Opencart无法加载模型

I am developing my own module for opencart 2.3.0.2 and everything was working fine. I have a model in admin/model/extension/module folder which is called vehicle.php. I try to load it in the controller like this:

$this->load->model('extension/module/vehicle');

But it throws Could not load model extension/module/vehicle! exception. And it happened suddenly. The model was loading fine 5 minutes ago. I have no idea why it suddenly stopped working.

I found it. It was very stupid mistake: I just named my file verhicle instead of vehicle.