A device for locking a drivetrain transmission in a motor vehicle

Abstract

A locking device for a drivetrain in a motor vehicle, comprising at least one gear (8), a rod (3) with a rod axis, the rod comprising a first portion (31) equipped with a right-hand external thread and a second portion (32) equipped with a left-hand external thread, a drive member (4) for rotating the rod, two locking members (1, 2) each comprising a sleeve (10, 20) and a projection (5, 6), the sleeve comprising an internal thread cooperating by complementary shape with an external thread of the rod, the projections comprising a free end forming a stop to prevent a tooth of the gear in both directions, and guide elements (7) to prevent rotation of the locking members about the rod axis but to allow their translation along the rod axis. Figure 1

Description

Title of the invention: Device for locking a drivetrain transmission in a motor vehicle

[0001] The invention relates to a device for locking a kinematic chain transmission in a motor vehicle.

[0002] This type of locking device is commonly called the parking brake and is typically used, particularly on vehicles with automatic transmissions. This type of locking device is also used in electric or hybrid vehicles. The transmission lock is activated when the driver positions the transmission selector lever in the "P" position, generally when the vehicle is stationary.

[0003] The locking device referred to here is distinct from and complementary to another braking system called the parking brake, also present on motor vehicles, and acting directly on the vehicle's wheels. This parking brake also serves as an emergency brake to slow down and immobilize the vehicle. Conversely, the parking brake that is the subject of the present invention is designed and intended to be engaged only at zero or near-zero speed.

[0004] Parking brake solutions are known in which a toothed pivoting element (latch or 'pawl') selectively interferes with a toothed wheel forming part of the transmission. However, it turns out that the known solutions occupy a considerable amount of space and, moreover, are not free from play. An example of such a solution is known from patent US2016223082.

[0005] The inventors sought to improve the situation and propose a new configuration to achieve the parking brake function.

[0006] To this end, a device for locking a drivetrain transmission in a motor vehicle is proposed, by mechanically engaging at least one locking member in a gear of the transmission, the device comprising at least: - a toothed wheel, mounted for rotation about a wheel axle, - a rod mounted for rotation in a housing around a rod axle, the rod comprising a first portion equipped with an external thread with a right-hand pitch and a second portion equipped with an external thread with a left-hand pitch, - a drive unit configured to selectively rotate the rod in one direction or the other, - a first locking element comprising a first sleeve centered on the rod axis and a first projection extending radially outwards from the sleeve, the sleeve comprising an internal thread, adapted to cooperate by complementary shape with an external thread of the rod, the first projection comprising a free end forming a stop to prevent a tooth of the gear from being held in a first direction of rotation, - a second locking member comprising a second sleeve centered on the shaft axis and a second projection extending radially outwards from the sleeve, the sleeve comprising an internal thread, adapted to cooperate by complementary shape with the other external thread of the shaft, the second projection comprising a free end forming a stop to prevent a tooth of the gear from engaging in a second direction of rotation, - guide elements to prevent the rotation of the first and second locking members around the rod axis but to allow the translation of the locking members along the rod axis.

[0007] Thanks to the threaded portions of the rod with opposite pitches, and the locking members with their respective corresponding internal threads engaged around the rod, when the rod rotates in a first direction, the locking members move closer together, and when the rod rotates in the other direction, the locking members move away from each other.

[0008] Thanks to these arrangements, when the locking members move towards each other, they frame one or more teeth of the gear, thus locking the gear. Conversely, when the locking members move away from each other, the rotation of the gear is released.

[0009] The proposed configuration is compact and simple to manufacture and assemble. It requires fewer parts than solutions in the known art and, moreover, advantageously, is lighter than known configurations in the art.

[0010] Other advantages will be seen below.

[0011] The term "kinematic chain" here generally means any system comprising an engine, whether internal combustion or electric, a transmission comprising a reducer with, where appropriate, several selectable reduction ratios, a differential and two wheel shafts connected respectively to a left wheel and a right wheel of a vehicle axle.

