WO2014188876A1 - Hybrid electric vehicle and method for controlling same - Google Patents

Abstract

In the present invention, when the amount of adhesion of a reducing agent to the SCR catalyst (17) of an exhaust gas purification system (16) is less than a pre-set lower limit value, a portion of the driving force of a diesel engine (5) is substituted with driving force from the traveling motor of a hybrid system (9), and when the amount of adhesion of the reducing agent to the SCR catalyst (17) is greater than a pre-set upper limit value, the traveling moor (6) is driven by a portion of the driving force of the diesel engine (5), thus generating electricity.

Description

Hybrid electric vehicle and control method thereof

The present invention relates to a hybrid electric vehicle and a control method therefor, and more particularly to a hybrid electric vehicle and a control method therefor that can improve fuel efficiency without lowering the NOx purification rate.

In recent years, hybrid electric vehicles (hereinafter referred to as “HEV”) in which part of the driving force generated by the internal combustion engine is replaced by a travel motor that uses a battery as a power source have attracted attention from the viewpoint of improving fuel efficiency and environmental measures. .

When a diesel engine is used for the internal combustion engine in this HEV, in order to remove harmful substances such as particulate matter (PM) and nitrogen oxide (NOx) contained in the exhaust gas of the diesel engine, as in conventional vehicles. A purification system is required. As for the former PM, a PM collection filter that collects PM with a filter made of a honeycomb-like porous body made of ceramics has been put into practical use. As for the latter NOx, a reducing agent SCR system using a reducing agent and a selective reduction catalyst (hereinafter referred to as “SCR catalyst”) has attracted attention.

This reductant SCR system is used in an exhaust gas by an SCR reaction in which ammonia or hydrocarbons (HC) of unburned fuel decomposed and generated from urea water supplied in the exhaust gas acts as a reducing agent in the presence of the SCR catalyst. It purifies NOx. As the SCR catalyst, a zeolite catalyst such as an iron ion exchange aluminosilicate or a copper ion exchange aluminosilicate is widely used. A slurry containing this zeolite catalyst applied to a carrier such as a ceramic honeycomb, or a molded product thereof is obtained from the SCR. It is designed to be used by attaching it to the exhaust pipe as a converter.

However, the above-mentioned SCR catalyst reduces the NOx purification rate unless an appropriate amount of reducing agent is adsorbed with respect to the amount of NOx to be purified. May be released inside.

Here, it is generally known that in a diesel engine, a decrease in the amount of NOx generated and fuel consumption are in a trade-off relationship. Therefore, if an attempt is made to reduce the amount of NOx generated in the diesel engine in accordance with the decrease in the NOx purification rate in the SCR catalyst as described above, the fuel efficiency will be deteriorated.

In order to solve such a problem, for example, as described in Japanese Patent Application Laid-Open No. 2001-37008 (Patent Document 1), the engine emits less harmful substances at the time of HEV power generation request. There has been proposed a control device that improves the exhaust composition and fuel consumption by regulating within an operating range and using electric power obtained within the range for engine output assist.

However, since the above control device performs control only when HEV power generation is requested, the effects of reducing NOx emissions and improving fuel efficiency are not sufficient.

Japanese Patent Application Publication No. 2001-37008

An object of the present invention is to provide a hybrid electric vehicle capable of improving the NOx purification rate without deteriorating fuel consumption, and a control method thereof.

The hybrid electric vehicle of the present invention that achieves the above object includes a hybrid system that uses at least one of an engine and a traveling motor as a drive source, a reducing agent supply means and an SCR that are interposed in the exhaust pipe of the engine in order from the upstream side. A hybrid electric vehicle including an exhaust gas purification system comprising a catalyst, wherein the control means for controlling the hybrid system and the exhaust gas purification system is configured such that the reducing agent adsorption amount on the SCR catalyst is lower than a preset lower limit value. When the amount is small, a part of the driving force of the engine is substituted with the driving force of the traveling motor, and when the amount of reducing agent adsorbed on the SCR catalyst is larger than a preset upper limit value, the driving force of the engine The traveling motor is driven by a part of the motor to generate electric power.

