Plunger driving structure

An oil pump comprises a rotation shaft having an eccentric part, a needle roller bearing supporting the eccentric part of the rotation shaft, a tappet abutting on the outer ring of the needle roller bearing and arranged in a radial manner, a plunger arranged on the tappet and reciprocated by the rotation of the rotation shaft, and a balancer arranged on both ends of the eccentric part. The balancer has a large diameter part and a small diameter part and when the large diameter part is arranged so as to face the direction opposite to an eccentric direction, the rolling space of a roller can be projected from an axial direction through the balancer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plunger driving structure used in a fuel pump of a diesel engine, an oil pump of a brake system and the like.

2. Description of the Background Art

Conventionally, an oil pump used in a car brake system and the like has been disclosed in Laid-open Japanese utility model publication No. 5-83372. As shown inFIG. 9, an oil pump1according to the document comprises a rotation shaft2having an eccentric part2a, a ball bearing3supporting the eccentric part2aof the rotation shaft2, a tappet4arranged on the ball bearing3in a radial manner, and a plunger5arranged on the tappet4and reciprocated by the rotation of the rotation shaft22.

In addition, as shown inFIG. 10, the ball bearing3comprises an inner ring3a, an outer ring3b, a plurality of balls3carranged between the inner ring3aand the outer ring3b, a retainer3dretaining the balls3, and a seal3earranged at both ends of the bearing to seal the inner space of the bearing.

The above oil pump1inhales and pressure feeds an oil while the plunger5is moved vertically by the rotation of the rotation shaft2.

In addition, in the above document, it is pointed out that the eccentric part2aof the rotation shaft2becomes unbalanced in its driven state, causing an oscillation and the like to damage the bearing and the output shaft of a motor and the like and to raise the operation sound of a transmission pump, as problems.

Thus, in order to solve the above problems, a balancer6having a large diameter part6aand a small diameter part6bis used as shown inFIG. 11. More specifically, when the large diameter part6ais arranged at both ends of the eccentric part2aso as to face the direction opposite to the eccentric direction, the dynamic unbalance while the rotation shaft is driven can be corrected by using a difference in centrifugal force between the large diameter part6aand the small diameter part6b.

When the distance between the eccentric part2aand the balancer6is large in the above plunger driving structure, since an oscillation could be generated at the time of driving, the distance between the ball bearing3and the balancer6is 0.3 mm to 0.47 mm in general, which is very small.

Although it is no problem in the bearing such as the ball bearing3in which grease is enclosed in the space in the bearing sealed by the seal3e, the balancer6could prevent the lubricant from flowing into the bearing in the bearing that requires the lubricant to be supplied from the outside.

Meanwhile, as the miniaturization of the oil pump is increasingly demanded recently, it is considered that a needle roller bearing that is a small in thickness in the diameter direction and the like is used instead of the ball bearing3. According to the needle roller bearing, however, the lubricant is to be supplied from the outside in general and the distance formed between track rings is small, so that it is inevitable that the lubricant supply is insufficient due to the balancer6.

In addition, although the rotation shaft2, the inner ring3aand the balancer6are integrally rotated in the above plunger driving structure, since the outer ring3bis fixed, friction resistance is generated at the contact part between the wall surface of the balancer6and the end surface of the outer ring3b. This friction resistance could cause an abnormal noise or oscillation while the oil pump11is driven.

Furthermore, surface finish such as grinding is not performed on the wall surface of the balancer6. Meanwhile, grinding is performed on the end surface of the outer ring3bto be a reference surface in an early stage, but even when it is scratched at a subsequent processing step, it is left as it is. As a result, the contact surfaces are rough and it is considered that this roughness causes an increase in friction resistance.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a plunger driving structure comprising a balancer having a configuration that does not prevent a lubricant from flowing into a bearing to support an eccentric part.

It is another object of the present invention to provide a plunger driving structure in which rotation resistance at a contact part between a bearing and a balancer is reduced and an abnormal noise or oscillation at the time of driving is suppressed.

A plunger driving structure according to the present invention comprises a rotation shaft having an eccentric part, a roller bearing comprising an outer ring and a plurality of rollers arranged along the track surface of the outer ring and supporting the eccentric part, a balancer arranged at a position adjacent to the roller bearing at the rotation shaft, and a plunger abutting on the outer ring and reciprocated by the rotation of the rotation shaft. Thus, the rolling space of the roller can be projected from an axial direction through the balancer.

As a concrete configuration of the balancer, the outer diameter outline of the balancer intersects with the circumscribed circle of the rollers. Alternatively, the balancer has a through hole in its wall surface opposed to the rolling space of the roller. In addition, the “circumscribed circle of the roller” in this specification designates a circle provided such that points where the rollers are in contact with the outer ring track surface are connected. In addition, the “rolling space of the roller” designates a space sandwiched by the inner ring track surface and the outer ring track surface.

According to the above constitution, since the lubricant can be smoothly supplied to the roller bearing supporting the eccentric part, the plunger driving structure can be superior in lubricating performance.

