Working principle of manual transmission

Manual transmission is a kind of transmission device, which is used to change the speed and torque transmitted by the engine to the driving wheels, so that the car can obtain different traction and speed under various working conditions such as starting in place, climbing, turning and accelerating, and at the same time make the engine work in a more favorable working range.

principle of operation

Basic variable speed principle

In fact, the principle of manual transmission is not difficult. Firstly, the principle of deceleration and torque increase of a single pair of gears is explained, and then the shifting principle of the transmission is explained through a simple model of a 2-speed gearbox. Finally, an example of a 5-speed gearbox is given.

The following figure shows a pair of gears that mesh with each other. I is the driving shaft (power input shaft) and II is the driven shaft (power output shaft). Assume that the number of teeth of the driving shaft gear is Z 1, the speed is n 1, the torque is T 1, the number of teeth of the driven shaft gear is Z2, the speed is n2, and the torque is T2.

Because the gear connection is rigid, the linear velocity of the meshing points on the driving wheel and the driven wheel is the same, that is, n 1×Z 1=n2×Z2, n 1/n2=Z2/Z 1. This ratio is recorded as I, and its name is transmission ratio. If the power loss such as friction in the transmission process is not considered, the power obtained by the driven gear is equal to the power of the driving gear, that is, n 1×T 1=n2×T2, so that n 1/n2=T2/T 1 can be obtained, and the following expression can be obtained.

I = n 1/N2 = Z2/z 1 = T2/t 1

It can be seen from this formula that if the number of teeth of the driving wheel is less than that of the driven wheel, that is, Z 1? & ltZ2, which one is me? & gt 1, then n1>; ? N2, the visible speed of the driven shaft? N2 drops, and then look at the torque relationship. Can you get T2? & gt？ T 1, visible torque of driven shaft T2? Increase, which is the role of deceleration and torque increase;

Conversely, if the number of teeth of the driving wheel is more than that of the driven wheel, the speed of the driven shaft will increase and the torque will decrease.

In manual transmission, each pair of meshing gears basically has the function of reducing speed and increasing torque (except for overdrive).

After understanding the deceleration principle of a single pair of gears, we can look at the speed change principle of the transmission. In order to better understand the working principle of the gearbox, let's first look at a simple model of a 2-speed gearbox (as shown in the figure below) and see how all parts cooperate:

The input shaft (green) is connected with the engine through a clutch, and the shaft and the upper gear are a part, called the gear shaft; The shaft and the gear (red) are called intermediate shafts. They rotate together. The rotation of the shaft (green) drives the rotation of the intermediate shaft through meshing gears, and the intermediate shaft can transmit the power of the engine at this time; The shaft (yellow) is a spline shaft and the output shaft of the transmission. Power is output through it, and now the car is driven through a differential. When the wheel rotates, it rotates with the spline shaft.

The gear (blue) is sleeved on the spline shaft and can rotate freely. When the engine stops, but the vehicle is still moving, the gear (blue) and the intermediate shaft are at rest, while the spline shaft still rotates with the wheel.

The gear (blue) and the spline shaft are connected by a sleeve, which can rotate with the spline shaft and slide freely on the spline shaft to mesh with the gear (blue).

If the shift handle is operated, the sleeve engages with the right gear (blue) through the shift fork, and the transmission will engage to 1, as shown in the following figure.

At this time, the input shaft (green) drives the intermediate shaft, which drives the right gear (blue), and the right gear is connected with the spline shaft through the shaft sleeve to transfer energy to the drive axle. At the same time, the left gear (blue) is also rotating, but it has no effect on the spline shaft because it is not engaged with the sleeve.

When the sleeve is between two gears, the gearbox is in neutral position, and both gears rotate freely on the spline shaft.

The rotation speed of the output shaft is determined by the engine speed, the number of teeth of the input shaft, the number of teeth of the intermediate shaft and the number of teeth (blue).