The hybrid electric vehicle control method of the present invention that achieves the above object includes a hybrid system that uses at least one of an engine and a travel motor as a drive source, and a reduction system that is interposed in the exhaust pipe of the engine in order from the upstream side. A control method for a hybrid electric vehicle comprising an agent supply means and an exhaust gas purification system comprising an SCR catalyst, wherein when the amount of reducing agent adsorbed on the SCR catalyst is less than a preset lower limit value, the engine When a part of the driving force is replaced by the driving force of the traveling motor and the amount of reducing agent adsorbed on the SCR catalyst is larger than a preset upper limit value, the traveling motor is driven by a part of the driving force of the engine. To generate electric power.

According to the hybrid electric vehicle of the present invention and the control method thereof, the adsorption amount of the SCR catalyst is appropriately controlled with respect to the NOx generation amount by reducing or increasing the engine torque of the diesel engine by the traveling motor. In addition, the NOx purification rate in the hybrid electric vehicle can be improved. Further, when the engine torque of the diesel engine is increased, energy corresponding to the increased amount is stored in the battery as electric power, so that the fuel efficiency of the vehicle can be prevented from deteriorating.

FIG. 1 is a configuration diagram of a hybrid electric vehicle according to an embodiment of the present invention. FIG. 2 is a flowchart for explaining a control method of the hybrid electric vehicle according to the embodiment of the present invention. FIG. 3 is a flowchart illustrating a method for controlling a hybrid electric vehicle according to another embodiment of the present invention. FIG. 4 is another example of the configuration diagram of the hybrid electric vehicle according to the embodiment of the present invention. FIG. 5 is still another example of the configuration diagram of the hybrid electric vehicle according to the embodiment of the present invention. FIG. 6 is a graph schematically illustrating an example of the division of the driving region of the hybrid electric vehicle. FIG. 7 is a graph showing the displacement of the operating region of the hybrid electric vehicle in the embodiment when the reducing agent adsorption amount on the SCR catalyst is insufficient. FIG. 8 is a graph showing the change over time in FIG. FIG. 9 is a graph showing the displacement of the operating region of the hybrid electric vehicle in the embodiment when the amount of reducing agent adsorbed on the SCR catalyst is excessive and there is a request to reduce the output of the diesel engine. FIG. 10 is a graph for explaining the change over time in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a hybrid electric vehicle according to an embodiment of the present invention. This hybrid electric vehicle (hereinafter referred to as “HEV”) 1 </ b> A includes a diesel engine 5 and a travel motor 6 that are connected via a transmission 4 to an output shaft 3 that transmits driving force to a pair of left and right drive wheels 2 and 2. And a hybrid system 9 having a battery 8 electrically connected to the traveling motor 6 through an inverter 7. A wet multi-plate clutch 10 and a fluid coupling 11 are sequentially provided between the transmission 4 and the diesel engine 5. In addition, a motor clutch 12 that connects and disconnects the driving force is interposed between the transmission 4 and the traveling motor 6.

Further, the HEV 1A includes an SCR converter 14 interposed in the exhaust pipe 13 through which the exhaust gas G of the diesel engine 5 flows, and urea water or unburned fuel injection nozzles 15 installed upstream of the SCR converter 14. The exhaust gas purification system 16 having An SCR catalyst 17 made of a zeolite catalyst is stored in the large-diameter SCR converter 14. Usually, an oxidation catalyst (DOC) and / or a PM collection filter (not shown) is provided between the diesel engine 5 and the injection nozzle 15. Further, a DOC (not shown) may be provided on the downstream side of the SCR converter 14.

The hybrid system 9 and the exhaust gas purification system 16 are connected to an ECU 18 as a control means through a signal line (indicated by a one-dot chain line).

A control method by the ECU 18 in the HEV 1A will be described below with reference to FIG.

The ECU 18 obtains a calculated adsorption amount K of the reducing agent to the SCR catalyst 17 from the output of the diesel engine 5 and the supply amount of the reducing agent from the injection nozzle 15 (S10), and the calculated adsorption amount K is preset. It is determined whether it is less than the lower limit (S12). The preset lower limit value is determined by the specifications of the diesel engine 5 and the SCR catalyst 17, but is, for example, in the range of 0.1 to 0.3 g / l, preferably 0.2 g / l for ordinary automobiles. .

