EXHAUST GAS RECIRCULATION VALVE DEVICE

Abstract: An exhaust gas recirculation valve device is prvided with a motor shaft 32, a stepping motor main body 20 driving the motor shaft 32, a valve shaft 6 having a tip 6a functioning as a proximal end which faces one end of the motor shaft 32 and a distal end provided with a valve 8, a spring 10 pushing the valve shaft 6 in a closing direction, and a spring holder 9 retaining the spring 10. In the case that the valve 8 is closed, the tip 6a of the valve shaft 6 and the spring holder 9 are caulked together at a distance between the tip 6a of the valve shaft 6 and the one end of the motor shaft 32 so that a distance L between the facing ends of the motor shaft 32 and the valve shaft 6 is equivalent to a difference between a stroke of the motor shaft 32 of the stepping motor main body 20 and a stroke of the valve on opening.

Description: FIELD OF THE INVENTION The present invention relates to a method for manufacturing an exhaust gas recirculation valve device disposed in an exhaust gas recirculation passage of an internal combustion engine for example of an automobile. BACKGROUND OF THE INVENTION PRIOR ART 1. Fig. 1 is a cross sectional figure showing the internal structure of a conventional exhaust gas recirculation valve device. In the figure, the valve housing 1 has an input port 2 communicating with an exhaust system (not shown) of an engine which is an internal combustion engine, an output port 3 communicating with an air intake system (not shown) of the engine and a passage 4 interposed between the output port 3 and the input port 2. A valve seat 5 is press fitted into the passage 4. 6 is a valve rod passing through a bush 7. A valve 8 is mounted on the lower end of the valve rod 6 to abut or separate with the valve seat 5. 9 is a spring holder pushed upwardly by a coil spring 10. A through hole 11 is formed in the central section of the spring holder 9. A tip 6a of the valve rod 6 is fixed by caulking through the through hole 11. The valve rod 6 and the spring holder 9 are integrated by such a caulking and the valve 8 mounted on the lower end of the valve rod 6 is normally pushed in a closed positioning with respect to the valve seat 5 by the coil spring 10. 12 is a cooling water passage cooling the valve body and the motor to be described below. 20 is a stepping motor main body, and is mounted on the top section of the valve housing 1 so that the axial centers are aligned by a mounting screw 21. 22 is a motor housing, 23 is a motor holder disposed concentrically between the motor housing 22 and the valve housing 1. 24 are bobbins which are wound coils 25.26 and 27 are yokes. A magnetic path is formed through the outer periphery of the yokes 26 and 27. 28 is a terminal which is electrically connected to the coils 25. The terminal 28 and the motor housing 22 form a connector. 29 is a plate which shields the two coil sections magnetically. 30 is a magnet. 31 is a rotor retaining the magnet 30. The rotor 31 has a threaded section 31a threadably attached to a threaded section 32a of the motor shaft 32. 33 is a bushing mounted on the upper end of the rotor 31. 34 is a ball supported by the bushing 33. 35 is an adjustment plate, and 36 is a ball bearing mounted at the lower end of the rotor 31. In the case that the valve housing 1 and the motor housing 22 above are assembled so that the axial centers are aligned by the mounting screw 21, an upper face of the tip 6a of the valve rod 6 near the valve housing 1 is set to oppose a lower face of the motor shaft 32 near the motor housing 22 at a required distance from the tip 6a. The operation of the invention will be described below. Firstly, when the engine is started and the valve is completely closed, the rotor 31 which contains a magnet 30 rotates in a stepwise manner in a direction of valve opening due to a pulsed voltage sent from the control unit (not shown) to the terminal 28 during the valve opening operation. The stepwise rotation is converted into linear motion by the threaded section 31a of the rotor 31 and the threaded section 32a of the motor shaft 32 and the motor shaft 32 displaces in a direction of valve opening (downwardly). As the displacement continues, at the moment when the upper face of the tip 6a of the valve rod 6 near the valve housing 1 touches to the lower face of the motor shaft 32 near the motor housing 22, the valve rod 6 is depressed by the drive force of the motor shaft 32 against the pushing upward force of the spring 10. Also the valve 8 which is mounted on the lower section of the valve rod 6 is lowered and opens with respect to the valve seat 5 and the input port 2 and the output port 3 are connected by the passage 4. During the valve closure operation, the rotor 31 which contains a magnet 30 rotates in a stepwise manner in a direction of valve closure due to a pulsed voltage sent from the control unit (not shown) to the terminal 28 in an operation which is the opposite of the above. The motor shaft 32 displaces in a direction of valve closure (upwardly) due to the rotation. In addition to the rotation, the valve rod 6 is raised by the upward pushing force of the spring 10 and the valve 8 shuts the passage between the valve 8 and the valve seat 5. It is noted that in the above exhaust gas recirculation valve device which uses a stepping motor, when a valve opening step varies, the rate of exhaust gas flow also varies. Therefore, in order to pass a target flow rate of the exhaust gas, the valve opening step must be constant. The valve opening step is determined by a distance L