Understanding Synchromesh vs. Constant Mesh Gearboxes
Automobiles and other machinery use various types of gearboxes to transfer power and control the speed of the engine. Two common types of gearboxes are the synchromesh gearbox and the constant mesh gearbox. These gearboxes share a similar design feature of having gear pairs always engaged, but they differ significantly in their operation and performance. In this article, we will explore the key differences between these two types of gearboxes, their historical context, and the advantages and disadvantages of each.
Introduction to Constant Mesh Gearboxes
The constant mesh gearbox is a design in which all the gear pairs are always engaged. This means that the gears are in constant contact and can always be selected, regardless of whether the vehicle is in motion. This design is often found in older machinery, particularly in trucks, which were commonly referred to as "crashboxes" due to the jerky and often loud shifting experience.
These gearboxes rely on the driver to manually synchronize the engine speed with the gear speed before engaging. This synchronization, known as double clutching, is a technique that involves the use of the clutch twice to match the gear speed before shifting. This process can be challenging without practice and skill, but it can be mastered with experience.
How Constant Mesh Gearboxes Work
In a constant mesh gearbox, all gears are free to spin at all times. When a driver selects a gear, the appropriate gear pair is engaged, and the others remain free to spin. Each gear pair in a constant mesh gearbox includes sliding gears that can be finely adjusted to match the desired speed. This continuous engagement and disengagement can lead to smooth gear changes if the driver is skilled and the gears are well-maintained.
Introduction to Synchromesh Gearboxes
A synchromesh gearbox is a more advanced variation of the constant mesh gearbox. It incorporates friction cones and brake rings to synchronize and engage the gears without the need for manual double clutching. This feature makes the gear changes smoother and more refined, reducing the noise and vibration associated with the constant mesh gearbox.
How Synchromesh Gearboxes Work
Unlike the constant mesh gearbox, a synchromesh gearbox uses a synchronization mechanism to bring two gears to the same speed before engaging. This synchronization is typically achieved using a friction cone, which is a type of clutch that matches the speed of the gear it is engaged with. The brake ring prevents the gears from contacting prematurely if the speeds are not matched, ensuring a smooth and gentle engagement of the gears.
When a gear is selected, the synchromesh mechanism brings the speed of the selected gear closely to the speed of the gear it will be engaging. This process can take a moment, and during this time, the gear lever may resist shifting. This resistance is a sign that the gears are not yet matched in speed, and the driver should wait until the resistance is gone before shifting.
The synchromesh mechanism can be found in modern passenger vehicles, making gear changes more intuitive and less demanding for the driver. The absence of the need for double clutching means that gear shifts can be made more quickly and with less effort.
Comparison of Constant Mesh and Synchromesh Gearboxes
The key difference between the constant mesh and synchromesh gearboxes lies in the gear synchronization process. In a constant mesh gearbox, the driver must manually synchronize the engine speed with the gear speed, while in a synchromesh gearbox, this synchronization is automatic through the use of friction cones and brake rings.
Another significant difference is the noise and vibration levels. Constant mesh gearboxes can be noisy and may produce a distinct "graunching" sound during gear changes, especially if the synchronization is not perfect. Synchromesh gearboxes, on the other hand, are generally quieter and offer a smoother gear change experience.
From a practical standpoint, constant mesh gearboxes are still used in heavy machinery and some manual transmissions in modern vehicles, particularly in off-road and agricultural applications. Synchromesh gearboxes, with their advanced features and user-friendly design, are more prevalent in passenger vehicles and high-performance applications.
Conclusion
The choice between a synchromesh gearbox and a constant mesh gearbox depends on the specific needs and application of the machinery. Constant mesh gearboxes, with their manual synchronization feature, are still relevant in certain contexts, particularly where quick and intuitive gear changes are not the primary concern. Synchromesh gearboxes, with their advanced synchronization and user-friendly design, offer a smoother and more reliable gear change experience, making them the preferred choice in modern passenger vehicles and high-performance applications.
Whether you are a mechanic, a driver, or simply curious about the mechanics of gearboxes, understanding the differences between synchromesh and constant mesh gearboxes can provide valuable insights into the workings of these vital components of machinery.