Lifting cylinder of a lifting frame of a mobile work machine

Abstract

Lifting cylinder (10) of a lifting frame (1) of a mobile working machine, in particular a forklift truck, wherein the lifting cylinder (10) has a cylinder housing (11) and a piston rod (12) longitudinally displaceable in the cylinder housing (11), wherein a mechanical stop (20) is provided for the extended piston rod (12), which is formed by cooperating stop surfaces (20a, 20b) of the piston rod (12) and a cylinder head (11c) of the cylinder housing (11), wherein a connection point (AP) is formed at the extending tip of the piston rod (12), with which the piston rod (12) is coupled to a liftable and lowerable component (4) of the lifting frame (1), characterized in that the stop surfaces (20a, 20b) on the piston rod (12) and on the cylinder head (11c) are inclined or curved such that in the extended end position of the piston rod (12) and interacting stop surfaces (20a,20b) results in an instantaneous center of rotation (MP) of the extended piston rod (12), which is located in the region of the connection point (AP) of the piston rod (12).

Description

[0001] The invention relates to a lifting cylinder of a lifting frame of a mobile working machine, in particular a forklift truck, wherein the lifting cylinder has a cylinder housing and a piston rod which is longitudinally displaceable in the cylinder housing, wherein a mechanical stop is provided for the extended piston rod, which is formed by cooperating stop surfaces of the piston rod and a cylinder head of the cylinder housing, wherein a connection point is formed at the extending tip of the piston rod, with which the piston rod is coupled to a liftable and lowerable component of the lifting frame.

[0002] Lifting cylinders of this type are used in the lifting masts, for example, multi-stage lifting masts, of industrial trucks such as forklifts. In multi-stage lifting masts, a lifting cylinder designed as a primary cylinder is connected to a load-handling attachment, such as a fork carriage, while one or more lifting cylinders designed as secondary cylinders are connected to a height-adjustable extension mast of the lifting mast, which is guided vertically within a fixed mast of the lifting mast. Such lifting masts can be configured with a single extension mast, a so-called duplex lifting mast, or with multiple extension masts, a so-called triplex lifting mast, each of which can be extended by means of corresponding secondary cylinders.

[0003] The lifting cylinder, designed as the primary cylinder, provides a so-called free stroke, the primary stroke of the load-handling attachment, which is a liftable and lowerable component of the lifting frame. Only when the primary cylinder is fully extended and reaches a stop do the secondary cylinders begin to extend, thus extending the extension mast(s) of the multi-stage lifting frame in a secondary stroke. This creates a free stroke in which the load-handling attachment can be lifted by the primary cylinder without the lifting frame extending upwards and without increasing its overall height. The primary cylinder is therefore also referred to as the free-stroke cylinder.In lifting masts with such a free stroke of the load-handling device, where the load-handling device can be lifted by means of the primary cylinder, the lifting cylinder forming the primary cylinder is arranged with a cylinder housing on the extension mast of the lifting mast, and a piston rod arranged to be longitudinally displaceable in the cylinder housing is in operative connection with the load-handling device. For this purpose, a connection point is formed at the extending tip of the piston rod, with which the piston rod is connected to the liftable and lowerable component of the lifting mast, for example, the load-handling device.

[0004] In lifting cylinders designed as primary cylinders of lifting frames, a mechanical stop is provided for the extended piston rod, which is formed by cooperating stop surfaces of the piston rod and a cylinder head of the cylinder housing and defines the extended end position of the piston rod.

[0005] It is known to arrange the stop surface of the piston rod and the stop surface of the cylinder head of the cylinder housing perpendicular to a longitudinal axis of the lifting cylinder, thus arranging the stop surfaces at right angles to the longitudinal axis of the lifting cylinder. When the piston rod extends and reaches its extended end position, the stop surfaces meet. Due to the perpendicular arrangement of the stop surfaces to the longitudinal axis of the lifting cylinder, the directions of action of the stop surfaces for a moment center of rotation of the piston rod are parallel to the longitudinal axis of the lifting cylinder. Geometrically speaking, the intersection of the directions of action of the stop surfaces forms the instantaneous center of rotation about which the extended piston rod can rotate with one degree of freedom at the moment the mechanical stop for the extended end position is reached.