When the calculated adsorption amount K is less than the lower limit value, the traveling motor 6 is driven to rotate and the motor clutch 12 is connected, so that a part of the driving force of the diesel engine 5 is driven by the driving force of the traveling motor 6. Assist (S14). By this operation, the engine torque of the diesel engine 5 is reduced, so that fuel consumption is suppressed, the temperature of the exhaust gas G is lowered, and the amount of NOx generated is reduced. When the temperature of the exhaust gas G decreases, the increase in the temperature of the SCR catalyst 17 is suppressed. Since the amount of the reducing agent that can be adsorbed increases as the temperature decreases, the SCR catalyst 17 promotes the adsorption of the reducing agent. At the same time, since the NOx generation amount of the diesel engine 5 is reduced, the NOx purification rate can be improved even when the reducing agent adsorption amount on the SCR catalyst 17 is insufficient.

The assist of the driving force by the traveling motor 6 is stopped when the calculated adsorption amount K is not less than the lower limit value so that the reducing agent adsorption amount on the SCR catalyst 17 does not become excessive (S20).

If the calculated adsorption amount K of the reducing agent is greater than or equal to the lower limit value, it is further determined whether or not the calculated adsorption amount K exceeds a preset upper limit value (S22). The preset upper limit value is determined by the specifications of the diesel engine 5 and the SCR catalyst 17, and is, for example, in the range of 0.4 to 0.6 g / l, preferably 0.5 g / l, for an ordinary automobile.

When the calculated adsorption amount K exceeds the upper limit, the motor clutch 12 is connected and the traveling motor 6 is used as a generator to charge the battery 8 through the inverter 7 (S24). By this operation, the engine torque of the diesel engine 5 increases, so that fuel consumption is promoted, the temperature of the exhaust gas G rises, and the amount of NOx generated increases. When the temperature of the exhaust gas G rises, the temperature of the SCR catalyst 17 increases, the adsorbing reducing agent volatilizes, and the adsorption amount decreases. Further, since the NOx generation amount increases, the reducing agent adsorbed on the SCR catalyst 17 is consumed, and the adsorption amount further decreases. Therefore, even when the reducing agent is excessively adsorbed on the SCR catalyst 17, the NOx purification rate can be improved. In addition, the release of reducing agent from the HEV 1A to the outside air (reducing agent slip) can be suppressed.

Note that energy corresponding to the increase in fuel consumption in the diesel engine 5 is stored in the battery 8 as electric power, so that the fuel efficiency of the vehicle does not deteriorate.

The power generation and charging by the traveling motor 6 is stopped when the calculated reducing agent adsorption amount K is less than or equal to the upper limit value so that the reducing agent adsorption amount on the SCR catalyst 17 is not greatly reduced (S30).

By performing the control by the ECU 18 as described above, the NOx purification rate can be improved without deteriorating the fuel consumption.

FIG. 3 shows a control method of a hybrid electric vehicle according to another embodiment of the present invention.

In this embodiment, when the calculated adsorption amount K exceeds the upper limit value in the above step S22, it is confirmed whether or not there is a request to reduce the output of the diesel engine 5 (S23). The clutch 12 is connected and the traveling motor 6 is used as a generator to charge the battery 8 (S24). Examples of the request for reducing the output of the diesel engine 5 include operations such as turning off the accelerator during traveling.

As described above, whether or not there is a request for reducing the output of the diesel engine 5 is that the temperature of the exhaust gas G decreases and the amount of NOx generated decreases when the output of the diesel engine 5 decreases. This is because, if the reducing agent is excessively adsorbed on 17, a reducing agent slip that is released from the HEV 1A to the outside air without being consumed may be generated.

Therefore, the reducing agent slip from HEV 1A can be more effectively suppressed by performing the control in step S23 in this way.

In any of the above-described embodiments, when the calculated adsorption amount K is smaller than the lower limit value in step S12, it is desirable to increase the supply amount of the reducing agent from the injection nozzle 15. Further, when the calculated adsorption amount K exceeds the upper limit in step S22, it is desirable to reduce the supply amount of the reducing agent from the injection nozzle 15.

By doing so, the increase and decrease in the amount of reducing agent adsorbed on the SCR catalyst 17 can be promoted, so that the NOx purification rate can be further improved.

In the HEV 1A, the diesel engine 5 and the traveling motor 6 are arranged in parallel. However, the configuration of the vehicle is not limited to this, and for example, the diesel engine 5 and the traveling motor 6 are arranged in series. HEV1B (refer FIG. 4), HEV1C (refer FIG. 5) etc. which directly connected the traveling motor 6 to the pair of drive wheels 2 and 2 may be used. 4 and 5, the ECU 18 performs control to turn on and off the driving force of the traveling motor 6 instead of connecting and disconnecting the motor clutch 12. Become.

