Differential lock actuator

Abstract

The present application is directed to a differential lock actuator for linearly moving a linear rod (40) for engaging and disengaging a differential lock, comprising a rotary shaft (4) mounted to be rotatable but unmovable in an axial direction defined by its rotary axis; an electric motor (8) for rotating the shaft (4) in a first or opposite second sense of rotation; first and second barrel cams (1, 2) of identical design which are mounted on the shaft (4) in a torque-proof manner but slidable in axial direction and which are oriented in opposite axial directions, wherein the first and second barrel cams are disposed between spaced apart end stops (5, 6) which are stationary in axial direction to limit axial movement of the first and second barrel cams (1, 2), wherein a spring mechanism (7) is disposed between the first and second barrel cams (1, 2) to bias them apart and towards the first and second end stops (5, 6). Each of the first and second barrel cams (1, 2) comprises a cam surface configuration and is configured to receive a respective one of a first and second cam follower (41, 42) fixed to the linear rod. The cam surface configuration comprises in circumferential sequence a recessed surface sector (10), followed by a drive sector (20) and terminated by a cam groove sector (26), wherein these sectors cooperate with the first and second cam followers (41, 42) in such a manner that the driving one of the first and second barrel cams (1, 2) is supported via the spring mechanism (7) on the other one of the first and second barrel cams (1, 2) such that any reaction force from the linear rod (40) resulting from the driving force on the linear rod is transmitted through the spring mechanism (7) such that the spring mechanism is compressed in case movement of the linear rod (40) is blocked.

Description

[0001] Differential lock actuator

[0002] The present invention is directed to a differential lock actuator for linearly moving a driven component for engaging and disengaging a differential lock, comprising a linear drive assembly configured to selectively drive the driven component to an engaged or disengaged position arranged to effect engagement or disengagement of a differential lock, wherein the linear drive assembly comprises: a rotary shaft mounted in a support to be rotatable but unmovable in an axial direction defined by its rotary axis; an electric motor for rotating the shaft in a first or opposite second sense of rotation; a barrel cam assembly being in torque-proof engagement with the shaft and having cam surface configuration; and a cam follower coupled to the driven component and cooperating with the rotating cam surface configuration to drive the driven component between the engaged and disengaged positions.

[0003] A differential lock actuator of this kind is disclosed in US 2022 / 0299110 A1 . A barrel cam assembly is coupled to and rotating with the rotary shaft. The barrel cam assembly has a cam surface configuration including cam grooves. A first cam follower which is connected to a disconnect fork as driven component, and a second cam follower is connected to a range fork as driven component, wherein the first and second cam followers are received in different cam grooves configured to move the disconnect fork and the range fork independently from each other in a pattern determined by the cam groove pattern of the cam surface configuration of the barrel cam assembly.

[0004] Another type of differential lock actuator utilizes pressurized fluid which is delivered to an actuation cylinder to selectively move a piston to move the piston which is acting on the differential lock to shift it from the disengaged state to the engaged state and vice versa. Such a differential lock actuator is for example described in US 2001 / 0041638 A1. Such actuators using pressurized fluid to generate the mechanical actuation force can to some extend deal with blockage situation in which the piston cannot moved due to the blocked differential lock. If in case of a blockage the piston cannot move and the actuator is activated by supply of pressurized fluid into a piston chamber, the supply of pressurized fluid results in a pressure increase in the piston chamber while the piston is still blocked. If the blockage is cleared and the increased pressure in the piston chamber still present, the piston is moved to the intended shifted position by the actuation powers stored in the increased pressure in the piston chamber. However, if the blockage persists for longer period of time the originally increased pressure in the piston chamber is not maintained at its original level and is decreasing, in particular if in case of a blockage the differential lock actuator is activated and the engine is switched off before the shift movement could be carried out, the prevented shift movement of the piston will not be made up for if the engine is switched on again. It is an object of the present invention to provide a differential lock actuator that can efficiently deal with blockage situations in which movement of the driven component is blocked, for example due to torque acting on the wheels connected to the differential which blocks disengagement, or due to a blocking misalignment between two dog wheels of the differential lock in case of an intended engagement. In such cases of blocked movement of the driven component the intended movement of the driven component has to be delayed in a simple and efficient manner until the cause of the blockage ceased.

[0005] According to the present invention a differential lock actuator for linearly moving a driving component for engaging and disengaging a differential lock comprises a linear drive assembly which is configured to selectively drive the driven component to an engaged or disengaged position suitable for effecting engagement or disengagement of a differential lock. The linear drive assembly comprises a rotary shaft mounted in a support to be rotatable but unmovable in an axial direction defined by its rotary axis; an electric motor for rotating the shaft in a first or opposite second sense of rotation; a barrel cam assembly being in torque-proof engagement with the shaft and having a cam surface configuration; and a cam follower coupled to the driven component and cooperating with the rotating cam surface configuration of the barrel cam assembly to drive the driven component between the engaged and disengaged positions.

[0006] According to the present invention the barrel cam assembly comprises a first and a second barrel cam which are of identical design and which are mounted on the shaft in a coaxial manner with the shaft and oriented in opposite axial directions with respect to each other; that means that an inner end of each of the first and second barrel cams is facing the inner end of the other one of the first and second barrel cams, the outer end of each of the first and second barrel cams is facing away from the other one of the first and second barrel cams. Furthermore, the first and second barrel cams engage the shaft in a torque-proof manner, but they are free to slide in axial direction along the shaft. The first and second barrel cams are disposed between spaced apart first and second end stops which are stationary in axial direction to limit axial movement of the first and second barrel cams. A spring mechanism is disposed between the first and second barrel cams to bias them apart and towards the first and second end stops, respectively. Each of the first and second barrel cams comprises a cam surface configuration which is due to the identical design of the first and second barrel cams, identical but oriented in opposite directions.

