A crankshaft is a part in a car engine driven by a piston group. It transfers torque to the flywheel, which in turn rotates the transmission gears. Further, the rotation is transmitted to the drive wheel axle shafts.
All cars under the hood of which are installed internal combustion engines, equipped with such a mechanism. This part is created specifically for the engine brand, not for the car model. During operation, the crankshaft is rubbed against the structural features of the internal combustion engine in which it is installed. Therefore, when replacing it, minders always pay attention to the development of rubbing elements and why it appeared.
What does the crankshaft look like, where is it located and what kind of malfunctions are there?
The crankshaft is installed in the lower part of the engine directly above the oil sump and consists of:
- the main journal - the supporting part of the part on which the main bearing of the motor crankcase is installed;
- connecting rod journal - stops for connecting rods;
- cheeks - connect all connecting rod journals with the main ones;
- toe - the output part of the crankshaft, on which the pulley of the gas distribution mechanism (timing) drive is fixed;
- shank - the opposite part of the shaft, to which the flywheel is attached, which drives the gears of the gearbox, the starter is also connected to it;
- counterweights - serve to maintain balance during the reciprocating movements of the piston group and relieve the load of centrifugal force.
The main journals are the axis of the crankshaft, and the connecting rods are always alternately displaced in the opposite direction from each other. Holes are made in these elements to supply oil to the bearings.
A crankshaft crank is an assembly consisting of two cheeks and one connecting rod journal.
Previously, prefabricated modifications of cranks were installed in cars. All engines today are equipped with one-piece crankshafts. They are made from high-strength steel by forging and then turning on lathes. Less expensive options are made from cast iron using casting.
Here's an example of creating a steel crankshaft:
The shape of the crankshaft depends on the number and location of the cylinders, their order of operation and the strokes that are performed by the cylinder-piston group. Depending on these factors, the crankshaft can be with a different number of connecting rod journals. There are motors in which the load from several connecting rods acts on one neck. An example of such units is a V-shaped internal combustion engine.
This part should be manufactured so that during rotation at high speeds vibration is minimized as much as possible. Counterweights can be used depending on the number of connecting rods and the order in which the crankshaft flares are generated, but there are also modifications without these elements.
All crankshafts fall into two categories:
- Full support crankshafts. The number of main journals is increased by one in comparison with the connecting rod. This is due to the fact that on the sides of each connecting rod journal there are supports, which also serve as the axis of the crank mechanism. These crankshafts are most commonly used because the manufacturer can use lightweight material, which affects engine efficiency.
- Partial bearing crankshafts. In such parts, there are fewer main journals than crank ones. Such parts are made of more durable metals so that they do not deform and break during rotation. However, this design increases the weight of the shaft itself. Basically, such crankshafts were used in low-speed engines of the last century.
The full-support modification has proven to be lighter and more reliable, therefore it is used in modern internal combustion engines.
What is a crankshaft for? Without it, the movement of the car is impossible. The part works on the principle of rotation of the bicycle pedals. Only car engines use more connecting rods.
The crankshaft works as follows. An air-fuel mixture ignites in the engine cylinder. The generated energy pushes the piston out. This sets in motion a connecting rod connected to the crankshaft crank. This part makes a constant rotational movement around the crankshaft axis.
At this moment, another part located on the opposite part of the axis moves in the opposite direction and lowers the next piston into the cylinder. The cyclical movements of these elements lead to even rotation of the crankshaft.
So the reciprocating motion is converted into rotary motion. The torque is transmitted to the timing pulley. The operation of all engine mechanisms depends on the rotation of the crankshaft - the water pump, oil pump, generator and other attachments.
Depending on the modification of the engine, there can be from one to 12 cranks (one per cylinder).
For details on the principle of operation of the crank mechanism and the variety of their modifications, see the video:
Although the crankshaft is made of durable metal, it can fail due to constant stress. This part is subjected to mechanical stress from the piston group (sometimes the pressure on one crank can reach ten tons). In addition, during operation of the motor, the temperature inside it rises to several hundred degrees.
Here are some of the reasons for the failure of the crank mechanism component.
The wear of the connecting rod journals is a common malfunction, since frictional force is generated in this unit at high pressure. As a result of such loads, workings appear on the metal, which impede the free movement of the bearings. Because of this, the crankshaft heats up unevenly and can subsequently deform.
Ignoring this problem is fraught with not only strong vibrations in the motor. Overheating of the mechanism leads to its destruction and, in a chain reaction, the entire engine.
The problem is solved by grinding the crankpins. At the same time, their diameter decreases. To ensure the size of these elements is the same on all cranks, this procedure should be performed exclusively on professional lathes.
Since after the procedure the technical gaps of the part become larger, after processing a special insert is installed on them to compensate for the resulting space.
Seizure occurs due to low oil level in the engine crankcase. The quality of the lubricant also affects the occurrence of a malfunction. If the oil is not changed on time, it thickens, from which the oil pump is not able to create the required pressure in the system. Timely maintenance will allow the crank mechanism to work for a long time.
The crank key allows torque to be transferred from the shaft to the drive pulley. These two elements are equipped with grooves into which a special wedge is inserted. Due to low-quality material and heavy load, this part in rare cases can be cut (for example, when the engine is jammed).
If the grooves of the pulley and KShM are not broken, then simply replace this key. In older motors, this procedure may not bring the desired result due to backlash in the connection. Therefore, the only way out of the situation is to replace these parts with new ones.
A flange with several holes for connecting a flywheel is attached to the crankshaft shank. Over time, these nests can break. Such faults are categorized as fatigue wear.
As a result of the operation of the mechanism under heavy loads, microcracks are formed in metal parts, due to which single or group depressions are formed on the joints.
The malfunction is eliminated by reaming holes for a larger bolt diameter. This manipulation must be performed with both the flange and the flywheel.
Two oil seals are installed on the main journals (one on each side). They prevent oil leakage from under the main bearings. If grease gets on the timing belts, this will significantly reduce their life.
Oil seal leaks may appear for the following reasons.
- Vibration of the crankshaft. In this case, the inside of the stuffing box wears out, and it does not fit snugly against the neck.
- Long downtime in the cold. If the machine stands outside for a long time, the oil seal dries up and loses its elasticity. And because of the frost, he dubs.
- The quality of the material. Budget parts always have a low working life.
- Installation error. Most mechanics will install with a hammer, gently driving the oil seal onto the shaft. In order for the part to function longer, the manufacturer recommends using a tool designed for this procedure (a mandrel for bearings and seals).
Most often, oil seals wear out at the same time. However, if there is a need to replace only one, the second should also be changed.
This electromagnetic sensor is installed on the engine to synchronize the operation of the injector and ignition system. If it is defective, the motor cannot be started.
The crankshaft sensor detects the position of the cranks at the dead center of the first cylinder. Based on this parameter, the vehicle's electronic control unit determines the moment of fuel injection into each cylinder and the supply of a spark. Until a pulse is received from the sensor, a spark is not generated.
If this sensor fails, the problem is solved by replacing it. Only the model that has been developed for this type of engine should be selected, otherwise the parameters of the position of the crankshaft will not correspond to reality, and the internal combustion engine will not function correctly.
For more details about the DPKV function and diagnostics of its malfunctions, see the video: