Front Fork for Motorcycle or the Like

1. Field of the Invention

The present invention relates to a front fork for use in a motorcycle or the like, in which an inner cylinder is slidably fitted in an outer cylinder, and, more particularly, to a front fork of a motorcycle or the like, which has its attenuating force at an extension stroke changed stepwise in accordance with the position of a main piston fitted in the leading end of the inner cylinder.

2. Description of the Prior Art

The front fork for use in a vehicle such as a motorcycle is designed to weaken its attenuating force to thereby have a soft shock absorbing effect in case the stroke (i.e., displacement) is small with respect to the position of the main piston when the motorcycle stops. In case that stroke is large, on the contrary, the front fork is required to strengthen the attenuating force at the beginning of the extension stroke thereof to thereby prevent an abrupt extension and to stepwise weaken the attenuating force to thereby restore it to its original state. This is acomplished by having a spring disposed under extension in the inner cylinder which is compressed to have its extending force increased.

It is, therefore, an object of this invention to meet those requirements and to provide a front fork for use in a motorcycle or the like, in which an attenuating force at an extension stroke is automatically changed in accordance with the position of a main piston fitted in the leading end of an inner cylinder.

The front fork according to the present invention is characterized in: that an outer cylinder is slidably fitted in an inner cylinder mechanism having a main piston at the lower end thereof; that the inner cylinder mechanism is fitted in a sheet pipe which is anchored at the bottom portion of the outer cylinder and which has an auxiliary piston at the lower end thereof; that the sheet pipe has its lower portion formed with an oil port at the side thereof; and that its attenuating force is stepwise weakened by orifice means for allowing the oil between the main and auxiliary pistons to flow therethough into the inner cylinder mechanism or the sheet pipe at the extension stroke of the front fork.

FIG. 1 is a front elevation showing in partial longitudinal section one embodiment of a front fork according to the present invention at the most compressed state thereof;

FIGS. 2 and 3 are similar to FIG. 1 but illustrate the operations of the aforementioned embodiment as will be hereinafter explained;

FIG. 4 is a front elevation showing in partial longitudinal section another embodiment of the present invention at the most compressed state thereof; and

FIGS. 5 to 7 are similar to FIG. 4 but illustrate the operations of the embodiment shown in FIG. 4 as will be hereinafter explained.

FIG. 1 shows one embodiment of the front fork according to the present invention and is a front elevation showing the same in partial longitudinal section in the compressed state i.e., having an inner cylinder inserted to its full stroke into an outer cylinder. In an outer cylinder 1 which connected to the axle of the front wheel of a motorcycle or the like, as shown, there is slidably fitted therein a main piston 3, which is disposed at the lower portion of an inner cylinder 2, such that it is filled with working oil. In the inner cylinder 2, moreover, there is slidably fitted an auxiliary piston 5 which is disposed at the upper end of a sheet pipe 4 anchored at the bottom portion of the outer cylinder 1. A spring 6 is sandwiched under extension between that auxiliary piston 5 and the upper portion of the inner cylinder 2 thereby to suspend the front portion of the motorcycle body. Moreover, the main piston 3 is equipped with a check valve 7 which is adapted to be opened during the downward stroke of the inner cylinder 2 and to be closed during the upward stroke. On the other hand, the sheet pipe 4 has its lower portion formed with an oil port 4a at the side thereof and its upper portion formed with an orifice 4b at the side thereof. The inner cylinder 2 also has its lower portion formed with an oil port 2a at the side thereof and its upper portion formed in the axial direction with an orifice 2b. Reference numerals 8 and 9 indicate a rebound spring and an oil seal, respectively.

The operations of the embodiment thus constructed will be described in the following.

First of all, at the beginning of the extension stroke, in which the front fork is extended and as a result the inner cylinder 2 is extended by the extending force of the spring 6 from the state having the spring 6 in the inner cylinder 2 fully closed, as shown in FIG. 1, the oil in the space A between the auxiliary piston 5 and the main piston 3 operates in the direction to reduce its volume to thereby close the check valve 7 as shown in FIGS. 2 and 3. As a result, the oil in the space A flows into the inside of the sheet pipe 4 by way of the orifice 4b. At this time, an attenuating force is established to prevent the front fork from abruptly extending.