The following figure is a schematic diagram of a five-speed transmission. The shifting principle is the same as that of the above 2-speed transmission. It is worth noting that the reverse gear is realized by adding a pinion (reverse intermediate gear).

The gear lever is connected with three forks through three connecting rods (as shown in the figure below).

There is a turning point in the middle of the shift lever. When you move the shift lever left and right, you are actually choosing different shift forks (different sleeves). When moving back and forth, select a different gear (blue).

Working principle of synchronizer

In the process of gear shifting, the peripheral speeds of a pair of gears to be engaged in the selected gear position must be equal (that is, synchronous) in order to make them engage in gear shifting smoothly. If the teeth of two gears are out of sync, the gears are forced to shift gears, which will inevitably produce impact and noise due to the speed difference between the two gears. This will not only make it difficult to shift gears, but also affect the service life of gear teeth, aggravate the wear of gear ends and even break teeth.

In order to make the gear shift smooth, the driver should take more complicated operations and complete them quickly and accurately in a short time. This can easily lead to fatigue, even for skilled drivers. Therefore, it is required to take measures in the transmission structure to ensure the smoothness of gears, simplify the operation and reduce the driver's labor. Synchronizer is designed to meet the second requirement.

The synchronizer is developed on the basis of the shift mechanism of the joint sleeve, in which besides the joint sleeve, spline hub and joint gear ring on the corresponding gear, there is also a mechanism to make the peripheral speed of the joint sleeve and the corresponding joint gear ring quickly reach and keep the same (synchronization), and a mechanism to prevent them from entering the joint before reaching synchronization to prevent impact.

Synchronizers are of normal pressure type, inertia type and self-pressurization type. At present, inertial synchronizer is widely used. The following figure shows the lock ring inertial synchronizer.

It is mainly composed of a connecting sleeve and a synchronous locking ring. Its characteristic is to achieve synchronization through friction. There are chamfers (locking angles) on the joint sleeve, the synchronous lock ring and the gear ring of the gear to be engaged, and the inner conical surface of the synchronous lock ring contacts with the outer conical surface of the gear ring of the gear to be engaged to generate friction. The locking angle and tapered surface have been properly selected in the design. The friction of the conical surface makes the gear sleeve to be engaged quickly synchronize with the gear ring, and at the same time, it will have a locking effect to prevent the gears from meshing before synchronization. When the inner conical surface of the synchronous lock ring contacts with the outer conical surface of the gear ring of the gear to be engaged, the rotational speed of the gear ring and the synchronous lock ring are rapidly equal under the action of friction torque, and they rotate synchronously, so the rotational speed of the gear ring relative to the synchronous lock ring is zero and the inertia torque disappears at the same time. At this time, driven by the axial force applied by the driver to the joint sleeve, the joint sleeve engages with the gear ring of the synchronous lock ring, and further engages with the gear ring of the gear to complete the shift process.

Working principle of control mechanism

The function of manual transmission control mechanism is to ensure that the driver can accurately shift the transmission into the required gear according to the driving state and using conditions of the car. There are two main types: direct control and remote control.

Most cars use direct control transmission control mechanism, and its gear lever and all shift control devices are arranged on the transmission cover, and the transmission is arranged near the driver's seat. The shift lever extends out from the cab floor, and the driver can directly operate the shift lever to toggle the shift control device in the transmission cover to shift gears. The structure is compact and the operation is simple and convenient.

The following figure shows the operating mechanism of the 6-speed manual transmission.

Both ends of the shift fork shaft are supported in corresponding holes in the transmission cover and can slide axially. All shifting forks and shifting blocks are elastically fixed on the corresponding shifting fork shafts. The upper ends of the third and fourth shifting forks are provided with shifting blocks, and the tops of the third and fourth shifting forks and all shifting blocks are provided with grooves.

