Blow-by gas treatment device for engine

A blow-by gas treatment device for an engine comprising:

• a valve train chamber provided on an upper portion of a cylinder head;
• a first breather chamber and a second breather chamber provided above the valve train chamber;
• a crank chamber provided inside a cylinder block;
• an intake passage leading to a combustion chamber;
• a throttle valve provided in the intake passage;
• a fresh-air introduction/blow-by gas discharge passage for communicating an upstream side of the throttle valve in the intake passage and the crank chamber with each other through a passage passing through the first breather chamber and the valve train chamber;
• a blow-by gas discharge exclusive passage for communicating a downstream side of the throttle valve in the intake passage and the crank chamber with each other through a passage passing through the second breather chamber and the valve train chamber;
• a PCV valve provided on the downstream side of the second breather chamber in the blow-by gas discharge exclusive passage and configured to adjust a flow rate of a blow-by gas in accordance with a negative pressure in the intake passage;
• and
• an opening portion which is formed in a bottom surface of the first breather chamber and through which fresh air and a blow-by gas pass, and an oil return hole for returning oil separated from the blow-by gas to the valve train chamber,
• wherein an upper end portion of a passage closer to the crank chamber than the first breather chamber in the fresh-air introduction/blow-by gas discharge passage is located so as to oppose to the opening portion in a vertical direction and a communication portion communicating with a space in the valve train chamber is provided between the upper end portion and the opening portion;
• and
• wherein when the blow-by gas flows to the intake passage from the fresh-air introduction/blow-by gas discharge passage in addition to the blow-by gas discharge exclusive passage, a communication area of the communicating portion is set so that an increase amount of a pressure in the valve train chamber with respect to the pressure in the first breather chamber is maintained in a range in which the oil returns from the first breather chamber to the valve train chamber.