SHOCK-ABSORBER CONTROLLING APPARATUS

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a shock-absorber controlling apparatus and, in particular to a shock-absorber controlling apparatus that controls the damping force of a shock absorber.

2. Description of the Related Art

[0002] A shock absorber produces damping force through the movement of a piston in a cylinder filled with working fluid. One such shock absorber is described in Japanese Patent Application Publication No. 59-187124 (JP-A-59-187124). This shock absorber is provided with a controller that causes the electric power generated using the flow of working fluid in the shock absorber to be consumed outside of its cylinder. Further, Japanese Patent Application Publication No. 08-135712 (JP-A-08-135712) describes a shock absorber in which, in order to produce proper damping force, a slanted face is formed near the concave portion of a valve seat so as to face a leaf valve.

[0003] According to the technology described in JP-A-59-187124, the working fluid in the shock absorber needs to be delivered to the outside of the shock absorber, and this is not desirable in view of product downsizing and cost reduction. According to the technology described in JP-A-08-135712, the damping force of the shock absorber is very small when the piston speed is low. If only small damping force is achieved in a low piston speed range, it may reduce the driving stability of the vehicle, and also it may even make the vehicle unstable.

SUMMARY OF THE INVENTION [0004] The invention provides a shock absorber that reduces the product size and the

product cost while producing proper damping force.

[0005] The first aspect of the invention relates to a shock-absorber controlling apparatus that controls the damping force of a shock absorber. The shock-absorber controlling apparatus has: a fluid passage for the working fluid in the shock absorber; a piston that moves in a cylinder while causing the working fluid in a fluid chamber located before the piston in the moving direction of the piston to flow to the fluid passage and then to a fluid chamber located after the piston in the moving direction of the piston; a flow-resistant member provided in the fluid passage and produces resistance against flow of the working fluid in the fluid passage; braking means for applying braking force to the flow-resistant member; and damping-force controlling means for controlling damping force that acts on the piston by controlling the braking force applied from the braking means to the flow-resistant member.

[0006] The shock-absorber controlling apparatus may be such that the flow-resistant member may be formed in the cylinder.

[0007] The shock-absorber controlling apparatus may be such that the flow-resistant member may be formed in the piston.

[0008] The shock-absorber controlling apparatus may be such that: the flow-resistant member is arranged to be rotated by flow of the working fluid in the fluid passage and thus produces resistance against the working fluid; and the braking means applies braking force to the flow-resistant member by braking the rotation of the flow-resistant member.

[0009] According to the shock-absorber controlling apparatus described above, because the flow-resistant member is provided in the piston and used to generate electric power using the flow of the working fluid, the product size and the product cost can be reduced as compared to a case where pipes for delivering the working fluid are provided outside of the shock absorber. According to the shock-absorber controlling apparatus of the first aspect of the invention, further, large damping force can be obtained by applying braking force to the flow resistant member, and this provides a higher driving stability of the vehicle and prevents the vehicle from becoming unstable when running.

[0010] The shock-absorber controlling apparatus may be such that: the braking

means includes power generating means for generating electric power through the rotation of the flow-resistant member and a variable resistor connected to the power generating means; the braking means applies braking force to the flow-resistant member by supplying electric current generated by the power generating means to the variable resistor; and the damping-force controlling means controls the damping force that acts on the piston by changing the braking force applied to the flow-resistant member by changing the resistance of the variable resistor.

[0011] According to this structure, the structure for applying braking force to the flow-resistant member can be simplified. Further, the damping force on the piston can be controlled by simply changing the resistance of the variable resistor, that is, the damping force of the shock absorber can be easily controlled.

[0012] The shock-absorber controlling apparatus may be such that the power generating means is provided outside the cylinder.

[0013] According to this structure, because the power generating means is not provided in the cylinder filled with the working fluid, the power generating means is easily serviced for maintenance.

[0014] The shock-absorber controlling apparatus may be such that: the damping-force controlling means changes the resistance of the variable resistor such that, when the piston moves in a first direction in the cylinder, the relation between the moving speed of the piston and the damping force on the piston is directly proportional; and the damping-force controlling means changes the resistance of the variable resistor such that, when the piston moves in a second direction that is opposite to the first direction, the relation between the moving speed of the piston and the damping force on the piston is directly proportional.

[0015] The shock-absorber controlling apparatus may be such that: the flow-resistant member rotates in a third direction in response to the working fluid flowing in the fluid passage as the piston moves in a first direction in the cylinder and the flow-resistant member rotates in a fourth direction, which is opposite to the third direction, in response to the working fluid flowing in the fluid passage as the piston moves in a second direction

that is opposite to the first direction; the variable resistor includes a first variable resistor and a second variable resistor both connected to the power generating means, a first diode arranged to prohibit electric current, that is generated by the flow-resistant member rotating in the fourth direction, from being supplied to the first variable resistor, and a second diode arranged to prohibit electric current, that is generated by the flow-resistant member rotating in the third direction, from being supplied to the second variable resistor; and the damping-force controlling means changes the resistances of the first variable resistor and the second variable resistor.

[0016] The shock-absorber controlling apparatus may be such that the resistance of the first variable resistor is different from the resistance of the second variable resistor.

[0017] Shock absorbers are more likely to receive a large impact when they contract, such as when the tyres run upon a bump on the road, than when they extend. According to the shock-absorber controlling apparatus described above, the damping force that acts on the piston when it moves in the first direction in the cylinder can be controlled by changing the resistance of the first variable resistor, and the damping force that acts on the piston when it moves in the second direction in the cylinder can be controlled by changing the resistance of the second variable resistor. Therefore, the damping force that acts on the piston when it moves in the first direction and the damping force that acts on the piston when it moves in the second direction can be separately controlled. As such, the shock absorber produces appropriate damping forces for both the cases, the impacts given to the shock absorber when it extends and the impacts given to the shock absorber when it contracts.

