JP2009103092A - Diesel engine control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diesel engine control device capable of raising an exhaust gas temperature to a temperature at which an ammonia selective reduction type NOx catalyst can exhibit an exhaust gas purifying function and preventing a lowering of exhaust gas purifying efficiency of the ammonia selective reduction type NOx catalyst. <P>SOLUTION: When an ECU 48 determines that the temperature of exhaust gas flowing into the ammonia selective reduction type NOx catalyst 36 is lower than a predetermined temperature, a part of an open period of an exhaust valve 78 overlaps with an open period of an intake valve of the same cylinder as the exhaust valve 78, and the exhaust valve 78 is opened/closed at first opening/closing timing at which only the valve opening start timing out of the valve opening start timing and valve closing completion timing is changed to the delay side or advance side with respect to second opening/closing timing. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for a diesel engine, and in particular, a diesel engine including an ammonia selective reduction type NOx catalyst that selectively reduces NOx in exhaust using ammonia as a reducing agent, and a valve timing switching mechanism that can change the opening / closing timing of an exhaust valve. It relates to the control device.

  As an exhaust purification device for purifying NOx (nitrogen oxide), which is one of the pollutants contained in the exhaust of a diesel engine (hereinafter referred to as the engine), an ammonia selective reduction type NOx catalyst (hereinafter referred to as SCR) is disposed in the exhaust passage of the engine. Exhaust gas purification devices are used that purify NOx in exhaust gas by providing a catalyst) and supplying ammonia as a reducing agent to the SCR catalyst.

  In the exhaust aftertreatment device using the SCR catalyst, urea water is supplied to the upstream side of the SCR catalyst, and ammonia generated by hydrolysis of the urea water by heat of the exhaust is supplied to the SCR catalyst. The ammonia supplied to the SCR catalyst is once adsorbed by the SCR catalyst, and NOx reduction is performed by promoting the denitration reaction between this ammonia and NOx in the exhaust gas by the SCR catalyst.

In order for the SCR catalyst to exhibit such an exhaust purification function satisfactorily, the temperature of the exhaust gas flowing into the SCR catalyst needs to rise to a temperature at which the SCR catalyst is activated.
However, during engine cold operation or deceleration operation, the temperature of the exhaust exhausted from the engine is low, and the exhaust pipe upstream of the SCR catalyst, the pre-stage oxidation catalyst, the particulate filter, etc. are sufficiently warmed. However, since the heat of the exhaust is taken away by these, the temperature of the exhaust flowing into the SCR catalyst is remarkably lowered. Due to such a decrease in the exhaust temperature, the SCR catalyst cannot perform the exhaust purification function as described above well.

In order to solve such a problem at the time of exhaust gas temperature decrease, an engine control device that performs post injection at a timing later than main injection and raises the exhaust gas temperature by reducing the intake air amount by the intake throttle valve is provided. Patent Document 1 proposes this.
In the control device of Patent Document 1, the amount of heat that is not used for power among the amount of heat generated by the fuel is increased by burning the fuel supplied by post-injection after the main injection at a timing that is difficult to be converted into engine output. The engine exhaust temperature rises. Furthermore, since the intake air amount is reduced by the intake throttle valve, the amount of exhaust flowing through the exhaust aftertreatment device is reduced, so that the heat capacity of the exhaust aftertreatment device is increased and the exhaust temperature is further increased.

Further, in the SCR catalyst that selectively reduces NOx using ammonia in the exhaust as a reducing agent, the ratio is highest when the ratio of NO (nitrogen monoxide) and NO ₂ (nitrogen dioxide) contained in the exhaust is approximately 1: 1. Purification efficiency can be obtained. Therefore, a pre-stage oxidation catalyst is provided on the upstream side of the SCR catalyst, and a part of NO in the exhaust gas is converted to NO ₂ by this pre-stage oxidation catalyst and supplied to the SCR catalyst.

By reducing the amount of intake air and performing post injection as described above, the concentration of HC (hydrocarbon) contained in the exhaust increases. Thus, a pre-stage oxidation catalyst is provided upstream of the SCR catalyst. Therefore, it is possible to further raise the temperature of the exhaust gas by oxidizing the HC contained in the exhaust gas with the pre-stage oxidation catalyst.
JP 2003-83139 A

However, when the temperature of the exhaust gas is raised by reducing the intake air amount and post-injection as in the control device of Patent Document 1, the oxidation function of the pre-stage oxidation catalyst is greater than that of HC contained in the exhaust gas. Therefore, the oxidation of NO in the exhaust gas by the pre-stage oxidation catalyst is inhibited.
As a result, even if the SCR catalyst is activated by the temperature rise of the exhaust and can exhibit a good selective reduction function, the ratio of NO ₂ to NO in the exhaust is insufficient for a while, and the purification efficiency of the SCR catalyst This causes a problem of lowering.

  The present invention has been made in view of the problems as described above, and an object of the present invention is to rapidly increase the exhaust temperature to a temperature at which the SCR catalyst can exhibit the exhaust purification function, and to purify the exhaust of the SCR catalyst. It is an object of the present invention to provide a control device for a diesel engine capable of preventing a decrease in efficiency.

  In order to achieve the above object, a diesel engine control device according to the present invention is disposed in an exhaust passage of a diesel engine, and selectively reduces NOx in exhaust using ammonia as a reducing agent. The upstream oxidation catalyst disposed in the exhaust passage upstream of the ammonia selective reduction type NOx catalyst and the opening / closing timing of the exhaust valve of the diesel engine are selectively selected from the first opening / closing timing and the second opening / closing timing. The second opening / closing timing is set so that a part of the valve opening period overlaps with the valve opening period of the intake valve of the same cylinder as the exhaust valve, and the first opening / closing timing is the exhaust valve A valve timing switching mechanism which is set by changing only the valve opening start timing to the retard side with respect to the second opening / closing timing, and the ammonia selective reduction type Control means for controlling the valve timing switching mechanism so that the exhaust valve opens and closes at the second opening / closing timing when it is determined that the temperature of the exhaust gas flowing into the Ox catalyst is lower than a predetermined temperature. (Claim 1).

According to the diesel engine control apparatus configured as described above, NOx in the exhaust of the diesel engine is selectively reduced by ammonia selective reduction-type NOx catalyst using ammonia in the exhaust as a reducing agent, thereby purifying the exhaust. At this time, part of the NO in the exhaust gas is converted into NO ₂ by the pre-stage oxidation catalyst and then flows into the ammonia selective reduction type NOx catalyst, so that the ammonia selective reduction type NOx catalyst exhibits exhaust with high purification efficiency.

  When the control means determines that the temperature of the exhaust gas flowing into the ammonia selective reduction type NOx catalyst is lower than a predetermined temperature, a part of the valve opening period of the exhaust valve is the valve opening period of the intake valve of the same cylinder as the exhaust valve. The exhaust valve opens and closes at the first opening / closing timing that is changed to the retarded side with respect to the second opening / closing timing only during the valve opening start timing and the valve closing completion timing. A valve timing switching mechanism is controlled.

  Alternatively, in order to achieve the above object, a control device for a diesel engine according to the present invention is provided in an exhaust passage of a diesel engine, and an ammonia selective reduction type NOx catalyst that selectively reduces NOx in exhaust gas using ammonia as a reducing agent, The opening / closing timing of the exhaust valve of the diesel engine can be selectively switched between a first opening / closing timing and a second opening / closing timing, and the second opening / closing timing has a part of the valve opening period that is different from that of the exhaust valve. The first opening / closing timing is set to overlap with the second opening / closing timing with respect to the second opening / closing timing. When it is determined that the set valve timing switching mechanism and the temperature of the exhaust gas flowing into the ammonia selective reduction type NOx catalyst are lower than a predetermined temperature, the second opening is performed. And a controlling means for controlling the valve timing switching mechanism as the exhaust valve is opened and closed by timing (claim 2).

