Electric air flow control device for internal combustion engines

Abstract

The purpose of this invention is to achieve an electric air flow control device comprising a motor rotor bearing structure having excellent wear resistance even with loads from striking caused by a high vibrational environment specific to an internal combustion engine. A cylindrical sintered metal slide bearing is used in at least one of a front bearing (16) and a rear bearing (17) that support a rotor shaft (14) of a motor (3) that is the rotary control drive source of a throttle valve (7) that controls the intake air flow to an internal combustion engine, and the bearing design is such that the relationship of the radial crushing strength and the compressive deformation rate of the cylindrical sintered metal bearing has the mechanical properties of a maximum radial crushing strength of 230 N/mm2 or greater and a maximum compressive deformation rate of 3.5% or greater at the maximum radial crushing strength.

Claims

1. An electric air flow control device for an internal combustion engine comprising: a throttle valve mechanism for directly controlling quantity of intake air to be supplied to an internal combustion engine; and a motor configured to operate as a rotary control drive source for the throttle valve mechanism, the motor comprising: a motor rotor shaft; and at least one bearing for supporting the motor rotor shaft, wherein the at least one bearing is a cylindrical shaped bearing made of a sintered metal and has a mechanical property of a maximum radial crushing strength of 230 N/mm.sup.2 or more and a compressive deformation rate of 3.5% or more at a state corresponding to the maximum radial crushing strength in a relationship between the radial crushing strength and the compressive deformation rate obtained from a compression strength evaluation of an actual body of the at least one bearing.

2. The electric air flow control device for an internal combustion engine according to claim 1, wherein the bearing made of a sintered metal includes a copper alloy system containing at least Cu, Sn and Ni.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a cross-section structural view of an electric air flow control device showing an embodiment of the present invention.

(2) FIG. 2 is an exploded side view illustrating the engagement of gear members between a motor and a throttle valve shaft

(3) FIG. 3 is a characteristic diagram comparison of a specific wear rate property for each bearing material specification in the evaluation of the rotational slide wear with static bearing load application.

(4) FIG. 4 is an explanatory photographic image showing an example of a damage state after the evaluation of a Cu—Sn-based bearing material in the evaluation of rotational slide wear with dynamic bearing load application.

(5) FIG. 5 is an explanatory photographic image showing an example of a damage state after the evaluation of a Cu—Sn—Ni-based bearing material in the evaluation of rotational slide wear with dynamic bearing load application.

(6) FIG. 6 is a characteristic diagram showing the property comparison between the radial crushing strength and the compressive deformation rate, obtained at the time of the compression evaluation of a cylindrical actual body bearing material.

(7) FIG. 7 is an explanatory photographic image showing a crack occurrence state seen at the time of the compression evaluation.

(8) FIG. 8 is an explanatory view showing the superiority determination in a wear resistance evaluation of a cylindrical actual body bearing material on the matrix of the radial crushing strength and compressive deformation rate.

DESCRIPTION OF EMBODIMENTS

(9) FIG. 1 is an overall cross-sectional view illustrating an embodiment of an electric air flow control device according to the present invention and FIG. 2 is an exploded side view viewed from the gear side of the various types of drive gear.

(10) In general, a body 1 that is often made of die-cast aluminum is integrally molded with an intake air passage 2 and a motor housing 4 for storing a motor 3.

(11) In the intake air passage 2 of the body 1, a throttle valve shaft 5 extending across the passage is arranged and supported by bearing structures 6a and 6b for keeping a stable rotary motion of the throttle valve shaft 5 (in the present embodiment, though needle-structured rolling bearings are shown, they may be ball-structured rolling bearings or simple cylindrical shaped slide bearings). Further, on the part of the throttle valve shaft 5 corresponding to the intake air passage 2, a throttle valve 7 for controlling to optimize the quantity of intake air to be sent to the internal combustion engine is integrated by fastening screws 8.

(12) An integrally molded metal, plate 9a of a throttle valve gear 9 is integrated with a step section 5a of the throttle valve shaft 5 with nuts 10. The throttle valve gear 9 is engaged with a small-diameter gear section 13a of an intermediate gear 13 arranged so as to be rotatable relative to an intermediate shaft 12 fixed into a hole 11 of the body 1 by press fitting.