[0018] The shock-absorber controlling apparatus may be such that: the piston has a first fluid passage and a second fluid passage that the working fluid flows therein, and a check valve that allows flow of the working fluid to the second fluid passage when the piston moves in a first direction in the cylinder and prohibits flow of the working fluid to the second fluid passage when the piston moves in a second direction that is opposite to the first direction; the flow-resistant member has a first flow-resistant member that rotate together with a second flow-resistant member; the first flow-resistant member is arranged

in the first fluid passage and rotates as the working fluid flows in the first fluid passage; the second flow-resistant member is arranged in the second fluid passage and rotates as the working fluid flows in the second fluid passage; and the braking means applies braking forces to the first flow-resistant member and the second flow-resistant member.

[0019] According to this structure, when the piston is moving in the first direction, the working fluid flows through both the first fluid passage and the second fluid passage, and when the piston is moving in the second direction, the working fluid flows through the second fluid passage only. As such, the speed at which the flow-resistant member rotates when the piston is moving in the first direction and the speed at which the flow-resistant member rotates when the piston is moving in the second direction are different. Thus, different braking forces can be applied depending upon whether the piston is moving in the first direction or in the second direction.

[0020] The shock-absorber controlling apparatus may be such that: the piston is arranged in the cylinder so as to divide the inside of the cylinder into a first chamber and a second chamber, and the piston incorporates a first check valve, a second check valve, a third check valve, and a fourth check valve; the first check valve allows flow of the working fluid from the first chamber to the fluid passage and prohibits flow of the working fluid from the fluid passage to the first chamber; the second check valve allows flow of the working fluid from the fluid passage to the second chamber and prohibits flow of the working fluid from the second chamber to the fluid passage; the third check valve allows flow of the working fluid from the second chamber to the fluid passage and prohibits flow of the working fluid from the fluid passage to the second chamber; the fourth check valve allows flow of the working fluid from the fluid passage to the first chamber and prohibits flow of the working fluid from the first chamber to the fluid passage; and the first to fourth check valves are arranged such that the direction the flow-resistant member rotates when the working fluid flows from the first check valve to the second check valve coincides with the direction the flow-resistant member rotates when the working fluid flows from the third check valve to the fourth check valve.

[0021] According to this structure, the flow-resistant member rotates in one direction

regardless of whether the piston is moving in the first direction or the second direction. Therefore, the rotation of the flow-resistant member is not reversed during reciprocation of the piston, and this prolongs the life of the flow resistant member.

[0022] The shock-absorber controlling apparatus may be such that: the piston has a valve that is located between a portion of the fluid passage, that is upstream of the flow-resistant member when the working fluid flows in the fluid passage by the piston moving in the cylinder, and a fluid chamber located behind the piston; and the valve opens in response to the pressure of the working fluid at the upstream portion of the fluid passage exceeding a predetermined value, allowing the working fluid to flow from the upstream portion to the fluid chamber behind the piston.

[0023] The shock-absorber controlling apparatus may be such that motion transmitting means is incorporated in a piston rod, that is connected to the piston, for transmitting the motion caused to the flow-resistant member outside the cylinder.

[0024] According to this structure, the flow-resistant member is prevented from rotating to an extent that the damping force of the shock absorber becomes larger than necessary, and therefore the working fluid smoothly flows between the respective fluid chambers. Further, because the flow-resistant member is prevented from rotating at a high speed, its life can be prolonged.

[0025] As such, the shock-absorber controlling apparatus of the invention reduces the product size and the product cost while producing a proper damping force.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a view showing the overall configuration of a vehicle incorporating a shock-absorber controlling apparatus according to the first example embodiment of the invention;

FIG. 2 is a cross-sectional view of the shock absorber of the first example embodiment of the invention;

FIG. 3 is a cross-sectional view taken along III-III in FIG. 2;

FIG. 4 is a graph illustrating the relation between the moving speed V of the piston of the shock absorber of the first example embodiment and the damping force F that acts on said piston;

FIG. 5 is a cross-sectional view of a shock absorber incorporated in a shock-absorber controlling apparatus of the second example embodiment of the invention;

FIG. 6 is a cross-sectional view taken along VI-VI in FIG. 5;

FIG. 7 is a graph illustrating the relation between the moving speed V of the piston of the shock absorber of the second example embodiment and the damping force F that acts on said piston;

FIG. 8 is a view showing the configuration of a variable resistor unit of the third example embodiment of the invention;

FIG. 9 is a graph illustrating the relation between the moving speed V of the piston of the shock absorber of the third example embodiment of the invention and the damping force F that acts on said piston;

FIG. 10 is a cross-sectional view of a shock absorber incorporated in a shock-absorber controlling apparatus of the fourth example embodiment of the invention;

FIG. 11 is a cross-sectional view of a shock absorber incorporated in a shock-absorber controlling apparatus according to the fifth example embodiment of the invention:

FIG. 12A is a view illustrating the flow path of the working fluid that is established when the piston moves down;

FIG. 12B is a view illustrating another flow path of the working fluid that is established when the piston moves down;

FIG. 13A is a view illustrating a flow path of the working fluid that is established when the piston moves up;

FIG. 13B is a view illustrating another flow path of the working fluid that is established when the piston moves up; and

FIG. 14 is a graph illustrating the relation between the flow rate Q of the working fluid that flows between the first chamber and the second chamber as the piston moves and the differential pressure δP between the first communication passage and the second communication passage.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] (First Example Embodiment)

FIG. 1 illustrates the overall configuration of a vehicle 10 incorporating a shock-absorber controlling apparatus 200 according to the first example embodiment of the invention. The vehicle 10 has a vehicle body 12 assembling four wheels 14. The shock-absorber controlling apparatus 200 has wheel speed sensors 16, shock absorbers ISA, motor generators 19, variable resistors 20, sprung G-sensors 22, and unsprung G-sensors 24, which are provided on the vehicle body 12 at positions corresponding to the respective wheels 14. The shock-absorber controlling apparatus 200 has a steering angle sensor 26 and an electronic control unit 30 (hereinafter be referred to as "ECU 30").

