Hydraulic brake wear detection apparatus and method

A hydraulic brake wear detection apparatus and a method for detecting a degree of pad wear of a brake pad of a hydraulic brake includes a caliper piston located at least partially within a caliper cavity and attached to the brake pad. The caliper piston includes a piston cavity extending from a caliper piston rim into a caliper piston body at a location longitudinally opposite, and spaced from, the brake pad. An internal piston is located at least partially within the piston cavity and is entirely enclosed in an internal space defined cooperatively by the piston cavity and the caliper cavity for reciprocal longitudinal motion with respect to the internal space. The internal piston is reciprocated by a predetermined volume of pressurized hydraulic fluid responsive to wear of the brake pad.

TECHNICAL FIELD

This disclosure relates to an apparatus and method for hydraulic brake wear detection and, more particularly, to a method of, and apparatus for detecting a degree of pad wear of a brake pad of a hydraulic brake including the brake pad, a brake rotor, and a caliper housing at least partially enclosing the brake pad and brake rotor for relative longitudinal motion therebetween,

BACKGROUND

Traditional service braking systems of a vehicle are typically hydraulic fluid based systems actuated by a driver depressing a brake pedal that generally actuates a master cylinder. In turn, the master cylinder pressurizes hydraulic fluid in a series of hydraulic fluid lines routed to respective actuators at brakes located adjacent to each wheel of the vehicle. Such hydraulic braking may be supplemented by a hydraulic modulator assembly that facilitates anti-lock braking, traction control, and vehicle stability augmentation features. The wheel brakes may be primarily operated by the manually actuated master cylinder with supplemental actuation pressure gradients supplied by the hydraulic modulator assembly during anti-lock, traction control, and stability enhancement modes of operation. Hydraulic brake systems are known to include dedicated brake wear sensors (e.g., clip-on sensors) generally placed upon or secured to the brake pad itself for detecting brake wear. Unfortunately, such clip-on sensors may not be robust, are costly, and may require replacement with worn brake pads.

More recent brake designs may include brake assemblies with an electromechanical park brake feature as part of the actuator. With such a feature, the driver merely presses a button to electrically actuate the brakes into a park brake mode. Additionally, recent brake system designs may be devoid of any hydraulics. Such systems are often known as brake-by-wire (BBW) systems that electrically actuate the brakes during both service and park brake modes of operation. Such systems with electro-mechanical attributes may still include the clip-on sensors already used for hydraulic systems to determine brake pad wear, with the same disadvantages thereof.

SUMMARY

In an aspect, a hydraulic brake wear detection apparatus for detecting a degree of pad wear of a brake pad of a hydraulic brake is disclosed. The hydraulic brake includes the brake pad, a brake rotor, and a caliper housing at least partially enclosing the brake pad and brake rotor for relative longitudinal motion therebetween. The caliper housing defines a caliper cavity in selective fluid communication with a reservoir of brake fluid and with a source of pressurized hydraulic fluid via a caliper passage. The brake wear detection apparatus comprises a caliper piston located at least partially within the caliper cavity and attached to a first side of the brake pad. The caliper piston is configured for reciprocal longitudinal motion with respect to the brake rotor to selectively place a second side of the brake pad, longitudinally opposite the first side of the brake pad, into contact with the brake rotor to provide a braking action thereto. The caliper piston includes a piston cavity extending from a caliper piston rim into a caliper piston body at a location longitudinally opposite, and spaced from, the brake pad. An internal piston is located at least partially within the piston cavity and is entirely enclosed in an internal space defined cooperatively by the piston cavity and the caliper cavity for reciprocal longitudinal motion with respect to the internal space. The internal piston is reciprocated by a predetermined volume of pressurized hydraulic fluid responsive to wear of the brake pad.

