Non-circulating ball nut drive for electromechanical brake

Abstract

The present invention relates to a non-circulating ball nut drive for an electromechanical brake. A ball nut assembly of an actuator assembly for a vehicle brake includes a spindle rotatable about an axis and having an outer raceway wrap and an inner recess. A piston integrated with the nut includes an inner raceway wrap and is positioned on the spindle so as to be movable along the axis in response to rotation of the spindle to apply the vehicle brake. A cage is disposed between the raceway wraps and includes openings for receiving bearing balls sized to be at least one of roll without interference and slide without interference within the raceway wraps. A cage return mechanism is disposed in the inner recess of the spindle. The cage moves in a first direction from a home position relative to the spindle with the nut to load the cage return mechanism in response to application of the brake and the cage return mechanism unloads to automatically move the cage back to the home position in a second, opposite direction in response to release of the brake.

Description

Technical Field

[0001] The present invention generally relates to an electromechanical brake, and more particularly to a ball nut drive device for an actuator assembly of an electromechanical brake. Background Technology

[0002] Most vehicles are equipped with braking systems used to slow or stop the vehicle's movement in a controlled manner. A typical braking system for modern cars or light trucks includes disc brake assemblies for each front wheel and disc brake assemblies for each rear wheel. The braking assemblies are actuated by hydraulic or pneumatic pressure generated when the vehicle operator presses the brake pedal. Future braking systems will replace hydraulic or pneumatic braking systems with electromechanical braking systems that use electricity to actuate subassemblies including an electric motor, transmission, and ball nut assemblies. These subassemblies can be used to actuate the service brake during typical or emergency events, and also to actuate the parking brake. In some cases, the bearings in the ball nut assembly circulate in a loop during the operation of the electromechanical braking system. Summary of the Invention

[0003] In one example, a ball screw drive for an actuator assembly of a vehicle brake includes a spindle rotatable about an axis and having an outer rail winding extending around the spindle and an inner recess extending axially into the spindle. A ball nut assembly for an actuator assembly of a vehicle brake includes a spindle rotatable about an axis and having an outer rail winding extending around the spindle and an inner recess extending axially into the spindle. A piston integrated with the nut includes an inner rail winding and is positioned on the spindle to move axially in response to rotation of the spindle, thereby applying the vehicle brake. A cage is disposed between the rail windings and includes openings for receiving bearing balls sized to be free from rolling interference and slip interference within the rail windings. A cage return mechanism is disposed within the inner recess of the spindle. In response to the application of a brake, the cage, together with the nut, moves axially and rotationally relative to the spindle in a first direction from the starting position to load the cage return mechanism, and in response to the release of the vehicle brake, the cage return mechanism unloads to automatically move the cage back to the starting position in the opposite second direction.

[0004] In another example, a ball screw drive for an actuator assembly of a vehicle brake includes a spindle rotatable about an axis and having an outer rail winding extending around the spindle and an inner recess extending axially into the spindle. A nut includes an inner rail winding and is positioned on the spindle to be movable axially in response to rotation of the spindle, thereby applying vehicle braking. A cage is located between the rail windings and includes an opening for receiving bearing balls configured to roll within the rail windings. A cage return mechanism is disposed in the inner recess of the spindle and includes an end cap disposed in the inner recess of the spindle. A biasing member biases the end cap toward the spindle. A shaft is screwed into the spindle to connect the end cap and the biasing member to the spindle and includes features allowing preload adjustment of the biasing member. In response to the application of braking, the cage, together with the nut, moves axially relative to the spindle in a first direction from a starting position to load the biasing member. In response to the stop of the braking application, the biasing member is unloaded to automatically move the cage back to the starting position in the opposite second direction.

[0005] In another aspect, either alone or in combination with any other aspect, the cage return mechanism includes an end cap disposed in a recess within the spindle. A biasing member biases the end cap toward the spindle. A thrust bearing allows for generally free rotation of the end cap. A shaft connects the end cap and the biasing member to the spindle. In response to the application of braking, the cage moves the end cap in a first direction against the biasing force of the biasing member, and in response to the release of the vehicle brake, the biasing member automatically moves the end cap in a second direction to return the cage to its initial position.

[0006] In another aspect, either alone or in combination with any other aspect, the biasing member is a compression spring.

[0007] In another aspect, either alone or in combination with any other aspect, the biasing member is a torsion spring.

[0008] In another aspect, either alone or in combination with any other aspect, the cage return mechanism also includes a support member fixed to the shaft and receiving a first end of the torsion spring. The bearing is movable relative to the shaft together with the end cap and receives a second end of the torsion spring.

[0009] In another aspect, either alone or in combination with any other aspect, the shaft is screwed into the mandrel, and a biasing member surrounds the shaft.

[0010] In another aspect, either alone or in combination with any other aspect, the end cap includes a flange that engages with a flange on the cage to prevent relative rotation between them during the application of braking.