[0028] The ECU 30 is constituted of a CPU (Central Processing Unit) that is used to execute various computations and calculations, a ROM (Read Only Memory) that is used to store various control programs, a RAM (Random Access Memory) that is used to store various data temporarily and also used as a work area for executing various programs, and the like. The ECU 30 controls various components and devices provided in the vehicle 10. The wheel speed sensor 16 sends signals indicating the rotational speeds of the respective wheels 14 to the ECU 30. Each shock absorber 18A is arranged between an unsprung suspension arm and a sprung support member that is provided on the vehicle compartment side. Thus arranged, the shock absorbers ISA absorb the impacts input to the vehicle and thus reduce the impacts transmitted to the vehicle compartment. The motor generators 19 are provided at the respective shock absorbers ISA, and the variable resistors 20 are connected to the respective motor generators 19. The variable resistors 20 are connected to the ECU 30, and the ECU 30 controls the resistance of each variable

resistor 20. The motor generators 19 may be connected to a battery. In this case, the electric power generated by each motor generator 19 can be used for the operation of the vehicle, that is, power regeneration can be performed.

[0029] The sprung G-sensors 22 are provided on a vehicle body (not shown in the drawings) at positions corresponding to the respective wheels 14. On the other hand, the unsprung G-sensors 24 are provided on a suspension member (not shown in the drawings) at positions corresponding to the respective wheels. 14. The suspension member is an unsprung casing member to which the respective suspension arms are linked. The four sprung G-sensors 22 are used to detect the vertical acceleration of the vehicle body on which they are provided. On the other hand, the four the unsprung G-sensors 24 are used to detect the vertical acceleration of the suspension member on which they are provided. The steering angle sensor 26 detects the turning angle of the steering wheel 28. The results of detections by the sprung G-sensors 22, the unsprung G-sensors 24, and the steering angle sensor 26 are output to the ECU 30.

[0030] FIG. 2 shows a cross section of each shock absorber 18 A. The shock absorber ISA has a cylinder 40, a piston 42, a piston rod 44, and an attachment portion 46. The attachment portion 46 is provided at the bottom of the cylinder 40. The attachment portion 46 is secured to the corresponding suspension arm, for example. The cylinder 40 is cylindrical, and a cylinder chamber 40a is formed in the cylinder 40.

[0031] A free piston 64 is provided below the cylinder chamber 40a, and a gas chamber 4Od is provided below the free piston 64. The gas chamber 4Od is filled with gas, such as air. The free piston 64 moves up and down according to the difference between the pressure in the cylinder chamber 40a and the pressure in the gas chamber 4Od.

[0032] The cylinder chamber 40a, which is located above the free piston 64 as mentioned above, is filled with oil as working fluid. The piston 42 is column-shaped and its outer diameter is substantially equal to the inner diameter of the cylinder 40. The piston 42 is disposed in the cylinder chamber 40a, dividing the cylinder chamber 40a into a first chamber 40b on the upper side and a second chamber 40c on the lower side.

The lower end of the piston rod 44, which has an elongated cylindrical shape, is coaxially connected to the upper end of the piston 42. A through hole is formed at the top of the cylinder 40, and the piston rod 44 protrudes up from the cylinder 40 through the through hole. As the piston 42 moves within the cylinder chamber 40a, the distance the piston rod 44 protrudes from the cylinder 40 changes, whereby the shock absorber ISA extends and contracts.

[0033] A fluid passage 42a for the working fluid is formed in the piston 42. As the piston 42 moves up in the cylinder chamber 40a, the working fluid flows from the first chamber 40b, which is located before the piston 42 at this time, to the second chamber 40c, which is located after the piston 42 at this time, through the fluid passage 42a. Conversely, as the piston 42 moves down in the cylinder chamber 40a, the working fluid flows from the second chamber 40c, which is located before the piston 42 at this time, to the first chamber 40b, which is located after the piston 42 at this time, through the fluid passage 42a. The upper and lower sides of the fluid passage 42a are flat and perpendicular to the axis of the piston 42, and the fluid passage 42a extends along a plain perpendicular to the axis of the piston 42.

[0034] A first gear 50 and a second gear 52 are disposed in the fluid passage 42a. The first gear 50 and the second gear 52 are identical in shape and characteristics (e.g., the number of gear teeth). The first gear 50 and the second gear 52 are in mesh with each other and their axes are parallel to the axis of the piston 42. The first gear 50 is fixed on a first shaft 54, and the second gear 52 is fixed on a second shaft 56. The first shaft 54 is supported by the piston 42 via bearings, and thus the first gear 50 is rotatable relative to the piston 42. Likewise, the second shaft 56 is supported by the piston 42 via bearings, and thus the second gear 52 is rotatable relative the piston 42.

[0035] In the following, the inside structure of the fluid passage 42a will be described in detail with reference to FIG. 3. FIG. 3 shows a cross section taken along HI-III in FIG. 2. Referring to FIG. 3, the fluid passage 42a has two arc-shaped portions slightly larger than the first gear 50 and the second gear 52 and two straight portions extending, in opposite directions, form the boundary between the two arc-shaped portions.

In the piston 42, further, a first communication passage 42b and is a second communication passage 42c are formed such that one of the straight portions of the fluid passage 42a and the fluid passage 42a communicate with each other and the other of the straight portions and the fluid passage 42a communicate with each other.