In an aspect, a method of detecting a degree of pad wear of a brake pad of a hydraulic brake is disclosed. The hydraulic brake includes the brake pad, a brake rotor, and a caliper housing at least partially enclosing the brake pad and brake rotor for relative longitudinal motion therebetween. The caliper housing defines a caliper cavity in selective fluid communication with a reservoir of brake fluid and with a source of pressurized hydraulic fluid via a caliper passage. A hydraulic brake wear detection apparatus is provided. The hydraulic brake wear detection apparatus includes a caliper piston located at least partially within the caliper cavity and attached to a first side of the brake pad. The caliper piston includes a piston cavity extending from a caliper piston rim into a caliper piston body at a location longitudinally opposite, and spaced from, the brake pad. The hydraulic brake wear detection apparatus includes an internal piston located at least partially within the piston cavity and entirely enclosed in an internal space defined cooperatively by the piston cavity and the caliper cavity. A normally open venting valve is interposed in the caliper passage hydraulically between the reservoir and both the source of pressurized hydraulic fluid and the caliper cavity. The caliper piston is moved reciprocally longitudinally with respect to the brake rotor to selectively place a second side of the brake pad, longitudinally opposite the first side of the brake pad, into contact with the brake rotor to provide a braking action thereto during a normal non-failure braking mode of operation. The internal piston is moved reciprocally longitudinally with respect to the internal space via a predetermined volume of pressurized hydraulic fluid responsive to wear of the brake pad. The normally open venting valve is selectively closed to isolate the predetermined volume of pressurized hydraulic fluid from the reservoir of brake fluid and thus provide a closed hydraulic loop between the source of pressurized hydraulic fluid and the caliper cavity to place the hydraulic brake wear detection apparatus into a detection mode of operation at least partially having the brake pad advanced into contact with the brake rotor. With the hydraulic brake wear detection apparatus in the detection mode of operation, the internal piston is retracted longitudinally away from the brake rotor into a detection piston position by the provision of negatively pressurized hydraulic fluid to the caliper cavity. With the hydraulic brake wear detection apparatus in the detection mode of operation, the negatively pressurized hydraulic fluid within the caliper cavity is rebalanced to a neutral level. With the hydraulic brake wear detection apparatus in the detection mode of operation, the internal piston is advanced longitudinally toward the brake rotor and out of the detection piston position by provision of the predetermined volume of pressurized hydraulic fluid to the internal space. After the predetermined volume of volume of pressurized hydraulic fluid is in the internal space, the hydraulic brake wear detection apparatus is returned to a service mode of operation. A pad wear status of the brake pad is determined, responsive to the predetermined volume of pressurized hydraulic fluid provided to the internal space with the hydraulic brake wear detection apparatus in the detection mode of operation.

In an aspect, a method of detecting a degree of pad wear of a brake pad of a hydraulic brake is disclosed. The hydraulic brake includes the brake pad, a brake rotor, and a caliper housing at least partially enclosing the brake pad and brake rotor for relative longitudinal motion therebetween. The caliper housing defines a caliper cavity in selective fluid communication with a reservoir of brake fluid and with a single-acting plunger type power transmission unit via a caliper passage. The method includes providing a hydraulic brake wear detection apparatus including a caliper piston located at least partially within the caliper cavity and attached to a first side of the brake pad. The caliper piston includes a piston cavity extending from a caliper piston rim into a caliper piston body at a location longitudinally opposite, and spaced from, the brake pad. The hydraulic brake wear detection apparatus includes an internal piston located at least partially within the piston cavity and entirely enclosed in an internal space defined cooperatively by the piston cavity and the caliper cavity. Pressurized hydraulic fluid is selectively provided via reciprocal longitudinal motion of a plunger of the power transmission unit. A normally open venting valve is interposed in the caliper passage hydraulically between the reservoir and both the power transmission unit and the caliper cavity. The caliper piston is moved reciprocally longitudinally with respect to the brake rotor to selectively place a second side of the brake pad, longitudinally opposite the first side of the brake pad, into contact with the brake rotor to provide a braking action thereto during a normal non-failure braking mode of operation. With the hydraulic brake wear detection apparatus in a detection mode of operation at least partially having the brake pad advanced into contact with the brake rotor:(1) a predetermined volume of positively pressurized hydraulic fluid is supplied to the caliper cavity,(2) the normally open venting valve is closed to isolate the predetermined volume of pressurized hydraulic fluid from the reservoir of brake fluid and thus provide a closed hydraulic loop between the power transmission unit and the caliper cavity,(3) the plunger of the power transmission unit is retracted to responsively move the internal piston in a first longitudinal direction, away from the brake rotor, under influence of negatively pressurized hydraulic fluid,(4) the normally open venting valve is opened to allow hydraulic fluid from the reservoir to enter at least one of the caliper cavity and the caliper passage responsive to negative pressure therein, thus rebalancing the negatively pressurized hydraulic fluid within the caliper cavity to a neutral level by providing an augmented volume of hydraulic fluid within at least the caliper cavity and the caliper passage,(5) the normally open venting valve is closed to isolate the augmented volume of hydraulic fluid from the reservoir,(6) the plunger of the power transmission unit is advanced to responsively move the internal piston in a second longitudinal direction, toward the brake rotor, under influence of positively pressured hydraulic fluid of the augmented volume,(7) a wear-indicating volume measurement is sensed responsive to the plunger advancement of (6),(8) advancement of the plunger of the power transmission unit in (6) is ceased responsive to detection of a predetermined hydraulic pressure value in at least one of the caliper cavity, the power transmission unit, and the caliper passage,(9) the wear-indicating volume measurement is communicated to an electronic control unit, and(10) a degree of pad wear is determined responsive to the sensed wear-indicating volume measurement.

