Patent Description:
Conventionally known is a jack device described in, for example, Patent Literature <NUM>. The jack devices described in the literature <NUM> includes a jack cylinder and a drive cylinder. The drive cylinder is composed of a hydraulic cylinder to shift the posture of the jack cylinder between a work posture and a storage posture. The work posture is a posture where the jack cylinder is upright, while the storage posture is a posture where the jack cylinder is tilted.

The inclusion of the drive cylinder, which is an actuator to actively move the jack device, in the jack device increases the frequency of maintenance for and failure in the jack device and complicates the construction of the jack device. On the other hand, to change the posture of the jack cylinder only by manual operation by an operator with nonuse of the drive cylinder may involve significantly increased burden on the operator.

It is an object of the present invention to provide a jack device that includes a jack cylinder and enables an operator to easily change the posture of the jack cylinder with no requirement for a device to actively move the jack cylinder.

Provided is a jack device mounted on a machine body of a work machine to lift up the machine body. The jack device includes an arm, a jack body, and a reaction-force application unit. The arm is mountable on the machine body so as to be rotatable about an arm rotation axis extending in a machine up-down direction, which is an up-down direction of the machine body. The jack body includes a jack cylinder expandable and contractable in a cylinder expansion-contraction direction, attached to the arm rotatably about a cylinder rotation axis to be shiftable between an upright posture and a storage posture. The upright posture is a posture where the machine body can be lifted up by expansion of the jack cylinder. The storage posture is a posture where the cylinder expansion-contraction direction is tilted from the machine up-down direction more largely than the upright posture and the jack cylinder lies along an upper surface of the arm. The reaction-force application unit is supported by the arm and applies a reaction force to the jack body in response to a force applied from the jack body. The reaction-force application unit makes a reaction-force moment act on the jack body in all postures from the upright posture to the storage posture. The reaction-force moment is a moment caused by the reaction force about the cylinder rotation axis, having a direction to make the jack body closer to the storage posture. The reaction-force application unit is configured to make the reaction-force moment greater than a self-weight moment act on the jack body in the storage posture and configured to make the reaction-force moment smaller than the self-weight moment act on the jack body in the upright posture. The self-weight moment is a moment caused by the weight of the jack body about the cylinder rotation axis, having a direction to make the jack body closer to the upright posture. Document <CIT> describes a jack device which is attached to a machine body of a work machine. This document discloses the preamble of claim <NUM>.

There will be described an embodiment of the present invention with reference to <FIG>.

<FIG> shows a work machine <NUM> according to the embodiment. The work machine <NUM> is a machine for performing work, for example, a construction machine for performing a construction work. The work machine <NUM> may be, for example, either a crane or an excavator.

The work machine <NUM> includes a machine body <NUM> and a plurality of jack devices <NUM>.

The machine body <NUM> is a main part of the work machine <NUM>. The machine body <NUM> may be either, for example, a lower traveling body or an upper turning body turnably mounted on the lower traveling body. The machine body <NUM> shown in <FIG> is the lower traveling body, including a pair of left and right crawlers <NUM> and a car body <NUM> disposed between the pair of crawlers <NUM>. The pair of crawlers <NUM> make motions to allow the entire machine body <NUM> to travel along the ground.

The machine body <NUM> has a machine up-down direction Z, a machine longitudinal direction, and a machine lateral direction. The machine up-down direction Z is the up-down direction of the machine body <NUM>, being a direction coincident with the vertical direction when the machine body <NUM> is placed on a horizontal plane. The following description is made about the case where the machine body <NUM> is placed on a horizontal plane. The machine front-rear direction is a direction orthogonal to the machine up-down direction Z and orthogonal to the machine lateral direction. The machine front-rear direction is, for example, a longitudinal direction of each of the crawlers <NUM>, <NUM>. The machine lateral direction is a direction orthogonal to each of the machine up-down direction Z and the machine front-rear direction, for example, being the direction in which the pair of crawlers <NUM> are arranged.

On the car body <NUM> is mounted each of the jack devices <NUM>. The plurality of jack devices <NUM>, in the present embodiment, include four jack devices <NUM>, namely, left and right front-side jack devices <NUM> aligned in the machine lateral direction along the front side of the car body <NUM>, and left and right rear-side jack devices <NUM> aligned in the machine lateral direction along the rear side of the car body <NUM>. To the car body <NUM> are connected the pair of crawlers <NUM> disposed on both outer sides of the car body <NUM> in the machine lateral direction, i.e., left and right sides, respectively. On the car body <NUM> is mounted a not-graphically-shown upper turning body, for example, through a turning bearing.

The car body <NUM> includes a top wall 13a, a pair of front and rear side walls 13c, 13c, and a bottom wall 13e shown in <FIG>, each of which is composed of, for example, a plate-like member. The top wall 13a forms an upper part of the car body <NUM>. The pair of side walls 13c, 13c form a front side part and a rear side art, respectively, the parts being opposite ends of the car body <NUM> in the machine front-rear direction, respectively. The bottom wall 13e shown in <FIG> forms the lower part of the car body <NUM>. The bottom wall 13e is disposed under the top wall 13a at a vertical distance from the top wall 13a. Each of the side walls 13c is disposed between the top wall 13a and the bottom wall 13e, having an upper end connected to the top wall 13a and a lower end connected to the bottom wall 13e. The front end of the top wall 13a, the front end of the bottom wall 13e, and the front side wall 13c out of the pair of side walls 13c define a front storage space S1 (on upper side in <FIG>), while the rear end of the top wall 13a, the rear end of the bottom wall 13e, and the rear side wall 13c out of the pair of side walls 13c define a rear storage space S1 (on lower side in <FIG>). Each of the storage spaces S1 is a space for storing the plurality of jack devices <NUM>.

Each of the jack devices <NUM> can be mounted on the machine body <NUM> to lift up the machine body <NUM>, that is, to raise the machine body <NUM> relatively to the ground. During work by, and transportation of, the work machine <NUM>, each of the jack devices <NUM> is shifted to a storage state of being stored in the storage space S1. As shown in <FIG>, for assembly and disassembly of the work machine <NUM>, each of the jack devices <NUM> is shifted to a use state for lifting up the machine body <NUM>.

Each of the jack devices <NUM> includes an arm <NUM>, a jack body <NUM>, and an assistance mechanism <NUM>.

The arm <NUM> interconnects the machine body <NUM> and the jack body <NUM>. The arm <NUM> is connected to the machine body <NUM> so as to be rotatable about an arm rotation axis 30a. The arm <NUM> has, for example, a box-shaped structure. The arm <NUM> according to the present embodiment includes an arm bottom wall <NUM>, a pair of arm side walls <NUM>, <NUM>, an arm top wall <NUM>, and an arm inner wall <NUM>.

The arm rotation axis 30a extends in the machine up-down direction Z. The arm <NUM> has an arm rotation-radius direction Ax and an arm width direction Ay. The arm rotation-radius direction Ax is a direction parallel to the rotation radius of the rotation of the arm about the arm rotation axis 30a, that is, a direction orthogonal to the rotation direction of the arm <NUM>, corresponding to the longitudinal direction of the arm <NUM>, in the present embodiment, when viewed along the machine up-down direction Z, that is, when viewed from above. The arm rotation-radius direction Ax involves an arm distal side Ax1 and an arm proximal side Ax2. The arm distal side Ax1 is a side far from the arm rotation axis 30a, and the arm proximal side Ax2 is the side opposite thereto, that is, a side close to the arm rotation axis 30a. The arm width direction Ay is a direction orthogonal to each of the arm rotation-radius direction Ax and the machine up-down direction Z. The shape of the arm <NUM> viewed along the arm width direction Ay is, for example, a substantially triangular shape.

The arm bottom wall <NUM> forms a lower part of the arm <NUM>, i.e., a part including a bottom surface. The arm bottom wall <NUM> is, for example, a plate-like member. The arm bottom wall <NUM> is disposed so as to extend in the arm width direction Ay and the arm rotation-radius direction Ax.

