GB2369661A

GB2369661A - Piezoelectric actuator for vehicle brakes

Info

Publication number: GB2369661A
Application number: GB0124849A
Authority: GB
Inventors: Kevin J Pavlov; Pahngroc Oh; Sohel Anwar
Original assignee: Visteon Global Technologies Inc
Current assignee: Visteon Global Technologies Inc
Priority date: 2000-10-17
Filing date: 2001-10-17
Publication date: 2002-06-05
Also published as: GB0124849D0; JP2002195321A

Abstract

A vehicle brake is actuated by at least one piezoelectric motor. One embodiment has a piezoelectric motor (156, fig 4) which acts on a nut and power screw by rotating a gear train. In other embodiments, an actuator 38 has a plurality of linear piezoelectric micro-motors which move a core spool 50 linearly to exert force on a brake pad 34. The micro-motors are supported from an actuator housing 40, from a bearing member 46 and from each other by springs 60. The piezoelectric actuator may act on a disk or drum brake (fig 5). A controller 58 for the micro-motors may receive signals from a brake by wire braking system.

Description

ACTUATOR ASSEMBLY FOR BRAKING SYSTEM

FIELD OF THE INVENTION The present invention relates generally to braking systems for vehicles, and to an actuator assembly for a braking system in a motor vehicle.

BACKGROUND OF THE INVENTION It is known to provide braking in a number of systems that are used in vehicles such as motor vehicles, work machines, and a variety of other applications. Typically, in motor vehicles, the braking systems are of a hydraulic type, such as, a fixed-caliper brake, floating-caliper brake, and drum brake.

It is also known that a Brake-by-Wire (BBW) technology is currently being developed by motor vehicle manufacturers. One such BBW technology is electro-hydraulic braking which also requires a set of valves to achieve desired braking actions. Valves are either actuated by an electromagnetic solenoid or through a pilot system. However, all electronically controlled valves are actuated by an electromagnetic solenoid.

Although the above electromagnetic solenoids have worked, they suffer from the disadvantage of electromagnetic interference (EMI). Another disadvantage is that the electromagnetic solenoids are unidirectional, i. e., they can only impart motion in only one direction. As a result, it is necessary to use two solenoids for most dual action valves, placed at both ends of the spool.

Therefore, it is desirable to provide an acte-or assembly for a braking system that eliminates electromagnetic interference. It is also desirable to provide an actuator assembly for either a disk type or drum type braking system that generates braking forces in a braking system of a motor vehicle. It is further desirable to provide an actuator assembly for a braking system that is hysteresis free, operates in wider range of temperatures, and is lightweight. Therefore, there is a need in the art to provide an actuator assembly for a braking system that meets these desires.

SUMMARY OF THE INVENTION Accordingly, in an embodiment of the present invention an actuator assembly for a braking system including a braking member for contacting a rotatable member of the braking system is provided. The actuator assembly also includes a piezoelectric actuator connected to the braking member to move the braking member for contacting the rotatable member in response to signals thereto.

One advantage of the present invention is that an actuator assembly is provided for a braking system that is of a piezoelectric (PZT) type. Another advantage of the present invention is that the actuator assembly uses a PZT actuator to generate braking force/torque for the braking system of either a disk or drum type and may be applicable to a parking brake apparatus. Yet another advantage of the present invention is that the actuator assembly generates brake force directly in the wheel-brake actuator and requires little maintenance (only pads and disks).

Still another advantage of the present invention is that the actuator assembly has no need to detect and adjust an

air gap-no force sensor or motor signal evaluation. A further advantage of the present invention is that actuator assembly eliminates electromagnetic interference, reduces components, and reduces entire system weight. Yet a further advantage of the present invention is that the actuator assembly has no hysteresis like magnetization curve, operates in wider range of temperatures, and has a larger torque density (Nm/m3) compared to electric motors. Still a further advantage of the present invention is that the actuator assembly is environmentally friendly due to the lack of brake fluids and still uses frictional material (brake pads).

Other features and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of an actuator assembly, according to an embodiment of the present invention, illustrated in operational relationship with a braking system of a motor vehicle; Figure 2 is a fragmentary elevational view of the actuator assembly and disk type braking system of Figure 1; Figure 3 is a fragmentary elevational view of the actuator assembly and the braking system of Figure 2; Figure 4 is a fragmentary elevational view of another

embodiment, according to the present invention, of the actuator assembly and a disk type braking system of Figure 1; and Figure 5 is a fragmentary elevational view of yet another embodiment, according to the present invention, of the actuator assembly and a drum type braking system of Figure 1.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings and in particular to Figures 1 through 3, one embodiment of an actuator assembly 10, according to the present invention, is illustrated in operational relationship with a braking system, generally indicated at 12, of a motor vehicle 14 (partially shown).