[0006] In known lifting cylinders designed as primary cylinders, where the piston rod's stop surface and the cylinder head's stop surface for the mechanical stop of the extended piston rod are each arranged perpendicular to a longitudinal axis of the lifting cylinder, contact noises and vibrations of the load-handling device occur when the mechanical stop is reached and thus during the transition from the primary stroke to the secondary stroke of the lifting mechanism. This occurs due to the contact of the interacting stop surfaces. The cause of these contact noises and vibrations of the load-handling device is that the rotational freedom of the extended piston rod is unfavorably oriented, since the stop surfaces arranged perpendicular to the longitudinal axis of the lifting cylinder intersect at infinity, and thus the instantaneous center of rotation is located at infinity.This causes the extended piston rod to wobble around its instantaneous center of rotation when it reaches the mechanical stop of its extended end position, and thus at the moment the stop surfaces make contact. This results in prolonged metallic contact noises, such as rattling, when the piston rod reaches its extended end position, and vibrations are transmitted to the load-bearing device until the extended piston rod comes to a stable stop in its extended end position.

[0007] From EP 0 622 331 A1, such a generic lifting cylinder of a lifting frame of an industrial truck with the features of the preamble of claim 1 is known.

[0008] From DE 40 32 765 A1 a cylinder-piston unit with a device for limiting the piston stroke is known.

[0009] DE 100 46 961 A1 reveals a piston-cylinder unit with adjustable stroke.

[0010] The present invention is based on the objective of providing a lifting cylinder of the type mentioned at the outset in which rattling noises can be avoided and vibration reduced by geometric design of the stop surfaces when the extended end position is reached.

[0011] This problem is solved according to the invention by inclined or curved the stop surfaces on the piston rod and on the cylinder head such that, in the extended end position of the piston rod and the interacting stop surfaces, an instantaneous center of rotation of the extended piston rod is created, which is located in the region of the connection point of the piston rod. According to the invention, the stop surfaces on the piston rod and on the cylinder head of the cylinder housing, which define the mechanical stop of the extended end position of the piston rod, are thus each designed and arranged such that the instantaneous center of rotation of the piston rod, when the extended end position is reached and thus at the moment of contact of the stop surfaces, is located in the region of the connection point of the piston rod.The geometric design of the stop surfaces on the piston rod and the cylinder head according to the invention ensures that, upon reaching the extended end position and thus at the moment the stop surfaces make contact, the instantaneous center of rotation is defined in the region of a point with the lowest movement potential of the extended piston rod, which is formed by the connection point of the piston rod.

[0012] This ensures that the piston rod assumes a stable position when striking the stop surfaces, so that a short contact noise occurs and vibrations of the extended piston rod are avoided.

[0013] According to an advantageous embodiment of the invention, the instantaneous center of rotation of the extended piston rod is located at the connection point of the piston rod. Upon reaching the extended end position, and thus at the moment the stop surfaces contact, the instantaneous center of rotation formed by the stop surfaces is therefore defined at the connection point of the piston rod and thus at the point with the least movement potential of the extended piston rod.

[0014] According to an advantageous embodiment of the invention, normals passing through the contact points of the interacting stop surfaces intersect the connection point in the extended end position of the piston rod. This ensures that the directions of action of the stop surfaces intersect at the connection point of the piston rod at the moment the mechanical stop is reached, and thus the instantaneous center of rotation of the extended piston rod is located at the connection point of the piston rod.

[0015] According to an advantageous embodiment of the invention, the stop surface on the piston rod and the stop surface on the cylinder head of the cylinder housing are each designed as inclined stop surfaces, arranged at an angle to a perpendicular to a longitudinal axis of the lifting cylinder, wherein the stop surface on the piston rod is oriented inwards and the stop surface on the cylinder head of the cylinder housing is oriented outwards. The stop surface on the piston rod is thus inclined radially inwards in the direction of the longitudinal axis of the lifting cylinder. Correspondingly, the stop surface on the cylinder head of the cylinder housing is inclined radially outwards in the direction of the cylinder housing. Such inclined stop surfaces can be manufactured on the piston rod and on the cylinder head with minimal manufacturing effort.

