How to speed up enemy after time?

Hello, my question is, how can i change my enemy speed, so it will get faster and faster, atm it is -8 (because it is inverted and enemy moves from up to down). For example, my 1st enemy comes with speed -8, next one already with -9 or smth, and so on.
I tried InvokeRepeating, but it doesnt work the way i want to, so i commented it out atm.
Thank you for your help! :slight_smile:


using UnityEngine;
using System.Collections;

public class enemyCarMove : MonoBehaviour {

float speed = -8f;
// Use this for initialization
void Start () {
	//InvokeRepeating ("speedy", 4.0f, 1.0f);

//void speedy () {
//	speed = speed + -5f;


// Update is called once per frame
void Update () {
	transform.Translate (new Vector3(0, 1, 0) * speed * Time.deltaTime);




float timeToIncrease = 1.0f; //this is the time between "speedups"
float currentTime;  //to keep track
float speed = 0f; //current Speed
float speedIncrement = 5f; //how much to increase the speed by

void Start()
currentTime = Time.time + timeToIncrease;

void Update()
if (Time.time >= currentTime)
speed += speedIncrement;
currentTime = Time.time + timeToIncrease;
//your movement code here