Constant Mesh Gear Box
Constant mesh gearbox is a type of Transmission in which all or the majority of the gears are always in mesh with each other, instead of a sliding-gear transmission, in which engagement can be obtained by sliding a few of the gears along a shaft into mesh. In a constant-mesh manual gearbox, Gear ratios are selected by small Clutches that connect the many gear sets to their shafts to ensure that power can be transmitted through them. The following diagram shows the set up of a constant mesh gear box
Construction and operating of a continuous mesh gear box
Constant gear mesh gearbox employed helical gears for power transmission. The gears are rigidly fixed in the lay shaft. The gears in result shaft rotates freely without engaging with shaft, thus not really transmitting power. The gears in both shafts are often meshed together.
To engage the gears with output shaft dog clutch can be used. the dog clutch is shifted by the seletor fork shifted by gear lever.To provide invert gearing a idler equipment is used.
When the gear lever is pushed, the apparatus selector fork pushes the dog clutch. The dog clutch engages the gear and the output shaft, therefore power from lay shaft now transmitted to output shaft.
CONSTANT MESH GEARBOX
A constant mesh transmission is that a type of manual transmission where sliding gears from the sliding mesh gearbox is replaced with the constantly meshed combines of gears and also the new shifting products named dog clutches square measure introduced which assists in transmittal the desired output to the many shaft by creating connection with the acceptable couple of the meshed gears.
A constant mesh transmission typically comes with 4 forward speeds and 1 reverse manual transmitting configuration.
Why will we wish Constant Mesh Transmission?
The introduction of initial transmission system i.electronic. sliding mesh transmission was an excellent success in cars trade as currently there was a system which can offer needed torsion and velocity ratios desire by the vehicle to face the road challenges however still there have been several vital issues with this gear that raised the query on its effectiveness and responsibility. the problems long-faced were as follows-
The shifting of gears wasn’t an easy task because the shifting needed a special technique that wasn’t in any respect everybody’s cup of tea, a talented driver was needed for driving such vehicle, the special technique needed being Double-de-clutching.
Note – Double-de-clutching- it’s the technique because the name indicates that needed dual engagement and disengagement of clutch for shifting one gear.
f i.e. once driver must shift the apparatus he preliminary presses the clutch pedal and create the apparatus to the neutral, than once more he releases the clutch pedal and accelerate in order to extend the rate of the lay-shaft to ensure that the meshing of applicable gear will happen, save for he presses the clutch pedal and produce the gear lever to the desired gear and unleash the clutch pedal and at last the required gear is obtained.
Since the gears are to be meshed square measure in continuous rotation with a totally different speed compared to the meshing of these gears may cause breakage to the gear teethes or continuous wear and tear is there.
The shifting of gears is actually a terribly clamant method.High maintenance is necessary as slippy and meshing of gears causes resistance to wear of shafts and gears.
MAIN PARTS
Clutch Shaft.
Lay Shaft or counter Shaft.
Main Shaft.
Dog clutch.
Gears.
There are various kinds of gears with both spur and helical gears like:
Clutch gear.
First gear.
Second gear.
Reverse gear.
WORKING PRINCIPLE:
In Constant Mesh Gearbox gearbox, all gears of the main shaft are in constantly meshed with the corresponding gears of the layshaft or countershaft. As well dog clutches are given on the primary shaft: one between your clutch gear and the second gear; and the various other between your first gear and reverse gear. The main shaft is made splined and all of the gears are free to move on it. Dog clutches can slide on the main shaft and rotates with it. All of the gears on the countershaft are permanently fixed with it.
When the left dog clutch is made to slide to the left by using the apparatus shift lever, it meshes with the clutch gear and the top speed gear is obtained. When the still left dog clutch meshes with the second gear on the primary shaft, the next speed equipment is achieved. Similarly, by sliding the right-hand dog clutch left and correct, the first speed gear and reverse equipment are attained respectively In this kind of gearbox, because all of the gears are in constant mesh, they are safe from being broken and unpleasant grinding audio does not occur while engaging and disengaging them.
