I am wanting to do a pitch automation.
I create a track envelope and can add "keyframes".  So far so good.

However, the scale does not go down far enough.   I create a keyframe and drag it right down as far as it goes and the pitch alters OK,  but I want to send the pitch down even further.

Is there a way of enlarging the scale of the keyframe so it can go down further?

Sorry, what's keyframe?

If it's a soft synth you're trying to automate then you need to set the bend range in the synth properties GUI

Most of them are defaulted to a range of +/- 2 semitones

A keyframe is a term used in Flash and other video/animation production/editing software, meaning a marker or 'event' point. What the OP is referring to are the 'dots' created that can be moved around when you draw automation and such. The scale of the possible bending of pitch depends on the VST you're using, like Bristol Jonesey said. If that synth can't bend the pitch far enough whilst staying in midi, then you could create instances of it in wav (audio) and bend it further each time as needed. i.e. bend it as far as it goes in midi, export to audio, bend it further, export again, bend again and so forth!

So these we would call automation nodes yes?

OK, so keyframes = automation nodes. That might help me in my future posts. I am simply using DropZone. Thats my synth. Its not bending the pitch down as far as I'd like. I thought I could simply increase the "scale" and go further down.

I would suggest if the scale doesn't go down far enough it's probably a limitation of the synth. The automation envelope can only relate to the parameter presented by the synth. AFAIK there's no way to offset the envelope to a parameter. i.e. increase/decrease scale.

I wonder then if there is a vst fx plugin that will do a pitch drop and perhaps I can automate the plugin?

There is a free pitch shifter you can try called KeroVee (there is a commercial version, too). It's fully automatable, but I have no idea what its limits are.