The pair of arm side walls <NUM>, <NUM> form opposite side parts of the arm <NUM> with respect to the arm width direction Ay, i.e., parts including left and right side surfaces, respectively. Each of the arm side walls <NUM>, <NUM> is, for example, a plate-like member. The arm side wall <NUM> shown in <FIG> includes a main part and a protruding part. The main part is located directly above the arm bottom wall <NUM>. The protruding part protrudes to the arm distal side Ax1 beyond the end of the arm bottom wall <NUM> on the arm distal side Ax1 (left side end in <FIG>). Each of the arm side walls <NUM>, <NUM> is disposed so as to extend in the arm rotation-radius direction Ax and the machine up-down direction Z.

The arm top wall <NUM> forms an upper part of the arm <NUM>, i.e., a part including an upper surface. The arm top wall <NUM> includes a top wall body, for example, formed of a plate-like member, and a cylinder rotation restriction member 33a.

The top wall body of the arm top wall <NUM> interconnects respective upper ends of the pair of (left and right) arm side walls <NUM> in the arm width direction Ay. The top wall body is disposed so as to extend in the arm width direction Ay. The top wall body, for example, extends obliquely downward toward the arm distal side Ax1, thus inclined to the arm rotation-radius direction Ax. The top wall body, alternatively, may be disposed so as to extend in a direction coincident with the arm rotation-radius direction Ax with no inclination to the arm rotation-radius direction Ax.

The cylinder rotation restriction member 33a projects upward from the upper surface of the top of the top wall body, for example, in the normal direction to the upper surface, i.e., upward to the arm distal side Ax1.

The arm inner wall <NUM> is disposed internally of the arm <NUM>. The arm inner wall <NUM> is, for example, a plate-like member. The arm inner wall <NUM> interconnects respective appropriate parts of the pair of (left and right) arm side walls <NUM> in the arm width direction Ay. The arm inner wall <NUM> is disposed so as to extend in the arm width direction Ay and the machine up-down direction Z, for example. The arm inner wall <NUM> shown in <FIG> includes an inner wall lower part and an inner wall upper part. The inner wall lower part extends in a direction coincident with the machine up-down direction Z. The inner wall upper part extends upward from the upper end of the inner wall lower part to the arm distal side Axl, thus inclined to the machine up-down direction Z. The arm inner wall <NUM> shown in <FIG> is disposed in a center region of the arm <NUM> with respect to the arm rotation-radius direction Ax. More specifically, the arm inner wall <NUM> is located in the vicinity of the center of the arm <NUM> with respect to the arm rotation-radius direction Ax and deviated from the center to the arm distal side Ax1.

The arm <NUM> defines a disposition space S2 and allows the assistance mechanism <NUM> to be disposed in the disposition space S2. The disposition space S2, in the present embodiment, is a space (cavity) between the pair of (left and right) arm side walls <NUM>, <NUM> and on the arm distal side Ax1 of the arm inner wall <NUM>.

The jack body <NUM> includes a jack cylinder <NUM>, a float <NUM>, and a jack weight <NUM>. The jack body <NUM> is supported by the arm <NUM> so as to be rotatable relatively to the arm <NUM> about a cylinder rotation axis 41a. The cylinder rotation axis 41a extends in the arm width direction Ay, which is the direction orthogonal to each of the machine up-down direction Z and the arm rotation-radius direction Ax.

The jack cylinder <NUM> is expandable and contractable in a cylinder expansion-contraction direction Cz. The jack cylinder <NUM> is, for example, a hydraulic cylinder. The cylinder expansion-contraction direction Cz is a direction along a cylinder center axis 41c, which is the center axis of the jack cylinder <NUM>, being the longitudinal direction of the jack cylinder <NUM> in the present embodiment. In <FIG>, the most-contraction state where the jack cylinder <NUM> is most contracted is indicated by the solid line, and a state where the jack cylinder <NUM> is more expanded than the most-contraction state is indicated by the two-dot chain line.

The jack body <NUM> including the jack cylinder <NUM> can be shifted between an upright posture shown in <FIG> and a storage posture shown in <FIG>, by rotation thereof relative to the arm <NUM> about the cylinder rotation axis 41a.

The upright posture is a posture where the jack cylinder <NUM> is upright. Specifically, the upright posture is a posture where the cylinder expansion-contraction direction Cz is coincident or substantially coincident with the machine up-down direction Z.

In the storage posture shown in <FIG>, the jack body <NUM> is disposed so as to lay the jack cylinder <NUM> substantially along the top of the arm <NUM> (e.g., the upper surface of the arm top wall <NUM>). The storage posture in the present embodiment is a posture where the cylinder center axis 40c of the jack cylinder <NUM> is tilted, being a posture where the tilt of the cylinder center axis 40c from the machine up-down direction Z is larger than that in the upright posture. In other words, the storage posture is a posture where the jack cylinder <NUM> is tilted toward the arm <NUM> compared to the upright posture, the cylinder center axis 40c being inclined to both the vertical direction and the horizontal direction. More specifically, in the storage posture, the cylinder expansion-contraction direction Cz is a direction extending downward to the arm distal side Ax1. In the storage posture, the jack cylinder <NUM> is prevented from rotation in a direction to increase the jack tilt angle θ, by contact of the jack cylinder <NUM> with the cylinder rotation restriction member 33a, thereby keeping the jack body <NUM> in the storage posture. The jack tilt angle θ is the angle of the cylinder center axis 41c to the machine up-down direction Z (the vertical direction when the machine body <NUM> is placed on a horizontal plane), as shown in <FIG>. The jack tilt angle θ is <NUM>° in the upright posture of the jack body <NUM>, increased with the displacement of the jack body <NUM> from the upright posture to the storage posture. The storage posture may be a posture where the cylinder expansion-contraction direction Cz.

As shown in <FIG>, the jack cylinder <NUM> includes a cylinder tube 41t, a cylinder rod 41r, and a lug part <NUM>.

The cylinder tube 41t is cylindrical around the cylinder center axis 41c and holds the cylinder rod 41r. The lug part <NUM> protrudes from the outer peripheral surface of the cylinder tube 41t to the arm proximal side Ax2 along the radius direction of the cylinder tube 41t. The lug part <NUM> is supported by the arm <NUM> so as to be rotatable about the cylinder rotation axis 41a. Specifically, the lug part <NUM> is rotatably supported by the arm <NUM> through a cylinder support shaft <NUM> having a center axis, which corresponds to the cylinder rotation axis 41a. The cylinder support shaft <NUM> passes through the lug part <NUM> and respective end parts of each of the arm side walls <NUM>, <NUM> on the arm distal side Ax1 side, in the arm width direction Ay, in the state where the lug part <NUM> and the pair of arm side walls <NUM>, <NUM> of the arm <NUM> overlap each other in the arm width direction Ay, thereby enabling the lug part <NUM> to be supported by the arm <NUM> through the cylinder support shaft <NUM> while allowing the lug part <NUM> to rotate relatively to the arm <NUM> about the center axis of the cylinder support shaft <NUM>.

The cylinder rod 41r is disposed radially inside the cylinder tube 41t, as shown in <FIG>. The cylinder tube 41t holds the cylinder rod 41r so as to render the cylinder rod 41r movable relatively to the cylinder tube 41t in the cylinder expansion-contraction direction Cz, thereby allowing the entire jack cylinder <NUM> to be expanded and contracted in the cylinder expansion-contraction direction Cz.

The cylinder expansion-contraction direction Cz involves a cylinder proximal side Cz1 and a cylinder distal side Cz2. The cylinder distal side Cz2 is a side to which the cylinder rod 41r protrudes beyond the cylinder tube 41t, being the lower side in the upright posture shown in <FIG>. The cylinder proximal side Cz1 is a side to which the cylinder rod 41r is retracted into the cylinder tube 41t, being the upper side in the upright posture shown in <FIG>.