[0007] The driven component is a linear rod which is supported radially outwardly with respect to the first and second barrel cams to be in moveable axial direction in a first direction and in an opposite second direction. The linear rod is provided with a first and second cam follower fixed to it at axially spaced locations and projecting inwardly. The first cam follower is received in the cam surface configuration of the first barrel cam, and the second cam follower is received in the cam surface configuration of the second barrel cam. The cam surface configuration of each of the first and second barrel cams comprises in circumferential sequence three subsequent sectors, namely (1) a recessed surface sector axially between a circumferentially extending inner boundary wall at an inner end adjacent the spring mechanism, and a circumferentially extending outer boundary wall at an outer end of the respective one of the first and second barrel cams, wherein the recessed surface sector allows axial movement of a respective one of the first and second cam followers between the inner boundary wall and the outer boundary wall; (2) a drive sector in which the circumferentially extending outer boundary wall of the recessed surface sector is continued and axially opposite thereto a helical drive track climbs away from the inner end towards the outer end of the respective one of the first and second barrel cams and configured to drive a respective one of the first and second cam followers when being rotated long it; and (3) a cam groove sector, wherein the drive sector is terminated with the helical drive track transitioning into the circumferentially extending cam groove sector terminating at a closed end thereof.

[0008] The first and second barrel cams are rotationally (about the rotary axis) oriented with respect to each other such that the cam groove sector of one of the first and second barrel cams is aligned with and circumferentially equally or less extensive than the recessed surface sector of the other of the first and second barrel cams, and such that the drive sector of one of the first and second barrel cams is aligned so that it overlaps with the drive sector and / or with the recessed surface sector of the other of the first and second barrel cams. This has the consequence that, when the drive sector of the first barrel cam is a rotated against the first cam follower in the first sense of rotation to drive the linear rod in the first axial direction towards the disengaged position, the second cam follower is in the drive sector or in the recessed surface sector of the second barrel cam and thus free to follow the axial movement to the disengaged position, and that, when the drive sector of the second barrel cam is rotated against the second cam follower in the second sense of rotation to drive the linear rod in the second axial direction towards the engaged position, the first cam follower is in the drive sector or in the recessed surface sector of the first barrel cam and thus free to follow the axial movement to the engaged position. It is important that the respective one of the first and second cam followers is in the recessed surface sector when the other one of the first and second cam followers is at the closed end of the cam groove sector so that the one of the first and second cam followers is free to follow the axial movement when, after a blockage, the spring mechanism expands to carry out the previously blocked movement step wherein the other one of the first and second cam followers is in the recessed surface sector free to follow this axial movement.

[0009] The fact that the first and second barrel cams are rotationally oriented with respect to each other such that the drive sector of one of the first and second barrel cams is aligned so that it overlaps with the drive sector and / or with the recessed surface sector of the other of the first and second barrel cams means that either only the drive sectors overlap, or one drive sector partially overlaps with the other drive sector end apart of the recessed surface sector, or the drive sector of one of the first and second barrel cams only overlaps with the recessed surface sector of the other of the first and second barrel cams. However, the last configuration would normally require that the helical drive track has a rather short circumferential extension and therefore require a steep slope of the helical drive track. Therefore, it is more preferred to let the drive sector extend over a larger circumferential distance and also partially overlap with the drive sector of the other one of the first and second barrel cams.

[0010] With this design of the present invention the differential lock actuator deals in the following manner with situations in which the driven linear rod is blocked. Due to the arrangement of the helical drive tracks in the first and second barrel cams, the leading one of the first and second barrel cams in axial drive direction is the one driving the linear rod, whereas the trailing one of the first and second barrel cams in drive direction is decoupled in the sense that the respective one of the first and second cam followers is in this phase in the recessed surface sector of the trailing one of the first and second barrel cams. The leading one of the first and second barrel cams is in this manner able to exert an axial drive force on the linear rod to move it in the driving direction. However, in case the linear rod encounters a blockage its drive force is not transferred further, and in this case Newtons third law requires that the drive force that the driving one of the first and second barrel cams is exerting on the linear rod results in an oppositely directed reaction force of the same magnitude acting on the driving one of the first and second barrel cams. In driving direction the first and second barrel cams have fixed supports, namely the first and second end stops; however, opposite to the driving direction there is no fixed support for the first and second barrel cams, but each of the first and second barrel cams is supported on the other one of the first and second barrel cams via the spring mechanism inbetween them. Thus, in case of a blockage the driving one of the first and second barrel cams will be displaced in opposite direction to the driving direction, thereby compressing the spring mechanism, and moving it closer to the trailing one of the first and second barrel cams. In this manner the integrated driving force that the driving one of the first and second barrel cams exerted on the blocked linear rod is converted and stored in the compressed state of the spring mechanism. As soon as the blockage of the differential lock ceases and the linear rod is no longer blocked the spring mechanism expands because there is no more counterforce, thereby moving the linear rod and the differential lock into the intended position which is reached when the driving one of the first and second barrel cams abuts its associated end stop.