between the tip 6a of the valve rod 6 and the lower face of the motor shaft 32. However, the distance L depends on the accuracy of dimension of parts such as bushing 33 and the ball 34, which are disposed on the upper section of the motor shaft 32. Therefore, the distance L, which is defined between the tip 6a of the valve rod 6 and the lower face of the motor shaft 32, must be adjusted when the valve housing 1 and the motor housing 22 do assembly about every exhaust gas recirculation valve device. According to the conventional adjustment method, firstly a distance L1 between the upper face of the tip 6a of the valve rod 6 and the upper face of the valve housing 1 and a distance L2 between the lower face of the motor shaft 32 and the lower face of the motor housing 22 are measured. In order to determine an appropriate distance L, a stroke of the motor shaft 32 is then considered to calculate an adjustment thickness L3. The adjustment plate 35 having a thickness corresponding to the adjustment thickness L3 is interposed between the both abutting sections of the valve housing 1 and the motor housing 22 to adjust the distance L so as to be constant. In other words, with the conventional adjustment method, since the distance L satisfies an equation of L=(L1-L2) + L3 and the distances L1 and L2 vary in all products, the distance L is adjusted by varying the adjustment thickness L3. However, since the conventional exhaust gas recirculation valve device is constituted as described above, when one kind of metallic plate functioning as the adjustment plate 35 having a thickness of 0.1mm, for example, is prepared, there are occasions when many metallic plates must be interposed there-between. This results in the manufacturing costs being raised. Therefore, in order to reduce the number of metallic plates interposed there-between, various kinds of metallic plate which function as an adjustment plate 35 are prepared with a thickness varying from 0.1mm to 0.5mm in increments of O.lmm. Therefore the use of the plates differs as a result of this processing. As a result, there are problems in time and effort with respect to the stock-control. PRIOR ART 2. JP-A-1997/256916 discloses an exhaust gas recirculation valve including a seat valve for opening/closing an exhaust gas circulation passage, and a valve actuator moving a valve body of the seat valve in a forward or backward direction to open/close the passage above. With the exhaust gas recirculation valve, seat parts with a variety of thicknesses are disposed between a valve shaft of the seat valve and a central piston of the valve actuator. Thus, the axial variations in component dimensions are absorbed in order to control a stroke of the valve on opening. However, with the exhaust gas recirculation valve, the seat parts for adjustment of thicknesses are also used, and the axial variations in component dimensions of the valve shaft and so on, are absorbed in a like manner of the prior art 1. Since the seat parts prepared have a variety of thicknesses, there are problems with respect to increases in manufacturing costs and in the time and effort expended in stock control. US 5,351,935 discloses an exhaust gas recirculation valve device in accordance with the preamble of claim 1 comprising a first shaft, a driving means driving the first shaft, a second shaft having a proximal end which faces one end of the first shaft and a distal end provided with a valve, a pushing means pushing the second shaft in a closing direction and a retaining means retaining the pushing means, wherein the second shaft is caulked to the retaining means and a washer. A structure having these features is also known from DE 19730998 A1. The present invention is made to resolve the problems above, and it is an object of the present invention to provide a method for manufacturing an exhaust gas recirculation valve device controlling a valve open timing with high accuracy. DISCLOSURE OF THE INVENTION The method according to the invention is described in claim 1. Preferred embodiments of the inventive method are described in the further claims. The exhaust gas recirculation valve device produced according to the present invention includes a first shaft arranged reciprocally in an axial direction, a driving means driving the first shaft, a second shaft having a proximal end which faces one end of the first shaft and a distal end provided with a valve, a pushing means pushing the second shaft in a closing direction, and a retaining means retaining the pushing means. Here, in the exhaust recirculation valve, a caulking length of the second shaft is determined to fix the retaining means so that a distance between the facing ends of the first and second shafts is equivalent to a specific value with the valve closure. In this way, it is not necessary to use the adjustment plates or the seat parts which have been used conventionally to control the distance and thus it is possible to simplify stock-control and to reduce the manufacturing costs of the exhaust gas recirculation valve device. It is also possible to perform flexibly stepless control of the distance and thus it is possible to control a valve open timing with high accuracy. with the exhaust gas recirculation valve device, the driving means is a stepping motor. In this way, it is possible to absorb effectively the distance between the facing ends of the first and second shafts due to a single working step of determining the amount of caulking of the second shaft. With the exhaust gas recirculation valve device, the second shaft has a central hole