Large and continuous loads require connections with a large contact area. These include slotted connections. The teeth along the entire length of the shaft allow the bushing to mix with the gear without stopping the mechanism. The transmission torque is several times greater than when transmitting through a key. In addition to the advantages of gear connections, there are also disadvantages.
Characteristics of splines
According to their design and method of torque transmission, splined joints can be classified as multi-keyed. Several planes of interaction during rotation, only instead of a large number of grooves and keys in them, only a splined shaft and a sleeve. There are no keys, they are replaced by slotted grooves and teeth cut directly on the mating parts. The design makes it possible to significantly reduce the manufacturing error and makes it possible to move the sleeve along the shaft axis without stopping the radial movement.
Splined joints include a shaft with teeth evenly distributed over the diameter and a bushing associated with it, with reciprocal grooves.
The dimensions of the splines are determined by the inner diameter of the shaft, their number and shape. In a spline connection, several contact planes are formed. The ability to transmit high torque increases several times compared to keys.
The tooth of the slot is cut with milling cutters on gear-cutting machines and broach. For movable nodes, subsequent grinding of the side surfaces is done. The length of the teeth can be any; for fixed splines it is equal to the height of the wheel hub. When the gear slides along the axis, the length of the cut protrusions on the shaft is determined by the size of the gear movement, its height and the technological allowance equal to the cutter radius for its exit during processing.
The diameter of the shaft along the outer surface is equal to the size of the sleeve along the depressions. The splined sleeve exactly copies the shaft profile with its hole and fits tightly on it. Slotted grooves are cut along the hole on a slotting machine. The manufacturing technology is long, it requires great accuracy, which the cutter cannot provide, since the length of the cutter is large relative to its cross section. When you try to speed up the processing, make more entry and feed, the tool squeezes out, the size turns into a minus.
When designing a unit and selecting pairs, the main parameter is the inner diameter of the slots. It is designed for torsion and bending. The splined bushing is subjected to smaller impacts. It is selected from the directory. Details are made of medium-carbon low-alloy steels: St 45, St40X, St 40XN. They have relatively high toughness and low brittleness in the normalized state and after bulk air quenching at a hardness of 320–350 HB.
You can determine the number of teeth during design from the tables. They are divided for each inner diameter into 3 load groups:
- light;
- average;
- heavy.
The more torque you need to transmit, the higher the slot itself and the greater their number. This increases the contact area.
Gear connections are calculated taking into account the manufacturing error. There is a connection gap between the surfaces of mating parts. When turning the leading part, it shifts in the opposite direction from the direction of the force. Ideally, all surfaces are in contact and loaded equally. In fact, gear joints are manufactured with an error of 0.01-0.03 mm, depending on the size and processing method. The coupling is in contact with one plane more strongly, with others less. When calculating the strength, a correction factor is selected from the table, which makes it possible to calculate the parameters of parts for strength, taking into account uneven load forces.
The gap in the connection determines the size of the idle stroke. Starting to move, the leading part first selects the clearance between the working planes, then the force action and rotation of the driven part and the entire assembly begin.
Classification
Details of splined nodes are normalized - there is a specific list of standard sizes, with corresponding pairs. Under them, a tool is made and equipment is configured. Depending on the working conditions and loads, spline connections are divided into several groups. They are characterized by:
- tooth shape;
- base surfaces;
- the possibility of displacement along the axis.
The shape of the protrusion is determined by the splined shaft. The bushing has only corresponding cutouts - grooves. Characteristics are determined by the types of slots:
- straight or straight;
- involute;
- triangular.
The classification is made according to the shape of the tooth in section across the joint.
Straight - spur
In straight-sided splines, the tooth in cross section is a rectangle. The width is the same throughout. They are most often found in mechanisms, since the manufacture is relatively simple. Spur spline connections are distinguished by the magnitude of the load: small, medium, high.
According to the method of movement along the axis, the types of connections are distinguished:
- one-piece;
- movable without load;
- moving under load.
One-pieces are used in gearboxes and other assemblies when transferring rotation between a permanent pair of parts.
An example of movable connections without load is the gearboxes of machine tools. When switching, the shaft shifts and the other pair engages. The gear ratio and rotation speed of the chuck or spindle are changed.
The car's gearbox does not require a complete stop to shift. There is a movement of the sleeve relative to the axis of rotation without stopping, under load.
The classification of splined joints also includes the method of centering. He can be:
- on the inner diameter - d;
- by outer diameter - D;
- on the sides, the width of the tooth - b.