According to the diesel engine control apparatus configured as described above, NOx in the exhaust of the diesel engine is selectively reduced by ammonia selective reduction-type NOx catalyst using ammonia in the exhaust as a reducing agent, thereby purifying the exhaust. At this time, part of the NO in the exhaust gas is converted into NO ₂ by the pre-stage oxidation catalyst and then flows into the ammonia selective reduction type NOx catalyst, so that the ammonia selective reduction type NOx catalyst exhibits exhaust with high purification efficiency.

  When the control means determines that the temperature of the exhaust gas flowing into the ammonia selective reduction type NOx catalyst is lower than a predetermined temperature, a part of the valve opening period of the exhaust valve is the valve opening period of the intake valve of the same cylinder as the exhaust valve. The exhaust valve opens and closes at the first opening / closing timing which is changed to the advance side with respect to the second opening / closing timing only during the valve opening start timing and the valve closing completion timing. A valve timing switching mechanism is controlled.

  According to the diesel engine control apparatus of the present invention, when the control means determines that the temperature of the exhaust gas flowing into the ammonia selective reduction type NOx catalyst is lower than the predetermined temperature, a part of the valve opening period of the exhaust valve is the same as that of the exhaust valve. The first opening / closing that overlaps the opening period of the intake valve of the cylinder and that only the valve opening start timing of the valve opening start timing and the valve closing completion timing is changed to the retard side with respect to the second opening / closing timing. Since the exhaust valve opens and closes at the timing, the pumping loss increases as the piston compresses the gas in the cylinder during the exhaust stroke, compared to when the exhaust valve opens and closes at the second opening and closing timing. In order to compensate for the increased pumping loss, the amount of fuel supplied to each cylinder is increased. As a result, the temperature of the exhaust discharged from the diesel engine rises.

  In addition, since the exhaust valve opening start timing is delayed, the amount of residual gas in the cylinder increases compared to when the exhaust valve is opened and closed at the second opening and closing timing, and the amount of fresh air drawn into the cylinder by that amount. The amount of decreases. Therefore, the amount of fresh air to which heat generated by the combustion of fuel is transmitted decreases, and as a result, the temperature of the exhaust gas flowing into the ammonia selective reduction type NOx catalyst rises.

In this way, the exhaust temperature can be quickly raised without supplying HC into the exhaust by post injection or the like, so that the conversion from NO in the exhaust to NO ₂ by the upstream oxidation catalyst is hindered. There is no. As a result, it is possible to satisfactorily maintain the purification efficiency of the ammonia selective reduction type NOx catalyst after the reduction function can be exhibited by the rise of the exhaust gas temperature.
Further, even when the exhaust valve is opened and closed at the first opening / closing timing, the exhaust valve continues to be opened until a part of the valve opening period overlaps with the valve opening period of the intake valve. Thus, a significant increase in residual gas in the cylinder can be prevented. Accordingly, the supply of fresh air into the cylinder is not greatly hindered by the residual gas, and the amount of fresh air sucked into the cylinder is not significantly reduced.

As a result, the exhaust temperature is quickly raised while preventing the discharge of black smoke or the like generated in accordance with a decrease in the intake amount of fresh air into the atmosphere, and the fuel is supplied from the fuel supplied into the cylinder by the main injection. The concentration of unburned HC in the exhaust can be kept low. Therefore, when the ammonia selective reduction type NOx catalyst can exhibit the selective reduction function due to the rise in the exhaust temperature, NO ₂ from the NO in the exhaust gas by the preceding oxidation catalyst is not hindered by the unburned HC in the exhaust gas. Thus, it is possible to prevent a reduction in the purification efficiency of the ammonia selective reduction type NOx catalyst.

  Alternatively, according to the diesel engine control apparatus of the present invention, when the control means determines that the temperature of the exhaust gas flowing into the ammonia selective reduction type NOx catalyst is lower than the predetermined temperature, a part of the valve opening period of the exhaust valve is the exhaust valve. The valve opening time of the intake valve of the same cylinder is overlapped, and only the valve opening start timing of the valve opening start timing and the valve closing completion timing is changed to the advance side with respect to the second opening / closing timing. Since the exhaust valve opens and closes at the opening and closing timing, the amount of exhaust exhausted when the exhaust valve is opened before part of the heat generated by the fuel is used for power will open and close the exhaust valve at the second opening and closing timing. And the temperature of the exhaust gas flowing into the ammonia selective reduction type NOx catalyst increases.

Further, since a part of the calorific value of the fuel is not used for power in this way, the engine output is lower than when the exhaust valve is opened and closed at the second opening / closing timing, but in order to compensate for the reduced engine output in this way. In addition, since the amount of fuel supplied to each cylinder is increased, the temperature of the exhaust discharged from the diesel engine rises as a result.
Thus, the exhaust gas temperature can be quickly raised without supplying HC into the exhaust gas by post injection or the like, so that the ammonia selective reduction type NOx catalyst can exhibit the selective reduction function by raising the exhaust gas temperature. Therefore, the conversion of NO in the exhaust gas from NO to NO ₂ by the upstream oxidation catalyst is not hindered, and it is possible to prevent the purification efficiency of the ammonia selective reduction type NOx catalyst from being lowered.

Further, even when the exhaust valve is opened and closed at the first opening / closing timing, the exhaust valve continues to be opened until a part of the valve opening period overlaps with the valve opening period of the intake valve. The residual gas in the cylinder does not increase and the supply of fresh air into the cylinder is not hindered by the residual gas, and a sufficient amount of fresh air can be secured in the cylinder.
As a result, the exhaust temperature is quickly raised while preventing the discharge of black smoke or the like generated in accordance with a decrease in the intake amount of fresh air into the atmosphere, and the fuel is supplied from the fuel supplied into the cylinder by the main injection. The concentration of unburned HC in the exhaust can be kept low. Therefore, when the ammonia selective reduction type NOx catalyst becomes capable of performing the selective reduction function due to an increase in the exhaust temperature, conversion from NO in the exhaust to NO ₂ by the pre-stage oxidation catalyst without being inhibited by unburned HC Thus, it is possible to prevent a reduction in the purification efficiency of the ammonia selective reduction type NOx catalyst.

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
The diesel engine control apparatus according to the first embodiment of the present invention is mounted on a vehicle. FIG. 1 is an overall configuration diagram of this diesel engine control device, and the configuration of the diesel engine control device will be described based on FIG. 1.
A diesel engine (hereinafter referred to as an engine) 1 has a high-pressure accumulator chamber (hereinafter referred to as a common rail) 2 common to each cylinder, and high-pressure fuel supplied from a fuel injection pump (not shown) and stored in the common rail 2 is supplied to each cylinder. The fuel is supplied to the injectors 4 provided, and fuel is injected from the injectors 4 into the respective cylinders.

  The intake passage 6 is equipped with a turbocharger 8. The intake air drawn from an air cleaner (not shown) flows into the compressor 8a of the turbocharger 8 from the intake passage 6, and the intake air supercharged by the compressor 8a is intercooler. 10 to the intake manifold 12. The air introduced into the intake manifold 12 is drawn into each cylinder of the engine 1 via an intake port (not shown) by opening an intake valve (not shown) provided in each cylinder. An intake air amount sensor 14 for detecting an intake air flow rate to the engine 1 is provided upstream of the compressor 8a in the intake passage 6.

  On the other hand, an exhaust port (not shown) through which exhaust gas is discharged from each cylinder of the engine 1 by opening an exhaust valve (not shown in FIG. 1) is connected to an exhaust pipe 18 via an exhaust manifold 16. Has been. An EGR passage 22 is provided between the exhaust manifold 16 and the intake manifold 12 to communicate the exhaust manifold 16 and the intake manifold 12 via the EGR valve 20.

The exhaust pipe 18 is connected to the exhaust aftertreatment device 24 after passing through the turbine 8 b of the turbocharger 8. The rotating shaft of the turbine 8b is connected to the rotating shaft of the compressor 8a, and the turbine 8b receives the exhaust flowing in the exhaust pipe 18 to drive the compressor 8a.
The exhaust aftertreatment device 24 includes an upstream casing 26 and a downstream casing 30 that is communicated with the downstream side of the upstream casing 26 through a communication passage 28. A upstream oxidation catalyst 32 is accommodated in the upstream casing 26, and a particulate filter (hereinafter referred to as a filter) 34 is accommodated downstream of the upstream oxidation catalyst 32. The filter 34 is provided to purify the exhaust of the engine 1 by collecting particulates in the exhaust.

