EQUIPMENT
EVOLUTION
ECONOMY IS ROTATING … ON BEARINGS
Getting harder can make a car cheaper!
Arkady ALEKSEEV
Technical, or rather, technological progress, is capable of such a thing. For decades, accustoming the buyer to the fact that the next, more sophisticated model should cost more than the previous one, automobile concerns waited for the same reproaches for the growing high cost. Some critics recalled the 1920s: $ 490 for a Ford, 1, 200 for a Cadillac. Someone counted how many months a worker worked to buy a Volkswagen Beetle in the 50s and a New Beatle in the late 90s … Yes, their equipment is incomparable, but still, why would modern cars not to be cheaper? Even if you shrug off nostalgia at past prices, there remains a very specific problem: now cars - from the point of view of the manufacturer - are too durable. But you need to sell new ones! And in the arsenal of seller’s gimmicks there appears an old, as the world, trick - we lower the price to sell more. Hardly the manufacturer of mass models comes to this inevitable conclusion, as his marketing department literally puts under the press designers and engineers.
Most techies know very well - the probability of coming up with something fundamentally new is higher when the task seems to be perplexing. We will not consider all the elements of the car’s construction here, but we will analyze a specific example: the hub unit and its main element, the bearing. To this day, most Russian cars are equipped with hubs of ancient, immemorial times, designs - two tapered bearings, the hub itself, the axle-axle and the adjusting nut with washers. Bearings are standard, produced in huge series and therefore inexpensive. What else to reduce the cost here? From the point of view of the operators, perhaps, there is nothing. And now let’s look through the eyes of a car assembly technologist: several mandrels are required to install the inner and outer rings, seals (gland), a grease gun, torque wrench and … a skilled worker who regulates the tightening of bearings. As you remember from the factory instructions, tightening is an operation quite responsible, not only the durability of bearings, but also traffic safety depends on it in many ways. Consequently, it will take quite a lot of time - if we believe that the manufacturer provides quality.
About thirty years ago, with the deployment of large-scale production of front-wheel drive cars, the traditional wheel hub was revised, installing a double-row ball bearing here. However, the widespread belief that a different type of drive required this is incorrect. Look at the Niva - it manages the front suspension with traditional tapered bearings! Just the introduction of double-row bearings and the “front-wheel drive revolution” are the links of one chain: any economist will tell you that with the release of more than 100 thousand copies a year, the classic layout model loses noticeably at cost. Let's get back to our worker: if before he needed a whole mountain of tools, now he needs only two mandrels and a “torque” key, because additional seals and lubrication for the assembled double-row bearing are not needed - he already has them. This saved a few minutes - but on each machine. And now we will multiply this by the total output, we will take into account the equipment loading, the salary … It seems that the conclusion is clear.
The next step was made with the advent of a hub unit of an integrated type: the bearing began to "grow together" with neighboring parts. Let's say the hub and the inner ring are one. Continuing the logic of the previous round of development, we can say: well, another assembly operation was transferred from the conveyor to a specialized enterprise. This, of course, is true, and a similar trend applies not only to hubs. For example, Volkswagen receives from frontiers (or rather, from satellite factories) a front panel with mounted headlights, a bumper, a radiator, a fan; motor shield with pedals, brake master cylinder, dashboard. What for? Yes, because highly specialized production of components is cheaper and more mobile than universal, at the head plant. We also mention another, no less important circumstance: with each step of improvement, the requirements for the conveyor technology proper are reduced! The collector is no longer involved in fine-tuning, but simply installs a ready-made node. And therefore, you can pay him less (per unit of output). For example, we again use the hub unit. The latest generation bearing includes a hub, as well as a flange for fastening with bolts - a worker with a pneumatic wrench will replace the worker with mandrels and a torque wrench … The operation of pressing, pressing in, fixing the bearing is excluded.
And the user is something, you say. These are factory problems - what to fasten with bolts and what to press in. In addition, the new bearing is clearly more expensive than the previous ones - when it fails, you will have to pay a fair amount. However, it is not difficult to note a plus - even the most unskilled repairman is unlikely to make a mistake during installation. Yes, and the repair will be required very soon: the technical task for this unit suggested that the bearing life should exceed the service life of the car. They didn’t even set such a task before! It is appropriate to distract from the economy, turning to technological problems.
Any bearing of previous generations requires two seats - for the inner and outer rings. These cylindrical surfaces are machined with very high accuracy: a too tight fit will violate the geometry of the raceways and lead to accelerated wear, a gap - to deteriorate heat dissipation, accelerated wear and “breaking” of the seat. Moreover, with each replacement of the bearing, the landing is weakened, the metal is crimped … In a good way, at the first signs of wear, the mating parts are not a sin to replace. However, show someone who does just that in Russia. On the contrary: “But I did it differently - and left another 15 thousand kilometers!” Although the resource of a node assembled by science would be ten times higher …
The hub of the latest generation is devoid of such shortcomings. In production, there is no need for precision precision machining of suspension parts and hubs. But the life of a conscientious repairman is becoming easier: he will no longer need a micrometer, and the quality of work (although, we repeat, it will be necessary only in case of an accident) will become much higher.
Why has this design not appeared before, since it has so many advantages? The fact is that until recently it was not possible to manufacture monolithic parts with variable properties - a certain hardness in the area of the ball race, a given impact strength in the hub part. Rather, they could do something like this, but not in conditions of large-scale production of relatively inexpensive parts. In fact, do not use a solid piece of expensive bearing steel for the hub …
Summing up our economic and technological excursion, we note: of course, not only the hub units are improved in a similar direction. Machine manufacturers seek to reduce costs, reduce the time required to assemble each specific car. It is also beneficial for customers - thanks to high-tech components created by specialized companies, cars become more durable, safer and … more affordable.
To illustrate our findings, we turned to the program of the Swedish company SKF, known in the world for the widest range of bearing products.
Double row ball bearing with seals was developed by SKF in 1943. In the 70s, its use became widespread, such bearings are installed on the front and rear axles of the car, for driving and non-driving wheels.
Double row tapered roller bearing is recommended only for rear axles of cars. It is much more load-carrying than a ball, but it is also more sensitive to the lateral load characteristic of steered wheels.
Bearing combined with a hub. This is called the "Hub Unit 2" ("hub unit-2"). It is applied to non-driving wheels; released more than 50 million pieces. By the way, a node of any type may include a vehicle speed sensor.
