JP5564368B2 - Rear cushion unit - Google Patents

Description

  The present invention relates to an improvement in a rear cushion unit that is interposed between a vehicle body and a rear wheel of a motorcycle to suppress vibrations of the vehicle body.

  2. Description of the Related Art Conventionally, a shock absorber interposed between a vehicle body and wheels of an automobile generally suppresses vibration of the vehicle body by exhibiting a damping force according to the piston speed.

  Here, considering the structure of the automobile, since the vehicle body is supported by a tire that acts as a spring and a suspension spring, if the vibration frequency input to the automobile is close to the natural frequency (resonance frequency) of the vehicle body, Will be excited.

  Therefore, if the shock absorber exerts a large damping force against vibration having a frequency around the resonance frequency of the vehicle body, the vibration of the vehicle body can be suppressed. However, if the shock absorber exerts an excessive damping force against vibrations other than those around the resonance frequency, the vibration insulation effect on the vehicle body by the suspension spring may be disturbed, and the ride comfort in the vehicle may be impaired. .

  Therefore, if the damping force is changed depending on the frequency of vibration input to the shock absorber, the ride comfort of the vehicle can be improved, and so-called frequency sensitive shock absorbers have been developed. Has been done.

  As this frequency-sensitive shock absorber, for example, a cylinder, a piston that is slidably inserted into the cylinder, and divides the inside of the cylinder into an upper chamber and a lower chamber, and an upper chamber and a lower chamber provided in the piston communicate with each other. A damping passage that provides resistance to the flow of liquid passing therethrough, a housing that is provided at the tip of the piston rod to form a pressure chamber, and is slidably inserted into the housing to communicate the pressure chamber with the upper chamber. A free piston that is divided into an upper chamber and a lower chamber that communicates with the lower chamber, and a coil spring that urges the free piston, and as shown in FIG. 5, has a relatively low frequency band. A large damping force is exhibited with respect to vibration, and a small damping force is exhibited with respect to vibration in a high frequency band (see, for example, Patent Documents 1 and 2).

JP 2006-336816 A JP 2007-78004 A

  As described above, the conventional shock absorber is a frequency sensitive shock absorber that exhibits a frequency-sensitive damping characteristic, and is very useful in that it can improve the riding comfort in the vehicle. There is a problem.

  In the configuration of the shock absorber, the attenuation characteristic as shown in the initial setting is exhibited. However, as described above, the initial setting determines the flow resistance of the passage that connects the attenuation passage and the pressure chamber to the upper chamber and the lower chamber, and free passage. Once determined by the cross-sectional area of the piston and the spring multiplier of the coil spring, once determined, it cannot be freely changed later, and it is difficult to realize an optimum damping characteristic for each individual vehicle. Of course, in order to make the damping force variable, as disclosed in Japanese Patent Application Laid-Open No. 2008-298227, it is impossible to provide a passage parallel to the attenuation passage and change the flow resistance in the passage. However, in this case, the curve of the damping characteristic in FIG. 5 can be shifted up and down as indicated by the arrow in FIG. 5, but the change width of the damping force itself cannot be changed. It is difficult to obtain characteristics.

  In the shock absorber, the upper chamber and the upper chamber are communicated by a passage having a relatively low flow resistance, but the lower chamber and the lower chamber are communicated by an orifice having a large flow resistance. . Then, in the expansion stroke of the shock absorber, the free piston is displaced by applying a pressure equivalent to that of the upper chamber compressed by the expansion to the upper chamber, while in the contraction stroke of the shock absorber, the contraction occurs due to the pressure loss due to the orifice. Since the pressure reduced by the pressure in the lower chamber compressed by the pressure acts on the lower chamber and the free piston is pushed by this reduced pressure, the displacement of the free piston is reduced in the contraction stroke compared to the expansion stroke. Will do. Therefore, the shock absorber has a characteristic that the change width corresponding to the frequency of the damping force in contraction is smaller than that in the extension stroke. When such a shock absorber is used as it is as a rear cushion unit incorporated in the body and rear wheel of a two-wheeled vehicle, the decrease in damping force is particularly small during the contraction stroke, so high-frequency thrust input from the road surface (impact shock) May not be sufficiently absorbed, and it may be difficult to obtain good riding comfort.

  Therefore, the present invention has been developed to improve the above-described problems, and the object of the present invention is to realize an optimum damping characteristic for suppressing vehicle body vibration of a two-wheeled vehicle and to provide a good riding comfort. Is to provide a rear cushion unit.

