Electronic EGR gas control system

A curved passage constituting part of an exhaust gas recirculation passage is installed inside a suction passage in the downstream of an electronic control throttle valve, of which initial position is the fully opened position, and an exhaust gas recirculation flow control valve is installed in the cylindrical portion extending coaxially from the curved passage into a suction passage. The control valve is a butterfly valve driven by a motor via a reduction gear mechanism. In addition, the control valve opening is sensed by a sensor and cooled exhaust gas flow is sensed by a flow sensor at the outlet of an exhaust gas cooler, and the control of the control valve is based on these sensor signals.

CLAIM OF PRIORITY

The present application claims priority from Japanese application serial no. 2003-377677, filed on Nov. 7, 2003, the content of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to an EGR gas control system used of an internal combustion engine of diesel motor car, particularly to an electronic EGR gas control system.

A conventional electronic EGR gas control system known as prior art has been so constructed that a simple valve is provided in the EGR gas passage near the connection of suction pipe to the EGR gas passage and the valve is controlled to open and close by motor via a reduction gear as shown in Japanese Laid-open Patent Publication of International Application No. Hei 2002-521610).

A system known as another prior art has been so constructed that a curved pipe for letting in the EGR gas is provided in the suction passage in the downstream of a throttle valve, the curved pipe is made open towards the downstream of the suction passage and a valve is provided in the EGR gas passage connected to the suction pipe, and the valve is controlled to open and close by negative-pressure actuator as shown in Japanese Laid-open Patent Publication No. Hei 10-213019.

SUMMARY OF THE INVENTION

The prior art has not been capable of controlling the system to move the exhaust gas recirculation ratio quickly to a target value. Part of the exhaust gas recirculation passage is projected in the suction passage and a control valve for controlling the exhaust gas flow is installed in the projected passage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention is described in detail hereunder, usingFIG. 1toFIG. 9.

FIG. 1is an oblique view of the overall exhaust gas recirculation system according to the present invention, part of which suction passage is cut open to show the inside.

FIG. 2is a vertical cross-sectional view of the exhaust gas recirculation system, andFIG. 3is a side view.

The overall construction is described hereunder, usingFIG. 1toFIG. 3.

The element45corresponds to the suction control unit45shown in the exhaust gas recirculation system diagram (FIG. 10).

The element416corresponds to the EGR (exhaust gas recirculation) control system416(which is referred to as an exhaust gas recirculation control system in this embodiment) in the system diagram (FIG. 10).

The suction control unit45comprises suction passage body45B formed in a cylindrical shape, rotating shaft3extending across the center axis of the cylindrical suction passage body45B and supported by the suction passage body45B to be able to rotate, and butterfly valve2(which may be called the throttle valve or suction control valve) fixed on the rotating shaft (which may be called the throttle shaft).

On the outside wall of the suction passage body45B, there is provided a motor casing formed in parallel with the rotating shaft3and together with the suction passage body45B. (Detailed description will be given when explainingFIG. 24andFIG. 25.)

A resin cover9contains inside a control circuit board (to be explained later) and a rotation angle sensor10(to be explained later) for the rotating shaft3.

The resin cover9is fixed to a specified position on the outside wall of the suction passage body45B with five screws45a.

A connector9A is resin-molded together with the resin cover9.

The connector9A has a terminal for sending a signal from the sensor10to an engine control unit, power supply terminal for motor, grounding terminal, and terminal for receiving an opening control signal of the suction control valve2from the engine control unit.

The exhaust gas recirculation control system416comprises a suction passage body made of concentric double pipes. The suction passage body has a hole on the sidewall and an exhaust gas inlet passage portion413dto be inserted into the hole is continued with a cylindrical portion413fthat extends from a curved portion413ealong the axis of the suction passage body.

To be concrete, an L-shaped curved passage body (comprising413d,413e, and413f) is inserted into the suction passage46from under the suction passage body and then the inlet passage portion413dis inserted into the hole in the sidewall.

In this installation, the curved passage body (comprising413d,413e, and413f) is first inserted into the suction passage46allowing an offset from the center of the suction passage46so that the cylindrical portion413fis clear of the hole in the sidewall, and when the end of the inlet passage portion413dis well positioned to fit in the hole in the sidewall, the curved passage body (comprising413d,413e, and413f) is then moved towards the center of the suction passage and the inlet passage portion413dis inserted into the hole in the sidewall. In order to realize this installation smoothly, the inside diameter of the suction passage body, outside diameter of the cylindrical portion413f, and length of the inlet passage portion413dup to the inside surface of the sidewall are so determined in this embodiment that the above offset can be allowed. In other words, the longest distance from the outside surface of the cylindrical portion413fto the end of the inlet passage portion413dis designed to be approximately equal to the inside diameter of the suction passage46so that the curved passage body (comprising413d,413e, and413f) can be inserted into the suction passage allowing an offset from the center of the suction passage46(in a direction the cylindrical portion413fbecomes clear of the hole in the sidewall). In this installation, the longest distance from the outside surface of the cylindrical portion413fto the end of the inlet passage portion413dcan be greater than the inside diameter of the suction passage46. However, when inserting the curved passage body (comprising413d,413e, and413f) into the suction passage46, it must be tilted and the inlet passage portion413dmust be set into the hole in the sidewall as is.

In order to facilitate smooth installation of the above, the length of the cylindrical portion413fis made longer than that of the inlet suction passage413d.

When the inlet passage portion413dis set in the hole in the sidewall of the suction passage46, the center axis of the cylindrical portion413fis aligned with that of the suction passage46, thus set as a double-wall construction.

The center axes of the two need not always be in perfect alignment but it may rather be preferable to allow a slight offset from the center of the suction passage46(in a direction the cylindrical portion413fbecomes clear of the hole in the sidewall) in view of the flow resistance or streamline.

Through holes are provided straight through the sidewall of the suction passage46and cylindrical portion413fof the curved passage body (comprising413d,413e, and413f) in series across the center axes.

The offset of the cylindrical portion413for insertion depth of the inlet passage portion413dinto the sidewall is so adjusted that these through holes are aligned straight.

A way for realizing the above is to insert a bar through the holes so as to determine the position of the two portions and then weld them accordingly.

Another way is to position them properly and weld together and then make the through holes.

The rotating shaft416S is inserted into the through holes well aligned straight and the butterfly valve416A is fastened with two screws416m.

The rotating shaft416S is supported to be able to rotate by two ball bearings416J and416K fixed on the through holes in the sidewall of the suction passage as shown inFIG. 4andFIG. 6. One end of the rotating shaft416S is sealed with a metal cover and the other end further protrudes from the ball bearing416K. A resin collar416U and final gear416R are mounted on this protruded portion and are fastened on the rotating shaft416S with nuts. Between the resin collar416U and sidewall of the suction passage, a return spring416M is placed over the bearing boss on which the bearing416K is mounted. One end of the return spring416M is hooked on a step on the outside wall of the suction passage so as not to move in the rotating direction and the other end is hooked on the resin collar416U.

The resin collar416U rotates together with the shaft. Accordingly, when the control valve rotates to open, the return spring is wound up and adds a closing direction force to the control valve.

The holes in the cylindrical portion of the exhaust gas passage body not only serve as holes for the rotating shaft to be inserted through but also effectively serve to prevent the ball bearing from being subjected to excessive force due to excessive deflection of the rotating shaft.

A motor casing is formed together with the suction passage body.

A motor416Dm is enclosed in the motor casing416D, which is fixed on the suction passage body.

A gear416N is fixed on the end of the rotating shaft of the motor416Dm. Between the final gear416R fixed on the rotating shaft416S and the gear416N, an intermediate gear comprising a large gear416P and small gear416Q, resin-molded in one piece, is provided on a fixed shaft416T to be able to rotate. The large gear416P is engaged with the gear416N.

The small gear416Q is engaged with the final gear416R. The reduction ratio of this reduction gear mechanism is about one-twentieth. Because of this reduction ratio, a big force for rotating the control valve (about 100 kg) can be generated. This is a considerably big force even in taking the return spring force of about 7 kg into account, and accordingly the control valve can be opened even if the valve is seized by unburnt product and/or tar in the exhaust gas. Since a force of about 20 to 30 kg is generally understood enough to release the tip of the control valve from seizure, sufficient yield strength can be ensured against seizure.

The exhaust gas directed from the curved passage body (comprising413d,413e, and413f) into the suction passage46is exhausted into the center of the suction passage46from the outlet416fof the cylindrical portion413fand mixed with fresh air flowing there. The diameter of the suction passage body at which the exhaust gas recirculation control valve is located is made greater than the diameter of the suction passage body at which the suction control valve is located by the projected cross-sectional area of the exhaust gas recirculation passage. With this construction, increase of the passage resistance can be prevented.

Since the exhaust gas does not contact the suction passage body directly, temperature increase of the suction passage body can be controlled lower. Accordingly, temperature of the bearings416J and416K will not increase and malfunction of the bearings resulting from melting of grease can be reduced.

A resin cover416C is fixed at a specified position on the outside wall of the double-pipe suction passage body with screws at four mounting holes416h.

This resin cover covers the reduction gear mechanism, and a sensor416E for sensing the rotation angle of the rotating shaft416S is mounted on it.

A connector416F is molded together with the resin cover when the cover is resin-molded. The connector has a terminal for outputting the opening signal of the rotating shaft to external device, terminal for supplying the power from external source to the motor, and grounding terminal.

The side of the resin cover of the rotating shaft416S extends up to the position the resin cover416C is located. A rotor416L of the rotation angle sensor416E is mounted on the flat portion of the resin cover416C to be able to rotate. A brush416X is mounted on the rotor416L.

A circuit board416W having a surface perpendicular to the rotating shaft is installed inside a lid416E of the resin cover416C. On this circuit board, a resistance conductor (not shown) is mounted at a position facing the brush416X. The resistance conductor is connected to the connector416F via the electrically conductive terminal416Y molded together with the resin cover416C. As the resin cover416C is fastened on the outside wall of the suction passage body, the end of the rotating shaft fits in the hole of the rotor416L and the rotor is locked by a leaf spring416n. Thus, the rotation of the rotating shaft416S rotates the brush416X via the rotor416L and a change in the position of the brush416X in reference to the resistance conductor is sent out as an electric signal to external device from the connector416F.

Thus, the real opening of the control valve416A for controlling the opening of the exhaust gas passage is sensed and utilized in computing the control signal to the motor416Dm. Accordingly, the response and control accuracy of the control valve improve.

This signal is sent to the engine control unit and used for the calculation of the target opening of the control valve416A (which consequently serves as the control signal of the motor416Dm) based on the EGR recirculation ratio.

It is also possible to send this signal to a control circuit200in the control unit of the suction control valve so as to make a similar calculation and send out a control signal for the motor416Dm as a target opening signal.

The suction control unit45and exhaust gas recirculation control system416explained above are installed side by side.

To explain more concretely, the upper end of the exhaust gas recirculation control system416is connected to the downstream end of the suction control unit45and they are fixed together with bolts45G using gasket45E (or seal rubber) between them. Each bolt45G is inserted into four bolt holes45D provided at an interval around the suction control body and fastens the upper flange45C and lower flange45F of the suction control valve with the flange416H of the suction passage body of the exhaust gas recirculation control system416to fix them together.

The above assembly is so designed that the rotating shafts3and416S are in parallel and the portion where the incoming exhaust gas flow from the cylindrical portion413finto the suction passage46becomes the largest coincides with the portion where the opening of the suction control valve becomes the largest so that the exhaust air is mixed with fresh air smoothly and that the exhaust gas is distributed evenly to each cylinder.

The above is so designed also that the resin covers9and416C of the two are located on the same side of the suction passage body. Since this design allows an access from the same side for connection with the connector, high workability is expected. In addition, this design is suitable for securing a space for installing a cooling unit (to be described later).