Each of the jack devices <NUM> further includes a cylinder fixing pin <NUM> shown in <FIG>. The cylinder fixing pin <NUM> is capable of restricting the rotation of the jack body <NUM> relative to the arm <NUM> about the cylinder rotation axis 41a in each of the upright posture and the storage posture, thereby enabling the jack body <NUM> to be fixed in each of the upright posture and the storage posture. Specifically, the lug part <NUM> of the jack cylinder <NUM> is provided with a pin insertion hole <NUM>, while each of the arm side walls <NUM>, <NUM> is provided with a first pin insertion hole 32a and a second pin insertion hole 32b. Each of the pin insertion hole <NUM> and the first and second pin insertion holes 32a, 32b has a hole diameter to allow the cylinder fixing pin <NUM> to be inserted into the hole with substantially no clearance. The first pin insertion hole 32a is positioned to enable the jack cylinder <NUM> to be fixed in the upright posture by the cylinder fixing pin <NUM> inserted into the first pin insertion hole 32a and the pin insertion hole <NUM>. The second pin insertion hole 32b is positioned to enable the jack cylinder <NUM> to be fixed in the storage posture by the cylinder fixing pin <NUM> inserted into the second pin insertion hole 32b and the pin insertion hole <NUM>. To restrict the rotation of the jack body <NUM> in each of the upright posture and the storage posture, alternatively, may be prepared different pins from each other, namely, an upright-posture holding pin and a storage-posture holding pin.

The float <NUM> is both connectable to the distal end of the cylinder rod 41r and contactable with the ground. The float <NUM> may make either indirect contact with the ground across an interposed object such as a plate or direct contact with the ground. The distal end of the cylinder rod 41r is the end of the cylinder rod 41r on the cylinder distal side Cz2. The float <NUM> is connected to the distal end of the cylinder rod 41r through a float connection pin <NUM> extending in the arm width direction Ay, being allowed to rotate about the center axis of the float connection pin <NUM>, that is, a rotation axis extending in the arm width direction Ay. The float <NUM> is detachably connected to the cylinder rod 41r through the float connection pin <NUM>. The float <NUM> may be connected to the cylinder rod 41r rotatably in a plurality of directions within a predetermined angular range or in all directions (i.e., freely). For example, a spherical bearing may be interposed between the cylinder rod 41r and the float connection pin <NUM>, or between the float connection pin <NUM> and the float <NUM>. Allowing the float <NUM> to rotate relatively to the cylinder rod 41r freely within a predetermined angular range enables the float <NUM> to be inclined following the inclination of the ground.

The jack weight <NUM> is a weight for adjusting a weight moment Ms, namely, a balance weight. The self-weight moment Ms is a moment caused by the weight of the jack body <NUM>, being a moment in a direction to make the jack body <NUM> closer to the upright posture from the storage posture (counterclockwise in <FIG> and <FIG>) when the jack cylinder <NUM> is in the most-contraction state. The jack weight <NUM> is incorporated into the jack body <NUM> to make the actual center of gravity of the jack body <NUM> closer to the cylinder rotation axis 41a than the center of gravity of the jack body <NUM> when the jack body <NUM> would not include the jack weight <NUM>, preferably attached to the jack cylinder <NUM> detachably. The jack weight <NUM> is attached to, for example, the end of the cylinder tube 41t on the cylinder proximal side Cz1 as specifically described later. The jack weight <NUM> may be either formed integrally with the cylinder tube 41t or built in the cylinder tube 41t.

The assistance mechanism <NUM> assists the jack body <NUM> to rotate about the cylinder rotation axis 41a relatively to the arm <NUM>. The assistance mechanism <NUM>, specifically, reduces a rotational operation force Fm required for an operator to manually (by human power) rotate the jack body <NUM>. At least a part of the assistance mechanism <NUM> is disposed within the disposition space S2 internal of the arm <NUM>. Preferably, the whole or substantially the whole of the assistance mechanism <NUM> is disposed in the disposition space S2.

As shown in <FIG>, the assistance mechanism <NUM> includes an arm connection member <NUM>, an arm-side pin <NUM>, a cylinder-side engagement member <NUM>, a reaction-force application unit <NUM>, and a cover <NUM>. The arm connection member <NUM> and the arm-side pin <NUM> connect the reaction-force application unit <NUM> to the arm <NUM> so as to render the reaction-force application unit <NUM> rotatable relatively to the arm <NUM> about a center axis extending in the cylinder width direction. The cylinder width direction is a direction orthogonal to the cylinder expansion-contraction direction Cz, being a direction parallel to the arm width direction Ay, in the present embodiment. The cylinder-side engagement member <NUM> is a member to be engaged with the reaction-force application unit <NUM> so as to transmit a force from the jack cylinder <NUM> to the reaction-force application unit <NUM> while allowing the reaction-force application unit <NUM> to rotate relatively to the jack cylinder <NUM> about the axis in the cylinder width direction. The cylinder-side engagement member <NUM> is indicated by the two-dot line in <FIG>.

The arm connection member <NUM> is fixed to the arm <NUM>. The arm connection member <NUM> shown in <FIG> includes a pair of side frames 51a, 51a and a connection part 51b. The pair of side frames 51a, 51a are disposed on both outer sides of the reaction-force application unit <NUM> with respect to the arm width direction Ay (on left and right outer sides). The connection part 51b interconnects the pair of side frames 51a, 51a. The arm connection member <NUM> may include a block-like member. The shape of each of the side frames 51a, 51a viewed in the arm width direction Ay is, for example, a substantially triangular shape. The arm connection member <NUM> may be either connected to the arm <NUM> detachably (separably from the arm <NUM>) or formed integrally with the arm <NUM>. The separability of the arm connection member <NUM> from the arm <NUM> enables assembly performance of the assistance mechanism <NUM> to be improved. For example, it enables the arm connection member <NUM> to be connected to the arm <NUM> after the assembly of at least a part of the assistance mechanism <NUM> outside the arm <NUM>. This enables the assistance mechanism <NUM> to be assembled easily in comparison with the case where the assistance mechanism <NUM> is assembled in the space inside the arm <NUM>.

Each of the side frames 51a, 51a of the arm connection member <NUM> shown in <FIG> includes a contact part 51c, and the arm connection member <NUM> is connected to the arm <NUM> through a pin <NUM> with contact, preferably, surface contact, of contact part 51c with the arm <NUM>. The pin <NUM> is, for example, connected to the upper part of each of the side frames 51a, 51a and the arm <NUM> while passing through the upper part and the arm <NUM>. The contact part 51c allows both the number of pins <NUM> required for stably fixing the arm connection member <NUM> to the arm <NUM> and the number of pin holes to allow the pin <NUM> to be inserted therethrough reduced, thereby making it possible to stabilize the posture of the arm connection member <NUM> relative to the arm <NUM> with securement of the high strength of the arm <NUM>. The arm connection member <NUM>, however, may be fixed to the arm <NUM> through a plurality of pins.

The arm-side pin <NUM> is a hinge pin for connecting the reaction-force application unit <NUM> to the arm <NUM>, that is, to the arm connection member <NUM>, so as to allow the reaction-force application unit <NUM> to rotate, in the present embodiment, about an axis in the arm width direction Ay. The arm-side pin <NUM> is attached to the arm <NUM> through the arm connection member <NUM>. The arm-side pin <NUM> is, for example, attached to respective ends of the pair of side frames 51a, 51a of the arm connection member <NUM> on the arm distal side Ax1. The arm-side pin <NUM>, in the present embodiment, is connected to the reaction-force application unit <NUM> through the cover <NUM>. The arm-side pin <NUM>, for example, can be provided as respective protrusions that protrude outward from both side surfaces in the arm width direction Ay of the cover <NUM>.

The cylinder-side engagement member <NUM> is engaged with the reaction-force application unit <NUM> while being fixed to the jack cylinder <NUM> shown in <FIG>, thereby allowed to transmit a force from the jack cylinder <NUM> to the reaction-force application unit <NUM> and to transmit a reaction force from the reaction-force application unit <NUM> to the jack cylinder <NUM>.