[0011] In another aspect, either alone or in combination with any other aspect, the flanges on the cage are truncated conical.

[0012] In another aspect, alone or in combination with any other aspect, the end cap includes: a base disposed in a recess; and a flange extending radially outward to the end surface of the spindle to engage the cage.

[0013] In another respect, either alone or in combination with any other respect, the bearing does not circulate within the track winding section.

[0014] In another aspect, either alone or in combination with any other aspect, the nut forms a brake piston.

[0015] Other objects and advantages of the invention, as well as a more complete understanding, will become apparent from the following detailed description and accompanying drawings. Attached Figure Description

[0016] Figure 1A This is a perspective view of an actuator assembly having an exemplary spindle drive according to the present invention.

[0017] Figure 1B This is a cross-sectional view of a part of the actuator assembly.

[0018] Figure 2A yes Figure 1A and Figure 1B An exploded view of an example non-cyclic spindle drive with actuator components.

[0019] Figure 2B yes Figure 2A A cross-sectional view of the spindle drive device.

[0020] Figure 3 This is a front view of the roller cage used in a spindle drive device.

[0021] Figure 4 It is used for Figure 2A An exploded view of the cage return mechanism of the spindle drive device.

[0022] Figure 5 This is a cross-sectional view of the spindle drive mechanism before the braking event.

[0023] Figure 6 This is a cross-sectional view of the spindle drive device during a braking event.

[0024] Figure 7 This is an anatomical view of another exemplary spindle drive device.

[0025] Figure 8 It was before the braking event. Figure 7 A cross-sectional view of the spindle drive device. Detailed Implementation

[0026] The present invention relates generally to electromechanical brakes, and more particularly to a non-cyclic ball screw drive for an actuator assembly of an electromechanical brake. Figures 1A to 1B An exemplary actuator assembly 10 for a vehicle brake according to one aspect of the present invention is shown.

[0027] The actuator assembly 10 includes a control assembly 12 and a drive assembly 14, which can be assembled into separate subunits. The control assembly 12 and the drive assembly 14 are arranged in a common housing 18 fixed to the brake caliper housing 20. The brake caliper housing 20 defines a clearance 22 for accommodating a brake rotor (not shown). A first brake pad BP1 and a second brake pad BP2 are disposed in the brake caliper housing 20 on opposite sides of the rotor.

[0028] The electric motor 28 provides torque to the drive assembly 14. For this purpose, the electric motor 28 can be coupled to the drive assembly 14 via a gear train 30 or directly coupled to the drive assembly (not shown). As shown, a frame 32 is fixed to the two housings 18, 20 and supports the gear train 30. The frame 32 also facilitates connecting the output of the gear train 30 to the drive assembly 14 in a known manner. For this purpose, the drive assembly 14 includes a ball nut assembly 72 rotatably connected to the output of the gear train 30.

[0029] Go to Figures 2A to 2B The ball nut assembly 72 includes a spindle 84 and a mating nut / piston 170, which is integrated as a single component. The spindle 84 does not contain any integrated (or machined) ball recirculation features. The spindle 84 extends from a first end 85 to a second end 87 along a centerline or axis 88. The spindle 84 includes a generally cylindrical base 90 having an outer surface 92 and an inner surface 94, the inner surface 94 defining a recess or cavity 98 extending from the second end 87 toward the first end 85. A threaded channel 100 extends from the recess 98 toward the first end 85.

[0030] Shaft 110 extends longitudinally from base 90. One end of shaft 110 includes a toothed portion 112 for fixed connection (e.g., spline connection) to the output end of gear train 30. Thus, spindle 84 rotates together with the output end of gear train 30. Due to this connection, motor 28 uses gear train 30 to control the rotation of ball nut assembly 72, which will be discussed below.

[0031] A helical winding portion 120 is provided along the outer side of the base 90. The helical winding portion 120 has a curved cross-section along its length and extends circumferentially along the outer surface 92 and the helical path. The continuous multiple turns of the winding portion 120 collectively define the thread 128.

[0032] Ball bearings 130 are disposed within the track winding portion 120. The ball bearings 130 may be formed of a durable material, such as metal. The cross-section of the track winding portion 120 is configured to ensure that the ball bearings 130 can roll freely along the length of the track winding portion, but is limited in its ability to deviate from the centerline of the track winding portion. In other words, the width of the track winding portion 120 is large enough to accommodate the ball bearings 130, but not large enough to allow the bearing to roll along the sides of the cross-section. Additionally, the width of the track winding portion 120 is large enough to accommodate the ball bearings 130 such that the ball bearings 130 can also slide / slide through the track winding portion undisturbed at the interface. Furthermore, the depth of the track winding portion 120 is configured such that approximately only half the volume of the ball bearings 130 is disposed within the track winding portion, while the remaining portion is located radially outside the outer surface 92 of the base 90.