6 to 11 show a comparison between the control method (example) of HEV 1A according to the embodiment of the present invention and the control method (comparative example) of the prior art. In these drawings, examples are shown by solid lines and comparative examples are shown by dotted lines.

In the present embodiment, as shown in FIG. 6, a map in which regions of loads required for the operation required for the HEV 1A (hereinafter referred to as “required loads”) are schematically divided is used for explanation. In this map example, the engine speed and engine torque of the diesel engine 5 are used as parameters.

The high load region corresponds to a case where the accelerator is depressed greatly when the HEV 1A starts, and the low load region corresponds to a case where the accelerator is slightly depressed such as when the HEV 1A is gently accelerated. Further, in the central portion of the high load region, there is a region where the exhaust gas temperature of the diesel engine 5 makes the catalyst temperature the activation temperature region (hereinafter referred to as “optimum exhaust gas temperature operation region”). The regenerative region corresponds to when the HEV 1A is braked, etc., and the traveling motor 6 generates power with regenerative energy, and the battery 8 is charged through the inverter 7 with the generated power.

(1) When the amount of reducing agent adsorbed on the SCR catalyst 17 is insufficient As shown in FIG. 7, the required load on the HEV 1A is within the high load range from the starting point (square mark) to the arrival point (circle mark). Assuming that

As shown in FIG. 8, when the accelerator is greatly depressed from time t0 to t1, in the comparative example, the amount of NOx generated increases as the engine torque increases, and then becomes constant. At this time, a large amount of the reducing agent adsorbed on the SCR catalyst 17 is consumed, and the rate of increase in the adsorption amount is suppressed. Therefore, if the initial amount of reducing agent adsorption is small, the reducing agent adsorption relative to the NOx generation amount Insufficient quantity. Therefore, the NOx purification rate in the SCR catalyst 17 becomes low, and the NOx emission amount from the HEV 1A to the outside air increases. Thereafter, the adsorption amount of the reducing agent catches up between times t2 and t4, so that the NOx emission amount becomes constant.

In contrast, in the embodiment, the assist by the traveling motor 6 is started at the time t1, the engine torque becomes constant, and the NOx generation amount becomes constant at a level lower than that of the comparative example. Accordingly, the consumption of the reducing agent adsorbed on the SCR catalyst 17 is reduced, and the rate of increase in the adsorption amount is higher than that of the comparative example. Therefore, even if the initial amount of reducing agent adsorption is small, And a sufficient amount of reducing agent adsorbed.

From time t4 to t5, since the reducing agent adsorption amount is at a sufficient level, the assist by the traveling motor 6 is stopped, so that the amount of NOx generated increases and the amount of NOx emission increases in the embodiment. However, since the reducing agent adsorption amount is sufficient, the NOx emission amount is smaller than that of the comparative example.

Note that the amount of reducing agent adsorbed is not excessive, and no reducing agent slip occurs in both the examples and comparative examples.

The transition of the operation state of the diesel engine 5 at this time passes through the optimum exhaust gas temperature operation region by performing the assist by the travel motor 6 in the embodiment as shown in FIG.

(2) When the amount of reducing agent adsorbed on the SCR catalyst 17 is excessive and there is a request to reduce the output of the diesel engine 5, as shown in FIG. 9, the required load on the HEV 1A is within a high load region. Assume that the vehicle descends from the starting point (square mark) to the arrival point (circle mark) in the low load area.

As shown in FIG. 10, when the vehicle travels constant from time t0 to t1 and then the accelerator is turned off from time t1 to t2, in the comparative example, it becomes constant after the engine torque decreases until time t2. Therefore, the NOx generation amount becomes constant after the engine torque is reduced, so that the reduction rate of the reducing agent adsorption amount on the SCR catalyst 17 becomes small. At this time, if the adsorption amount of the reducing agent exceeds the upper limit value, excess reducing agent is discharged from HEV 1A. Since the NOx generation amount is constant at time t2, the subsequent NOx emission amount is also constant.

