Patent Description:
Vehicular gearboxes usually include synchromesh devices to synchronize the speeds of the gearbox input shaft and of the shaft of the gear being selected.

A synchromesh device includes an externally toothed hub fixed to the input shaft and an internally toothed sleeve adapted to axially slide onto the external surface of the hub under the action of a driving mechanism.

The synchromesh device also includes a synchronizer ring arranged between the sleeve and one of the gearwheels of the selected gear. The synchronizer ring has an external surface provided with teeth arranged to interact axially with the internal teeth of the sleeve and an internal conical friction surface that is arranged to cooperate with a corresponding conical surface on the body of the adjacent gearwheel.

While the sleeve is moved toward the gearwheel, the internal teeth of the sleeve meet the external teeth of the synchronizer ring without meshing therewith. This causes the synchronizer ring to be pushed toward the gearwheel.

Hence, the sleeve presses the synchronizer ring against the body of the gearwheel, such that the friction between the cooperating conical surfaces causes a smooth acceleration of the gearwheel and of the corresponding shaft until the speed thereof approaches the one of the input shaft.

Here, when the speeds are synchronized, the external teeth of the synchronizer ring start to mesh with the internal teeth of the sleeve, such that the external teeth form an axial guide for the internal teeth.

Thus, the sleeve slides further toward the gearwheel until it reaches an engaging position, in which the gear is engaged.

It comes up that the synchronizer ring is a key component to assure a smooth gearshift without production of noise. However, the conical surface of the synchronizer ring is inevitably subject to wear.

Once the frictional material of the synchronizer ring is worn out, the synchronization become noisy and, even worse, the lubricating oil of the transmission starts to be contaminated by the lost frictional material.

Therefore, the need is felt to detect preventively a fault in progress of the synchromesh device before the wear conditions become compromised.

An aim of the invention is to satisfy the above-mentioned need.

<CIT> discloses a method for determining a wear condition of a synchronizer ring, wherein the synchronizer ring is associated with a gear stage of a shiftable transmission of an agricultural working machine, wherein the synchronizer ring is shifted during a synchronizing process from a neutral position into a synchronizing position, wherein the synchronizer ring in the synchronizing position bears with a friction surface against a gear wheel and wherein at least the synchronizing position is detected. The wear condition is determined by means of a comparison of the detected synchronization position with a reference synchronization position.

<CIT> discloses an estimation apparatus for a synchronization device provided with a gear, a synchronizing sleeve, a synchronizer ring, a stroke sensor that can detect a shift stroke amount of the synchronizing sleeve, a stroke difference calculation unit that calculates a stroke difference which is a difference between a shift stroke amount at the start of synchronization and a shift stroke amount at the end of a gear-in operation on the basis of the detection value of the stroke sensor acquired during the gear-in operation, and an abrasion estimation unit that estimates an abrasion amount or an abrasion degree of a synchronizing element of the synchronization device on the basis of the stroke difference.

The aforementioned aim is reached by a method and a system for monitoring wear of a synchromesh device, as claimed in the appended set of claims.

Dependent claims set out particular embodiments of the invention.

For a better understanding of the present invention, preferred embodiments are described in the following, by way of non-limiting examples, with reference to the attached drawings wherein:.

In <FIG>, reference numeral <NUM> indicates a vehicular gearbox including an external housing <NUM> and a synchromesh device <NUM> (shown in <FIG>) placed within the housing <NUM>.

As shown in <FIG>, the gearbox <NUM> further includes a system <NUM> within the housing <NUM> for monitoring wear of the synchromesh device <NUM>.

Synchromesh device <NUM> comprises a hub <NUM> that is rotationally fixed to a not shown input shaft of the gearbox <NUM>, in particular by means of a spline coupling. Making also reference to <FIG>, hub <NUM> has an axis A and an annular splined external surface <NUM>. In other words, hub <NUM> is externally toothed, i.e. is provided with external teeth <NUM>.