Preferably, the roller bearing is a needle roller bearing comprising needle rollers as the rollers. When the present invention is applied to the plunger driving structure comprising the needle roller bearing in which the lubricating property is largely influenced by the existence of the balancer, a greater effect can be expected.

Preferably, the balancer has a small diameter part and a large diameter part, and the outline of the small diameter is positioned inside the inner diameter of the outer ring. According to the above structure, since the wall surface of the small diameter part of the balancer and the bearing outer ring are not in contact with each other, the rotation resistance at the time of driving can be reduced. As a result, the plunger driving structure in which an abnormal noise or oscillation is suppressed can be provided.

Preferably, the end surface of the large diameter part in a circumferential direction has a chamfered part. Since higher rotation resistance is generated when the corner part of the end surface of the large diameter part in the circumferential direction, that is, the end surface of the large diameter part that is in contact with the small diameter part comes into contact with the end surface of the outer ring, the abnormal noise or oscillation can be effectively suppressed by chamfering the corner part.

Preferably, the surface roughness of the end surface of the outer ring opposed to the balancer is Rz≦0.8 μm, and the surface roughness of the wall surface of the balancer opposed to the outer ring is Rz≦3.2 μm. As describe above, when the surface roughness of the end surface of the outer ring and the wall surface of the balancer that are in contact with each other are set to the predetermined value or less, the rotation resistance at the time of driving can be reduced. As a result, the plunger driving structure in which the abnormal noise or oscillation is suppressed can be provided. In addition, the “Rz” in this specification designates the surface roughness using ten-point average roughness.

Preferably, the end surface of the outer ring opposed to the balancer is lapped. In addition, preferably, the wall surface of the balancer opposed to the outer ring is barreled. Thus, the surface roughness of the contact surface can be the predetermined value or less.

In addition, the “lapping” in this specification designates a method in which a product is slid on a lapping plate that is covered with a processing liquid mixed with abrasive grains while it is pressurized, to finish the surface with high precision. In addition, the “barreling” designates a grinding method in which a product is put in a barrel-shaped container together with a particulate abrasive material and a compound and the barrel-shaped container is rotated and moved vertically.

According to the present invention, the balancer having the structure that does not prevent the lubricant from flowing to the bearing to support the eccentric part is used, so that the plunger driving structure in which the lubricating property is excellent can be provided.

In addition, according to the present invention, the plunger driving structure in which the rotation resistance at the time of driving is reduced and the abnormal noise or oscillation is suppressed can be provided by smoothing the end surface of the outer ring and the wall surface of the balancer that are in contact with each other.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A plunger driving structure for an oil pump according to one embodiment of the present invention will be described with reference toFIGS. 1 to 3hereinafter.

As shown inFIG. 1, an oil pump11comprises a rotation shaft12having an eccentric part12a, a needle roller bearing13supporting the eccentric part12aof the rotation shaft12, a tappet14abutting on the outer ring of the needle roller bearing13and arranged in a radial manner, a plunger15arranged on the tappet14and reciprocated by the rotation of the rotation shaft12, and a balancer16arranged both ends of the eccentric part12a.

As shown inFIG. 2, the needle roller bearing13comprises an inner ring13a, an outer ring13b, a plurality of needle rollers13carranged between the inner ring13aand the outer ring13b, and a retainer13dretaining the needle rollers13c. Alternatively, the needle roller bearing13may be a bearing that does not have the inner ring13aand comprises needle rollers13carranged along the track surface of the outer ring13b. When such needle roller bearing13is used as the bearing for supporting the eccentric part12a, the oil pump11can be miniaturized.

As shown inFIG. 3, the balancer16has a large diameter part16aand a small diameter part16band an outer diameter outline16cintersects with the circumscribed circle of the rollers13c. When the balancer16is arranged such that the large diameter part16amay face the direction opposite to the eccentric direction as shown inFIG. 1, the rolling space of the roller13ccan be projected from the axial direction through the balancer16.

The oil pump11can be miniaturized by using the needle roller bearing13that is small in thickness in the diameter direction as the bearing to support the eccentric part12a. At the same time, since the balancer shown inFIG. 3does not prevent the flow of a lubricant supplied to the needle roller bearing13, the plunger driving structure can be superior in lubricating property.

In addition, according to the oil pump11having the above constitution, the end surface of the outer ring13bthat is opposed to the balancer16is lapped so that its surface roughness becomes Rz≦0.8. Furthermore, the wall surface of the balancer36that is opposed to the outer ring13bis barreled so that its surface roughness becomes Rz≦3.2. At this time, it is to be noted that no projected scratch is to be left especially.

As described above, when the end surface of the outer ring13band the wall surface of the balancer16that are in contact with each other when the oil pump11is driven are smoothed, the rotation resistance at the time of driving can be reduced. As a result, the plunger driving structure in which an abnormal noise or oscillation is suppressed can be provided.

