In normal braking, the operation of an electric motor is controlled according to the amount of operation of a brake pedal to drive a pressing member through a belt drive mechanism and a ball-screw mechanism, thereby pressing a piston to generate a fluid pressure in a master cylinder to obtain a brak
In normal braking, the operation of an electric motor is controlled according to the amount of operation of a brake pedal to drive a pressing member through a belt drive mechanism and a ball-screw mechanism, thereby pressing a piston to generate a fluid pressure in a master cylinder to obtain a braking force. A predetermined reaction force is applied to the brake pedal by a reaction force spring of a stroke simulator, and a gap is maintained between the pressing member and a movable member, thereby eliminating an uncomfortable feeling in a brake operation caused by fluid pressure variations in the master cylinder. When the electric motor fails, the movable member abuts against the pressing member and directly presses the piston to maintain the braking function. The rear end of the pressing member is inserted into a guide member and the reaction force spring to reduce the axial size.
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1. An electric motor-driven booster having an electric motor operating in response to an operation of an input rod connected to a brake pedal, and a propulsion mechanism driven by the electric motor to propel a piston in a master cylinder, the electric motor and the propulsion mechanism being provid
1. An electric motor-driven booster having an electric motor operating in response to an operation of an input rod connected to a brake pedal, and a propulsion mechanism driven by the electric motor to propel a piston in a master cylinder, the electric motor and the propulsion mechanism being provided in a housing, the electric motor-driven booster comprising: a pressing member provided between the piston and the propulsion mechanism, the pressing member being movable relative to a rectilinearly moving member of the propulsion mechanism, the pressing member being movable by either one of the input rod and the propulsion mechanism to press the piston at a distal end of the pressing member; anda reaction force generating mechanism supported by the housing and connected with the input rod to apply a reaction force against the operation of the input rod,the pressing member being movable together with the rectilinearly moving member by the propulsion mechanism with a gap between the input rod and the pressing member, or caused to abut against the input rod due to movement of the input rod and moved while separated from the rectilinearly moving member, andthe pressing member and the reaction force generating mechanism being disposed so as to overlap each other in an axial direction. 2. The electric motor-driven booster of claim 1, wherein the pressing member has a proximal end disposed in the reaction force generating mechanism. 3. The electric motor-driven booster of claim 1, wherein the pressing member is slidably supported by a guide part provided closer to the master cylinder than the reaction force generating mechanism. 4. The electric motor-driven booster of claim 3, wherein the guide part is provided on the housing. 5. The electric motor-driven booster of claim 3, wherein the propulsion mechanism is a hollow rotation-rectilinear motion conversion mechanism provided in the housing on a same axis as the pressing member; the guide part being provided on the rectilinearly moving member of the rotation-rectilinear motion conversion mechanism. 6. The electric motor-driven booster of claim 3, wherein a part of the pressing member that is supported by the guide part has a length greater than a maximum propulsion length of the piston of the master cylinder. 7. The electric motor-driven booster of claim 1, wherein the propulsion mechanism is a hollow rotation-rectilinear motion conversion mechanism provided in the housing on a same axis as the pressing member; the reaction force generating mechanism and the rectilinearly moving member of the rotation-rectilinear motion conversion mechanism being disposed so as to overlap each other in the axial direction. 8. The electric motor-driven booster of claim 7, wherein the reaction force generating mechanism has one end disposed inside the rectilinearly moving member of the rotation-rectilinear motion conversion mechanism. 9. The electric motor-driven booster of claim 1, wherein the propulsion mechanism has: a propelling member abutting against the pressing member;a rotation-rectilinear motion conversion mechanism having the rectilinearly moving member which is rectilinearly movable along an axis disposed parallel to an axis of the pressing member; anda link member causing the propelling member to move by rectilinear movement of the rectilinearly moving member. 10. The electric motor-driven booster of claim 1, wherein the pressing member is disposed so as to face the input rod across the gap at least when the brake pedal is not operated. 