In a system so designed as above, not only the rotating shafts are installed in parallel but also the motor case is installed in parallel, and so the rotating shaft of the motor is also installed in parallel with these rotating shafts.

The element414is the cooling unit that cools the exhaust gas by heat exchange between the engine cooling water and exhaust gas. Cooling water enters the cooling unit from an inlet header414A, flows through the passage in which corrugated fins414aare installed as shown inFIG. 4, and is discharged from a cooling water outlet header414B.

The exhaust gas enters from an inlet header413aand flows through the parallel passage of the heat exchanger in the arrow direction, and then it is collected to an outlet header413band directed through a connection passage413cup to the exhaust gas inlet passage portion413dinstalled in the suction passage body.

While the exhaust gas is at 500° C. at the inlet, the temperature goes down to 200° C. after heat exchange with the engine cooling water at 100° C. Accordingly, the exhaust gas can be directly let into the center of the suction passage body.

The element415(156) is an exhaust gas flow sensor, which is installed in the connection passage413dof the cooling unit outlet and senses the cooled exhaust gas flow. Accordingly, because of less change in the gas temperature, measurement accuracy improves.

Lowering the EGR gas temperature allows to increase the gas density (decrease the volume) so as to widen the upper limit of the recirculation ratio and reduce NOx. In addition, lower gas temperature allows to decrease the combustion temperature of the engine.

The element413G are screws for fastening the exhaust gas passage to the inlet opening413kof the suction passage body.413hare mounting holes for the above.

Although the curved passage body of the exhaust gas recirculation control system416is designed to be formed separately and then installed inside the suction passage in this embodiment, they can be formed together in the following way by die forming.

InFIG. 2, forming dies for the inside and outside portions of the curved passage of the double-pipe suction passage body of the exhaust gas recirculation control system416are so designed that the upstream portion and downstream portion can be formed separately. Then, the third forming die for the right-hand portion of the figure is provided. Thus, this assembly can be formed together.

Next, the resin cover portion of the suction control unit is described in detail hereunder, usingFIG. 7.

The terminal5A of the motor5is electrically connected with a receiving terminal14mounted on the resin cover9. In this embodiment, the terminal14molded together with the resin cover9is also a male terminal. Accordingly, a relay terminal5B having female terminals on both sides is provided between the male terminal5A on the motor side and male terminal14on the cover side.

A conductor extending up to the terminal14is electrically connected with a bonding wire202of which one end is brazed onto the bonding pad installed on one side of the control circuit board200. An aluminum radiation plate is sandwiched between the control circuit board200and inside wall of the resin cover. A set of terminals to be connected with the opening sensor10via a bonding wire201of which one end is soldered onto the bonding pad are provided on the other end of the control circuit board. One end of an electric conductor10wis connected with the resistor board of the sensor and the other end with the bonding wire201.

12is a partition for isolating the control circuit board surface from the gear section (it may hereinafter be called the control unit cover). It not only prevents foreign substance from entering the control circuit section but also prevents the intermediate gear7from becoming loose in a thrust direction.

On a sensor cover10c, annular projections for supporting the rotation of the rotor10R are provided at a portion around the rotating shaft. The tip of the shaft is fit in the center hole of the rotor and the rotor is fixed on the rotating shaft3with a C-ring10P.

The element10dis a seal rubber that seals between the rotor10R and sensor cover10c.

The element4cis a metal bracket for protecting the seal, and4dis a lip type seal. This seal prevents exhaust gas component resulting from the back flow of the exhaust gas from entering a sensor chamber and control circuit chamber.

Effects of the above embodiment are summarized as follows.

(1) Since the control valve is opened with a big force, response time can be shorter (about 100 ms from the fully opened state to fully closed state) and the time to reach the target recirculation ratio can be shorter even if the suction rapidly changes under a transient condition in acceleration or deceleration.

(2) According to a prior art in which the EGR gas is let in from the side of the suction passage, the gas is not distributed evenly. According to this embodiment, however, since the EGR gas is let into the center of the suction passage, excellent gas mixture is realized and accordingly smooth distribution into the cylinders is realized.

(3) Because of the cooling effect that the exhaust gas temperature of 500° C. at the inlet is cooled down to 200° C. at the outlet, there is produced an effect that change in the gas temperature is lessened and accordingly measurement accuracy improves. In addition, by lowering the EGR gas temperature so as to increase the gas density (decrease the volume), the upper limit of the recirculation ratio can be widened and accordingly NOx can be reduced. Furthermore, there is another effect that lower gas temperature allows to decrease the combustion temperature of the engine and accordingly reduce NOx.

(4) In addition, while the EGR gas contacts the suction passage body itself when entering into the suction passage in the prior art, the exhaust gas is directed into the suction passage by the exhaust gas passage in this embodiment and so the suction passage body itself is not heated directly by the exhaust gas. Accordingly, bearings of the shaft can no way be heated and so a problem resulting from melted grease can be eliminated.

An electronic control throttle unit of diesel engine to which the present invention applies is described hereunder, usingFIG. 21toFIG. 35.

To begin with, the system configuration of the electronic control throttle unit of this embodiment is described, usingFIG. 21.

FIG. 21is a block diagram of the electronic control throttle unit according to the first embodiment of the present invention.

The electronic control throttle unit of this embodiment comprises an electronic throttle body (ETB)100and throttle actuator control unit (TACU)200.

The electronic throttle body (ETB)100comprises a throttle valve that is supported inside the throttle body to be able to rotate, actuator for the motor that drives the throttle valve, and some others. Detailed construction will be described later, usingFIG. 24toFIG. 31.

The throttle actuator control unit (TACU)200so controls that the opening of the throttle valve of the electronic throttle body (ETB)100conforms to a throttle valve target opening sent from the engine control unit (ECU)300. According to the target opening sent from ECU300, TACU200outputs to ETB100a motor control duty signal for rotating the throttle valve of ETB100. The opening of the throttle valve that has been rotated according to this duty signal is sensed by a throttle position sensor and supplied as a throttle sensor output to TACU200. Under a normal control condition, TACU200controls the opening of the throttle valve by a feedback control so that the throttle sensor output conforms to the target opening. The construction and operation of TACU200will be described later, usingFIG. 24toFIG. 31.

Next, the opening of the throttle valve in the electronic control throttle unit of this embodiment is described hereunder, usingFIG. 22andFIG. 23.

FIG. 22is a chart explaining the opening characteristic of the throttle valve in the electronic control throttle unit according to the first embodiment of the invention.FIG. 22(A)is a chart explaining the static characteristic of the throttle valve opening andFIG. 22(B)is a chart explaining the dynamic characteristic of the throttle valve opening.

First, the static characteristic of the throttle valve opening is described hereunder, usingFIG. 22(A). InFIG. 22(A), the vertical axis represents the duty of the motor control duty signal supplied from TACU200to ETB100and the horizontal axis represents the throttle valve opening. A force in the opening direction is added to the throttle valve by the return spring, about which description will be given later. Accordingly, when the duty is 0%, that is, when the motor is not energized, the throttle valve is rotated back in the opening direction by the return spring and so the throttle valve opening is at the maximum.

When the duty is in a range of 0% to X1%, a driving force is generated by the motor but, because it is smaller than the force added by the return spring, the throttle valve opening is kept at the maximum. When the duty increases to a range of X1% to X2%, the driving force of the motor becomes greater than the force added by the return spring and accordingly the throttle valve opening decreased gradually towards the minimum and it becomes the minimum at the duty of X2%. When the duty is over X2%, the throttle valve opening is kept at the minimum. Duties of X1% and X2% depend upon the force added by the return spring and driving force generated by the motor, but they can be, for example, X1%=15% and X2%=30%. Accordingly, when a motor control signal for a duty of 22.5% (=(15+30)/2) is sent to the motor, the throttle valve opening is kept at the middle of the maximum and minimum.

The above explains the static relationship between the duty and throttle valve opening. On the other hand, dynamic characteristic shown inFIG. 22(B)is used when the throttle valve opening is changed from one to another. InFIG. 22(B), the vertical axis represents time, upper vertical axis represents opening, and lower vertical axis represents duty. When, for example, the throttle valve opening is changed from the maximum to the minimum as shown at the top inFIG. 22(B), a signal for a duty of 100% is outputted at time t1and continued for a length of time T1as shown at the bottom inFIG. 22(B)so as to quickly change the throttle valve opening from the maximum to the minimum. Then, after the length of time T1has elapsed, a signal for a duty of −Y1% is outputted and continued for the length of time T2. A duty with negative sign means the direction of current applied to the motor is reverse and so the motor rotates in the reverse direction. In short, a signal for a duty of 100% is supplied to dive the throttle valve opening quickly towards the minimum and, after the length of time T1has elapsed, another signal for rotating the motor in the reverse direction is supplied to brake the motor so that the target opening is reached quickly. Then, a feedback control is applied by changing the duty so that the output opening of the throttle sensor coincides with the target opening. Concrete values of time T1and T2and −Y1% depend upon the control system but, in case that the opening is to be changed from the maximum to the minimum within a response time of 100 ms, for example, T1=30 to 50 ms, −Y1=−100%, and T2=3 to 6 ms. These values T1, T2and −Y1% are obtained from PID calculation and depend upon the control variables of the PID calculation.

Next, the definition of the throttle valve opening in the electronic control throttle unit of this embodiment is described hereunder, usingFIG. 23.

FIG. 23is a chart explaining the definition of the throttle valve opening in the electronic control throttle unit according to the first embodiment of the invention.

Throttle valve has two openings: control opening and mechanical opening. The opening explained inFIG. 22is a control opening. Control opening is the opening controlled by TACU200and the minimum to maximum opening is, for example, 0 to 100%. 0% means the control opening is fully closed and 100% means the control opening is fully opened. A range of 0 to 100% is called the throttle opening control area.

In the mean time, the ETB100is equipped with two stoppers for mechanically controlling the throttle valve opening. The position where the throttle valve is stopped by the minimum side stopper and ceases its operation is the mechanical opening fully closed position. The position where the throttle valve is stopped by the maximum side stopper and ceases its operation is the mechanical opening fully opened position. A range of mechanical opening fully closed position to fully opened opening is called the throttle operation area. The throttle operation area is wider than the throttle opening control area as shown inFIG. 23.

Each opening can be expressed in physical angle as follows, for example. When the position at which the throttle valve becomes perpendicular to the air flow is regarded 0°, the mechanical opening fully closed position Z1is, for example, 6.5° and control opening fully closed position Z2is, for example, 7°. And the control opening fully opened position Z3is, for example, 90° and mechanical opening fully opened position Z4is, for example, 93°.

In addition, as shown inFIG. 23, the EGR control or DPF control area (V1to V2) lies within the throttle opening control area. That is to say, when the target opening sent from the ECU300to the TACU200is within a range from V1to V2, the TACU200can judge that the EGR control or DPF control is in operation. In the control area (0 to 100%), V110% and V2is 80% for example.

Next, the construction of the electronic control throttle unit of this embodiment is described hereunder, usingFIG. 24toFIG. 31.

FIG. 24is a vertical cross section of the electronic control throttle unit according to the first embodiment of the present invention.FIG. 25shows a V—V view ofFIG. 4.FIG. 26is an oblique view of the throttle position sensor used in the electronic control throttle unit of the first embodiment of the present invention.FIG. 27is a circuit diagram of the throttle position sensor used in the electronic control throttle unit of the first embodiment of the present invention.FIG. 28,FIG. 29andFIG. 30are view A ofFIG. 24without the gear cover.FIG. 31is a plan view of the gear used in the electronic control throttle unit in an embodiment. In each figure, the same symbol represents the same part or component.