[0012] According to one aspect, each of the first and second projections is formed as a finger extending along an extension direction (XI,X2) inclined relative to the shaft axis. Whereby the tip of the finger can be interposed between two teeth of the gear. The inclination of the finger allows it to absorb a force resulting from a torque exerted by the gear; the finger works primarily in compression, and the cantilever effect is minimized.

[0013] It is noted that the term 'arm' can also be used to designate the projection instead of 'finger'.

[0014] According to one aspect, the fingers are directed towards each other. They can thus grip a tooth of the gear in a vise-like fashion, like a pair of pliers. The functional backlash can therefore be reduced to a very small value or even to zero.

[0015] According to one aspect, the extension direction (XI,X2) is inclined at an angle θ with respect to the shaft axis, θ being between 35° and 60° and preferably between 40° and 50°. This provides a clamping effect for the rotation stop direction where the finger works in compression. The chosen angle (or angular range) results from a compromise between the clamping effect and the precision required for the finger to interlock between two successive teeth of the gear.

[0016] According to one aspect, the ends of the first and second projections are moved in translation along a tangent to a primary circle of the gear. It is noted that this direction of movement is a distinctive feature compared to the known art in which the moving element approaches the gear radially. The radial clearance relative to the axis of the gear is also reduced.

[0017] According to one aspect, the shaft axis (A) is perpendicular to the wheel axis (W). Therefore, it is not necessary to implement a rotation axis parallel to the gear axis near the gear. Apart from the gear axis (W), the shaft axis (A) is the only axis required in the proposed function configuration.

[0018] According to one aspect, the first and second projections generally extend in a radial plane (PR) perpendicular to the wheel axis (W). This results in a reduced overall size with a flat configuration that is favorable for easy and compact integration into a transmission.

[0019] According to one aspect, the first and second projections act on the same tooth of the gear. The locking system can thus be localized to a smaller area relative to the gear. The chain of ribs is therefore as short as possible.

[0020] According to one aspect, the number of teeth on the toothed wheel is between 10 and 20. Thanks to this, the probability of being able to directly block a tooth with the two fingers of the locking members coming together can be maximized.

[0021] According to one aspect, the rod is mounted and interposed between a bearing of the drive unit and an opposing bearing connected to the transmission housing. As a result, the rod rotates within these two bearings, and the assembly exhibits good mechanical robustness and can withstand axial and radial forces.

[0022] According to one aspect, the internal and external threads are fine pitch threads, the pitch of the PF threads being less than 12% of the diameter of the rod D3. The external diameter D3 of the rod can be between 8 cm and 16 cm, preferably for example between 10 cm and 12 cm.

[0023] This contributes to the irreversibility of the force path. In particular, when a vehicle is parked on an incline, whether going uphill or downhill, gravity (i.e., the vehicle's weight) generates a torque (static or even dynamic) on the gear, which is transmitted to the locking mechanisms, the threads, and the shaft. However, with a small thread pitch, the torque applied to the shaft is insufficient to rotate the motor or the geared motor (the actuator).

[0024] The invention also relates to a transmission for a motor vehicle comprising a locking device as described above.

[0025] The invention will be further detailed by describing non-limiting embodiments, and based on the accompanying figures illustrating variants of the invention, in which: - [Fig.1] schematically illustrates an example of a parking brake, in elevation view, according to the present invention; - [Fig.2] shows a partial view of the threaded rod with opposing screw threads; - [Fig.3] shows a cross-sectional view of the rod and a locking element with translational guidance; - [Fig.4] schematically illustrates an embodiment according to the invention with the parking brake function not engaged; - [Fig.5] schematically illustrates an embodiment according to the invention with the parking brake function engaged; - [Fig.6] is similar to [Fig.5] and schematically illustrates a particular situation before blockage; - [Fig. 7] illustrates the inclined orientation of the locking fingers.

[0026] In the various figures, the same reference numerals designate identical or similar elements. For clarity, some elements are not necessarily shown to scale.

[0027] In the various figures, the same reference numerals designate identical or similar elements. For the sake of clarity, some elements are not necessarily shown to scale.

[0028] Figure 1 shows an example of an embodiment of a locking device as proposed. The locking device is housed in a transmission casing, labeled 9. The transmission may be an automatic transmission, but a manual transmission is also possible. The transmission may also be an electric or hybrid vehicle transmission.