[0036] The first gear 50 and the second gear 52 are disposed in the two arc-shaped portions of the fluid passage 40a, respectively, and are in mesh with each other. For example, when the piston 42 moves up, the working fluid enters the fluid passage 42a from the first communication passage 42b, whereby the pressure on the first communication passage 42b side of the first gear 50 and the second gear 52 becomes higher than the pressure on the second communication passage 42c side. At this time, because the first gear 50 and the second gear 52 are in mesh with each other as described above, the pressure difference causes the first gear 50 to rotate clockwise and causes the second gear 52 to rotate counterclockwise (anticlockwise) as viewed in FIG. 3. On the other hand, when the piston 42 moves down, the first gear 50 rotates counterclockwise (anticlockwise) and the second gear 52 rotates clockwise as viewed in FIG. 3. By this rotation, the first gear 50 and the second gear 52 produce a resistance against the flow of working fluid. That is, the first gear 50 and the second gear 52 serve as a flow-resistant member. The rotational speeds of the first gear 50 and the second gear 52 depend upon the flow rate of the working fluid flowing through the fluid passage 42a.

[0037] Referring back to FIG. 2, a gear 58 is fixed at the upper end of the first shaft 54. A rotational shaft 62 is provided in the piston rod 44, and a gear 60 is fixed at the lower end of the rotational shaft 62. The gear 58 and the gear 60 are in mesh with each other. As the first gear 50 rotates, the rotational shaft 62 rotates via the gears 58, 60.

[0038] The motor generator 19 is provided at the upper end of the piston rod 44. The rotational shaft 62 is coupled with the internal structure of the motor generator 19, and the motor generator 19 generates electric power according to the rotational speed of the rotational shaft 62. It is to be noted that the motor generator 19 is a known motor generator and therefore the process of power generation by the motor generator 19 is not described in this specification. A variable resistor 20 is connected to the motor

generator 19 such that the electric current generated by the motor generator 19 is supplied to the variable resistor 20. Please be noted that the rectangular box stands for a resistor. As electric power is thus consumed at the variable resistor 20, braking force is applied to the first gear 50. At this time, the braking force is also applied to the second gear 52 that is in mesh with the first gear 50. As such, the motor generator 19 and the variable resistor 20 serve as braking means for applying braking force to the first gear 50 and to the second gear 52. The braking force applied from the motor generator 19 to the first gear 50 depends upon the rotational speed of the first gear 50. The following expression (1) represents the torque applied to the first gear 50 and the second gear 52:

(1) T = q x δP / 2π where "T" represents torque (N/m), "q" represents the discharge rate of a gear pump (cc/rev), and "δP" represents the differential pressure between the first communication passage 42b side and the second communication passage 42c side of the fluid passage 42a.

[0039] The following expression (2) is a theoretical torque formula for the motor generator 19.

(2) T = Ke x Kt x N / R where "Ke" is a counter electromotive force constant (V-sec/rad), "Kt" is a torque constant (N-m/A), "N" represents the rotational speed of the first gear 50 (rad/sec), and "r" represents the resistance of the variable resistor 20 (ω).

[0040] Based on the expressions (1) and (2), δP can be expressed as the expression (3) indicated below.

(3) δP = 2π x Ke x Kt x N / (R x q)

As is known from this expression, the value of δP can be changed by changing the resistance of the variable resistor 20.

[0041] Thus, the ECU 30 adjusts the braking force applied to the first gear 50 and the second gear 52 by changing the resistance of the variable resistor 20 and thereby controls the damping force acts on the piston 42. As such, the ECU 30 serves as damping-force controlling means.

[0042] The ECU 30 sets the target damping force of each shock absorber 18A by applying to, for example, equations of motion and/or transfer functions based on the skyhook theory, the detection of the wheel speed sensor 16, the sprung G-sensors 22, the unsprung G-sensors 24, and the steering angle sensor 26. Then, the ECU 30 calculates the target resistance of the variable resistor 20 required to achieve the target damping force of the shock absorber ISA. Then, the ECU 30 changes the resistance of the variable resistor 20. The procedure for setting the target damping force of the shock absorber ISA using equations of motions and/or transfer functions based on the skyhook theory may be selected from those known in the art, and therefore it is not described in this specification. However, it is to be understood that, if appropriate, the target damping force of the shock absorber ISA may be determined in various other methods without using equations of motions and/or transfer functions based on the skyhook theory.

[0043] In the first example embodiment, the ROM of the ECU 30 stores a map describing the relation between the target damping force of the shock absorber ISA for its extension and the target damping force for its contraction. According to this map, the target damping forces for extension and contraction of the shock absorber ISA are separately set. Further, the map is formulated such that the target damping forces of the shock absorber ISA are set in steps according to the difference between the sprung vertical acceleration and the unsprung vertical acceleration, that is, according to the acceleration of the piston 42 relative to the cylinder 40. The ECU 30 calculates the speed of the vehicle 10 based on the results of detections by the wheel speed sensor 16. Further, the ECU 30 determines whether the shock absorber ISA is currently extending or contracting based on the results of detections by the sprung G-sensor 22 and the unsprung G-sensor 24. As such, using the map, the ECU 30 sets the target damping force of the shock absorber ISA based on the calculated speed of the vehicle 10, the result of the determination as to whether the vehicle 10 is currently extending or contracting, the turning angle of the steering wheel 28, and the results of detections by the sprung G-sensor 22 and the unsprung G-sensor 24. If appropriate, a travel sensor may be

provided to detect the travel of the shock absorber ISA. In this case, the ECU 30 may refer to the results of detections by the travel sensor in determining whether the shock absorber ISA is currently extending or contracting.

