Cam gearbox: opportunities and scope

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:41

Optimizing the working resources of the engine during management has occupied the minds of designers since the release of the first car. This was achieved in many ways, but one of the basic ones was to increase efficiency when interacting with the gearbox (gearbox). The very mechanics of pairing two nodes requires a certain amount of dynamic effort, but it is impossible to do without this function. One of the most energy-efficient systems for changing the torque frequency is a cam gearbox, which, however, has significant limitations in use.

Features of the device mechanism

Although cam "boxes" are superior to standard transmissions in a number of characteristics, their design can be considered as simplified relative to conventional mechanics. The main feature from the point of view of the technical device isgetting rid of synchronizers. Together with them, the device of a whole group of elements was optimized, which were supposed to make the transmission control easier, but they also lengthened the period for issuing a command through several nodes. As a result, the whole infrastructure with fine teeth was replaced by a set of cam rows. At this type of gearbox, one clutch can contain up to 7 cams, which increases the margin of the hitch area in width. At the same time, the size of the gear in this system is larger than in standard gearboxes, not to mention the replacement of the beveled shape of the teeth with a straight one. The latter was due to the need to reduce friction losses and minimize the axial load on the shaft.

Operation principle

Technique can be sequential or search. In the first case, sequential gear shifting is implemented, and in the second - the usual one, as in a standard gearbox. In practice, it is the sequential principle that is more often used, since it allows to reflect the capabilities of the cam design to a greater extent. Switching can be carried out up and down, as well as on the sides. Control from the driver is made through a lever connected to the shaft. For example, switching a cam gearbox on a VAZ-2108 is characterized by rigidity, reliability and simplicity. The lever moves the wave-shaped grooved shaft, turning it by a certain degree. As a result, either the “neutral” or the transmission is activated. By the way, in order to further save time, the gear knob itself is made large and high so that the driver spends less time on manipulationswith mechanical control. In technical terms, the semi-automatic cam systems occupy the highest stage of development, in which the driver only needs to wait for the desired switching by electronics.

Operational capability

The operating torque when handling the cam shifting system is significantly reduced, saving time. Regardless of the characteristics of the engine, the rate of change of torque in a cam transmission is faster than in a conventional transmission. The time to complete the operation is 0.4-0.6 s, which is noticeable when compared with disengaging / engaging the clutch on a car with a standard “box”. More importantly, the design of sequential mechanisms expands the possibilities for tuning. This applies to cases of complete conversion of the car into a racing modification with a foot shift. In this case, it is necessary to install, together with the gearbox pairs, the main differential pair, which can correct the dynamic qualities of the machine. Again, an ordinary driver is unlikely to need such an update, but for a connoisseur of sports tuning it will provide a new driving quality.

Application of cam gear models

On passenger cars intended for public roads, such mechanisms are rarely used. For such provision, there must be certain grounds related to increasing the dynamics or simplifying the structural base of the transmission unit. Often cam gearboxesused in single tuning events to demonstrate certain capabilities of conceptual models. In the case of the Japanese sports car Mitsubishi Lancer Evolution, the combination of a sequential “box” and a 420 hp engine, in particular, made it possible to accelerate to 100 km / h in 3.5 s.

VAZ gearbox cam mechanism

In Russia, the production of components for transmission cam units is carried out by the Lada Special Transmission plant. This group produces sequential mechanisms suitable for VAZ cars. According to users, domestic products demonstrate high stability, clarity of operation and reliability. But you can also turn to solutions from Eastern European manufacturers like TST and Dogbox. In the lines of these companies, you can find the closest sequential gearboxes on the VAZ. Cam mechanisms of foreign production are usually delivered in a collapsible form. For example, kits without mounting hardware are often offered, which forces us to additionally look for accessories for fixing the unit to the carrier base. Sometimes automatic transmissions are taken as donor kits.

Cam gears for "classics"

Of course, the need for equipment with cam “boxes” is not limited to domestic cars. Classic sedans and hatchbacks that are used on public roads can be converted to sequential gear shifting. To do this, use special modifications of the cam gearboxes on the VAZ and"classic" in one configuration or another. As a rule, these are mechanisms with a cam clutch and gear units with 5-7 elements on the surface. The more cams, the higher the resource of the unit in a pair of clutch-gear. On the other hand, the complexity of the design increases the price and complicates the integration process of the device. And even if the basis of the product fits into the mounting base in terms of parameters, then additional difficulties can be caused by the refinement of the gear shift fork. Often, standard fixtures are used for these purposes, which are finalized by welding or milling. Ready-made "boxes" assemblies may well be used, but this mainly applies to obsolete 5-cam mechanisms.

Cam boxes and race mechanics

Sports cars are still the target niche for cam gears. An example of a sports car from Mitsubishi has already been given, and the use of this unit in cars is not limited to this. This practice is continued by the Subaru Impreza, provided with a sequential “box”. And with regard to this model, it is worth noting the differences in approaches to completing the cam unit. In civilian versions of the sports car, it is precisely the consistent principle of changing torque that is used. But in the rally modification, this decision is prohibited, so the basic search switching mechanism is left. A striking example of the use of this design is the cam row of the Toyota MR2 gearbox. This is a two-seater sports car, the latest modifications of which received a five-speed sequential “box” SMT. To the features of this siteclaim that it is able to withstand loads from engines with a capacity of about 800 hp

Restrictions on the use of sequential checkpoints

Even if we discard the fact that only drivers with relevant experience in the physical control of the transmission can handle the cam "boxes", there are several fundamentally important kinematic nuances of operating such devices. Sequential shifting reduces the vehicle's maneuverability when performing complex lane changes on public roads. In other words, even a nimble racing driver will have a big loss when shifting the forks due to the need for re-gassing with sharp transitions from lower to upper stages. On a straight track, where constant and confident maintenance of a high speed is necessary, the cam gearbox shows its best side, but in a civilian car its advantages turn into disadvantages.

Conclusion

The concept of sequential shifting, with all its features, retains the prospects for technological development. This is confirmed by the active merging of such transmission mechanisms with electronics. For example, today there are cam units operating on the commands of the Motec programming computer. One of the main functions of the electronic unit in a car with such a filling, as the developers say, will be the automatic control of the ignition system and the performance of regassing.