DESCRIPTION OF ASPECTS OF THE DISCLOSURE

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which the present disclosure pertains.

The invention comprises, consists of, or consists essentially of the following features, in any combination.

FIGS.1-2schematically depict a partial view of a brake system100including aspects of the present invention. The brake system100could be of any desired type such as, but not limited to, the brake system disclosed in U.S. patent application Ser. No. 17/366,682, filed 2 Jul. 2021 by Blaise A. Ganzel and titled “Apparatus and Method for Control of a Hydraulic Brake By Wire System”, which is hereby incorporated by reference in its entirety.

The brake system100includes a hydraulic brake wear detection apparatus102for detecting a degree of pad wear of at least one brake pad104of a hydraulic brake106. (While the brake system100shown in the Figures includes two brake pads104per brake, one of ordinary skill in the art will appreciate that the present hydraulic brake wear detection apparatus102can be used to detect wear of one or more brake pads104, or other consumable structures, of an associated hydraulic brake106. The hydraulic brake106includes the brake pad104, a brake rotor108, and a caliper housing110at least partially enclosing the brake pad104and brake rotor108for relative longitudinal motion therebetween. The “longitudinal” direction, as referenced herein, is substantially parallel to arrow “L”, which extends substantially horizontally, in the orientation ofFIGS.1-2. The caliper housing110defines a caliper cavity112in selective fluid communication with a reservoir114of brake fluid and with a source of pressurized hydraulic fluid via a caliper passage118. The source of pressurized hydraulic fluid may be, for example, a power transmission unit116of any desired type configured to provide both negatively and positively pressurized hydraulic fluid. For the sake of description, the power transmission unit116will be described herein as being described herein as being a single-acting plunger type power transmission unit116, but one of ordinary skill in the art will readily be able to provide a suitable source of pressurized hydraulic fluid for a particular use environment.

A caliper piston120is located at least partially within the caliper cavity112and is attached to a first side122of the brake pad104. The caliper piston120is configured for reciprocal longitudinal motion with respect to the brake rotor108to selectively place a second side124of the brake pad104, longitudinally opposite the first side122of the brake pad104, into contact with the brake rotor108to provide a braking action to the brake rotor108. The caliper piston120includes a piston cavity126extending from a caliper piston rim128into a caliper piston body130at a location longitudinally opposite, and spaced from, the brake pad104. That is, the caliper piston120is of a “cup” shape, with the closed end of the “cup” pressing against the first side122of the brake pad104to apply the brake. Optionally, and as shown herein, a relief space132may be provided to assist with venting of at least a portion of the hydraulic brake106as desired (e.g., as shown herein, venting an air pocket that may occur under the internal piston138).

As shown in the Figures, the caliper housing110may include an annular groove134in fluid communication with the caliper cavity112and circumferentially surrounding the caliper piston body130. A caliper piston seal136is retained at least partially within the annular groove134for concurrent contact with the caliper housing110and an outer surface of the caliper piston body130. Also as shown in the Figures, the caliper piston seal136, when present, may have a substantially square cross section and be configured to bias the caliper piston120longitudinally away from the brake rotor108under shear force. This known “seal rollback” feature can help pull back the brake pad104away from the brake rotor108when the braking pressure is released, to end the brake application event.

In addition, in the depicted brake system100including the hydraulic brake wear detection apparatus102, use of the caliper piston seal136can allow for intentional “walking” of the caliper piston120toward the left, in the orientation of the Figures, as the brake pad104wears and thins. This “walking” or shifting of the caliper piston120with respect to the caliper piston seal136can be seen in the schematic depiction of the relatively unworn brake pad104ofFIG.1to the thinner, more worn brake pad104ofFIG.2. It should be noted that the Figures of the present application are not drawn to scale, but the brake pad104ofFIG.1is shown as having a first thickness T1, which is larger than the worn thickness T2shown inFIG.2for the same brake pad104after some time period of operation of the brake system100.