[0033] See Figure 3 A ball retainer 140 is provided for the spindle 84, and the ball retainer 140 has a cylindrical shape defining an inner surface 142 and an outer surface 144. The inner surface 142 defines a central channel 145. An opening 146 extends radially through the ball retainer 140 and together defines a track winding portion 147 for receiving bearing balls 130. In particular, the openings 146 are discrete openings R1, R2, R3...R n Arranged circumferentially and helically around the ball cage. Opening R1-R n They are discrete from one another and are usually arranged end to end so as to be circumferentially and helically wound around the circumference of the cage 140 as they move along the length of the cage.

[0034] In other words, the helical winding of the mandrel 84 and the nut / piston 170 is connected by a series of openings R1-R n The defined spiral winding section is the same, with a series of openings R1-R n The track winding portion 147 is defined together and is similar to the track winding portion 120 in the mandrel 84. Although the track winding portion 120 is continuous from one end to the other, the track winding portion 147 is formed by discrete, spaced segments. A lip or flange 148 is provided at the bottom of the ball retainer 140 (as shown) and extends radially inward, such that the channel 145 narrows in the region of the flange. In one example, the flange 148 is truncated conical.

[0035] like Figure 4As shown, the ball nut assembly 72 also includes a cage return mechanism 150, which automatically returns the cage 140 to its initial starting position once the brake is fully released, thus removing any load from the bearing balls 130. In one example, mechanism 150 includes an end cap 152 having an internal space 154 leading to a central opening 156. A flange 158 extends radially outward from the end cap 152.

[0036] The shaft 160 is aligned with the end cap 152 and includes a longitudinally extending shaft 161 extending from the head 162. The shaft 161 terminates in a threaded portion 163 with a decreasing diameter. A compression spring 164, a spacer 166, and a thrust bearing assembly 168 are disposed within the end cap. The thrust bearing assembly 168 includes one or more washers 169 and pins 171.

[0037] Nut 170 is cylindrical and includes an outer surface 172 and an inner surface 174 defining a central channel 176. The central channel 176 extends along the length of nut 170 and terminates at an end wall 178. That is, one end of nut 170 is closed. Track winding portion 180 is disposed along the inner surface 174 and may present, for example, a spiral pattern, which is similar to the contour of track winding portion 120 on mandrel 84.

[0038] Furthermore, the width of the track winding portion 180 is large enough to accommodate the bearing balls 130, allowing the bearing balls 130 to slide undisturbed across / through the track winding portion at the interface. Additionally, the depth of the track winding portion 180 is configured such that approximately only half the volume of the bearing balls 130 is disposed within the track winding portion, with the remaining portion positioned radially inward on the inner surface 174. It should be understood that the nut 170 can also be referred to as the piston 170, as it performs the function of a piston in a brake caliper.

[0039] Figure 5 A fully assembled ball nut assembly 72 is shown, wherein a nut 170 is positioned on a spindle 84 such that tracks 120, 180 are radially aligned with each other. Bearing balls 130 are positioned in and between tracks 120, 180, and are capable of rolling and sliding within tracks 120, 180. A cage 140 is radially positioned between tracks 120, 180, wherein the bearing balls 130 are positioned in an opening 146 and extend to opposite sides of the cage wall.

[0040] A spherical washer 190 extends on the outer surface 92 of the base 90 adjacent to the shaft 110. A retaining ring 192 may optionally be provided (see...). Figure 2BA ball washer 190 is attached to the base 90 to help secure the ball washer 190 to the base 90. The ball washer 190 extends radially outward enough to engage with the top of the cage 140. A thrust bearing 194 is axially positioned between the ball washer 190 and the brake caliper housing 20. A flanged bearing sleeve 196 is positioned in the brake caliper housing 20 and receives the shaft 110 of the spindle 84. The bearing sleeve 196 is held in place by an annular spacer 198 and a retaining ring 199.

[0041] The base 90 of the spindle 84 is positioned within the central channel 176 of the nut 170. The end cap 152 is positioned within a recess 98, wherein the opening 156 aligns with the threaded channel 100. The threaded portion 163 of the shaft 160 extends through the opening 156 and forms a threaded connection with the threaded channel 100. A thrust bearing assembly 168 extends on the shaft 161 and engages with the head 162. A spacer 166 slides on the shaft 161 and engages the thrust bearing assembly 168.

[0042] A compression spring 164 surrounds shaft 161 and is axially constrained by spacer 166 and the underside of end cap 152. Shaft 160 is screwed into threaded channel 100, thus securely fixing shaft 160 to spindle 84. The lengths of spring 164, spacer 166, shaft 161, and end cap 152 are all designed to achieve the required compression level of spring 164, which is necessary for the cage 140 and mounted bearing balls 130 to automatically return to their original position when the brake is fully released.