In order to solve the above-described object, the problem solving means in the present invention includes a cylinder connected to one of a rear wheel and a vehicle body of a two-wheeled vehicle, a slidable insertion in the cylinder, and an extension side chamber and a compression side in the cylinder. A piston that is partitioned into a chamber, one end of which is connected to the piston and a piston rod that is connected to the rear wheel of the two-wheeled vehicle and the other of the vehicle body, and a liquid that is provided in the piston and communicates with and passes through the extension side chamber and the pressure side chamber In a rear cushion unit that includes a damping passage that provides resistance to the flow of the air and exhibits damping force that suppresses vibration of the vehicle body, a housing that forms a pressure chamber, and a pressure slidably inserted into the pressure chamber A free piston that divides the chamber into an extension side pressure chamber and a compression side pressure chamber, an extension side passage that communicates the extension side chamber and the extension side pressure chamber, the pressure side chamber, and the pressure side pressure Preparative a spring element which exerts a pressure side passage to maintain pressure equalized and the compression side chamber and the pressure side pressure communicated with the biasing force of suppressing the displacement with respect to the housing of the free piston, provided in the middle of the extension side passage And a variable valve that makes the flow resistance of the extension side passage variable, and the housing is provided with either a port communicating with the pressure side chamber and the inside of the housing or an annular groove. A port that opens from the outer periphery and communicates with the extension side pressure chamber and the other of the annular groove are provided. When the free piston is in the neutral position, the port and the annular groove face each other, and the free piston is displaced by a predetermined amount from the neutral position. Then, the facing area between the port and the annular groove is reduced .

According to the rear cushion unit of the present invention, the reduction range of the damping force in the contraction stroke can be increased, so that vibrations (impact shock) with a high frequency and a large amplitude, such as when a two-wheeled vehicle passes a protrusion on the road surface, are produced. Even if is inputted, the impact shock can be sufficiently absorbed and a good riding comfort can be obtained.
Furthermore, after the free piston begins to close the port, the area where the port and the annular groove overlap (wrap area) decreases according to the amount of displacement, and the port is squeezed so that the liquid flows through the port. The flow path resistance given to is gradually increased as the amount of displacement of the free piston increases.
Then, when the vibration frequency is relatively high, the rear cushion unit generates a relatively low damping force until the free piston is displaced to a position where the port starts to close the port, but the free piston starts to close the port. When the displacement exceeds the position, the flow path resistance at the port gradually increases, so the moving speed of the free piston to the further stroke end side is reduced, and the flow through the pressure chamber is reduced. The amount of liquid movement between the extension side chamber and the pressure side chamber also decreases, and the amount of liquid passing through the attenuation passage increases accordingly, and the generated damping force of the rear cushion unit gradually increases.
When the free piston reaches the stroke end, the liquid no longer moves between the extension side chamber and the pressure side chamber via the pressure chamber, and the liquid passes only through the damping passage until the rear cushion unit expands and contracts. As a result, the rear cushion unit loses the damping force reduction effect and exhibits a large damping force depending on the leaf valve.

Further, in this rear cushion unit, the flow resistance in the extension side passage is adjusted by a variable valve, so that the pressure in the extension side pressure chamber can be controlled by adjusting the variable valve. it can.
Controlling the pressure in the expansion side pressure chamber leads to controlling the displacement amount of the free piston, and by controlling the displacement amount of the free piston, it is possible to adjust the bypass flow rate of the attenuation passage, and to expand and contract It is possible to adjust the variation range of the damping force in the damping characteristics in both processes, and to obtain the optimum damping characteristics for suppressing the vehicle body vibration of the two-wheeled vehicle.

It is a longitudinal cross-sectional view of the rear cushion unit in one embodiment. It is an expansion longitudinal cross-sectional view of the piston part of the rear cushion unit in one Embodiment. It is the figure which showed the damping characteristic with respect to the vibration frequency of the rear cushion unit in one Embodiment. It is a figure explaining the damping force change width | variety in the damping characteristic of the expansion-contraction both strokes of the rear cushion unit in one Embodiment. It is the figure which showed the damping characteristic in the conventional shock absorber.