As shown inFIG. 24, the throttle body1forms the air passage and supports various components. In the air passage, suction air flows in the arrow “AIR” direction from the top to the bottom. The throttle body1is for example die-cast from aluminum. The throttle valve2is fixed on the throttle shaft3with screws. The throttle shaft3is supported in the throttle body1by ball bearings to be able to rotate. No duty is applied to the motor. Under the condition as shown, the throttle valve2is held at the mechanical opening fully closed position by the force added by the return spring. A DC motor5is enclosed and fixed in a space inside the throttle body1. The drive force of the DC motor5is transmitted to the throttle shaft3via a gear (not shown) and rotates the throttle valve2.

The throttle shaft3is supported in the throttle body1by the ball bearings4aand4bto be able to rotate. A gear8is fixed on the throttle shaft3. A return spring11is held between the gear8and throttle body1. The return spring11adds a force to the gear8and throttle shaft3so that the throttle valve2moves towards the fully opened direction.

The DC motor5is enclosed and fixed in a space inside the throttle body1. A gear6is fixed on the output shaft of the motor5. A gear7is supported to be able to rotate by the throttle shaft7A fixed in the throttle body1. The gears6,7and8are engaged with each other and the drive force of the motor5is transmitted to the throttle shaft via the gears6,7and8. As the throttle valve2is rotated, the suction air into the engine is electronically controlled.

A throttle actuator control unit (TACU)200is supported on a gear cover9. A control unit cover12is fastened onto the gear cover9so that no water droplet contacts the TACU200. The gear cover9is resin molded and a connector terminal14is molded together. One end of the connector terminal14is electrically connected with the TACU200. When the gear cover9is mounted on the throttle body1, the other end of the connector terminal contacts the motor terminal5A of the motor5, and so the TACU200can be electrically connected with the motor5. When a duty signal is outputted to the motor5, the DC motor5generates a rotating force.

The throttle position sensor10for sensing the position of the throttle valve2comprises a moving part, brush10aand fixed part, resistor10b. The brush10ais so constructed that when it is engaged with the throttle shaft3, it is rigidly fasted onto the throttle valve2. The resistor is contained in the gear cover9. It is so designed that when the brush10acontacts the resistor10b, the position of the throttle valve2is converted into voltage and outputted to the control unit12.

The construction of the throttle position sensor10is described hereunder, usingFIG. 26andFIG. 27. As shown inFIG. 26, the throttle position sensor10comprises four brushes10a1,10a2,10a3and10a4and four resistors10b1,10b2,10b3and10b4. The brushes10a1and10a2and resistors10b1and10b2constitute the first throttle position sensor, and brushes10a3and10a4and resistors10b3and10b4constitute the second throttle position sensor. This embodiment employs a throttle position sensor for gasoline engine system, that is, a construction equipped with two sets of the throttle position sensors. For a diesel engine, however, only one of the two sets of the throttle position sensors is employed.

On one set of the throttle position sensor, as shown inFIG. 27, the brushes10a1and10a2slide on and contact with the resistors10b1and10b2. Direct current voltage is supplied to both ends of the resistor10b2from a power supply V. By measuring the voltage at the resistor10b1, the position of the brush10a, that is, the position of the throttle valve2can be sensed as a voltage signal.

Under a normal control, the TACU200controls the valve by a feedback control using the output of the throttle position sensor10so that the position of the throttle valve2coincides with the target opening.

A washer15is installed between the gear7and throttle body1. The washer15is made of abrasion resisting plastic material, for example, PA66 nylon containing molybdenum. When the motor5is off, the motor5does not generate any driving force. Under this condition, the throttle valve2is held at the mechanical opening fully opened position by the return spring11. While the gear6and gear8are fastened rigidly onto the motor shaft and throttle shaft3, respectively, the gear7is supported freely over the shaft7A. Since the throttle control unit of this embodiment is installed on a vehicle, if the gear7like the above is mounted to be able to move freely, the gear7would vibrate in the thrust direction of the shaft7A due to the vibration of the vehicle and so the edge of the gear7would hit the throttle body1, resulting in generation of abnormal sound and damage or abrasion of the throttle body1. In the mean time, while the throttle body1is made of aluminum die cast, the gear is made of sintered metal which is harder than aluminum. In order to prevent generation of abnormal sound and damage, the washer15made of abrasion resisting plastic material is used.

FIG. 28is the view A ofFIG. 25without the gear cover9. The motor5is fixed as the motor mounting plate5B is fastened onto the throttle body1with screws. A power terminal5A of the motor5protrudes from the opening of the plate5B.

A mechanical opening fully closed position stopper13A is mounted near the gear9on the throttle body1. When a signal for a duty of 100% is supplied to the motor5, the gear8rotates in the arrow B1direction (closing direction of the throttle valve2) and the stopper end8A mounted on the gear8contacts the mechanical opening fully opened position stopper13A. Thus, the valve is held at the mechanical opening fully opened position.

The electronic control throttle unit for a diesel engine is so designed that, if any failure of the DC motor5or throttle position sensor10is sensed by the control unit12, power supply to the DC motor5is immediately shut off or control duty is immediately fixed to 0% so that the valve returns to the mechanical opening fully opened position only by the force added by the return spring11in the opening direction.

FIG. 29shows the same as inFIG. 28but without the gear7. The shape of the gear8is nearly a trisection. One end of the gear8functions as the stopper end8A and the other end also functions as the stopper end8B. A mechanical opening fully opened position stopper13B is mounted near the gear9on the throttle body1. When no duty signal or voltage is supplied to the motor5, the stopper end8B is moved by the force added by the return spring11in the opening direction to contact the mechanical opening fully opened position stopper13B. Thus, the throttle valve2is held at the mechanical opening fully opened position. In short, so far as no duty is applied to the motor5, the throttle valve2remains at the mechanically opening fully opened position.

FIG. 30shows the same as inFIG. 29but without the gear8. Only one return spring11is used. One end11A of the return spring11is hooked on a portion1A of the throttle body1and the other end11B is hooked on the gear8, adding a force to the throttle valve2in the opening direction.

FIG. 31is a plan view of the gear cover9. The gear cover9is equipped with a connector terminal14. The gear cover9is also equipped with a connector9A for connection with the ECU300and power supply, and the terminal inside it is connected with the TACU200.

Next, the system configuration of the throttle actuator control unit (TACU)200of this embodiment is described, usingFIG. 32.

FIG. 32is a block diagram of the throttle actuator control unit (TACU) of the electronic control throttle unit according to the first embodiment of the present invention. The same symbol as inFIG. 21,FIG. 24andFIG. 25represents the same part or component.

The throttle actuator control unit (TACU)200comprises a CPU210and motor drive circuit (MDC)230. The CPU210comprises a differential calculator212, PID calculator214, control variable calculator216and controller218.

The differential calculator212calculates the differential opening Δθthbetween the target opening θobjoutputted from the ECU300and real opening θthof the throttle valve outputted from the PID sensor10. The PID calculator214calculates the PID control variable u(t) based on the differential opening Δθthoutputted from the differential calculator212. The PID control variable u(t) obtained from the PID calculation is calculated as (Kp·Δθth+Kd·(dΔθth/dt)+Ki·ΣΔθth·dt), wherein Kp is a proportional constant, Kd is a differential constant, and Ki is an integration constant. The control variable calculator216turns an on/off selector switch of the H bridge circuit234(which will be explained later) and determines the flow direction of current based on the PID control variable u(t), and also determines a duty for turning on/off the switch of the H bridge circuit and outputs a control variable signal. The controller218, which will be explained in detail later, usingFIG. 34, judges whether the EGR control or DPF control is in operation based on the target opening θth. If neither EGR control nor DPF control is in operation, it accomplishes a necessary control for fully opening the throttle valve and also controls to open or close the switch SW1for supplying a voltage VB to the PID calculator214, control variable calculator216and MDC230as required.

The motor drive circuit (MDC)230has a logic IC232and H bridge circuit234. The logic IC232outputs an on/off signal to the four switches of the H bridge circuit234based on the control variable signal outputted from the control variable calculator216. The H bridge circuit234is switched on or off in accordance with an on/off signal and supplies necessary current to the motor5to rotate the motor5in the normal direction or reverse direction.

Next, the construction of the H bridge circuit234used in the electronic control throttle unit of this embodiment is described, usingFIG. 33.

FIG. 33is a circuit diagram of the H bridge circuit used in the electronic control throttle unit according to the first embodiment of the present invention.

The H bridge circuit234comprises four transistors TR1, TR2, TR3and TR4and four diodes D1, D2, D3and D4, which are connected with each other as shown so as to supply current to the motor5. For example, when the gate signal G1and gate signal G4are high level and so the transistors TR1and TR4are turned on, current runs as shown by a broken line C1. When this applies, for example, the motor5rotates in the normal direction. When the gate signal G2and gate signal G3are high level and so the transistors TR2and TR3are turned on, current runs as shown by a broken line C2. When this applies, for example, the motor5rotates in the reverse direction. Furthermore, when the gate signal G3and gate signal G4are high level and so the transistors TR3and TR4are turned on, current runs as shown by a broken line C3. When this applies, an external driving force is transmitted to the drive shaft of the motor5and, as the rotor of the motor5is rotated, the motor5functions as a generator and accordingly regenerative braking can be operated. It is also possible to cause regenerative braking if the transistors TR1and TR2are turned on at the same time.

In this embodiment, a one-chip microcomputer containing integrated H bridge circuit is employed and so the transistors can be controlled to be on or off freely by sending a digital signal to the logic IC. However, either an H bridge circuit comprising four transistors or using an integrated one-chip IC will serve the purpose so far as it can control the condition of the motor drive circuit.

Next, the control by the controller218of the electronic control throttle unit of this embodiment is described, usingFIG. 24andFIG. 25.

FIG. 24is a flowchart of the control by the controller of the electronic control throttle unit according to the first embodiment of the present invention.FIG. 25is a diagram explaining the control by the controller of the electronic control throttle unit according to the first embodiment of the present invention.

On step s100, the controller218judges whether the EGR control or DPF control is complete. If it is not complete yet, a normal feedback control is continued on step s110. If it is complete, a target angle control to the fully opened position is performed on step s120.

In making a judgment on step s100, the controller218judges whether the EGR control or DPF control is complete from the target opening inputted from the ECU300. For example, if the throttle opening control area is 0 to 100%, the range from V1to V2(10 to 80% for example) is the EGR control or DPF control area as explained inFIG. 23. Accordingly, if the target opening inputted from the ECU300is within a range from 10 to 80%, the controller218judges that the EGR control or DPF control is in operation. If the target opening is in a range from 0 to 10% or 80 to 100%, the controller218judges that the EGR control or DPF control is complete. In addition, it is possible to so construct the system that the completion of the control is judged by whether a flag of EGR control complete or DPF control complete is received from the ECU300.

Next, the target angle control to the fully opened position on step s120is described, usingFIG. 25. InFIG. 25, the horizontal axis represents time t. The vertical axis represents the throttle opening (control opening) θthand motor duty Du. The throttle opening θthcloser to the origin is towards the fully closed position and farther from the origin is towards the fully opened position. The motor duty Du closer to the origin is towards 100% and farther from the origin is towards 0%.

In the figure, a bold line θthshows the change of the throttle opening and broken line Du shows the duty applied to the motor. The figure shows that the EGR control or DPF control is in operation up to time t3and that the EGR control or DPF control is complete on and after time t3. The bold line θthshows the change of the throttle opening where the control according to this embodiment is in operation after time t3and the dashed line shows the change of the throttle opening where the control according to this embodiment is not operated.

Up to time t3, the EGR control or DPF control is in operation by way of the processing on step s110. The duty Du applied to the motor changes according to the target opening θobjinputted from the ECU300and the throttle opening θthalso changes accordingly.

At time t3when the EGR control or DPF control is judged complete, power to the motor is shut off if the control according to this embodiment is not in operation. That is to say, the motor duty becomes 0%. As a result of this, the throttle valve is moved towards the fully opened position as shown by a dashed line by the force added by the return spring. Then at time t4, the valve contacts the fully opened position stopper and, after repeating bound on the stopper and return by the return spring, it finally stops at the control opening fully opened position. For example, the length of time T4from time t3to t4is 150 ms. When the throttle valve is returned by the return spring at a high speed like the above and impacts with the fully opened position stopper, an impact sound is generated and life of mechanical parts deteriorates due to the impact load.