[0016] According to an advantageous embodiment of the invention, the stop surface on the piston rod and the stop surface on the cylinder head of the cylinder housing are each formed by a conical surface, the apex of which is arranged facing a cylinder base of the cylinder housing. This achieves a simple geometric design of the stop surfaces in which the stop surface on the piston rod is inclined radially inwards towards the longitudinal axis of the piston cylinder, and the stop surface on the cylinder head of the cylinder housing is inclined radially outwards towards the cylinder housing.

[0017] The lifting cylinder according to the invention can be used in a single-stage lifting frame, in which a load-handling device, for example a fork carriage, arranged in a support mast of the lifting frame, can be raised and lowered by means of the lifting cylinder. Particular advantages arise when the lifting frame is designed as a multi-stage lifting frame and the lifting cylinder forms a primary lifting cylinder for raising a load-handling device, in particular a fork carriage. With the lifting cylinder according to the invention, the noise and vibration at the load-handling device during the transition from the primary stroke to the secondary stroke can thus be reduced with minimal construction effort in a multi-stage lifting frame.

[0018] Advantageously, according to a further development of the invention, a deflection pulley is rotatably mounted about an axis of rotation at the tip of the extending piston rod, and the pivot point is arranged on the axis of rotation of the deflection pulley. If the lifting cylinder is provided with a deflection pulley over which a lifting device for raising and lowering the load-bearing device is guided, the noise and vibration of the extended piston rod when reaching the upper end position can be reduced with minimal construction effort by the inventive positioning of the instantaneous center of rotation of the extended piston rod on the axis of rotation of the deflection pulley.

[0019] Further advantages and details of the invention are explained in more detail with reference to the exemplary embodiment shown in the schematic figures. Here, Fig. 1 a lifting frame with a lifting cylinder according to the invention, Fig. 2 a state-of-the-art lifting cylinder in a longitudinal section and Fig. 3 a lifting cylinder according to the invention in a longitudinal section.

[0020] In the Fig. Figure 1 shows a lifting frame 1 of a forklift truck with a lifting cylinder 10 according to the invention.

[0021] In the illustrated embodiment, the lifting mast 1 is designed as a multi-stage lifting mast, for example a duplex lifting mast, with a support mast 2 and an extension mast 3 that extends upwards along the support mast 2. A load-handling device 4, for example a fork carriage, is arranged in the extension mast 3 and can be raised and lowered. A load fork consisting of fork tines can be arranged on the load-handling device 4.

[0022] The lifting frame 1 consists of two laterally spaced lifting frame columns, formed by corresponding lifting frame profiles 2a, 2b of the upright mast 2 and lifting frame profiles 3a, 3b of the extendable mast 3, which are connected to the upright mast 2 and the extendable mast 3, respectively, by corresponding cross braces (not shown). Lifting cylinders designed as secondary cylinders 5a, 5b are provided for raising and lowering the extendable mast 3 relative to the upright mast 2. In the illustrated embodiment, the secondary cylinders 5a, 5b are attached to the upright mast 2 by cylinder tubes 6a, 6b. Piston rods 7a, 7b, which extend within the cylinder tubes 6a, 6b, are connected to the extendable mast 3.

[0023] A hydraulic cylinder 10, designed as a primary cylinder and thus as a free-lift cylinder, is provided for raising and lowering the load-handling device 4 relative to the extension mast 3. The hydraulic cylinder 10 is arranged on the extension mast 3. In the illustrated embodiment, the primary cylinder 10 is arranged between the lifting frame profiles 3a, 3b of the extension mast 3. The primary cylinder 10 has a cylinder housing 11 and an extendable and retractable piston rod 12. In the illustrated embodiment, the cylinder housing 11 is arranged and attached to the extension mast 3, and the piston rod 12 is operatively connected to the load-handling device 4 as a liftable and lowerable component of the lifting frame 1 for raising and lowering the load-handling device 4. A connection point AP for the liftable and lowerable component of the lifting frame 1 is formed at the extending tip of the piston rod 12.In the illustrated embodiment, a deflection pulley 13 is rotatably arranged about a pivot axis D at the extending tip of the piston rod 12. A lifting device (not shown in detail), for example a lifting chain, is guided over this pulley from the extension mast 3 to the lifting carriage 4. The lifting device is attached at one end to the extension mast 3 and at the other end to the load-handling device 4, so that extending the piston rod 12 of the primary cylinder 10 causes the load-handling device 4 to be lifted by means of the lifting device.