11. The electric motor-driven booster of claim 1, wherein the reaction force generating mechanism has a coil spring, the coil spring being disposed so as to overlap the pressing member. 12. An electric motor-driven booster comprising: a housing attachable to a vehicle;an electric motor provided in the housing to operate in response to an operation of an input rod connected to a brake pedal;a propulsion mechanism provided in the housing, and driven by the electric motor to rectilinearly propel a piston in a master cylinder;a pressing member provided between the piston and the propulsion mechanism, the pressing member being movable relative to a rectilinearly moving member of the propulsion mechanism, the pressing member being movable by either one of the input rod and the propulsion mechanism to press the piston at a distal end of the pressing member; anda reaction force generating mechanism having a coil spring supported at one end thereof by the housing, the coil spring being connected at the other end thereof with the input rod, the reaction force generating mechanism applying a reaction force against the operation of the input rod,the pressing member being movable together with the rectilinearly moving member by the propulsion mechanism with a gap between the input rod and the pressing member, or caused to abut against the input rod due to movement of the input rod and moved while separated from the rectilinearly moving member, andthe pressing member having a proximal end disposed closer to the input rod than the one end of the coil spring that is supported by the housing. 13. The electric motor-driven booster of claim 12, wherein the proximal end of the pressing member is disposed inside the coil spring. 14. The electric motor-driven booster of claim 12, wherein the pressing member is slidably supported by a guide part provided closer to the master cylinder than the reaction force generating mechanism. 15. The electric motor-driven booster of claim 14, wherein the propulsion mechanism is a hollow rotation-rectilinear motion conversion mechanism provided in the housing on a same axis as the pressing member; the guide part being provided on the rectilinearly moving member of the rotation-rectilinear motion conversion mechanism. 16. The electric motor-driven booster of claim 12, wherein the propulsion mechanism is a hollow rotation-rectilinear motion conversion mechanism provided in the housing on a same axis as the pressing member; the coil spring and the rectilinearly moving member of the rotation-rectilinear motion conversion mechanism being disposed to overlap each other in an axial direction. 17. The electric motor-driven booster of claim 16, wherein the one end of the coil spring is disposed inside the rectilinearly moving member of the rotation-rectilinear motion conversion mechanism. 18. The electric motor-driven booster of claim 12, wherein the proximal end of the pressing member is disposed axially apart from a distal end of the input rod at least when the brake pedal is not operated. 19. An electric motor-driven booster comprising: a housing attachable to a vehicle;an electric motor provided in the housing so as to operate in response to an operation of an input rod connected to a brake pedal;a hollow rotation-rectilinear motion conversion mechanism having a rectilinearly moving member provided in the housing on a same axis as the input rod, the rectilinearly moving member being driven by the electric motor to propel a piston in a master cylinder;a reaction force generating mechanism having a coil spring supported at one end thereof by the housing, the coil spring being connected at the other end thereof with the input rod, the reaction force generating mechanism applying a reaction force against the operation of the input rod; anda pressing member provided between the piston and the rotation-rectilinear motion conversion mechanism, the pressing mechanism being movably relative to the rectilinearly moving member, the pressing member being movable by either one of the input rod and the rectilinearly moving member to press the piston at a distal end of the pressing member,the pressing member being movable together with the rectilinearly moving member by the propulsion mechanism with a gap between the input rod and the pressing member, or caused to abut against the input rod due to movement of the input rod and moved while separated from the rectilinearly moving member,the pressing member being slidably supported by a guide part provided on the rectilinearly moving member at a position closer to the master cylinder than the reaction force generating mechanism, andthe pressing member having a proximal end disposed closer to the input rod than the one end of the coil spring that is supported by the housing. 20. The electric motor-driven booster of claim 19, wherein the proximal end of the pressing member is disposed axially apart from a distal end of the input rod at least when the brake pedal is not operated.
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