In this embodiment, the braking system 12 is of a disk type. The braking system 12 includes a rotatable disk brake 16 connected to an axle (not shown) of the motor vehicle 14 and for connection to a wheel (not shown) of the motor vehicle 14. The braking system 12 also includes a brake housing 18 connected to vehicle structure 20 of the motor vehicle 14 by suitable means such as fasteners 22. The brake housing 18 is generally cylindrical in shape and has a cavity 24 therein to receive a portion of the actuator assembly 10. The brake system 12 further includes a brake caliper 26 connected to the brake housing 18 and extending over the disk brake 16. The brake system 12 includes a first back plate 28 connected to the caliper 26 on one side of the disk brake 16 and a second back plate 30 coupled to the actuator assembly 10. The brake system 12 further includes a first brake pad 32 connected to the first back plate 28 and a second brake pad 34 connected to the second back plate 30. It should be

appreciated that the braking system 12 may be either of a disk or drum type. It should also be appreciated that, except for the actuator assembly 10, the braking system 12 is conventional and known in the art.

Referring to Figures 1 through 3, the actuator assembly 10, according to the present invention, includes a piezoelectric actuator 38 operatively connected to the first back plate via the caliper 26 for moving the first brake pad 32 into contact with the disk brake 16 and to the second back plate 30 via a pin 54 for moving the second brake pad 34 into contact with the disk brake 16.

The piezoelectric actuator 38 includes a housing 40 having a chamber 42. As illustrated, the housing 40 has a generally cylindrical configuration although any other suitable configuration may be used. The housing 40 has an aperture 44 extending longitudinally through each end thereof. The housing 40 is made of a metal material such as aluminum. The housing 40 is a two-piece structure having a first portion 40a disposed in the cavity 24 of the brake housing 22 and a second portion 40b spaced longitudinally from the first portion 40a and disposed in a recess 40c of the brake caliper 26. The first portion 40a and second portion 40b are sealed to the brake housing 22 and brake caliper 26 by a seal 41 disposed in an annular groove 41a in the first portion 40a and second portion 40b.

The piezoelectric actuator 38 includes a rotatable bearing member 46 disposed between the first portion 40a and the second portion 40b of the housing 40. The bearing member 46 extends longitudinally and is generally cylindrical in shape. The bearing member 46 has an annular recess 47 at each longitudinal end. The piezoelectric actuator 38 also

includes an annular bearing 48 disposed each recess 47 between the bearing member 46 and the brake housing 24 and the brake caliper 26. The bearing 48 is of a roller ball type and is conventional and known in the art. It should be appreciated that the bearing member 46 is allowed to rotate relative to the brake housing 24 and brake caliper 26 via the bearings 48.

The piezoelectric actuator 38 also includes a core spool 50 disposed in the chamber 42 of the housing 40 and movable therein. The core spool 50 has a shaft portion 51 extending axially and through the apertures 44 of the housing 40. The shaft portion 51 is generally cylindrical in shape with a generally circular shaped cross-section.

The core spool 50 has an enlarged diameter end portion 52 at each end of the shaft portion 51. The core spool 50 is made of a metal material such as steel.

The actuator assembly 10 includes a plate member 53 connected to one of the end portions 52. The plate member 53 is connected or coupled to the second back plate 30 of the brake system 12 by suitable means such as a pin 54.

The piezoelectric actuator 38 also has at least one, preferably a plurality of, preferably eight, piezoelectric motors 56 extending radially from and spaced circumferentially around and axially along the core spool 50 for a function to be described. The piezoelectric motors 56 are generally rectangular in shape. The piezoelectric motors 56 are of a linear motor type and similar to that disclosed in U. S. Patent No. 5,453, 653 to Zumeris, the disclosure of which is hereby incorporated by reference. The piezoelectric motor 56 is based on a piezoceramic plate, which under excitation drive and

ceramic geometry, enables it to excite a transverse bending vibration mode at close frequency proximity to a longitudinal extension mode.

The actuator assembly 10 further includes a controller 58 for supplying power to the piezoelectric motors 56. The piezoelectric motors 56 are connected to the controller 58 by suitable means such as wires (not shown). It should be appreciated that the controller 58 is conventional and known in the art.