[0024] In the Fig. 2 and Fig. Figure 3 shows longitudinal sections of the lifting cylinder 10, which is designed as a primary lifting cylinder, wherein the Fig. 2 a lifting cylinder 10 of the state of the art and the Fig. Figure 3 shows a lifting cylinder 10 according to the invention. Identical components are provided with the same reference numerals.

[0025] The cylinder housing 11 of the lifting cylinder 10 consists of a cylinder base 11a, a cylinder tube 11b and a cylinder head 11c. The piston rod 12, which is arranged to be longitudinally displaceable in the cylinder housing 11, is provided at its extending tip with the connection point AP, which in the illustrated embodiment is located on the axis of rotation D of the deflection roller 13.

[0026] A mechanical stop 20 is provided for the extended piston rod 12, which prevents the movement in the Fig. 2 and Fig. Figure 3 defines the extended end position of the extended piston rod 12. The mechanical stop 20 is formed by a stop surface 20a of the piston rod 12 and a stop surface 20b of the cylinder head 11c of the cylinder housing 11, which interact when the extended end position of the piston rod 12 is reached.

[0027] In the lifting cylinder 10 of the state of the art according to the Fig. In the following sections, the stop surface 20a of the piston rod 12 and the stop surface 20b of the cylinder head 11c of the cylinder housing 11 are each arranged perpendicularly and thus at right angles to a longitudinal axis L of the lifting cylinder 10. Due to this right-angled arrangement of the stop surfaces 20a, 20b to the longitudinal axis L of the lifting cylinder 10, the directions of action W of the stop surfaces 20a, 20b, which run parallel to the longitudinal axis L of the lifting cylinder 10, result for a moment center of the piston rod 12 in its extended end position. The intersection of the directions of action W of the stop surfaces 20a, 20b, which defines the moment center of the extended piston rod 12, is therefore located at infinity.

[0028] In the case of the lifting cylinder 10 of the state of the art according to the Fig. 2. This leads to the extended piston rod 12 tilting around its instantaneous center of rotation when it reaches the mechanical stop 20 for the extended end position, and thus at the moment the stop surfaces 20a, 20b make contact. This results in prolonged metallic contact noises, such as rattling noises, when the piston rod 12 reaches its extended end position, and vibrations are transmitted to the load-bearing device 4 until the extended piston rod 12 comes to a stable stop in the extended end position.

[0029] According to the invention, in the lifting cylinder 10 according to the invention, the Fig. 3. The stop surfaces 20a, 20b on the piston rod 12 and on the cylinder head 13 are geometrically designed and configured relative to each other such that, in the extended end position of the piston rod 12 and the interacting stop surfaces 20a, 20b, an instantaneous center of rotation MP of the extended piston rod 12 is obtained, which is located in the region of the connection point AP of the piston rod 12. In the Fig. In the embodiment shown in Figure 3, the instantaneous pole MP of the extended piston rod 12 is arranged at the connection point AP of the piston rod 12 and is therefore identical to the connection point AP of the piston rod 12.

[0030] In the Fig.In the extended end position of the piston rod 12 shown in Figure 3, normals N, which pass through the contact points of the interacting stop surfaces 20a, 20b, i.e., lines perpendicular to the stop surfaces 20a, 20b, intersect the connection point AP. For the piston rod 12 in its extended end position, the normals N represent the directions of action W of the stop surfaces 20a, 20b, the intersection of which defines the instantaneous center of rotation MP of the extended piston rod 12.

[0031] In the illustrated embodiment, the stop surface 20a on the piston rod 12 and the stop surface 20b on the cylinder head 11c of the cylinder housing 11 are each designed as inclined stop surfaces 20a, 20b. The stop surfaces 20a, 20b are each inclined at an angle α to a perpendicular S of the longitudinal axis L of the lifting cylinder 10, i.e., inclined at an angle α to a line perpendicular to the longitudinal axis L. The stop surface 20a of the piston rod 12 is oriented inwards and thus inclined radially inwards towards the longitudinal axis L of the lifting cylinder 10. The stop surface 20b on the cylinder head 11c of the cylinder housing 11 is arranged facing outwards and thus inclined radially outwards towards the cylinder housing 11c.