  Hereinafter, the present invention will be described with reference to the drawings. As shown in FIGS. 1 and 2, the rear cushion unit RCU of the present invention includes a cylinder 1 connected to a rear wheel of a two-wheeled vehicle (not shown) and one of the vehicle bodies, and a cylinder 1 that is slidably inserted into the cylinder 1. The piston 2 is divided into an extension side chamber R1 and a pressure side chamber R2, one end is connected to the piston 2 and the piston rod 3 is connected to the rear wheel of the two-wheeled vehicle not shown and the other of the vehicle body. Attenuating passages 4 and 5 that communicate with the extension side chamber R1 and the pressure side chamber R2 and provide resistance to the flow of the liquid passing therethrough, a housing 6 that forms the pressure chamber C, and a pressure slidably inserted into the pressure chamber C. A free piston 9 that divides the chamber C into an expansion side pressure chamber 7 and a compression side pressure chamber 8, an expansion side passage 10 that communicates the expansion side chamber R1 and the expansion side pressure chamber 7, a compression side chamber R2, and a compression side pressure chamber 8. Pressure side passage 11 communicating with A spring element 12 that exerts an urging force that suppresses the displacement of the free piston 9 with respect to the housing 6 and a variable valve 13 that is provided in the middle of the extension side passage 10 and makes the flow resistance of the extension side passage 10 variable. It is configured and exhibits damping force during expansion and contraction to suppress vibration of a vehicle body (not shown).

  Then, the extension side chamber R1, the pressure side chamber R2, and the pressure chamber C are filled with a liquid such as hydraulic oil, and a tank T is connected to the lower side of the cylinder 1, and the inside of the tank T is The liquid chamber is partitioned into a liquid chamber (not shown) that is filled with liquid and communicated with the lower chamber R2 through a tank communication hole 40 provided in the cylinder 1 and an air chamber (not shown) that is filled with gas. The tank T absorbs excess and deficiency of the liquid generated in the cylinder 1 by changing the volume of the air chamber as the piston rod 3 advances and retreats in the cylinder 1. In the tank T, the partition between the liquid chamber and the air chamber may be partitioned by, for example, a sliding partition that slides in the tank T, or a bellows or a bladder in which the inside functions as an air chamber is provided. You may make it accommodate and perform. Although depending on the stroke length in the rear cushion unit RCU, the tank T may be eliminated if an air chamber can be formed in the cylinder 1, and an outer cylinder covering the outer periphery of the cylinder 1 is provided. The tank T can be abolished also when it is provided and is set to a double cylinder type in which an air chamber is formed between the cylinder 1 and the outer cylinder. As the liquid filled in the extension side chamber R1, the pressure side chamber R2, and the pressure chamber C, for example, a liquid such as water or an aqueous solution can be used in addition to the hydraulic oil.

  Hereinafter, each part of the rear cushion unit RCU will be described in detail. The piston 2 is connected to one end 3a of a piston rod 3 movably inserted into the cylinder 1, and the piston rod 3 is outwardly passed through the inner periphery of an annular rod guide 15 fixed to the upper end of the cylinder 1 in the figure. It is protruded to. The piston rod 3 and the rod guide 15 are sealed with a seal member 16 and the inside of the cylinder 1 is kept in a liquid-tight state.

  The piston 2 includes damping passages 4 and 5 that communicate the expansion side chamber R1 and the pressure side chamber R2, and the lower end of the damping passage 4 in FIG. 1 is opened and closed by a leaf valve 17, and the upper end of the damping passage 5 in FIG. 1 is opened and closed by a leaf valve 18 as a damping valve stacked above the piston 2 in FIG. Yes. The leaf valve 17 is annular and is attached to one end 3a of the piston rod 3 together with the piston 2, and the liquid passes through the damping passage 4 during the extension stroke of the rear cushion unit RCU in which the piston 2 moves upward in FIG. When the fluid flows from the extension side chamber R1 toward the pressure side chamber R2, the damping passage 4 is opened and resistance is given to the flow of the liquid, and the damping passage 4 is closed against the reverse flow. The damping passage 4 is set as a one-way passage that allows only the flow from the expansion side chamber R1 to the compression side chamber R2. On the other hand, the leaf valve 18 is annular and is attached to the one end 3a of the piston rod 3 together with the piston 2, so that the liquid passes through the damping passage 5 during the contraction stroke of the rear cushion unit RCU in which the piston 2 moves downward in FIG. When the fluid flows from the compression side chamber R2 toward the extension side chamber R1, the damping passage 5 is opened and resistance is given to the flow of the liquid, and the damping passage 5 is closed against a reverse flow. The damping passage 5 is set as a one-way passage that allows only the flow from the compression side chamber R2 to the extension side chamber R1. That is, the leaf valve 17 functions as an expansion-side damping valve that provides resistance to the flow of liquid flowing through the attenuation passage 4 during the extension stroke, and the leaf valve 18 provides resistance to the flow of liquid flowing through the attenuation passage 5 during the contraction stroke. Functions as a compression side damping valve. As described above, when a plurality of attenuation passages 4 and 5 are provided, the attenuation passage may be set to be one-way so that the liquid flows only during the extension stroke or during the contraction stroke. The passage may allow bidirectional flow and provide resistance to the flow of liquid passing therethrough. Various damping valves such as a poppet valve, an orifice, and a choke can be used as a damping valve that serves as a damping passage that gives resistance to the flow of liquid passing through the damping passage.