The piezoelectric actuator 38 also includes at least one, preferably a plurality of supporting springs 60 disposed in the chamber 42 between the piezoelectric motors 56 and bearing member 46 and between the piezoelectric motors 56 and the housing 40. The supporting springs 60 are connected by suitable means to the piezoelectric motors 56, bearing member 46, and the housing 40. It should be appreciated that piezoelectric motor 56 has a wide travel range and is not susceptible to electromagnetic interference. It should also be appreciated that the piezoelectric motor 56 offers intrinsic stalling force when no electric field is applied. It should further be appreciated that when an electric field is applied the crystalline structure of the piezoelectric motor 56 changes shape, producing dimensional changes in the material.

In operation of the actuator assembly 10, the brake pedal (not shown) of the brake system 12 would transmit a signal to the controller 58, which would then send a corresponding command or signal to the piezoelectric actuator 38 to move the second brake pad 34 or the first brake pad 32 toward each other to brake the disk brake 16

and slow or stop rotation of the disk brake 16. Power from the controller 58 is received by the piezoelectric motors 56 that places a driving frequency on the core spool 50. Because the piezoelectric motors 56 are coupled to the core spool 50, a non-symmetrical driving force is exerted on the core spool 50, causing movement. The periodic nature of the driving force at frequencies much higher than the mechanical resonance of the core spool 50 allows continuous smooth motion for unlimited travel, while maintaining high resolution and positioning accuracy. The linear movement of the core spool 50, in turn, moves either the second back plate 30 and second brake pad 34 linearly to engage the disk brake 16 or the first back plate 28 and first brake pad 32 linearly to engage the disk brake 16 to slow or stop rotation of the disk brake 16. It should be appreciated that the second brake pad 34, second back plate 30, plate member 53, core spool 50, motors 56, and bearing member 46 may rotate as a unit. It should also be appreciated that the piezoelectric motor 56 can effect operation in either direction according to the transmitted electrical signals.

It should further be appreciated that the braking force/torque generated by the actuator assembly 10 can be calculated from multiplication of number of piezoelectric motors 56, maximum force of each piezoelectric motor 56 and braking factor.

Referring to Figure 4, another embodiment 110, according to the present invention, of the actuator assembly 10 is shown. Like parts of the actuator assembly 10 have like reference numerals increased by one hundred (100). In this embodiment, the actuator assembly 110 has a rotational piezoelectric actuator 138, which is capable of generating motion in both rotational directions, used

in combination with a gear train 182 to operate the brake system 12. The piezoelectric actuator 138 includes the housing 140 having the chamber 142. As illustrated, the housing 140 has a generally cylindrical configuration although any other suitable configuration may be used. The housing 140 has a bore 143 extending longitudinally and an aperture 144 at one end of the bore 143. The housing 140 is made of a metal material such as aluminum. The housing 140 is a two-piece structure having a first portion 140a disposed in the cavity 24 of the brake housing 22 and a second portion 140b at the longitudinal end opposite the aperture 144.

The piezoelectric actuator 138 includes a rotatable power screw 162 disposed in the bore 143. The power screw 162 extends longitudinally and is generally cylindrical in shape. The power screw 162 has a plurality of threads 164 at one longitudinal end for a function to be described.

The piezoelectric actuator 138 also includes an annular bearing 148 disposed in the bore 143 between the power screw 162 and the housing 140. The bearing 148 is of a roller ball type and is conventional and known in the art.

It should be appreciated that the power screw 162 is allowed to rotate relative to the housing 140 via the bearing 148.

The piezoelectric actuator 138 also includes a nut 166 disposed in the bore 143 of the housing 140 and movable linearly therein. The nut 166 is generally cylindrical in shape with a generally circular shaped cross-section. The nut 166 has a passageway 168 extending axially therethrough and a plurality of threads 170 along the passageway 168 to cooperate with the threads 164 on the power screw 162.

The piezoelectric actuator 138 includes a piston 172 connected at one end to the nut 166. The piston 172 is generally cylindrical in shape with a generally circular shaped cross-section. The piston 172 has a shaft portion 173 extending axially and having a reduced diameter. The shaft portion 173 is generally cylindrical in shape with a generally circular shaped cross-section. The shaft portion 173 has a cavity 173a for receiving one end of the power screw 162. The piston 172 is sealed to the housing 140 by a seal 174 disposed in an annular groove 176 in the piston 172.

The piezoelectric actuator 138 also includes at least one piezoelectric motor 156 extending axially and spaced radially from the power screw 162 for a function to be described. The piezoelectric motor 156 is generally circular in shape. The piezoelectric motor 156 is of a rotational motor type. The piezoelectric motor 156 is based on a piezoceramic plate, which under excitation drive and ceramic geometry, enables it to excite a transverse bending vibration mode at close frequency proximity to a longitudinal extension mode. The piezoelectric motor 156 is connected to the housing 140 by suitable means such as fasteners (not shown). The piezoelectric motor 156 is electrically connected to a controller 158 by suitable means such as wires (not shown).