In the target angle open-loop control up to the fully opened position according to this embodiment, however, the controller218outputs a control signal to the control variable calculator216so that the duty decreases gradually, starting from the time when the EGR control or DPF control is judged complete (time t3), and comes to 0% at time t5as shown by the motor duty Du. The control variable calculator216outputs a control signal to the logic IC232so that the duty decreases gradually, starting from time t3, and comes to 0% at time t5. As a result of the above, the motor is rotated according to the duty signal shown by the dotted line Du in the figure and accordingly the throttle opening θthis gradually moved towards the fully opened side, starting from the time when the EGR control or DPF control is judged complete (time t3), and reaches the fully opened position at time t5as shown by the bold line in the figure. Since the duty signal is gradually decreased in the above operation so that the length of time T5from time t3to t5becomes, for example, 500 ms, the speed of impact of the gear8with the fully opened position stopper13A at the time when the throttle valve is returned to the fully opened position can be decreased and accordingly the generation of impact sound and deterioration of life of mechanical parts due to the impact load can be prevented.

If the motor drive duty to be applied under the open-loop control is set to have slower response (T4<T5) than in case the valve is returned only by the spring force added in the fully opened direction, the sound and energy of the impact of the fully opened position stopper with the motor drive gear can be decreased. In case of a control as disclosed in the Japanese Patent Application Laid-open Publication 2003-214196 where a predetermined duty is applied to the motor for a length of time, it is possible that control for driving the motor is continued even after the throttle valve has returned to the fully opened position because dispersion of response time varying from product to product cannot be completely covered by the control, and accordingly the motor may be damaged due to over-current. In this embodiment, however, there will not be caused any such problem that the control is continued even after the valve has returned to the fully opened position stopper.

The controller218controls the throttle opening by an open-loop control by applying a target duty. In this open-loop control, target may be applied by way of either a monotonously decreasing linear expression as shown inFIG. 25or a parabolical expression or any other so far as the duty is so applied that the time for the valve to return is shorter than in case it is returned only by the force added by the return spring11. Then, the noise and load of the impact of the gear8with the fully opened position stopper13can be reduced.

In this embodiment, when the EGR control or DPF control is judged complete and so the throttle valve is moved to the fully opened position, the duty applied to the motor is decreased gradually as explained above. Thus, the speed of the impact of the gear with the fully opened position stopper can be decreased and accordingly the generation of impact sound and deterioration of life of mechanical parts due to the impact load can be prevented.

Next, the control by the controller218of the electronic control throttle unit according to the second embodiment of the present invention is described, usingFIG. 26andFIG. 27.

The system configuration of the electronic control throttle unit of this embodiment is similar to that inFIG. 21. The construction of the electronic control throttle unit of this embodiment is similar to that shown inFIG. 24toFIG. 31. Also, the system configuration of the throttle actuator control unit (TACU)200of the electronic control throttle unit of this embodiment is similar to that inFIG. 32. Also, the construction of the H bridge circuit234used in the electronic control throttle unit of this embodiment is similar to that inFIG. 33.

FIG. 36is a flowchart of the control by the controller of the electronic control throttle unit according to the second embodiment of the present invention.FIG. 37is a diagram explaining the control by the controller of the electronic control throttle unit according to the second embodiment of the present invention. The same step number represents the same control as inFIG. 34.

InFIG. 37, the horizontal axis represents time t. The vertical axis represents the throttle opening (control opening) θth. The throttle opening θthcloser to the origin is towards the fully closed position and farther from the origin is towards the fully opened position.

On step s100, the controller218judges whether the EGR control or DPF control is complete. If it is not complete yet, a normal feedback control is continued on step s110. If it is complete, a motor drive circuit condition control is performed on step s210, and then a motor drive stop control is performed on step220. The processing from s100to s220is repeated at a cycle of 3 ms for example.

On step s210, the controller218outputs a control signal to the control variable calculator216so that regenerative braking is caused on the motor. As explained inFIG. 33, when an ON signal is supplied to the gates G3and G4of the transistors TR3and TR4, and if the motor5is rotating, current runs in the arrow C3direction and accordingly the regenerative braking is caused on the motor5. Then, the controller218outputs a control signal to the control variable calculator216so that the transistors TR3and TR4are turned on. The control variable calculator216then outputs a control signal to logic IC232so that the transistors TR3and TR4are turned on. In this operation, the throttle valve2is moved towards the fully opened direction by the return spring11. Since the movement of the throttle shaft is transmitted to the motor5via the gears8,7and6, regenerative braking is caused on the motor5. Because of this regenerative braking of the motor5, the movement of the throttle valve towards the fully opened direction is braked.

An important point in this construction is that, although the motor drive mechanism is rotated in the fully opening direction by the force added by the return spring11when the motor is turned off, turning on/off the transistors of the H bridge circuit is so controlled that, by setting the motor circuit active, the rotating force of the DC motor5acts opposite to the force added by the return spring11. With this control, the throttle valve2moves slowly as in case the motor drive circuit is connected as shown inFIG. 37and accordingly sudden impact of the gear8with the fully opened position stopper can be prevented.

Then, on step s220, the controller218outputs a control signal to the control variable calculator216so that the motor drive is stopped. That is, the controller218outputs a signal to the control variable calculator216so that the motor duty Du becomes 0%. The control variable calculator216outputs a control signal to the logic IC232so that the motor duty Du becomes 0%. As a result of this, power to the motor is shut off and accordingly the throttle valve2is moved towards the fully opened direction by the return spring11.

The motor drive stop control may be such that power to the motor5is shut off. That is, the controller218turns off the switch SW1shown inFIG. 32so as to stop supplying power to the motor5from a power supply VB via the motor drive circuit230. In the motor drive stop control, as explained above, power to the motor is shut off to stop driving the motor either by setting the motor duty Du to 0% to turn off the transistors in the H bridge circuit or by turning off the switch installed on a power line from the power supply to the motor.

That is to say, the movement of the throttle valve towards the fully opened direction is momentarily braked by the processing on step s210and then the valve is released from braking and moved towards the fully opened position by the processing on step s220. The processing from step s100to s220is repeated at a cycle of 3 ms for example. Accordingly, when the EGR control or DPF control is judged complete, the braking control on step s210and non-braking control on step s220are repeated for the above length of time and so the throttle valve is gradually moved towards the fully opened side and reaches the fully opened position for example at time t6.

The length of time T4in the figure is the same as shown inFIG. 35, where no braking is applied to the throttle opening. In this embodiment, however, since braking is applied cyclically during the movement, the length of time from time t3to t6becomes longer than the time T4and accordingly the speed of impact of the gear8with the fully opened position stopper13A at the time when the throttle valve is returned to the fully opened position can be decreased and so the generation of impact sound and deterioration of life of mechanical parts due to the impact load can be prevented.

In this embodiment, as explained above, when the EGR control or DPF control is judged complete and so the throttle valve is moved towards the fully opened position, a signal is outputted from the controller of the CPU so that the regenerative braking is caused on the motor, that is, the motor drive circuit in the control unit is kept connected with the motor, and hence a braking force caused by the rotating force of the motor in the opposite direction to the return spring force that is so added as to move the valve towards the fully opened direction. Accordingly, the energy of the impact of the fully opened position stopper with the component parts of the motor drive mechanism such as gear can be decreased and so the generation of impact sound and deterioration of life of mechanical parts due to the impact load can be prevented.

Next, the control by the controller218of the electronic control throttle unit according to the third embodiment of the present invention is described, usingFIG. 38.

The system configuration of the electronic control throttle unit of this embodiment is similar to that inFIG. 21. The construction of the electronic control throttle unit of this embodiment is similar to that shown inFIG. 24toFIG. 31. Also, the system configuration of the throttle actuator control unit (TACU)200of the electronic control throttle unit of this embodiment is similar to that inFIG. 32. Also, the construction of the H bridge circuit234used in the electronic control throttle unit of this embodiment is similar to that inFIG. 33.

FIG. 38is a flowchart of the control by the controller of the electronic control throttle unit according to the third embodiment of the present invention. The same step number represents the same control as inFIG. 34andFIG. 36.

In this embodiment, the processing on steps s310and s320is added to the processing inFIG. 36.

When the EGR control or DPF control is judged complete on step s100, step s310checks a self-check flag. The self-check result is checked on this step and, if no failure is sensed, regenerative braking and motor drive stop control are performed on steps s210and s220similarly as in case the motor circuit is connected and accordingly the throttle valve contacts slowly with the fully opened position stopper.

If any failure is sensed as a result of the self-check, on step s320the controller218turns off all the transistors in the H bridge circuit and accordingly the throttle valve is moved quickly towards the fully opened position as shown by the dashed line inFIG. 35.

If any failure is sensed as a result of the self-check, braking is releases as quickly as possible as explained above and accordingly abnormal behavior of the vehicle can be prevented.

Next, the control by the controller218of the electronic control throttle unit according to the fourth embodiment of the present invention is described, usingFIG. 39andFIG. 40.

The system configuration of the electronic control throttle unit of this embodiment is similar to that inFIG. 21. The construction of the electronic control throttle unit of this embodiment is similar to that shown inFIG. 24toFIG. 31. Also, the system configuration of the throttle actuator control unit (TACU)200of the electronic control throttle unit of this embodiment is similar to that inFIG. 32. Also, the construction of the H bridge circuit234used in the electronic control throttle unit of this embodiment is similar to that inFIG. 33.

FIG. 39is a flowchart of the control by the controller of the electronic control throttle unit according to the fourth embodiment of the present invention.FIG. 40is a diagram explaining the control by the controller of the electronic control throttle unit according to the fourth embodiment of the present invention. The same step number represents the same control as inFIG. 34andFIG. 36.

InFIG. 40, the horizontal axis represents time t. The vertical axis represents the throttle opening (control opening) θthand motor duty Du. The throttle opening θthcloser to the origin is towards the fully closed position and farther from the origin is towards the fully opened position. Bold line represents the target opening θobjand broken like represents the real opening θth(real). The motor duty Du is shown by dotted line, where closer to the origin is towards 100% and farther from the origin is towards 0%.

On step s410, the controller218receives the target opening θobjoutputted from the ECU300and uses it as the criterion for position control.

Next, on step s420, the controller judges whether the target opening θobjreceived on step is greater than a specified value A and also the change ratio Δθobjof the target opening θobjis smaller than a specified value B. The specified value A is, for example, 80% and the controller judges whether the EGR control or DPF control is complete as on step s100inFIG. 24. The change ratio Δθobjof the target opening θobjis used as the criterion of judgment so that the controller can judge whether the target opening θobjis steadily greater than the specified value A excluding a case where the target opening θobjbecomes greater than the specified value momentarily. The change ratio Δθobjis 0.25% for example. That is, when the target opening θobjis greater than the specified value (80% for example) and also the change ratio Δθobjof the target opening θobjis smaller than the specified value (0.25% for example), the controller judges that the EGR control or DPF control is complete and the processing proceeds to step s430. If not, the processing proceeds to step s460.

On step s460, a count C is initialized and cleared to 0. That is, the count C is 0 under normal EGR control or DPF control. On the next step s470, the controller judges whether a variable E is 0. The variable E can be either 0 or 1. When the variable E is 0, it means that the control is in operation and, when the variable E is 1, it means that the control is not in operation. When the control is in operation and so the variable E is 1, the processing proceeds to step s110and a feedback control is performed so that the throttle opening becomes the target opening. InFIG. 40, the throttle valve opening is controlled by a normal feedback control through to time t3. Since the EGR control or DPF control has been complete by this time, any position near the fully opened position is set as the throttle valve position and the target angle control is performed according to this target opening and the opening is held for a length of time (time until C>D is met on step s440).

