Servomechanism and its importance in Automotive

You can't think of anything electronic in automotive that actuates via a button pushed?

A servo system implies some form of feed back, not just a push button.

How would you define a servomechanism?

In an automotive hydraulic braking system, why don't the brakes work very effectively when the engine is not running?

A system that has feedback that can be used to correct errors. I don't see that in a standard braking system. http://en.wikipedia.org/wiki/Servomechanism

Duh, power steering and speed control. Modern cars have anti roll or stabilization systems, automated steering systems that park cars etc. I am sure that someone that is in the biz can add to my short list.

"Duh, power steering and speed control."

From the link you cited:

"Another device commonly referred to as a servo is used in automobiles to amplify the steering or braking force applied by the driver. However, these devices are not true servos, but rather mechanical amplifiers. (See also Power steering or Vacuum servo.)"

And then there's ABS ...

I didn't refer to braking. Power steering is a servo system. The feedback is mechanical. Obviously power steering must provide much more than just amplification because the wheel must not only move but is must move as the driver desires Look at the section of the rotary valve http://auto.howstuffworks.com/steering4.htm

"I didn't refer to braking ..." - I'm not suggesting you did, but I was making the point that an ABS would surely be defined as a servomechanism.

I'm not getting into a flame war here, but please re-read the quotation, with specific attention to the items I've highlighted in bold face:

"Another device commonly referred to as a servo is used in automobiles to amplify the steering or braking force applied by the driver. However, these devices are not true servos, but rather mechanical amplifiers. (See also Power steering or Vacuum servo.)"

If you have an issue with your citation, please address it to Wikipedia.

Good night.

The fundamental of a servo system (as others here have implied) is that the controlling system responds to where things have moved to, not just where the controller has commanded the system to go to. When I explain this principle, I frequently use the steering of an automobile as an active servo system. I don't mean the proportional hydraulic control of the power steering system, I'm talking about the carbon based control system sitting behind the steering wheel that spins the wheel. The person behind the wheel does not calculate how many degrees of rotation the steering wheel must be turned for taking that five degree right hand banked turn that I'm approaching. All of the parameters of how quickly to turn, how far to turn and when to turn are done by feedback through the grey matter processor of the driver monitoring if the car stays in lane.

Some systems in a car now have silicon processors doing some feedback control. One subtle often overlooked system is the idle speed adjustment. Before this feedback control became common, many throttle plates on carburetors and injection systems slowly became varnished with unburned fuel coatings. (I think this was predominantly from fuel coating immediately after engine stopping but I digress.) As this varnish filled the space between throttle plate and wall, less air entered the intake manifold and richer fuel burning conditions happened in the engine at lower RPMs. Thus more pollutants either entered the atmosphere or had to be burned by the catalytic converter. Monitoring for the idle position of the throttle, the RPM at idle and controlling the amount of air entering the intake manifold removed this gradual failure mode from happening. The only draw back of this system is that many people go excessive periods of time without having their throttle mechanism cleaned.

This should be one of the most obvious automotive servo system you'll find. The basic rule of looking for feedback for setting a value is what you should be looking for.

thanks to all the guru's and members for the participation...now need more help.I am luking for more discussion about servomechanism in general.

studcentury,

I direct you to the CR4 policy on homework. This forum has a very good policy against forum discussions doing a student's homework. That doesn't mean we won't make pertinent suggestions to your search or that when you find information that baffles you we won't help. When baffled, try to explain what you do understand and if possible why something confuses you. This will give us a hint of your level of understanding, so our responses to answer your questions maybe tailored to a suitable level and focus on the confusion. But for very good reasons we won't do your work.

One characteristic I expect you will not find in your search of servo systems found in automotive systems comes from feedback theory. Negative feedback is the very basis of all servo systems. It regulates a system to produce the desired result. Positive feedback causes systems to cause a runaway condition. The classic positive feedback condition occurs when somebody with a PA microphone steps in front of the PA speakers. Now sometimes the speed that something can be moved causes enough lag that what was intended to be negative feedback or 180° out of phase gets delayed another 180° by the lag in motion. Thus a positive feedback condition occurs inadvertently. Strictly speaking, positive feedback for certain frequencies cannot be avoided. So to prevent disruptive actions from occurring, positive feedback frequencies must have a gain of less than one. So instead of growing, they decay.

Have Fun

Would you classify your response as positive feedback?

I remember the term dual servo brakes from my early learning years. I just can't remember the meaning of it though. I would suggest our op get a factory automobile service manual, and go to the index in the back of the manual. Look for the word servo. Then go to each page that has a servo. That should give some examples, as well as how the servos are used.

Servo mechanism is a brake booster attached with main brake master cylinder, it reduces braking force upon brake pedal while stopping your vehicle. simply it consists of two champers separated with a diaphragm , one side of champers vented to atmosphere, the other side connected to engine suction manifold through a flexible connection and control valve . When you press brake pedal, control valve will open and creating negative pressure in vacuum chamber. Pressure difference between the two chambers will create a pressure force upon the diaphragm which is connected to the piston of main brake cylinder. The result is additional force pushing piston of brake cylinder, slight press upon brake pedal will be magnified through servo mechanism creating more pressing force for braking piston in main brake cylinder.

You can check importance of servo mechanism by your self. Simply stop engine while your vehicle is running and press brake pedal. You will feel how it's difficult to press brake pedal and difficult to stop car. Start engine and press pedal again, you will feel the different,

Caution: don't do this test in side town , it should be done in empty straight road

Would the wheel cylinders from a drum brake design be a dual servo? One servo pushing in two directions. Comments anyone?

No feedback, therefore no servo. The vacuum boost system to increase the hydraulic pressure that makes the pistons of the wheel cylinder to lean on the drum, depending on the design, can be a servo system.