What if you connected the crank shaft directly to the drive shaft which is linked directly to the drive wheels of a car without involving any kind of a gear system? Sure, you Motor Heads will say, that’s what a lock-up torque converter is doing, IIRC. Ah! But, the lower gears got you up to speed before the overdrive engaged at cruising speeds!
What if you started such a car from rest at a red light. How sluggish would this car be? Woud you hate to be the guy behind me? What other disadvangtages are to this direct-drive system? Excessive wear and tear? Too much of a load on the engine? Would I now need more horsepower to compensate? What else…? Hmm, would the car even move, or would the resistance inherent in the design be too great for the engine to overcome?
When answering, please tell me what kind of car you’re picturing. For example, “a Geo might not budge, but a Ram pick-up would do ok.” …to give me some scale by which to gauge responses. This would be very helpful.
The only way you could regulate car speed would be engine speed. With no low end torque you couldn’t get started. At high speeds the engine would exceed redline.
Assuming a normal final drive ratio, it would be like only having high gear in a non-overdrive car. It would be difficult to get moving from a stop (impossible at the bottom of a steep enough hill) and very sluggish at slower speeds. You’d need a clutch or torque converter to have any reasonable chance of taking off, and said clutch or torque converter would be badly stressed and wouldn’t last long. Engine horsepower would be of little or no help, low-range torque would help a lot. The particular type of car doesn’t matter much, as engine size is generally more or less proportional to vehicle weight (Geos don’t have Ram pickup-sized engines, and vice versa). Sportier models, with a high power-to-weight ratio, would fare better than, say, big sedans with the smallest engine offered.
Without a clutch the vehicle’s engine could not be started without the vehicle being put in motion.
With a clutch, but without any assistance from gears (even rearend gears if I read the OP correctly), the response would be determined by the power/weight ratio of the engine to the vehicle. A powerful engine in a light vehicle would still bog down on takeoff but would become more responsive as vehicle speed increased.
To demonstrate this theory to yourself pull away from a stop in your vehicle’s highes gear (if manual) and see how much the engine strains to move the vehicle. The highest gear in a manual is usually close to 1 to 1 with OD transmissions being as high as .8 to 1 so this replicates not having transmission gears. But, you still have rearend gears to assist the engine and depending on the gear teeth themselves could be assisting to the tune of 2.5, 3 or 4 to 1.
My 4WD in Low Range has an effective gear reduction of 20 to 1, more or less, and could climb a tree if it could get traction. But, without the gears wouldn’t pull out of it’s own tracks. On the other hand, a small dirtbike frame with an all aluminum 427 Ford engine and direct chain drive would do just fine.
If the car had no clutch the engine would have to be stopped anytime the car was stopped. If the starter motor was powerful enough and the gear was low enough you could crank the motor and push the car forward at the same time. I belive some go carts use a direct drive (no clutch) and one gear, they get push started but their normal operating speed is right in the engines peak power range. One advantage to this would be less drivetrain power loss.
With or without a clutch you would have to pick between a gear ratio that is to high or low. A higher gear ratio would require you to ride the clutch to get going and be very sluggish at low speeds. A lower gear ratio would limit your top speed and require a high RPM at any normal speed.
Now that I re read the OP it calls for no gears at all. I belive this would be the equivilent of one of the higher gears in a manual transmission. Without a clutch it would probably not get moving at all. With a clutch you would have to seriously ride the clutch to get moving, the clutch would not last long at all.
What happens when you excede redline depends on the design of the motor. Most modern engines have some sort of electronic limiter to prevent exceding redline. Assuming you didn’t have the linter or bypassed it somehow… Sometimes you will just have a dramatic drop in power. It is also possible that you could float the valves, this means the valves do not close all the way. On some engine designs it is possible for the piston to hit the valves when this happens.
Originally posted by zabrain
Without a clutch the vehicle’s engine could not be started without the vehicle being put in motion.
What I mean here is; without a clutch to disengage the power between the engine and the wheels once the engine turns over so do the wheels.
In other words, without a clutch the engine can’t be started and allowed to sit and idle.
What you are saying is that a vehicle can be driven with a faulty clutch and this is true. Turn off the engine at stops and turn the key when you’re ready to roll - very nerve-wracking.
I have driven cars with manual transmissions with no clutch quite a few times for freinds when the clutch mechanism would not work.
Start the car in neutral and warm it up. Make sure it starts on the very first crank.
stop motor. Shift into first gear. start. The starter will move the car and the motor will start. You can then gradually sift up.
By going slowly and trying to synchronize with traffic lights you can drive quite a distance stopping the motor the few few times you have to come to a complete standstill. This will allow you to get to a garage for repair. I have saved some friends quite a few bucks for a tow by doing this.