Synchromesh device <NUM> further comprises a sleeve <NUM> that is arranged around axis A in a radially external position with respect to hub <NUM>. Sleeve <NUM> is coupled to hub <NUM> in a rotationally fixed and axially movable manner; specifically, sleeve <NUM> is internally splined or has internal teeth <NUM> meshing with external teeth <NUM> to axially slide onto hub <NUM>.

Sleeve <NUM> and hub <NUM> are arranged between two gearwheels of gearbox <NUM>, of which only respective portions <NUM> are shown in <FIG> and <FIG>. The gearwheels are pertained to respective gears of gearbox <NUM> and are mounted on a same not shown output shaft of gearbox <NUM>. Portions <NUM> are provided with external teeth <NUM>, which are adapted to mesh with internal teeth <NUM> of sleeve <NUM>. In other words, the sleeve <NUM> can be axially moved toward any one of the portions <NUM> to be engaged therewith.

Synchromesh device <NUM> comprises an assembly <NUM> (schematically represented in <FIG>) adapted to drive the sleeve <NUM> axially. For example, the assembly <NUM> may include an actuator or a manually drivable mechanism.

In order to allow a smooth engagement between the sleeve <NUM> and any one of the portions <NUM>, synchromesh device <NUM> further comprises one synchronizer ring <NUM> for each portion <NUM> arranged between the sleeve <NUM> and the corresponding portion <NUM>. Like portions <NUM>, synchronizer rings <NUM> are identical to each other, whereby only one of them will be described hereinafter.

Synchronizer ring <NUM> has a splined external surface <NUM> or external teeth <NUM> that are configured to cooperate in contact with the internal teeth <NUM> of the sleeve <NUM> during an axial movement toward the corresponding portion <NUM>. Moreover, synchronizer ring <NUM> has an internal frictional conical surface <NUM> that is arranged to cooperate in contact with a corresponding external conical surface <NUM> of the portion <NUM>.

More in detail, during the axial movement of the sleeve <NUM> toward one portion <NUM>, the internal teeth <NUM> are brought in axial contact with the external teeth <NUM> of the synchronizer ring <NUM>. Here, the shape of the external teeth <NUM> is configured such that they do not perfectly mesh immediately with the internal teeth <NUM>, but an axial thrust is exerted by the sleeve <NUM> onto the synchronizer ring <NUM> through the axial contact between the internal teeth <NUM> and the external teeth <NUM>. In this manner, the conical surfaces <NUM>, <NUM> are pressed against each other due to the axial thrust, such that friction is generated between the synchronizer ring <NUM> and the corresponding portion <NUM>.

The generated friction causes a synchronization of the speeds of the hub <NUM>, synchronizer ring <NUM>, and the portion <NUM>, i.e. of the speeds of the input and the output shaft of gearbox <NUM>. During the synchronization, the same friction, and the cooperation between teeth <NUM>, <NUM> cause the sleeve <NUM> to stop its axial movement and constantly stay in a stable position for the time needed for the completion of the synchronization. Nevertheless, the stable position remains constant for more than one time instant.

When the synchronization is completed, the internal teeth <NUM> are arranged to match the grooves defined by the splined surface <NUM>. In other words, the internal teeth <NUM> can mesh with the external teeth <NUM> and the sleeve <NUM> can axially slide onto the synchronizer ring <NUM>. In other words, the external teeth <NUM> or the synchronizer ring <NUM> are configured to guide the entire movement of the internal teeth <NUM> or the sleeve <NUM>.

Immediately after the completion of the synchronization, the sleeve <NUM> is axially moved further toward the portion <NUM> until the internal teeth <NUM> mesh with the external teeth <NUM>. Here, the gear associated to the meshing portion <NUM> is correctly engaged.

Therefore, to summarize, an engagement of a gear comprises an axial movement of the sleeve <NUM> by means of the assembly <NUM> from a first position, in which the gear is disengaged (i.e., in particular, the sleeve <NUM> is spaced from the synchronizer ring <NUM>), to a third position, in which the gear is correctly engaged, passing through a second position, which is the stable or constant position described above, where the sleeve <NUM> rests in a pressed status against the synchronizer ring <NUM> that rests, in turn, in a pressed status against the portion <NUM>.