Since the front-stage oxidation catalyst 32 oxidizes NO in the exhaust gas to generate NO ₂ , by arranging the front-stage oxidation catalyst 32 and the filter 34 in this way, the particulates collected and deposited in the filter 34 are It reacts with NO ₂ supplied from the pre-stage oxidation catalyst 32 to oxidize, and the filter 34 is continuously regenerated.
On the other hand, an ammonia selective reduction type NOx catalyst (hereinafter referred to as an SCR catalyst) that adsorbs ammonia in the exhaust gas in the downstream casing 30 and selectively reduces NOx in the exhaust gas by using the adsorbed ammonia as a reducing agent to purify the exhaust gas. 36 is accommodated. The SCR catalyst 36 can exhibit the highest purification efficiency when the ratio of NO and NO _{2 in} the exhaust gas is substantially equal to each other. A part of the NO ₂ generated by the pre-stage oxidation catalyst 32 is part of the filter 34. By flowing into the SCR catalyst 36 together with NO in the exhaust discharged from the engine 1 without contributing to the continuous regeneration, a high purification rate is maintained.

A downstream oxidation catalyst 38 for oxidizing the ammonia flowing out from the SCR catalyst 36 to N ₂ is accommodated downstream of the SCR catalyst 36. The post-stage oxidation catalyst 38 also has a function of oxidizing CO (carbon monoxide) generated when the particulates are incinerated by forced regeneration of the filter 34, which will be described later, and discharging it to the atmosphere as CO ₂ (carbon dioxide). is doing.
The communication passage 28 is provided with a urea water injector 40 for injecting urea water into the exhaust gas in the communication passage 28. The urea water is supplied from a urea water tank 42 in which urea water is stored by a supply pump (not shown). As a result, urea water is injected from the urea water injector 40 into the exhaust gas in the communication passage 28.

The urea water injected from the urea water injector 40 is hydrolyzed by the heat of the exhaust to become ammonia, and is supplied to the SCR catalyst 36 together with the exhaust. The SCR catalyst 36 adsorbs the supplied ammonia and promotes a denitration reaction between the adsorbed ammonia and NOx in the exhaust gas, thereby purifying the exhaust gas with NOx being harmless N ₂ .
At this time, when ammonia flows out of the SCR catalyst 36 without reacting with NOx, the ammonia is oxidized by the post-stage oxidation catalyst 38 and is released into the atmosphere as harmless N ₂ . .

An inlet side temperature sensor 44 that detects the exhaust temperature on the inlet side of the SCR catalyst 36 is provided on the upstream side of the SCR catalyst 36 in the downstream casing 30.
Further, the engine 1 is provided with a valve timing switching mechanism (not shown in FIG. 1) for switching the opening / closing timing of the exhaust valve provided in each cylinder. Although details of the valve timing switching mechanism will be described later, the opening / closing timing of the exhaust valve can be switched by controlling the supply of hydraulic oil to the valve timing mechanism. The hydraulic oil control valve 46 shown in FIG. 1 is for controlling the supply of hydraulic oil to the valve timing switching mechanism.

An ECU (control means) 48 is provided to perform comprehensive control including operation control of the engine 1 configured as described above. The ECU 48 includes a CPU, a memory, a timer counter, and the like. The ECU 48 calculates various control amounts and controls various devices connected to the ECU 48 based on the control amounts.
On the input side of the ECU 48, in addition to the intake flow rate sensor 14 and the inlet side temperature sensor 44 described above, in order to collect information necessary for various controls, a rotation speed sensor 52 for detecting the rotation speed of the engine 1 and an accelerator (not shown) Various sensors such as an accelerator opening sensor 54 for detecting the pedal depression amount are connected. Further, various devices such as the injector 4, the EGR valve 20, the urea water injector 40, and the hydraulic oil control valve 46 of each cylinder that are controlled based on the calculated control amount are connected to the output side of the ECU 48.

  The ECU 48 also performs calculation of the fuel supply amount to each cylinder of the engine 1 and control of fuel supply from the injector 4 based on the calculated fuel supply amount. The fuel supply amount (main injection amount) necessary for the operation of the engine 1 is stored in advance based on the rotational speed of the engine 1 detected by the rotational speed sensor 52 and the accelerator opening detected by the accelerator opening sensor 54. It is determined by reading from the map. The amount of fuel supplied to each cylinder is adjusted by the valve opening time of the injector 4, and each injector 4 is driven to open in a driving time corresponding to the determined fuel amount, and main injection is performed in each cylinder. As a result, an amount of fuel necessary for the operation of the engine 1 is supplied.

In addition to such fuel supply control to each cylinder, the ECU 48 also performs control for forcibly regenerating the filter 34 to restore its function.
The particulates deposited on the filter 34 are oxidized and removed by continuous regeneration using the pre-stage oxidation catalyst 32 as described above. However, such continuous regeneration alone may not sufficiently remove particulates accumulated on the filter 34. If such a state continues, particulates may be excessively accumulated in the filter 34 and the filter 34 may be clogged. Therefore, the temperature of the filter 34 is appropriately increased according to the particulate accumulation state in the filter 34. By performing forced regeneration, the exhaust gas purification function of the filter 34 is maintained.

The particulate accumulation state is estimated based on the differential pressure upstream and downstream of the filter 34, the detection value of the intake air amount sensor 14, and the like, and when it is determined that the particulate accumulation amount on the filter 34 has reached a predetermined amount. The forced regeneration control is started.
In forced regeneration of the filter 34, HC (hydrocarbon) is supplied into the exhaust gas by performing post injection from the injector 4. Then, the temperature of the exhaust gas flowing into the filter 36 is raised by the HC oxidation reaction in the pre-stage oxidation catalyst 32, and the particulates deposited on the filter 34 are incinerated.

Further, the ECU 48 obtains a target supply amount of urea water necessary for selectively reducing NOx in the exhaust gas by the SCR catalyst 36, and controls the urea water injector 40 based on the target supply amount, whereby the urea water injector 40 is controlled. Is supplied to the exhaust gas upstream of the SCR catalyst 36.
As described above, the urea water injected from the urea water injector 40 is hydrolyzed by the heat of the exhaust gas to become ammonia, and is supplied to the SCR catalyst 36. The SCR catalyst 36 adsorbs the supplied ammonia and promotes a denitration reaction between the adsorbed ammonia and NOx in the exhaust, thereby reducing NOx to harmless N ₂ and purifying the exhaust.

In order to perform such selective reduction of NOx by the SCR catalyst 36 satisfactorily, in order to supply the SCR catalyst 36 with NO ₂ having an appropriate ratio to the NO in the exhaust gas flowing into the SCR catalyst 36. The pre-stage oxidation catalyst 32 and the SCR catalyst 36 for selectively reducing NOx must be activated.
Therefore, in the control device of the present embodiment, when the exhaust temperature does not reach such a temperature, the exhaust temperature is raised by changing the opening / closing timing of the exhaust valve.

Hereinafter, the configuration of the valve timing switching mechanism provided in each cylinder in order to change the opening / closing timing of the exhaust valve will be described with reference to FIGS.
2 is a view showing the assembly of the first rocker arm 58 and the second rocker arm 60 constituting the valve timing switching mechanism 56, FIG. 3 is a top view of the valve timing switching mechanism 56, and FIG. 4 shows the assembled state of the second rocker arm 60. FIG.

  Each cylinder of the engine 1 is provided with a first rocker arm 58 and a second rocker arm 60 adjacent to each other so as to be swingably supported by the rocker shaft 62. The first rocker arm 58 is provided with a boss portion 64 through which the rocker shaft 62 is inserted, and the first rocker arm 58 is pivotally supported by the rocker shaft 62 via the boss portion 64. Further, a shaft portion 66 that protrudes from the boss portion 64 of the first rocker arm 58 in the axial direction of the rocker shaft 62 and passes through the rocker shaft 62 is fitted into the boss portion 68 of the second rocker arm 60, so that the second rocker arm 60 is inserted. Is pivotally supported by the shaft portion 66 of the first rocker arm 58, so that the second rocker arm 60 can swing with respect to the rocker shaft 62.