[0043] A flange 148 on the ball retainer 140 extends between the bottom thread 128 of the spindle 84 and the flange 158 of the end cap 152. In this configuration, the flange 148 on the ball retainer 140 can engage with or be spaced apart from the flange 158. In any case, the flange 148 on the ball retainer 140 extends to a position where it radially overlaps with the flange 158 on the end cap 152.

[0044] See further Figure 1B The ball nut assembly 72 extends through the sleeve 200 defined by the brake caliper housing 20 and is aligned / adjacent to the first brake pad BP1. A toothed portion 112 is rotatably coupled to a gear train 30 to enable torque transmission between them. With this in mind, the ball nut assembly 72 is configured such that rotation of the spindle 84 causes axial movement of the nut 170 along axis 202 and along the inner cylindrical running surface 204 of the sleeve 200. The axial movement of the nut 170 controls the movement of the first brake pad BP1 toward and away from the rotor. A piston dust sleeve / dust scraper 201 and a piston seal 203 are radially disposed between the nut 170 and the inner surface 204.

[0045] The sleeve 200 and nut 170 may be provided with anti-rotation features that cooperate to prevent the nut from rotating relative to the sleeve, thereby allowing the nut to move along (not about) axis 202. In one example, the brake caliper housing 20 includes an axially extending groove 70 that engages with a key (not shown) fixed to and movable with the nut 170. Thus, the spindle 84 and nut 170 have an advantageous cooperative configuration that helps to maximize the efficiency of converting rotation of the spindle 84 into axial movement of the nut 170.

[0046] During operation, see Figure 6 The vehicle operator presses the brake pedal (not shown), or the vehicle initiates braking operation autonomously. In either case, the vehicle controller actuates motor 28, which ultimately transmits torque to the toothed portion 112 of the ball nut assembly 72. Spindle 84 rotates about axis 202 in manner T (counterclockwise as shown), but is prevented from axially translating along the axis.

[0047] Rotation of spindle 84 in mode T causes nut / piston 170 to translate away from spindle 84 in direction D along axis 202 and toward first brake pad BP1. Continued rotation of spindle 84 in mode T eventually causes nut 170 to engage first brake pad BP1 and move the first brake pad against brake rotor in direction D. In response to the reaction forces acting inside actuator assembly 10 and brake caliper housing 20, and the force acting on first brake pad BP1, second brake pad BP2 is also pressed against brake rotor, thereby braking the vehicle.

[0048] As the nut 170 moves toward the first brake pad BP1 in direction D, the cage 140 and the bearing balls 130 both travel axially relative to the spindle 84 in direction D together with the nut 170. More specifically, the cage 140 travels axially away from the initial or starting position of its adjacent washer 190 along with the nut 170, thereby disengaging from the washer 190. Simultaneously, the cage 140 and the bearing balls 130 both travel / rotate in direction T together with the spindle 84. Due to the rolling of the bearing balls 130 when clamping force is generated, in one example, the movement of the cage 140 and the bearing balls 130 relative to the spindle 84 and the nut 170 is approximately half the rotation of the spindle 84 and half the axial travel of the nut 170, respectively.

[0049] Axial movement of the cage 140 and nut 170 causes flange 148 to push against the bias of spring 164, pushing flange 158 on end cap 152. As flange 148 of the cage 140 pushes flange 158, the cage 140 and end cap 152 travel together due to thrust bearing assembly 168 (which adapts to rotation and has minimal reverse torque) and spring 164 (which adapts to axial travel), without relative movement between them. Finally, overcoming the bias of spring 164, end cap 152 moves axially relative to spindle 84 from its initial / starting position, thereby compressing spring 164 between end cap 152 and spacer 166 and creating a gap between end cap flange 158 and spindle 84. In other words, applying a brake loads the cage return mechanism 150.

[0050] During the axial translation of the nut 170 along the spindle 84, the bearing balls 130 are forced to travel through corresponding track windings 120, 180 while maintaining connection with the spindle 84. Finally, the bearing balls 130 have a fixed position relative to the cage 140, but when the spindle 84 rotates and the nut 170 translates axially, the bearing balls 130 rotate within the opening 146. The bearing balls 130 are supported between the spindle 84 and the nut 170 with clearance to facilitate relative movement between the spindle and the nut.

[0051] In other words, under relatively low clamping loads, although the bias load on spring 164 is not yet achieved through the loads generated at cage 140 and end cap 152, bearing balls 130 have a sliding friction interface with track windings 180. When the load on bearing balls 130 increases due to the load causing piston 170 to slide and / or the clamping load increases to the point of overcoming the bias of spring 164, bearing balls 130 transition to a rolling friction interface with track windings 120, 180. Simultaneously, the tapered / truncated tapered interface between flanges 148, 158 helps prevent relative rotation between flanges 148, 158 during brake application (i.e., whenever braking force is applied). Therefore, the interface between flanges 148, 158 allows compression spring 164 to become and remain loaded as long as the brake is applied to a certain minimum extent. Specifically, the reaction force generated by applying braking is sufficient to prevent relative rotation between flange 158 and flange 148, thus biasing flange 158 into engagement with flange 148.

