Drive for a forklift truck

Abstract

Drive system for a forklift truck with a drive motor 1 and a gearbox 2, partially filled with gearbox oil and arranged in a gearbox housing 3. The gearbox 2 has at least one planetary stage 6, which has a planet carrier 11 with at least one planet gear pin 10 on which a planet gear 9 with a coaxial bore 16 is rotatably mounted. The planet carrier 11 is non-rotatably connected to an output shaft 4, and at least one planet gear 9 can be rotatably driven directly or indirectly by the drive motor 1. The planet gear 9 is rotatably mounted on the planet gear pin 10 by means of a sliding bearing.

Description

The invention relates to a drive for a industrial truck having a drive motor and a transmission which is arranged in a transmission housing and is partly filled with a transmission oil, wherein the transmission has at least one planetary stage which has a planet carrier having at least one planetary gear bolt on which a planetary gear having a coaxial bore is rotatably mounted, and wherein the planet carrier is connected to an output shaft in a rotationally fixed manner and the at least one planetary gear can be driven rotatably directly or indirectly by the drive motor.In such a drive for a industrial truck, it is known to mount the planetary gear on the planetary gear pin by means of a roller bearing. The use of rolling bearings requires a large installation space, wherein the structural size and load-bearing capacity are determined by the diameter of the planetary gear bolt and by the diameter of the planetary gear and the minimum material thickness of the planetary gear. If, for reasons of installation space, the planet wheel bolt and / or the bore of the planet wheel are to serve as a running surface, the requirements imposed on the surface and machining quality of these parts are high.Due to the rolling contacts of the rolling bodies with the counter-running surfaces on the inner ring or planetary gear pin as well as the outer ring and planetary gear, orderings and harmonics are produced which can have a negative influence on the transmission noise.The rolling bearings are highly loaded because of the small installation space available. As a result, they are sensitive to contamination of abrasion or material particles in the transmission oil, as a result of which the service life of the rolling bearings is greatly reduced by this contamination.It is therefore the object of the invention to provide a drive for a industrial truck of the type mentioned at the beginning which avoids these disadvantages and, with a simple construction with a smaller installation space requirement, can bear high specific loads and is substantially less sensitive to contamination of the transmission oil and has good emergency running properties and generates only low noises.This object is achieved for a wheel drive according to the invention in that the planetary gear is rotatably mounted on the planetary gear pin by means of a slide bearing.Plain bearings bear high specific loads and are insensitive to contamination of the transmission oil. They have good emergency running properties and have less tendency to excite noise than rolling bearings.Furthermore, the required installation space is small.The coaxial bore of the planetary gear may be coated with a sliding material.If the planetary gear pin is surrounded with radial play by a plain bearing bushing on which the planetary gear is arranged with its coaxial bore in a rotationally fixed manner, a lubricating film forms in the pressure zone during operation of the drive between the inner diameter of the plain bearing bushing and the outer diameter of the planetary gear pin, which film counteracts the tooth forces at the tooth meshings of the planetary gear. Opposite the pressure zone is a non-pressure zone. Due to the rotational speed of the planetary gear on the planetary gear pin, a relative movement takes place in the pressure zone between the plain bearing bushing and the planetary gear pin. The inner parts of the transmission always enter into the transmission oil, so that a transmission oil supply for the sliding bearing takes place by the centrifugal force during rotation of the planetary carrier.The plain bearing bush can have a coating made of a sliding material, such as a PTFE-containing sliding material, for reducing friction losses.Alternatively, a plain bearing bushing coated with sliding material in the region surrounded by the planetary gear can also be arranged fixedly on the planetary gear pin, in particular by pressing, on which the planetary gear slides with radial play.Alternatively, the sliding material may be applied to the planetary gear pin.The plain bearing bush is preferably mounted axially secured on the planetary gear bolt.For this purpose, the plain bearing bush can be axially secured in a simple manner, saving installation space and easily mountable, by at least one securing ring which is inserted into an annular groove in the radially encircling outer lateral surface of the planetary gear bolt.On an axial end face, the plain bearing bush can bear axially on a shoulder of the planetary carrier.Another possibility for axial securing is that the planetary gear has, on at least one of its end faces, a thrust washer, via which the planetary gear and / or the plain bearing bushing axially rests in sliding contact on the securing ring and / or the shoulder of the planetary carrier.For low-wear axial support of the planetary gear, the planetary gear can have a thrust washer on at least one of its end faces, via which the planetary gear and / or the plain bearing bushing axially rests in sliding contact on the securing ring and / or the shoulder of the planetary carrier.A good guarantee of the lubrication of the plain bearing is that the plain bearing bush has lubrication holes and / or lubrication grooves and / or lubrication pockets on its inner radially encircling lateral surface facing the planetary gear pin.It is weight-saving if the planetary gear bolt has a coaxial through bore.If one or more radial through-holes are formed in the planetary gear bolt from the through-hole to the radially encircling outer lateral surface of the planetary gear bolt, a good supply of transmission oil to the bearing point of the planetary gear takes place via the through-hole and the radial through-holes.Exemplary embodiments of the invention are illustrated in the drawings and are described in more detail below. The following are shown: FIG. 1 shows a longitudinal section of a drive for a industrial truck with a drive motor FIG. 2 shows an enlarged detail in the region of a planetary gear of the drive according to FIG. 1 FIG. 3 is an enlarged cross section in the region of a planet wheel of the drive according to FIG. 3. 