The cylinder-side engagement member <NUM> illustrated in <FIG> integrally includes a center arm 55c and a pair of side arms <NUM> and <NUM>. On the other hand, the reaction-force application unit <NUM> includes a pair of reaction-force application members <NUM>, <NUM> arranged in the arm width direction Ay, as will be specifically described below. The center arm 55c is attached to the lug part <NUM> of the jack cylinder <NUM> through a pair of first pin 56A and second pin 56B in a posture where the center arm 55c extends in the cylinder expansion-contraction direction Cz while being located between the pair of reaction-force application members <NUM>, <NUM> as shown in <FIG>. The pair of side arms <NUM>, <NUM> are branched from the center arm 55c to both outer sides with respect to the arm width direction Ay, respectively, and disposed on both outer sides of the pair of reaction-force application members <NUM>, <NUM> with respect to the arm width direction Ay. As shown in <FIG> and <FIG>, the center arm 55c of the cylinder-side engagement member <NUM> has a first end part to be connected to the lug part <NUM> through the first pin 56A and a second end part, which is opposite to the first end part, to be connected to the lug part <NUM> through the second pin 56B. Each of the side arms <NUM>, <NUM> has an end part to be connected to the lug part <NUM> through the second pin 56B as well as the second end part. As shown in <FIG>, the first end part of the center arm 55c is provided with a pin insertion hole <NUM> that allows the first pin 56A to be inserted therethrough. Between the inner peripheral surface enclosing the pin insertion hole <NUM> and the outer peripheral surface of the first pin 56A is given a gap, by which a slight relative displacement to the jack cylinder <NUM> is allowed for the cylinder-side engagement member <NUM>.

The reaction-force application unit <NUM> passively makes a reaction force act on the jack body <NUM>. Specifically, the reaction-force application unit <NUM> generates a reaction force in response to a force applied from the jack cylinder <NUM> of the jack body <NUM>, and applies the generated reaction force to the jack cylinder <NUM>. The reaction force assists the jack body <NUM> in rotation about the cylinder rotation axis 41a. The reaction-force application unit <NUM> is, thus, an assistance force generation mechanism. The reaction-force application unit <NUM> is supported by the arm <NUM>. For example, the reaction-force application unit <NUM> is attached to the arm <NUM> rotatably about a reaction-force-application-unit rotation axis 60a. The reaction-force-application-unit rotation axis 60a is an axis extending in the arm width direction Ay, i.e., an axis parallel to the cylinder rotation axis 41a. The reaction-force application unit <NUM> according to the present embodiment is supported by the arm <NUM> shown in <FIG> through the cover <NUM>, the arm-side pin <NUM>, and the arm connection member <NUM> shown in <FIG>. The reaction-force application unit <NUM> is engaged with the jack cylinder <NUM> so as to be rotatable relatively to the jack cylinder <NUM> about an axis in the cylinder width direction. The engagement allows a force to be transmitted between the reaction-force application unit <NUM> and the jack cylinder <NUM>. The reaction-force application unit <NUM> may be connected to the jack cylinder <NUM> either inseparably or separably. The pair of reaction-force application members <NUM> of the reaction-force application unit <NUM> according to the present embodiment makes a force act on the jack cylinder <NUM> through the engagement pin <NUM> and the cylinder-side engagement member <NUM> (for example, presses the jack cylinder <NUM> thereagainst).

The reaction-force application unit <NUM> according to the present embodiment, as described above, includes the pair of reaction-force application members <NUM>, <NUM> shown in <FIG>. The reaction-force application members <NUM>, <NUM> have respective longitudinal directions equal to each other, each being expandable and contractable in the longitudinal direction. The reaction-force application unit according to the present invention may include either only a single reaction-force application member or three or more reaction-force application members.

The reaction-force application unit <NUM> is disposed in the disposition space S2 defined internally of the arm <NUM>. It is necessary to prevent the reaction-force application unit <NUM> from interference with another member, such as the cylinder fixing pin <NUM> or the arm <NUM>, involved by the rotation of the reaction-force application unit <NUM> relative to the arm <NUM> about the reaction-force-application-unit rotation axis 60a. It is preferable therefor to render the rotational trajectory of the reaction-force application unit <NUM> about the reaction-force-application-unit rotation axis 60a, that is, the area through which the reaction-force application unit <NUM> passes, as small as possible. Specifically, it is preferable to locate the reaction-force-application-unit rotation axis 60a in the center region of the reaction-force application unit <NUM> with respect to the longitudinal direction of the reaction-force application unit <NUM>, more specifically, the longitudinal direction of each of the reaction-force application members <NUM>, <NUM> included in the reaction-force application unit <NUM>. The center region is the intermediate region of three regions obtained by dividing the reaction-force application member <NUM> in the state of being most extended into three equal portions in the longitudinal direction. The reaction-force-application-unit rotation axis 60a illustrated in <FIG> is located at a position coincident or substantially coincident with the midpoint of the most extended reaction-force application member <NUM> with respect to the longitudinal direction.

The reaction-force application unit <NUM> is a passive device that generates a reaction force corresponding to an external force only when the external force is applied to the reaction-force application unit <NUM>. In other words, the reaction-force application unit <NUM> differs from an active device, such as a hydraulic cylinder or an air cylinder, that converts energy, such as fluid pressure or power, into power to move other members.

Each of the reaction-force application members <NUM>, <NUM> included in the reaction-force application unit <NUM> according to the present embodiment is composed of a gas spring that utilizes the elasticity of a gas (e.g., an inert gas). Specifically, each of the reaction-force application members <NUM>, <NUM> includes a gas housing <NUM> and a piston rod <NUM>.

The gas housing <NUM> is a cylindrical container with a center axis in a gas-spring expansion-contraction direction, filled with a gas for generating the reaction force, namely, a reaction-force generation gas. The gas-spring expansion-contraction direction is coincident with the longitudinal direction of the reaction-force application member <NUM>, namely, the gas spring. The reaction-force generation gas may be accumulated in a member other than the reaction-force application member <NUM>, for example, an accumulator. The gas housing <NUM> has opposite end parts in the gas-spring expansion-contraction direction, namely, a head-side end part <NUM> and a rod-side end part 61r.

The piston rod <NUM> integrally includes a piston loaded in the gas housing <NUM> and a rod extending in the gas spring expansion-contraction direction from the piston, the rod protruding out of the gas housing <NUM> through the rod-side end part 61r of the gas housing <NUM>. The piston rod <NUM> is capable of relative movement to the gas housing <NUM> in the gas-spring expansion-contraction direction, which movement causes the entire reaction-force application member <NUM> to be expanded and contracted in the gas-spring expansion-contraction direction. The reaction-force application member <NUM> has a characteristic of a typical gas spring, that is, the characteristic of being expandable and contractable in the gas-spring expansion-contraction direction and generating a substantially constant reaction force regardless of the stroke in the gas-spring expansion-contraction direction.

The engagement pin <NUM> transmits a force between the jack cylinder <NUM> and the gas housing <NUM>. The engagement pin <NUM> is fixed to respective head end parts <NUM> of the gas housings <NUM> of the pair of reaction-force application members <NUM>. The engagement pin <NUM> extends in a direction orthogonal to the gas-spring expansion-contraction direction, specifically, in a direction parallel to the cylinder width direction, to penetrate the respective head-side end parts <NUM> of the pair of reaction-force application members <NUM> in the cylinder width direction. The engagement pin <NUM> is engaged with the cylinder-side engagement member <NUM> to allow a force to be transmitted between the gas housing <NUM> and the cylinder-side engagement member <NUM>. Specifically, each of the center arm 55c and the pair of side arms <NUM>, <NUM> of the cylinder-side engagement member <NUM> is formed with a recess 55a, with which the engagement pin <NUM> is fitted. The recess 55a includes a slope having a shape with a depth increased with a displacement from the cylinder distal side Cz2 of the jack cylinder <NUM> toward the cylinder proximal side Cz1, allowing the engagement pin <NUM> to smoothly reach the bottom of the recess 55a along the slope. The recess 55a may be replaced with a pin hole formed in the cylinder-side engagement member <NUM> or the lug part <NUM> to allow the engagement pin <NUM> to be inserted through the pin hole. The above-described engagement between the engagement pin <NUM> and the recess 55a, however, facilitates assembly of the jack device <NUM>.

