Developing device having spaced cover portion and frame

A developing device comprising:

• a rotatable developing member configured to carry a developer containing toner and a carrier to a developing position where an electrostatic latent image formed on an image bearing member is developed;
• a first frame configured to accommodate the developer;
• a second frame mounted on said first frame and configured to cover part of an outer peripheral surface of said rotatable developing member;
• a regulating portion provided opposite to said rotatable developing member and configured to regulate, at a position closest to said rotatable developing member, an amount of the developer carried on said rotatable developing member, said regulating portion being positioned below a rotation center of said rotatable developing member in a state that said developing device is in a position where the electrostatic latent image formed on the image bearing member is developed;
• a magnet provided fixedly inside said rotatable developing member and configured to generate a magnetic field for peeling off the developer, passed through the developing position, from an outer peripheral surface of said rotatable developing member, said magnet including a plurality of magnetic poles including a first magnetic pole and a second magnetic pole which is provided adjacently to said first magnetic pole on a side downstream, with respect to a rotational direction of said rotatable developing member, of a first peak position where magnetic flux density of said first magnetic pole is a maximum and which has the same polarity as said first magnetic pole;
• a cover portion provided opposite to said rotatable developing member along the outer peripheral surface of said rotatable developing member and provided between said second frame and said rotatable developing member over a rotational axis direction of said rotatable developing member, said cover portion being disposed so as to form a clearance between itself and said rotatable developing member with respect to a radial direction of said rotatable developing member and to form a clearance between itself and said second frame with respect to the radial direction of said rotatable developing member,
• wherein as seen in a cross section perpendicular to the rotational axial direction of said rotatable developing member in a state that said developing device is in the position where the electrostatic latent image formed on the image bearing member is developed,
• with respect to the rotational direction of said rotatable developing member, a most upstream end of said cover portion is positioned downstream of the developing position and upstream of a most upstream position of a half-width of magnetic flux density of said first magnetic pole, and
• with respect to the rotational direction of said rotatable developing member, a most downstream end of said cover portion is positioned downstream of the first peak position and upstream of a position where the magnetic flux density of said first magnetic pole is a minimum on a side downstream of the first peak position and upstream of a second peak position where magnetic flux density of said second magnetic pole is a maximum,
• wherein the following relationship is satisfied:
• L1≤L2+L3, and
• L2≤L3,
• where with respect to the radial direction of said rotatable developing member, L1 is a minimum of the clearance formed between said second frame and said rotatable developing member, L2 is a minimum of the clearance formed between said rotatable developing member and said cover portion, and L3 is a minimum of the clearance formed between said second frame and said cover portion.