On the other hand, in the embodiment, since power generation by the traveling motor 6 is started at time t1 and the engine torque does not decrease and remains constant, the amount of NOx generated is also greater than that in the comparative example between times t1 and t3. It becomes constant at a high level. However, since the reducing agent adsorption amount on the SCR catalyst 17 is excessive, the reducing agent adsorption amount becomes a sufficient level with respect to the NOx generation amount, so that the NOx purification rate is maintained. Even if the reducing agent adsorption amount is excessive, a large amount of the reducing agent adsorbed is consumed, so that the occurrence of reducing agent slip can be prevented.

Even if the power generation by the traveling motor 6 is stopped from time t3 to t4, the reducing agent adsorption is at an appropriate level, so that no reducing agent slip occurs.

As shown in FIG. 9, the transition of the operation state of the diesel engine 5 at this time passes through the optimum exhaust gas temperature operation region after the operation state of the HEV 1 </ b> A remains constant at a high level in the high load region. To come.

1A ~ 1C HEV
5 Diesel Engine 6 Traveling Motor 9 Hybrid System 12 Motor Clutch 13 Exhaust Pipe 15 Injection Nozzle 16 Exhaust Gas Purification System 17 SCR Catalyst 18 ECU

Claims (9)

A hybrid electric vehicle comprising: a hybrid system having at least one of an engine and a traveling motor as a drive source; and an exhaust gas purification system comprising a reducing agent supply means and an SCR catalyst that are sequentially provided in the exhaust pipe of the engine from the upstream side. There,
Control means for controlling the hybrid system and the exhaust gas purification system,
When the amount of reducing agent adsorbed on the SCR catalyst is smaller than a preset lower limit value, a part of the driving force of the engine is replaced by the driving force of the travel motor,
A hybrid electric vehicle characterized in that, when the amount of reducing agent adsorbed on the SCR catalyst is larger than a preset upper limit value, a driving motor is driven by a part of the driving force of the engine to generate electric power. When the reducing agent adsorption amount on the SCR catalyst is larger than a preset upper limit value, the travel motor is driven by a part of the driving force of the engine until the reducing agent adsorption amount becomes equal to or less than the upper limit value. The hybrid electric vehicle according to claim 1, wherein the hybrid electric vehicle is driven to generate electric power. When the amount of reducing agent adsorbed on the SCR catalyst exceeds a preset upper limit value and a request for reducing the driving force of the engine is issued, the travel motor is driven by a part of the driving force of the engine. The hybrid electric vehicle according to claim 1, wherein the hybrid electric vehicle is driven to generate electric power. When the amount of reducing agent adsorbed on the SCR catalyst is smaller than a preset lower limit value, a part of the driving force of the engine is replaced with the driving force of the travel motor, and the reduction from the reducing agent supply means The hybrid electric vehicle according to any one of claims 1 to 3, wherein the supply amount of the agent is increased. When the amount of reducing agent adsorbed on the SCR catalyst is larger than a preset upper limit value, the traveling motor is driven by a part of the driving force of the engine to generate electric power, and the reduction from the reducing agent supply means The hybrid electric vehicle according to any one of claims 1 to 4, wherein a supply amount of the agent is reduced. The hybrid electric vehicle according to any one of claims 1 to 5, wherein the reducing agent supplied from the reduction supply means is ammonia or hydrocarbon. A hybrid electric vehicle comprising: a hybrid system having at least one of an engine and a traveling motor as a drive source; and an exhaust gas purification system comprising a reducing agent supply means and an SCR catalyst that are provided in the exhaust pipe of the engine in order from the upstream side. A control method,
When the amount of reducing agent adsorbed on the SCR catalyst is smaller than a preset lower limit value, a part of the driving force of the engine is replaced by the driving force of the travel motor,
Control of a hybrid electric vehicle characterized in that when the amount of reducing agent adsorbed on the SCR catalyst is greater than a preset upper limit value, a driving motor is driven by a part of the driving force of the engine to generate electric power. Method. When the reducing agent adsorption amount on the SCR catalyst is larger than a preset upper limit value, the travel motor is driven by a part of the driving force of the engine until the reducing agent adsorption amount becomes equal to or less than the upper limit value. The method for controlling a hybrid electric vehicle according to claim 7, wherein the method is driven to generate electric power. When the amount of reducing agent adsorbed on the SCR catalyst exceeds a preset upper limit value and a request for reducing the driving force of the engine is issued, the travel motor is driven by a part of the driving force of the engine. The method of controlling a hybrid electric vehicle according to claim 7 or 8, wherein the hybrid electric vehicle is driven to generate electric power.

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