The cover <NUM> covers at least a part of the reaction-force application unit <NUM> to thereby improve the weather resistance of the reaction-force application unit <NUM>. The cover <NUM> illustrated in <FIG> has a box-shape and internally houses at least a part of the reaction-force application unit <NUM>. Specifically, the cover <NUM> covers the piston rod <NUM> so as to receive at least a part of the piston rod <NUM>, preferably, the whole of the piston rod <NUM>. The cover <NUM>, more preferably, covers both of the piston rods <NUM> of the pair of reaction-force application members <NUM>, <NUM>. The cover <NUM>, further preferably, houses a part of the gas housing <NUM> in addition to the piston rods <NUM>. The cover <NUM> illustrated in <FIG> houses the piston rod <NUM> and the rod-side end part 61r of the gas housing <NUM>. The interior of the cover <NUM> may be either sealed or communicated with the exterior through a gap. For example, there may be a gap between the cover <NUM> and respective outer surfaces of the pair of reaction-force application members <NUM>, <NUM> (more specifically, respective outer peripheral surfaces of the gas housings <NUM>). The gap may be provided with a member for closing the gap (for example, sponge rubber, etc.). Since rain or the like hardly enters the cover <NUM> from the lower side, at least a part of the lower part of the cover <NUM> may be opened, for example, as shown in <FIG>.

The cover <NUM> according to the present embodiment serves as also a link interconnecting the arm-side pin <NUM> and the reaction-force application unit <NUM>. In detail, the cover <NUM> interconnects the arm-side pin <NUM> and respective piston rods <NUM> of the pair of reaction-force application members <NUM>, <NUM> in the reaction-force application unit <NUM>. Specifically, the cover <NUM> has a distal end part <NUM> on the arm distal side Ax1 and a proximal end part <NUM> on the arm proximal side Ax2 with respect to the arm rotation-radius direction Ax, and the distal end part <NUM> is connected to the arm connection member <NUM> through the arm-side pin <NUM> rotatably about the reaction-force-application-unit rotation axis 60a, which is the center axis of the arm-side pin <NUM>, while the distal end part of the piston rod <NUM> is fixed to the proximal end part <NUM>. This allows the gas housing <NUM> of each of the reaction-force application members <NUM>, <NUM> to make relative movement to the cover <NUM> in the gas-spring expansion-contraction direction, which is the longitudinal direction of the reaction-force application member <NUM>, with the expansion and contraction of the reaction-force application member <NUM>.

The action of each of the jack devices <NUM> is as follows.

When the work machine <NUM> shown in <FIG> is transported and when work is performed by the work machine <NUM>, each of the jack devices <NUM> is shifted to the storage state indicated by the dashed line in <FIG> and shown in <FIG>, i.e., the state of being stored in the storage space S1. In the storage state, the arm <NUM> is disposed along the side wall 13c of the car body <NUM> in the machine body <NUM>. This renders the arm rotation-radius direction Ax of the arm <NUM> coincident with or substantially coincident with the machine lateral direction of the machine body <NUM>. Meanwhile, the jack body <NUM> in the jack device <NUM> is brought into a storage posture, in which the cylinder fixing pin <NUM> is inserted into the second pin insertion holes 32b of the pair of arm side walls <NUM>, <NUM> in the arm <NUM> and the pin insertion hole <NUM> of the lug part <NUM> in the jack cylinder <NUM>, thereby restricting the rotation of the jack body <NUM> relative to the arm <NUM> about the cylinder rotation axis 41a to hold the jack body <NUM> in the storage posture. In the storage state, the float <NUM> of the jack body <NUM> is allowed to be left connected to the cylinder rod 41r through the float connection pin <NUM>. In short, float incorporation storage can be done. The present invention, however, does not absolutely require the float incorporation storage. In other words, it is not excluded to remove the float <NUM> from the cylinder rod 41r in the storage state.

Each of the jack devices <NUM> is shifted from the storage state to the use state as follows. First, the arm <NUM> is rotated about the arm rotation axis 30a relatively to the machine body <NUM> to be thereby deployed into a projection position indicated by the solid line in <FIG> from a storage position indicated by the dashed line in <FIG>. This renders the arm rotation-radius direction Ax substantially coincident with the machine front-rear direction. Next, the cylinder fixing pin <NUM> is extracted from the first pin insertion hole 32a of the arm <NUM> and the pin insertion hole <NUM> of the jack cylinder <NUM>. This allows the jack body <NUM> including the jack cylinder <NUM> to rotate relatively to the arm <NUM> about the cylinder rotation axis 41a in the direction to approach the upright posture shown in <FIG> from the storage posture. The rotation of the jack body <NUM> is manually performed by an operator (by human power), as will be described in detail later. In this state where the jack body <NUM> has thus reached the upright posture shown in <FIG>, the cylinder fixing pin <NUM> is inserted through the first pin insertion holes 32a of the pair of arm side walls <NUM>, <NUM> in the arm <NUM> and the pin insertion hole <NUM> of the jack cylinder <NUM>, thereby holding the jack body <NUM> in the upright posture. In this upright posture, the jack cylinder <NUM> is driven in the expansion direction, specifically, the cylinder rod 41r of the jack cylinder <NUM> is moved relatively to the cylinder tube 41t toward the cylinder distal side Cz2, whereby the bottom surface of the float <NUM> reaches the ground. The jack cylinder <NUM> is further expanded to thereby lift up the machine body <NUM> relatively to the ground.

Each of the jack devices <NUM> can be returned to the storage state from the use state by a reverse action to the above action. Specifically, the jack cylinder <NUM> is contracted to land the machine body <NUM> on the ground, and the jack cylinder <NUM> is further contracted, for example, to the most-contraction state to thereby float up the float <NUM> from the ground. The cylinder fixing pin <NUM> is then extracted out of the first pin insertion holes 32a of the arm <NUM> and the pin insertion hole <NUM> of the jack cylinder <NUM>, thereby allowing the jack body <NUM> including the jack cylinder <NUM> to rotate relatively to the arm <NUM> about the cylinder rotation axis 41a in the direction to return to the storage posture shown in <FIG> from the upright posture. The rotation of the jack body <NUM> is also manually performed by an operator as will be specifically described below. In the state where the jack cylinder <NUM> has been returned to the storage posture shown in <FIG>, the cylinder fixing pin <NUM> is inserted through the second pin insertion holes 32b of the arm <NUM> and the pin insertion hole <NUM> of the jack cylinder <NUM>, thereby holding the jack body <NUM> including the jack cylinder <NUM> in the storage posture. In this state, the arm <NUM> is rotated about the arm rotation axis 30a to reach the storage position to lie along the side wall 13c in the storage space S1, whereby the jack device <NUM> is returned to the storage state.

<FIG> shows curves Cs, Cr, and Cf that indicate respective characteristics of the self-weight moment Ms, the reaction-force moment Mr, and the rotational operation force Fm, for the jack tilt angle θ shown in <FIG>, respectively. Each of the self-weight moment Ms and the reaction-force moment Mr is a moment caused by a force acting on the jack body <NUM> shown in <FIG>, about the cylinder rotation axis 41a.

The self-weight moment Ms is a moment caused by the self-weight of the jack body <NUM>, i.e., a moment caused by gravity acting on the jack body <NUM>, having a direction to make the jack body <NUM> closer to the upright posture shown in <FIG> from the storage posture shown in <FIG> (counterclockwise in <FIG> and <FIG>) when the jack cylinder <NUM> is in the most contraction state. In the case where the jack body <NUM> is rotated about the cylinder rotation axis 41a while the float <NUM> is left connected to the cylinder rod 41r, the self-weight of the jack body <NUM> includes the self-weight of the float <NUM>. In the case where the jack body <NUM> includes the jack weight <NUM>, the self-weight of the jack body <NUM> includes the self-weight of the jack weight <NUM>. In general, the center of gravity of the jack body <NUM> is deviated from the cylinder rotation axis 41a, and the distance therebetween is the moment radius of the self-weight moment Ms. Moreover, the rotation of the jack body <NUM> about the cylinder rotation axis 41a changes the positional relationship between the center of gravity of the jack body <NUM> and the cylinder rotation axis 41a, thereby changing the moment radius. Specifically, in the example shown in <FIG>, the self-weight moment Ms is local maximum at a particular jack tilt angle θ, and the curve Cs indicating the characteristic thereof is convex upward.