extending from the proximal end to the vicinity of the retaining means. In this way, it is possible to reduce the volume of the caulking fixation section in the second shaft and thus it is possible to shorten the time required in order to fix the second shaft with caulking. With the exhaust gas recirculation valve device, the proximal end of the second shaft includes a caulking fixation section and a height-adjustment section formed at a top of the caulking fixation section and formed its diameter smaller than the caulking fixation section. In this way, it is possible to ensure a sufficient caulking force of the second shaft with respect to the retaining means due to the caulking fixation section. It is also possible to ensure a sufficient height of the proximal end of the second shaft after caulking with respect to the retaining means due to the height-adjustment section and thus it is easy to control the distance above. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross sectional figure showing the internal structure of an exhaust gas recirculation valve device according to the prior art 1. Fig. 2 is a cross sectional figure showing the internal structure of an exhaust gas recirculation valve device according to a first embodiment of the present invention. Fig. 3(A) and Fig. 3(B) are enlarged views showing a caulking section of a valve shaft in the exhaust gas recirculation valve device of FIG. 2, Fig. 3(A) is a plan view, and Fig. 3(B) is a front view. Fig. 4(A) and Fig. 4(B) are enlarged views showing a caulking section of a valve shaft in an exhaust gas recirculation valve device according to a second embodiment of the present invention, Fig. 4(A) is a plan view, and Fig. 4(B) is a front view. Fig. 5 is an enlarged view showing a caulking section of a valve shaft in an exhaust gas recirculation valve device according to a third embodiment of the present invention. PREFERRED EMBODIMENTS OF THE INVENTION In order to describe the invention in greater detail, the preferred embodiments will be outlined below with reference to the accompanying figures. Embodiment 1 Fig. 2 is a cross sectional figure showing the internal structure of an exhaust gas recirculation valve device according to a first embodiment of the present invention. Fig. 3(A) and Fig. 3(B) are enlarged views showing a caulking section of a valve shaft in the exhaust gas recirculation valve device of FIG. 2, Fig. 3(A) is a plan view, and Fig. 3(B) is a front view. Those components of the first embodiment of the present invention which are the same as those of the conventional exhaust gas recirculation valve device as shown in Fig. 1 are denoted by the same reference numerals and further description will be omitted. With the embodiment 1, as shown in Fig. 3(A) and Fig. 3(B), the tip (made in a solid line) 6a, which is a proximal end of the valve rod 6 acting as the second shaft, is formed as a cylindrical solid section. The tip 6a of the valve rod 6 is inserted into the through hole 11 of the spring holder 9. A shoulder section 6b is caulked and fixed to the spring holder 9 with a state that the shoulder section 6b abuts with a lower face 9a of the spring holder 9 which is arranged around the through hole 11. A height of the tip 6a after caulked and fixed to an upper face 9b of the spring holder 9 is set so that the distance L, which is defined between a lower end of the motor shaft 32 acting as the first shaft and an upper end of the tip (made in a broken line) 6a of the valve shaft 6 after caulked, is equivalent to a difference between a stroke of the motor shaft 32 of the stepping motor main body 20 acting as the driving means and a stroke of the valve 8 on opening when the motor housing 22 is mounted on the valve housing 1 so that the axial centers are aligned by the mounting screw 21. In this way, it is not necessary to prepare the adjustment plates 35 or the seat parts, which have been used conventionally for controlling the distance L, and thus it is possible to simplify the stock-control and to reduce the manufacturing costs of the exhaust gas recirculation valve device. It is also possible to perform flexibly stepless control of the distance and thus it is possible to control a valve open timing with ease and high accuracy without using the adjustment plates 35 or the seat parts. As shown above, according to the embodiment 1, it is not necessary to prepare the adjustment plates 35 or the seat parts, which have been used conventionally for controlling the distance L, and thus it is possible to simplify the stock-control and to reduce the manufacturing costs of the exhaust gas recirculation valve device. According to the embodiment 1, if the variations in dimension of the parts and the stroke of the driving means occur, it is not necessary to use the adjustment plates 35 or the seat parts and it is possible to perform flexibly stepless control of the distance L. In this way, it is possible to control a valve open timing with high accuracy and thus is it possible to keep the valve opening step constant. With the embodiment 1, the stepping motor is taken as an example of the driving means. Alternatively, a DC motor or a variety of pushing means may be used as the driving means. Embodiment 2 Fig. 4(A) and Fig. 4(B) are enlarged views showing a caulking section of a valve shaft in an exhaust gas recirculation valve device according to a second embodiment of the present invention, Fig. 4(A) is a plan view, and Fig. 4(B) is a front view. The embodiment 2 is characterized in that a central hole 6c is formed at the tip 6a of the valve rod 6. In