1 FIG. 4 shows a schematic illustration of the sliding bearing of the planetary gear according to FIG. 1 FIG. 5 is a perspective view of a planet pin of the drive according to FIG. 1 FIG. 6 shows an enlarged detail in the region of a planetary gear of the drive according to FIG. 1 with a further exemplary embodiment of the planetary gear bolt.The drive for a industrial truck shown in FIG. 1 shows a drive motor 1 designed as an electric motor, from which a driven shaft 4 with a driven flange 7 can be driven rotatably about a wheel axis 22 via a transmission 2 arranged in a transmission housing 3. A vehicle wheel, not shown, can be arranged on the output flange 7.Two drives can form a drive axle of a floor conveyor vehicle.The transmission has a spur gear stage 5 and a planetary gear stage 6.The planetary gear stage 6 has a sun gear 8 which can be driven rotatably by the spur gear stage 5 and which is engaged by planetary gears 9 which are rotatably mounted on planetary gear bolts 10 of a planetary carrier 11.The planetary gears 9 in turn engage in a ring gear 12 surrounding the planetary gears 9, which ring gear is arranged in the transmission housing 3 in a rotationally fixed manner.The planet carrier 11 is fixedly connected to the output shaft 4, which is rotatably mounted in the transmission housing 3 via two rows of rolling bearings 13.The transmission housing 3 filled with a transmission oil up to a level 14 is sealed off from the outside by a seal 15 arranged between the two rows of rolling bearings 13.As can be seen in more detail in FIG. 2, the planet wheel 9 receives in its coaxial bore 16 a slide bearing bushing 17 which is seated with radial play on the planet wheel bolt 10 and which is coated on its side bearing against the planet wheel bolt 10 with a coating of a slide material.Arranged on the two end faces of the planetary gear 9 are thrust washers 18 which limit the axial movement of the planetary gear 9 on the planetary gear bolt 10.The right thrust washer 18 is in turn supported axially on an annular shoulder 19 of the planet carrier 11, while the left thrust washer 18 is secured axially by a securing ring 20 which is designed as a snap ring inserted into an annular groove 21 on the radially encircling outer circumferential surface of the planet wheel bolt 10.When the sun gear 8 is driven, it rotates about the wheel axle 22, and a tooth force is effective due to the driving torque in meshing engagement between the sun gear 8 and the planetary gear 9.Due to the torque equilibrium about the axis of rotation 22 of the planetary gear 9, the same tooth force is also effective in the tooth engagement of the planetary gear 9 and the ring gear 12. Due to the equilibrium of forces, a pressure zone 24 with a pressure is formed between the inner diameter of the plain bearing bush 17 and the outer diameter of the planetary gear bolt 10, which pressure acts against the tooth forces at the tooth meshings. Opposite the pressure zone 24 is the pressure-free zone 25; the sun wheel 8 rotates at a speed about the wheel axle 22.Due to the rotational speed of the planetary gear 9 on the planetary gear pin 10, a relative movement takes place in the pressure zone 24 between the plain bearing bush 17 and the planetary gear pin 10. Since the inner parts of the transmission 2 are lubricated with transmission oil, transmission oil is also available for lubricating the plain bearing.To support a build-up of lubricating film in the pressure zone 24, the planetary gear 9 dips into the transmission oil, which is filled into the transmission housing 3 up to the level 14, during each revolution of the planetary carrier 11. The transmission oil can thus penetrate laterally via the end faces of the plain bearing bush 17 into the pressureless zone 25. In addition, transmission oil reaches the unpressurized zone 25 through a coaxial through-bore 26 and radial through-bores 27 and a lubrication groove 28 in the planetary gear bolt 10.FIG. 3 shows the sliding bearing of the planetary gear 9 schematically. The plain bearing bush 17 rotates relative to the planetary gear pin 10 at a rotational speed. The inner diameter of the plain bearing bush 17 is somewhat larger than the outer diameter of the planetary gear pin 10, which results in a lubrication gap 29 which comprises the unpressurized zone 25 and the pressure zone 42. The difference in diameter of the plain bearing bush 17 and of the planetary gear pin 10 corresponds to the maximum possible thickness of the lubrication gap 29. The transmission oil which reaches the lubrication gap 29 adheres on account of adhesion forces to the surfaces of the plain bearing bush 17 and / or of the planetary gear pin 10 and is transported into the pressure zone 24 on account of the relative movement of the two parts with respect to one another. As a result, a hydrodynamic lubrication film can build up in the pressure zone 24, which reduces the solid-state friction between the plain bearing bush 17 and the planetary carrier 11 or even prevents it under favorable operating conditions.As seen in the embodiment of FIG. 6, in order to assist the transmission of the transmission oil through the radial through holes 27 with the aid of the centrifugal force due to the rotational movement of the planetary carrier 11 about the wheel axle 22, the through hole 26 in the planetary gear pin 10 can be designed such that they widen from both outer end sides of the planetary gear pin 10 in the direction of the radial through holes 27.In order to supply the slide bearings with oil in a targeted manner, an oil feed with pressurized oil can also be provided, which transports the oil as far as into the lubrication gap 29.Reference numerals denote reference numerals1 Drive pinion 2 Transmission 3 Transmission housing 4 Output shaft 5 Spur gear stage 6 Planetary gear stage 7 Output flange 8 Sun gear 9 Planetary gears 10 Planetary gear bolt 11 Planetary carrier 12 Ring gear 13 Rolling bearing 14 Level 15 Seal 16 Coaxial bore 17 Plain bearing bush 18 Thrust washers 19 Shoulder 20 Securing ring 21 Annular groove 22 Wheel axis 23 Axis of rotation 24 Pressure zone 25 Pressureless zone 26 Through bore 27 Radial through bore 28 Lubrication groove 29 Lubrication gap