[0029] From a general point of view, the drivetrain comprises an engine, whether internal combustion or electric, a transmission comprising a reduction gear with the optionally several selectable reduction ratios, a differential and two wheel shafts each connected to the respective wheels of an axle.

[0030] It is noted that in the proposed configuration, only one locking device is needed to lock both wheels of an axle.

[0031] In the illustrated example, the housing 9 contains various gears and pinions. In particular, [Fig. 1] illustrates a transmission gear identified as 81 permanently engaged via its peripheral teeth 81a with a gear wheel 8. It is the gear wheel 8 that will be locked in certain use cases by the device that will be described later.

[0032] The toothed wheel 8, via the transmission gear 81, is generally rotationally fixed to the wheels of an axle or at least to a wheel shaft. Locking the toothed wheel 8 therefore immobilizes the wheels of the vehicle's axle. A differential (not shown) may be interposed between the gear 81 and the wheel shafts.

[0033] The gear wheel 8 is mounted to rotate about a wheel axle denoted W. The gear wheel 8 is mounted on a shaft, rotating or not, linked to the housing 9.

[0034] The gear 8 can have 10 teeth as illustrated in the figures. Generally, the number of teeth on the gear 8 is between 10 and 20. For example, the number of teeth on the gear can be 12, or the number of teeth on the gear can be 16.

[0035] The teeth have a trapezoidal profile with steep flanks. According to one embodiment, the flanks 87 can be parallel to each other.

[0036] The outer diameter D8 of the gear 8 can be between 10 cm and 25 cm, for example preferably between 16 cm and 20 cm. The gear 8 is made of metal like a conventional pinion or gear.

[0037] The locking device includes a rod 3. The rod 3 is rotationally mounted in the housing around a rod axis denoted A.

[0038] The rod 3 is made of, for example, steel. The rod 3 comprises a first journal near its first end on the drive member side, and a second journal at its second end. The first journal is received in a bearing 34 of the drive member 4. The second journal is received in an opposite bearing 39. The bearing 39 can be connected by a support 38 to the housing or can be integrated directly into a bored form of the housing casting 9.

[0039] The pivoting in the bearings is lubricated by the oil present in the transmission housing through a splashing effect on the moving parts. The rod 3 is further immobilized along the axis A by the bearings. Thus, the only degree of freedom conferred on the rod 3 is rotation about the axis of rod A.

[0040] The rod 3 comprises two threaded portions with opposite pitches. More specifically, the rod 3 comprises a first portion 31 equipped with an external thread 31a with a right-hand pitch and a second portion 32 equipped with an external thread 32a with a left-hand pitch.

[0041] The internal and external threads are preferably fine-pitch threads. As illustrated in [Fig. 2], the thread pitch, denoted PF, corresponds to the distance between two successive threads. In the example shown, the pitch PF is less than 12% of the diameter of the rod D3. For example, for a rod diameter of 8 millimeters, the pitch PF is less than 1 millimeter.

[0042] An unthreaded portion 30 can be interposed between the two threaded portions. It should be noted that the invention covers all types of threads, including standard pitch threads.

[0043] The outside diameter D3 of the rod 3 can be between 8 mm and 16 mm, for example preferably between 10 mm and 12 mm.

[0044] On each of the two threaded portions is mounted a locking member, movable along the axis of rod A.

[0045] The locking device comprises a first locking member 1 and a second locking member 2.

[0046] The first locking member 1 comprises a first sleeve 10 centered on the axis of rod A. The first locking member 1 comprises a projection called herein first projection 5 which extends radially outwards from the first sleeve 10.

[0047] The first projection is shaped like a finger or an arm. This finger or arm extends from the sleeve along an axis XI inclined relative to the axis of the rod A. The axis XI is inclined relative to the axis of the rod A at an angle θ. θ is between 35° and 60°. Preferably, θ is between 40° and 50°.

[0048] The first sleeve 10 includes an internal thread, adapted to cooperate by complementary shape with the external thread 31a of the rod.

[0049] The first projection includes a free end 51 forming a stop to prevent a tooth of the gear from engaging in a first direction of rotation SI (see [Fig. 4]). The first projection includes a portion furthest from the shaft axis called the dorsal portion of the finger, denoted 52, the purpose of which will be seen later.