  Subsequently, in the case of this embodiment, the pressure chamber C is formed by a hollow housing 6 that is screwed into a screw portion 3b provided on the outermost outer periphery of the one end 3a of the piston rod 3. The piston 2 and the leaf valves 17 and 18 also function as a piston nut that fixes the piston rod 3 to one end 3a.

  The pressure chamber C formed in the housing 6 is a free piston 9 that is slidably inserted into the pressure chamber C. The expansion side pressure chamber 7 in the upper part in FIG. 2 and the pressure side pressure chamber in the lower part in FIG. 2, the free piston 9 can be displaced in the vertical direction in FIG. 2 with respect to the housing 6 in the pressure chamber C.

  Specifically, the housing 6 includes a nut portion 20 that is screwed into a screw portion 3b formed at one end 3a of the piston rod 3, and a cylinder that is suspended from the outer periphery of the nut portion 20 and in which the free piston 9 is slidably contacted. A pressure chamber C is defined in the pressure side chamber R2 by including a portion 21 and an annular spring receiver 22 screwed into the lower end opening in FIG. In addition, when integrating the cylinder part 21 and the spring receiver 22, in addition to screwing, other methods such as caulking and welding can be employed.

  The nut portion 20 includes a screw portion 20a that is screwed into the screw portion 3b of the piston rod 3 on the inner periphery thereof, and has a shape other than a circle so that the outer cross-sectional shape can be gripped by a tool (not shown). A shape that matches the tool, for example, a shape in which a part is cut out, a hexagon, or the like is formed, the outer periphery of the nut portion 20 is gripped by a tool, and the nut portion 20 is rotated in the circumferential direction. A predetermined tightening torque can be applied to 20 and screwed to the screw portion 3b. The cylinder portion 21 is provided with a port 21a on a side portion, and the pressure chamber C and the pressure side chamber R2 are communicated with each other through the port 21a.

  The spring receiver 22 is screwed to the lower end opening end of the cylindrical portion 21 and is annular and forms a pressure side passage 11 on the inner periphery. The pressure side pressure chamber 8 communicates with the pressure side chamber R2 through the pressure side passage 11. doing.

  The expansion side pressure chamber 7 communicates with the expansion side chamber R1 by an expansion side passage 10 that leads from the side of the piston rod 3 facing the expansion side chamber R1 to the end of the one end 3a. This extension side passage 10 is composed of a horizontal hole 10a that opens from the side facing the extension side chamber R1 of the piston rod 3, and a vertical hole 10b that opens from the end of one end 3a and communicates with the horizontal hole 10a. A cylindrical valve seat member 23 is fixed, and the valve seat member 23 forms an annular valve seat 23 a in the extension side passage 10.

  The flow path resistance of the pressure side passage 11 formed in this way is as large as possible so that no pressure loss occurs, so that the pressure side chamber R2 and the pressure side pressure chamber 8 can be kept at the same pressure. It has become.

  Further, the piston rod 3 is provided with a hollow portion 3d leading from the other end 3c to the vertical hole 10b, and a control rod 24 is inserted into the hollow portion 3d, and the lower end of the control rod 30 in FIG. A needle type valve element 25 is integrally provided at the tip. This needle-type valve body 25 has a conical shape whose inclination angle changes midway, and a base end is set to be smaller than the outer diameter of the control rod 24, and a step portion is provided. An annular seat portion 26 that can be attached to and detached from the annular valve seat 23a is formed.

  As shown in FIG. 2, the needle-type valve body 25 can block the extension side passage 10 when the seat portion 26 is seated on the annular valve seat 23a, and the seat portion 26 can be disconnected from the annular valve seat 23a. When separated, an annular clearance is formed between the inner edge of the annular valve seat 23a and the extension-side passage 10 can be opened. Then, by moving the needle type valve body 25 away from the annular valve seat 23a, the cross-sectional area (flow channel area) of the annular gap can be changed, and the extension side passage 10 is a liquid that passes through the annular gap. The needle valve body 25 and the annular valve seat 23a constitute the variable valve 13. Even if the needle-type valve body 25 moves away from the annular valve seat 23a as much as possible and opens the extension-side passage 10 to the maximum, a sufficient flow resistance is given to the flow of the liquid, resulting in a pressure loss. It is like that.