When the transmission is in neutral, the grooves are aligned on the transverse plane, and the ball head at the lower end of the fork shift lever extends into these grooves. When the gear is selected, the gear lever can swing transversely around the spherical fulcrum in its middle part, and its lower end pushes the fork-shaped gear lever to rotate around the axis of the gear shifting shaft, so that the ball head at the lower end of the fork-shaped gear lever is aligned with the gear shifting block groove corresponding to the selected gear position, and then the gear lever swings longitudinally, driving the gear shifting fork shaft and the gear shifting fork to move forward or backward to realize gear shifting.

The control mechanism should ensure that the transmission can be accurately engaged in the selected gear and can work reliably in the selected gear, so it is equipped with self-locking device, interlocking device and reverse locking device.

(1) self-locking device

The self-locking device can prevent automatic gear shifting and automatic gear shifting, and ensure the full tooth length meshing of the transmission gears in all gears. The picture below shows the self-locking device of a car.

Three deep holes are drilled in the convex part of the front end of the transmission cover, and the self-locking steel ball 1 and the self-locking spring 2 are installed in the holes, and the holes are located right above the fork shaft 6. The surface of each shift fork shaft facing the steel ball is provided with three grooves along the axial direction, and the depth of the grooves is smaller than the diameter of the steel ball.

The middle groove is in neutral position when it is aligned with the steel ball, and the front or back groove is in a certain working gear when it is aligned with the steel ball. When the groove faces the steel ball, the steel ball is embedded in the groove under the pressure of the self-locking spring. The axial position of the shift fork shaft is fixed, and its shift fork and the corresponding joint sleeve or sliding gear are fixed in neutral or a certain working gear, so it is impossible to shift gears by itself.

When it is necessary to shift gears, the driver applies a certain axial force to the shift fork shaft through the shift lever to overcome the pressure of the spring, and the self-locking steel ball is squeezed out of the groove of the shift fork shaft and pushed back into the hole, so that the shift fork shaft slides over the steel ball and drives the shift fork and the corresponding shift element to move axially. When the shift fork shaft moves to another groove to align with the steel ball, the steel ball is pressed into the groove again, and the transmission just shifts into a certain working gear or retreats to neutral. The distance between adjacent grooves ensures that the gear is in full tooth length meshing or completely disengaged.

(2) Interlock device

The interlocking device can ensure that two gears are not engaged at the same time, and prevent two gears engaged at the same time from locking each other due to different transmission ratios, causing motion interference and even damaging parts. The picture below shows the interlocking device of a car.

The interlocking pin 6 is installed in the hole of the intermediate fork shaft 3, and its length is equal to the diameter of the fork shaft minus the radius of the interlocking steel ball; Interlocking steel balls 2 and 4 are installed in the transverse holes of the transmission cover.

In the neutral position, the left and right fork shafts 1, 5 are opposite to the steel balls 2, 4, and the middle fork shaft is provided with grooves on the left and right sides, in which holes for locking pins 6 are provided.

The interlock device can ensure that the driver can move the shift fork shaft only when the transmission is in neutral position. If one shift fork shaft is moved into gear, the other two shift fork shafts are fixed in neutral position by interlocking device and cannot move axially.

(3) Reverse locking device

The invention can prevent the wrong gear from shifting into reverse gear, prevent the car from causing huge impact and damaging parts when moving forward, and prevent the wrong gear from shifting into reverse gear to cause safety accidents when starting the car.

The function of the reverse gear locking device is to let the driver engage the reverse gear, and a large force needs to be exerted on the gear lever before shifting into the reverse gear, as shown in the following figure.

The lever of the reverse lock pin 1 is equipped with a reverse lock spring 2, and the nut at the right end of the reverse lock pin can adjust the pre-tightening force of the spring and the length of the reverse lock pin. When the driver wants to engage the reverse gear, he must use greater force to make the lower end of the shift lever compress the reverse gear spring, and then push the reverse gear lock pin to the right, so that the lower end of the shift lever enters the groove of the reverse gear shift block, thereby shifting the I and reverse gear shift fork shafts and retreating into the reverse gear.