(13) The motor 3 as a drive source for controlling the open and close motion of the throttle valve 7 is composed of a rotor 14a integrated with a rotor shaft 14, a magnet 15, a front bearing 16 and a rear bearing 17 for supporting the rotor shaft 14 stably, a case member 18 supporting and fixing various components and other members, and the motor 3 is fixed and housed in the motor housing 4 by fastening motor fixing screws 19.

(14) A small-diameter driving gear 20 is integrated with an end of the rotor shaft 14 of the motor 3 and engaged with a large-diameter gear section 13b of the intermediate gear 13.

(15) The rotary motion of the motor 3 controlled as needed is transmitted through a double reduction gear mechanism constituted by engagement of the drive gear 20 and the large-diameter gear section 13b of the intermediate gear 13 and engagement of the small-diameter gear section 13a of the intermediate gear 13 and the throttle valve gear 9, and the rotary motion results in the open and close motion of the intake air passage 2 of the throttle valve 7 finally.

(16) In a space between the rear surface of the throttle valve gear 9 and the body 1, a torsion spring 21 is fixed by being sandwiched and respective ends of the torsion spring 21 are engaged with the body 1 and the throttle valve gear 9, and the throttle valve shaft 5 is preloaded in the rotating direction relative to the body 1.

(17) An air flow control device is usually integrated with an intake pipe at the aggregation part of intake pipes diverging into respective cylinders of the internal combustion engine and is subjected to a high temperature and a high vibration specific to internal combustion engines; however the motor can be subjected to a severer vibrational environment than the body 1 fixed directly to the intake pipe in consideration of the usual overhung fixing structure of the motor 1 for the open and close control drive of the throttle valve 7, fixed and housed in the motor housing 4.

(18) In the embodiment in FIG. 1, as bearings supporting the rotor shaft 14 of the motor 3, a rolling bearing constituted by inner and outer rings and steel balls is shown as a front bearing 16 and a simple cylindrical slide bearing is shown as a rear bearing 17; however, even if both are slide bearing structures, no problem occurs with the structure of the product.

(19) The loads that these bearings receive are roughly divided into a general rotational sliding load from the rotor shaft 14 of the motor 3 and a collision (striking) load from the rotor shaft 14, caused from transmission of vibrational environment which the air flow control device receives from the internal combustion engine.

(20) In order to ensure high reliability of the motor 3 as a drive source of the throttle valve 7 controlling directly the air flow, enhancement of proof strength of the bearing structure supporting the rotor shaft 14 of the motor 3 is an important point, and improvement of the wear resistance of the simple cylindrical slide bearing shown as the rear bearing 17 in the embodiment in FIG. 1 is important. In particular, a wear resistance enhancement design against the striking load caused from a vibrational environment of the internal combustion engine decides the quality of the products.

(21) With regard to a slide bearing made of a sintered metal, even if the strength of the base material of the sintered metal is the same, impregnation design, which is a feature of sintered metal, namely, an optimization design of the type of oil for impregnation into holes can improve the lubrication performance, and thus, the enhancement of wear resistance can be achieved (refer to FIG. 3) in a general rotational sliding load environment. However, the effects of impregnating oil design for enhancing the resistance to striking wear caused by a collision load are close to nothing, and thus, the enhancement of the strength of base material of the sintered metal itself is essential.

(22) Further, as a feature of damage forms resulting from a striking phenomenon caused by a collision load, there is a problem of chip occurrence in the neighborhood of the corner part of both end surfaces of the bearing inner circumferential surface as well as simple wear on the bearing inner circumferential surface, and with regard to the design of the base material of sintered metal itself, improvement of ductility (toughness) that is an index of brittleness of the design material is an extremely important design factor as well as improvement of the breaking strength (radial crushing strength).

(23) As evaluation example of various properties of the materials of the bearing (cylindrical rear bearing 17 made of sintered metal) for the rotor shaft 14 of the motor 3 described above employed according to the present invention and conventional bearing materials, the comparison of wear resistance of the designed component materials shown in Table 1 will be described.