The piezoelectric actuator 138 includes a rotatable shaft 178 connected at one end to the piezoelectric motor 156. The shaft 178 is generally cylindrical in shape with a generally circular shaped cross-section. The shaft 178 extends through an aperture 180 of the housing 140 and is generally parallel to the power screw 162.

The piezoelectric actuator 138 includes a gear train, generally indicated at 182, connected at one end to the power screw 162 and shaft 178. The gear train 182 includes a first gear 184 connected to one end of the power screw 162 and a second gear 186 connected to one end of the shaft 178. The gear train 182 includes at least one third gear 188 interconnecting the first gear 184 and second gear 186. The gears 184,186, and 188 are of a spur type. It should be appreciated that the function of the gear train 182 is mainly to reduce speed and increment transmitted torque. It should also be appreciated that worm gears can be used instead of spur gears.

The actuator assembly 110 includes a plate member 153 connected to the end of the piston 172. The plate member 153 is connected or coupled to the second back plate 30 of the brake system 12 by suitable means such as a pin 154.

In operation of the actuator assembly 110, the brake pedal (not shown) of the brake system 12 would transmit a signal to the controller 158, which would then send a corresponding command or signal to the piezoelectric actuator 138 to move the second brake pad 34 or the first brake pad 32 toward each other to brake the disk brake 16 and slow or stop rotation of the disk brake 16. Power from the controller 158 is received by the piezoelectric motor 156 that places a driving frequency on the shaft 178. Because the piezoelectric motor 156 is coupled to the shaft 178, a non-symmetrical driving force is exerted on the shaft 178, causing movement. The periodic nature of the driving force at frequencies much higher than the mechanical resonance of the shaft 178 allows continuous

smooth motion for unlimited travel, while maintaining high resolution and positioning accuracy. The rotational movement of the shaft 178, in turn, will rotate the gear train 182 to cause the power screw 162 and nut 166 to convert rotary motion to linear motion. This linear motion is used to actuate the brake pads 32 and 34 against the brake disk 16. It should be appreciated that the power screw 162, nut 166, and bore 143 are installed to change rotation to linear actuation.

Referring to Figure 5, yet another embodiment 210, according to the present invention, of the actuator assembly 10 is shown. Like parts of the actuator assembly 10 have like reference numerals increased by one hundred (100). In this embodiment, the actuator assembly 210 has a piezoelectric actuator 238, which is capable of generating motion in both linear directions, used in combination with drum brakes of the brake system 12. In this embodiment, the braking system 12 is of a drum type.

The braking system 12 includes a rotatable brake drum 216 connected to an axle (not shown) of the motor vehicle 14 and for connection to a wheel (not shown) of the motor vehicle 14. The brake drum 216 is generally cylindrical in shape and has a cavity 217 therein to receive a portion of the actuator assembly 210. The braking system 12 also includes a leading brake shoe 219a and a trailing brake shoe 219b connected to vehicle structure 20 of the motor vehicle 14 by suitable means such as fasteners 221. The brake system 12 further includes a friction pad 223 on each of the brake shoes 219a and 219b for engaging the brake drum 216 to reduce or stop rotation thereof. The brake system 12 includes at least one, preferably a plurality of springs 225 interconnecting the brake shoes 219a and 219b for urging the brake shoes 219a and 219b

toward each other. The brake system 12 further includes a caliper 227 interconnecting lower ends of the brake shoes 219a and 219b for adjusting the brake shoes 219a and 219b relative to the actuator assembly 210. The actuator assembly 210 is disposed between upper ends of the brake shoes 219a and 219b for expanding the brake shoes 219a and 219b against a brake surface of the brake drum 216. It should be appreciated that, except for the actuator assembly 210, the braking system 12 is conventional and known in the art.

The actuator assembly 210, according to the present invention, includes a piezoelectric actuator 238 having a housing 240 with a chamber 242 therein. As illustrated, the housing 240 has a generally cylindrical configuration although any other suitable configuration may be used. The housing 240 has an aperture 244 extending longitudinally through one end thereof. The housing 240 is made of a metal material such as aluminum. The housing 240 is a two-piece structure having a first portion 240a and a second portion 240b connected to the first portion 240a.

The piezoelectric actuator 238 also includes a core spool 250 disposed in the chamber 242 of the housing 240 and movable therein. The core spool 250 is generally cylindrical in shape with a generally circular shaped cross-section. The core spool 250 extends axially and through the aperture 244 of the housing 240. The core spool 250 has a guide cavity 290 at one end extending axially therein and a guide 292 extending axially and into the housing 240 and the passageway 290 to guide the core spool 250 linearly. The core spool 250 is made of a metal material such as steel.