  A roller 74 abutting on the first cam 72 is rotatably mounted on the end of the arm 70 extending to one side of the first rocker arm 58, and the valve shaft of the exhaust valve 78 is mounted on the end of the arm 76 extending to the other side. It is connected. The roller 74 of the first rocker arm 58 is pressed against the first cam 72 by receiving the urging force of a valve spring (not shown) provided in the exhaust valve 78 connected to the arm 76 of the first rocker arm 58. Has been.

  Further, the end of the arm 80 extending in the same direction as the arm 70 of the first rocker arm 58 from the boss portion 68 of the second rocker arm 60 contacts the second cam 82 having a cam profile different from that of the first cam 72. A contact roller 84 is rotatably mounted. The second rocker arm 60 is urged in a direction in which the roller 84 is pressed against the second cam 82 by a return spring 88 that engages with an end of a thick portion 86 formed on the upper portion of the boss portion 68.

  The boss portion 64 of the first rocker arm 58 is formed with a cylinder portion 90 having an axis in a direction substantially perpendicular to the axis of the rocker shaft 62, and the operating piston 92 slides on the cylinder portion 90. Installed as possible. The working piston 92 is driven by receiving the hydraulic pressure of the working oil supplied to the oil chamber 96 formed below the working piston 92 via an oil passage 94 formed inside the rocker shaft 62 as will be described later. When the hydraulic oil is not supplied to the oil chamber 96 and is not driven, it is pressed by the return spring 98 and located at the lower part of the cylinder portion 90 as shown in FIG. The operating piston 92 resists the return spring 98 by the hydraulic pressure of the operating oil and moves to the upper part of the cylinder portion 90 as shown in FIG.

As shown in FIGS. 5 and 6, the operating piston 92 is formed with an engaging groove 104 including a deep groove portion 100 and a shallow groove portion 102. Corresponding to the engagement groove 104, an engagement protrusion 106 projects from the second rocker arm 60 toward the first rocker arm 58 side and extends toward the working piston 92 above the arm 70 of the first rocker arm 58. It is installed.
As shown in FIG. 6, the engagement protrusion 106 is provided with the second rocker arm 60 driven by the second cam 82 when the hydraulic oil is supplied to the oil chamber 96 and the operating piston 92 is positioned at the upper part of the cylinder portion 90. As the swaying motion proceeds, it moves into the shallow groove portion 102 of the working piston 92 and comes into contact with the working piston 92 in the swaying direction, thereby transmitting the swaying motion of the second rocker arm 60 to the first rocker arm 58.

  On the other hand, as shown in FIG. 5, when the operating piston 92 is positioned below the cylinder portion 90 without supplying hydraulic oil to the oil chamber 96, the second rocker arm 60 driven by the second cam 82 is swung. Accordingly, the engaging protrusion 106 enters the deep groove portion 100 of the operating piston 92. At this time, the engaging protrusion 106 does not contact the operating piston 92 in the swing direction, and the swing of the second rocker arm 60 is the first. Transmission to the rocker arm 58 is prevented.

The supply of the hydraulic oil to the oil chamber 96 and the discharge of the hydraulic oil from the oil chamber 96 are performed by the ECU 48 controlling the hydraulic oil control valve 46 as described above.
The cam profiles of the first cam 72 and the second cam 82 are set so that the lift amount of the exhaust valve 78 by the first cam 72 is always equal to or less than the lift amount of the exhaust valve 78 by the second cam 82. Accordingly, the hydraulic oil is supplied to the oil chamber 96 as described above, and the engagement protrusion 106 comes into contact with the operation piston 92 located at the upper part of the cylinder portion 90, thereby causing the second rocker arm 60 to swing. When transmitting to 58, the first rocker arm 58 swings according to the cam profile of the second cam 82, whereby the exhaust valve 78 is opened and closed.

On the other hand, when hydraulic oil is not supplied to the oil chamber 96 and the operating piston 92 is positioned below the cylinder portion 90, the swing of the second rocker arm 60 is not transmitted to the first rocker arm 58 as described above. The rocker arm 58 swings according to the cam profile of the first cam 72, whereby the exhaust valve 78 is opened and closed.
In this embodiment, the cam profiles of the first cam 72 and the second cam 82 are such that the opening / closing timing based on the lift amount and the crank angle when the exhaust valve 78 is driven by the respective cams has the characteristics shown in FIG. Is set to

  That is, in FIG. 7, the lift amount and opening / closing timing (first opening / closing timing) of the exhaust valve 78 due to the cam profile of the first cam 72 are indicated by the curve EX1, and the lift amount of the exhaust valve 78 due to the cam profile of the second cam 82 The opening / closing timing (second opening / closing timing) is indicated by a curve EX2. A curve IN in FIG. 7 shows the lift amount and opening / closing timing of the intake valve used in combination with the exhaust valve 78.

  As shown by the curve EX2 in FIG. 7, when the exhaust valve 78 is opened and closed by the second cam 82, the opening timing of the exhaust valve 78 is earlier than the bottom dead center (BDC) of the expansion stroke, and the valve closing is completed. The timing is later than the opening start timing of the intake valve, and a part of the opening period of the exhaust valve 78 overlaps with the opening period of the intake valve. Such characteristics of the second cam 82 are equivalent to those of a cam for driving an exhaust valve used in a general diesel engine not provided with a valve timing switching mechanism.

  On the other hand, when the exhaust valve 78 is opened and closed by the first cam 72, the opening start timing of the exhaust valve 78 is the opening of the exhaust valve 78 by the second cam 82 as shown by the curve EX1 in FIG. It is retarded from the valve start timing, and the crank angle is retarded by A1 (°) from the bottom dead center (BDC) in the expansion stroke. The retardation amount A1 from the BDC is set to 40 to 70 ° for the reason described later. Further, a part of the opening period of the exhaust valve 78 overlaps with the opening period of the intake valve, and the closing timing of the exhaust valve 78 is the closing timing of the exhaust valve 78 in the case of the second cam 82. Is consistent with

  As described above, the valve opening start timing of the exhaust valve 78 is greatly retarded from the valve opening start timing when the exhaust valve 78 is opened and closed by the second cam 82, but the exhaust valve 78 is opened and closed by the first cam 72. In this case, by setting the lift amount L1 of the exhaust valve 78 to 1/5 to 1/3 of the lift amount L2 of the exhaust valve 78 in the case of the second cam 82, the exhaust valve 78 is opened and closed by the first cam 72. Even in this case, the change rate of the lift amount of the exhaust valve 78 is set to an appropriate range so that the exhaust valve 78 can be opened and closed without any trouble.

  That is, when the exhaust valve 78 is opened and closed by the second cam 82, the exhaust valve 78 closing timing is substantially coincided and only the valve opening start timing is retarded by 40 to 70 ° from the BDC. If the lift amount remains at L2, the surplus load of the valve spring of the exhaust valve 78 is remarkably reduced, causing problems in the dynamic characteristics of the exhaust valve 78 such as jumping of the exhaust valve 78. Therefore, in order to prevent such a problem, it is necessary to set the lift amount L1 of the exhaust valve 78 to 1/5 to 1/3 of the lift amount L2 of the exhaust valve 78 in the case of the second cam 82. .

Next, the temperature rise of the exhaust using the valve timing switching mechanism 56 configured as described above will be described.
FIGS. 8 and 9 show that the engine 1 is operated with a medium and medium load at a constant operating state, and the exhaust valve 78 is opened and closed by the first cam 72 in the control device of the present embodiment. The relationship between the opening timing of the exhaust valve 78 and the exhaust temperature Tti when only the opening timing is gradually delayed from the opening / closing timing of the general exhaust valve 78 that opens and closes the valve 78. FIG. 8 is a graph showing the relationship between the valve opening start timing of the exhaust valve 78 and the excess air ratio λ (FIG. 9). The valve opening start timing of the exhaust valve 78 is represented by a crank angle, where BDC is 0 ° and the advance side of BDC is represented by a positive value and the retard side is represented by a negative value. The exhaust temperature Tti is the inlet side temperature of the turbine 8b of the turbocharger 8.