(24) TABLE-US-00001 TABLE 1 CHEMICAL COMPONENT % (CATALOG VALUE) ALLOY MATERIAL Cu Sn Ni C MoS2 Cu—Sn SYSTEM REMAINDER 8-11 — — 4-7 Cu—Sn—Ni SYSTEM REMAINDER 9-12 2-4 1-3 —

(25) FIG. 3 shows the relationship between the bearing load and the ratio (ratio indicated on the assumption that the specific wear rate at the time of the minimum bearing load evaluation of the Cu—Sn-based material shown as the specific wear rate property 31 is 1.0) of the specific wear rate (wear volume during a unit distance slide) as an example of wear property evaluation of a common rotational slide of two materials of a Cu—Sn system and a Cu—Sn—Ni system. The Cu—Sn—Ni-based specific wear rate property 32 for which he optimization of alloy components has been considered and is shown by a broken line can achieve an excellent property that restrains the wear amount up to the high PV value level compared with the Cu—Sn-based specific wear rate property 31 shown by an alternate long and short dash line. Further, depending on the optimization of lubricating oil for impregnation into holes particular to a sintered metal, the specific wear rate property 23 which is more excellent despite the same designed alloy material and is shown by a continuous line also can be achieved.

(26) In Table 2, as a maximum bearing load environment of a bearing on an optional internal combustion engine, the ratios of specific wear rate are compared at a PV value of 4.0 in FIG. 3. The wear amount of a Cu—Sn—Ni-based material can reduce to approximately 27% of the wear amount of a Cu—Sn-based material, and further, a Cu—Sn—Ni-based material to which the optimization of impregnating oil is applied can reduce to approximately 17%.

(27) TABLE-US-00002 TABLE 2 RATIO OF SPECIFIC WEAR RATE AT ASSUMED IMPREGNATING MAXIMUM BEARING COM- ALLOY OIL LOAD (PV PAR- MATERIAL TYPE INDEX VALUE = 4) ISON Cu—Sn FLUORINE SYSTEM 6.70 1.00 SYSTEM (VISCOSITY INDEX: LOW) Cu—Sn—Ni FLUORINE SYSTEM 1.83 0.27 SYSTEM (VISCOSITY INDEX: LOW) FLUORINE SYSTEM 1.17 0.17 (VISCOSITY INDEX: HIGH)

(28) Next, as the limit of bearing wear amount required based on the guaranteed life of the bearing on the vehicle, the PV values that are bearing loads when the ratio of the specific wear rate reaches 3.0 in FIG. 3 are compared in Table 3.

(29) The Cu—Sn—Ni-based material can endure a bearing load 1.85 times greater than the load that the Cu—Sn-based material can endure, and further the Cu—Sn—Ni-based material with the impregnating of optimized can endure a high bearing load 2.72 times greater than the load.

(30) TABLE-US-00003 TABLE 3 BEARING LOAD AT ASSUMED LIMIT OF BEARING WEAR IMPREGNATING AMOUNT (RATIO COM- ALLOY OIL OF SPECIFIC WEAR PAR- MATERIAL TYPE RATE = 3) ISON Cu—Sn FLUORINE SYSTEM 3.05 1.00 SYSTEM (VISCOSITY INDEX: LOW) Cu—Sn—Ni FLUORINE SYSTEM 5.63 1.85 SYSTEM (VISCOSITY INDEX: LOW) FLUORINE SYSTEM 8.30 2.72 (VISCOSITY INDEX: HIGH)

(31) The properties shown in FIG. 3, and Tables 2 and 3 described above are the comparison of specific wear rate obtained by the rotational slide evaluation under a static pressure load environment. Fluctuating loads caused by vibrations of internal combustion engines themselves or the like are applied to many products mounted on the internal combustion engines, including an electric air flow control device according to the present invention. That is, impulsive striking loads caused by vibrations during a rotational slide movement are applied and thus enhancement of proof strength under a complex environment in consideration of the striking load is important, as well as wear resistance against a general rotational slide.

(32) Table 4 shows the comparison of wear amount on the bearing inner circumferential surface obtained by the forward-reverse rotational slide evaluation under the vibrational environment of the actual machine. The vibration condition is in accordance with an optional specification proposed by a customer. This endurance specification, in view of the parts sharing, includes specification environments of both of the gasoline engine and the diesel engine, and the sine wave excitation and the random wave excitation of the combined evaluation of a vibration acceleration close to the actual driving condition are compared.

(33) TABLE-US-00004 TABLE 4 ALLOY VIBRATION EVALUATION INNER DIAMETER MATERIAL CONDITION TIME h WEAR AMOUNT μm REMARKS Cu—Sn SINE WAVE 600 573 APPROX. 41 SYSTEM EXCITATION TIMES WEAR RANDOM WAVE 1360 1873 APPROX. 99 EXCITATION TIMES WEAR Cu—Sn—Ni SINE WAVE 600 14 — SYSTEM EXCITATION RANDOM WAVE 1360 19 — EXCITATION

(34) As a wear amount of the bearing inner diameter, the dimensional change of the inner diameter relative to the initial situation is shown, and in both cases of the sine wave and the random wave, the Cu—Sn-based material exhibits a wear amount which is approximately 41-99 times greater than that of the Cu—Sn—Ni-based material.