Claims

Drive for a industrial truck having a drive motor (1) and a transmission (2) which is arranged in a transmission housing (3) and is partly filled with a transmission oil, wherein the transmission (2) has at least one planetary stage (6) which has a planet carrier (11) having at least one planetary gear pin (10) on which a planetary gear (9) having a coaxial bore (16) is rotatably mounted, and wherein the planetary carrier (11) is connected to an output shaft (4) in a rotationally fixed manner and the at least one planetary gear (9) can be driven rotatably directly or indirectly by the drive motor (1), characterized in that the planetary gear (9) is rotatably mounted on the planetary gear pin (10) by means of a plain bearing.Drive according to Claim 1, characterized in that the planet wheel bolt (10) is surrounded with radial play by a plain bearing bush (17), on which the planet wheel (9) is arranged with its coaxial bore (16) in a rotationally fixed manner.Drive according to Claim 2, characterized in that the plain bearing bush (17) has a coating made of a sliding material.Drive according to one of the preceding claims, characterized in that the plain bearing bush (17) is mounted on the planetary wheel bolt (10) in an axially secured manner.Drive according to Claim 4, characterized in that the plain bearing bush is axially secured by at least one securing ring (20) which is inserted into an annular groove (21) in the radially encircling outer lateral surface of the planetary wheel bolt (10).Drive according to one of the preceding claims 4 and 5, characterized in that the plain bearing bush (17) bears axially against a shoulder (19) of the planet carrier (11).Drive according to Claims 5 and / or 6, characterized in that the planetary wheel (9) has, on at least one of its end faces, a thrust washer (18), via which the planetary wheel (9) and / or the plain bearing bush (17) axially bears in sliding contact against the securing ring (20) and / or the shoulder (19) of the planetary carrier (11).Drive according to one of the preceding claims, characterized in that the plain bearing bush (17) has lubricant holes and / or lubricant grooves and / or lubricant pockets on its inner radially encircling lateral surface facing the planetary wheel pin (10).Drive according to one or more of the preceding claims, characterized in that the planetary wheel bolt (10) has a coaxial through bore (26).Drive according to Claim 9, characterized in that one or more radial through-holes (27) are formed in the planetary wheel bolt (10) from the through-hole (26) to the radially encircling outer lateral surface of the planetary wheel bolt (10).

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