[0044] At this time, the ECU 30 may set the damping force of the shock absorber 18A larger the higher the vehicle speed is. Meanwhile, when the vehicle is turning, large compression forces are applied to the shock absorbers ISA at the outer wheels that are located far from the turning point. Therefore, when it is detected that the vehicle 10 is turning right or left, the ECU 30 may make the damping forces of the shock absorbers ISA at the outer wheels larger than when the vehicle 10 is running straight. Further, the ECU 30 may make the damping forces of the outer wheels larger the larger the turning angle detected by the steering angle sensor 26 is. Further, the ECU 30 may make the damping forces of the shock absorbers 18A at the outer wheels larger the higher the turning speed of the vehicle 10 is.

[0045] The graph of FIG. 4 illustrates the relation between a moving speed V of the piston and a damping force F that acts on the piston. In the graph, the solid line represents said relation obtained with the shock absorber ISA and the dotted line represents said relation obtained with a shock absorber not incorporating the first gear 50, the motor generator 19, and the variable resistor 20. As shown in the graph, when the shock absorber ISA is used, the relation between the piston speed V and the damping force F is linear, and therefore the damping force F that acts on the piston 42, in a region where the piston speed V is low, is large as compared to when the shock absorber not incorporating the first gear 50, the motor generator 19, and the variable resistor 20 is used.

[0046] (Second Example Embodiment)

FIG. 5 shows a cross section of a shock absorber ISB incorporated in a shock-absorber controlling apparatus 200 of the second example embodiment of the invention. Note that the structure of the shock-absorber controlling apparatus 200 of the second example embodiment is identical to that of the shock-absorber controlling apparatus 200 of the first example embodiment except that the shock absorbers ISA are replaced with the

shock absorbers 18B. Please be noted that the rectangular box stands for a resistor. The parts and portions of the shock absorber 18B that are identical to those of the shock absorber 18A are denoted by the same reference numerals and they are not described again.

[0047] The shock absorber 18B has a piston 80. The piston 80 is column-shaped, and the outer diameter of the piston 80 is substantially equal to the inner diameter of the cylinder 40. The piston 80 is disposed in the cylinder chamber 40a, dividing the cylinder chamber 40a into the first chamber 40b and the second chamber 40c. The lower end of the piston rod 44 is coaxially secured to the upper end of the piston 80.

[0048] A first fluid passage 80a and a second fluid passage 80b for the working fluid are formed in the first fluid passage 80a. The upper and lower sides of each fluid passage 80a, 80b are flat and perpendicular to the axis of the piston 80, and the axis of each fluid passage 80a, 80b is perpendicular to the axis of the piston 80. As viewed in the direction of the axis of the piston 80, the shape of each fluid passage 80a, 80b is identical to the shape of the fluid passage 42a.

[0049] The first gear 50 and the second gear 52 are disposed in the first fluid passage 80a, and a third gear 86 and a fourth gear 88 are disposed in the second fluid passage 80b. In the first fluid passage 80a, the first gear 50 and the second gear 52 are in mesh with each other and their axes are parallel to the axis of the piston 80. In the second fluid passage 80b, the third gear 86 and the fourth gear 88 are in mesh with each other and their axes are parallel to the axis of the piston 80. The first gear 50 and the third gear 86 are fixed on a first shaft 82, and the second gear 52 and the fourth gear 88 are fixed on a second shaft 84. The first shaft 82 is supported by the piston 80 via bearings, and thus the first gear 50 and the third gear 86 are rotatable relative to the piston 80. Likewise, the second shaft 84 is supported by the piston 80 via bearings, and thus the second gear 52 and the fourth gear 88 are rotatable relative to the piston 80.

[0050] FIG. 6 shows a cross section taken along VI-VI in FIG. 5. Note that FIG. 6 does not show the piston rod 44 and the rotational shaft 62. In the piston 80, a first communication passage 80c leading to the first chamber 40b and a second

communication passage 8Od leading to the second chamber 40c are formed with the first gear 50, the second gear 52, the third gear 86, and the fourth gear 88 interposed therebetween. The first fluid passage 80a and the second fluid passage 80b are each connected to the first communication passage 80c and to the second communication passage 8Od.

[0051] A first check valve 90 and a second check valve 92 are provided in the piston 80. Because the first check valve 90 and the second check valve 92 are known valves, their structures are not described in this specification. The first check valve 90 allows the flow of the working fluid from the second fluid passage 80b to the first communication passage 80c and prohibits the flow of the working fluid from the first communication passage 80c to the second fluid passage 80b. The second check valve 92 allows the flow of the working fluid from the second communication passage 8Od to the second fluid passage 80b and prohibits the flow of the working fluid from the second fluid passage 80b to the second communication passage 8Od.

[0052] Thus, when the shock absorber 18B extends, as indicated by the arrow Fl in FIG. 6, the working fluid flows from the first chamber 40b to the second chamber 40c through the first fluid passage 80a only. On the other hand, when the shock absorber 18B contracts, as indicated by the arrow F2 in FIG. 6, the working fluid flows from the second chamber 40c to the gas chamber 4Od through both the first fluid passage 80a and the second fluid passage 80b. As such, the damping force that acts on the piston 80 during contraction of the shock absorber 18B is smaller than the damping force that acts on the piston 80 during extension of the shock absorber 18B.

[0053] The graph of FIG. 7 illustrates the relation between the moving speed V of the piston of the shock absorber and the damping fprce F that acts on the piston. In the graph, the solid line represents said relation obtained with the shock absorber 18B and the dotted line represents said relation obtained with the shock absorber ISA of the first example embodiment. Note that the piston speed V of the piston when the shock absorber extends, that is, when the piston moves up is indicated in the positive side of the graph.