  The upper end in FIG. 1, which is the end of the control rod 24 on the opposite side where the needle type valve element 25 is provided, is conical and has a tapered surface 24a. On the other hand, a bracket 27 for fixing the other end 3c of the piston rod 3 to a vehicle body (not shown) is attached to the other end 3c of the piston rod 3, and an adjustment port 27a that opens from the side of the bracket 27 is provided in the adjustment port 27a. An adjusting screw 28 having a conical tip 28a is screwed. The tip 28a of the adjusting screw 28 is in contact with the tapered surface 24a of the stove roll rod 24, and the adjusting screw 28 is rotated and advanced and retracted into the adjusting port 27a in the manner of a feed screw mechanism. The control rod 24 can be moved up and down within the piston rod 3. That is, the needle type valve element 25 can be moved closer to the annular valve seat 23a by rotating the adjusting screw 28 by an external operation. When the adjustment screw 28 is moved in the direction to retract from the adjustment port 27a and the needle type valve element 25 is moved away from the annular valve seat 23a, the control rod 24 is energized by the pressure in the extension side pressure chamber 7 and the extension side chamber R1. Therefore, the needle-type valve body 25 can be moved away from the annular valve seat 23a without using a spring that urges the needle side valve body 25 away from the annular valve seat 23a. In this case, the control rod 24 and the needle type valve body 25 are integrated, but they may be provided separately, and the mechanism for moving the needle type valve body 25 away from the annular valve seat 23a is limited to the above. However, hydraulic pressure or the like may be used. Furthermore, a feed screw mechanism may be arranged on the control rod 24 itself, and a motor may be used to drive the feed screw mechanism.

  The free piston 9 inserted into the pressure chamber C includes a disk-shaped mirror part 30 and a sliding contact cylinder 31 that is continuous with the outer periphery of the mirror part 30 and that is in sliding contact with the inner periphery of the cylinder part 21 of the housing 6. The housing 6 is partitioned into an expansion side pressure chamber 7 that communicates with the expansion side chamber R1 and a pressure side pressure chamber 8 that communicates with the compression side chamber R2. The free piston 9 includes an annular groove 32 provided over the entire outer periphery of the sliding contact cylinder 31, and a communication hole 33 that communicates the annular groove 32 with the expansion-side pressure chamber 7. When facing the port 21a formed in the cylindrical portion 21 of the housing 6, the compression side chamber R2 communicates with the expansion side pressure chamber 7, and the annular groove 32 does not face the port 21a and the port 21a is slid by the sliding cylinder 31. Is closed, the communication between the compression side chamber R2 and the expansion side pressure chamber 7 is cut off. In the case of this embodiment, the port 21a is provided with an orifice O in the middle thereof, which gives resistance to the flow of liquid passing therethrough and causes a predetermined pressure loss. The compression side chamber R2 and the expansion side pressure chamber A differential pressure is generated between 7 and 7.

  Furthermore, in order to apply an urging force to the free piston 9 to suppress the displacement in proportion to the displacement amount of the free piston 9 with respect to the housing 6, the nut portion 20 and the free piston 9 are disposed in the expansion side pressure chamber 7. Coil springs 34 and 35 are both compressed as spring elements 12 between the mirror portion 30 and between the spring receiver 22 and the mirror portion 30 of the free piston 9 in the pressure side pressure chamber 8. The free piston 9 is sandwiched from above and below by the spring elements 12 of the coil springs 34 and 35 and positioned at a predetermined neutral position in the pressure chamber C and is elastically supported. The neutral position does not indicate the axial center of the pressure chamber C, but a position where the free piston 9 is positioned by the spring element 12.

  As the spring element 12, it is only necessary to elastically support the free piston 9, and other elements than the coil springs 34 and 35 may be employed. For example, the free piston 9 is elastically supported using an elastic body such as a disc spring. You may make it do. When a single spring element whose one end is connected to the free piston 9 is used, the other end may be fixed to the nut portion 20 or the spring receiver 22.

  The upper end of the coil spring 34 in FIG. 2 is fitted into the inner periphery of the fitting recess 20b formed at the lower end of the nut portion 20 in FIG. 2 and positioned in the radial direction. The lower end of the coil spring 35 in FIG. They are fitted in the inner circumference of a fitting recess 22a formed in the inner circumference of the spring receiver 22 and positioned in the radial direction. As described above, the coil springs 34 and 35 are centered together as described above, and the positional displacement with respect to the free piston 9 is prevented, so that a biasing force can be applied to the free piston 9 stably. It has become.