(35) Enlarged photographic images of the vicinity of the inner circumferential part facing the rotating shaft after the completion of the evaluation for a Cu—Sn-based material is shown in FIG. 4 and for a Cu—Sn—Ni-based material in FIG. 5. What should be noted is the chips seen on nearly entire circumference of an inner diameter corner part 42 as well as dimensional enlargement of an inner diameter part 41 of the Cu—Sn-based material shown in FIG. 4. There is no chip occurrence on a corner part 52 of the inner diameter of the Cu—Sn—Ni-based material shown in FIG. 5, and thus it can be said that the Cu—Sn-based material is apparently inferior in ductility and exhibits brittleness (fragility) compared with the Cu—Sn—Ni-based material having an excellent striking wear resistance.

(36) For a cylindrical product made of sintered metal or the like, the radial crushing strength which is stipulated in Japanese Industrial Standards and is calculated according to the following equation is commonly used for comparison for the evaluation of actual body strength, and examples of the property evaluation of radial crushing strength of products in the same shape corresponding to various design materials are shown in FIG. 6.

(37) $\mathrm{Radial}\mathrm{crushing}\mathrm{strength}\text{:}K=\frac{F\left(D-e\right)}{L.Math.e^2}\left(N\text{/}{\mathrm{mm}}^2\right)$

(38) wherein F: Applied load in compression direction (N) L: Length of hollow cylinder (mm) D: Outer diameter of hollow cylinder (mm) e: Wall pressure of hollow cylinder (mm)

(39) The vertical axis indicates the radial crushing strength calculated based on a cylindrical compression load, and the horizontal axis indicates the compressive deformation rate during the compression load application as defined above.

(40) In FIG, 6, the property examples 61 and 62 denote Cu—Sr-based materials and the property examples 63 to 66 denote Cu—Sn—Ni-based materials. Any property has a similar tendency to the general compression strength property of metals in which as the radial crushing strength (applied load in the compression direction) increases, the deformation amount in the compression direction increases.

(41) At the maximum values of radial crushing strength 61a to 66a of respective properties, cracks occur at the portions having the maximum tensile stress on the cylindrical outer circumferential horizontal parts and the property begins to decline. With further application of the load, the declination of the property becomes once smaller; however at the inflection points 61b to 66b of respective properties, cracks are added at the portions having the maximum tensile stress on the cylindrical inner circumferential vertical parts, and after this, the property exhibits a rapid declination. (An example of an actual body external appearance after the completion of radial crushing strength property evaluation is shown in FIG. 7 for reference. Signs 71a and 71b denote cracks that occurred when the maximum points of radial crushing strength 61a to 66a were reached, and signs 72a and 72b denote cracks that occurred when radial crushing strength points 61b to 66b were reached.)

(42) When the maximum values of radial crushing strength 61a to 66a of respective property examples 61 to 66 is noticed, it is understood that the radial crushing strength of the vertical axis corresponds to a material strength index value for determining a general rotational slide wear property of a design material, and the compressive deformation rate of the horizontal axis corresponds to a ductility index value for determining proof strength against a striking load caused by dynamic load fluctuation such as a vibration.

(43) The specimens in Table 4 (inner diameter wear amount comparison) FIGS. 4 and 5 (both are enlarged photographic images after the completion of the evaluation) shown as specific evaluation examples made in consideration of a dynamic striking load such as a vibration have the same specification as specimens of the property examples 61 and 63 shown in the radial crushing strength property in FIG. 6.

(44) The material of the property example 63 exhibits excellent wear resistance and improvement of chip resistance without enlargement of the inner diameter or falling-off of the corner part. The property example 62 which has the same material system as the property example 61 and whose radial crushing strength is attempted to improve (the maximum value of radial crushing strength 62a is equivalent to the maximum value 63a of the property example 63) is also evaluated by taking into account a dynamic striking load such as a vibration similarly to the above-described manner but does riot exhibit an excellent wear resistance or enhancement of the chip resistance seen in the material of the property example 63.