In addition, as the balancer used in the above oil pump11, a balancer36shown inFIG. 5may be used. According to the balancer36, rotation resistance between the outer ring13band the balancer36can be more reduced when the oil pump11is driven in addition to the above effect.

In addition, although the example in which the large diameter part16aand the small diameter16bare provided and the center of the arc of the small diameter part16bis cut is shown in the above embodiment, the present invention is not limited to this. For example, a through hole may be provided in the wall surface of the balancer on one side.

For example, like a balancer46shown inFIG. 4A, a large through hole46amay be provided or like a balancer56shown inFIG. 4B, small through holes56amay be provided. In this case, a lubricant can be supplied to the bearing through the through holes46aand56a, and the degree of centrifugal force can be adjusted according to the size or the number of the through holes46aand56awithout providing the small diameter part and the large diameter part in the balancers46and56.

Another embodiment of the balancer will be described with reference toFIGS. 5 and 6hereinafter. In addition, the point common to the above embodiment will be omitted and the point different from the above will be described.

Since a higher rotation resistance is generated at a shaded area and a corner part36binFIG. 5when they are in contact with the end surface of the outer ring, an abnormal noise or oscillation can be effectively prevented by cutting the shaded area and chamfering the corner part36b.

In addition, the chamfering of the corner part36bis performed by a tumbling process. The tumbling process is a process in which the balancer36and iron pieces are put in a rotation drum and rotated to round the corner part36bby friction or impact.

According to the above balancer36, dynamic unbalance when the rotation shaft12is driven can be corrected by using a difference in centrifugal force between the large diameter part16aand the small diameter part16bwhen the large diameter part16ais arranged so as to face the direction opposite to the eccentric direction as shown inFIG. 1.

In addition, the balancer36has a large diameter part36aand a small diameter part36b, and a shaded area in the drawing is cut so that the outline of the small diameter36bmay be positioned inside the outer ring13b. Thus, the rotation resistance between the outer ring13band the balancer36when the oil pump11is driven can be reduced.

In addition, as shown inFIGS. 4A and 4B, a through hole may be provided in the wall surface of the balancer36. Thus, a lubricant can be supplied to the bearing through the through hole. In addition, as the bearing to support the eccentric part12a, when the needle roller bearing13that requires the lubricant to be supplied from the outside is used, the effect can be expected more.

A plunger driving structure for an oil pump according to another embodiment of the present invention will be described with reference toFIGS. 7 and 8hereinafter. In addition the point common to the above embodiment will be omitted and the point different to the above will be described.

As shown inFIG. 7, an oil pump21comprises a rotation shaft22, a needle roller bearing23supporting the rotation shaft22, a tappet24abutting on the outer ring of the needle roller bearing23and arranged in a radial manner, a plunger25arranged on the tappet24and reciprocated by the rotation of the rotation shaft22, and a balancer26arranged on both ends of the needle roller bearing23like the balancer shown inFIGS. 3 to 5.

In addition, as shown inFIG. 8, the needle roller bearing23comprises an eccentric inner ring23ahaving different thicknesses in diameter direction circumferentially, an outer ring23b, a plurality of needle rollers23carranged between the eccentric inner ring23aand the outer ring23b, and a retainer23dretaining the needle rollers23c.

Since this needle roller bearing23has the eccentric inner ring23a, it is not necessary to provide an eccentric part at the rotation shaft22. As a result, in addition to the effect provided in the embodiments shown inFIGS. 1 to 6, the manufacturing cost of the rotation shaft22can be reduced.

Although the needle roller bearings13and23shown inFIGS. 2 and 8have the retainers13dand23dretaining the needle rollers13cand23c, respectively, the present invention is not limited to this. For example, the bearing may be a full type roller bearing in which adjacent needle rollers13aor23care in contact with each other without the retainers13dor23d. Since the load capacity of the needle roller bearings13or23is increased as the number of needle rollers13cor23cis increased, when the full type roller bearing housing the needle rollers13cor23cas many as possible is used, the plunger supporting bearing can have high load capacity.

In addition, although the needle roller bearing is used as the bearing to support the eccentric part in the above embodiments, the present invention is not limited to this. The present invention can be applied to various kinds of bearings that require the lubricant to be supplied from the outside, and the same effect as the above can be expected.

In addition, although the balancer is applied to the plunger driving structure of the oil pump used in a car brake system shown inFIGS. 3 to 5in the above embodiment, the present invention is not limited to this. For example, it can be applied to a plunger driving structure for a fuel pump in a diesel engine and the like.

Furthermore, according to the present invention, when the characteristic parts in the above embodiments are combined arbitrarily, a synergetic effect can be expected.

Although the embodiments of the present invention have been described with reference to the drawings in the above, the present invention is not limited to the above-illustrated embodiments. Various kinds of modifications and variations may be added to the illustrated embodiments within the same or equal scope of the present invention.

The present invention can be advantageously applied to the plunger driving structure for the oil pump.