This application is a 35 U.S.C. ยง371 National Stage Application of PCT/EP2013/062687, filed on Jun. 19, 2013, which claims the benefit of priority to Serial No. FR 1256008, filed on Jun. 25, 2012 in France, the disclosures of which are incorporated herein by reference in their entirety.
The present disclosure relates to an electric brake booster comprising an electric motor activating a booster piston acting on the master-cylinder when the brake pedal is activated, the booster piston being driven in the direction of the action of same on the master-cylinder by an electric motor linked to a mechanical transmission comprising a screw carried by the shaft of the motor and meshing with two symmetrical worm gears, each integral with a transmission shaft carrying a spur gear meshing with a rack of the booster piston, each shaft being housed in a bearing of the body of the brake booster.
Electric brake boosters of the type defined above are known. In these brake boosters, since the booster piston is driven symmetrically, balanced by two symmetrical transmissions relative to the plane passing through the axis of the booster piston and the drive screw, but since mechanically it is impossible to have perfect symmetry, in order to balance the drive by the two symmetrical transmissions, a clearance is left for the booster piston, that is to say for the racks, such that the booster piston can be positioned with the racks thereof so that the spur gears meshing therewith engage with the two racks in a balanced manner. However, the clearance that must be left for the booster piston is not suitable for the desirable accuracy of the operation of the brake booster or for the reliability thereof.
The object of the present disclosure is to perfect the guidance and the drive of the booster piston by the transmission linking the electric drive motor to the booster piston, and in particular to make it possible to reduce the clearance of the booster piston in the guiding seat thereof in the brake booster.
To this end, the disclosure relates to an electric brake booster of the type defined above, characterized in that the shafts are free in translation relative to the screw and to the body of the electric brake booster but are integrally interconnected in the translational movement thereof.
The freedom provided to the two shafts carrying the worm gears meshing with the screw carried by the output shaft of the drive motor makes it possible to naturally balance the engagement clearance of the racks, the spur gears meshing with the racks being able to move in translation along the geometric axis thereof relative to the racks. Since the angle of the teeth of the two worm gears in the symmetrical positions, in the region of contact thereof with the screw, have slopes inclined in opposite directions relative to the plane of symmetry passing through the axis of the screw and the axis of the booster piston, a balancing position making it possible to engage the two racks with the same force or the same torque is necessarily reached.
This balancing movement corresponds to a translation of the two shafts with the worm screws so as to move up or down slightly relative to the median plane passing through the geometric axis of the screw.
Consequently, this natural balancing of the two symmetrical transmissions does not require any specific clearance of the booster piston or the racks, which makes it possible to perform the machining with a good level of accuracy, ensuring smooth functioning, silent functioning and reliability. The machining is preferably performed in accordance with a sliding adjustment.
In accordance with a further advantageous feature, the shafts are integrally connected in translation by a coupling member formed by a crosspiece carrying two rotary bearings each locked on a shaft and cooperating with an axial guide parallel to the geometric axis of the two transmission shafts. This embodiment of the coupling member integrally connecting the two shafts in translation has the advantage of simultaneously contributing to the guidance of the two shafts.
In accordance with an advantageous feature, the coupling member is formed of a crosspiece terminated by two loops each receiving the outer ring of one of the rotary bearings. This embodiment is particularly simple and facilitates the mounting of the mobile equipment, since it is sufficient to clip the rotary bearings into the loops, in particular if the loops are open loops. These loops simultaneously ensure the sliding of this part of the mobile equipment in the guide seat of the body of the brake booster.
This coupling member is preferably made of a plastics material.
In accordance with a further advantageous feature, each transmission shaft is equipped with a rotary bearing on either side of the spur gear meshing with the rack thereof.
In accordance with a further advantageous feature, the low bearing at the end of the transmission shaft on the side opposite that carrying the worm screw is a needle roller bearing and the high bearing between the spur gear and the worm screw is a ball bearing.
As already discussed above, the axial sliding of the coupling member is produced by an axial seat receiving on the one hand each rotary bearing of each shaft directly connected to the coupling member and also an axial seat receiving the other rotary bearing of each shaft.
The rotary bearings associated with the coupling member are advantageously ball bearings.
In accordance with a further advantageous feature, the two shafts are integrally connected in translation along the axis thereof by a coupling member formed by a first disk integral with one shaft and a double disk integral with the other shaft and overlapping the edge of the aforesaid disk, the guidance in translation of the shafts being produced by cylindrical seats receiving the rotary bearings carried by each shaft.
The present disclosure will be described hereinafter in greater detail with the aid of exemplary embodiments of an electric brake booster shown schematically in the accompanying drawings, limited to those parts forming the subject of the disclosure.
Thus:
According to
The electric brake booster 100 is formed of a body 110 housing the booster piston 101 guided in a cylinder 111 along an axis of translation yy perpendicular to the plane of
The electric motor has an output shaft carrying the screw 102 of geometric axis perpendicular to the plane of
The booster piston 101 comprises two racks 103 arranged symmetrically with respect to the plane PP for the drive of the piston 101 from the screw 102 by means of two symmetrical transmissions each formed by a worm screw 121 meshing with the screw 102 and integral with the transmission shaft 120 carrying a spur gear 122 each meshing with a rack 103. The toothing of the two worm screws 121 is identical. Due to the symmetrical position of the two transmissions with respect to the plane PP and with respect to the screw 102, the rotation of the screw meshing with the worm screws 121 is produced by movements of opposite rotation of the two spur gears 122, which thus drive the booster piston 101 by the racks 103.
The transmission shaft 120 is mounted via the low end thereof in accordance with the orientation of
The coupling member 150 of
The loops 152 of the coupling member 150 are guided in translation in the direction perpendicular to the plane of
The coupling member 250 according to this variant is formed by a circular crown or a disk 251 carried by the first transmission shaft 120 (x1x1) and by a double crown 252 overlapping the edge of the disk 251 of the first transmission shaft 120 so as to allow the free rotation, but integrally connected movement in translation of the two shafts 120.
Number | Date | Country | Kind |
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12 56008 | Jun 2012 | FR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2013/062687 | 6/19/2013 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2014/001162 | 1/3/2014 | WO | A |
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5570606 | Irie | Nov 1996 | A |
7144126 | Ro | Dec 2006 | B2 |
20090247360 | Ben-Shabat | Oct 2009 | A1 |
20100114444 | Verhagen | May 2010 | A1 |
20100126167 | Nagel | May 2010 | A1 |
20120031716 | Flodin | Feb 2012 | A1 |
Number | Date | Country |
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198 23 568 | May 1999 | DE |
10254127 | Jun 2004 | DE |
10 2006 010 483 | Sep 2007 | DE |
10 2009 027 468 | Jan 2011 | DE |
2 465 741 | Jun 2012 | EP |
60501123 | Jul 1985 | JP |
2011003643 | Jan 2011 | WO |
WO-2014077449 | May 2014 | WO |
Entry |
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International Search Report corresponding to PCT Application No. PCT/EP2013/062687, mailed Oct. 14, 2013 (German and English language document) (5 pages). |
Number | Date | Country | |
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20150197231 A1 | Jul 2015 | US |