  As shown in FIG. 8, it can be seen that the exhaust gas temperature Tti increases as the opening start timing of the exhaust valve 78 is retarded, but the valve opening start timing is changed to a crank angle of 40 ° (−40 ° BBDC) after BDC. By retarding after the angle, an exhaust temperature of 400 ° C. or higher can be secured, while the delay range of the valve opening start timing is set to a crank angle of 70 ° (−70 ° BBDC) after BDC. Thus, an excess air ratio λ of 2.0 or more is secured. Thus, the reason why the exhaust gas temperature rises by delaying the valve opening start timing of the exhaust valve 78 is as follows.

  In other words, since the opening timing of the exhaust valve 78 is greatly delayed, the pumping loss of each cylinder increases due to the piston compressing the gas in the cylinder, but the ECU 48 detects the accelerator opening detected by the accelerator opening sensor 54. In order to obtain an engine output corresponding to the above, the amount of fuel supplied from the injector 4 to each cylinder is increased so as to compensate for the increased pumping loss in this way, and as a result, the temperature of the exhaust discharged from the engine 1 rises. It is.

Further, since the start timing of opening of the exhaust valve 78 is delayed, the residual gas in the cylinder is increased as compared with the case where the exhaust valve 78 is opened and closed by the second cam 82, and the amount of fresh air sucked into the cylinder correspondingly increases. The amount decreases. Accordingly, the amount of fresh air to which heat generated by fuel combustion is transmitted is small, and the temperature of the exhaust gas rises.
Accordingly, the temperature of the exhaust can be raised without supplying HC into the exhaust by post injection or the like. As a result, the problem that the HC in the exhaust gas flows into the upstream oxidation catalyst 32 and the conversion from NO to NO ₂ by the upstream oxidation catalyst 32 does not occur does not occur. Maintaining exhaust purification of the SCR catalyst 36 with high purification efficiency by making the ratio of NO and NO ₂ in the exhaust gas flowing into the SCR catalyst 36 appropriate when the selective reduction function is exhibited. Can do.

Further, even if the opening start timing of the exhaust valve 78 is retarded to a crank angle of about 70 ° after BDC, the excess air ratio λ does not decrease greatly for the following reason.
That is, even when the opening timing of the exhaust valve 78 is delayed, as described above, the exhaust valve 78 is opened until a part of the valve opening period of the exhaust valve 78 overlaps with the valve opening period of the intake valve. The valve continues. For this reason, although the residual gas in the cylinder increases due to the retarded opening timing of the exhaust valve, it does not increase significantly. Therefore, the supply of fresh air into the cylinder is not greatly hindered by the residual gas, and a sufficient excess air ratio can be ensured without greatly reducing the amount of fresh air supplied.

The fuel supplied to each cylinder of the engine 1 by the main injection may not be completely combusted but may be partly discharged from the engine 1 together with the exhaust as unburned gas. The concentration of HC increases. However, in this embodiment, since the sufficient excess air ratio λ is ensured as described above, the HC concentration in the exhaust does not increase greatly. Therefore, in terms of the influence of the excess air ratio λ, the conversion of NO to NO ₂ by the pre-stage oxidation catalyst 32 is not hindered, and the exhaust purification of the SCR catalyst 36 is maintained with high purification efficiency. be able to.

  When the excess air ratio λ decreases, it is known that black smoke is likely to be generated when the value falls below 1.5, but the delay angle range of the valve opening start timing is set to a crank angle of 70 ° after BDC. As described above, since the excess air ratio λ of 2.0 or more is ensured as described above, black smoke is not generated due to a decrease in the excess air ratio λ. Therefore, by setting the opening timing of the exhaust valve 78 to a crank angle of 40 to 70 ° after the BDC, a satisfactory temperature rise of the exhaust gas is realized while maintaining the excess air ratio λ at a value that does not generate black smoke. It becomes possible.

  In FIG. 9, the alternate long and short dash line in FIG. 9 shows the opening / closing timing of the exhaust valve while keeping the valve opening period constant by changing the phase of the crankshaft and the exhaust camshaft as a comparative example for comparison with the present embodiment. It shows the relationship between the exhaust valve opening start timing and the excess air ratio λ ′ when the variable valve timing changing mechanism is used to advance the exhaust valve opening start timing. .

  As shown in the comparative example of FIG. 9, when both the valve opening start timing and the valve closing completion timing of the exhaust valve are advanced, the excess air ratio λ ′ is greatly increased with the advancement of the valve opening start timing. It turns out that it falls. In this way, the excess air ratio λ ′ decreases because the exhaust valve opening start timing advances and the valve closing completion timing also advances, so the exhaust valve closes before the intake valve opens. This is probably because a large amount of gas remaining in the cylinder significantly impedes the intake of fresh air into the cylinder.

As described above, in the comparative example, the air excess ratio λ ′ is significantly reduced, so that the concentration of HC contained in the unburned gas in the exhaust gas is significantly increased and black smoke is generated. Due to such an increase in the HC concentration, the conversion from NO to NO ₂ by the pre-stage oxidation catalyst is hindered, and the exhaust gas flowing into the SCR catalyst 36 when the SCR catalyst 36 exhibits a selective reduction function becomes present. The ratio of NO to NO ₂ cannot be made appropriate, and the purification efficiency of the SCR catalyst 36 is reduced.

On the other hand, in the present embodiment, as described above, the excess air ratio does not decrease significantly, and not only does the reduction in the purification efficiency of the SCR catalyst 36 due to the increase in the HC concentration in the exhaust gas occur, but also the black Since smoke is not generated, it can be seen that it is greatly superior to the comparative example shown in FIG.
Using the valve timing switching mechanism 56 as described above, the ECU 48 performs exhaust gas temperature raising control according to the operating state of the engine 1. This exhaust temperature raising control is repeatedly executed during the operation of the engine 1 at a predetermined control cycle based on the flowchart of FIG.

  When the exhaust gas temperature raising control is started, first, in step S1, the ECU 48 determines whether or not the exhaust gas temperature Tex detected by the inlet side temperature sensor 44 is equal to or higher than a predetermined temperature Ts. The predetermined temperature Ts is set based on the temperature at which the oxidization catalyst 32 and the post-stage oxidation catalyst 38 including the SCR catalyst 36 can be activated, and the ECU 48 determines that the exhaust temperature Tex is equal to or higher than the predetermined temperature Ts. As a result, it is determined that the exhaust temperature has reached a temperature at which the SCR catalyst 36, the front-stage oxidation catalyst 32, and the rear-stage oxidation catalyst 38 can be activated.

Therefore, if the ECU 48 determines in step S1 that the exhaust temperature Tex is lower than the predetermined temperature Ts, the ECU 48 determines that the exhaust temperature has not reached a temperature at which each of the catalysts can be activated, and the process proceeds to step S2. The opening and closing of the exhaust valve 78 by the first cam 72 is selected, and the control cycle ends.
That is, in step S <b> 2, the ECU 48 controls the hydraulic oil control valve 46 so that the hydraulic oil is not supplied to the valve timing switching mechanism 56 in order to select the first cam 72 as a cam for driving the exhaust valve 78. In the valve timing switching mechanism 56, the operating oil 92 is not supplied, so that the operating piston 92 of the first rocker arm 58 is positioned below the cylinder portion 90 as described above. For this reason, since the engaging protrusion 106 of the second rocker arm 60 enters the deep groove portion 100 of the operating piston 92, the engaging protrusion 106 does not contact the operating piston 92 in the swinging direction, and the second rocker arm 60 does not swing. The movement is not transmitted to the first rocker arm 58.