[0011] The differential lock actuator acts in both driving direction, namely from disengaged into engaged position and vice versa, in a “sprung” or “compliant” drive mode in which the axial movement of the linear rod is not strictly coupled in a stiff manner to the rotary movement of the first and second barrel cams, but is partially decoupled in the following sense: If the linear rod encounters only a resistance with a force resisting its linear movement below a threshold the linear movement of the rod is carried out by the rotating barrel cams, whereas in case of a resistance force above the threshold the linear rod is blocked (stuck) and does not move in axial direction; the consequence of this blocked state is that the driving one of the first and second barrel cams is experiencing a reaction force from the blocked linear rod of the same magnitude but oppositely directed to the driving direction exerted, wherein this reaction force displaces the driving one of the first and second barrel cams away from its associated end stop and towards the other one of the first and second barrel cams, thereby compressing the spring mechanism between the first and second barrel cams. In other words, in this sprung or compliant drive mode the spring mechanism is always in the force transmission path from the rotary shaft to the linear rod. If the resistance or blocking force experience by the linear rod is above the threshold, the linear rod does not move an axial direction and instead the driving force exerted on the blocked linear rod results in an oppositely directed reaction force on the driving one of the first and second barrel cams, which reaction force leads to a axial displacement of the driving one of the first and second barrel cams in opposite direction which compresses the spring mechanism, thereby storing the integrated driving force for the linear rod in the compressed state of the spring mechanism. As soon as the resistance or blocking force diminishes below the threshold the spring mechanism expands, thereby driving the linear rod to the intended position. In other words, the blocked axial movement of the linear rod into the intended position is converted into a compression of the spring mechanism, thereby storing the drive force, and the intended linear movement of the linear rod is performed in a delayed manner as soon as the resistance or blocking force sufficiently dropped to allow the compressed spring mechanism to expand again which then moves the linear rod to the intended one of the engaged and disengaged positions, thereby making up for the previously blocked movement.

[0012] The differential lock actuator of the present invention allows to mechanically store the complete integrated driving force for a complete driving step into the disengaged or engaged position by compressing the spring mechanism when the linear rod is blocked, wherein the driving one of the first and second barrel cams is able to complete its rotational driving step which brings the respective one of the first and second cam followers to the closed end of the cam groove sector of the driving one of the first and second barrel cams without any movement of the linear rod. The complete integrated driving force of the driving one of the first and second barrel cams is stored mechanically in the compressed state of the spring mechanism. This integrated stored drive force remains available for an, in principle, unlimited period of time and can be released to perform the intended shift step as soon as the blocked condition of the linear rod ceased.

[0013] Furthermore, the design of the differential lock actuator is compact and space saving because a single compression spring in the spring mechanism is sufficient to convert and store drive force in either axial direction exerted by one of the first and second barrel cams. In a preferred embodiment the cam surface configuration of the first and second barrel cams and their rotational orientation with respect to each other are arranged such that, when the first cam follower is located at the closed end of the cam groove sector of the first barrel cam, the second cam follower is at an axially extending end wall of the recessed surface sector of the second barrel cam, and when the second cam follower is located at the closed end of the cam groove sector of the second barrel cam, the first cam follower is at the axially extending end wall of the recessed surface sector of the first barrel cam. Since the first cam follower and the second cam follower come into abutment on a wall a well-defined rotational end position of the first and second barrel cams is determined, without risk that the first and second barrel cams could be rotated beyond the intended engaged or disengaged position.

[0014] In a preferred embodiment the cam surface configuration has a circumferential extension along the recessed surface sector, the drive sector and the cam groove sector close to 360° around each of the first and second barrel cams. A large circumferential extension is preferred to make maximum use of the barrel cam surface for functional purposes, but it should remain below 360° to avoid overlap. In particular a large circumferential extension allows the drive sector to have a circumferential extension that allows to achieve an intended stroke length of the linear rod movement with the moderate slope of the helical drive track.

[0015] In a preferred embodiment the shaft is a shaft with non-circular cross-section which is received in throughgoing openings of the first and second barrel cams, which openings have cross- sectional shapes complementary to the cross-section of the shaft, for example the shaft may be a splined shaft and the openings comprise axially extending projection which engage the axially extending grooves of the splined shaft to establish a torque-proof engagement of the barrel cams with the shaft, while allowing axial movements of the barrel cams along the shaft.

[0016] In a preferred embodiment the two end stops are fixed to the shaft. In this manner it is ensured that the two end stops are, as the shaft, stationary in axial direction. In addition, the first and second end stops are rotating with the shaft, as do the first and second barrel cams so that there is no relative rotational movement between the first and second end stops and the first and second barrel cams which are bias by the spring mechanism against the two end stops.

[0017] In a preferred embodiment the distance between the first and second end stops, the dimensions of the first and second barrel cams and of the spring mechanism in-between are arranged such that the spring mechanism is under a predetermined preload and exerts oppositely directed forces on the first and second barrel cams to bias them against the first and second end stops, respectively. By establishing a predetermined preload of the spring mechanism a threshold for the resistance force level experienced by the linear rod, when being moved towards the engaged or disengaged position, is determined, wherein for resistance values above this threshold the driving force generated by the differential lock actuator is, without moving the linear rod in axial direction, converted to axial movement of the driving one of the first and second barrel cams and thereby into an increasing spring compression to store the drive force. In other words, the resistance force experience by the linear rod has to exceed the threshold determined by the preload for causing the axial shift movement of the driving one of the first end second barrel cams which compresses the spring mechanism. As soon as the resistance force experienced by the linear rod, dropped below a limit, which is determined by the preload of the spring mechanism plus the further compression of the spring mechanism in the compressed state, the spring mechanism starts to expand thereby driving the linear rod to be intended one of the engaged or disengaged positions.

[0018] In a preferred embodiment the cam groove sector is in a region adjacent to its closed end formed with the cam groove width in axial direction that is enlarged and larger than the width of the first and second cam followers to establish a free play for the linear rod in axial direction when the linear rod is in the engaged and disengaged position. Due to this design one of the first and second cam followers is in the enlarged width region near the closed end of the cam groove sector of one of the first and second barrel cams in the engaged and the disengaged position of the linear rod. As will be explained in more detail below this arrangement establishes a detent mechanism which acts against any external interfering force acting on the linear rod attempting to pull it out of any of the engaged and disengaged positions and which returns the linear rod to the respective one of the engaged or disengaged positions after the interfering external force ceased. This counter-acting returning force is generated, when the external force acts on the linear rod and displaces it, wherein this displacement is accompanied by a further compression of the spring mechanism and is therefore only possible against the counter-acting spring mechanism as will be explained in more detail below.