An internal piston138of the hydraulic brake wear detection apparatus102is located at least partially within the piston cavity126formed in the caliper piston120. The internal piston138is entirely enclosed in an internal space140defined cooperatively by the piston cavity126and the caliper cavity112. The internal piston138is configured for reciprocal longitudinal motion with respect to the internal space140. For example, and as shown in the Figures, the internal piston138may be free-floating within the piston cavity126. In such an arrangement, the internal piston138may be urged longitudinally leftward and rightward (in the orientation of the Figures) within the internal space140responsive to flow of pressurized hydraulic fluid into and out of the caliper cavity, respectively.

The internal piston138is reciprocated by a predetermined volume of pressurized hydraulic fluid responsive to wear of the brake pad. That is, a larger quantity of pressurized hydraulic fluid may be utilized to reciprocate the internal piston138along a full stroke range of motion when the brake pad104is in a more worn condition, than the quantity of pressurized hydraulic fluid which is used to reciprocate the internal piston138for a less worn brake pad104. This distinction will be discussed further below, but is schematically depicted by the difference in available internal space140being larger inFIG.2(with a relatively more worn brake pad104) than inFIG.1(with a relatively less worn brake pad104).

At least one of an internal wall of the piston cavity126and an external surface of the internal piston138may include an annular groove142in fluid communication with the internal space140of the piston cavity126and circumferentially surrounding the internal piston138. An internal piston seal144may be retained at least partially within the annular groove142, when present, for concurrent contact with the internal wall of the piston cavity126and the external surface of the internal piston138. The internal piston seal144, when present, may be configured to have lower frictional drag on the “sealed” components than would a seal having a square cross-section, such as the caliper piston seal136. For example, the internal piston seal144may be a lip seal in some use environments of the hydraulic brake wear detection apparatus102, which could (when present) be oriented to resist passage of relatively high pressure brake fluid directionally, as desired. The internal piston seal144assists with centering, guiding, and/or facilitating sliding longitudinal motion of the internal piston138with respect to the piston cavity126.

A normally open venting valve146may be interposed in the caliper passage118hydraulically between the reservoir114and both the source of pressurized hydraulic fluid (here, power transmission unit116) and the caliper cavity112. As a result, when present, the normally open venting valve146may be selectively closed to isolate the predetermined volume of pressurized hydraulic fluid (which is used to reciprocate the internal piston138) from the reservoir114of brake fluid and thus selectively provide a closed hydraulic loop, containing that predetermined volume of pressurized hydraulic fluid, between the power transmission unit116and the caliper cavity112, as will be described with reference to operation of the hydraulic brake wear detection apparatus102below.

A pressure sensor148, of any desired type, may be provided at any suitable location along the caliper passage118for selectively sensing pressure of the hydraulic fluid within that caliper passage118. The pressure sensor148may be particularly helpful in operation of the hydraulic brake wear detection apparatus102when the closed hydraulic loop is created by closure of the venting valve146, as just mentioned.

Turning now toFIG.3, a brake system100including a pair of hydraulic brake wear detection apparatuses102as previously described with reference toFIGS.1-2is depicted schematically. It is contemplated that one or more hydraulic brake wear detection apparatuses102may be provided to a brake system100, in a symmetrical or asymmetrical manner, as desired for a particular use environment. In the brake system100shown inFIG.3, hydraulic wheel brakes106R and106L are operatively associated, respectively, with selected right and left front wheels of a vehicle as labeled. Each of the hydraulic wheel brakes106includes the components previously described inFIGS.1-2such as, but not limited to, a brake pad104R,104L and a brake rotor108R,108L.

In the brake system100ofFIG.3, a single reservoir114is provided for selectively supplying hydraulic fluid to both the left front and right front wheel brakes106L,106R. At least one hydraulic brake wear detection apparatus102L,102R is interposed hydraulically between the reservoir114and the brake pad104L,104R of the corresponding hydraulic wheel brake106L,106R.

At least one power transmission unit116is configured to selectively supply pressurized hydraulic fluid to at least one hydraulic wheel brake106. At least one normally open venting valve146is interposed hydraulically between the reservoir114and both a corresponding power transmission unit116and a corresponding hydraulic wheel brake106. At least one pressure sensor148is provided to a corresponding caliper passage118. As shown inFIG.3by dashed boxes “R” and “L”, the left front hydraulic brake106L and the right front hydraulic brake106R are each associated with a corresponding, dedicated set of power transmission unit116L,116R, venting valve146L,146R, and pressure sensor148L,148R, for redundancy, ease of design, ease of control, or for any other desired reason.

An electronic control unit150may be provided to the brake system100and be configured to control operation of at least one of the power transmission units116L,116R, the venting valves146L,146R, and the hydraulic wheel brakes106L,106R. While one electronic control unit150is shown schematically inFIG.3as controlling operation of all four wheel brakes in that FIG., it is contemplated that a second electronic control unit, not shown, may be provided for redundancy, ease of control, or any other reason. For example, when a second electronic control unit is provided, each electronic control unit could control one power transmission unit116L,116R and the diagonally arranged one of any rear electromechanical brake that is provided.

