.

Firstly, in the idling state ST1, since the engine speed falls within the low rotation region AR4, the exhaust throttle valve20is brought into a full open state.

Next, in the accelerator full open state ST2(rated point) in which the operator turns on the accelerator to be fully open, since the idling state ST1is changed to the accelerator full open state ST2, the fuel injection amount transitions from the low rotation region AR4to the high load region AR3and the exhaust throttle valve20is kept in the full open state.

Lastly, when the working vehicle1is brought into the deceleration state ST3, since the accelerator is turned off and the brake is put on, the fuel is not injected and the fuel injection amount transitions from the high load region AR3to the low load region

AR1, whereby the exhaust throttle valve20is further kept in the full open state.

Here, at the transition from the accelerator full open state ST2to the low load region AR1, the fuel injection amount falls within and then out of the medium load region AR2in which the open degree of the exhaust throttle valve20is changed. However, even when the operator switches from the accelerator full open state to an accelerator-off state, an actual operation of the working vehicle1in response to the accelerator operation is delayed. Accordingly, due to the delayed response, the open degree of the exhaust throttle valve20on the map MAP directly transitions to the low load region AR1without transitioning to the medium load region AR2, so that the open degree of the exhaust throttle valve20is kept to be fully open and the sliding distance of the exhaust throttle valve20is not increased.

Subsequently, when the working vehicle1starts a digging operation of earth and sands and the like, the fuel injection amount of the diesel engine2falls within the medium load region AR2and the open degree of the exhaust throttle valve20is controlled based on the fuel injection amount according to a working load.

According to the exemplary embodiment, even when the state of the working vehicle1transitions from the idling state ST1to the accelerator full open state ST2and further to the deceleration state ST3, the open degree of the exhaust throttle valve20is kept in a full open state in the low load region AR1and the high load region AR3. Accordingly, even when the fuel injection amount is changed from the fuel amount in the low load region AR1to the fuel amount in the high load region AR3, the sliding distance of the exhaust throttle valve20is not increased, thereby minimizing wear of the bush29of the exhaust throttle valve20, so that an operation failure of the exhaust throttle valve20is preventable. Particularly, since the working vehicle1such as the wheel loader performs typical operations of transition from the idling state ST1to the accelerator full open state ST2and the deceleration state ST3, the exemplary embodiment is effective.

[12] Modification in Exemplary Embodiment

The invention is by no means limited to the above-described exemplary embodiment, but encompasses modifications described below.

In the above-described exemplary embodiment, the open degree of the exhaust throttle valve20in the low rotation region AR4of the engine speed is set to be fully open, but not limited thereto and may also be set at the same degree as in the high rotation region AR5.

In the above-described exemplary embodiment, the working vehicle1is a wheel loader. However, the application of the invention is not limited thereto and the invention may be applied to a wheel type backhoe, a forklift and the like. In short, the invention is applicable to a wheel working vehicle.

In the above-described exemplary embodiment, the open degree of the exhaust throttle valve20provided in the exhaust passage11is controlled. However, the invention is applicable not only to the exhaust throttle valve20but also to an intake throttle valve.

Further, the specific arrangements and configurations of the invention may be altered in any manner in actual implementation as long as the modifications and improvements are compatible with the invention.