[0019] In a preferred embodiment the enlarged width region adjacent to the closed end of the cam groove of each of the first and second barrel cams is formed by a recess in an outer side wall of the two opposing side walls defining the cam groove.

[0020] The invention will now be described with reference to a preferred embodiment shown in the drawings, in which:

[0021] Fig. 1 shows a side view of a differential lock actuator according to the present invention;

[0022] Fig. 2 shows, partly as a side view and partly in cross-section, the differential lock actuator of Fig. 1 ;

[0023] Figs. 3 a) - d) show a sequence of rotational states of the differential lock actuator when it is operated to drive its linear rod from the disengaged to the engaged position without blockage; Figs. 4 a) - e) show a sequence of rotational states of the differential lock actuator when it is operated to drive its linear rod from the disengaged to the engaged position but with a temporary obstruction of the linear rod, wherein the obstruction is effective during the entire rotational movement needed for driving to the engaged position, whereafter the obstruction ceases at a point in time between the states of Figs. 4 d) and e);

[0024] Figs. 5 a) - d) show a sequence of rotational states of the differential lock actuator when it is operated to drive its linear rod from the disengaged to the engaged position without blockage;

[0025] Figs. 6 a) - d) show a sequence of rotational states of the differential lock actuator when it is driven from the engaged to the disengaged position but with a temporary obstruction of the linear rod, wherein the obstruction is effective during the entire rotational movement needed for driving to the disengaged position, whereafter the obstruction ceases at a point in time between the states in Figs. 6 d) and e);

[0026] Fig. 7 is a schematic side view of the differential lock actuator in the disengaged position, wherein above the differential lock actuator a symbolic diagram including vertical lines and springs is shown to illustrate a detent effect, and

[0027] Fig. 8 is a side view of the differential lock actuator as Fig. 7 but in the engaged state.

[0028] It is noted that in most of the Figures (Figs. 3 - 8) illustrating the working principle of the differential lock actuator, a linear rod as the driven component and first and second cam followers connected to the linear rod are illustrated in a simplified manner, namely the cam followers as circles, and the linear rod is simplified by two thick lines connecting the first and second cam followers 41 , 42.

[0029] With reference to Figs. 1 and 2 an overview over the main components of the differential lock actuator and their arrangement will be given. The differential lock actuator comprises a rotary shaft 4, illustrated as a splined shaft, which is supported to be rotatable but unmovable in axial direction (unmovable with respect to a support (not shown) suitable for mounting the differential lock actuator in a vehicle). The axial direction is defined by the rotary axis of the shaft 4. The shaft 4 carries close to its end on the right hand side a gear wheel which meshes with a gear wheel driven by an electric motor 8 which is configured to selectively rotate the shaft 4 in a first sense of rotation and in a second, opposite sense of rotation.

[0030] A first barrel cam 1 and a second barrel cam 2 are mounted on the shaft 4 in a coaxial manner, wherein the shaft 4 extends through central openings of the first and second barrel cams 1 , 2. These central openings have a complementary cross-sectional shape with respect to the splined shaft 4. In this manner the first and second barrel cams 1 , 2 are in torque-proof engagement with the shaft 4, wherein the engagement permits that the first and second barrel cams 1 , 2 are able to slide in axial direction along the splines of the splined shaft 4. In Fig. 2 the second barrel cam 2 is shown in cross-section which makes the shaft 4 extending through the central opening of the second barrel cam visible, wherein the shaft is not shown in crosssection. Also shown in cross-section in Fig. 2 is a roller bearing on the right hand side which rotatably supports the shaft 4.

[0031] The first and second barrel cams 1 , 2 are of identical design, and they are disposed on the shaft 4 in opposite axial orientation. That means that like ends of the first and second barrel cams 1 , 2 are disposed adjacent the spring mechanism 7 and are facing each other, namely the inner ends with the inner boundary wall 14 are facing each other, whereas outer ends with outer boundary walls 16 are disposed at opposite ends of the arrangement of the first and second barrel cams 1 and 2.

[0032] The first and second barrel 1 , 2 cams are disposed on the shaft 4 between two spaced apart end stops 5, 6 which are stationary in axial direction; in the illustrated embodiment the end stops 5, 6 are fixed to the shaft 4 so that they rotate with the shaft 4, and are in this manner, as the shaft 4, unmovable in axial direction.

[0033] A spring mechanism 7 is disposed between the first and second barrel cams 1 , 2 which rest on the spring mechanism 7 in-between. The spring mechanism 7 is dimensioned such that it exerts bias forces in opposite directions on the first and second barrel cams 1 , 2 so that the first and second barrel cams 1 and 2 are biased towards the first and second end stops 5 and 6, respectively. In other words, the spring mechanism 7 is under preload and exerts oppositely directed forces on the first and second barrel cams 1 and 2 to press them against the first and second end stops 5 and 6, respectively.

[0034] The linear rod 40 is a component that is supported to be linearly movable parallel to the rotary axis of the shaft 4. The linear rod 40 is provided with first and second cam followers 41 , 42 which are circumferentially aligned and spaced apart in axial direction. The cam followers 41 , 42 are cylindrical projections projecting inwardly and pointing to the rotary axis of the shaft 4. Each of the first and second barrel cams 1 , 2 is provided with a cam surface configuration which is formed by recessed surface areas which have a sufficient depth so that the first and second cam followers 41 , 42 can be received in the recessed surface areas. Each cam surface configuration comprises in circumferential sequence circumferential sectors, namely a recessed surface sector 10, continued by a drive sector 20 and completed by a cam groove sector 26. An overview over the cam surface configuration and its three subsequent sectors will now be given with reference to Figs. 3 a) - d).

