BRAKE ACTUATING DEVICE

Abstract: A brake device comprising an ultrasonic motor (5) having a rotor rotatable by an elastic travelling wave generated by a piezoelectric vibrator on a stator of the motor, and torque converting means (7) for converting a rotating torque produced by said ultrasonic motor (5) into a pressing force for pressing a friction member (2, 3) against a member (1) to be braked, which is transmitted to said friction member (2, 3).

Description: The present invention relates to a brake device having an electric motor employed as a drive source for pressing a friction member against a member to be braked, thereby producing a braking force. Heretofore, an electric brake device having a wound-rotor type motor used as drive source for braking automobiles has been proposed. In such an electric brake device, in order to obtain a necessary and sufficient braking torque, the wound-rotor type motor used has to be large in size and heavy in weight. Therefore, the electric brake device presents an installation problem and poses a disadvantage with respect to a battery power supply owing to its large power consumption. EP-A-0153265 discloses arrangements using rotary torque motors as the driving source for a wheel braking device and in which the motor rotary motion is converted into a pressing force. These arrangements are intended for aeroplane brakes, are large, and employ a multiplicity of motors per wheel braking arrangement. The present invention seeks to provide a brake device driven by an electric motor and suitable for use in an automobile, in particular, the brake device being small in size, light in weight, and capable of producing necessary and sufficient braking forces with a small power consumption. According to the present invention there is provided a brake device arranged to press a friction member against a member to be braked, thereby applying a braking action to said member to be braked, said brake device comprising: a motor for producing a rotating torque; and torque converting means for converting a rotating torque produced by said motor into a pressing force for pressing the friction member against the member to be braked, said pressing force being transmitted to said friction member: characterised in that said motor is an ultrasonic motor. For a better understanding of the present invention reference will now be made to the accompanying drawings in which, by way of example: Fig. 1 is a cross-sectional view of a brake device according to an embodiment of the present invention; Fig. 2 is a cross-sectional view of a brake device according to another embodiment of the present invention; and Fig. 3 is a side elevational view of a drum brake in the embodiment of Fig. 2. Embodiments of the present invention will hereinafter be described in detail with reference to the accompanying drawings. Fig. 1 shows an embodiment of the present invention which is applied to a disc-type brake device, which includes a brake pad 2 arranged at one side of a disc rotor 1 of an automobile wheel and a brake pad 3 mounted on a caliper 4, so that the disc rotor 1 is sandwiched between the brake pads 2 and 3 and the brake pad 2 is pressed against one side of the disc rotor to produce braking action. An ultrasonic motor 5 is mounted on the caliper 4, the ultrasonic motor comprising (not shown) a stator, a rotor and a piezoelectric vibrator mounted on said stator to produce an elastic travelling wave to rotate said rotor. The ultrasonic motor has output shaft 6, the rotating speed of which is reduced by a planetary gear mechanism 7 for an increased torque and then the rotation of the output shaft 6 is transmitted to a linear converter mechanism 8 by which the rotation is converted into a linear movement that presses a pressure plate 9 on which the brake pad 2 is mounted against the disc rotor 1. The planetary gear mechanism 7 comprises a first sun gear 71 mounted on the output shaft 6, a planet gear 72, disposed between the meshing with the sun gear 71 and an internal gear 73 attached to the caliper 4, a second sun gear 75 mounted on the planet gear 72 by a planet carrier 74, a planet gear 76 disposed between and meshing with the second sun gear 75 and the internal gear 73, and a coupling gear 78 mounted on the planet gear 76 by a planet carrier 77. The linear converter mechanism 8 comprises a hollow ball nut 81 rotatably mounted in the caliper 4 by bearings 28, 29, and a ball screw 82 threadedly engaged in the ball nut 81 with balls 83 therebetween and axially movable in response to rotation of the ball nut 81. The ball nut 81 has a gear 84 formed on one end thereof wich is held in mesh with the coupling gear 78 of the planetary gear mechanism 7, so that the rotation of the planetary gear mechanism 7 can be transmitted to the ball nut 81. The pressure plate 9 is fixed to the ball screw 82. A controller 10 reads a signal from a potentiometer 12 which is indicative of the amount of depression of a brake pedal 11. The controller 10 then applies a motor drive voltage controlled to produce a torque dependent on the amount of depression of the brake pedal 11 to the ultrasonic motor 5. Denoted at 13 is a power supply. In operation, when the brake pedal 11 is depressed, the ultrasonic motor 5 is energized under the control of the controller 10 dependent on the amount of depression of the brake pedal 11. The speed of rotation of the output shaft 6 is reduced by the planetary gear mechanism 7 for an increased torque. Then, the rotation from the output shaft 6 is converted by the linear converter mechanism 8 into a linear movement that causes the pressure plate 9 to press the brake pad 2 against the disc rotor 1. The disc rotor 1 is clamped between the brake pads 2, 3 to produce braking forces commensurate with the amount of depression of the brake pedal 11. FIG. 2 shows another embodiment of the present invention which is applied to a drum-type brake device. The brake device includes an ultrasonic motor 5 mounted on a back plate 14. The ultrasonic motor 5 has an output shaft 6, the rotation speed of which is reduced by a planetary gear mechanism 7 for an increased torque. The rotation is then transmitted through a rotatable shaft 15 coupled to splines 79 on the output member of the planetary gear mechanism 7 to rotate an eccentric camshaft 18 which spreads out lining plates 17 in a drum brake 16 (FIG. 3). The lining plates 17 have rollers 30 engaging a cam 19 of the eccentric camshaft 18 so that the lining plates 17 can easily be spread outwardly by the cam 19. The planetary gear mechanism 7 is of substantially the same structure as that of the planetary mechanism shown in FIG. 1. Therefore, identical parts of the planetary gear mechanism 7 are denoted by identical reference numerals in FIG. 1. In operation of the brake device of FIGS. 2 and 3, when the brake pedal 11 is depressed, the ultrasonic motor 5 is energized under the control of the controller 10 dependent on the amount of depression of the brake pedal 11. The speed of rotation of the output shaft 6 is reduced by the planetary gear mechanism 7 for an increased torque. Then, the rotation causes the shaft 15 to rotate the eccentric camshaft 18 through a predetermined angle, whereupon the cam 19 spreads the lining plates 17 outwardly to press linings 20 against a drum surface 21, thereby generating braking forces commensurate with the amount of depression of the brake pedal 11. The drum brake 16 shown in FIG. 3 has an automatic adjuster for keeping the clearance between the linings 20 and the drum surface 21 at a constant level as the linings 20 are worn. Denoted by 22 is such an adjuster, 23 an anchor pin, 24 return springs for the lining plates 17, 25 an overload spring, and 26 a strut. As described above, the brake device of the present invention employs an ultrasonic motor 5 as a drive source for effecting braking operation. since the moment of inertia of the rotor of the ultrasonic motor 5 is small, highly accurate braking forces can be produced which are highly responsive to the depression of the brake pedal 11, with the output torque being precisely controlled dependent on the amount of depression of the brake pedal 11. The ultrasonic motor 5 itself, serving as a drive source for generating necessary and sufficient braking torque, is smaller and lighter than the ordinary wound-rotor type motor, and can appropriately be installed in position. The ultrasonic motor can produce a large braking torque with a small power consumption, and hence is advantageous for use with a battery power supply. When the ultrasonic motor 5 is de-energized, it produces a large retentive torque, preventing the output shaft from becoming free as is the case with the ordinary wound-rotor type motor. It is thus possible to arrange the brake device to provide a parking brake function when the power supply is cut off. Although not shown, the speed of rotation of the disc rotor 1 may be detected by a rotation sensor, and the speed of travel of the automobile is detected by a speed sensor. The controller 10 may read output signals from these sensors, respectively, and determines a slip rate of the automobile according to a predetermined formula. If the determined slip rate is higher than a preset threshold, then the controller 10 may determine that the automobile is skidding. In this manner, an anti-lock braking capability may be provided for turning on and off the ultrasonic motor 5 to effect pumping brake action under the control of the controller 10. It will be understood that the brake device of the invention employs an ultrasonic motor as a brake drive source, and the torque of the ultrasonic motor is effectively converted. The brake device as a whole is small in size and light in weight, and can produce necessary and sufficient braking forces with a small power consumption. The brake device is also capable of well controllable and highly responsive braking control.

