Abstract:
An internal-gear pump with a partition plate, comprising: an arcuate chamfer formed at an inner edge of an end face of the partition plate rotationally opposing an inner gear of the pump and having a curvature at least greater than that of tooth tip edges of the inner gear.

Description:
BACKGROUND OF THE INVENTION 
     (i) Field of the Invention 
     This invention relates to an internal or inscribing type gear pump with a partition plate, which has improved durability at high speed rotation. 
     (ii) Description of the Prior Art 
     The internal gear pumps which are incorporated into fluid couplings of motor vehicles for supply of pressurized oil receive strong impacts at the tooth tips of an inner gear due to interference impacts which take place between the tooth tips and an inner edge of an end face of the partition plate as a result of abrasive wear of rotational shafts or the like, lowering durability considerably, particularly in the case of high speed engines which are widely used these days. In order to avoid this problem, it has been the general practice to provide a greater clearance at the tooth top, but such a measure naturally invites drops in pumping capacity. If the tooth width is increased as a countermeasure, the pump requires a greater driving torque which is disadvantageous in view of the uneconomical mileage which would result. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an internal-gear pump with a partition plate, which is constructed to endure sufficiently the impact forces which may be caused by interference impacts between edge portions of the partition plate and tooth tips of the gear after high speed operation over a long period of time. 
     According to the present invention, there is provided an internal-gear pump with a partition plate, comprising: 
     an arcuate chamfer formed at an inner edge of an end face of the partition plate rotationally opposing an inner gear of the pump and having a curvature at least greater than that of tooth tip edges of the inner gear. 
     The internal-gear pump with the above-described construction according to the invention has a number of advantageous effects as follows. 
     (a) The internal-gear pump of the invention can eliminate the problem of the conventional gear type oil pumps which are incorporated into automatic transmissions of motor vehicles with high-speed engines, i.e., the problem that the function of an automatic transmission is lowered by degradation of the pump function. 
     (b) The measure of increasing the clearance at the gear tooth top for prevention of interference impacts between a partition plate and tooth tips is unnecessary to avoid degradation in the performance quality of the pump. 
     (c) The pump of the invention avoids the problem of uneconomical mileage as caused by an increase in pump driving torque when a drop in pumping capacity due to an increase of the tooth top clearance is compensated for by an increase of tooth width. 
     (d) The partition plate is same as its conventional counterpart in fundamental shape and needs only a localized chamfering operation in the machining stage, so that the present invention can lengthen the service life of the pump to a significant degree, without incurring much expense. 
     The above and other objects, features and advantages of the invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings which show by way of example preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a schematic plan view of an internal-gear pump according to the invention, showing its major component parts; 
     FIG. 2 is a sectional view taken on line II--II of FIG. 1; 
     FIG. 3 is an enlarged fragmentary view of a conventional internal-gear pump showing the position where a rotating gear approaches a partition plate; 
     FIGS. 4 and 5 are views similar to FIG. 3 but showing the internal-gear pump according to the invention; 
     FIG. 6 is a vertical section of an automatic transmission of a motor vehicle incorporating the gear pump of the invention; and 
     FIG. 7 is a schematic plan view of the gear-pump mounted in position on the transmission, with one side of the pump housing being removed for the convenience of illustration. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is illustrated an internal-gear pump with a partition plate, embodying the present invention, in which denoted at 1 is an inner wall of the pump housing, at 2 an inner gear, at 16 an outer gear, at 3 a rotational shaft of the inner gear 2, at 4 a partition plate interposed between inner and outer gears, at 5 a fluid inlet and at 6 a fluid outlet. 
     In the gear pump of the above-described construction, a fluid which is confined in spaces B between the partition plate 4 and inner gear 2 is quickly moved from the inlet 5 to the outlet 6 when the inner and outer gears form only a small gap with the inner and outer curved surfaces of the partition plate 4 (in the form of a curved plate with a crescent shape in plan view), thereby sending the fluid to the outlet 6 under pressure. The clearance C (tooth top clearance) between the inner gear 2 and partition plate 4 is required to be as small as possible without causing contact between the tooth top and partition plate 4, for the purpose of maintaining a high pumping capacity by holding to a minimum the amount of fluid which tends to leak out of the spaces B upon pressurization and to flow back toward the inlet 5. 
     However, a gear pump with a partition plate, which is driven from an engine to supply a high oil pressure as an operating medium to an automatic transmission of a motor vehicle, undergoes accelerating abrasive wear especially in its rotational shaft portion in high speed type engines. Therefore, coupled with abnormal vibrations in some cases, the tooth top clearance which is initially set at a small value approaches zero and finally an interference gap is formed between the tip ends of teeth of the inner gear 2 and an inner edge portion of the end face of the partition plate 4 which rotationally opposes the inner gear 2, with the possibility of destroying the gear by impact in a worse case. 
     The partition plate which is used in the conventional internal-gear pump has its end edge portion 4a formed in an acute angle almost a right angle, as shown in FIG. 3 which illustrates the area around the fluid inlet 5 of the pump on an enlarged scale. Accordingly, if interference impacts occur between the tips of the gear teeth and the end edge portion 4a, an extremely large impact stress is imposed per unit area of a tip end of each gear tooth since the contact area is very small and the gear is rotated at a high speed, giving rise to a problem of safety. 
     In the first embodiment illustrated for the internal-gear pump with a partition plate according to present invention, this problem is solved by chamfering the partition plate 4 at the inner edge of its end face which rotationally opposes the inner gear 2, arcuately in a concave shape as indicated at 4b of FIG. 4. By chamfering the inner edge of the partition plate 4 in this manner, the contact area between a tooth tip and the inner edge portion of the partition plate is suitably broadened even in the case of an interference impact therebetween, as compared with the partition plate 4 shown in FIG. 3. Consequently, the impact force per unit area of the contacting portion at the tip of each gear tooth is reduced to a considerable degree, precluding the possibility of gear destruction. 
     As indicated in FIG. 4, each tooth on the inner gear 2 has a tip portion defined by curved edges 18 and 20 with a radius of curvature &#34;R&#39;&#34; and a top face 22. The curvature of the arc R of the concavely chamfered surface is preferred to be at least two times greater than that (R&#39;) of the tip edge of the gear tooth to provide a broad contact area. However, a curvature which is more than ten and several times greater than that of the tooth tip is undesirable since it would unduly broaden the tooth top clearance C over a substantial distance along the inner side of the partition plate 4. 
     Referring to FIG. 5, there is shown a second embodiment of the invention, in which the inner edge portion 4c of the partition plate 4 is arcuately rounded off. In this case, the curvature of the arc is preferred to be more than two times greater than that of the tooth tip. 
     The chamfered surface at the inner edge of the partition plate is not necessarily restricted to the above-described shapes and may consist of a combination of a flat surface and a curved surface or a combination of two or more curved surfaces of different curvatures. What is important here is to shape the inner edge of the partition plate such that, when the gear and partition plate are forced into collision against each other, the contact surfaces of the two parts are gradually drawn nearer and engaged with each other over relatively broad areas. 
     Illustrated in FIGS. 6 and 7 is an example of a vehicular automatic transmission incorporating the internal-gear pump with a partition plate according to the present invention. In these figures, denoted at 8 is housing of the automatic transmission, at 9 is a fluid coupling, at 10 is a transmission gear mechanism, at 11 is an input shaft of the transmission, and at 12 is a pump gear, and at 13 and 14 are split type pump housings.