[0050] The second locking member 2 comprises a second sleeve 20 centered on the axis of rod A. The second locking member 2 comprises a projection, here called second projection 6, which extends radially outwards from the second sleeve 20.

[0051] The second sleeve 20 includes an internal thread, with a left-hand thread, adapted to cooperate by complementary shape with the external thread 32a of the rod.

[0052] The second projection 6 includes a free end 61 forming a stop to stop a tooth of the gear (the same tooth or another) according to a second direction of rotation S2.

[0053] It is noted that the fingers are directed towards each other, as in the case of a pair of pliers or pincers.

[0054] As illustrated in [Fig.7], the rod axis A is separated from the wheel axis W by a distance denoted D6. When the locking members are in the locking position, the axes XI and X2 intersect at a point P12, separated from the rod axis A by a distance D7.

[0055] D7 can be between 25% of D6 and 50% of D6 depending on the diameter of the wheel.

[0056] Furthermore, the device includes guiding elements 7. As illustrated in the [Fig. 3], finger 5 extends between a first bearing 71 which prevents it from turning to the left and a second bearing 72 which prevents it from turning to the right. Other types of guidance are not excluded, such as legs arranged diametrically opposite to the fingers.

[0057] In a generic way, the guide elements 7 prevent the rotation of the locking members 1,2 around the axis of rod A but allow the translation of the locking members 1,2 along the axis of rod A.

[0058] The first and second projections 5,6 generally extend in a radial plane denoted PR perpendicular to the wheel axis W. The PR plane passes through the axis A.

[0059] As can be seen in [Fig. 3], the configuration of the assembly of the elements is substantially flat in the Y direction. Indeed, the gear 8 and the fingers 5 and 6 extend on either side of the radial median plane PR. Furthermore, the footprint of the elements, rod 3 and locking members (1 and 2), does not exceed the outside diameter DI of the sleeves. Such an assembly is therefore easy to install in a confined space within a transmission.

[0060] The locking members have internal threads corresponding respectively to the thread of the rod. The first locking member has an internal thread with a right-hand pitch, while the second locking member has an internal thread with a left-hand pitch.

[0061] Even if the first thread is a right-hand thread and the second thread is a left-hand thread, of course the reverse is possible, with the corresponding reverse on the threads of the rod portions.

[0062] It is noted that the rod diameter can be reduced (< D3) beyond the threaded portions in order to be able to insert the sleeves of the locking elements from the end of the rod to their position in the threaded portions 31,32.

[0063] Thanks to the threaded portions 31a, 32a of the rod with opposing threads, when the rod 3 rotates in a first direction T1, the locking members 1,2 move closer to each other the other. When the rod 3 rotates in the other direction T2, the locking members 1,2 move away from each other.

[0064] The drive element 4 can be, for example, an electric motor. The drive element may include a gearbox, in which case it is a geared motor. The output shaft, e.g., the motor rotor or the gearbox output shaft, is engaged with the rod 3, for example, by a splined interface. A female sleeve is integral with the motor rotor 4. The end of the rod on this side is a male splined type. Other solutions, such as a keyway or the use of a through pin, are also possible.

[0065] It should be noted that the drive element 4 can be arranged outside the housing 9, and the rod 3 can be longer or shorter depending on the integration configurations. This flexibility in positioning the drive element facilitates the integration of the proposed solution into a given transmission configuration.

[0066] The drive unit is controlled by a control unit not shown in the figures. This control unit receives the vehicle speed information and can command the engagement of the parking brake when the vehicle speed is zero or, alternatively, when the vehicle speed is below a very low threshold, for example, less than 3 km / h.

[0067] We start from the situation represented in [Fig.4] where the toothed wheel can rotate freely around the axis W. When the conditions are met, the control unit can command the engagement of the parking brake.

[0068] To this end, the control unit, by means of the electric motor 4, drives the rotation of the rod in the direction T1 so that the locking members move closer together. [Fig. 5] shows the final situation where the tooth 8a is framed above by the finger 5 of the first locking member 1 and below by the finger 6 of the second locking member 2.