[0052] When the desired clamping force is generated on the rotor, the rotation of the motor 28 stops. In this case, when the vehicle decelerates at a speed desired by the vehicle driver or the autonomous system controlling the vehicle, the motor 28 remains energized and maintains the desired clamping force.

[0053] Subsequently, to release the clamping force, the motor 28 is commanded to rotate in the opposite direction (opposite to direction T) at a rate desired by the vehicle driver or autonomous system. As the clamping force decreases, at a predetermined low clamping force, the spring 164 carries a sufficient load to force the cage 140 and bearing balls 130 back to their original or initial position via the end cap 152, where the end cap 152 abuts the spindle 84. More specifically, the bias of the spring 164 at the predetermined low clamping force is now sufficiently large to overcome the friction between the bearing balls 130 and the track windings 120, 180, thereby forcing the cage 140 and bearing balls 130 back to their original or initial position.

[0054] The predetermined low clamping force is also consistent with the fact that the reaction force from the clamping force is lower than the compression spring force, thus allowing the compression spring 164 to expand and thereby push the cage 140 [through the contact at flanges 148, 152], causing the cage to rotate toward its original position. Specifically, since the spacer 166 has a fixed position relative to the spindle 84, the spring 164 automatically expands upward (as shown) to push the end cap 152 toward the spindle 84 [in the direction opposite to direction D] and reduce the clearance. As the end cap 152 moves toward the spindle 84, the flange 158 pushes the cage 140 and bearing balls 130 back towards... Figure 5 The starting position is shown.

[0055] Understandably, since flange 158 extends radially beyond flange 148 on cage 140, the force generated by the flange on cage is distributed parallel and uniformly around axis 88 of spindle 84. In other words, during the return stroke of the cage back to the starting position, cage return mechanism 150 does not apply lateral (in this case radial) force to cage 140. This ensures that cage 140 maintains a uniform or substantially uniform radial spacing between spindle 84 and nut 170, thereby maximizing the efficiency of bearing balls 130 rolling within track windings 120, 180 and returning the cage to the starting position.

[0056] Additionally, under the predetermined low clamping force, the bearing balls 130 roll within the track winding portions 120 and 180, but since the spindle 84 and nut 170 are stationary, the cage 140 rotates relative to the spindle 84 and nut 170 about axis 202. The spring 164 expands to rotate the cage 140 until the flange 158 of the end cap 152 abuts the second end 87 of the spindle 84, causing the cage and bearing balls 130 to return to their original positions. Figure 5 The starting position. In other words, stopping the application of brakes at a lower than predetermined clamping force will cause / allow the cage return mechanism 150 to unload and automatically return the cage 140 to its initial position.

[0057] Once the braking operation is complete, the motor 28 rotates in the opposite direction, causing the spindle 84 to rotate in the opposite direction to direction T (clockwise as shown in the figure). It can be understood that by operating the motor 28, the nut 170 is moved to the retracted position, which is associated with lifting the first brake pad BP1 and the second brake pad BP2 away from the brake rotor.

[0058] Understandably, as brake pads BP1 and BP2 wear over time, the distance between the end of nut 170 and its first brake pad BP1 will typically increase over time. Since nut 170 has a limited range of travel relative to spindle 84, for example, from approximately 5 mm to approximately 7 mm, the effectiveness of spindle assembly 74 in braking the vehicle will decrease over time without adjustment during use.

[0059] Keeping this in mind, the return position of the nut / piston 170 will automatically adjust over time. Specifically, as the brake pads BP1 and BP2 wear, the return position of the nut 170 will drift / displace in the direction toward the brake pads to ensure that the travel distance required to apply braking is constant or substantially constant over time. This movement is achieved, for example, by sensing the feedback current of the motor 28 and adjusting its retraction accordingly. When the motor 28 completes its retraction target, the load at the first brake pad BP1 is reduced to substantially zero, specifically as described in the previous paragraphs, and therefore, the cage 140 and the integrated bearing balls 130 are repositioned to their initial positions due to the preloaded spring 164.

[0060] In other words, due to the interaction between the retainer return mechanism 150 and the retainer 140, the retainer returns to the same starting position regardless of any movement of the nut 170. The specific position of the bearing balls 130 within the track winding section 120 will change before braking to account for the axial movement of the nut 170 relative to the retainer 140, thus taking into account brake pad wear. In other words, the operation of the retainer return mechanism 150 remains unchanged throughout the lifespan of the brake pads BP1 and BP2.