The reaction-force moment Mr is a moment caused by a reaction force that the reaction-force application unit <NUM> applies to the jack cylinder <NUM>, having a direction to make the jack body <NUM> including the jack cylinder <NUM> closer to the storage posture (clockwise in <FIG> and <FIG>). The reaction-force-application-unit rotation axis 60a is set at a position deviated from the cylinder rotation axis 41a in a direction orthogonal to the cylinder rotation axis 41a, and the length of a perpendicular line drawn down from the cylinder rotation axis 41a to the center axis of the reaction-force application member <NUM> in <FIG> is the moment radius of the reaction-force moment Mr. Moreover, the rotation of the jack body <NUM> about the cylinder center axis 41c changes a reaction-force application angle, which is the angle of the longitudinal direction of the pair of reaction-force application members <NUM> of the reaction-force application unit <NUM>, i.e., the gas-spring expansion-contraction direction, to the cylinder expansion-contraction direction Cz. For example, compared to respective reaction-force application angles when the jack tilt angle θ is <NUM>° (the angle corresponding to the upright posture) and when the jack tilt angle θ is the maximum angle θmax (the angle corresponding to the storage posture), the reaction-force application angle is great at the intermediate jack tilt angle θ therebetween. The reaction-force moment Mr, therefore, is great at the intermediate jack tilt angle θ as compared with the cases where the jack tilt angle θ is <NUM>° and the maximum angle θmax. Hence, as shown in <FIG>, the curve Cr indicating the characteristic of the reaction-force moment Mr for the jack tilt angle θ is convex upward like the curve Cs indicating the characteristic of the self-weight moment Ms.

The rotational operation force Fm is a force required to be made act on the jack body <NUM> manually by an operator to rotate the jack body <NUM> about the cylinder rotation axis 41a. The characteristic of the rotational operation force Fm indicated by the curve Cf in <FIG> assumes that the rotational operation force Fm is applied to the lower part of the jack cylinder <NUM> in the jack body <NUM>.

The reaction-force application unit <NUM> is set to allow the reaction-force moment Mr and the self-weight moment Ms to satisfy the following first and second conditions. The first condition is that the reaction-force moment Mr is greater than the self-weight moment Ms of the jack body <NUM> in the storage posture. The second condition is that the self-weight moment Ms of the jack body <NUM> in the upright posture is greater than the reaction-force moment Mr, that is, the reaction-force moment Mr is smaller than the self-weight moment Ms in the upright posture. For satisfaction of both the first and second conditions, it is required that the magnitude relationship between the reaction-force moment Mr and the self-weight moment M is reversed odd number of times (once in the example shown in <FIG>) during the change in the jack tilt angle θ from the minimum angle of <NUM>° to the maximum angle θmax, i.e., that the curves Cr, Cs shown in <FIG> meet at odd number of points.

The satisfaction of the first condition, which is the condition that the reaction-force moment Mr is greater than the self-weight moment Ms when the jack body <NUM> is in the storage posture, enables the jack body <NUM> to maintain the storage posture, i.e., to have the stabilized posture, with no need for an operator to lift up the jack body <NUM>, i.e., to apply the rotational operation force Fm to the jack body <NUM>. In other words, the jack body <NUM> does not rotate in a direction to approach the upright posture shown in <FIG> without application of a rotational operation force F to an appropriate part of the jack body <NUM>, specifically, a part on the arm distal side Ax1 of the cylinder rotation axis 41a, in a push-down direction or application of a rotational operation force F to a part on the arm proximal side Ax2 of the cylinder rotation axis 41a in a push-up direction, by an operator. This enables an operator to perform insertion and removal of the cylinder fixing pin <NUM> while leaving the hand away from the jack body <NUM>, thereby allowing the insertion and removal to be performed by a single operator.

By application of a rotational operation force Fm to an appropriate part of the jack body <NUM> in the storage posture by an operator, the jack body <NUM> is rotated in a direction to approach the upright posture shown in <FIG>. This rotation of the jack body <NUM> from the storage posture to the upright posture involves only a small difference between the reaction-force moment Mr and the self-weight moment Ms. This allows the rotational operation force Fm required for the rotation to be reduced. The rotational operation force Fm required to be made act on the jack cylinder <NUM> in the push-down direction by an operator, although depending on the weight of the jack body <NUM> and the like, can be reduced, in general, to a few kilograms (e.g., about <NUM>). This allows the operation to be made only by a single operator.

The coincidence of the jack tilt angle θ with a balance angle θa as shown in <FIG> renders the self-weight moment Ms and the reaction-force moment Mr equal to each other. This enables an operator to rotate the jack body <NUM> about the cylinder rotation axis 41a by only making a small rotational operation force Fm act on the jack body <NUM>. The rotational operation force Fm is, for example, a slight one such as a resistance force due to damper action of the reaction-force application member <NUM> and a frictional force between the jack body <NUM> and the arm <NUM>. The characteristic shown in <FIG>, where the rotational operation force Fm is small enough to be negligible, involves regarding the rotational operation force Fm when the jack tilt angle θ is equal to the balance angle θa as <NUM>.

When the jack tilt angle θ is smaller than the balance angle θa, that is, when the jack body <NUM> is in a posture closer to the upright posture shown in <FIG> than the posture corresponding to the balance angle θa, the self-weight moment Ms is greater than the reaction-force moment Mr. This causes the jack body <NUM> to be rotated in a direction to approach the upright posture by the self-weight moment Ms due to the weight of the jack body <NUM>, even if an operator makes no operation force Fm on the jack body <NUM> in the push-down direction, that is, an operator releases the hand from the jack body <NUM>.

The satisfaction of the second condition, which is the condition that the self-weight moment Ms is greater than the reaction-force moment Mr when the jack body <NUM> is in the upright posture shown in <FIG>, causes the jack body <NUM> to automatically maintain itself in the upright posture, that is, to be kept stable. At this time, the jack body <NUM> is not rotated in a direction to approach the storage posture shown in <FIG> from the upright posture without application of the rotational operation force Fm in a lift-up direction to the jack body <NUM> by an operator. This enables an operator to perform insertion and removal of the cylinder fixing pin <NUM> while leaving the hand away from the jack body <NUM>, thereby allowing the insertion and removal to be performed only by a single operator.

By application of a rotational operation force Fm in the push-up direction to an appropriate part of the jack body <NUM> in the upright posture by an operator, the jack body <NUM> is rotated in a direction to approach the storage posture shown in <FIG>. The rotational operation force Fm required to be made act on the jack cylinder <NUM> in the push-down direction by an operator, although depending on the weight of the jack body <NUM>, etc., can be reduced, in general, to a few kilograms (e.g., about <NUM>). This allows the operation to be made only by a single operator.

When the jack tilt angle θ is greater than the balance angle θa, that is, when the jack body <NUM> is in a posture closer to the storage posture shown in <FIG> than the angle corresponding to the balance angle θa, the reaction-force moment Mr is greater than the self-weight moment Ms. This causes the jack body <NUM> to be rotated in a direction to approach the storage posture shown in <FIG> by the reaction force applied to the jack body <NUM> by the reaction-force application unit <NUM> to reach the storage posture, even if an operator makes no rotational operation force Fm act on the jack body <NUM> in the push-up direction, that is, even if the operator releases the hand from the jack body <NUM>.

For effective reduction in the rotational operation force Fm, the reaction-force application unit <NUM> is required to make the reaction-force moment Mr act on the jack body <NUM> over the entire range of the jack tilt angle θ, that is, in all postures from the upright posture to the storage posture. Especially to the jack body <NUM> in the storage posture shown in <FIG>, the pair of reaction-force application members <NUM> each being in the substantially most-expansion state are required to apply the necessary reaction force (initial reaction force). Each of the reaction-force application members <NUM>, composed of the gas spring, can reliably apply the initial reaction force to the jack body <NUM>.

For effective reduction in the rotational operation force Fm, it is preferable that the self-weight moment Ms and the reaction-force moment Mr are approximately equal to each other. If each of the reaction-force application members <NUM> is composed of the gas spring, the reaction-force application unit <NUM> can have a characteristic of generating a substantially constant reaction force from the most-expansion state to the most-contraction state with respect to the gas-spring expansion-contraction direction. This allows the reaction-force moment Mr to be set to be substantially equal to the self-weight moment Ms.