[0054] Referring to FIG. 7, when the shock absorber 18B is used, the damping force F corresponding to the piston speed V can be made smaller than it is when the shock absorber ISA of the first example embodiment is used, while maintaining the relation between the piston speed V and the damping force F linear. That is, for example, when the wheel 14 runs upon a bump on a road, a large impact is applied upwardly to the wheel 14. On the other hand, when the wheel 14 runs over a hollow in a road, normally the impact to the wheel 14 is not so large. For this reason, it is often' required for shock absorbers to produce, at the same piston speed V, a larger damping force during extension than during contraction, and the shock absorbers ISB can provide such different damping forces by a simple structure.

[0055] (Third Example Embodiment)

FIG. 8 shows the configuration of a variable resistor unit 100 of the third example embodiment of the invention. Please be noted that the rectangular box stands for a resistor. Note that the parts and portions of the shock absorber 18A of the third example embodiment that are identical to those of the shock absorber ISA of the first example embodiment are denoted by the same reference numerals and they are not described again.

[0056] In the third example embodiment, the variable resistor unit 100 is connected to the motor generator 19. The variable resistor unit 100 has a first variable resistor 102, a second variable resistor 104, a first diode 106, and a second diode 108.

[0057] The directions that the first gear 50 and the second gear 52 rotate when the piston 42 moves up are opposite to those when the piston 42 moves down. Therefore, the direction the current generated by the motor generator 19 flows in the variable resistor unit 100 when the piston 42 moves up and the direction the current generated by the motor generator 19 flows in the variable resistor unit 100 when the piston 42 moves down are opposite to each other. The first diode 106 is arranged so as to prohibit the flow of current to the first variable resistor 102 when current is generated at the motor generator 19 as the piston 42 moves down, and the second diode 108 is arranged so as to prohibit the flow of current to the second variable resistor 104 when current is generated

at the motor generator 19 as the piston 42 moves up. With this arrangement, when the shock absorber 18A extends, no current is supplied to the second variable resistor 104, that is, the generated current is supplied only to the first variable resistor 102. On the other hand, when the shock absorber ISA contracts, no current is supplied to the first variable resistor 102, that is, the generated current is supplied only to the second variable resistor 104. The first variable resistor 102 and the second variable resistor 104 are set to different values. For example, the resistance of the first variable resistor 102 is lower than that of the second variable resistor 104.

[0058] The graph of FIG. 9 illustrates the relation between the moving speed V of the piston and its damping force F. In the graph, the solid line represents said relation obtained with the shock absorber 18A connected to the variable resistor unit 100 of the third example embodiment and the dotted line represents said relation obtained with the shock absorber 18A of the first example embodiment. Note that the piston speed V obtained when the shock absorber extends, that is, when the piston moves up is indicated in the positive side of the graph.

[0059] According to the variable resistor unit 100 configured as described above, different damping forces F can be easily set for extension of the shock absorber ISA and for contraction by setting the first variable resistor 102 and the second variable resistor 104 to different values. Therefore, by setting the resistance of the first variable resistor 102 smaller than that of the second variable resistor 104, the damping force F corresponding to the piston speed V can be made smaller than it is when the shock absorber 18A of the first example embodiment is used, while maintaining the relation between the piston speed V and the damping force F linear.

[0060] (Fourth Example Embodiment)

FIG. 10 shows a cross section of each shock absorber ISC incorporated in a shock-absorber controlling apparatus 200 of the fourth example embodiment of the invention. Note that the structure of the shock-absorber controlling apparatus 200 of the fourth example embodiment is identical to that of the shock-absorber controlling apparatus 200 of the first example embodiment except that the shock absorbers ISA are

replaced with the shock absorbers 18C. The parts and portions of the shock absorber 18C that are identical to those of the shock absorber ISA of the first example embodiment are denoted by the same reference numerals and they are not described again.

[0061] The shock absorber 18C has a piston 120. FIG. 10 shows the peripheral structure of the piston 120. Other structures of the shock absorber 18C that are not shown in FIG. 10 are identical to those of the shock absorber 18A. As in the first example embodiment, the shock absorber 18C has the first gear 50 and the second gear 52 that are in mesh with each other. FIG. 10 is a cross-sectional view cutting through the meshing point between the first gear 50 and the second gear 52 and showing the second gear 52 side of the piston 120.

[0062] The piston 120 is column-shaped, and the outer diameter of the piston 120 is substantially equal to the inner diameter of the cylinder 40. The piston 120 is disposed in the cylinder chamber 40a, dividing the cylinder chamber 40a into the first chamber 40b and the second chamber 40c. The lower end of the piston rod 44 is coaxially secured to the upper end of the piston 120. Note that the piston rod 44 and the rotational shaft 62 are not shown in FIG. 10.

[0063] A fluid passage 120a for the working fluid is formed in the piston 120. The shape of the fluid passage 120a is identical to the fluid passage 42a of the first example embodiment. Further, the first gear 50 and the second gear 52 are supported in the piston 120 as they are in the fluid passage 42a of the first example embodiment. A first communication passage 120b is formed in the piston 120 such that the first chamber 40b and the fluid passage 120a communicate with each other via the first communication passage 120b, and a third communication passage 12Od is formed in the piston 120 coaxially with the first communication passage 120b such that the second chamber 40c and the fluid passage 120a communicate with each other via the third communication passage 12Od. Further, a fourth communication passage 12Oe is formed in the piston 120 such that the fluid passage 120a and the first chamber 40b communicate with each other via the fourth communication passage 12Oe, and a second communication passage

120c is formed coaxially with the fourth communication passage 12Oe such that the second chamber 40c and the fluid passage 120a communicate with each other via the second communication passage 120c. The first communication passage 120b and the third communication passage 12Od are provided on one side of the first gear 50 and the second gear 52, and the second communication passage 120c and the fourth communication passage 12Oe are provided on the other side.