[0061] exist Figures 7 to 8 A second configuration of the cage return mechanism 150a is shown. Figures 7 to 8In this configuration, the biasing member is constructed as a combined torsion / compression spring 210, having a first end 212 fixed to a bearing 220 and a second end 214 connected to a support member 230. Both the bearing 220 and the support member 230 extend along a shaft 161. The bearing 220 extends through an opening 156 in an end cap 152 and downward along the shaft 161. A pin 234 extends through an opening 232 in the shaft 161 and abuts the bearing 220 to prevent rotation of the bearing relative to the shaft in one direction, but allows rotation of the bearing relative to the shaft in the opposite direction to load the spring 210 during braking operations. The pin 234 also helps to support the preload torque from the torsion spring 210.

[0062] Bearing 220 is configured to support lateral loads generated during braking applications by loading torsion spring 210. Bearing 220 also helps to keep torsion spring 210 concentric with shaft 161 of shaft 160. Support member 230 is splined to head 162 of shaft 160 to prevent relative rotation between them. That is, ends 212, 214 of torsion spring 210 are held by corresponding members 220, 230.

[0063] During braking, spindle 84 rotates together with shaft 160 and support member 230 in mode T to advance nut 170 in direction D, thereby applying brake pad BP1 to the rotor. For this purpose, as noted, end cap 152 is preloaded against the end of spindle 84, and therefore, end cap 152 also experiences the rotation of the spindle. Keeping this in mind, at the start of braking, components 84, 152, 162, 230, 220, and 210 will all rotate together. If there is a small axial clearance between flanges 148 and 158, ball 130 will rotate somewhat and cage 140 will advance until contact is established between the flanges.

[0064] When contact is formed between flanges 148 and 158, the cage 140 is prevented from rotating, thereby preventing the ball 130 from rolling within the winding portions 120 and 180. This then forces the ball 130 to slide between the piston / nut 170 until the load on the nut reaches a predetermined amount, at which point the ball will begin to roll. Specifically, the ball 130 will roll when the movement of the nut 170 is resisted by sufficient force to force the ball to be "squeezed" between the winding portions 120 and 180 of the spindle 84 and the piston 170. When this load is high enough (reaching the predetermined amount), sliding is no longer possible, and the ball 130 will roll. As the ball 130 rolls, the cage 140 must move to allow the ball 130 to roll along the winding portions 120 and 180 to a new position.

[0065] Before the ball bearing 130 begins to roll, the end cap 152 has no relative movement with respect to the spindle 84. However, when the ball bearing 130 begins to roll, the rotation of the cage 140 will be slower than that of the spindle 84—the cage will lag. Since the cage 140 rotates slower than the spindle 84, and the cage is connected to the support member 230, the support member will also have a slower rotational speed than the spindle 84. This speed difference will cause an increase in the potential energy of the torsion spring 210. In other words, the second end 214 of the torsion spring 210 is wound more tightly relative to the first end 212, thereby loading the torsion spring when a clamping force is generated between the brake pads BP1 and BP2.

[0066] At the same time, the ball retainer 140 pushes the flange 158 of the end cap 152 in direction D, thereby causing the first end 212 of the bearing 220 and the torsion spring 210 to move axially toward the brake pad BP1 and relative to the shaft 160 and the support member 230.

[0067] As in the previous example, the rotation of the motor 28 in this example stops when the desired clamping force is generated on the rotor. In this case, the motor 28 remains energized and maintains the desired clamping force as the vehicle decelerates at a speed desired by the vehicle driver or the autonomous system controlling the vehicle.

[0068] Subsequently, to release the clamping force, the motor 28 is commanded to rotate in the opposite direction (opposite to direction T) at a rate desired by the vehicle driver or autonomous system. As the clamping force decreases, under a predetermined low clamping force (at which point the load on the bearing balls 130 decreases toward zero), the torsion spring 210 contains a sufficient load to force the cage 140 and bearing balls 130 back to their initial position or starting position adjacent to the mandrel 84 via the end cap 152. More specifically, the bias of the spring 210 is large enough to overcome the friction between the bearing balls 130 and the track windings 120, 180, thereby repositioning the cage 140 and bearing balls 130 back to their initial position or starting position.

[0069] Because the support member 230 has a fixed position relative to the spindle 84, the torsion spring 210 automatically expands / unfolds upward (as shown) to push the end cap 152 toward the spindle 84 and reduce the gap. As the end cap 152 moves toward the spindle 84, the flange 158 pushes the cage 140 and the bearing balls 130 backward toward the starting position.

[0070] It should be understood that since flange 158 extends radially beyond flange 148 on cage 140, the direction of the force exerted by the flange on cage is parallel to the axis 88 of spindle 84. In other words, during the return stroke of the cage back to the starting position, cage return mechanism 150a does not exert a lateral (in this case, radial) force on cage 140. This ensures that cage 140 maintains a uniform or substantially uniform radial spacing between spindle 84 and nut 170, thereby maximizing the efficiency of bearing balls 130 rolling within track winding portions 120, 180 and returning the cage to the starting position.