Also as shown inFIG.3, the brake system100may include a deceleration signal transmitter152configured to produce a braking command signal responsive to at least one of actuation by a vehicle operator and actuation by an autonomous vehicle controller (not shown). That is, as shown inFIG.3, the deceleration signal transmitter152may include a brake pedal154which is manipulable by a vehicle operator to indicate a desired braking command. The deceleration signal transmitter152then translates that desired braking command from the vehicle operator into a braking command signal that is sent, in a wired or wireless manner, to other components of the brake system100for use in operating the hydraulic brakes106in a normal, non-failure braking mode. Alternatively, and particularly when the brake system100is incorporated into an at least partially autonomous vehicle, the autonomous vehicle controller may actuate the deceleration signal transmitter152or otherwise generate a suitable braking command signal responsive to a desired application or release of the hydraulic brakes106in the autonomous braking mode. The electronic control unit150, when present, controls at least one of the power transmission units116L,116R, the venting valves146L,146R, and the hydraulic wheel brakes106L,106R responsive to receiving the braking command signal, regardless of the source of that braking command signal.

At least one electromechanical wheel brake156may be operatively connected to a wheel of the vehicle spaced apart from a wheel with a corresponding hydraulic wheel brake106. In other words, the wheel(s) with a hydraulic wheel brake106(whether or not a hydraulic brake wear detection apparatus102is supplied to that wheel) is/are different from the wheel(s) with an electromechanical wheel brake156. In the brake system100shown inFIG.3, the electromechanical wheel brakes156L,156R are located on the left and right rear wheels of the vehicle, respectively. Each electromechanical wheel brake156L,156R, when present, may include a brake motor158configured for actuation by the electronic control unit150in a known manner responsive to the braking command signal. When two or more electronic control units150are provided to the brake system100, it is contemplated that each electromechanical wheel brake156may be controlled by the same electronic control unit150as the diagonally-located hydraulic wheel brake106, for redundancy (e.g., left-front and right-rear by one electronic control unit150, and right-front/left-rear by a second electronic control unit, when present.

It is contemplated that the brake system100may include any desired combination of hydraulic wheel brakes, power transmission unit types, multiplex features, control schemes, and any other configuration as desired by one of ordinary skill in the art for use with the hydraulic brake wear detection apparatus102.

Regardless of the particular nature of the brake system100, the hydraulic brake wear detection apparatus102as depicted inFIGS.1-3and described elsewhere herein may be used to carry out a method of detecting a degree of pad wear of a brake pad104the hydraulic brake106.FIG.4schematically depicts a flow chart for carrying out at least a portion of a method400of using the hydraulic brake wear detection apparatus102. In the method step402, a hydraulic brake wear detection apparatus102is provided. The above description of the hydraulic brake wear detection apparatus102in the brake system100in general will largely be omitted with reference to the method400herein, for brevity.

The method400recognizes that, as previously mentioned, a normally open venting valve146is interposed in the caliper passage118hydraulically between the reservoir114and both the source of pressurized hydraulic fluid (here, the power transmission unit116) and the caliper cavity112. In method step404, the caliper piston120is moved reciprocally longitudinally with respect to the brake rotor108to selectively place a second side124of the brake pad104, longitudinally opposite the first side122of the brake pad104, into contact with the brake rotor108. In this way, the brake system100provides a braking action to the brake rotor108, which is used to retard rotational motion of the attached wheel as desired during a normal non-failure braking mode of operation. This method step404can include, for example, advancing a plunger of a power transmission unit116with the venting valve146in a closed position to “push” the caliper piston120leftward, in the orientation ofFIGS.1-2, and thereby advance the brake pad104toward the brake rotor108.

In method step406, the internal piston138is moved reciprocally longitudinally in at least one direction with respect to the internal space140via a predetermined volume of pressurized hydraulic fluid responsive to wear of the brake pad104. This reciprocal longitudinal motion of the internal piston138, as carried by the caliper piston120serves to apply and release the hydraulic brake106during normal non-failure operation of the braking system100.

In certain use environments, the internal piston138will be located adjacent to, or in contact with, the bottom of the piston cavity126“cup” at substantially all times during normal non-failure braking mode of operation of the brake system100. Since the caliper piston120“walks” longitudinally toward the brake rotor108as the brake pad104wears, one of ordinary skill in the art will understand that, in those selected use environments, the predetermined volume of pressurized hydraulic fluid within the caliper cavity112will gradually increase (albeit potentially a very slight increase, depending on dimensions and arrangement of the brake system100) as the brake pad104wears.