[0069] The fingers grip tooth 8a in a vise-like grip.

[0070] It is noted that if tooth 8a is not exactly in the correct position at the time of tightening, one of the fingers can move tooth 8a, and therefore the entire wheel 8, into the correct position. The fine pitch of the threaded portions allows a significant force to be applied along axis A.

[0071] It is noted that the fingers are moved in translation along a tangent TG to the primary circle of the gear. This configuration is ideal for the finger to push a tooth of the gear 8 by its flank 87 in a circumferential direction and rotate the gear 8.

[0072] We thus have a recentering function if the tooth is not well positioned.

[0073] According to another case shown in [Fig. 6], assuming that fingers 5 and 6 do not grip a tooth when they approach each other, then as soon as the wheel 8 turns slightly, a tooth of the wheel can dislodge one of the fingers to become lodged in the gap between the free ends of the fingers. This traps the first tooth that passes through the gap.

[0074] For this purpose, a flexing of the finger is provided by pressure on the back 52 of the finger. As illustrated in [Fig.6], it is the second finger 6 of the second locking member 2 that flexes upwards when a tooth passes into contact with it, the wheel 8 rotating clockwise.

[0075] Depending on the rigidity of the finger and the shaft, the shaft may also flex slightly when a tooth passes over the back of a finger. Such flexibility may be desirable to achieve the trapping of a tooth even if the fingers, in their approaching movement, have not already gripped a tooth.

[0076] The rod and locking members are made of metal, e.g. steel.

[0077] It is noted that the helical interface between the rod 3 and the sleeves 10, 20 is lubricated by the oil splashing from the transmission.

Claims

Demands

1. A device for locking a kinematic chain transmission in a motor vehicle, by mechanically engaging at least one locking member in a gear of the transmission, the device comprising at least: - a gear (8), mounted for rotation about a gear axle (W), - a rod (3) mounted for rotation in a housing about a rod axle (A), the rod comprising a first portion (31) equipped with an external thread having a right-hand pitch and a second portion (32) equipped with an external thread having a left-hand pitch, - a drive member (4) configured to selectively rotate the rod in one direction or the other (T1,T2), - a first locking member (1) comprising a first sleeve (10) centered on the rod axle and a first projection (5) extending radially outwards from the sleeve, the sleeve comprising an internal thread,adapted to cooperate by complementary shape with one of the external threads of the rod, the first projection comprising a free end forming a stop to prevent a tooth of the gear from engaging in a first direction of rotation (S1), - a second locking member (2) comprising a second sleeve (20) centered on the axis of the rod and a second projection (6) extending radially outwards from the sleeve, the sleeve comprising an internal thread adapted to cooperate by complementary shape with the other of the external threads of the rod, the second projection comprising a free end forming a stop to prevent a tooth of the gear from engaging in a second direction of rotation (S2), - guide elements (7) to prevent the rotation of the first and second locking members around the axis of the rod but to allow the translation of the locking members along the axis of the rod.

2. Locking device according to claim 1, wherein each of the first and second projections is formed as a finger which extends along an extension direction (XI,X2) inclined with respect to the axis of the rod.

3. A locking device according to claim 2, wherein the respective fingers of the first and second projections are directed towards each other.

4. A locking device according to any one of claims 1 to 3, wherein the ends of the first and second projections are moved in translation along a tangent to a primary circle of the gear.

5. Locking device according to any one of claims 1 to 4, wherein the rod axis (A) is perpendicular with respect to the wheel axis (W).

6. Locking device according to any one of claims 1 to 5, wherein the first and second projections generally extend in a radial plane (PR) perpendicular to the wheel axis (W).

7. Locking device according to any one of claims 1 to 5, wherein the first and second projections act on the same tooth of the gear.

8. Locking device according to any one of claims 1 to 6, wherein the number of teeth on the toothed wheel (8) is between 10 and 20.

9. Locking device according to any one of claims 1 to 7, wherein the rod is mounted and interposed between a bearing (34) of the drive member and an opposite bearing (39) connected to the transmission housing (9).

10. Vehicle transmission comprising a locking device according to any one of claims 1 to 9.

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