The weight moment Ms of the jack body <NUM> is preferably small, which renders the reaction force required of the reaction-force application unit <NUM> small to allow the reaction-force application unit <NUM> to be downsized, thereby enabling the reaction-force application unit <NUM> to be disposed within the limited disposition space S2. The weight moment Ms is decreased with a decrease in the distance between the center of gravity of the jack body <NUM> and the cylinder rotation axis 41a. There is, however, a limit in setting the position of the cylinder rotation axis 41a so as to make the cylinder rotation axis 41a closer to the center of gravity of the jack body <NUM>. The position of the cylinder rotation axis 41a is restricted by the stroke of the jack cylinder <NUM>, the space to be occupied by the jack cylinder <NUM> when the jack device <NUM> is stored in the storage space S1, the strength required by the jack device <NUM> being used, and the like.

The jack weight <NUM> makes the center of gravity of the jack body <NUM> closer to the cylinder rotation axis 41a, thereby allowing the self-weight moment Ms to be small with no change in the position of the cylinder rotation axis 41a. Specifically, the position of the jack weight <NUM> incorporated in the jack body <NUM> is set so as to make the actual center of gravity of the jack body <NUM> including the jack weight <NUM> closer to the cylinder rotation axis 41a than the center of gravity of the jack body <NUM> without the jack weight <NUM>. For example, when the center of gravity of the jack body <NUM> without the jack weight <NUM> is on the cylinder distal side Cz2 of the cylinder rotation axis 41a, the attachment of the jack weight <NUM> to a part on the cylinder proximal side Cz1 of the cylinder tube 41t in the jack cylinder <NUM> can make the center of gravity of the jack body <NUM> closer to the cylinder center axis 41c to reduce the self-weight moment Ms. This renders the reaction force required to be generated by the reaction-force application unit <NUM> small to allow the reaction-force application unit <NUM> to be downsized, thereby enabling the reaction-force application unit <NUM> to be easily disposed in the limited disposition space S2. Besides, the jack weight <NUM> improves the flexibility in the design of the position of the reaction-force-application-unit rotation axis 60a and the position of the point at which the reaction force acts on the jack body <NUM> from the reaction-force application unit <NUM>.

The storage of the jack device <NUM> into the storage space S1 with connection of the float <NUM> to the cylinder rod 41r, namely, the float incorporation storage, involves an operation of rotating the jack cylinder <NUM> about the cylinder rotation axis 41a with the connection of the float <NUM> to the cylinder rod 41r. The center of gravity of the jack body <NUM> in which the float <NUM> is thus connected to the cylinder rod 41r is closer to the cylinder distal side Cz2 than the center of gravity of the jack body <NUM> in which the float <NUM> is detached from the cylinder rod 41r to thereby render the self-weight moment Ms great. The jack weight <NUM>, however, can be offset with the mass of the float <NUM>, when being incorporated into the jack body <NUM> so as to shift the center of gravity of the jack body <NUM> to the cylinder proximal side Cz1, that is, makes the center of gravity closer to the cylinder rotation axis 41a. This allows the jack body <NUM> to have the small self-weight moment Ms in spite of including the float <NUM>.

Increasing the angle of the reaction-force application member <NUM> to the cylinder expansion-contraction direction Cz in the gas-spring expansion-contraction direction, that is, the angle of the direction of the reaction force from the reaction-force application unit <NUM> to the jack body <NUM> to the cylinder expansion-contraction direction Cz, namely, the reaction-force application angle, makes it possible to increase the reaction-force moment Mr without increasing the reaction force applied to the jack body <NUM> from the reaction-force application unit <NUM>. The increase in the reaction-force application angle requires an increase in the angle of the rotation of the reaction-force application unit <NUM> about the reaction-force-application-unit rotation axis 60a involved by the rotation of the jack cylinder <NUM> about the cylinder rotation axis 41a. Increasing the rotation angle of the reaction-force application unit <NUM>, however, may hinder the reaction-force application unit <NUM> from being disposed in the disposition space S2. For example, the location of the reaction-force-application-unit rotation axis 60a at the longitudinal end of the reaction-force application unit <NUM> renders the swing area of the reaction-force application unit <NUM> large, which may hinder the reaction-force application unit <NUM> from being disposed in the disposition space S2. In contrast, the location of the reaction-force-application-unit rotation axis 60a at the center in the longitudinal direction of the reaction-force application unit <NUM>, in the embodiment, renders the space required for allowing the reaction-force application unit <NUM> to rotate about the reaction-force-application-unit rotation axis 60a small, enabling the reaction-force application unit <NUM> to be easily disposed in the disposition space S2. The reaction-force-application-unit rotation axis 60a, however, may be disposed in a part other than the longitudinal center part of the reaction-force application unit <NUM>.

During the assembly of the jack device <NUM> (for example, during the manufacturing or maintenance, etc. thereof), the jack body <NUM> is set in the assembly posture shown in <FIG> to allow the reaction-force application unit <NUM> to be mounted between the arm <NUM> and the jack cylinder <NUM>. The jack tilt angle θ in the assembly posture is greater than the jack tilt angle θ in the storage posture shown in <FIG>. In the storage posture shown in <FIG>, the rotation of the jack cylinder <NUM> in the direction to increase the jack tilt angle θ is restricted by the cylinder rotation restriction member 33a. However, the removal of the cylinder rotation restriction member 33a from the arm <NUM> during the assembly allows the jack body <NUM> to be shifted to the assembly posture with the jack tilt angle θ greater than that in the storage posture. In the state where the jack body <NUM> is thus set in the assembly posture and the pair of reaction-force application members <NUM> are most expanded, the reaction-force application unit <NUM> can be arranged without interference thereof with the jack cylinder <NUM>. The assembly posture is preferably arranged so as to allow the engagement pin <NUM> to be engaged with and disengaged from the recess 55a of the cylinder-side engagement member <NUM> with no contraction of the reaction-force application member <NUM>.

To reveal the effect of the reaction-force application unit <NUM>, the following case is assumed in which the jack body <NUM> is rotated in a direction to approach the upright posture shown in <FIG> when an operator releases the hand from the jack body <NUM> in the storage posture shown in <FIG>. In this case, in order to rotate the jack body <NUM> about the cylinder rotation axis 41a to shift the jack body <NUM> from the upright posture to the storage posture, the operator is required to manually hold the jack cylinder <NUM> in the storage posture until fixing the jack cylinder <NUM> to the arm <NUM> by the cylinder fixing pin <NUM>. Such operation of inserting and removing the cylinder fixing pin <NUM> while holding the jack body <NUM> is difficult for only a single operator. Besides, when the operator erroneously releases the hand from the jack cylinder <NUM> to allow the jack cylinder <NUM> to be rotated in the direction to return to the upright posture shown in <FIG>, the operator is required to perform further operation of lifting up the jack cylinder <NUM>. Moreover, in order to prevent the operator's hand or the like from coming into contact with the jack cylinder <NUM> from which the operator has erroneously released the hand to allow the jack cylinder <NUM> to be rotated, the operator has to perform the operation carefully with much time and effort.

Assumed is a case of using a coil spring to assist the jack body <NUM> to rotate from the upright posture to the storage posture, for example, a case of attaching the coil spring to the cylinder support shaft <NUM>. In this case, to allow sufficient assistance force to be applied from the coil spring to the jack body <NUM> in the storage posture, an operation is required for attaching the coil spring to the cylinder support shaft <NUM> while bringing the coil spring into a large excess compression (initial compression), but such operation is not easy. Reducing the excess compression to allow the operation to be done involves insufficiency of assistance force to be applied to the jack body <NUM> in the storage posture, increasing the burden of the work of rotating the jack body <NUM>.

