I believe differentials distribute power to the other wheel right? Where would the power go to if both wheels are braking?
In: Engineering
What power? You’re not hitting the brakes and the gas at the same time. If you’re not accelerating the driveshaft will just slow down.
Even if you did cars are designed with far more braking power than the engine can overcome and it would still slow down.
I think car brakes will break on all wheels simultaneously (although more braking force may be applied to the front wheels). Also, the engine should generally not transmit any power to the wheels when you are braking.
But sure, if you want to try and break a car (or any machine for that matter) you can try to push down the gas pedal and the brake simultaneously (I don’t know what the electronics in modern car would do in this case). In such cases usually the weakest element in the chain will break/deform or similar.
Everyone’s talking as if this can’t happen. In fact it’s the usual method of braking for manual cars, hitting the brakes while the engine and transmission are still coupled.
Your assumption is that the engine somehow can overcome a braking force on its own and it’ll break something. That assumption is just false. It would stall before that happens. Engines operate on a torque/rpm ratio, and when you press on the gas pedal, what you’re really increasing is the torque.
As you press down on the pedal, more fuel mixture is thrown into the engine, alongside more air. This increases the engine’s torque output. If the output exceeds the torque needed to keep the car at its current speed, the engine’s RPM is able to increase, and the car accelerates.
Conversely, if you take your foot off the pedal, the engine’s torque output will decrease, and if it’s no longer enough to maintain the current RPM, the engine will slow down. So, how does this behavior factor into braking?
When you apply the brakes, you increase the torque needed to rotate the wheels tremendously. Such a sudden increase overwhelms the engine’s current torque output and, as explained above, the RPM drops dramatically as a result. When it drops under a certain threshold (around under 800 RPM for gas engines, around 650 for diesel), the engine is in a critical operating state where it may no longer be able to sustain its own rotation and might stall. If you apply the brakes suddenly enough, it most certainly will.
Does this apply extra strain on the shaft, clutch and other internal components? Yes. Is it enough to break them? Not by a long shot. Not if the internals are in decent condition anyway. Learning to drive manual would get you used to this concept, considering how often instructors will just slam the brakes while in traffic without hitting the clutch, and stalling the engine.
>Where would the power go to if both wheels are braking?
Power comes from pressing down on the accelerator. If you are doing it correctly, the accelerator and the brake pedal will not be in use at the same time. This is a good argument for using the right foot for both, even with an automatic transmission. ~~(or left foot, if you are in a~~ *~~drive on the left side of the road~~* ~~country)~~ edit
Cars have torque converters (automatics) or clutches (manuals) that mean that the power from the engine is only mostly transmitted to the wheels. In a manual, the driver chooses when to use the clutch that disconnects the engine from the wheels. In an automatic the torque converter does it automatically.
Torque converters are kinda like two sets of fan blades pointed at each other, one has a motor and the other doesn’t. When one turns it starts to turn the other but if something keeps the other from turning it won’t (unless the first fan spins fast enough to make enough power to overcome whatever is keeping it from moving).
Unless you’re trying to both brake and accelerate at the same time, you’re not gonna destroy anything. Braking systems work by the person applying force to the pedal, the booster creating a proportionally larger amount of force, the brake fluid getting moved to the brake cylinders and creating contact between the pads/shoes and rotors/drums. Tires are a consumable so any time you accelerate, move, brake, this causes the tire to wear but not destroy, and the drive shaft and differential won’t get destroyed unless you’re constantly doing hard accelerations every 5 minutes and you’re locking up the brakes immediately after.
The driveshaft isn’t directly connected all the way to the wheels with sets of rigid gears/attachments. If they were, then you couldn’t brake without slowing the engine down. There’s something called a torque converter, which is like a disc filled with fluid with two fan blades pointed at each other. One fan blade connects to the engine side, one fan blade connects to the wheel side. When the engine spins the driveshaft, it turns one of the fan blades, which starts moving the fluid around, which will start to push the other fan blade around, which turns the wheels. If the wheels can’t move, either because you’re on an uphill or because you’re braking, then the second fan blade can’t turn, and the energy from the motor just goes into swirling that fluid around and pushing harder on the second fan blade. So that’s how it’s possible to be in gear and rev an engine but not have the drive shaft snap.
When you are braking, the wheels are still spinning. When you are off the accelerator the engine goes into overrun and actually help the brakes as the engine provides negative torque to the driveshaft.
If you come to a stop, some form of clutch, whether operated by the driver in a manual. Or automatically in an automatic, will open up and decouple the engine from the wheels. The engine at this point will fuel again and idle.
If you were to press both the accelerator and brakes. And were somehow able to keep the clutch engaged, in a manual for example. If the wheels don’t spin, the torque from the brakes is too strong and the engine will stall.
On essentially every car out there, the brakes are large enough that the at full application, the engine does not produce enough power/torque to move the wheels.
The reason drive train components don’t break is that they are properly sized for the maximum possible engine performance. If my car’s engine can put out 200 lb-ft of torque max, it doesn’t matter if the wheels are being held by brakes or free too move. The drive shaft and transmission will still never see more than 200 lb-ft of torque because the engine can’t make more than that.
Imagine two box fans sitting directly in front of each other, you turn on fan A. because of the proximity this will cause the blades on fan B to turn. You can get fan B to move faster and nearly match the speed if you move it closer. But if you stopped fan B from moving fan A does not stop. That is a torque converter.
torque converter for automatic transmission vehicles. Internally it is filled with hydraulic fluid (Automatic transmission fluid) and there are two major parts, the first part is a spinning disc connected to the engine called the impeller, the second part is called a turbine. As the impeller is turned via engine power, centrifugal force causes the fluid to be moved around the casing, subsequently spinning the turbine and transferring speed and power to the transmission then to the drive shaft then the differential then the axles then wheels.
If the wheels come to a sudden stop via your cars braking system the engine will not stall. SLipping between the pump and turbine happens because of the fluid connection. There is a lot more going with more parts, ABS and your cars internal computers but that is a simplified version.
[https://www.youtube.com/watch?v=bRcDvCj_JPs](https://www.youtube.com/watch?v=bRcDvCj_JPs)
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