[0032] The inclination angle α is to be selected according to the stroke cylinder geometry, in particular the diameter of the stroke cylinder 10 and the length of the piston rod 12, in order to achieve the desired position of the instantaneous center of rotation MP of the extended piston rod 12.

[0033] In the illustrated embodiment, the stop surface 20a on the piston rod 12 and the stop surface 20b on the cylinder head 11c of the cylinder housing 11 are each formed by a cylindrical surface M1, M2 of a cone directed towards the cylinder base 11a, the apex of which KS1, KS2 each intersects the longitudinal axis L of the lifting cylinder 10 and is arranged facing the cylinder base 11a of the cylinder housing 11.

[0034] The inventive design of the stop surfaces 20a, 20b of the mechanical stop 20 on the piston rod 12 and the cylinder head 11c ensures that, upon reaching the extended end position and thus at the moment the stop surfaces 20a, 20b abut each other, the instantaneous center of rotation MP of the extended piston rod 12 is defined in the region of the point with the least potential for movement of the extended piston rod 12, which is formed by the connection point AP of the piston rod 12. When the stop surfaces 20a, 20b abut, the extended piston rod 20 thus assumes a stable position, so that, in the lifting cylinder 10 according to the invention, only a brief contact noise occurs when the mechanical stop is reached, and vibrations of the extended piston rod 12 are avoided, which would otherwise be transmitted to the load-handling device 4, for example its fork tines, and to a load picked up by the load-handling device 4.

Claims

[1] Lifting cylinder (10) of a lifting frame (1) of a mobile working machine, in particular a forklift truck, wherein the lifting cylinder (10) has a cylinder housing (11) and a piston rod (12) which is longitudinally displaceable in the cylinder housing (11), wherein a mechanical stop (20) is provided for the extended piston rod (12), which is formed by cooperating stop surfaces (20a, 20b) of the piston rod (12) and a cylinder head (11c) of the cylinder housing (11), wherein a connection point (AP) is formed at the extending tip of the piston rod (12), with which the piston rod (12) is coupled to a liftable and lowerable component (4) of the lifting frame (1), characterized by, that the stop surfaces (20a, 20b) on the piston rod (12) and on the cylinder head (11c) are inclined or curved in such a way that in the extended end position of the piston rod (12) and cooperating stop surfaces (20a, 20b) an instantaneous center of rotation (MP) of the extended piston rod (12) is obtained, which is located in the area of ​​the connection point (AP) of the piston rod (12). [2] Lifting cylinder according to claim 1, characterized by , that the instantaneous pole (MP) of the extended piston rod (12) is located at the connection point (AP) of the piston rod (12). [3] Lifting cylinder according to claim 1 or 2, characterized by , that in the extended end position of the piston rod (12) normals (N) passing through contact points of the cooperating stop surfaces (20a, 20b) intersect the connection point (AP). [4] Lifting cylinder according to any one of claims 1 to 3, characterized by, that the stop surface (20a) on the piston rod (12) and the stop surface (20b) on the cylinder head (11c) of the cylinder housing (11) are each designed as inclined stop surfaces (20a, 20b) which are arranged inclined at an angle of inclination (α) to a perpendicular (S) of a longitudinal axis (L) of the lifting cylinder (10), wherein the stop surface (20a) on the piston rod (12) is oriented inwards and the stop surface (20b) on the cylinder head (11c) of the cylinder housing (11) is arranged inwards. [5] Lifting cylinder according to any one of claims 1 to 4, characterized by , that the stop surface (20a) on the piston rod (12) and the stop surface (20b) on the cylinder head (11c) of the cylinder housing (11) are each formed by the cylindrical surface (M1, M2) of a cone, the apex of which (KS1, KS2) is arranged facing a cylinder base (11a) of the cylinder housing (11). [6] Lifting cylinder according to any one of claims 1 to 5, characterized by , that the lifting frame (1) is designed as a multi-stage lifting frame and the lifting cylinder (10) forms a primary lifting cylinder for lifting a load handling device (4), in particular a fork carriage. [7] Lifting cylinder according to any one of claims 1 to 6, characterized by , that a deflection roller (13) is rotatably mounted at the tip of the extending piston rod (12) about an axis of rotation (D) and the pivot point (AP) is arranged on the axis of rotation (D) of the deflection roller (13).

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