For the sake of clarity, the first position identifies a position of the sleeve <NUM> in which the specific gear that has to be engaged is actually disengaged; however, this does not means that no other gears are engaged. In particular, for example, the engagement of the gear including one of the illustrated portions <NUM> may start from a first position in which the gear including the other opposite portion <NUM> is actually engaged.

The second position is also known in the field as the "synchro engagement position". Hereinafter, the latter expression will be used to identify the second position.

The synchro engagement position is automatically left by the sleeve <NUM> once the speeds of the sleeve <NUM> and of the portion <NUM> are the same. In case the assembly <NUM> is electronically controlled, the axial thrust provided to the sleeve <NUM> may for example remain constant during the whole engagement process. Otherwise, in case of manual actuation of the assembly <NUM>, the thrust depends by the operator that actuates the same assembly <NUM>.

Regarding the synchro engagement position, the Applicant discovered that the actual location of the sleeve <NUM> depends on the wear conditions of the synchromesh device <NUM>, i.e. on the conditions of the frictional conical surface <NUM> of the synchronizer ring. Therefore, the entire displacement of the sleeve <NUM> during a gear engagement actually depends on the wear conditions.

For example, <FIG> shows the displacements of the sleeve <NUM> according to a computer simulation of a plurality of complete gear engagements under the respective assumptions of different wear conditions. In <FIG>, the displacement for each gear engagement is represented in the ordinate axis with a dimensionless parameter taking values between zero and one, where zero represents the first position and one the third position. Clearly, the intermediate values represent respective intermediate positions. The displacement is represented as a function of time, which defines the abscissa axis of the chart in <FIG>. Hence, each line in <FIG> or possibly a portion thereof represents a time function indicative of the displacement of the sleeve <NUM>.

In <FIG>, the horizontal portions of the lines represent or indicate the respective synchro engagement positions based on the wear of the simulated synchromesh device <NUM>. Each of those horizontal portions may be represented or indicated, for example, by a single position value.

The different wear conditions are represented in the legend of <FIG> by a wear parameter that, in particular, is expressed by a percentage value. Here, the shown percentages in <FIG> come from a ratio of two further percentages. The first percentage is given by the ratio between the lost volume of frictional material of the synchronizer ring <NUM> and the original volume before use. The other percentage is a threshold identifying an unacceptable value of the first percentage for the sake of safety. For this reason, the percentage shown in <FIG> may overcome the <NUM>% value.

The time functions that represent the displacement of the sleeve <NUM>, as well as the values of the synchro engagement position, are indicative of a wear parameter, such as the percentage of <FIG>, and thus of the wear conditions of the synchromesh device <NUM>.

In particular, the higher is the value of the synchro engagement position, the higher is the wear.

This has been confirmed also experimentally by the Applicant. For example, <FIG> shows experimental measurements of the displacement of a sleeve of two further synchromesh devices, of which one is normally healthy (solid line) and the other one is completely worn out (dashed line). Evidently, the displacement of the sleeve of the worn out synchromesh device presents a significantly higher value of the synchro engagement position.

In view of the established correlation between the displacement of the sleeve <NUM> with the wear conditions of the synchromesh device <NUM>, the system <NUM> is adapted to determine the actual wear conditions of the synchromesh device <NUM> and preferably to signal those conditions to a user.

System <NUM> comprises an electronic control or processing unit ECU, which stores or comprises information representative of the above correlation. In practice, time functions indicative of the displacement of the sleeve <NUM> or position values thereof, e.g. the values of the synchro engagement position, make part of a relative first set, according to the mathematical meaning of the term "set", whose elements are linked by a functional or statistical relationship to the elements of a second set defined by the values of a wear parameter, such as the percentage of <FIG>.