(45) By enhancing the radial crushing strength which is the material strength index value of a cylindrical member, proof strength can be enhanced against general rotational slide wear; however it is understood that a design for improving the compressive deformation rate as a ductility index of design material is more important for a striking phenomenon caused by a vibrational load environment such as an internal combustion engine, as well as enhancement of the radial crushing strength.

(46) Although the property example 62 of the Cu—Sn-based material shown in FIG. 6 is designed to have the same component as the property example 61, the sintered density design value of the property example 61 is smaller than that of the property example 62. Further the property examples 64 to 66 of the Cu—Sn—Ni-based materials are also designed to have the same component as the property example 63 but the sintered density design value has the following relationship: property example 63<property example 64<property example 65<property example 66.

(47) The resistance property to the wear of general rotational slide at the time of static load application to specimens of the property examples 61 to 66 of the radial crushing strength property in FIG. 6 and the striking wear resistance property at the time of dynamic load application under an exciting environment are arranged in Table 5 for each of the radial crushing strength and compressive deformation rate by using four kinds of judgment signs x, Δ, □ and ∘. FIG. 9 shows the relationship of the maximum values of radial crushing strength, the compressive deformation rates at the maximum radial crushing strength, and the overall judgment signs of each specimen shown in Table 5.

(48) The materials with signs ∘ denoting the judgment of adoptability exist in the area of the high radial crushing strength and high compressive deformation rate. On the other hand, the material with the sign Δ denoting the judgment of unadoptability because the resistance is insufficient to the wear of a general rotational slide with a static load and the resistance to striking wear from a dynamic load such as a vibration is also greatly inferior exists in the area of the low radial crushing strength and low compressive deformation rate.

(49) Further, the material with the sign □ having a radial crushing strength equivalent to the lowest radial crushing strength of a material with the sign ∘ denoting adoptability in the overall judgment and however having a small compressive deformation rate satisfies the resistance to the wear of a general rotational slide with a static load; however the employment of this material is not favorable because the resistance to striking wear from dynamic load such as a vibration shows a considerably inferior damage situation similarly to the material with the overall judgment sign Δ.

(50) TABLE-US-00005 TABLE 5 JUDGMENT OF ACTUAL BODY WEAR MAXIMUM RESISTANCE RADIAL ROTATIONAL SLIDE CRUSHING COMPRESSIVE WEAR STRIKING WEAR STRENGTH DEFORMATION (STATIC LOAD (DYNAMIC LOAD OVERALL N/mm2 RATE % APPLICATION) APPLICATION) JUDGMENT 191 2.0 Δ x Δ (MEDIUM WEAR) (EXCESSIVE WEAR, UNADOPTABLE LARGE CHIP) 249 2.7 ∘ x □ (MILD WEAR) (EXCESSIVE WEAR, UNADOPTABLE MEDIUM CHIP) 259 4.2 ∘ ∘ ∘ (MILD WEAR) (MILD WEAR, NO ADOPTABLE CHIP) 300 4.4 ∘ ∘ ∘ (MILD WEAR) (MILD WEAR, NO ADOPTABLE CHIP) 334 4.9 ∘ ∘ ∘ (MILD WEAR) (MILD WEAR, NO ADOPTABLE CHIP) 376 5.3 ∘ ∘ ∘ (MILD WEAR) (MILD WEAR, NO ADOPTABLE CHIP)

(51) Consequently, to achieve an electric air flow control device with high reliability, optimization of the radial crushing strength which is the index of base material strength and the compressive deformation rate which is the index of ductility is extremely important.

REFERENCE SIGNS LIST

(52) 1 body 2 intake air passage 3 motor 4 motor housing 5 throttle salve shaft 6a, 6b bearing structure 7 throttle valve 8 screw 9 throttle valve gear 9a metal plate 10 nut 11 hole 12 intermediate shaft 13 intermediate gear 13a small-diameter gear section 13b large-diameter gear section 14 rotor shaft 14a rotor 15 magnet 16 front bearing 17 rear bearing 18 case member 19 motor fixing screw 20 drive gear 21 torsion spring 31-33 specific wear rate property 41 inner diameter part 42, 52 inner diameter corner part 61-66 example of radial crushing strength property 61a-66a maximum value of radial crushing strength 61b-66b inflection point of radial crushing strength 71a, 71b crack on outer circumferential part 72a, 72b crack on inner circumferential part 71, 72 example of radial crushing strength property dependent on density