It should be noted that, as previously mentioned, a caliper piston seal136may be retained at least partially within an annular groove134of the caliper housing110. With the caliper piston seal136, the caliper piston120is biased longitudinally away from the brake rotor108under shear force, such as that developed during pressurized application of the brake pad104toward the brake rotor108during normal non-failure operation of the brake system100. The “walking” of the caliper piston120mentioned in the previous paragraph, as well as earlier in this application, has effective gradually shifting the caliper piston120longitudinally toward the brake rotor108with respect to the caliper piston seal136responsive to wear of the brake pad104. As a result of this longitudinal shift of the caliper piston136toward the brake rotor108, the internal volume of the caliper cavity112increases responsive to a longitudinal shift of the caliper piston120toward the brake rotor108.

In method step408, the normally open venting valve146is selectively closed to isolate the predetermined volume of pressurized hydraulic fluid from the reservoir114of brake fluid and thus provide a closed hydraulic loop between the source of pressurized hydraulic fluid (here, the power transmission unit116) and the caliper cavity112to place the hydraulic brake wear detection apparatus102into a detection mode of operation. The brake pad104is selectively advanced into contact with the brake rotor108for at least part of the detection mode of operation.

Turning now to method step410, with the hydraulic brake wear detection apparatus102in the detection mode of operation, the internal piston138is retracted longitudinally away from the brake rotor into a detection piston position (shown inFIG.2) by the provision of negatively pressurized hydraulic fluid to the caliper cavity112. For example, the power transmission unit116could be operated to provide suction upon the caliper passage120to pull the internal piston138rightward, in the orientation ofFIGS.1-2. When the power transmission unit116is of the aforementioned single-acting plunger type, method step410may include retracting the plunger of the power transmission unit116with the venting valve146in a closed position, to urge the internal piston138away from the brake rotor108. The term “negative pressure” is used herein to indicate a fluid pressure below atmospheric pressure, which tends to urge hydraulic fluid away from the affected component and toward a source of such pressure. As a result of this negative pressure or suction, the hydraulic brake wear detection apparatus102enters the configuration shown inFIG.2, the detection mode, with the internal piston138spaced apart from the bottom of the “cup” of the piston cavity126.

In method step412, and again with the hydraulic brake wear detection apparatus102in the detection mode of operation, the negatively pressurized hydraulic fluid within the caliper cavity112is rebalanced to a neutral level. This rebalancing may include, for example, selectively opening the venting valve146to allow flow of hydraulic fluid from the reservoir114through the venting valve146and into the caliper passage118under negative pressure from the power transmission unit116, when the plunger thereof is retracted. It should be noted that this rebalancing flow may also or instead facilitate desired collapse of a hydraulic fluid vapor bubble within the system, since the negative pressure application in method step410may have resulted in both liquid and vapor forms of the hydraulic fluid being present.

With reference now to method step414ofFIG.4, and still with the hydraulic brake wear detection apparatus102in the detection mode of operation, the internal piston138is advanced longitudinally toward the brake rotor108and out of the (rightmost, in the orientation ofFIGS.1-2) detection piston position by providing the predetermined volume of pressurized hydraulic fluid to the internal space140. For many use environments, the venting valve146will be closed before performance of method step414, to again isolate the reservoir114from a “closed loop” comprising the power transmission unit116, caliper passage118, and caliper cavity112. This advancement of the internal piston138may be at least partially accomplished, for example, by advancing the plunger of the power transmission unit116with the venting valve146in a closed position.

It should be noted that the predetermined volume of pressurized hydraulic fluid which is provided to the internal space140in method step414may be the same as, or different than, a predetermined volume of hydraulic fluid which is provided to various components of the hydraulic brake wear detection apparatus102during other phases of operation thereof.

The predetermined volume of pressurized hydraulic fluid provided to the internal space140in method step414will be described here as a “measured predetermined volume of pressurized hydraulic fluid”, since the hydraulic brake wear detection apparatus102measures or otherwise determines (directly or indirectly) how much hydraulic fluid is needed to advance the internal piston138a predetermined distance toward the brake rotor108. For example, once the internal piston138comes into proximity and/or contact with an internal “cup bottom” surface of the piston cavity126, further provision of pressurized hydraulic fluid will not move the internal piston138further, but will instead cause pressure within at least one of the internal space140and the caliper passage118to rise. That increase of pressure can be measured (e.g., via pressure sensor148), and the onset of the increase can be characterized as indicative of the internal space140being “full”. Since the amount of pressurized hydraulic fluid provided to the caliper passage118to move the internal piston138is known (e.g., via measurement of movement of the plunger of a single acting plunger-type power transmission unit116), one of ordinary skill in the art will be able to calculate the amount of longitudinal movement of the internal piston138which is allowed for a presently measured brake pad104wear condition, as compared to the amount of longitudinal movement of the internal piston138which would be permitted when the brake pad104is newly installed, and has a maximum thickness.

