Window shade and spring drive system thereof

A spring drive system for a window shade, comprising:

• a housing;
• a first cord drum and a first gear fixedly connected with each other and pivotally connected with the housing, the first cord drum being respectively connected with a first and a second suspension cord;
• a second gear pivotally connected with the housing;
• a first and a second spring reel respectively connected pivotally at two opposite sides of the second gear so that the first and second spring reels are respectively rotatable relative to the second gear, the second gear and the first and second spring reels being disposed in a coaxial manner;
• a third gear pivotally connected with the housing and respectively meshed with the first and second gears, the third gear being respectively connected fixedly with a first and a second take-up reel at two opposite sides of the third gear;
• a first spring disposed around the first spring reel and having an end anchored with the first take-up reel, and a second spring disposed around the second spring reel and having an end anchored with the second take-up reel;
• a second cord drum and a fourth gear fixedly connected with each other and pivotally connected with the housing, the second cord drum being respectively connected with a third and a fourth suspension cord, wherein the second suspension cord and the third suspension cord exit the housing at a first end thereof, the first suspension cord and the fourth suspension cord exit the housing at a second end thereof opposite to the first end;
• a fifth gear pivotally connected with the housing;
• a third and a fourth spring reel respectively pivotally connected at two opposite sides of the fifth gear so that the third and fourth spring reels are respectively rotatable relative to the fifth gear, the fifth gear and the third and fourth spring reels being disposed in a coaxial manner;
• a sixth gear pivotally connected with the housing and respectively meshed with the fourth and fifth gears, the sixth gear being respectively connected fixedly with a third and a fourth take-up reel at two opposite sides of the sixth gear;
• and
• a third spring disposed around the third spring reel and having an end anchored with the third take-up reel, and a fourth spring disposed around the fourth spring reel and having an end anchored with the fourth take-up reel;
• wherein the first and second springs respectively unwind from the first and second spring reels and respectively wind around the first and second take-up reels when the first cord drum rotates for unwinding the first and second suspension cords, and the first and second springs respectively unwind from the first and second take-up reels and respectively wind around the first and second spring reels to urge the first cord drum in rotation for winding the first and second suspension cords;
• and
• wherein the third and fourth springs respectively unwind from the third and fourth spring reels and respectively wind around the third and fourth take-up reels when the second cord drum rotates for unwinding the third and fourth suspension cords, and the third and fourth springs respectively unwind from the third and fourth take-up reels and respectively wind around the third and fourth spring reels to urge the second cord drum in rotation for winding the third and fourth suspension cords.