When centering on the inside diameter, the minimum manufacturing tolerances are given for the size of the shaft along the cavity and the inside diameter of the sleeve. A gap is formed between the top of the tooth on the shaft and the bottom of the spline. Connection accuracy is achieved by grinding the bushing hole on internal grinding machine. The processing of a smaller diameter on the shaft is carried out with an abrasive wheel along the axis.
When centered on the outer diameter, a snug fit occurs along the top of the protrusion on the shaft and the diameter along the cavity on the sleeve. In this case, the shaft is externally ground and finished - grooving, bushings.
Centering, or rather landing on the side surfaces, is possible only for one-piece connections, when it is necessary to exclude idling at the beginning of the movement.
The slots are made with high accuracy in terms of the width of the tooth and its location relative to the axis. The sleeve is pressed onto the shaft. There are gaps in both diameters.
The drawing shows a cross-section of a connection with one tooth and diameters with a dotted line. The sleeve is shaded. Spur splines on the main view are indicated by the extension of a line with characteristics. The decoding includes the letter designation of the centering method, the number and width of splines, the size of the inner and outer diameters, indicating the accuracy class and the finish of all surfaces.
involute
The connection got its name from the shape of the side surface in the form of an involute, like a cylindrical gear. A large contact area and a wide tooth at the base allow for a huge amount of force to be transmitted. The tooth has a high bending strength.
make splined shafts on gear cutting machines. It turns out high accuracy when using standard equipment. Centering is done on the outer diameter for mechanisms operating with high precision, and on the lateral surface for heavily loaded nodes. The connection is immovable. With lateral displacement, a large friction force arises.
The drawing indicates one tooth and its shape, by analogy with spur gears. In addition to the diameters and the processing class, under the extension line, GOST is indicated, according to which the splines were made.
To transmit rotation with thin-walled hubs, splined connections with a triangular profile are made. They are connected rigidly and are used for low-power forces that require high accuracy in transmitting rotation.
The tooth is manufactured according to industry standards with an angle of 30°, 36° and 45°. The teeth are small, the quantity is large, within 20 - 70 pcs. centering is done only on the side surfaces.
They stand on the wiper drive in cars, torsion shafts of trimmers.
Advantages and disadvantages
When designing mechanisms that transmit rotation with a high load, they most often stop at the choice of a spline connection. It has in certain cases huge benefits and can replace multiple keyed connections. There are also disadvantages. It is necessary to weigh all the arguments for and against, choosing a connection method.
Compared to dowels, the advantages of spline connections include:
the ability to reduce the length of the hub; small radial clearances; increase in service life; no load on the cut and low bending due to the large contact patch; several lines of application of forces, the ability to transfer large forces by shafts with a small diameter; axial movement; there are only 2 parts in the connection; compactness; precise centering. The slots are manufactured in accordance with GOST and Standards, they have strictly normalized dimensions and it is easy to select the details for the connection. Simplified assembly of units and fitting of parts.
The disadvantages of splined joints include:
- high cost of parts;
- complex manufacturing technology;
- use of special equipment and tools.
When overloaded, the key is simply cut off, preventing the transfer of increased load to the working mechanism and preventing its breakage. The part is simple and cheap, easy to change.
In splined connections, in an emergency, a tooth or the entire machine may break. Replacing parts is difficult and expensive.
Application
The need for the use of gear connections arises when it is necessary to transmit a large torque and high demands are placed on the coaxiality of the driving and driven parts and the accuracy of movement. The splines allow the hub to move along the axis, changing the gear ratio without stopping the mechanism. Due to this, they are used in gearboxes of cars, machine tools, loading units.
The purpose of the spline, like the key, is to transmit torque at a given angular velocity.
The distribution of the load relative to the axis of rotation is uniform, according to the number of teeth, radial runout is excluded. This is used in precision instruments where precision is required.
Rotation with triangular teeth is found in household appliances, power tools:
- mixers;
- lawn mowers;
- drills;
- robotic vacuum cleaners.
In all areas of mechanical engineering, machine tool building, machines and other vehicles, a compact and powerful rotation transmission unit is used.
State standards
Spur splined shafts and bushings are manufactured in accordance with GOST 6033-80, which provides for the designation of splines according to the inner and outer diameter of the shafts, indicating the method of alignment: D, d, b, the number of teeth, and the manufacturing accuracy class of mating parts. For example: d - 8 × 36H7 / h7 × 40H12 × 7D9, where:
- d - centering on a small diameter;
- 8 teeth;
- 36 - inner diameter;
- H7/h7, H12, D9 tolerance of the corresponding dimensions;
- 40 - outer diameter;
- 7 - tooth width.
The standard provides for writing characteristics on the extension line in one line without spaces.
Download GOST 6033-80
