PROBLEM #180
Valve – tension roller
A forum member with a pseudonym Experienced asked motorists a tricky question: “There are many valves in a modern engine and its systems. And in the timing, and in the cooling system, and in the crankcase ventilation, and in many others. But there is a valve that is always open when the engine is running. Maybe he’s not the only one?
Which valve is always open when the engine is running?
Short answers will not be considered.
Send the answer marked “Competition” before December 1, 2022 to the address: 107045, Moscow, Seliverstov per., 10, building 1; e-mail: [email protected].. Please provide your phone number or any other means of fast communication.
Below we summarize the results of the connoisseur competition published on December 1, 2022.
In the task, readers had to explain why when cars were placed in a parking lot with greater side spacing, there was more damage from open doors – and to be reminded of the connection to presses for stamping auto parts and even operation of the engine. Of course, those readers who answered with a few words like “strong wind” or used unprintable expressions about car-loving neighbors cannot claim victory. But our winner explained everything in detail.
The heroine (or anti-heroine) of the problem is the kinetic energy of a spinning body – the car door. When we open a door, we apply force to it. The work done in this case is equal to the product of the moment of force and the angle of rotation (in radians) or (same thing) the product of the force and radius of motion of the point of engagement and the angle of rotation (in radians): M = F *r*Δφ.
The work done is converted into the kinetic energy of the revolving door. Obviously, the longer we apply force to the door handle, the more work we do, and the greater the angular velocity of the door and its kinetic energy will be.
Diagonal parking not only facilitates entry and exit, but also allows you to reduce lateral intervals.
To stop the movement of the door, it is necessary to “take” energy from it by applying a force moment opposite to the original. Of course, it is optimal to hold the door by the handle. But it’s not always easy. If we accelerate it by 2/3 of the opening angle of the door, then the braking force must be greater than the original one to stop on the remaining 1/3 of the path.
What if a child opens the door? What if it gets caught in the wind?
The “excellent” kinetic energy will be used for elastic and plastic deformation of the metal of its own and neighboring machines, as well as for heating deformable parts and creating sound waves on impact.
When the door is opened at a small angle, the applied force does not have time to disperse it, and the effect on the neighboring machine is relatively weak – the metal deforms elastically and can recover its shape after the load is removed. If the lateral interval between cars is large, the door will pick up a lot of speed, stopping it will require significant effort and will be accompanied by serious deformations. Think how the doorstop can hold it open under the pressure of the wind, but breaks when the same door swings open by the same wind.
Kinematic scheme of the crank press: 1 – intermediate shaft; 2 – gear, which is coupled to the gear 3; 4 – multi-friction clutch; 5 – crankshaft; 6 – stamping table; 7 – slider; 8 – connecting rod; 9 – brake; 10 – a pulley with a flywheel connected by a V-belt drive; 11 – engine.
The kinetic energy of a spinning body can not only damage, but also create car parts. Crank presses are widely used for stamping. Their drive is a combination of an asynchronous electric motor and a flywheel connected by a belt drive. The crank connected to the flywheel converts the rotary motion into a reciprocating motion of the die.
Such presses are peak load machines. During idling, the electric motor accelerates the flywheel, increasing its kinetic energy. When performing a technological operation, the speed of rotation of the flywheel decreases, and the accumulated energy is spent on performing work on the deformation of the steel sheet. The use of a flywheel allows you to reduce the power of the electric motor, increase the efficiency of its use and increase the efficiency of the press due to the accumulation of kinetic energy and its consumption directly during the working process.
The same laws of physics apply to engine operation. During the power stroke, during the combustion of the mixture, thermal energy is released, which is converted by means of a crank mechanism into the kinetic rotational energy of the crankshaft and related parts, in particular the flywheel. After the end of the working stroke, the crankshaft continues to rotate, using the accumulated kinetic energy to overcome frictional forces, remove exhaust gases, draw in and compress a new portion of the working mixture. The presence of several cylinders distributes the work cycles according to the positions of the crankshaft, but does not completely eliminate the cyclical processes of energy accumulation and return.
Evgeny Bobkov congratulations on the victory!
- “Drive” can now be read in Telegram.