To provide the characteristic of the reaction-force moment Mr as indicated by the curve Cr in <FIG>, the reaction-force application unit <NUM> is required to generate a sufficient reaction force (initial reaction force) in the storage state shown in <FIG>. The reaction-force application unit <NUM> is further required to generate a relatively constant reaction force over a wide range from the storage posture to the upright posture. Although using a coil spring having a weak spring constant in a greatly deformed state, in place of the gas spring, may provide a characteristic of the reaction-force moment Mr as shown in <FIG>, this requires great deformation in the spring material forming the coil spring with the weak spring constant and typical spring materials do not have sufficient strength to withstand such deformations, which may cause plastical deformation therein. In contrast, the reaction-force application member <NUM> composed of a gas spring can provide the characteristic of the reaction-force moment Mr shown in <FIG> without the above-described inconvenience. The specific configuration of the reaction-force application unit <NUM>, however, is not limited except for the first and second conditions, allowed to include, for example, a coil spring.

A jack device is, thus, provided, being mountable on a machine body of a work machine to lift up the machine body. The jack device includes an arm, a jack body, and a reaction-force application unit. The arm is mountable on the machine body so as to be rotatable about an arm rotation axis extending in a machine up-down direction, which is an up-down direction of the machine body. The jack body includes a jack cylinder expandable and contractable in a cylinder expansion-contraction direction, attached to the arm rotatably about a cylinder rotation axis to be shiftable between an upright posture and a storage posture. The upright posture is a posture where the machine body can be lifted up by expansion of the jack cylinder. The storage posture is a posture where the cylinder expansion-contraction direction is tilted from the machine up-down direction more largely than the upright posture and the jack cylinder lies along an upper surface of the arm. The reaction-force application unit is supported by the arm and applies a reaction force to the jack body in response to a force applied from the jack body. The reaction-force application unit makes a reaction-force moment act on the jack body in all postures from the upright posture to the storage posture. The reaction-force moment is a moment caused by the reaction force about the cylinder rotation axis, having a direction to make the jack body closer to the storage posture. The reaction-force application unit is configured to make the reaction-force moment greater than a self-weight moment act on the jack body in the storage posture and configured to make the reaction-force moment smaller than the self-weight moment act on the jack body in the upright posture. The self-weight moment is a moment caused by the weight of the jack body about the cylinder rotation axis, having a direction to make the jack body closer to the upright posture.

The reaction-force application unit can be configured by a passive device that applies the reaction-force moment to the jack body in response to a force applied from the jack body in all postures from the upright posture to the storage posture. This allows the frequency of maintenance of and failure in the jack device to be reduced and allows the jack device to have a simple configuration, as compared to the case where the reaction-force application unit is composed of an active device that actively changes the posture of the jack body, such as a hydraulic actuator.

The jack body in the upright posture can be maintained in the upright posture by the self-weight moment greater than the reaction-force moment, without application of an external force to the jack body. The jack body in the storage posture, conversely, can be maintained in the storage posture by the reaction-force moment greater than the self-weight moment, without application of an external force to the jack body. These release an operator from necessity of applying a rotational operation force to the jack body in order to maintain the storage posture in the situation where the jack body has been shifted to the storage posture from the upright posture, and also necessity of applying a rotational operation force to the jack body in order to maintain the upright posture in the situation where the jack body has shifted to the upright posture from the storage posture. The operator is thus enabled to easily perform an operation for changing the posture of the jack body. In addition, the effect can be obtained with no use of any active device for actively changing the posture of the jack body.

Preferably, the reaction-force application unit includes at least one reaction-force application member, which is composed of a gas spring. The gas spring includes a gas housing filled with a reaction-force application gas and generates the reaction force by the reaction-force application gas with expansion and contraction in a gas-spring expansion-contraction direction in response to the force applied from the jack body.

The at least one reaction-force application member composed of the gas spring improves the flexibility in the design of the reaction-force application unit to allow the reaction-force application unit to be easily mounted on the arm. For example, in the case of using a coil spring in place of the gas spring, the coil spring can generate little or no reaction force even with slight contraction from the most expansion state thereof. In contrast, the gas spring can generate a reaction force (initial reaction force) having a suitable magnitude even with slight contraction from the most expansion state. Besides, unlike the coil spring, the reaction-force application member composed of the gas spring can generate a stable reaction force regardless of the stroke in the gas-spring expansion-contraction direction, which makes it easy to set the characteristic of the reaction-force moment generated by the reaction-force application member to a favorable characteristic, for example, to make the characteristic of the reaction-force moment close to the characteristic of the self-weight moment. This improves the flexibility in the design of the reaction-force application unit (e.g., the design of the magnitude of the reaction force, the position of the point at which the reaction force acts on the jack body, the position of the axis about which the reaction-force application unit rotates if it is rotatable, etc.) to satisfy the condition (the first and second conditions in the above embodiment) required of the reaction-force application unit, thereby enabling the reaction-force application unit to be easily disposed in the disposition space defined in the arm.

Besides, the reaction-force application member is enabled to restrain the jack body from steep rotation by the damper effect provided by the gas spring. This reduces the necessity for an operator to keep watch for the steep rotational movement during the operation of shifting the posture of the jack body, thereby enabling the operator to perform the operation more easily.

Preferably, the gas-spring expansion-contraction direction is a longitudinal direction of the reaction-force application member, and the reaction-force application unit is supported by the arm rotatably about a reaction-force-application-unit rotation axis, which is located at a center part of the reaction-force application member with respect to the longitudinal direction. This allows a space required for the rotation of the reaction-force application unit about the counter-force-applying part rotation axis to be reduced.

Preferably, the jack device further includes a cover that covers at least a part of the reaction-force application unit. Specifically, in the case where the gas spring includes the gas housing and a piston rod held by the gas housing capably of relative movement to the gas housing in the gas spring expansion-contraction direction, the cover may be configured to cover at least the piston rod of the gas spring, which restrains the piston rod from being directly exposed to wind or rain. This can improve the weather resistance of the reaction-force application unit and restrain failure from occurring in the reaction-force application unit. The failure includes, for example, occurrence of rust in the piston rod and gas leakage due thereto.

The jack body, preferably, further includes a jack weight. The jack weight is incorporated into the jack body so as to make the center of gravity of the jack body closer to the cylinder rotation axis than the center of gravity of the jack body without the jack weight to thereby reduce the self-weight moment of the jack body. This increases the flexibility in the design of the reaction-force application unit (e.g., the design of the magnitude of the reaction force, the position of the point at which the reaction force acts on the jack body, the position of the reaction-member rotation axis, etc.) for satisfying the conditions required of the reaction-force application, thereby allowing the reaction-force application unit to be easily supported by the arm. Besides, reducing the self-weight moment reduces the reaction force required to be applied by the reaction-force application unit to allow the reaction-force application unit to be downsized, thereby enabling the reaction-force application unit to be easily disposed in the disposition space defined in the arm.

Claim 1:
A jack device (<NUM>) attached to a machine body (<NUM>) of a work machine (<NUM>) including the machine body to be able to lift up the machine body, the jack device comprising:
an arm (<NUM>) mountable on the machine body so as to be rotatable about an arm rotation axis (30a) extending in a machine up-down direction, which is an up-down direction of the machine body;
a jack body (<NUM>) including a jack cylinder (<NUM>) expandable and contractable in a cylinder expansion-contraction direction and attached to the arm rotatably about a cylinder rotation axis (41a) to be shiftable between an upright posture and a storage posture, the upright posture being a posture where the jack body is capable of lifting up the machine body by expansion of the jack cylinder and the storage posture being a posture where the cylinder expansion-contraction direction is tilted from the machine up-down direction more largely than the upright posture and the jack cylinder lies along an upper surface of the arm, characterised in that
a reaction-force application unit is supported by the arm and configured to apply a reaction force to the jack body in response to a force applied from the jack body to make a reaction-force moment (Mr) act on the jack body in all postures from the upright posture to the storage posture, the reaction-force moment being a moment caused by the reaction force about the cylinder rotation axis and having a direction to make the jack body closer to the storage posture, wherein
the reaction-force application unit (<NUM>) is configured to make the reaction-force moment greater than a self-weight moment (Ms) act on the jack body in the storage posture and configured to make the reaction-force moment smaller than the self-weight moment act on the jack body in the upright posture, the self-weight moment being a moment caused by a weight of the jack body about the cylinder rotation axis and having a direction to make the jack body closer to the upright posture.