Control unit ECU stores or comprises the relationship, which may be functional or statistical, between the first and the second set, such that the same control unit ECU is configured to associate a time function or a position value to a value of a wear parameter indicative of the wear conditions of the synchromesh device <NUM>.

System <NUM> further comprises a sensor or transducer T1 configured to measure a quantity indicative of the displacement of the sleeve <NUM>. More precisely, the transducer T1 is configured to detect the quantity and accordingly generate a signal related to the detected quantity. Transducer T1 is a known-kind component and therefore is not described with further detail.

Control unit ECU is connected to transducer T1 to receive the signal generated thereby and extract information from the signal about the detected quantity. More in general, Control unit ECU acquires the information about the measured quantity from transducer T1.

With this information about the displacement of the sleeve <NUM>, control unit ECU is configured to evaluate an actual value or time function belonging to the first set and to determine an actual value of the wear parameter from the evaluated actual value or time function, based on the stored relationship.

Control unit ECU may for example evaluate a single position value or a displacement, possibly partial, of the sleeve <NUM> as a function of time. The stored relationship is suited based on what entity the control unit ECU evaluates as a member of the first set (i.e. a function of time or a single value). In any case, the control unit ECU obtains the actual value of the wear parameter as a function of the evaluated element of the first set.

For example, with reference to <FIG>, the control unit ECU may evaluate based on the acquired information from transducer T1 a function of time corresponding to one of the lines shown. The stored relationship is used by the control unit to link directly the evaluated function of time to the corresponding percentage value of the wear parameter.

The function of time may be expressed, for example, in an analytic form or in a parametric form, such that the control unit ECU may store the relationship by just storing actually the parameters expressing the function of time.

The actual value of the wear parameter is indicative of the wear conditions, which may be communicated to the user. In particular, system <NUM> comprises a signaling device S1 for signaling the wear conditions. For instance, the signaling device S1 may include any one of a light indicator, a display, a sound emitter, and the like. Signaling device S1 is connected to control unit ECU to receive therefrom information about the wear conditions of the synchromesh device <NUM>.

Preferably, control unit ECU also stores a wear scale having a plurality of wear ranges respectively associated to a plurality of ranges of the wear parameter. For example, the wear scale is defined by three wear ranges or levels, which are conveniently associable to respective distinct colors or, more in general, distinct identification signs.

The lower wear range, for example between <NUM>% and <NUM>% of <FIG>, identifies a healthy condition; the intermediate range, for example between <NUM>% and <NUM>%, identify a warning condition; and the higher range, for example from <NUM>% up, identifies a worn condition. In particular, the three colors may be green for the lower range of wear, yellow for the intermediate range, and red for the higher range. Signaling device S1 shows the colors to the user based on the actual value of the wear parameter.

Preferably, the elements of the first set, i.e. the position values or the time functions are indicative of the synchro engagement constant position of the sleeve <NUM>. For example, the elements of the first set may be the constant portions of the displacement of the sleeve <NUM>, e.g. the horizontal lines in <FIG>, or the single position value of the synchro engagement position.

More preferably, the position values or the time functions are indicative of a difference between the value of the synchro engagement positon and a reference position that is indicative of a healthy condition of the synchromesh device <NUM>.

Such a reference position may be stored in the control unit ECU or being determined by the latter based on measurements carried out by the transducer T1.

With greater detail, control unit ECU acquires the actual value of the synchro engagement position during a gear engagement and computes a difference between this actual value and the reference position in order to obtain a difference value. The stored relationship associates the difference value to the actual value of the wear parameter. Alternatively, control unit ECU may compute a difference between the entire or a partial displacement as a function of time and a corresponding reference displacement to obtain a difference function; in this case, the stored relationship associates the difference function to the actual value of the wear parameter.