[0035] In Fig. 3 a) the first cam follower 41 is disposed at a closed end 30 of a circumferentially extending cam groove 28 which forms the cam groove sector 26. When the first and second barrel cams 1 , 2 have been rotated to the state of Fig. 3 b) the first cam follower 41 has left the cam groove sector 26 and has entered the drive sector 20. The drive sector 20 comprises a recessed surface region which is bounded by an outer boundary wall 16 and a helical drive track 22. After further rotation of the first and second barrel cams 1 , 2 the first cam follower 41 is in Fig. 3 c) still in the drive sector 20 and disposed axially between the outer boundary wall 16 and the helical drive track 22. Between the rotational states of Fig. 3 c) and d) the helical drive track 22 of the first barrel cam 1 transitions to a circumferentially extending inner boundary wall 14, wherein this transition defines the starting point of the recessed surface sector 10 which is defined as a recessed surface area between the circumferentially extending outer boundary wall 16 and inner boundary wall 14. In the state of Fig. 3 d) rotation of the first and second barrel cams 1 , 2 has stopped and the first cam follower has reached an axially extending end wall 14 of the recessed surface sector 10 of the first barrel cam 1 , while the second cam follower 42 is at the closed end 30 of the circumferentially extending cam groove 28.

[0036] In the rotational sequence of Figs. 3 a) - d) the relative movement of the second cam follower 42 is, compared to the above-describe movement of the first cam follower 41 , in opposite direction through the cam surface configuration of the second barrel cam 2. In particular, the second cam follower 42 is in the state of Fig. 3 a) close to the axially extending end wall 12 of the recessed surface sector 10 of the second barrel cam 2. In Fig. 3 b) the second cam follower is leaving the recessed surface sector 10 and entering the drive sector 20 by reaching the helical drive track 22. In this case the second barrel cam 2 is the leading one of the first and second barrel cams in drive direction of the linear rod 40, and is the one which is driving the movement of the linear rod 40 from the disengaged to the engaged position. In Fig. 3 c) the drive sector 20 is further rotated along the second cam follower 42 which is further driven by the helical drive track 22. In Fig. 3 d) the second barrel cam 2 has been rotated further so that the second cam follower 42 eventually left the drive sector 20 and passed along the cam groove sector 26 to eventually reach the closed end 30 of the circumferentially extending cam groove 29 of the cam groove sector 26 of the second barrel cam 2.

[0037] In the following the operation of the differential lock actuator will be described when the linear rod 40 is shifted from a position corresponding to disengaged differential lock to a position corresponding to engaged differential lock for both cases without blockage (Figs. 3 a) - d)) and with a temporary blockage of the linear rod (Figs. 4 a) - e)).

[0038] In Fig. 3 a) the linear rod 40 is in the position corresponding to disengaged differential lock. In the disengaged position the first cam follower 41 is close to the closed end 30 of circumferentially extending cam groove 28 in the cam groove sector 26 of the first barrel cam 1 , while the second cam follower 42 is close to the axially extending end wall 12 of the recessed surface sector 10 of the second barrel cam 2. To operate the differential lock actuator for driving it to the engaged position the electric motor rotates the shaft 4 and thereby the first and second barrel cams 1 , 2 in the direction indicated by the semi-circular arrow which is in the second sense of rotation. Due to this rotation the first barrel cam 1 is rotated such that the first cam follower 41 left the cam groove sector 26 in Fig. 3 b) and is already in the drive sector 20 of the first barrel cam 1 , while in this state the second cam follower 42 is leaving the recessed surface sector 10 of the second barrel cam 2 and is at the beginning of the drive sector 20 of the second barrel cam 2. Upon further rotation the helical drive track 22 of the drive sector 20 of the second barrel cam 2 is rotated against the second cam follower 42 which thereby is driven in the second axial direction to follow the second helical drive track 22 closer to the outer end of the second barrel cam 2. The second barrel cam 2 is the leading one in drive direction and is the one of the first and second barrel cams 1 ,2 that is driving the movement of the linear rod. During the rotation of the second barrel cam 2 between the states in Fig. 3 c) and d) the drive sector 20 has been rotated past the second cam follower 42 and has been rotated further to the end position in Fig. 3 d) in which the second cam follower has been moved into the circumferentially extending cam groove 28 and eventually to a position near the closed end 30 thereof. During the movement of the second cam follower 42 along the helical drive track 22 of the drive sector 20 and further into the circumferentially extending cam groove 28 of the cam groove sector 26 the first cam follower 41 has been moved relative to the cam surface configuration of the first barrel cam 1 along the drive sector 20 of the first barrel cam 1 in Figs, b) and c) and further into the following recessed surface sector 10 of the first barrel cam 1 so that it eventually comes close to the axially extending end wall 14 of the recessed surface sector 10 of the first barrel cam 1 .

[0039] In Figs. 4 a) - e) the same operation of the differential lock actuator from the disengaged to the engaged position is illustrated for the case of a temporary blockage of the linear rod during its operation. The first rotational movement phase from Fig. 4 a) to b) corresponds to the first operation phase in Figs. 3 a) - b). During the rotation of the first and second barrel cams 1 , 2 between the state of Fig. 4 b) and c) the helical drive track 22 of the drive sector 20 is rotated against the second cam follower 42 thereby exerting a drive force on the linear rod 40 in the second axial direction. In case of a blockage of the linear rod 40 the drive force on the linear rod 40 is not transferred to axial movement of the linear rod 40 because of the blockage, and therefore the driving force on the second cam follower 42, which cannot move in axial direction in this phase, results in an oppositely directed reaction force on the second barrel cam 2 which therefore is moved in the first axial direction to be displaced away from its associated end stop 6. This axial displacement of the second barrel cam 2 is accompanied by a compression of the spring mechanism 7. Upon further rotation from the state in Fig. 4 c) to Fig. 4 d) the spring mechanism is further compressed by rotating the remaining part of the helical drive track 22 past the second cam follower 42, wherein the rotation is eventually completed when the second cam follower 42 has entered the cam groove sector 26 and has been moved along the circumferentially extending cam groove 28 to a position near its closed end 30. In this state the rotational drive operation of the shaft 4 and the first and second barrel cams 1 and 2 has been completed and the electric motor has already been stopped. In this state of Fig. 4 d) the blockage of the linear rod 40 still persists so that the linear rod 40 remains at its original position in axial direction and the spring mechanism 7 remains in its compressed state, wherein the integrated drive force generated by rotating the drive sector 20 at the second barrel cam 2 past the second cam follower 42 is stored in the compressed state of the spring mechanism 7. As soon as the blockage ceases the spring mechanism 7 expands and shifts the second barrel cam 2 in the second axial direction to its end position in abutment on the end stop 6. Due to this shift movement of the second barrel cam 2 to its end position by the expanding spring mechanism 7, the previously blocked movement of the linear rod 40 to the engaged position is carried out in a delayed manner upon clearance of the blockage.