The piezoelectric actuator 238 also has at least one, preferably a plurality of, preferably six, piezoelectric motors 256 extending radially from and spaced circumferentially around and axially along the core spool 250 for a function to be described. The piezoelectric motors 256 are generally circular in shape. The piezoelectric motors 256 are of a linear motor type and similar to that disclosed in U. S. Patent No. 5,453, 653 to Zumeris, the disclosure of which is hereby incorporated by reference. The piezoelectric motor 256 is based on a piezoceramic plate, which under excitation drive and ceramic geometry, enables it to excite a transverse bending vibration mode at close frequency proximity to a longitudinal extension mode. The piezoelectric motors 256 are connected to a controller 258 by suitable means such as wires (not shown).

The piezoelectric actuator 238 also includes at least one, preferably a plurality of supporting springs 260 disposed in the chamber 242 between the piezoelectric motors 256 and the housing 240. The supporting springs 260 are connected by suitable means to the piezoelectric motors 256 and the housing 240. It should be appreciated that the piezoelectric motor 256 has a wide travel range and is not susceptible to electromagnetic interference. It should also be appreciated that the piezoelectric motor 256 offers intrinsic stalling force when no electric field is applied. It should further be appreciated that when an electric field is applied the crystalline structure of the piezoelectric motor 256 changes shape, producing dimensional changes in the material.

In operation of the actuator assembly 210, the brake pedal (not shown) of the brake system 12 would transmit a signal

to the controller 258, which would then send a corresponding command or signal to the piezoelectric actuator 238 to move the brake shoes 219a and 219b away from each other and into engagement with the brake drum 216 to brake the brake drum 216 and slow or stop rotation of the brake drum 216. Power from the controller 258 is received by the piezoelectric motors 256 that places a driving frequency on the core spool 250. Because the piezoelectric motors 256 are coupled to the core spool 250, a non-symmetrical driving force is exerted on the core spool 250, causing movement. The periodic nature of the driving force at frequencies much higher than the mechanical resonance of the core spool 250 allows continuous smooth motion for unlimited travel, while maintaining high resolution and positioning accuracy. The linear movement of the core spool 250, in turn, moves the housing 240 linearly to rotate or expand the brake shoes 219a and 219b against a brake surface of the brake drum 216 to slow or stop rotation of the brake drum 216. It should be appreciated that the piezoelectrically actuated drum braking system 12 operates in a similar manner to the piezoelectrically actuated disk braking system 12 described in connection with FIGS. 1 through 3. It should also be appreciated that the linear piezoelectric motors 256 are assembled to push the brake shoes 219a and 219b radially outward into engagement with the brake drum 216 of the braking system 12. It should further be appreciated that the rotational piezoelectric motor 156 with the gear train 182 and the screw-nut 162-166 described in connection with Figure 4 can replace the linear piezoelectric actuator 238.

The present invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.

Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.

Claims

1. An actuator assembly for a braking system on a vehicle comprising: a braking member for contacting a rotatable member of the braking system; and a piezoelectric actuator connected to said braking member to move said braking member for contacting the rotatable member in response to signals thereto.

2. An actuator assembly as set forth in claim 1 wherein said piezoelectric actuator includes a housing and a movable member disposed in said housing and connected to said braking member.

3. An actuator assembly as set forth in claim 2 wherein said piezoelectric actuator includes at least one piezoelectric motor disposed in said housing and cooperating with said movable member to move said movable member.

4. An actuator assembly as set forth in claim 3 wherein said piezoelectric actuator includes a least one supporting spring interconnecting said at least one piezoelectric motor and said housing.

5. An actuator assembly as set forth in claim 2 wherein said housing has an aperture extending axially through one end thereof.

6. An actuator assembly as set forth in claim 2 including a connecting member interconnecting said braking member and one end of said movable member.

7. An actuator assembly as set forth in claim 2 includes a plurality of piezoelectric motors disposed in said housing and cooperating with said movable member to move said movable member.

8. An actuator assembly as set forth in claim 7 including a plurality of supporting springs interconnecting said piezoelectric motors and said housing.

9. An actuator assembly as set forth in claim 7 wherein said piezoelectric motors are spaced axially along said movable member.

10. An actuator assembly as set forth in claim 9 wherein said piezoelectric motors are spaced circumferentially about said movable member.

11. An actuator assembly substantially as herein described with reference to any one embodiment shown in the accompanying drawings.