It is contemplated that the action of method step414may, in essence, result in application of the hydraulic brake106, by moving the caliper piston120sufficiently to urge the brake pad104toward—even into contact with—the brake rotor108. As a result, testing of the pad wear thickness via the detection mode of operation of the hydraulic brake wear detection apparatus102will often be done when the vehicle carrying the brake system100is stopped, and such testing may be accomplished as often as desired. For example, the test may be done about once every ignition cycle of the vehicle, such as at “key-off”, when the vehicle is stopped and in a “park” gear.

Returning now to the method shown inFIG.4, in method step416, after the (measured) predetermined volume of pressurized hydraulic fluid is in the internal space140, the hydraulic brake wear detection apparatus102is returned to a service, or normal non-failure braking, mode of operation. This return to a service mode of operation may include retraction of the caliper piston120, such as by the aforementioned rollback of the caliper piston seal136and/or by exertion of negative pressure upon hydraulic fluid within the caliper passage118by the power transmission unit116. It is contemplated, though, that for most use environments of the hydraulic brake wear detection apparatus102, the caliper piston seal136will be configured to exert enough friction against the caliper piston120during use that exertion of negative pressure will not be sufficient to overcome the seal force and retract the caliper piston120.

Finally, in method step418, the hydraulic brake wear detection apparatus102, or any other suitable component of the brake system100(e.g., an electronic control unit150) or the vehicle may determine, responsive to the (measured) predetermined volume of pressurized hydraulic fluid provided to the internal space140with the hydraulic brake wear detection apparatus102in the detection mode of operation, a pad wear status of the brake pad104. That pad wear status of the brake pad104could be communicated, in a wired or wireless manner, to at least one of a vehicle operator, an electronic control unit of the vehicle, a vehicle servicer, a vehicle manufacturer, a service database, a log file, or any other suitable recipient for pad wear status information.

In some use environments, a method of detecting a degree of pad wear of a brake pad104of a hydraulic brake106through use of a hydraulic brake wear detection apparatus102such as that shown and described in the present application could be performed, for example, in a manner similar to the following.

Pressurized hydraulic fluid may be selectively supplied via reciprocal longitudinal motion of a plunger of the power transmission unit116. A normally open venting valve146is interposed in the caliper passage118hydraulically between the reservoir114and both the power transmission unit116and the caliper cavity112. The caliper piston120is moved reciprocally longitudinally with respect to the brake rotor108to selectively place a second side124of the brake pad104, longitudinally opposite the first side122of the brake pad124, into contact with the brake rotor108to provide a braking action thereto during a normal non-failure braking mode of operation.

With the hydraulic brake wear detection apparatus102in a detection mode of operation which at least partially has the brake pad104advanced into contact with the brake rotor108, the following steps may be carried out such as, but not limited to, in the numerical order listed:(1) a predetermined volume of positively pressurized hydraulic fluid is supplied to the caliper cavity112,(2) the normally open venting valve146is closed to isolate the predetermined volume of pressurized hydraulic fluid from the reservoir114of brake fluid and thus provide a closed hydraulic loop between the power transmission unit116and the caliper cavity112,(3) the plunger of the power transmission unit116is retracted to responsively move the internal piston138in a first longitudinal direction, away from the brake rotor108, under influence of negatively pressurized hydraulic fluid,(4) the normally open venting valve146is opened to allow hydraulic fluid from the reservoir114to enter at least one of the caliper cavity112and the caliper passage118responsive to negative pressure therein, thus rebalancing the negatively pressurized hydraulic fluid within the caliper cavity112to a neutral level by providing an augmented volume of hydraulic fluid within at least the caliper cavity112and the caliper passage118,(5) the normally open venting valve146is closed to isolate the augmented volume of hydraulic fluid from the reservoir114,(6) the plunger of the power transmission unit116is advanced to responsively move the internal piston138in a second longitudinal direction, toward the brake rotor108, under influence of positively pressured hydraulic fluid of the augmented volume,(7) a wear-indicating volume measurement of hydraulic fluid is sensed or otherwise made, in any suitable manner, responsive to the plunger advancement of (6),(8) advancement of the plunger of the power transmission unit116in (6) is ceased responsive to detection of a predetermined hydraulic pressure value in at least one of the caliper cavity112, the power transmission unit116, and the caliper passage118,(9) the wear-indicating volume measurement is communicated to an electronic control unit150, and(10) a degree of pad wear is determined responsive to the sensed wear-indicating volume measurement.

