accumulative movement speed with touch


I am looking for a smooth movement solution for this. i want to move one object in x axis with two button. But i want to adjust acceleration with hold time of buttons. for example: in single touch x axis speed will change 1.0f and if touching phase continue change of speed will increase 0.1f per second or something like this. But i can not find proper way to achieve this. every solution i found isnt working smooth enough.

If you have a Rigidbody or Rigidbody2D attached to your object you can do something like this

	void FixedUpdate () {
		if (Rigidbody.velocity < limit)
			Rigidbody.addForce (Input.GetAxis("Horizontal") * multiplier, 0, 0)