Accordingly, the first rocker arm 58 is driven by the first cam 72, and the exhaust valve 78 is opened and closed according to the cam profile of the first cam 72. As a result, as described above, the valve opening start timing of the exhaust valve 78 is retarded by 40 to 70 ° with respect to the crank angle after BDC, and the temperature of the exhaust is increased.
Even after the next control cycle, as long as it is determined in step S1 that the exhaust temperature Tex has not reached the predetermined temperature Ts, the ECU 48 proceeds to step S2, and the exhaust valve 78 is moved by the first cam 72 as described above. By opening and closing, the temperature of the exhaust continues to rise.

  Therefore, when the engine 1 is in a cold operation state and the exhaust temperature has not risen to a temperature at which each of the catalysts can be activated, or when the operation state has changed, the exhaust temperature has decreased below the temperature at which each of the catalysts can be activated. In some cases, the exhaust valve 78 is opened and closed by the first cam 72, whereby the temperature of the exhaust is raised, and it is possible to quickly raise the temperature to a temperature at which each catalyst can be activated.

On the other hand, when it is determined in step S1 that the exhaust temperature Tex is equal to or higher than the predetermined temperature Ts, the ECU 48 proceeds to step S3, selects opening / closing of the exhaust valve 78 by the second cam 82, and ends the control cycle. .
That is, in step S3, the ECU 48 controls the hydraulic oil control valve 46 so that the hydraulic oil is supplied to the valve timing switching mechanism 56 in order to select the second cam 82 as a cam for driving the exhaust valve 78. In the valve timing switching mechanism 56, the working piston 92 of the first rocker arm 58 is positioned above the cylinder portion 90 as described above by supplying the working oil. For this reason, the engaging protrusion 106 of the second rocker arm 60 enters the shallow groove portion 102 of the operating piston 92, so that the engaging protrusion 106 abuts the operating piston 92 in the swinging direction, and the second rocker arm 60 swings. It is transmitted to the first rocker arm 58. Accordingly, the first rocker arm 58 is driven by the second cam 82, and the exhaust valve 78 is opened and closed according to the cam profile of the second cam 82. As a result, the exhaust gas temperature is not raised by delaying the valve opening start timing of the exhaust valve 78 as described above, and the normal operation of the engine 1 is performed.

Even after the next control cycle, as long as it is determined in step S1 that the exhaust temperature Tex is equal to or higher than the predetermined temperature Ts, the ECU 48 proceeds to step S3, and the exhaust valve 78 is moved by the second cam 82 as described above. Opened and closed.
As described above, when the ECU 48 performs the exhaust gas temperature raising control, when the exhaust temperature Tex of the engine 1 does not reach the predetermined temperature Ts, the exhaust valve 78 is opened and closed by the first cam 72, and the exhaust valve 78 is opened. By delaying the valve opening start timing, the exhaust temperature can be raised quickly. At this time, since it is not necessary to supply HC into the exhaust by post injection or the like, the HC in the exhaust flows into the pre-stage oxidation catalyst 32 and the conversion from NO to NO ₂ by the pre-stage oxidation catalyst 32 is inhibited. There is nothing. As a result, when the SCR catalyst 36 exhibits a selective reduction function due to the temperature rise of the exhaust gas, the ratio of NO and NO ₂ in the exhaust gas flowing into the SCR catalyst 36 is made appropriate, and high purification efficiency is achieved. Thus, the exhaust gas purification of the SCR catalyst 36 can be maintained.

  When the exhaust temperature Tex has not reached the predetermined temperature Ts and the exhaust valve 78 is opened and closed by the first cam 72 as described above, the valve opening period of the exhaust valve 78 is set as described above. Since the exhaust valve 78 continues to be opened until a part of the intake valve overlaps with the valve opening period of the intake valve, the supply of fresh air into the cylinder is not greatly hindered by the residual gas. Qi inhalation does not decrease significantly.

Therefore, not only the black smoke is not generated due to the decrease in the excess air ratio λ, but also the increase in the HC concentration in the exhaust gas due to the significant decrease in the excess air ratio λ does not occur. As a result of this decrease, the problem that the conversion from NO to NO ₂ by the pre-stage oxidation catalyst 32 is inhibited does not occur.
Next, a diesel engine control apparatus according to a second embodiment of the present invention will be described below.

  In the first embodiment, as shown in FIG. 7, the first cam 72 having a cam profile set so that only the valve opening start timing is retarded with respect to the opening and closing of the exhaust valve 78 by the second cam 82 is used. The exhaust gas temperature was raised by opening and closing the exhaust valve 78. In the second embodiment, the relationship between the cam profiles of the first cam 72 and the second cam 82 is different from that of the first embodiment. Except for the relationship of the cam profiles of the first cam 72 and the second cam 82, the configuration itself of the control device for the diesel engine according to the second embodiment is the same as that of the first embodiment, and therefore the corresponding configuration. Will be described using the same reference numerals. In the following, description of the same parts as those of the first embodiment will be omitted, and description will be made focusing on parts different from the first embodiment.

  In the second embodiment, as described above, the relationship between the cam profiles of the first cam 72 and the second cam 82 is different from that in the first embodiment, and specifically, as shown in FIG. It has become. That is, in the present embodiment, the cam profiles of the first cam 72 and the second cam 82 have the characteristics shown in FIG. 11 in terms of the opening / closing timing based on the lift amount and the crank angle when the exhaust valve 78 is driven by each cam. It is set to be.

  In FIG. 11, the lift amount and opening / closing timing (second opening / closing timing) of the exhaust valve 78 due to the cam profile of the first cam 72 are indicated by a curve EX1, and the lift amount and opening / closing of the exhaust valve 78 due to the cam profile of the second cam 82 are shown. The timing (first opening / closing timing) is indicated by a curve EX2. A curve IN in FIG. 11 indicates the lift amount and opening / closing timing of the intake valve used in combination with the exhaust valve 78.

  As shown by the curve EX1 in FIG. 11, when the exhaust valve 78 is opened and closed by the first cam 72, the exhaust valve 78 is opened and closed by the second cam 82 in the first embodiment described above. The opening timing of the valve 78 is earlier than the bottom dead center (BDC) of the expansion stroke, and the closing timing is later than the opening timing of the intake valve. It overlaps with the valve opening period of the intake valve. Such characteristics of the first cam 72 are equivalent to those of a cam for driving an exhaust valve used in a general diesel engine not provided with a valve timing switching mechanism.

  On the other hand, when the exhaust valve 78 is opened and closed by the second cam 82, the opening start timing of the exhaust valve 78 is the opening of the exhaust valve 78 by the first cam 72, as shown by the curve EX2 in FIG. The angle is advanced from the start time, and the crank angle is advanced by A2 (°) from the bottom dead center (BDC) in the expansion stroke. The advance amount A2 from the BDC is set to 120 to 150 ° for the reason described later. Further, a part of the opening period of the exhaust valve 78 overlaps with the opening period of the intake valve, and the closing timing of the exhaust valve 78 is the closing timing of the exhaust valve 78 in the case of the first cam 72. Is consistent with

Next, the temperature rise of the exhaust using the valve timing switching mechanism 56 configured as described above will be described.
FIGS. 12 and 13 show that the engine 1 is operated with a medium speed and medium load in a constant operation state, and when the exhaust valve 78 is opened and closed by the second cam 82 in the control device of the present embodiment, the exhaust is performed by the first cam 72. The relationship between the opening timing of the exhaust valve 78 and the exhaust temperature Tti when only the opening timing is gradually advanced from the opening / closing timing of the general exhaust valve 78 that opens and closes the valve 78. FIG. 12 is a graph showing the relationship between the valve opening start timing of the exhaust valve 78 and the excess air ratio λ (FIG. 13). The valve opening start timing of the exhaust valve 78 is represented by a crank angle, and BDC is 0 °, and the advance side of BDC is represented by a positive value. The exhaust temperature Tti is the inlet side temperature of the turbine 8b of the turbocharger 8.