Next, when the orifice 2b of the inner cylinder 2 reaches a position above the auxiliary piston 5, as shown in FIG. 2, the oil in that space A flows from the oil port 2a by way of the clearance between the inner cylinder 2 and the outer cylinder 1 in addition to the preceding passage via the orifice 4b until it flows from the orifice 2b into the inner cylinder 2. As a result, the attenuating force at this time is made weaker than that at the beginning by means of those two orifices 2b and 4b. In other words, the extension becomes faster than that at the beginning so that the original state is restored. When the oil port 2a comes to a position above the auxiliary piston 5, moreover, the oil in the space A is confined therein, as shown in FIG. 3, to establish an oil lock, by which the extension of the front fork is abruptly depressed as well as by the action of the rebound spring 8. For such purpose, the oil port 2a is so arranged as to come a position above the auxiliary piston 5 at the longest extension stroke. The description of the embodiment under consideration is directed to the case in which the orifice 2b formed in the inner cylinder 2 is one. Nevertheless, the attenuating force can be stepwise changed at a lower rate by forming a plurality of orifices in the axial direction.

A second embodiment of the present invention will now be described in detail which reference to FIGS. 4 through 7, where the same elements as those of the aforementioned embodiment are indicated by the same reference numerals.

This second embodiment is difference from the foregoing embodiment of FIGS. 1-3 in that another cylinder 10 is interposed between the sheet pipe 4 and the inner cylinder 2 and in that the orifice at the side of the upper portion of the sheet pipe 4 is omitted. More specifically, the cylinder having a predetermined length is fitted in the inner wall of the lower portion of the inner cylinder 2 at a predetermined spacing in between, and the cylinder 10 has its lower portion formed with an oil port 10a at the side thereof and its upper portion formed in the axial direction with a plurality of (e.g., three, as shown) orifices 10b', 10" and 10b' which are arranged from the upper end portion thereof at a predetermined spacing between the adjacent two. Here, the effective area of the oil port 10a is made larger than the sum of the effective areas of the respective orifices 10b', 10b" and 10b'". On the other hand, the auxiliary piston 5, which is disposed at the upper end of the sheet pipe 4 anchored at the bottom portion of the outer cylinder 1, is slidably fitted in the aforementioned cylinder 10. Moreover, the sheet pipe 4 has its lower portion formed with the oil port 4a at the side thereof. In this case, the uppermost orifice 10b' is positioned above the auxiliary piston 5 when the inner cylinder 2 is the most fully compressed.

The operations of the second embodiment shown in FIGS. 4 through 7 will be described in the following.

First of all, at the beginning of the extension stroke, in which the front fork is extended and as a result the inner cylinder 2 is to be extended by the extending force of the spring 6 in the cylinder 2 from the state having the spring fully compressed, as shown in FIG. 4, i.e., from the state having the essential portion shown in an enlarged scale in FIG. 5, the oil in the space A' between the sheet pipe 4 and the cylinder 10 operated in the direction to reduce its volume to thereby to close the check valve 7. As a result, the oil in the space A' mainly flows from the oil port 10a via the clearance between the cylinder 10 and the inner cylinder 2 until it flows from the orifice 10b' into the inner cylinder 2. At this time, an attenuating force is established to prevent the front fork from abruptly extending.

Next, when the orifice 10b" comes to a position above the auxiliary piston 5, the oil flows out of the orifice 10b", although it has previously only flowed out of orifice 10b' so that the attenuating force becomes weaker than that at the beginning. Likewise, if the oil begins to also flow out of the orifice 10b'", the extension is speeded up so that the original state is restored. Moreover, when the oil port 10a comes to the position of the auxiliary piston 5, the oil in the space A' is confined therein similarly to the foregoing embodiment, as shown in FIG. 7, to establish an oil lock, by which the extension of the front fork is abruptly depressed as well as by the action of the rebound spring 8.

By forming the cylinder 10 in that way with the plural orifices 10b', 10b" and 10b'" in the axial direction, the attenuating force can be stepwise changed at a low rate in accordance with the position of the fork pipe at the extending step of the inner cylinder 2.

As has been described in detailed hereinbefore, according to the present invention, the attenuating force, by which the extension is slow at the beginning but fast at the end, can be automatically established at the extending stroke of the front fork in accordance with the position of the main piston by the simple construction illustrated, in which the cylinder is fitted in the inner cylinder, thereby to advantageously provide a front fork which can ensure a comfortable ride.