[0040] It should be noted that the spring mechanism is in the phase of compression illustrated in Fig. 4 c) and 4 d) in a simplified manner because the axial distance between subsequent windings is not shown reduced as it is actually the case when a spring is compressed, but instead simply the axial length of the spring is reduced, i.e. less windings are shown in Figs. 4 c) - d) instead of the original number of windings with reduced axial distance between the windings.

[0041] Figs. 5 a) - d) illustrate the operation of the differential lock actuator when it is operated to shift from the engaged position (Fig. 5 a)) to the disengaged position (Fig. 5 d)). In the engaged position of Fig. 5 a) the first cam follower 41 is close to the end wall 12 of the recessed surface sector 10 of the first barrel cam 1 , while the second cam follower 42 is close to the closed end 30 of the circumferentially extending cam groove 28 of the second barrel cam 2. The electric motor 8 is activated to rotate the shaft 4 and the first and second barrel cams 1 , 2 in the first sense of rotation (opposite to the second sense of rotation illustrated in Figs. 3 a) - d)). This rotates the first recessed surface sector 10 of the first barrel cam 1 past the first cam follower 41 which in the state of Fig. 5 b) already entered the drive sector 20, wherein the helical drive track 22 of the first barrel cam 1 is rotated against the first cam follower 41 which is thereby moved in the first axial direction closer towards the outer end of the first barrel cam 1. In this case the first barrel cam 1 is the one leading in drive direction and is the one that drives the movement of the linear rod 40. The second cam follower 42 is in the state of Fig. 5 b) in the drive sector 20 of the second barrel cam and can thus follow the axial movement driven by the first cam follower 41. Upon further rotation the first barrel cam 1 is rotating with the outer end portion of the helical drive track 22 past the first cam follower 41 (Fig. 5 c)), while the second cam follower 42 is approaching the end of the drive sector 20 of the second barrel cam 2, whereafter upon further rotation the first cam follower 41 leaves the drive sector 20 of the first barrel cam 1 and moves along the circumferential the extending cam groove 28 of the first barrel cam 1 towards its closed end 30. During entry and movement of the first cam follower 41 along the cam groove sector 26 of the first barrel cam 1 the second cam follower 42 is already in the recessed surface sector 10 of the second barrel cam 2 between the circumferentially extending inner and outer boundary walls 14, 16. Rotation of the shaft 4 and the barrel cams 1 , 2 is stopped when the state of Fig. 5 d) with the linear rod 40 in the disengaged position has been reached.

[0042] Figs. 6 a) - e) illustrate the same operation of the differential lock actuator driving it from the engaged to the disengaged position as in Fig. 5 a) - d), but in case of Figs. 6 a) - e) with a temporary blockage of the linear rod during the drive operation. During rotation from the state of Fig. 6 a) (engaged position) to the rotational state of Fig. 6 b) the first recessed surface sector 10 of the first barrel cam has already been rotated past the first cam follower 41 which in Fig. 6 b) already reached a starting portion of the helical drive track 22 in the drive sector 20 of the first barrel cam 1. Since the linear rod 40 is in a blocked state in this case the driving force exerted by the rotating helical drive track 22 of the first barrel cam 1 on the first cam follower 41 results in an oppositely directed reaction force on the first barrel cam 1 which is therefore displaced in the second axial direction away from its end stop 5 so that already a small gap between the end stop 5 and the outer end of the first barrel cam 1 is visible in Fig. 6 b). Upon further rotation of the drive sector 20 of the first barrel cam 1 along the first cam follower 41 the first barrel 1 is displaced further away from the end stop 5, thereby increasingly compressing the spring mechanism 7, as shown in Fig. 6 c). During the rotation between the states of Fig. 6 c) and d) the first cam follower 41 completed its movement along the helical drive track 22 of the drive sector 20 and already entered into the cam groove sector 26 of the first barrel cam and reached the closed end 30 of the circumferentially extending cam groove 28. During the rotation phase when the first cam follower 41 entered and moved along the cam groove sector 26 the second cam follower 42 was already in the recessed surface sector 10 of the second barrel cam 2 and remained close to the outer boundary wall 16 because of the blocked state of the linear rod 40. In the state of Fig. 6 d) the operation of the differential lock actuator is completed and the electric motor 8 stopped. Again, the total integrated drive force exerted by the rotation of the drive sector 20 past the first cam follower 41 has been stored in the compressed state of the spring mechanism 7, wherein this stored drive force remains available for an, in principle, unlimited period of time until the blockage ceases. As soon as the blockage diminishes and the resistance force experienced by the linear rod 40 dropped below the spring force of the spring mechanism 7 the latter expands thereby driving the linear rod 40 in the first axial direction to the intended disengaged position which is reached when the expanding spring mechanism shifted the first barrel cam 1 back into abutment on its associated end stop 5. The second cam follower 42 in this situation was in the recessed surface sector 10 of the second barrel cam 2 so that the second cam follower 42 was free to follow the axial movement of the first barrel cam 10 caused by the expanding spring mechanism 7.

