Difference Between Crankshaft and Camshaft？

Crankshaft VS Camshaft

The crankshaft is located at the bottom of the engine block. The crankshaft is in the shape of a point S-shaped connection. The up-and-down movement of the piston connecting rod drives the crankshaft to twist and rotate so that the reciprocating motion of the piston is converted into the rotational motion of the crankshaft, and the average of the original piston is converted into the rotation of the crankshaft, thereby outputting engine powered.

The camshaft is often located in the cylinder head or engine block. The camshaft is a shaft with a bulge on it. The bulge is used to push the valve. The cam sets the intake and exhaust valves of the cylinder to control the opening and closing of the valve to drive the valve. The crankshaft and camshaft are important moving parts of the engine. Due to the special structure of the workpiece and the large and uneven cutting amount, the workpiece is easily bent and deformed due to the large force, so the machining accuracy is difficult to guarantee, which affects the quality of subsequent machining. At the same time, there are many equipment and personnel.

Essentially, the crankshaft is responsible for converting energy into motion. The camshaft, on the other hand, manages the engine intake and exhaust processes.

1. The Development of Camshaft Roughing

In the early days, the main journal of the camshaft was generally roughed by a single-tool or multi-tool ordinary lathe, and the cam was generally completed by a single-tool or multi-tool copy turning by a mechanical model lathe. Single-tool turning has low efficiency; multi-tool turning is difficult to ensure the quality of parts, and after rough turning, processes such as straightening and rough grinding must be arranged, resulting in low production efficiency.

In multi-tool turning and profiling, due to the large force during cutting, the workpiece is prone to bending deformation and vibration, the tool life is low, the tool is frequently beaten, and the defect rate is high. After rough turning, it is necessary to arrange straightening, rough grinding, and other processes. When the workpiece is changed, the template needs to be replaced, the adjustment time is long, the switching efficiency is low, and the cost is high. The new process camshaft main journal adopts a CNC lathe, and the cam adopts CNC external milling for high-speed milling (forging blanks of alloy steel parts) or CBN strong grinding (casting blanks of cast iron). The rough machining of the camshaft has gone through the development process of single-tool turning, multi-tool turning, CNC turning, and CNC high-speed external milling.

2. The Development of Crankshaft Roughing

Before the 1970s, multiple turning tools were used to process the outer circle, fillet, side, and steps of the journal at one time, but different parts of the same part required multiple processes to complete the rough machining of the journal and connecting rod journal. In multi-tool turning, there is a large allowance, the side of the balance block is processed intermittently, and it is easy to generate vibration and knife problems. The tool life is low, the defect rate is high, and the cutting efficiency is low. In the 1970s and 1980s, CNC turning, CNC external milling, and CNC internal milling appeared in the rough machining of crankshafts. In the late 1980s and early 1990s, car-pulling and car-car-pulling processes were developed. This process has the advantages of high precision and high efficiency. In the mid-1990s, CNC high-speed external milling was developed. It has higher production efficiency than CNC turning, CNC internal milling, and turning-turning for the crankshaft that needs to be processed on the side of the balance weight.

For reasons of machining accuracy and machining efficiency, turning is generally only used for main journal machining. Crankshaft internal milling and high-speed external milling cannot process axial undercut grooves. When the crankshaft has axial undercut grooves, it should be processed by the turning-turning method. When the side of the crankshaft balance block needs to be processed, the milling process is much better than the turning process. It has the advantages of high cutting speed, short process time, small cutting force, low-temperature rise, high tool life, less tool change, high precision, and good mechanical flexibility.

Today, hydrodynamic bearings are used almost everywhere in automotive engines. But that hasn't always been the case. In the 1920s and 1930s, rolling element bearings were the technology of choice to support the crankshaft and connecting rod bearings. Today, rolling element bearings are usually only used in two-stroke engines. Rolling element bearings do have a more immediate advantage over hydrodynamic bearings in terms of ultimate friction reduction, especially at high rotational speeds. These bearings can be equipped with solid or separate rings and cages depending on their design constraints. Such techniques can also be applied to balance shafts, with further results in terms of friction.