Speed control

[Sam3090]

Can we customize the speed limiter of the car ?? that means if i give 10km speed limit the car should controlled to 10km speed and likewise 20km to 50km speed.. can u mention what is needed to do so..

[shorod]

I'll bite. This question is very vehicle-specific and you make no mention of what vehicle you are referring to. So, what vehicle are you referring to?

-Rod

[Sam3090]

Sir, the vehicle is car and it may be of any manufacturer..i thought this as a concept so i didn't mentioned the vehicle..
Is there any speed limiter that we can customize speed ??

[shorod]

Well, there won't be one solution that works for every application. Most new cars are going to throttle by wire and include electronically controlled ABS, electronically controlled transmissions, and traction control systems. In this type of application, the concept of accurate speed limiting is much simpler to implement than in an old, purely mechanical system. In a modern car, all the controls and valving are already in the vehicle, although interfacing to the software is not a trivial task. And, as a matter of fact, some modern cars already have software in place to do what you are asking. For example, some modern Ford cars have a "My Key" system. The intelligent access key fob can be programmed to be an Admin key or a "valet" key. In this system the "valet" key can be programmed with a speed limit. I don't recall if the system, as implemented, allows a large range of speed limiting (probably for safety reasons) but clearly the technology is there.

For an older vehicle with no ABS, no traction control, no fuel injection, and a cable activated throttle, the hardware needed to accurately limit vehicle speed. Limiting the control to just the throttle would not provide much accuracy as there would be very little control over speed if the vehicle were going down hill. You could add some means of also modulating the brakes based off vehicle speed, but again that's much more involved, and more mechanical, than a similar implementation on a vehicle already equipped with appropriate hardware. And then there's the safety aspect of adding control equipment on to the braking and/or throttle control of a vehicle that will be sharing the road with others.

-Rod

[Sam3090]

Thank you for your reply sir..It is helpful.

[Sam3090]

Hi, i am searching for the controller used in the electronic instrumentation panel or car dashboard containing speedometer and so on..Can you help me?? Can we modify it according to our requirement?? as i need to get speed of the car from the panel..

[shorod]

Again, that's a very make/model-specific request. There is not one controller used for all electronic instrument clusters.

Now that at least you're narrowing the scope down to electronically controlled speedometers (and ignoring the cable driven speedometers of years ago) there is a possible solution. Vehicles with electronic speedometers generally use 1 of 2 methods to source vehicle speed. Either they use a Vehicle Speed Sensor (VSS) that derives speed from the transmission or they use one of the wheel speed sensors for the Anti-lock Braking System (ABS) to derive speed.

Using either the VSS or a wheel speed sensor will require some computation of the signal to get actual ground speed. The VSS can be an analog DC voltage that varies in amplitude by vehicle speed. The wheel speed sensor is a square wave that will vary in frequency depending upon vehicle speed.

Since whatever means you choose to implement this would require additional hardware, why not include a GPS chip in your solution as the primary speed source with an input for either a DC or square wave as a backup in the event GPS coverage is lost or upon initial powerup before the GPS has gained a good lock? You'll want to have some form of a fail-safe such that if the primary speed source is lost the vehicle doesn't accelerate abruptly or aggressively. A backup speed source would be one way to accomplish this, and since GPS chips have the ability to provide a loss of lock and signal integrity output, that output could be used to predictably switch to the backup source or alert the driver that the system will be shutting off due to unstable input sources.

-Rod

[Sam3090]

How speed limiters of a vehicle works..??? Is there any microcontroller used in those speed limiters to program any speed??

[shorod]

Again, that will depend on the application. Years ago the speed control servos were vacuum actuated and used a cable to control the throttle valve. Then the vacuum servo began to get replaced with the electronic servos that used the vehicle speed sensor to identify the desired speed. The microcontroller used was probably not consistent across the manufacturers, but the 68HC11 was a popular platform for many automotive applications. Even more recently, as electric throttle bodies started to be implemented, there was no longer a need for a separate speed control servo and cable. It could all be integrated in to the main engine control module.

Typically the speed control has some minimum speed threshold such as 35 mph. That's probably for safety reasons. If you're somewhere where the speed limit is that low, you're not likely to be on a drive where foot fatigue will be an issue.

-Rod