Limit & Scaling Translation Rate.

So, I am tying to use a system that moves an object around by translation, but, I want it to be able to scale up, and down to simulate acceleration during the period of time the defined input is held. I have a basic idea for that. (In C#)

 void Moving ()
     {
         if (Input.GetAxis ("Vertical") > 0) 
         {
             gameObject.transform.Translate (0f, 0f, translateRate + (translateRate * translateRateScalingUp * Time.deltaTime));
         }
 
         if (Input.GetAxis ("Vertical") < 0) 
         {
             gameObject.transform.Translate (0f, 0f, translateRate + (translateRate * translateRateScalingDown * Time.deltaTime));
         }
 
         if (Input.GetAxis ("Horizontal") < 0 || Input.GetAxis ("Horizontal") > 0) 
         {
             transform.Rotate (0f, Input.GetAxis ("Horizontal") * rotationRate, 0f);
         }
     }
 

The scaling is the easy part, I am not sure how to limit translation rate. Although there is a Rigidbody on what I'm translating (so I can still get gravitational effects), I don't think Rigidbody speed limiting would work here.

Any suggestions?