[0043] In the following a detent mechanism will be described which holds the linear rod in the engaged position and the disengaged position, respectively, and urges the linear rod to return to the engaged and disengaged position, respectively, in case an interfering external force attempted to move the linear rod out of the engaged position and disengaged position, respectively. Fig. 7 shows the differential lock actuator with the linear rod 40 in the disengaged position so that the first cam follower is near the closed end 30 of the circumferentially extending cam groove 28. As shown in Fig. 7 the side wall of the cam groove 28 closer to the outer end is in the region adjacent to the closed end 30 formed with a recess 32 creating extra space, or in other words forming an enlarged width portion of the cam groove 28. This enlarged width end region of the cam groove 28 has an axial width that is larger than the width of the first cam follower 41 so that there is free play for the first cam follower 41 at the end of the circumferentially extending cam groove 28 in the disengaged position. The preload of the spring mechanism 7 urges the first and second barrel cams 1 , 2 apart so that the first barrel cam 1 is biased to a position in which the first cam follower 41 is in abutment on the inner side wall of the cam groove 28 opposite to the recess 32. If an external force is now acting on the linear rod 40 and attempting to move it in axial direction further towards and beyond the disengaged position this force can displace the linear rod 40 against the preload of the spring mechanism 7 which is thereby further compressed, and this movement can continue until the first cam follower 41 contacts the bottom of the recess 32 which forms a hard end stop against further movement of the linear rod 40 in this direction. As soon as the external force ceases the compressed spring mechanism 7 expands and returns the linear rod 40 to the disengaged position.

[0044] If an external force is acting on the linear rod in the opposite direction, attempting to pull it out of the disengaged position towards the engaged position, the linear rod 40 reacts with a displacement which moves the second cam follower 42 further in axial direction into the recessed surface sector 10 of the second barrel cam, i.e. away from the inner boundary wall 14. Such displacement of the linear rod 40 can only occur with a corresponding displacement of the first barrel cam 1 by the same distance against the preload of the spring mechanism 7 which provides an increasing return force on the linear rod 40 with increasing displacement. In this direction there is no hard end stop for the displacement of the linear rod 40 but only the increasing counter-force of the spring mechanism 7 (the outer boundary wall 16 of the recessed surface sector 10 of the second barrel cam would in principle be an end stop but it is to far away to be effective). The characteristics of this detent mechanism are illustrated in Fig. 7 in a schematic manner in a diagram on the left hand side of the differential lock actuator, which diagram shows two horizontal lines, spring symbols and a double arrow indicating displacement of the linear rod in any of the two axial directions. The central vertical line indicates the disengaged rest position of the linear rod without external interference. If an external interference force displaces the linear rod 40 downwards this results in an increasing counter-force of the spring mechanism 7 due to its compression for permitting the displacement. Further displacement of the linear rod downwards is limited by the hard end stop indicated by the lower horizontal line. This end stop becomes effective if the first cam follower 41 contacts the surface of the recess 32 thereby stopping any further displacement. In the displacement direction upwards the diagram in Fig. 7 shows a spring which illustrates the increasing counter force with increasing displacement if the linear rod is displayed in the direction upwards. In this direction, as explained above, there is no hard end stop so that no horizontal line is shown on top of the upper spring.

[0045] Fig. 8 shows the differential lock actuator in the engaged position of the linear rod. In this case the second cam follower 42 is near the closed end 30 of the circumferentially extending cam groove 28 of the second barrel cam 2, wherein in this region the recess 32 provides free play for the linear rod 40 in the same manner as described above for the first cam follower 41 in Fig. 7. It is apparent that the detent mechanism in the position of Fig. 8 works in a symmetrical manner to the situation of Fig. 7, wherein the detent function is indicated in the diagram on the right hand side of the differential lock actuator in Fig. 8. Again, the central horizontal line indicates the rest position of the linear rod 40 without interfering external force. The upper horizontal line indicates the hard end stop which is reached when the linear rod 40 is displaced such that the second cam follower 42 contacts the bottom of the recess 32. In the opposite direction there is no hard end stop, but with increasing displacement the spring mechanism 7 exerts an increasing counter force to return the linear rod 40 to the engaged position.

[0046] Reference numerals:

