When I last arc with 4 pulses down 60 bpm I realize that the bow is not very stable and is a bit shaky, someone would know some exercise to solve this?
One reason your bow may be shaky and unstable is excessive tightening of the bow, please make sure you tighten it only enough. Another reason might be an incorrect bow hold. Incorrect bow hold would manifests itself when you are playing long notes. Please take assistance from your teacher for correct bow holding as these things are best demonstrated practically.
In any case here's a youtube video on bow hold and one on how much you should tighten it:
Make sure your fourth finger is separated from the other fingers and on top of the bow's screw (or near it) and your other fingers somewhat loosely gripping the bow (without tension or stiffness.) As for any particular exercises that will improve your bow technique, I believe practicing whatever material your teacher has provided you should help. Basic problems go away in the course of time through more practice. Try practicing playing long notes after making the correct adjustments and with the proper posture.
Obviously a consistent tone requires consistent movement and pressure of the bow hair on the string. Not quite equally obvious is that the pressure of the bow from its own weight varies between tip and frog since the bowing hand acts as a pivot. The bowing hand itself can put additional pressure on, pivoting around the thumb and balancing forces between index finger and pinky (the latter should be placed on the turnscrew lightly). Since the leverage varies wildly between tip and frog, your bowing action needs to adopt accordingly.
Practice pointing, touching, turning, pivoting, rolling and otherwise manipulating the bow deftly on its own (not involving the violin). It needs to become an extension of your arm like giant chopsticks.
Your arm needs to be supple: try feeling the vibrations of the string as they travel through the bow and your hand and up your arm, while playing the full bow length with a soft tone. If you can feel the string action throughout the whole length of bowing, your bow contact is likely supple and elastic, avoiding a shaky tone.
Many players, even good ones, cheat on the full bow length. You often see them not using the pinky at all and, quite correlated, cop out on the lowest one or two hand spans of the bow length. The latter is a reasonable compromise for fast play, but for slow sensual sounds, you want to be in control of the bow and its sound over the whole changing length.