Claims: 1. A brake device arranged to press a friction member (2, 3; 20) against a member to be braked (1; 21), thereby applying a braking action to said member to be braked (1; 21), said brake device comprising: a motor (5) for producing a rotating torque; and torque converting means (7, 8; 7, 18) for converting a rotating torque produced by said motor (5) into a pressing force for pressing the friction member (2, 3; 20) against the member to be bracked (1; 21), said pressing force being transmitted to said friction member (2, 3; 20): characterised in that said motor (5) is an ultrasonic motor. 2. A brake device according to claim 1 wherein said ultrasonic motor (5) comprises a stator, a rotor, and a piezoelectric vibrator mounted on said stator to generate an elastic travelling wave to drive said rotor. 3. A brake device according to claim 1 or 2, in which said torque converting means includes a speed reducing gearing (7) for increasing a torque and a linear converting mechanism (8) for converting a rotating torque to a linear propulsion force, which is used to press a brake pad (2, 3) against a disk rotor (1) of a disk-type brake device. 4. A brake device according to claim 1 or 2 in which said torque converting means includes a speed reducing gearing (7) for increasing a torque and an eccentric camshaft (18) driven by a rotating torque of the speed reducing gearing, said eccentric camshaft having a cam (19) thereon which is arranged to spread out lining plates (17) of a drum-type brake device. 5. A brake device according claim 3 or 4, in which the speed reducing gearing (7) is a planetary gear mechanism. 6. A brake device according to claim 3, in which said linear converting mechanism includes a hollow ball nut (81) rotatably mounted in a caliper (4) of the brake device by means of a bearing (28, 29) and a ball screw (82) threadedly engaged in said ball nut (81) for axial movement by rotation of said ball nut (81). 7. A brake device according to any preceding claim, including means (12) for detecting an amount of depression of a brake pedal (11) to produce a signal indicating the amount of depression, and a controller (10) for controlling the ultrasonic motor (5) to produce a braking force dependent upon the amount of depression of the brake pedal (11) in accordance with said signal. 8. A brake device according to any preceding claim, including means for detecting a skid state of a vehicle to produce a skid state indicating signal, and a controller (10) for controlling the ultrasonic motor (5) to drive intermittently said motor (5) in accordance with said skid state detecting signal, thereby effecting a pumping braking action.

Inventors: OGURA, MASAMI, YAMATOH, KOUHEI
Applicants: HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1988
Main classification: F16D65
IPC codes: F16D65, B60T8, B60T13, F16D51, H02N2, B60T1