[0071] Furthermore, it should be understood that the conical / truncated conical interface between the peripheries / ranges of flanges 148 and 158 helps ensure that the two components are fixed to each other as long as a clamping load is present at the first brake pad BP1. That is, the interface ensures that flanges 148 and 158 do not move relative to each other during brake application, thereby ensuring the transmission of torsional and axial forces so that the torsion spring 210 can become and remain loaded during brake application so that the retainer 140 automatically returns to its initial position upon brake release, i.e., when the clamping load drops to zero.

[0072] Additionally, under the predetermined low clamping force, the bearing balls 130 roll within the track winding portions 120 and 180, but since the spindle 84 and nut 170 are stationary, the cage 140 rotates relative to the spindle 84 and nut 170 about axis 202. The torsion spring 210 expands to rotate the cage 140 until the flange 158 of the end cap 152 abuts the second end 87 of the spindle 84, returning the cage and bearing balls 130 to their initial position. In other words, stopping the applied brake causes / allows the cage return mechanism 150a to unload the cage 140 and automatically return it to its initial position.

[0073] Once the braking operation is complete, the motor 28 rotates in the opposite direction, causing the spindle 84 to rotate in the opposite direction to direction T (clockwise as shown in the figure). It can be understood that by operating the motor 28, the nut 170 is moved to the retracted position, which is associated with lifting the first brake pad BP1 and the second brake pad BP2 away from the brake rotor.

[0074] Understandably, in both configurations of the biased component, the preload level of the biased component can be adjusted. Figures 5 to 6 In the example shown, the thickness of the spacer (in direction D) can be adjusted to change the degree to which the compression spring is preloaded. Figures 7 to 8In the example shown, the spline connection between the head of the support member and the shaft allows the rotational position of the support member to be set / adjusted before braking. Therefore, the degree to which the torsion spring is preloaded can be selected by choosing which splines on the mating components engage with each other.

[0075] The advantage of this invention lies in the specific dimensions and construction of the track windings and bearing balls to precisely indicate when the cage return mechanism can automatically return the cage to its original or starting position during braking operation. For this purpose, the bearings are specifically sized to have a diameter slightly smaller than the diameter of each track winding on which it rolls / slides, ensuring that the bearing balls are precisely unloaded when the braking force is removed (or reaches a predetermined, nominal amount). Specifically, the bearing balls are allowed to roll and slide within the track windings during braking application or release. This helps ensure that when the load on the bearing balls 130 decreases to substantially zero load upon brake release, the cage return mechanism quickly and accurately returns the cage to its original position.

[0076] Furthermore, current non-recirculating ball nut assemblies (nrBNA) are preloaded sufficiently to allow the piston to slip under braking forces of up to 100 or 200 N during an applied event. This is because the piston in these nrBNA designs can only travel axially a maximum of approximately 2.0 mm under load, and therefore, clamping force must be applied immediately once the balls begin rolling; otherwise, most / all of the piston stroke is “wasted,” occupying the air gap. In other words, in these current nrBNA designs, the short piston stroke requires a relatively large preload to initiate braking as quickly as possible during the stroke.

[0077] On the other hand, the much longer loading stroke (ball rolling stroke) of the nrBNA of the present invention (e.g., up to about 7 mm) means that the cage is preloaded at a much lower level—primarily to reset the cage after the applied event. In other words, the preload is not configured to help apply braking force quickly, but simply to reset the cage when needed. Therefore, the cage preload in the present invention can be much lower than the cage preload required in current nrBNAs. Along the same line, the much larger loading stroke in the present invention allows the nrBNA to transition to the ball rolling stroke almost immediately during a braking application event, because the long stroke of 7 mm can accommodate the gap between the bushing and the rotor, and still has a sufficiently large stroke to apply high clamping loads.

[0078] Another advantage of this invention is that replacing the standard circulating spindle assembly with a non-circulating configuration improves the mechanical efficiency of the spindle assembly. Specifically, during brake application or release, the cage return mechanism does not apply lateral loads to the ball cage, nor does it eliminate any metal-to-metal sliding friction, thereby reducing drag loss and minimizing efficiency loss. For this purpose, the use of the cage and bearing balls eliminates / prevents any direct contact between the spindle and nut, and between the cage and the spindle or nut—all relative rotation between components occurs via the bearing balls. Furthermore, the typically present ball return / circulation feature can be omitted.

[0079] The examples described above are examples of the invention. It is certainly impossible to describe every conceivable combination of components or methods for the purposes of describing the invention, but those skilled in the art will recognize that many other combinations and arrangements of the invention are possible. Therefore, the invention is intended to include all such changes, modifications, and variations that fall within the spirit and scope of the appended claims.