[0064] A first check valve 122 is provided in the first communication passage 120b, a second check valve 124 is provided in the second communication passage 120c, a third check valve 126 is provided in the third communication passage 12Od, and a fourth check valve 128 is provided in the fourth communication passage 12Oe. It is to be noted that the check valves 122 to 128 are known check valves and therefore their structures are not described in this specification.

[0065] The first check valve 122 allows the flow of the working fluid from the first chamber 40b to the fluid passage 120a and prohibits the flow of the working fluid from the fluid passage 120a to the first chamber 40b. The second check valve 124 allows the flow of the working fluid from the fluid passage 120a to the second chamber 40c and prohibits the flow of the working fluid from the second chamber 40c to the fluid passage 120a. The third check valve 126 allows the flow of the working fluid from the second chamber 40c to the fluid passage 120a and prohibits the flow of the working fluid from the fluid passage 120a to the second chamber 40c. The fourth check valve 128 allows the flow of the working fluid from the fluid passage 120a to the first chamber 40b and prohibits the flow of the working fluid from the first chamber 40b to the fluid passage 120a.

[0066] According to the above-described structure, when the piston 120 moves up, the working fluid in the first chamber 40b flows to the fluid passage 120a via the first communication passage 120b and then to the second chamber 40c via the second communication passage 120c as indicated by the arrow F3 in FIG. 10. Thus, when the piston 120 moves up, the working fluid flows toward left in FIG. 10 through the first gear 50 and the second gear 52. On the other hand, when the piston 120 moves down, the

working fluid in the second chamber 40c flows to the fluid passage 120a via the third communication passage 12Od and then to the first chamber 40b via the fourth communication passage 12Oe as indicated by the arrow F4 in FIG. 10. Thus, when the piston 120 moves down the working fluid flows toward left in FIG. 10 through the first gear 50 and the second gear 52, as it does when the piston 120 moves up. As suϋh, the first gear 50 and the second gear 52 each rotate in the same direction when the piston 120 moves up and when it moves down. That is, the rotations of the first gear 50 and the second gear 52 are not reversed during reciprocation of the piston 120, and this prolongs the lives of the first gear 50 and the second gear 52.

[0067] (Fifth Example Embodiment)

FIG. 11 is a cross-sectional view of each shock absorber 18d incorporated in a shock-absorber controlling apparatus 200 according to the fifth example embodiment of the invention. Note that the structure of the shock-absorber controlling apparatus 200 of the fifth example embodiment is identical to that of the shock-absorber controlling apparatus 200 of the first example embodiment except that the shock absorbers ISA are replaced with the shock absorbers ISD. The parts and portions of the shock absorber 18D that are identical to those of the shock absorber 18A of the first example embodiment are denoted by the same reference numerals and they are not described again.

[0068] The shock absorber 18D has a piston 140. FIG. 11 shows the peripheral structure of the piston 140. Other structures of the shock absorber 18D that are not shown in FIG. 11 are identical to those of the shock absorber 18A.

[0069] A fluid passage 140a for the working fluid is formed in the piston 140. The shape of the fluid passage 140a is identical to the fluid passage 42a of the first example embodiment. As in the first example embodiment, the shock absorber 18D has the first gear 50 and the second gear 52 that are in mesh with each other. FIG. 11 is a cross-sectional view cutting through the meshing point between the first gear 50 and the second gear 52 and showing the second gear 52 side of the piston 140. The first gear 50 and the second gear 52 are supported in the fluid passage 140a as they are in the fluid

passage 42a of the first example embodiment.

[0070] The piston 140 is coupled with a piston rod 158. A rotational shaft 162 is rotatably disposed in the piston rod 158 so as to be coaxial with the rotational shaft 162. The first gear 50 is connected to the rotational shaft 162 via a gear (not shown in the drawings), and the rotational shaft 162 rotates together with the first gear 50. The rotational shaft 162 is connected to the motor generator 19. Therefore, as the first gear 50 rotates, the motor generator 19 generates electric power, thereby supplying current to the variable resistor 20. As such, in the shock-absorber controlling apparatus of the fifth example embodiment braking force is applied to the first gear 50 and the second gear 52 from the motor generator 19 and the variable resistor 20 as in the foregoing example embodiments.

[0071] In the piston 140, a first communication passage 140b is formed such that the second chamber 40c and the fluid passage 140a communicate with each other via the first communication passage 140b, and a second communication passage 140c is formed such that the first chamber 40b and the fluid passage 140a communicate with each other via the second communication passage 140c. The second communication passage 140c is provided on the side opposite from the first communication passage 140b across the first gear 50 and the second gear 52.

[0072] Further, in the piston 140, a third communication passage 14Od is formed such that the first communication passage 140b and the first chamber 40b communicate with each other via the third communication passage 14Od, and a fourth communication passage 14Oe is formed such that the second communication passage 140c and the second chamber 40c communicate with each other via the fourth communication passage 14Oe. A first relief valve 142 is provided in the third communication passage 14Od. When closed, the first relief valve 142 shuts the third communication passage 14Od, interrupting communication between the gas chamber 4Od and the third communication passage 14Od. The first relief valve 142 opens in response to the pressure of the working fluid in the third communication passage 14Od exceeding a predetermined pressure, opening the third communication passage 14Od and thus allowing the flow of the working fluid from the

first communication passage 140b to the first chamber 40b via the third communication passage 14Od. On the other hand, a second relief valve 144 is provided in the fourth communication passage 14Oe. When closed, the second relief valve 144 shuts the fourth communication passage 14Oe, interrupting communication between the second chamber 40c and the fourth communication passage 14Oe. The second relief valve 144 opens in response to the pressure of the working fluid in the fourth communication passage 14Oe exceeding a predetermined pressure, opening the fourth communication passage 14Oe and thus allowing the flow of the working fluid from the second communication passage 140c to flow to the second chamber 40c via the fourth communication passage 14Oe. The first relief valve 142 and the second relief valve 144 are each constituted of a spring, a valve seat, and a ball that is pressed against the valve seat by the urging force of the spring.