On the other hand, when the EGR control or DPF control is complete, “1” is added to the count C on step s430. Then, on step s440, the controller judges whether the count C has exceeded a specified value D. This judgment on step s440is to judge whether a specified length of time has elapsed since the EGR control of DPF control was judged complete on step s430. The specified value D shall be equivalent to the length of time from t3to t7inFIG. 40, which is for example the length of time needed for counting 200 ms. This length of time is set longer than the time needed for the throttle valve to be moved towards the fully opened position by the force added by the return spring as shown by the dashed line inFIG. 35(takingFIG. 35for example, longer than the length of time T4(150 ms for example)).

If the condition on step s440is not met, for example, if 200 ms have not yet elapsed since the completion of the EGR control or DPF control, the controller judges whether a variable E is 0 or not. Since the control is in operation and so the variable E is “0”, the processing proceeds to step s110, where a feedback control is performed so that the throttle opening coincides with the target opening. That is to say, the throttle valve opening is controlled by a normal feedback control even for the length of time from time t3to t6inFIG. 40.

With this control, abrasion of the sliding resistance of the throttle sensor can be reduced. In case of an electronic control throttle unit using contact type throttle sensor, if the length of time for holding a constant opening (for example, the length of time it is held at the fully opened position) is longer, the resistor may be partly abraded due to vibration. This partial abrasion may result in abnormal output from the contact type throttle position sensor. With this embodiment, however, where the control is maintained until the length of time equivalent to the specified value D has elapsed even after the EGR control or DPF control has been complete, the valve is held at a position for the length of time from time t3to t7and accordingly the length of time the valve is held at the mechanical fully opened position can be as short as the time from time t7to t8. Because of this short holding time, the life of the throttle position sensor can be prolonged.

Next, if the count C is judged to have exceeded the specified value D on step s440, that is, if the elapsed time is time t7inFIG. 40, the braking control by the regenerative braking explained inFIG. 36and non-braking control are repeated on steps s210and s220and so the gear9contacts slowly with the fully opened position stopper13. In this processing on steps s210and s220, the processing on step s210can be omitted. That is to say, since the throttle valve has been held at a specified position near the fully opened position for a specified length of time by the processing on step s110, even if power to the motor is shut off on step s220and so the valve is moved immediately from the specified position to the fully opened position, energy of the impact of the gear8with the fully opened position stopper13A is small in most cases because the distance of movement is shorter.

Then, on step s450, the control condition flag (E) is set to “1” and the loop control is ended.

In this embodiment, after time t7by which time the valve opening is in the EGR area (after time t3) and also the length of time where the condition (C>D) is met has elapsed, braking and powering off the motor are repeated and the throttle valve condition is switched from controlled to non-controlled as explained above so that the gear8contacts slowly with the fully opened position stopper13.

In order to go back to the EGR control or DPF control after the EGR control or DPF control is complete, any one of the “target opening>A”, “target opening change ratio<B” or “C>D” shall be met. In this operation, since the throttle valve has already come into non-controlled condition, the control condition flag is E=1. Accordingly, based on the judgment on step s470, the processing proceeds to step s480and the control variables are cleared.

The PID controller214repeats the PID calculation for obtaining the duty under the EGR control or DPF control is in operation and also under the EGR control not in operation as explained inFIG. 32. That is, the PID control variable u(t)=(Kp·Δθth+Kd·(dΔθth/dt)+Ki·ΣΔθth·dt) is calculated. When the motor is off, the deviation between the target opening and real opening lies more on the closing side and so a portion that functions as integration term has excessive control duty in the closing direction. Normally, in a throttle position control, braking is applied near the target opening so as to achieve better convergence. However, if a value equivalent to the integration term has excessively accumulated in the closing direction as explained above, properly braking cannot be applied but excessive overshoot may possibly be caused, resulting in poor convergence.

To solve the above, in this embodiment, the control variables are cleared to 0 on step s480. The variables to be cleared may be those concerning the integration terms or all relating to the duty to be applied. With this operation, the control performance including the response time can improve. Then, on step s490, the control condition flag is set to E=0 to go into a normal operation and the loop control is ended.

Also in this embodiment, the energy of the impact of the fully opened position stopper with the component parts of the motor drive mechanism such as gear can be decreased and so the generation of impact sound and deterioration of life of mechanical parts due to the impact load can be prevented. In addition, the length of time to hold the valve at the fully opening position can be made shorter and accordingly the life of the contact type throttle sensor can be prolonged. Furthermore, since the control variables are cleared to zero when the valve condition is switched from controlled to non-controlled, the control performance including the response time can improve.

Next, the system configuration of the electronic control throttle unit according to another embodiment of the present invention is described, usingFIG. 41.

FIG. 41is a block diagram of the electronic control throttle unit according to another embodiment of the present invention.

Although the TACU200and ECU300are constructed separately in each embodiment above, the TACU200and ECU300can be constructed into one unit as shown inFIG. 41.

The characteristic and control of the throttle valve unit used as a throttle valve for the motor control in each embodiment above are summarized as follows:

A known electronic position control of a throttle valve is such that, as disclosed in the Japanese Application Patent Laid-Open Publication No. Hei 07-332136, a control variable according to the deviation between the real opening and target opening of the throttle valve is calculated by a method such as the PID control, the calculated control variable is converted into a duty ratio which is the ratio of the on-time pulse drive to off-time, a PWM signal is supplied to a direct-current motor via the H bridge circuit, the motor generates torque, and then the throttle valve is driven by the generated torque via gears and throttle shaft.

Although the electronic control throttle units like the above are all for gasoline engine, an electronic control throttle unit is about to be employed for diesel engine nowadays in order to improve the EGR efficiency and improve dieseling. Since the electronic control throttle unit for diesel engine, differently from that for gasoline engine, performs control mainly to improve the EGR efficiency and to burn soot in the DPF (diesel particular filter) by throttling the suction and increasing the exhaust temperature, the motor control is not in operation when the EGR control or DPF control is not in operation and so the throttle valve is positioned at the fully opened position. Accordingly, significant differences are 1) the throttle valve is held at the fully opened position for a long time, 2) there exists a condition where the motor control in operation is switched to not in operation or vise versa, and 3) a default mechanism that supplies a certain amount of air at an optional valve opening when the motor is off is not necessary because the unit has no out-of-control mode.

On the electronic control throttle unit for diesel engine, control on the air flow is no longer needed when the EGR control or DPF control is complete, and so power to the motor is shut off and the throttle valve is returned by the return spring to the fully opened position where the pressure loss becomes the minimum. That is, differently from the electronic control throttle unit for gasoline engine that continues controlling the throttle valve all the time, there always exists a condition where the control in operation is switched to not in operation or where the control not in operation is switched to start operation.

When considering a condition where the control in operation is switched to not in operation and assuming that, when the control is ceased, power to the motor is simply tuned off or the duty to be applies is set to 0% so as to move the throttle valve position towards the fully opened position only by the force added in the opening direction by the return spring, there arises a problem that the fully opened position stopper impacts heavily with the drive mechanism components and accordingly impact sound is generated and the life of mechanical parts deteriorates due to the impact load.

In order to solve the above problem, there is a known electronic control throttle unit as disclosed in the Japanese Application Patent Laid-Open Publication No. 2002-256892, wherein a cushion mechanism is installed between the fully opened position stopper and gear so as to eliminate the mechanical impact.

There is another known electronic control throttle unit as disclosed in the Japanese Application Patent Laid-Open Publication No. 2003-214196, for example, where a predetermined duty is applied to the motor for some time to move the motor slower than in a normal control and accordingly so control to avoid the impact.

With the prior art disclosed in the Japanese Application Patent Laid-Open Publication No. 2002-256892, however, there arises a problem of increased cost for the cushion mechanism, lowered effect due to the deterioration of the cushion mechanism and lowered reliability due to the increase in the number of parts.

With the prior art disclosed in the Japanese Application Patent Laid-Open Publication No. 2003-214196, where a predetermined duty is applied to the motor for some time, it is possible that control for driving the motor is continued even after the throttle valve has returned to the fully opened position because dispersion of response time varying from product to product cannot be completely covered by the control, and accordingly there arises a problem that the motor may be damaged due to over-current and mechanical parts may be subjected to overload resulting from the damage and may also be damaged.

The embodiment of the present invention offers an electronic control throttle unit with which the above problems are solved, reliability improves, no damage is given to the motor or mechanical parts, and sound and energy of the impact with mechanical parts can be decreased.

According to this embodiment:

(1) In order to achieve the above object, there is provided an electronic control throttle unit equipped with an electronic throttle body comprising an actuator that drives a throttle valve supported by a throttle body to be able to rotate, single return spring that adds a force so that the throttle valve returns in the fully opened direction, and throttle position sensor that senses the opening of the throttle body, and with a throttle actuator control unit that drives the actuator according to the throttle valve opening sensed by the throttle position sensor and target opening; wherein the throttle actuator control unit is equipped with a controller that controls the actuator so that, when the EGR control or DPF control is complete, the throttle valve is moved towards the fully opened direction taking longer time than when the throttle valve is moved towards the fully opened direction simply by the return spring.

With the above construction, reliability improves, no damage is given to the motor or mechanical parts, and sound and energy of the impact with mechanical parts can be decreased.

(2) In (1) above, it is preferable that the controller performs an open-loop control by outputting to the actuator a control signal that can be used as a target angle for the throttle valve to be moved gradually towards the fully opened direction.

(3) In (2) above, it is preferable that the controller gradually decreases the duty in the duty signal to be outputted to the actuator.

(4) In (1) above, it is preferable that, when the EGR control or DPF control is complete, the controller repeats setting the actuator to a controlled condition and non-controlled condition.

(5) In (4) above, it is preferable that, in the controlled condition, the controller operates the actuator as a brake.

(6) In (4) above, it is preferable that, in the controlled condition, the controller controls the actuator to cause regenerative braking.

(7) In (4) above, it is preferable that, in the non-controlled condition, the controller shuts off power to the actuator.

(8) In (7) above, it is preferable that the controller sets the duty in the duty signal to be outputted to the actuator to 0%.

(9) In (4) above, it is preferable that, if the self-check of the throttle position sensor results in a failure, the controller shuts off power to the actuator.

(10) In (4) above, it is preferable that the controller first controls the throttle valve opening so that it is held near the fully opened position for a specified length of time after the EGR control or DPF control is judged complete and then repeats setting the actuator in the controlled condition and non-controlled condition.

(11) In (1) above, it is preferable that, after the EGR control or DPF control is judged complete, the controller controls the throttle valve opening so that it is held near the fully opened position for a specified length of time and then sets the actuator to a non-controlled condition.

(12) In (11) above, it is preferable that, after the EGR control or DPF control is judged complete, the controller controls the throttle valve opening so that it is held near the fully opened position for a specified length of time and then repeats setting the actuator to a controlled condition and to the non-controlled condition.

(13) In (11) above, it is preferable that the controller judges the EGR control or DPF control is complete if such a condition continues longer than a specified length of time that the target opening of the throttle valve exceeds a specified target opening, and also the change of the target opening is less than a specified change of the opening, and also the target opening is less than a specified opening and the change is less than a specified change of the opening.

(14) In (12) above, it is preferable that, after the EGR control or DPF control is judged complete, the controller starts controlling the actuator if at least any one of the above three conditions is not met.

(15) In (13) above, it is preferable that, when the controller starts controlling the actuator, the controller first initializes the value in a calculator of the actuator drive duty to be applied to the actuator and then starts control.

(16) In (15) above, it is preferable that, in initializing the value in a calculator of the actuator drive duty to be applied to the actuator, the controller initializes at least the integration terms or variables equivalent to them.