the case that the height of the tip 6a after caulked is set to a minimum level for example, it is necessary to caulk the tip 6a more which is subjected to a caulking processing and thus to take a long time for the caulking processing. Therefore, it is possible to shorten the time for the caulking processing considerably due to the central hole 6c by reducing the volume of the tip 6a. The central hole 6c extends from the upper end of the tip 6a to the vicinity of the spring holder 9. The size and length of the central hole 6c are determined as appropriate by making a comparison between a point in that it is necessary to ensure a sufficient caulking force applied to the spring holder 9 due to the caulking processing with respect to the tip 6a of the valve rod 6 and the other point in that it is necessary to ensure a sufficient height of the tip 6a with respect to the upper face 9b of the spring holder 9 after caulking in order to keep the distance L constant. As shown above, according to the embodiment 2, the central hole 6c is arranged at the tip 6a of the valve rod 6 and thus it is possible to have the same effect as the embodiment 1. It is also possible to shorten extensively the time for the caulking processing by reducing the volume of the tip 6a. Embodiment 3 Fig. 5 is an enlarged view showing a caulking section of a valve shaft in an exhaust gas recirculation valve device according to a third embodiment of the present invention. The embodiment 3 is characterized in that the tip 6a of the valve rod 6 includes a caulking fixation section 6d having an inverse-truncated conical shape and a height-adjustment section 6e formed at a top of the caulking fixation section and formed its diameter smaller than the caulking fixation section. In the case that the height of the tip 6a after being caulked is set to a maximum level for example, the length of the tip 6a which is subjected to a caulking processing is short and thus it is difficult to ensure a sufficient caulking force. In this way, the caulking fixation section 6d for ensuring the sufficient caulking force with a slight length subjected to the caulking processing and the height-adjustment section 6e for ensuring a sufficient height of the tip 6a after caulked are stacked. In order to caulk and fix the tip 6a to the spring holder 9, a jig is rotated about a vertex of the inverse-truncated conical shape on an outermost periphery of the conical shape and thus it is possible to perform effectively a working of the caulking processing. As shown above, according to the embodiment 3, it is possible to have the same effect as the embodiment 1. It is possible to ensure a sufficient caulking force applied to the spring holder 9 due to the tip 6a of the valve rod 6 and to ensure the sufficient height of the tip 6a with respect to the upper face 9b of the spring holder 9 after caulking. INDUSTRIAL APPLICATION As shown above, with the exhaust gas recirculation valve device according to the present invention, a length of the second shaft subjected to a caulking processing with respect to the retaining means is determined so that a distance between the facing ends of the first and second shafts is equivalent to a specific value with the valve closure. In this way, it is not necessary to prepare the adjustment plates or the seat parts which have been used conventionally to control the distance and thus it is possible to simplify the stock-control and to reduce the manufacturing costs of the exhaust gas recirculation valve device. It is also possible to perform flexibly stepless control of the distance and thus it is possible to control a valve open timing with high accuracy.

Claims: Method for manufacturing an exhaust gas recirculation valve device comprising a first shaft (32) arranged reciprocally in an axial direction, a driving means (20) driving the first shaft, a second shaft (6) having a proximal end which faces one end of the first shaft (32) and a distal end provided with a valve (8), a pushing means (10) pushing the second shaft (6) in a closing direction and a retaining means (9) retaining the pushing means (10), wherein the second shaft (6) is subjected to a caulking process with respect to the retaining means (9), characterized in that a length of the second shaft (6) is determined by a caulking process alone such that adjustment plates are not necessary to control the distance between the facing ends of the first (32) and second shafts (9), in order to control a valve closure timing. A method according to claim 1, wherein the driving means is a stepping motor (20). A method according to claims 1 or 2, wherein the second shaft (6) has a central hole (6c) extending from the proximal end to the vicinity of the retaining means (9). A method according to claim 1, wherein the proximal end of the second shaft (6) includes a caulking fixation section (6d) having an inverse-truncated conical shape and a height-adjustment section (6e) formed at a bottom of the caulking fixation section (6d) and formed its diameter smaller than the caulking fixation section (6d). A method according to claim 2, wherein the proximal end of the second shaft (6) includes a caulking fixation section (6d) and a height-adjustment section (6e) formed at a bottom of the caulking fixation section (6d) and formed its diameter smaller than the caulking fixation section (6d).

Inventors: IKAI TAKESHI, KATO YASUHIKO, YOKOYAMA HISASHI, IKAI, TAKESHI, KATO, YASUHIKO, YOKOYAMA, HISASHI
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1999
Main classification: F16K31
IPC codes: F16K31, F02M25