Brake apparatus for vehicle

1. A brake apparatus for a vehicle, comprising:

a brake pad configured to press a brake disk, the brake pad including a back plate and a friction member coupled to the back plate, the back plate having a first coupling hole formed in a center of the back plate and the friction member having a coupling groove formed in a portion facing the center of the back plate;

a screw bar located in a caliper body, and rotatable by power received from a motor unit;

a spindle linearly movable by rotation of the screw bar, and coupled to the brake pad, the spindle including:

a spindle contact part configured to contact the brake pad; and

a coupling part configured to pass through the coupling groove of the friction member and be inserted into the first coupling hole formed on the center of the back plate and a second coupling hole formed on the spindle contact part to couple the back plate and the spindle contact part without directly coupling the friction member and the spindle contact part, wherein the first coupling hole and the second coupling hole are aligned facing each other so that the coupled brake pad and spindle linearly move together and the screw bar is inserted into the spindle and is aligned with the first coupling hole and the second coupling hole;

a piston coupled to the spindle so as to cover an outside of the spindle, made of a material having lower hardness than that of the spindle, and movable with the spindle; and

a sealing member installed in the caliper body, and contacting the piston.

2. The brake apparatus of claim 1 , wherein the spindle comprises:

a spindle body engaged and coupled to the screw bar, linearly movable by the rotation of the screw bar, and having an outer surface covered by the piston; and

the spindle contact part is further configured to be connected to the spindle body.

3. The brake apparatus of claim 2 , wherein the spindle body has a serration part formed on an outer surface thereof.

4. The brake apparatus of claim 2 , wherein the piston comprises:

a first piston portion coupled to the spindle body; and

a second piston portion connected to the first piston portion coupled to the spindle body, and having an outer diameter smaller than an outer diameter of the first piston portion,

wherein a boot coupling groove is formed by a level difference between the first piston portion and the second piston portion.

5. The brake apparatus of claim 4 , further comprising a boot part mounted on the caliper body and coupled to the boot coupling groove.

6. The brake apparatus of claim 2 , wherein the piston has a rounded corner contacting the spindle contact part,

wherein an O-ring is inserted between the rounded corner and the spindle contact part.

7. The brake apparatus of claim 2 , wherein the piston has an O-ring coupling groove formed at a portion contacting the spindle contact part,

wherein an O-ring is inserted into the O-ring coupling groove.