  As described above, the free piston 9 is elastically supported by the coil springs 34 and 35 as the spring element 12 in the housing 6 and is in a neutral position in the housing 6 in a state where no force other than the urging force by the spring element 12 is applied. The annular groove 32 always faces the port 21a so that the extension-side pressure chamber 7 and the compression-side chamber R2 are communicated with each other when in the neutral position. On the other hand, when the free piston 9 is displaced to some extent from the neutral position, the outer periphery of the sliding contact cylinder 31 of the free piston 9 completely overlaps the port 21a and closes it. The amount of displacement from the neutral position at which the free piston 9 begins to close the port 21a can be arbitrarily set, and the side of the expansion side pressure chamber 7 that is the upper side in FIG. 2 of the free piston 9 that starts to close the port 21a. The displacement amount from the neutral position to the neutral position may be set differently from the displacement amount of the free piston 9 starting to close the port 21a from the neutral position toward the pressure side pressure chamber 8 which is the lower side in FIG.

  That is, in the case of this rear cushion unit RCU, when the displacement amount from the neutral position of the free piston 9 becomes a predetermined displacement amount, the port 21a starts to face the outer periphery of the sliding cylinder 31 from the situation where the port 21a faces the annular groove 32. As the situation shifts, the channel area of the port 21a begins to decrease gradually, and the channel resistance gradually increases.

  Therefore, the predetermined displacement amount can be arbitrarily set by setting the vertical width in FIG. 2 of the annular groove 32 and the opening position of the port 21a. In this embodiment, the flow area of the port 21a gradually decreases as the displacement amount of the free piston 9 increases, and when the free piston 9 reaches the stroke end, the port 21a is completely closed, The extension side pressure chamber 7 communicates only with the extension side chamber R1 through the extension side passage 10.

  In this embodiment, two ports 21a are provided, but the number thereof is arbitrary, an annular groove is provided on the inner periphery of the cylindrical portion 21, and the outer peripheral side of the free piston 9 and the extension side pressure chamber 7 are provided. A port that communicates may be provided in the free piston 9.

  Next, the basic operation of the rear cushion unit RCU will be described. First, the operation in the case where the amount of displacement from the neutral position in the free piston 9 is within the range where the port 21a does not begin to be closed will be described. In this case, the free piston 9 becomes constant without the port 21a being maintained in a completely connected state and the flow path resistance at the port 21a being unchanged.

  First, when the rear cushion unit RCU is in the contraction stroke, the free piston 9 is freely displaced with respect to the housing 6 in accordance with the differential pressure between the expansion side pressure chamber 7 and the pressure side pressure chamber 8. The pressure-side pressure chamber 8 is compressed through the pressure-side passage 11 and maintained at the same pressure as the pressure of the pressure-side chamber R2 that becomes high pressure, while the extension-side pressure chamber 7 is extended through the extension-side passage 10. Although the pressure side chamber 7 is also connected to the compression side chamber R2 through the port 21a, the pressure in the expansion side pressure chamber 7 becomes higher than that of the expansion side chamber R1 due to the pressure loss of the port 21a. Since the pressure is much smaller than the pressure, the displacement amount of the free piston 9 is increased.

  On the other hand, when the rear cushion unit RCU is in the extension stroke, the free piston 9 is freely displaced with respect to the housing 6 according to the differential pressure between the extension side pressure chamber 7 and the pressure side pressure chamber 8. In this case, the pressure-side pressure chamber 8 is expanded through the pressure-side passage 11 and is kept at the same pressure as the pressure of the pressure-side chamber R2 which becomes low pressure, while the expansion-side pressure chamber 7 is compressed and increased in pressure. Therefore, the pressure in the expansion side pressure chamber 7 is only an intermediate pressure between the expansion side chamber R1 and the pressure side chamber R2, and the free piston 9 is displaced. The amount is small compared to the contraction stroke.

  Further, if the amplitude of the vibration input to the rear cushion unit RCU is the same, the higher the vibration is, the larger the differential pressure between the expansion side pressure chamber 7 and the pressure side pressure chamber 8 is, and the displacement of the free piston 9 is increased. The amount also increases.

  The displacement amount of the free piston 9 apparently passes through the pressure chamber C and indicates the flow rate of the liquid, and the flow rate passing through the pressure chamber C is a flow rate bypassing the damping passages 4 and 5. The greater the amount of displacement, the greater the detouring flow rate and the higher the effect of reducing the damping force generated by the rear cushion unit RCU. That is, as shown in FIG. 3, the rear cushion unit RCU exhibits a high damping force for low-frequency vibrations, a small damping force for high-frequency vibrations, and a change in damping force during the extension stroke. It exhibits a damping characteristic in which the damping force change width Y during the contraction stroke is larger than the width X.