The above example method may include a further step of (11) communicating the determined degree of pad wear to a designated observer.

After the completion of steps (1)-(10), whether or not the communication step of (11) is carried out, the normal non-failure brake mode of operation may be reinstated at least via the steps of:(12) opening the normally-open venting valve146to allow fluid flow between the reservoir114and at least one of the power transmission unit116, the caliper cavity112, and the caliper passage118; and(13) retracting the plunger in the first longitudinal direction to draw hydraulic fluid through the normally-open venting valve146from the reservoir114and thereby refill the power transmission unit116for the normal non-failure brake mode of operation.

As used herein, the singular forms “a”, “an”, and “the” can include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising”, as used herein, can specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.

It will be understood that when an element is referred to as being “on”, “attached” to, “connected” to, “coupled” with, “contacting”, “adjacent”, etc., another element, it can be directly on, attached to, connected to, coupled with, contacting, or adjacent the other element, or intervening elements may also be present. In contrast, when an element is referred to as being, for example, “directly on”, “directly attached” to, “directly connected” to, “directly coupled” with, “directly contacting”, or “directly adjacent” another element, there are no intervening elements present. It will also be appreciated by those of ordinary skill in the art that references to a structure or feature that is disposed “directly adjacent” another feature may have portions that overlap or underlie the adjacent feature, whereas a structure or feature that is disposed “adjacent” another feature might not have portions that overlap or underlie the adjacent feature.

Spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper”, “proximal”, “distal”, and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms can encompass different orientations of a device in use or operation, in addition to the orientation depicted in the figures. For example, if a device in the figures is inverted, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features.

As used herein, the phrase “at least one of X and Y” can be interpreted to include X, Y, or a combination of X and Y. For example, if an element is described as having at least one of X and Y, the element may, at a particular time, include X, Y, or a combination of X and Y, the selection of which could vary from time to time. In contrast, the phrase “at least one of X” can be interpreted to include one or more Xs.

While aspects of this disclosure have been particularly shown and described with reference to the example aspects above, it will be understood by those of ordinary skill in the art that various additional aspects may be contemplated. For example, the specific methods described above for using the apparatus are merely illustrative; one of ordinary skill in the art could readily determine any number of tools, sequences of steps, or other means/options for placing the above-described apparatus, or components thereof, into positions substantively similar to those shown and described herein. In an effort to maintain clarity in the Figures, certain ones of duplicative components shown have not been specifically numbered, but one of ordinary skill in the art will realize, based upon the components that were numbered, the element numbers which should be associated with the unnumbered components; no differentiation between similar components is intended or implied solely by the presence or absence of an element number in the Figures. Any of the described structures and components could be integrally formed as a single unitary or monolithic piece or made up of separate sub-components, with either of these formations involving any suitable stock or bespoke components and/or any suitable material or combinations of materials. Any of the described structures and components could be disposable or reusable as desired for a particular use environment. Any component could be provided with a user-perceptible marking to indicate a material, configuration, at least one dimension, or the like pertaining to that component, the user-perceptible marking potentially aiding a user in selecting one component from an array of similar components for a particular use environment. A “predetermined” status may be determined at any time before the structures being manipulated actually reach that status, the “predetermination” being made as late as immediately before the structure achieves the predetermined status. The term “substantially” is used herein to indicate a quality that is largely, but not necessarily wholly, that which is specified—a “substantial” quality admits of the potential for some relatively minor inclusion of a non-quality item. Though certain components described herein are shown as having specific geometric shapes, all structures of this disclosure may have any suitable shapes, sizes, configurations, relative relationships, cross-sectional areas, or any other physical characteristics as desirable for a particular application. Any structures or features described with reference to one aspect or configuration could be provided, singly or in combination with other structures or features, to any other aspect or configuration, as it would be impractical to describe each of the aspects and configurations discussed herein as having all of the options discussed with respect to all of the other aspects and configurations. A device or method incorporating any of these features should be understood to fall under the scope of this disclosure as determined based upon the claims below and any equivalents thereof.

Other aspects, objects, and advantages can be obtained from a study of the drawings, the disclosure, and the appended claims.