Claims

1. A ball nut assembly for an actuator assembly of a vehicle brake, the ball nut assembly comprising: A mandrel, rotatable about an axis, and including an outer track winding extending around the mandrel and an inner recess extending axially into the mandrel; A piston integrated with a nut, the piston including an inner rail winding and positioned on the spindle so as to move along the axis in response to rotation of the spindle, thereby applying the vehicle brake; A retainer disposed between the track winding portions and including an opening for receiving bearing balls, the bearing balls being sized to be free from at least one of rolling interference and sliding interference within the track winding portions; and A cage return mechanism is disposed in the recess of the spindle, wherein the cage, together with the nut, moves axially and rotationally relative to the spindle in a first direction from a starting position to load the cage return mechanism in response to the application of braking, and wherein, in response to the release of the vehicle brake, the cage return mechanism unloads to automatically move the cage back to the starting position in the opposite second direction.

2. The ball nut assembly according to claim 1, wherein, The cage return mechanism includes: An end cap, wherein the end cap is disposed in the recess of the mandrel; A biasing member for biasing the end cap toward the mandrel; A thrust bearing, wherein the thrust bearing is used to allow the end cap to rotate generally freely; and A shaft for connecting the end cap and the biasing member to the spindle, wherein, in response to applying a brake, the retainer moves the end cap in a first direction against the biasing force of the biasing member, and wherein, in response to releasing the vehicle brake, the biasing member automatically moves the end cap in a second direction to return the retainer to the starting position.

3. The ball nut assembly according to claim 2, wherein, The biasing component includes a compression spring.

4. The ball nut assembly according to claim 2, wherein, The biasing component includes a torsion spring.

5. The ball nut assembly according to claim 4, wherein, The cage return mechanism further includes: A support member, fixed to the shaft and receiving a first end of the torsion spring; and A bearing that is movable relative to the shaft together with the end cap and receives the second end of the torsion spring.

6. The ball nut assembly according to claim 5, wherein, The shaft is screwed into the mandrel, and the biasing member surrounds the shaft.

7. The ball nut assembly according to claim 5, wherein, The support member and the shaft have a spline connection, thereby allowing adjustment of the preload on the torsion spring.

8. The ball nut assembly according to claim 2, wherein, The end cap includes a flange that engages with a flange on the cage to prevent relative rotation between them during braking.

9. The ball nut assembly according to claim 8, wherein, The flange is truncated conical.

10. The ball nut assembly according to claim 2, wherein, The end cap includes: a base disposed in the recess; and a flange extending radially outward to the end surface of the mandrel to engage the retainer.

11. The ball nut assembly according to claim 1, wherein, The bearing balls do not circulate within the track winding section.

12. The ball nut assembly according to claim 1, wherein, When the load on the piston is lower than a predetermined amount, the bearing ball has a sliding interface with the track winding portion, and when the load on the piston reaches the predetermined amount, the bearing ball has a rolling interface with the track winding portion.

13. The ball nut assembly according to claim 11, wherein, The piston has a single-stroke axial movement of up to 7 mm in each braking event.

14. The ball nut assembly according to claim 11, wherein, The cage return mechanism does not apply braking until the bearing balls begin to engage with the rolling interface of the track winding.

15. A ball nut assembly for an actuator assembly of a vehicle brake, the ball nut assembly comprising: A mandrel, rotatable about an axis, and including an outer track winding extending around the mandrel and an inner recess extending axially into the mandrel; A piston integrated with a nut, the piston including an inner rail winding and positioned on the spindle so as to move along the axis in response to rotation of the spindle, thereby applying the vehicle brake; A retainer, the retainer being disposed between the track winding portions and including a flange and an opening for receiving bearing balls, the bearing balls being sized to be free from at least one of rolling interference and sliding interference within the track winding portions; A cage return mechanism, wherein the cage return mechanism is disposed in the recess of the mandrel, the cage return mechanism comprising: An end cap having: a base disposed in a recess of the spindle; and a flange extending radially outward to an end surface of the spindle for engaging with a flange on the cage to prevent relative rotation between them during braking. A biasing member for biasing the end cap toward the mandrel; A thrust bearing, wherein the thrust bearing is used to allow the end cap to rotate generally freely; and A shaft, fixed to the spindle, is used to connect the end cap and the biasing member to the spindle, wherein the cage, together with the nut, moves axially and rotationally relative to the spindle in a first direction from a starting position in response to the application of braking to load the cage return mechanism, and wherein, in response to the release of the vehicle brake, the cage return mechanism unloads to automatically move the cage back to the starting position in the opposite second direction.

16. The ball nut assembly according to claim 15, wherein, The biasing component includes a compression spring.

17. The ball nut assembly according to claim 15, wherein, The biasing component includes a torsion spring.

18. The ball nut assembly according to claim 17, wherein, The cage return mechanism further includes: A support member, fixed to the shaft and receiving a first end of the torsion spring; and A bearing that is movable relative to the shaft together with the end cap and receives the second end of the torsion spring.

19. The ball nut assembly according to claim 18, wherein, The support member and the shaft have a spline connection, thereby allowing adjustment of the preload on the torsion spring.

20. The ball nut assembly according to claim 18, wherein, The flange is truncated conical.

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