[0047] 1 First barrel cam

[0048] 2 Second barrel cam

[0049] 4 Shaft

[0050] 5, 6 End stops

[0051] 7 Spring mechanism

[0052] 8 Electric motor

[0053] 10 Recessed surface sector

[0054] 12 End wall of recessed surface sector

[0055] 14 Inner boundary wall of recessed surface sector

[0056] 16 Outer boundary wall of recessed surface sector

[0057] 20 Drive sector

[0058] 22 Helical drive track

[0059] 26 Cam groove sector

[0060] 28 Circumferentially extending cam groove 30 Closed end of the cam groove

[0061] 32 Recess for enlarged cam groove width

[0062] 40 Linear rod

[0063] 41 First cam follower 42 Second cam follower

Claims

Claims1 . Differential lock actuator for linearly moving a driven component for engaging and disengaging a differential lock, comprising a linear drive assembly configured to selectively drive the driven component to an engaged or disengaged position arranged to effect engagement or disengagement of a differential lock, wherein the linear drive assembly comprises: a rotary shaft (4) mounted in a support to be rotatable but unmovable in an axial direction defined by its rotary axis; an electric motor (8) for rotating the shaft (4) in a first or opposite second sense of rotation; a barrel cam assembly being in torque-proof engagement with the shaft and having cam surface configuration; and a cam follower coupled to a driven component and cooperating with the rotating cam surface configuration to drive the driven component between the engaged and disengaged positions; characterized in that the barrel cam assembly comprises a first (1) and a second barrel cam (2) which are of identical design and which are mounted on the shaft (4) in a coaxial manner with the shaft and oriented in opposite axial directions with respect to each other, and which are mounted to be slidable in axial direction along the shaft (4), wherein the first and second barrels cams (1 , 2) are disposed between spaced apart first and second end stops (5, 6) which are stationary in axial direction to limit axial movement of the first and second barrel cams (1 , 2), wherein a spring mechanism (7) is disposed between the first and second barrel cams (1 , 2) to bias them apart and towards the first and second end stops (5, 6), respectively, each of the first and second barrel cams (1 , 2) comprising a cam surface configuration, the driven component is a linear rod (40) being supported radially outwardly with respect to the first and second barrel cams (1 , 2) and movable in axial direction in a first direction and in an opposite second direction, wherein the linear rod (40) is provided with first and second cam followers (41 , 42) fixed to it at axially spaced locations and projecting inwardly, the first cam follower (41) being received in the cam surface configuration of the first barrel cam (1), the second cam follower (42) being received in the cam surface configuration of the second barrel cam (2), the cam surface configuration of each of the first and second barrel cams (1 , 2) comprises in circumferential sequence a recessed surface sector (10) in axial direction between a circumferentially extending inner boundary (14) wall at an inner end adjacent the spring mechanism (7) and a circumferentially extending outer boundary wall (16) at an outer end of the respective one of the first and second barrel cams (1 , 2), whichrecessed surface sector (10) allows axial movement of a respective one of the first and second cam followers (41 , 42) between the inner boundary wall (14) and the outer boundary wall (16), followed by a drive sector (20) in which the circumferentially extending outer boundary wall (16) of the recessed surface sector is continued and opposite thereto a helical drive track (22) is climbing away from the inner end towards the outer end of the respective one of the first and second barrel cams (1 , 2) for driving the respective one of the first and second cam followers (41 , 42), which drive sector is terminated where the helical drive track (22) transitions into a cam groove sector (26) defined by a circumferentially extending cam groove (28) terminating at a closed end (30) thereof, and the first and second barrel cams (1 , 2) are rotationally oriented with respect to each other such that the cam groove sector (26) of one of the first and second barrel cams (1 , 2) is aligned with and circumferentially equal or less extensive than the recessed surface sector (10) of the other of the first and second barrel cams (1 , 2), and such that the drive sector (20) of one of the first and second barrel cams (1 , 2) is aligned so that it overlaps with the drive sector (20) and / or with the recessed surface sector (10) of the other of the first and second barrel cams (1 , 2) so that, when the drive sector (20) of the first barrel cam (1) is rotated against the first cam follower (41) in the first sense of rotation to drive the linear rod (40) in the first axial direction towards the disengaged position, the second cam follower (42) is in the drive sector (20) or the recessed surface sector (10) of the second barrel cam (2) and thus free to follow the axial movement to the disengaged position, and so that, when the drive sector (20) of the second barrel cam (2) is rotated against the second cam follower (42) in the second sense of rotation to drive the linear rod (40) in the second axial direction towards the engaged position, the first cam follower (41) is in the drive sector (20) or the recessed surface sector (10) of the first barrel cam (1) and thus free to follow the axial movement to the engaged position.

2. Differential lock actuator according to claim 1 , characterized in that the cam surface configuration of the first and second barrel cams (1 , 2) and their rotational orientation with respect to each other adapted such that, when the first cam follower (41) is located at the closed end (30) of the cam groove sector (26) of the first barrel cam (1), the second cam follower (42) is at an axially extending end wall (12) of the recessed surface sector (10) of the second barrel cam (2), and when the second cam follower (42) is located at the closed end (30) of the cam groove sector (26) of the second barrel cam (2), the firstcam follower (41) is at the axially extending end wall (12) of the recessed surface sector (10) of the first barrel cam (1).

3. Differential lock actuator according to any of the preceding claims, characterized in that the of the cam surface configuration has a circumferential extension along the recessed surface sector (10), the drive sector (20) and the cam groove sector (26) up to its closed end (30) of more than 320° around each of the first and second barrel cams (1 , 2).

4. Differential lock actuator according to any of the preceding claims, characterized in that the shaft (4) is a shaft with non-circular cross-section which is received in throughgoing openings of the first and second barrel cams (1 , 2), which openings have cross-sectional shapes complementary to the non-circular cross-section of the shaft (4), optionally wherein the shaft (4) is a splined shaft.

5. Differential lock actuator according to any of the preceding claims, characterized in that the first and second end stops (5, 6) are fixed to the shaft (4).

6. Differential lock actuator according to any of the preceding claims, characterized in that the distance between the first and second end stops (5, 6) , the dimensions of the first and second barrel cams (1 , 2) and of the spring mechanism (7) in-between are arranged such that the spring mechanism (7) is under a predetermined preload and exerts oppositely directed forces on the first and second barrel cams (1 , 2) to bias them against the first and second end stops (5, 6), respectively.

7. Differential lock actuator according to any of the preceding claims, characterized in that the cam groove sector (26) is in a region adjacent to its closed end (30) formed with a cam groove width in axial direction that is enlarged and larger than the width of the first and second cam followers (41 , 42) to establish a free play for the linear rod (40) in axial direction when the linear rod (40) is in the engaged and disengaged position in which the second cam follower (42) in the enlarged width region adjacent to the closed end (30) of the cam groove sector (26) of the second barrel cam (2) and in which the first cam follower (41) in the enlarged width region adjacent to the closed end (30) of the first barrel cam (1), respectively, wherein this free play of the linear rod in the engaged and disengaged position in cooperation with the spring mechanism (7) provides a detentmechanism biasing the linear rod (40) to return to the respective one of the engaged and disengaged positions.

8. Differential lock actuator according to claim 7, characterized in that the enlarged width region adjacent to the closed end (30) of the cam groove (28) of the first and second barrel cams (1 , 2) is formed by a recess (32) in an outer side wall of the two opposing side walls defining the cam groove (28).

Images