  As shown in FIG. 12, it can be seen that the exhaust gas temperature Tti increases as the valve opening start timing of the exhaust valve 78 is advanced, but the valve opening start timing is advanced before the crank angle of 120 ° before BDC. As a result, an exhaust temperature of 400 ° C. or higher can be secured, while an advance angle range of the valve opening start timing is set to a crank angle of 150 ° before BDC, so that an excess air ratio λ of 2.0 or more is secured. Is done. As described above, the exhaust gas temperature rises by advancing the valve opening start timing of the exhaust valve 78. The heat generation amount of fuel in the cylinder is increased by the valve opening start timing of the exhaust valve 78 being advanced. This is because the exhaust valve is opened before a part of the exhaust gas is used for power, and high-temperature exhaust is discharged.

  Further, since a part of the calorific value of the fuel in the cylinder is not used for motive power in this way, the engine output decreases with the advance angle of the opening timing of the exhaust valve 78, but the ECU 48 detects by the accelerator opening sensor 54. In order to obtain an engine output corresponding to the accelerator opening, the amount of fuel supplied from the injector 4 to each cylinder is increased so as to compensate for such a decrease in engine output. As a result, the exhaust discharged from the engine 1 Temperature rises.

Accordingly, the temperature of the exhaust can be raised without supplying HC into the exhaust by post injection or the like. As a result, the HC in the exhaust gas does not flow into the upstream oxidation catalyst 32 and the conversion of NO to NO ₂ by the upstream oxidation catalyst 32 is not hindered, and the SCR catalyst 36 is selectively reduced by the temperature rise of the exhaust gas. The exhaust gas purification of the SCR catalyst 36 with high purification efficiency can be maintained by setting the ratio of NO and NO ₂ in the exhaust gas flowing into the SCR catalyst 36 to an appropriate value when the function comes to be demonstrated. .

In addition, the excess air ratio λ is not greatly reduced even when the opening timing of the exhaust valve 78 is advanced to a crank angle of about 150 ° before BDC for the following reason.
That is, even when the valve opening start timing of the exhaust valve 78 is advanced, as described above, the exhaust valve 78 is opened until a part of the valve opening period of the exhaust valve 78 overlaps with the valve opening period of the intake valve. The valve continues. For this reason, the residual gas in a cylinder does not increase. Accordingly, the supply of fresh air into the cylinder is not hindered by the residual gas, and a sufficient excess air ratio can be ensured.

As described above, the fuel supplied to each cylinder of the engine 1 by the main injection may not be completely burned but may be partially discharged from the engine 1 together with the exhaust as unburned gas, resulting in a decrease in the excess air ratio λ. At the same time, the concentration of HC in the exhaust gas increases. In the present embodiment, since the sufficient excess air ratio λ is secured as described above, the HC concentration in the exhaust does not increase greatly due to the advance angle of the valve opening start timing of the exhaust valve 78. Therefore, in terms of the influence of the excess air ratio λ, the conversion of NO to NO ₂ by the pre-stage oxidation catalyst 32 is not hindered, and the exhaust purification of the SCR catalyst 36 is maintained with high purification efficiency. be able to.

  As described above, when the excess air ratio λ decreases and the value falls below 1.5, black smoke is likely to be generated. However, the advance angle range of the valve opening start timing is set to a crank angle of 150 ° before BDC. Since the excess air ratio λ of 2.0 or more is secured as described above, the black smoke is not generated due to the reduction of the excess air ratio λ. Therefore, by setting the opening timing of the exhaust valve 78 to a crank angle of 120 to 150 ° before BDC, a satisfactory temperature rise of the exhaust gas is realized while maintaining the excess air ratio λ at a value at which black smoke does not occur. It becomes possible.

In addition, the dashed-dotted line in FIG. 13 is shown in order to contrast the comparative example shown in FIG. 9 with this embodiment compared with 1st Embodiment mentioned above.
As shown in the comparative example of FIG. 13, when both the valve opening start timing and the valve closing completion timing of the exhaust valve are advanced, the excess air ratio λ ′ is greatly increased with the advancement of the valve opening start timing. Since it decreases, the concentration of HC contained in the unburned gas in the exhaust gas increases significantly, and black smoke is generated as described above. Then, due to such an increase in the HC concentration, the conversion from NO to NO ₂ by the pre-stage oxidation catalyst is inhibited, and the SCR catalyst 36 flows into the SCR catalyst 36 when it exhibits a selective reduction function. The ratio of NO and NO ₂ in the exhaust gas cannot be made appropriate, and the purification efficiency of the SCR catalyst 36 is reduced.

On the other hand, in the present embodiment, as described above, the excess air ratio does not decrease significantly, and not only does the reduction in the purification efficiency of the SCR catalyst 36 due to the increase in the HC concentration in the exhaust gas occur, but also the black Since smoke is not generated, it can be seen that it is greatly superior to the comparative example shown in FIG.
Using the valve timing switching mechanism 56 as described above, the ECU 48 performs exhaust gas temperature raising control according to the operating state of the engine 1. This exhaust temperature raising control is repeatedly executed during the operation of the engine 1 at a predetermined control cycle based on the flowchart of FIG.

  When the exhaust gas temperature raising control is started, first, in step S11, the ECU 48 determines whether or not the exhaust gas temperature Tex detected by the inlet side temperature sensor 44 is equal to or higher than a predetermined temperature Ts. The predetermined temperature Ts is set based on the temperature at which the oxidization catalyst 32 and the post-stage oxidation catalyst 38 including the SCR catalyst 36 can be activated, and the ECU 48 determines that the exhaust temperature Tex is equal to or higher than the predetermined temperature Ts. As a result, it is determined that the exhaust temperature has reached a temperature at which the SCR catalyst 36, the front-stage oxidation catalyst 32, and the rear-stage oxidation catalyst 38 can be activated.

Therefore, if the ECU 48 determines in step S11 that the exhaust temperature Tex is lower than the predetermined temperature Ts, the ECU 48 determines that the exhaust temperature has not reached a temperature at which each of the catalysts can be activated, and the process proceeds to step S12. The opening and closing of the exhaust valve 78 by the second cam 82 is selected, and the control cycle ends.
That is, in step S12, the ECU 48 controls the hydraulic oil control valve 46 so that the hydraulic oil is supplied to the valve timing switching mechanism 56 so as to select the second cam 82 as a cam for driving the exhaust valve 78. End the cycle. In the valve timing switching mechanism 56, the working piston 92 of the first rocker arm 58 is positioned above the cylinder portion 90 as described above by supplying the working oil. For this reason, the engaging protrusion 106 of the second rocker arm 60 enters the shallow groove portion 102 of the operating piston 92, so that the engaging protrusion 106 abuts the operating piston 92 in the swinging direction, and the second rocker arm 60 swings. It is transmitted to the first rocker arm 58. Accordingly, the first rocker arm 58 is driven by the second cam 82, and the exhaust valve 78 is opened and closed according to the cam profile of the second cam 82. As a result, as described above, the valve opening start timing of the exhaust valve 78 is advanced to a crank angle of 120 to 150 ° before BDC, and the temperature of the exhaust is increased.

Even after the next control cycle, as long as it is determined in step S11 that the exhaust temperature Tex has not reached the predetermined temperature Ts, the ECU 48 proceeds to step S12, and the exhaust valve 78 is moved by the second cam 82 as described above. By opening and closing, the temperature of the exhaust continues to rise.
Therefore, when the engine 1 is in a cold operation state and the exhaust temperature has not risen to a temperature at which each of the catalysts can be activated, or when the operation state has changed, the exhaust temperature has decreased below the temperature at which each of the catalysts can be activated. In some cases, the exhaust valve 78 is opened and closed by the second cam 82 to raise the temperature of the exhaust, and the temperature can be quickly raised to a temperature at which each catalyst can be activated.

On the other hand, if it is determined in step S11 that the exhaust temperature Tex is equal to or higher than the predetermined temperature Ts, the ECU 48 proceeds to step S13, selects opening / closing of the exhaust valve 78 by the first cam 72, and ends the control cycle. .
That is, in step S13, the ECU 48 controls the hydraulic oil control valve 46 so that the hydraulic oil is not supplied to the valve timing switching mechanism 56 so as to select the first cam 72 as a cam for driving the exhaust valve 78. In the valve timing switching mechanism 56, the operating oil 92 is not supplied, so that the operating piston 92 of the first rocker arm 58 is positioned below the cylinder portion 90 as described above. For this reason, since the engaging protrusion 106 of the second rocker arm 60 enters the deep groove portion 100 of the operating piston 92, the engaging protrusion 106 does not contact the operating piston 92 in the swinging direction, and the second rocker arm 60 does not swing. The movement is not transmitted to the first rocker arm 58.