Constant mesh gearbox is used for the smooth operating of an automobile. They are used to increase the rotating power (Torque); that is accompanied by a decrease in rate. It is a kind of manual transmitting. The invention of earliest manual gear system could be traced back to the nineteenth century. There are multiple gear ratios present which provides various torque and velocity ratio. Along with this, the reverse mechanism can be present. This manual transmissions which are developed recently contain all the gears mesh at any given point of time.
In technical terms, it can be thought as a gearbox in which all of the gears are at all times in a state of mesh. The gears remain fixed at their original positions. The gears will stay engaged all the time. Find out more about its structure, working, advantages, drawbacks and applications in this post.
Construction:
It is made up of subsequent components:
1. Counter shaft or Lay Shaft:
This shaft is in direct contact with the clutch and the main shaft. Keeping in mind according to the equipment ratio, the swiftness of the counter shaft could be much less that the speed of the engine. The gear ratio can be defined as the ratio of one’s teeth of driven equipment to one’s teeth of the driver gear.
2. Main shaft:
This shaft operates the speed of the automobile. The power is manufactured available to the primary shaft through the gears from the counter shaft. This is done relative to the gear ratio.
3. Dog clutch:
Dog clutch is particular feature of continuous mesh gearbox. It is utilized for the coupling of any two shafts. That is carried out by interference. Using a dog clutch, different gears can be locked to the result and input shafts.
4. Gears:
The primary work of the gears may be the transmission of power between the shafts. If the apparatus ratio is several, the primary shaft will work at a quickness that is slower than the counter shaft, and vice versa. The set up of both reverse, and also forward gears, is present.
Working:
Forward gear selection:
From the input shaft, the power starts flowing and is divided into four parts. Each component goes to among the output gears, namely first, second, third and fourth. Gear ratios can be acquired for each of these. This can be done by the proper sliding of dog clutch over one’s teeth of the selected gearwheel. After this the path of the energy movement completes. This happens due to the locking motion of the output shaft.
Reverse gear selection:
The power will flow from the input shaft to the reverse gears. The power is then transmitted from the invert gear to the invert idler. The idler wheel changes the direction of the rotation. Regarding forwarding direction equipment selection, the output gears will rotate in a direction opposite to the input gears. However in the case of reverse equipment selection, the rotation can be in the same direction as the insight shaft.
The steps are taken to change any gear in the constant mesh gearbox system:
1. The first rung on the ladder when one wants to modify the gear would be the pressing of the clutch. Following this comes the neutral state of the automobile to be performed. Proper optimization of the engine’s speed is required.
2. After the neutral gear, one moves ahead to the first gear. The first equipment. This process is known as dual clutching. Inefficiency in executing the above methods might result in a harsh and gnashing sound.
Advantages and Disadvantages of Constant Mesh Gearbox:
Advantages:
The first and foremost benefit of the constant gear mesh is the utilization of helical gears. The double helical gears and the helical gears are extremely beneficial due to their quieter operating capabilities
There are many conditions which might cause harm. In the case of constant mesh gearbox, any damage is suffered entirely by your dog clutch teeth. One’s teeth belonging to the apparatus wheels remain intact. This is simply not the case for sliding mesh equipment box.
The other equipment boxes are noisy and create an unwanted din.
Disadvantages:
It is less efficient than the others due to higher mesh teeth. Skill is required for it.
The dual clutch mesh is required. This is required to possess the spinning movements of the shaft.
Application:
Some of the vehicles which use this type of gearboxes are farm trucks, motorcycles, and heavy machinery.
In this type of gearbox, all of the gears of the main shaft are in continuous mesh with the corresponding gears of the counter shaft or lay shaft.
Two dog clutches are given on the main shaft i.e. one in between the clutch gear and the second gear, and the additional between the first equipment and the reverse gear.
The dog clutch can slide on the shaft and rotate with it. While, all of the gears on the counter shaft are rigidly set with it.
As so when the left hands dog clutch was created to slide to the left by means of the apparatus shift lever, it meshes with the clutch equipment and the top speed gear is obtained. When the left hand dog clutch meshes with second gear, the second gear is obtained.
Similarly, by sliding right hand dog clutch left and right, the 1st speed gear and reverse gear are obtained respectively.
In this kind of gearbox, all of the gears are in continuous mesh and hence because of this, they are safe from being damaged and irritating grinding sound does not take place while engaging and disengaging.

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