Therefore, according to this rear cushion unit RCU, since the reduction range of the damping force in the contraction stroke can be increased as compared with the conventional rear cushion unit , the high frequency as when the two-wheeled vehicle passes through the protrusion on the road surface is increased. Even when vibration (impact shock) having a large amplitude is input, the impact shock can be sufficiently absorbed and a good riding comfort can be obtained.

  In the rear cushion unit RCU, the flow resistance in the extension side passage 10 can be adjusted by the variable valve 13, and the pressure in the extension side pressure chamber 7 is controlled by the adjustment in the variable valve 13. Be able to. Controlling the pressure in the expansion side pressure chamber 7 leads to control of the displacement amount of the free piston 9, and by adjusting the displacement amount of the free piston 9, the bypass flow rate of the damping passages 4 and 5 is adjusted. Therefore, as shown in FIG. 4, it is possible to adjust the damping force change width in the damping characteristics in both the expansion and contraction processes. That is, the attenuation characteristic can be adjusted within the hatched area in FIG. Thus, in the conventional shock absorber, the damping characteristic curve could only be shifted up and down. However, in the rear cushion unit RCU of the present invention, the range of change in damping force in the damping characteristic can be adjusted. It is possible to obtain an optimum damping characteristic for suppressing the vehicle body vibration.

  Further, the extension side passage 10 is arranged so as to communicate with one end from the side facing the extension side chamber R1 of the piston rod 3 so as to communicate with the pressure chamber C of the housing 6 connected to the one end 3a of the piston rod 3. Therefore, the variable valve 13 to be provided in the middle of the extension side passage 10 can be efficiently arranged in the piston rod 3 while the housing 6 functions as a piston nut for fixing the piston 2 to the piston rod 3. . Further, the piston rod 3 is provided with a hollow portion 3d communicating with the expansion side passage 10, and a control rod for driving the needle type valve element 25 is inserted into the hollow portion 3d, so that the rear can be easily operated by an external operation. The damping characteristic of the cushion unit RCU can be adjusted.

  In addition, the above-mentioned effect can be enjoyed irrespective of the presence or absence of the port 21a and the annular groove 32. That is, the above-described effect can be obtained even if a configuration in which the extension side pressure chamber 7 and the pressure side chamber R2 are not communicated with each other through a passage having a flow path resistance is employed. Next, advantages of providing the port 21a and the annular groove 32 will be described.

  When the frequency of vibration input to the rear cushion unit RCU is high and the amplitude is large, the amount of displacement from the neutral position in the free piston 9 also increases, and the free piston 9 begins to close the port 21a, and the free piston 9 moves to the stroke end. When reaching, the port 21a is completely blocked.

  Thus, after the free piston 9 starts to close the port 21a, the area (wrap area) where the port 21a and the annular groove 32 overlap is reduced according to the amount of displacement, and the port 21a is narrowed down. The flow path resistance given to the flow of liquid passing through the port 21a gradually increases as the displacement amount of the free piston 9 increases. Then, when the vibration frequency is relatively high, the rear cushion unit RCU generates a relatively low damping force until the free piston 9 is displaced to a position where the free piston 9 starts to close the port 21a. As the displacement of the port 21a begins to close, the flow resistance at the port 21a gradually increases, so that the moving speed of the free piston 9 toward the stroke end is further reduced. The amount of liquid movement between the extension side chamber R1 and the pressure side chamber R2 via the pressure chamber C is also reduced, and the amount of liquid passing through the damping passages 4 and 5 is increased accordingly, and the rear cushion unit RCU The generated damping force gradually increases.

  When the free piston 9 reaches the stroke end, the liquid no longer moves between the expansion side chamber R1 and the pressure side chamber R2 via the pressure chamber C, and the liquid is attenuated until the expansion / contraction direction of the rear cushion unit RCU changes. Only the passages 4 and 5 pass, and the rear cushion unit RCU loses the damping force reduction effect and exhibits a large damping force depending on the leaf valves 17 and 18.