Accordingly, the first rocker arm 58 is driven by the first cam 72, and the exhaust valve 78 is opened and closed according to the cam profile of the first cam 72. As a result, the exhaust gas temperature is not raised by delaying the opening timing of the exhaust valve 78 as described above, and the engine 1 is operated normally.
As described above, when the ECU 48 performs the exhaust gas temperature raising control, when the exhaust temperature Tex of the engine 1 does not reach the predetermined temperature Ts, the exhaust valve 78 is opened and closed by the second cam 82, and the exhaust valve 78. As the valve opening start timing is advanced, the exhaust gas temperature can be quickly raised. At this time, since it is not necessary to supply HC into the exhaust by post injection or the like, the HC in the exhaust flows into the pre-stage oxidation catalyst 32 and the conversion from NO to NO ₂ by the pre-stage oxidation catalyst 32 is inhibited. No problem occurs. As a result, when the SCR catalyst 36 exhibits a selective reduction function due to the temperature rise of the exhaust gas, the ratio of NO and NO ₂ in the exhaust gas flowing into the SCR catalyst 36 is made appropriate, and high purification efficiency is achieved. Thus, the exhaust gas purification of the SCR catalyst 36 can be maintained.

  Further, when the exhaust temperature Tex has not reached the predetermined temperature Ts and the exhaust valve 78 is opened and closed by the second cam 82 as described above, as described above, the valve opening period of the exhaust valve 78 is set. The exhaust valve 78 continues to be opened until a part of the valve overlaps with the valve opening period of the intake valve, and the supply of fresh air into the cylinder is not hindered by the residual gas. For this reason, the intake amount of fresh air is not significantly reduced due to the advance of the opening timing of the exhaust valve 78.

Therefore, not only the black smoke is not generated due to the decrease in the excess air ratio λ, but also the HC concentration in the exhaust gas is not significantly increased due to the decrease in the excess air ratio λ. As a result of this decrease, the problem that the conversion from NO to NO ₂ by the pre-stage oxidation catalyst 32 is hindered does not occur.
Although the description about the control apparatus for a diesel engine according to one embodiment of the present invention is finished as above, the present invention is not limited to the first and second embodiments.

For example, in the first and second embodiments, the exhaust post-treatment device 24 includes the filter 34 and the post-stage oxidation catalyst 38 in addition to the front-stage oxidation catalyst 32 and the SCR catalyst 36. The configuration of 24 is not limited to this, and the filter 34 and the post-stage oxidation catalyst 38 can be changed as necessary.
In the first and second embodiments, the valve timing switching mechanism 56 includes the first rocker arm 58 driven by the first cam 72 and the second rocker arm 60 driven by the second cam 82. Although the opening / closing timing of the exhaust valve 78 is changed by switching the transmission of the swing from the first rocker arm 58 to the second rocker arm 60 and the interruption of the transmission, the configuration of the valve timing switching mechanism 56 is limited to this. Instead, any configuration that can switch between the first opening / closing timing and the second opening / closing timing in the present invention may be used.

  In the first and second embodiments, the temperature of the exhaust gas flowing into the SCR catalyst 36 is detected by the inlet side temperature sensor 44, but the position of the temperature sensor for detecting the exhaust gas temperature is limited to this. is not. That is, since the exhaust gas flowing into the SCR catalyst 36 passes through the front-stage oxidation catalyst 32 and the filter 34, for example, the temperature of the exhaust gas detected by a temperature sensor provided on the inlet side of the front-stage oxidation catalyst 32 or the filter 34, for example, The temperature of the exhaust gas flowing into the SCR catalyst 36 may be used as it is, or may be used with some correction. Further, it may be estimated by calculating from the operating state of the engine 1 without using a temperature sensor.

It is a block diagram of the control apparatus of the diesel engine which concerns on 1st Embodiment of this invention. It is a figure which shows the assembly | attachment of the 1st rocker arm which comprises a valve timing switching mechanism, and a 2nd rocker arm. It is a top view of a valve timing switching mechanism. It is a figure which shows the assembly | attachment state of a 2nd rocker arm. It is a fragmentary sectional view of a valve timing switching mechanism, and is a figure showing the non-driving state of an operation piston. It is a fragmentary sectional view of a valve timing switching mechanism, and is a figure showing the drive state of an operation piston. It is a figure which shows the relationship between the valve lift amount and opening / closing timing of the exhaust valve by the 1st cam and the 2nd cam in 1st Embodiment of this invention. 6 is a graph showing a change in exhaust temperature when the retard amount of the valve opening start timing of the exhaust valve opened and closed by the first cam is changed in the first embodiment of the present invention. In 1st Embodiment of this invention, it is a graph which shows the change of the excess air ratio when changing the amount of retardation of the valve opening start timing of the exhaust valve opened and closed by the 1st cam with a comparative example. It is a flowchart of the exhaust gas temperature raising control in 1st Embodiment of this invention. It is a figure which shows the relationship between the valve lift amount of the exhaust valve by the 1st cam and the 2nd cam, and the opening / closing timing in 2nd Embodiment of this invention. In the second embodiment of the present invention, it is a graph showing the change of the exhaust temperature when the advance amount of the valve opening start timing of the exhaust valve opened and closed by the second cam is changed. In 2nd Embodiment of this invention, it is a graph which shows the change of the excess air ratio when changing the advance amount of the valve opening start timing of the exhaust valve opened and closed by the 2nd cam with a comparative example. It is a flowchart of the exhaust gas temperature raising control in 2nd Embodiment of this invention.

Explanation of symbols

1 Diesel engine 18 Exhaust pipe (exhaust passage)
32 Pre-stage oxidation catalyst 36 SCR catalyst (ammonia selective reduction type NOx catalyst)
48 ECU (control means)
56 Valve timing switching mechanism 78 Exhaust valve

Claims (2)

An ammonia selective reduction-type NOx catalyst that is disposed in an exhaust passage of a diesel engine and selectively reduces NOx in exhaust using ammonia as a reducing agent;
A pre-stage oxidation catalyst disposed in the exhaust passage upstream of the ammonia selective reduction type NOx catalyst;
The opening / closing timing of the exhaust valve of the diesel engine can be selectively switched between a first opening / closing timing and a second opening / closing timing, and the second opening / closing timing has a part of the valve opening period that is different from that of the exhaust valve. The first opening / closing timing is set so as to overlap with the opening timing of the intake valve of the same cylinder, and only the opening start timing of the exhaust valve is changed to the retard side with respect to the second opening / closing timing. A set valve timing switching mechanism;
Control means for controlling the valve timing switching mechanism so that the exhaust valve opens and closes at the first opening / closing timing when it is determined that the temperature of the exhaust gas flowing into the ammonia selective reduction type NOx catalyst is lower than a predetermined temperature. A control device for a diesel engine. An ammonia selective reduction-type NOx catalyst that is disposed in an exhaust passage of a diesel engine and selectively reduces NOx in exhaust using ammonia as a reducing agent;
A pre-stage oxidation catalyst disposed in the exhaust passage upstream of the ammonia selective reduction type NOx catalyst;
The opening / closing timing of the exhaust valve of the diesel engine can be selectively switched between a first opening / closing timing and a second opening / closing timing, and the second opening / closing timing has a part of the valve opening period that is different from that of the exhaust valve. The first opening / closing timing is set to overlap with the second opening / closing timing with respect to the second opening / closing timing. A set valve timing switching mechanism;
Control means for controlling the valve timing switching mechanism so that the exhaust valve opens and closes at the first opening / closing timing when it is determined that the temperature of the exhaust gas flowing into the ammonia selective reduction type NOx catalyst is lower than a predetermined temperature. A control device for a diesel engine.

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