[0073] A first main valve unit 146 is provided on the upper side of the piston 140. The first main valve unit 146 is constituted of a first valve-seat member 148 and a first main valve 150. The first valve-seat member 148 is fixed on the upper side of the piston 140, and the first main valve 150 attached on the first valve-seat member 148. The first main valve 150 is a leaf valve. As the first main valve 150 deforms away from the upper face of the first valve-seat member 148, the third communication passage 14Od and the first chamber 40b become in communication. That is, as long as the first main valve 150 remains attached on the first valve-seat member 148, said communication between the first chamber 40b and the third communication passage 14Od is interrupted.

[0074] On the other hand, a second main valve unit 152 is provided on the lower side of the piston 140. The second main valve unit 152 is constituted of a second valve-seat member 154 and a second main valve 156. The second valve-seat member 154 is fixed on the lower side of the piston 140, and the second main valve 156 attached on the second valve-seat member 154. The second main valve unit 152 is a leaf valve. As the second main valve unit 152 deforms away from the lower face of the second valve-seat member 154, the fourth communication passage 14Oe and the second chamber 40c become in communication. That is, as long as the second main valve 156 remains

attached on the second valve-seat member 154, said communication between the second chamber 40c and the fourth communication passage 14Oe is interrupted.

[0075] FIG. 12A illustrates the flow path of the working fluid that is established when the piston 140 moves down. Even when the piston 140 moves down, the first relief valve 142 remains closed as long as the pressure of the working fluid in the first communication passage 140b is lower than the predetermined pressure. In this state, the working fluid in the second chamber 40c flows from the first communication passage 140b to the gas chamber 4Od via the fluid passage 140a and the second communication passage 140c without flowing through the third communication passage 14Od.

[0076] FIG. 12B illustrates another flow path of the working fluid that is established when the piston 140 moves down. When the pressure of the working fluid in the first communication passage 140b becomes higher than the predetermined pressure as the piston 140 moves down, the first relief valve 142 opens and thus places the first communication passage 140b and the first chamber 40b in communication, so that a portion of the working fluid in the first communication passage 140b flows to the gas chamber 4Od via the third communication passage 14Od and the first main valve unit 146.

[0077] FIG. 13 A illustrates a flow path of the working fluid that is established when the piston 140 moves up. Even when the piston 140 moves up, the first relief valve 142 remains closed as long as the pressure of the working fluid in the second communication passage 140c is lower than the predetermined pressure. In this state, the working fluid in the first chamber 40b flows from the second communication passage 140c to the second chamber 40c via the fluid passage 140a and the first communication passage 140b without flowing through the fourth communication passage 14Oe.

[0078] FIG. 13B illustrates another flow path of the working fluid that is established when the piston 140 moves up. When the pressure of the working fluid in the second communication passage 140c becomes higher than the predetermined pressure as the piston 140 moves up, the second relief valve 144 opens and thus places the second communication passage 140c and the second chamber 40c in communication, so that a portion of the working fluid in the second communication passage 140c flows to the

second chamber 40c via the fourth communication passage 14Oe and the second main valve unit 152.

[0079] The graph in FIG. 14 illustrates the relation between a flow rate Q of the working fluid that flows between the first chamber 40b and the second chamber 40c as the piston 140 moves and a differential pressure δP between the first communication passage 140b and the second communication passage 140c. In FIG. 14, the flow rate obtained when the working fluid flows from the second chamber 40c to the first chamber 40b is indicated in the positive side of the graph, and the differential pressure δP represents the value obtained by subtracting the fluid pressure in the second communication passage 140c from the fluid pressure in the first communication passage 140b.

[0080] As the differential pressure between the working fluid in the first communication passage 140b and that in the second communication passage 140c increases, the rotational speeds of the first gear 50 and the second gear 52 increase accordingly, and therefore the braking force produced by the motor generator 19 and the variable resistor 20 increases. Therefore, as long as the first relief valve 142 and the second relief valve 144 remain closed, even if the differential pressure δP continues to increase, the flow rate Q of the working fluid flowing between the first chamber 40b and the second chamber does not increase as indicated by the dotted line in FIG. 14. In view of this, in this example embodiment, each relief valve 142, 144 is adapted to open in response to the pressure of the working fluid in the fluid passage 140a exceeding the predetermined pressure, whereby the differential pressure between the first communication passage 140b and the second communication passage 140c decreases. Accordingly, the flow rate Q increases as the differential pressure δP increases as indicated by the solid curve in FIG. 14.

[0081] Further, the higher the rotational speeds of the first gear 50 and the second gear 52, the larger the loads on the first gear 50 and the second gear 52 become. Therefore, by providing the first relief valve 142 and the second relief valve 144, the loads on the first gear 50 and the second gear 52 can be reduced, and this prolongs the

lives of the first gear 50 and the second gear 52.

[0082] In this example embodiment, as described above, the first relief valve 142 and the second relief valve 144 open when the pressure of the working fluid becomes higher than the predetermined pressure. However, the first main valve 150 and the second main valve 156 may be used instead of the first relief valve 142 and the second relief valve 144 to control the flow path of the working fluid as described above. Further, the first relief valve 142 and the second relief valve 144 are not necessarily both provided in the piston 140. That is, the piston 140 may be provided with only one of the first relief valve 142 and the second relief valve 144.

[0083] While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various example combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.