The reference position or displacement may be stored in the control unit ECU as a result of an arbitrary choice or of a calibration procedure of the synchromesh device <NUM> performed before the actual assembly in the gearbox <NUM> or possibly when the synchromesh device <NUM> is deemed in the healthy condition, for example when the actual value of the wear parameter computed by control unit ECU is in the lower range or before a given number of gear engagements from the first use of the synchromesh device <NUM> is carried out.

The reference position is a function of one or more measurements of the synchro engagement position during respective gear engagements, e.g. by the transducer T1. Possibly, the reference position may be a mean of the measurements such as an arithmetic mean or a weighted mean, for instance based on the number of past gear engagements.

The operation of the system <NUM> during a gear engagement is the implementation of a method according to the invention. <FIG> shows the step of an embodiment of the method. Block <NUM> corresponds to the identification of a relationship between a first set of values or time functions indicative of a displacement of the sleeve <NUM> and a second set of values of a wear parameter of the synchromesh device <NUM>.

Block <NUM> corresponds to the measurement of a quantity indicative of the displacement of the sleeve <NUM>.

Block <NUM> corresponds to the evaluation of a first actual value or time function of the first set from the measured quantity.

Block <NUM> corresponds to the determination of a second actual value of the wear parameter from the evaluated first actual value or time function, based on the identified relationship.

Block <NUM> is optional and corresponds to the signal of the wear condition of the synchromesh device <NUM> to a user based on the determined second actual value.

Preferably, a wear scale is identified with a plurality of wear levels respectively associated to a plurality of ranges of the wear parameter. In this manner, the actual wear level may be determined as the level corresponding to the second actual value according to the identified scale.

More preferably, the actual wear level is signaled to the user.

In view of the foregoing, the advantages of system <NUM> and of the method according to the invention are apparent.

Thanks to the direct association between the synchro engagement position and the wear conditions of the synchromesh device <NUM>, such wear conditions can be directly monitored by simply measuring the displacement of the sleeve <NUM> during gear engagement.

Just only one transducer T1 is needed to measure such a displacement; therefore, system <NUM> has a simple hardware, such that the method is simple to be implemented.

System <NUM> and the method allow the monitoring of the wear during operation of the gearbox <NUM>, specifically during a gear engagement. Therefore, the user can know the actual conditions without the need of performing tests to be carried out through specific test benches.

Furthermore, the user is informed about the progress of the fault, such that the same user can choose the most appropriate time to replace the synchronizer device <NUM>.

Finally, it is clear that modifications can be made to the described system and method, which do not extend beyond the scope of protection defined by the claims.

For example, the system may include also the synchromesh device <NUM> or the gearbox <NUM>.

Claim 1:
A method for monitoring wear of a synchromesh device (<NUM>) during an engagement of a gear, wherein the synchromesh device (<NUM>) comprises a synchronizer ring (<NUM>) and a coaxial sleeve (<NUM>), and wherein the sleeve (<NUM>) is driven to be axially moved from a first position, in which the gear is disengaged, to a third position, in which the gear is engaged, through an intermediate second position, in which the sleeve (<NUM>) presses the synchronizer ring (<NUM>) against a frictional surface (<NUM>) of a gear member (<NUM>); the method comprising:
- identifying (<NUM>) a relationship between a first set of values or time functions indicative of a displacement of the sleeve (<NUM>) and a second set of values of a wear parameter of the synchromesh device (<NUM>);
- measuring (<NUM>) a quantity indicative of the displacement of the sleeve (<NUM>);
- evaluating (<NUM>) a first actual value or time function of the first set from the measured quantity; and
- determining (<NUM>) a second actual value of the wear parameter from the evaluated first actual value or time function, based on the identified relationship;
wherein said values or time functions of the first set are indicative of said second position, the second position being a substantially constant position for a time interval;
wherein said values or time functions of the first set are indicative of a difference between said second position and a corresponding reference position indicative of a healthy condition of the synchromesh device (<NUM>);
the method is characterized in that the identified relationship is represented by the displacements of the sleeve (<NUM>) according to a computer simulation of a plurality of complete gear engagements under the respective assumptions of different wear conditions.