(17) In (a) above, it is preferable that the electronic throttle body is equipped with the first gear fixed on the output shaft of the actuator, second gear fixed on the throttle shaft that supports the throttle valve, and intermediate gear that transmits drive force from the first gear to the second gear, and further equipped with washer made of abrasion resisting material mounted between the intermediate gear and throttle body that supports the intermediate gear.

(18) In addition, in order to achieve the above object, there is provided an electronic control throttle unit equipped with an electronic throttle body comprising an actuator that drives a throttle valve supported by a throttle body to be able to rotate, single return spring that adds a force so that the throttle valve returns in the fully opened direction, and throttle position sensor that senses the opening of the throttle body, and with a throttle actuator control unit that drives the actuator according to the throttle valve opening sensed by the throttle position sensor and target opening; wherein the throttle actuator control unit is equipped with a controller that performs an open-loop control by outputting to the actuator a control signal that can be used as a target angle for the throttle valve to be moved gradually towards the fully opened direction so that the throttle valve is moved towards the fully opened direction when the EGR control or DPF control is complete, taking longer time than when the throttle valve is moved towards the fully opened direction simply by the return spring.

With the above construction, reliability improves, no damage is given to the motor or mechanical parts, and sound and energy of the impact with mechanical parts can be decreased.

(19) In addition, in order to achieve the above object, there is provided an electronic control throttle unit equipped with an electronic throttle body comprising an actuator that drives a throttle valve supported by a throttle body to be able to rotate, single return spring that adds a force so that the throttle valve returns in the fully opened direction, and throttle position sensor that senses the opening of the throttle body, and with a throttle actuator control unit that drives the actuator according to the throttle valve opening sensed by the throttle position sensor and target opening; wherein the throttle actuator control unit is equipped with a controller that repeats setting the actuator to a controlled condition and non-controlled condition after the EGR control of DPF control is complete so that the throttle valve is moved towards the fully opened direction when the EGR control or DPF control is complete, taking longer time than when the throttle valve is moved towards the fully opened direction simply by the return spring.

With the above construction, reliability improves, no damage is given to the motor or mechanical parts, and sound and energy of the impact with mechanical parts can be decreased.

(20) In addition, in order to achieve the above object, there is provided an electronic control throttle unit equipped with an electronic throttle body comprising an actuator that drives a throttle valve supported by a throttle body to be able to rotate, single return spring that adds a force so that the throttle valve returns in the fully opened direction, and throttle position sensor that senses the opening of the throttle body, and with a throttle actuator control unit that drives the actuator according to the throttle valve opening sensed by the throttle position sensor and target opening; wherein the throttle actuator control unit is equipped with a controller that first controls the throttle valve opening so that it is held near the fully opened position for a specified length of time after the EGR control or DPF control is judged complete and then repeats setting the actuator to the controlled condition and non-controlled condition so that the throttle valve is moved towards the fully opened direction when the EGR control or DPF control is complete, taking longer time than when the throttle valve is moved towards the fully opened direction simply by the return spring.

With the above construction, reliability improves, no damage is given to the motor or mechanical parts, and sound and energy of the impact with mechanical parts can be decreased.

(21) In addition, in order to achieve the above object, there is provided an electronic control throttle unit equipped with an electronic throttle body comprising an actuator that drives a throttle valve supported by a throttle body to be able to rotate, single return spring that adds a force so that the throttle valve returns in the fully opened direction, and throttle position sensor that senses the opening of the throttle body, and with a throttle actuator control unit that drives the actuator according to the throttle valve opening sensed by the throttle position sensor and target opening; wherein the throttle actuator control unit is equipped with a controller that first controls the throttle valve opening so that it is held near the fully opened position for a specified length of time after the EGR control or DPF control is judged complete and then sets the actuator to a non-controlled condition so that the throttle valve is moved towards the fully opened direction when the EGR control or DPF control is complete, taking longer time than when the throttle valve is moved towards the fully opened direction simply by the return spring.

With the above construction, reliability improves, no damage is given to the motor or mechanical parts, and sound and energy of the impact with mechanical parts can be decreased.

(22) In addition, in order to achieve the above object, there is provided an electronic control throttle unit equipped with an electronic throttle body comprising an actuator that drives a throttle valve supported by a throttle body to be able to rotate, single return spring that adds a force so that the throttle valve returns in the fully opened direction, and throttle position sensor that senses the opening of the throttle body, and with a throttle actuator control unit that drives the actuator according to the throttle valve opening sensed by the throttle position sensor and target opening; wherein the electronic throttle body is equipped with the first gear fixed on the output shaft of the actuator, second gear fixed on the throttle shaft that supports the throttle valve, and intermediate gear that transmits drive force from the first gear to the second gear, and further equipped with washer made of abrasion resisting material mounted between the intermediate gear and throttle body that supports the intermediate gear.

An EGR gas control system to which the present invention applied is described hereunder.

FIG. 10shows the construction of an embodiment of an exhaust gas recirculation system of an internal combustion engine to which the present invention applies.

Dust in the air to be sucked into the engine is removed by an air cleaner41, and a suction flow G1is sensed by a suction flow sensor42. The signal of the sensed suction flow G1is inputted into the engine control unit (ECU)421and exhaust gas recirculation controller (EGRCONT)420. The suction air pressurized by a compressor43of turbo charger flows through a suction pipe44and the flow or pressure is controlled by a suction flow control valve5. The suction air further flows into a suction manifold6and then distributed to each cylinder of the engine47.

The opening of the suction flow control valve45is controlled according to a suction flow control signal CTH outputted from the exhaust gas recirculation controller420. The suction flow control valve45is, for example, a motor-driven butterfly type valve, and an opening signal of the butterfly valve is sensed and inputted into the exhaust gas recirculation controller420as an opening signal θTH.

Fuel for combustion is supplied into the cylinders of the engine47from a fuel injection valve419installed on the engine47. Fuel supply to the fuel injection valve419is done by a fuel pump17via a fuel pipe418. The injection volume from the fuel injection valve419is controlled by the ECU421, that is, the ECU421outputs a fuel injection volume signal FINJ to the fuel injection valve419.

Exhaust gas after the combustion in the engine is collected into an exhaust manifold48and, after passing through a turbine49of the turbo charger, exhausted into air via a catalyst410and exhaust pipe411. The exhaust manifold48has a branch412, where part of the exhaust gas from the engine is branched. The branched exhaust gas is then directed into a recirculation pipe413aas the recirculation gas. A recirculation gas cooler414is installed on the recirculation pipe413a. The recirculation gas cooled down by the recirculation gas cooler414is then recirculated into the suction manifold46via a recirculation pipe413band recirculation gas control valve416.

The opening of the recirculation control valve416is controlled according to an opening control signal CEG of the recirculation gas control valve416outputted from the exhaust gas recirculation controller420. The recirculation control valve416is for example a seat type valve, and a stroke of the seat valve is sensed and inputted into the exhaust gas recirculation controller420as a stroke signal STEG. If, for example, a butterfly type valve is used as the recirculation gas control valve416, an opening signal of the butterfly valve is inputted into the exhaust gas recirculation controller420.

A recirculation gas flow sensor415is installed on the recirculation pipe413bto measure the recirculation gas flow G2inside the recirculation pipe. The measured recirculation gas flow G2is inputted into the exhaust gas recirculation controller420. In this construction, the exhaust gas cooler414is installed to cool down the exhaust gas temperature, but it can be omitted.

Not only a rotation speed signal NE of the engine7and suction flow signal G1from the suction flow sensor2but other signals (not shown in the figure) showing the condition of the engine and vehicle are also inputted into the ECU421. The ECU21runs calculations based on these signals and sends a control command value to each device. The ECU421judges the operating condition of the engine7based on signals including the rotation speed signal NE of the engine47and suction flow signal G1. The ECU421outputs a recirculation gas recirculation ratio command value RSET to the exhaust gas recirculation controller420.

The exhaust gas recirculation controller420calculates the exhaust gas recirculation ratio R from the suction flow T1and recirculation gas flow G2. The opening of the suction flow control valve45and/or recirculation gas control valve16is controlled by a feedback control so that the obtained recirculation ratio R coincides with the recirculation gas recirculation ratio command value RSET. That is, it is a characteristic of this embodiment that not only the recirculation gas control valve416but also the suction flow control valve45is controlled so that the recirculation volume of the exhaust gas coincides with the target value.

Next, the control of the exhaust gas recirculation controller in the exhaust gas recirculation system of this embodiment of an internal combustion engine is described, usingFIG. 11andFIG. 12.

FIG. 11is a block diagram of the control system of the exhaust gas recirculation system of an internal combustion engine to which the present invention applies.FIG. 12is a flowchart showing the control of the exhaust gas recirculation controller in the exhaust gas recirculation system of an internal combustion engine to which the present invention applies. The same symbol represents the same part or component as inFIG. 10.

As shown inFIG. 11, the recirculation gas recirculation ratio command value RSET outputted from the ECU421, suction flow signal G1sensed by the suction flow sensor42, and recirculation gas flow G2sensed by the recirculation gas flow sensor415are inputted into the exhaust gas recirculation controller420. The exhaust gas recirculation controller420outputs an opening control signal CEG to the recirculation gas control valve416and a suction flow control signal CTH to the suction flow control valve5and controls these valves416and45so that the recirculation ratio R of the exhaust gas coincides with the target value RSET. The exhaust gas recirculation controller420calculates the exhaust gas recirculation ratio R from the suction flow signal G1and recirculation gas flow G2by a formula (G2/(G1+G2)).

In the description below, it is assumed that the response of the suction flow control valve45is faster than that of the recirculation gas control valve416. To be concrete, provided that the suction flow control valve45is a butterfly valve having a bore of 50 mm and the recirculation gas control valve416is a seat valve having a seat diameter of 30 mm, the response of the suction flow control valve45is faster than that of the recirculation gas control valve416.

Next, the control of the exhaust gas recirculation controller is described, usingFIG. 12. The controls described below are all performed by the exhaust gas recirculation controller420.

On step s500inFIG. 12, the exhaust gas recirculation controller420calculates the exhaust gas recirculation ratio R from the suction flow signal G1and recirculation gas flow G2by a formula (G2/(G1+G2)).

Next, on step s510, the controller judges whether a variation ΔRSET in the target value RSET of the exhaust gas recirculation ratio R inputted from the ECU421is greater than a predetermined reference value ΔR0. If the variation ΔRSET is greater than the reference value ΔR0, the processing proceeds to step s520and, if not, to step s550. That is, step s510judges whether the target value RSET of the exhaust gas recirculation ratio R has significantly changed or not. When the operating condition of the internal combustion engine has temporarily varied, whether it becomes necessary to quickly change the exhaust gas recirculation ratio so as to decrease toxic material content in the exhaust gas is judged here.

If the variation ΔRSET is greater than the reference value ΔR0, that is, if it becomes necessary to quickly change the exhaust gas recirculation ratio, the controller judges whether the exhaust gas recirculation ratio R calculated on step s510is equal to the target value RSET of the exhaust gas recirculation ratio R on step s520.

If the recirculation ratio R is greater than the target value RSET, on step s530, the controller decreases the opening control signal CTH to be outputted to the suction flow control valve45so as to narrow the opening of the suction flow control valve5. And then, the processing returns to step s520and the above processing is repeated until the recirculation ratio R becomes equal to the target value RSET.

On the other hand, if the recirculation ratio R is smaller than the target value RSET, on step s540, the controller increases the opening control signal CTH to be outputted to the suction flow control valve45so as to widen the opening of the suction flow control valve45. And then, the processing returns to step s520and the above processing is repeated until the recirculation ratio R becomes equal to the target value RSET.

A feedback control is performed by repeating the processing of steps s520, s530and s540as explained above until the recirculation ratio R becomes equal to the target value RSET. In this operation, since the response of the suction flow control valve5is assumed to be faster than that of the recirculation gas control valve416, the exhaust gas recirculation ratio can be changed quickly to a specified target value even if quick change of the exhaust gas recirculation ratio is needed.