  That is, even if high-frequency and large-amplitude vibration that causes the free piston 9 to be displaced to the stroke end is input to the rear cushion unit RCU, the rear cushion unit RCU is displaced from the neutral position of the free piston 9. Since the generated damping force is gradually increased before the free piston 9 reaches the stroke end when the displacement exceeds an arbitrary amount of displacement, there is no sudden change from a low damping force to a high damping force. That is, when the free piston 9 reaches the stroke end and the liquid exchange between the extension side chamber R1 and the pressure side chamber R2 through the pressure chamber C becomes impossible, the magnitude of the damping force does not change suddenly. The damping force change from the low damping force to the high damping force becomes gentle. Furthermore, since the generated damping force is gradually increased when the free piston 9 reaches the stroke ends at both ends in the pressure chamber C, the function of suppressing a sudden change in the damping force is the pressure increase of the rear cushion unit RCU. It is demonstrated in both processes. Therefore, in this rear cushion unit RCU, even if a vibration with a high frequency and a large amplitude is input, the generated damping force changes gently, and the passenger is made to perceive a shock due to the change in the damping force. As a result, the ride comfort in the vehicle can be improved.

  In the rear cushion unit RCU, the urging force for returning the free piston 9 to the neutral position is applied to the free piston 9 by the coil springs 34 and 35, so that a sudden change in the damping force occurs when necessary. It is possible to avoid a situation in which the function to suppress cannot be exhibited.

 This is the end of the description of the embodiment of the present invention, but the scope of the present invention is of course not limited to the details shown or described.

  The rear cushion unit of the present invention can be used for vibration control of motorcycles.

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Piston 3 Piston rod 3a Piston rod one end 3b Piston rod screw part 3c Piston rod other end 3d Piston rod hollow part 4, 5 Damping passage 6 Housing 7 Extension side pressure chamber 8 Pressure side pressure chamber 9 Free piston 10 Extension side passage 10a Horizontal hole 10b Vertical hole 11 Pressure side passage 12 Spring element 13 Variable valve 14 Sliding partition 15 Rod guide 16 Seal member 17, 18 Leaf valve 20 Nut portion 21 Tube portion 22 Spring support 20a Screw portion 20b Fitting recess 21a Port 23 Valve seat member 23a Annular valve seat 24 Control rod 25 Needle-type valve body 26 Seat part 27 Bracket 27a Adjustment port 28 Adjustment screw 28a Adjustment screw tip 24a Tapered surface 30 Mirror part 31 Sliding cylinder 32 Annular groove 33 Communication holes 34, 35 Coil spring 40 tank as a spring element Hole C pressure chamber O orifices R1 expansion side chamber R2 compression side chamber RCU rear cushion unit T tank

Claims (3)

A cylinder connected to one of the rear wheel and the vehicle body of the two-wheeled vehicle, a piston that is slidably inserted into the cylinder and divides the cylinder into an extension side chamber and a pressure side chamber, and one end connected to the piston and the two-wheeled vehicle A piston rod connected to the other of the rear wheel and the vehicle body; and a damping passage provided in the piston for communicating the extension side chamber and the pressure side chamber and for resisting the flow of liquid passing therethrough. In a rear cushion unit that exhibits a damping force to be suppressed, a housing that forms a pressure chamber, and a free piston that is slidably inserted into the pressure chamber and divides the pressure chamber into an expansion side pressure chamber and a pressure side pressure chamber , pressure to maintain an equal pressure and the compression side chamber and the pressure side pressure communicates with the extension side passage communicating with the expansion side chamber and the expansion side pressure chamber and the compression side chamber and the pressure side pressure chamber A passage, a spring element that exerts an urging force that suppresses displacement of the free piston with respect to the housing, and a variable valve that is provided in the middle of the extension side passage and makes the flow resistance of the extension side passage variable. The housing is provided with either one of a port and an annular groove communicating with the pressure side chamber and the inside of the housing, and the free piston is connected with the other of the port and the annular groove that opens from the outer periphery and communicates with the extension side pressure chamber. The rear cushion is characterized in that when the free piston is in a neutral position, the port and the annular groove face each other, and when the free piston is displaced from the neutral position by a predetermined amount, a facing area between the port and the annular groove is reduced. unit. The housing functions as a piston nut that is screwed to one end of the piston rod to fix the piston to the piston rod, and the extension side passage extends from the side of the piston rod facing the extension side chamber to one end. The extension side pressure chamber and the extension side chamber in the housing communicate with each other, and the variable valve is provided with an annular valve seat provided in the middle of the extension side passage, and the extension side passage close to the annular valve seat. 2. The rear cushion unit according to claim 1, further comprising a needle-type valve body that changes a flow passage area . The piston rod includes a hollow portion that communicates with the extension side passage, and a control rod that drives the needle type valve body is inserted into the hollow portion, and the needle type valve body is operated by operating the control rod externally. The rear cushion unit according to claim 2 , wherein the flow path area of the variable valve can be changed by moving it closer to the annular valve seat .

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