On the other hand, if the variation ΔRSET is judged less than the reference value ΔR0on step s510, that is, if the change in the exhaust gas recirculation ratio is not so big, the controller judges whether the exhaust gas recirculation ratio R calculated on step s510is equal to the target value RSET of the exhaust gas recirculation ratio R on step s550.

If the recirculation ratio R is greater than the target value RSET, on step s560, the controller decreases the opening control signal CEG to be outputted to the recirculation gas control valve416so as to narrow the opening of the recirculation gas control valve416. And then, the processing returns to step s550and the above processing is repeated until the recirculation ratio R becomes equal to the target value RSET.

On the other hand, if the recirculation ratio R is smaller than the target value RSET, on step s570, the controller increases the opening control signal CEG to be outputted to the recirculation gas control valve416so as to widen the opening of the recirculation gas control valve416. And then, the processing returns to step s550and the above processing is repeated until the recirculation ratio R becomes equal to the target value RSET.

A feedback control is performed by repeating the processing of steps s550, s560and s570as explained above until the recirculation ratio R becomes equal to the target value RSET. In this operation, since the response of the recirculation gas control valve416is slower than that of the suction flow control valve45, much more sensitive opening control is available and so the exhaust gas recirculation ratio can be changed to a specified target value accurately.

In the description above, it is assumed that the response of the suction flow control valve45is faster than that of the recirculation gas control valve416but there may be a case where the response of the recirculation gas control valve416is faster than that of the suction flow control valve45. To be concrete, provided that the suction flow control valve45is a butterfly valve having a bore of 30 mm and the recirculation gas control valve416is a seat valve having a seat diameter of 50 mm, the response of the recirculation gas control valve416becomes faster than that of the suction flow control valve45. In a case like the above, the recirculation gas control valve416having faster response shall be controlled if quick change of the exhaust gas recirculation ratio is needed and, if no quick change is needed, the suction flow control valve45having slower response shall be controlled to improve the control accuracy.

As explained above, if quick change of the exhaust gas recirculation ratio is needed, controlling a control valve having faster response enables to cope with the quick change. If no quick change is needed, controlling a control valve having slower response enables to improve the control accuracy.

The relationship between the response of the suction flow control valve45and that of the recirculation gas control valve416as explained above in connection with the need for quick change of the exhaust gas recirculation ratio applies to the constructions where the recirculation gas control valve416is a butterfly valve as in a previous embodiment or it is installed inside the suction passage as in a previous embodiment.

Next, the feedback control by the exhaust gas recirculation controller in the exhaust gas recirculation system of this embodiment of an internal combustion engine is described, usingFIG. 13.

FIG. 13shows a model covering from the suction flow control valve45on the suction side of the engine7to the turbine49of the turbo charger on the exhaust side in the exhaust gas recirculation system of an internal combustion engine according to an embodiment of the present invention. The same symbol represents the same part or component as inFIG. 10.

InFIG. 13, when the flow and pressure through the suction flow control valve is defined as G1and p1, the flow and pressure through the turbine9of the turbo charger is defined as G3and p3, and the flow and pressure through the recirculation pipe413aof the recirculation gas control valve416, located on the exhaust side of the engine47viewing from the engine7, is defined as G2and p2, respectively, relationship in this system can be expressed by a simultaneous equation comprising expressions (1), (2) and (3) below.
G1+G2=G3=f3(ne, ηv, p2)  (1)
G1=f1(p1, p2, ζ)  (2)
G2=f2(p2, p3, ζ′)  (3)

ne: engine speed, η: volumetric efficiency of the engine, v: displacement of the engine, p1: suction pressure, p2: back pressure of the engine, p3: back pressure of the turbine of the turbo charger, ζ: loss factor of the suction flow control valve, ζ′: loss factor of the recirculation gas control valve, f1: flow characteristic of the suction flow control valve, f2: flow characteristic of the recirculation gas control valve.

On the other hand, the recirculation gas recirculation ratio R is defined as R=G2/(G1+G2) as explained above. That is, if the flow G1through the suction flow control valve5and flow G2through the recirculation gas control valve are defined, this ratio is determined univocally.

As expressed by the expression (2), the flow G1through the suction flow control valve5can be controlled using the loss factor ζ, that is, opening of the suction flow control valve45. Similarly, as expressed by the expression (3), the flow through the recirculation gas control valve416can be controlled using the loss factor ζ′, that is, opening of the recirculation gas control valve416. In short, combining a feedback system with the command system of the valve openings of the suction flow control valve45and recirculation gas control valve416based on the flow G1and G2enables to control the recirculation gas recirculation ratio R.

In addition, if the flow characteristics of the suction flow control valve45and recirculation gas control valve416are known in advance, control speed can improve. That is, for example, be aware of a flow change per unit time in case the suction flow control valve45is operated to change the suction flow and a flow change per unit time in case the recirculation gas control valve416is operated to change the suction flow in advance. Then, if the flow change per unit time in case the suction flow control valve45is operated to change the suction flow is faster than the flow change per unit time in case the recirculation gas control valve416is operated to change the suction flow, that is, if the response of the suction flow control valve45is faster than that of the recirculation gas control valve416, controlling the suction flow control valve45enables to change the exhaust gas recirculation ratio quickly to a specified target value when quick change of the exhaust gas recirculation ratio is needed, and accordingly the control speed improves.

Next, the construction of the recirculation gas flow sensor415used in the exhaust gas recirculation system of this embodiment of an internal combustion engine is described, usingFIG. 14andFIG. 15.

FIG. 14is a partial cross-sectional view showing the first construction of the recirculation gas flow sensor used in the exhaust gas recirculation system of an internal combustion engine to which the present invention applies.FIG. 15is a partial cross-sectional view showing the second construction of the recirculation gas flow sensor used in the exhaust gas recirculation system of an internal combustion engine to which the present invention applies.

The recirculation gas flow sensor415shown inFIG. 14measures the recirculation gas flow based on the pressure inside the recirculation pipe. A throat is formed on part of the inside wall of the recirculation pipe13b. A low-pressure side pressure sensor152is so installed that the probe is made open at the throat153. A high-pressure side pressure sensor151is so installed that the probe is made open at a position of the recirculation pipe413bwhere throat153is not formed. The inside pressure of the recirculation pipe413bis measured by the low-pressure side pressure sensor152and high-pressure side pressure sensor151. Since the low-pressure side pressure sensor152is installed at the throat153, a ventury effect based on the Bernoulli's theorem can be employed. The exhaust gas recirculation controller420can sense the recirculation gas flow G2inside the recirculation pipe413bfrom the pressure difference between the two pressure sensors151and152. In addition, there is provided a temperature sensor154for sensing the recirculation gas temperature inside the recirculation pipe413b. The exhaust gas recirculation controller420corrects the recirculation gas flow G2obtained from the pressure difference between the pressure sensors151and152, using the recirculation gas temperature sensed by the temperature sensor4154. It is permissible that the recirculation gas flow sensor415contains inside a circuit element for obtaining the recirculation gas flow G2from the pressure difference between the sensors151and152and then correcting it using the recirculation gas temperature sensed by the temperature sensor154and that the recirculation gas flow sensor15itself outputs a sensor signal of the recirculation gas flow G2to the exhaust gas recirculation controller420.

The recirculation gas flow sensor415A shown inFIG. 15measures the recirculation gas flow by a hot-wire type sensor. A recirculation gas flow sensor416is installed on the wall of the recirculation pipe413b. The recirculation gas flow sensor416has a sensing element157for sensing the recirculation gas flow inside the recirculation pipe413B. Current is applied to the sensing element157so that it is heated to a constant temperature. Heating value removed from the sensing element varies in accordance with the recirculation gas flow. If a control is performed so that the temperature of the sensing element157remains constant, then the current through the sensing element157turns to be a signal representing the recirculation gas flow. Since a hot-wire type sensor is employed in the above method, the mass flow, i.e. G2can be measured directly.

The above has explained the construction of the recirculation gas flow sensor415. For the suction flow sensor2, either a sensor type for sensing the pressure as shown inFIG. 14or a hot-wire type as shown inFIG. 15can be employed.

Next, the characteristic of the suction flow control valve45used in the exhaust gas recirculation system of this embodiment of an internal combustion engine is described, usingFIG. 16andFIG. 17.

FIG. 16andFIG. 17shows the characteristic of different drive method of the suction flow control valve used in the exhaust gas recirculation system of an internal combustion engine according to an embodiment of the present invention. InFIG. 16andFIG. 17, the horizontal axis represents the time and vertical axis represents the opening of the suction flow control valve. The valve opening on the vertical axis is shown in percentage, where the maximum opening is 100%.

InFIG. 16, bold line X1shows the characteristic of the valve opening in case an electronic control type throttle actuator is employed as the suction flow control valve45. Bold line X2shows the characteristic of the valve opening in case a negative-pressure type throttle actuator is employed as the suction flow control valve45.

Because no more than two openings, i.e. the valve opening A and fully opened position B can be controlled with the negative-pressure type throttle actuator shown by the bold line X2, it is difficult to control the recirculation gas recirculation ratio by the afore-mentioned feedback control.

On the other hand, when the electronic control type throttle actuator shown by the bold line X1is employed, the valve opening can be controlled steplessly from the opening0to the fully opened position B and accordingly a feedback control can be realized easily. For this reason, it is suitable to employ an electronic control type throttle actuator as the suction flow control valve45used in this embodiment.

Next,FIG. 17shows the characteristic of different drive method of an electronic control type throttle actuator. Bold line Y1represents the response of a throttle actuator in which the throttle valve is driven by a direct-current motor. Bold line Y2represents the response of a throttle actuator in which the throttle valve is driven by a step motor.

Since step motor rotates in accordance with the drive pulse, it can be controlled by an open-loop control. As shown by the bold line Y2, however, the response speed is slower than that of direct-current motor. Generally, the speed of step motor cannot be made faster because of a limitation such as for avoiding an out-of-step operation, and pursuing for higher speed results in larger size of the step motor and consequently higher cost.

On the other hand, a high-speed type small direct-current motor is available. In addition, with the aid of a feedback control of the position, it is very much suitable as a small and high-speed drive source.

In view of the control resolution, the control resolution of a step motor is nothing but the drive step itself, which opposes to the need of higher speed. On the other hand, that of a direct-current motor depends upon the resolution of the position sensor used for the feedback control and so, if a continuous output type sensor like potentiometer is employed, a feedback system having high resolution can easily be constructed.

Accordingly, a direct-current motor is suitable as a drive source of an electronic control type throttle actuator. In case a brushless motor is employed, a similar result as for the direct-current motor is found.

As explained above, according to this embodiment, even if quick change of the exhaust gas recirculation ratio is needed, controlling a control valve having faster response enables to cope with the quick change. On the other hand, if no quick change is needed, controlling a control valve having slower response enables to improve the control accuracy.

Next, the construction and operation of the exhaust gas recirculation system of an internal combustion engine according to another embodiment of the present invention is described, usingFIG. 18toFIG. 20. The construction of an engine system using the exhaust gas recirculation system of this embodiment of an internal combustion engine is the same as shown inFIG. 10.

FIG. 18is a block diagram of the control system of the exhaust gas recirculation system of an internal combustion engine according to another embodiment of the present invention. The same symbol represents the same part or component as inFIG. 10.FIG. 19shows a map of the exhaust gas recirculation system of an internal combustion engine according to another embodiment of the present invention.FIG. 20is a flowchart of the control of the exhaust gas recirculation controller in the exhaust gas recirculation system of an internal combustion engine according to another embodiment of the present invention. The same symbol represent the same part or component inFIG. 12.

As shown inFIG. 18, in this embodiment, a exhaust gas recirculation controller420A is equipped inside with a three-dimensional map420B. The recirculation gas recirculation ratio command value RSET outputted from the ECU421, suction flow signal G1sensed by the suction flow sensor42, recirculation gas flow G2sensed by the recirculation gas flow sensor415, opening signal θTHfrom the suction flow control valve45, and stroke signal STEG from the recirculation gas control valve416are inputted into the exhaust gas recirculation controller420A.

The exhaust gas recirculation controller420A calculates the exhaust gas recirculation ratio R from the suction flow signal G1and recirculation gas flow G2by a formula (G2/(G1+G2)). The exhaust gas recirculation controller420A first outputs an opening control signal CEG to the recirculation gas control valve416and suction flow control signal CTH to the suction flow control valve45, using the map420B, and then outputs an opening control signal CEG to the recirculation gas control valve416and suction flow control signal CTH to the suction flow control valve45, using a feedback control, to control these valves416and45so that the recirculation ratio R of the exhaust gas coincides with the target value RSET.

Next, the content of the three-dimensional map420B is explained, usingFIG. 19. The map420B is a three-dimensional map containing a fresh air passage opening θTH(%), recirculation passage opening STEG (%) and recirculation ratio (%). The fresh air passage opening θTH(%) represents the opening signal θTHin percentage, where the maximum opening is 100% in case the suction flow control valve45is a butterfly type valve and the circulation passage opening STEG (%) represents the stroke signal in percentage, where the maximum stroke of the seat valve is 100% in case the recirculation gas control valve416is a seat type valve.

If the recirculation gas control valve416is a butterfly type valve as in a previous embodiment, the opening signal θTHis shown in percentage, where the maximum opening is 100%, similarly as for the suction flow control valve45.

FIG. 19shows the answer of the afore-mentioned equations (1), (2) and (3) under some operating condition of the engine. In this figure, because of a limitation to indication in the figure, the range of the opening of the suction flow control valve45is 5% to 25% and that of the recirculation gas control valve414is 0% to 60%. The grid points on the three-dimensional map show the relationship between the suction flow control valve45and recirculation gas control valve416that satisfies the recirculation gas recirculation ratio. The three-dimensional map420B has multiple three-dimensional maps corresponding to different operating conditions of the engine. By using one of the maps suitable for the operating condition of the engine, the controller selects a grid point on the map and can control the recirculation gas recirculation ratio by a feedback control.

When the change in the gas recirculation ratio in accordance with the change of the opening of the suction flow control valve5and recirculation gas control valve416shown inFIG. 19is examined, the change ratio of the gas recirculation ratio in accordance with the change of the opening of the suction flow control valve45is greater than that of the suction flow control valve5. In addition, an electronic control type throttle actuator that can operate from the valve opening 0% up to 100% within a length of time of 100 mses or less had been put into practice, and so it can operate in the range from 5% to 25% shown inFIG. 19in about 20 msec. Accordingly, in an embodiment shown inFIG. 19, the response of the suction flow control valve45is faster than that of the recirculation gas control valve416and so, even in case the recirculation gas recirculation ratio command value RSET suddenly changes in pulses, the controller can cope with the change of the command value in pulses if the electronic control type throttle actuator as the suction flow control valve5is mainly operated. That is, it can cope with a temporary variation of the operating condition of the engine.

Next, the control of the exhaust gas recirculation controller420B is described, usingFIG. 20. The controls described below are all performed by the exhaust gas recirculation controller420B. The same step number represents the same processing as inFIG. 12. In this embodiment, the processing in steps s610to s640are added to that inFIG. 12.

On step s500inFIG. 20, the exhaust gas recirculation controller420B calculates the exhaust gas recirculation ratio R from the suction flow signal G1and recirculation gas flow G2by a formula (G2/(G1+G2)).

Next, on step s510, the controller judges whether a variation ΔRSET in the target value RSET of the exhaust gas recirculation ratio R inputted from the ECU421is greater than a predetermined reference value ΔR0. If the variation ΔRSET is greater than the reference value ΔR0, the processing proceeds to step s610and, if not, to step s630. That is, step s510judges whether the target value RSET of the exhaust gas recirculation ratio R has significantly changed or not. When the operating condition of the internal combustion engine has temporarily varied, whether it becomes necessary to quickly change the exhaust gas recirculation ratio so as to decrease toxic material content in the exhaust gas is judged here.

If the variation ΔRSET is greater than the reference value ΔR0, that is, if it becomes necessary to quickly change the exhaust gas recirculation ratio, a target fresh air passage opening θTH(%) is obtained on step s610from the recirculation ratio R corresponding to the recirculation gas recirculation ratio command value RSET and recirculation passage opening STEG (%), using a three-dimensional map420B suitable for the operating condition of the engine at that time.

Then, on step s620, the controller outputs an opening control signal CTH to be used as the target fresh air passage opening θTH(%) to the suction flow control valve5and controls it by an open-loop control so that the opening of the suction flow control valve45coincides with the target fresh air passage opening θTH(%). By controlling the suction flow control valve45to reach the fresh air passage opening θTH(%) by an open-loop control as above, it becomes possible to control it to quickly reach near the target fresh air passage opening θTH(%).

Next, the controller judges whether the exhaust gas recirculation ratio R calculated on step s510is equal to the target value RSET of the exhaust gas recirculation ratio R on step s520.

If the recirculation ratio R is greater than the target value RSET, on step s530, the controller decreases the opening control signal CTH to be outputted to the suction flow control valve45so as to narrow the opening of the suction flow control valve45. And then, the processing returns to step s520and the above processing is repeated until the recirculation ratio R becomes equal to the target value RSET.

On the other hand, if the recirculation ratio R is smaller than the target value RSET, on step s540, the controller increases the opening control signal CTH to be outputted to the suction flow control valve45so as to widen the opening of the suction flow control valve45. And then, the processing returns to step s520and the above processing is repeated until the recirculation ratio R becomes equal to the target value RSET.

A feedback control is performed by repeating the processing of steps s520, s530and s540as explained above until the recirculation ratio R becomes equal to the target value RSET. Since the response of the suction flow control valve45is faster than that of the recirculation gas control valve416as explained above, the exhaust gas recirculation ratio can be changed quickly to a specified target value even if quick change of the exhaust gas recirculation ratio is needed.

On the other hand, if the variation ΔRSET is judged less than the reference value ΔR0on step s510, that is, if the change in the exhaust gas recirculation ratio is not so big, a target fresh air passage opening θTH(%) is obtained on step s630from the recirculation ratio R corresponding to the recirculation gas recirculation ratio command value RSET and recirculation passage opening STEG (%), using a three-dimensional map420B suitable for the operating condition of the engine at that time.

Then, on step s240, the controller outputs an opening control signal CEG to be used as the target recirculation passage opening STEG (%) to the recirculation gas control valve416and controls it by an open-loop control so that the opening of the recirculation gas control valve416coincides with the target recirculation passage opening STEG (%).

Next, the controller judges whether the exhaust gas recirculation ratio R calculated on step s510is equal to the target value RSET of the exhaust gas recirculation ratio R on step s550.

If the recirculation ratio R is greater than the target value RSET, on step s560, the controller decreases the opening control signal CEG to be outputted to the recirculation gas control valve416so as to narrow the opening of the recirculation gas control valve416. And then, the processing returns to step s550and the above processing is repeated until the recirculation ratio R becomes equal to the target value RSET.

On the other hand, if the recirculation ratio R is smaller than the target value RSET, on step s570, the controller increases the opening control signal CEG to be outputted to the recirculation gas control valve416so as to widen the opening of the recirculation gas control valve416. And then, the processing returns to step s550and the above processing is repeated until the recirculation ratio R becomes equal to the target value RSET.

A feedback control is performed by repeating the processing of steps s550, s560and s570as explained above until the recirculation ratio R becomes equal to the target value RSET. In this operation, since the response of the recirculation gas control valve416is slower than that of the suction flow control valve45, much more sensitive opening control is available and so the exhaust gas recirculation ratio can be changed to a specified target value accurately.

In the description above, it is assumed that the response of the suction flow control valve45is faster than that of the recirculation gas control valve416but there may be a case where the response of the recirculation gas control valve416is faster than that of the suction flow control valve45. In a case like the above, the recirculation gas control valve416having faster response shall be controlled first by an open-loop control and then by a feedback control if quick change of the exhaust gas recirculation ratio is needed and, if no quick change is needed, the suction flow control valve5having slower response shall be controlled to improve the control accuracy.

As explained above, according to this embodiment, even if quick change of the exhaust gas recirculation ratio is needed, a control valve having faster response is first controlled by an open-loop control to move the valve quickly near the target opening position and then by a feedback control to converge to the target opening so as to be able to cope with the quick change. On the other hand, if no quick change is needed, controlling a control valve having slower response enables to improve the control accuracy.

The characteristics of the EGR control system of this embodiment as explained above can be summarized as follows:

For an internal combustion engine such as diesel engine, exhaust gas recirculation control is important for purification of the exhaust gas, particularly for reducing the emission of nitrogen oxides. In a conventional exhaust gas recirculation system as disclosed in the Japanese Application Patent Laid-Open Publication Nos. 2003-83034, Japanese Patent 3329711, and Japanese Application Patent Laid-Open Announcement No. 2003-516496, the opening of the exhaust gas recirculation valve is controlled to achieve a specified exhaust gas recirculation ratio.

With a conventional method that control the opening of the exhaust gas recirculation valve, however, there arises a problem that an appropriate control is difficult throughout the operation area of the internal combustion engine particularly when there is a need for quickly changing the exhaust gas recirculation ratio so as to cope with temporary variation of the operating condition and reduce hazardous material content in the exhaust gas.

An object of the present invention is to offer an exhaust gas recirculation system having improved response and accuracy in controlling the exhaust gas recirculation flow of the internal combustion engine.

(1) In order to achieve the above object, according to the present embodiment, there is provided an exhaust gas recirculation system of an internal combustion engine equipped with a recirculation gas control valve that controls the recirculation flow in the exhaust gas recirculation passage of the internal combustion engine and suction control valve that controls the flow in the suction passage of the internal combustion engine; further equipped with a suction flow sensor that senses the flow in the suction passage, recirculation flow sensor that senses the exhaust gas recirculation flow in the exhaust gas recirculation passage, and a controller that controls the suction control valve and/or circulation gas control valve by a feedback control so that the exhaust gas circulation ratio obtained based on the outputs from the suction flow sensor and recirculation flow sensor coincides with a target recirculation ratio.

With the above construction, the response speed and accuracy in controlling the exhaust gas recirculation flow of the internal combustion engine.

(2) In (1) above, it is preferable that the controller controls either the suction control valve or the recirculation gas control valve, whichever having faster response, by a feedback control in case the target recirculation ratio varies suddenly.

(3) In (1) above, it is preferable that the system is equipped with multiple three-dimensional maps to be defined by a combination of the opening of the recirculation gas control valve, that of the suction control valve and recirculation ratio and that the controller selects the three-dimensional map suitable for the operating condition of the internal combustion engine and controls the suction control valve and/or circulation gas control valve so that the exhaust gas circulation ratio obtained based on the outputs from the suction flow sensor and recirculation flow sensor coincides with a target recirculation ratio.

(4) In (2) above, it is preferable that the controller controls either the suction control valve or the recirculation gas control valve, whichever having faster response, in case the target recirculation ratio varies suddenly.

(5) In (1) above, it is preferable that the exhaust gas recirculation flow sensor is a sensor that senses the recirculation flow based on the pressure difference between two or more points in the exhaust gas recirculation passage or a sensor that senses mass flow in the exhaust gas recirculation passage, and the suction flow sensor is a sensor that senses the suction flow based on the pressure difference between two or more points in the suction passage or a sensor that senses mass flow in the suction passage.

(6) In (1) above, it is preferable that the suction control valve is an electronic control type throttle actuator.

According to the present invention, control response increases because the recirculation flow of the exhaust gas is controlled inside the suction passage.