Roll restrictor system for an automotive powertrain

An aspect of the invention provides a roll restrictor system for an automotive powertrain, comprising: a torque roll restrictor bracket configured for attachment to the automotive powertrain; wherein attachment is mediated by a bushing; wherein the bushing is provided within a bearing which facilitates rotation of the bushing within the torque roll restrictor bracket.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Great Britain Patent Application No. 1705023.8, filed Mar. 29, 2017. The entire contents of the above-referenced application are hereby incorporated by reference in its entirety for all purposes.

FIELD

The present disclosure relates to a roll restrictor for preventing unwanted translation and rotation of an automotive powertrain.

Automotive powertrains, particularly powertrains used with front wheel drive vehicles and featuring an engine and transaxle mounted in a conventional east-west direction—i.e., with the engine's crankshaft perpendicular to the longitudinal center line of the vehicle—utilize roll restrictors to prevent unwanted rotation of the engine and transaxle about an axis which, if not coincidental with the engine's crankshaft center axis, is at least parallel thereto.

Known automotive powertrain roll restrictors utilize brackets for attaching the roll restrictor to the transaxle or engine. An example of known roll restrictor bracket is described in published US patent application US2015/152953 and shown inFIG. 1.

Downsized powertrains such as those including a three-cylinder engine are inherently imbalanced due to increased roll/yaw motion as compared to four-cylinder engines. To address the increased roll/yaw motion, it is necessary to minimize the translational and especially the rotational stiffness of the roll restrictor system.

One way of reducing translational and rotational stiffness of the roll restrictor system is to use a softer material in the rubber bushes that mediate attachment of the roll restrictor bracket to the engine or transaxle. However, use of a softer material, while providing noise, vibration and harshness (NVH) benefits may result in a decrease in durability and lifespan of the rubber bushes due to rotational wear of the bushes as they rotate in the roll restrictor bracket.

Rotational wear can be partially addressed by pressing a sleeve into the roll restrictor bracket and pressing the rubber bush into the sleeve as described in published US patent application US2015/0283891. However, such a configuration does not adequately address rotational wear of the rubber bush as it is still able to rotate relative to the sleeve. Furthermore, the sleeve would wear as it rotates relative to the roll restrictor bracket. Under cornering load the rubber bush may become displaced laterally relative to the engine or transaxle risking failure of the connection therebetween. The application of heat from the powertrain further exacerbates the issues of low durability and increased failure risk.

It is against this background that the present invention has arisen.

An aspect of the invention provides a roll restrictor system for an automotive powertrain, comprising: a torque roll restrictor bracket configured for attachment to the automotive powertrain; wherein attachment is mediated by a bushing; wherein the bushing is provided within a bearing which facilitates rotation of the bushing within the torque roll restrictor bracket.

Use of a bearing in which the bushing is mounted significantly reduces rotational strain on the bushing, thus greatly increasing the durability thereof. Furthermore, the reduced rotational strain exhibited by the bushing enables a softer material to be used thus providing noise, vibration and harshness (NVH) benefits.

The bushing may be a voided bushing. Use of a voided bushing may result in greater softening of the rubber material at temperature as compared to a solid bushing. Softening of the rubber results in reduced translational and rotational stiffness of the roll restrictor system and improved NVH benefits.

The voided bushing may comprise at least two arms which support the voided bushing in an opening through the torque roll restrictor bracket. The at least two arms may comprise four arms. The use of arms to interface with the bearing provides at least two points of contact between the bushing and the bearing thus further reducing the rotational and translational stiffness of the bushing.

The bushing may be a solid bushing. Use of a solid bushing imparts lesser strain to the bushing as compared to a voided bushing due to having more material than a comparable voided bushing and consequently a greater stiffness.

The bearing may be a ball-bearing. Use of a ball bearing is advantageous as the bearing is inserted into the inner ring of the ball bearing. The inner ring rotates relative to the race and the bushing is not in direct contact with any moving surface. Therefore, the longevity of the bushing is increased due to the only cause of wear being a small degree of repetitive rotation of the bushing within the inner ring as the powertrain moves relative to the roll restrictor bracket. The ball bearing may be a self-aligning ball bearing. Use of a self-aligning ball bearing allows for both low rotational and transitional stiffness in the bushing thus further increasing durability of the bushing.

The bearing may be a roller bearing. Use of a roller bearing is advantageous as the bearing acts directly on the bushing, or a sleeve within which the bushing is pressed. A tight fit between the rollers and bushing dictates that the rollers cannot detach from the bearing under normal loads. Roller bearings are durable and accurate and the friction produced in use is minimal as compared to other types of bearing.

The roll restrictor bracket may be attached to the powertrain in at least two places and to a vehicle chassis or sub-frame in at least one place. The bearing may have an outer surface that is coated with a vibration absorbing material.

Coating of the outer surface of the bearing with a vibration absorbing material provides additional NVH benefits which may be desirable in certain applications where noise, vibration or harshness is recognised as a problem.

DETAILED DESCRIPTION

As shown inFIG. 1, an automotive powertrain10includes a prior art roll restriction system12comprising a core14that is attached to a vehicle sub-frame of a vehicle2, e.g. via a link bolt16; and a housing18that is in turn connected to a mounting bracket20via a bolt22through a bushing24. The mounting bracket20is mounted to the transmission clutch housing26via one or more further bolts28. The vehicle2may be a wheeled motor vehicle for travel on a road.

FIG. 2illustrates one solution that results in reduced translational and rotational stiffness of the roll restriction system10. The bushing24has a key shaped aperture30therethrough for receiving a bolt22. The bushing24is voided such that it is supported in the mounting bracket20by two diametrically opposed rubber arms32instead of a solid rubber bush.

The bushing24is either bonded directly to the mounting bracket20, or to a sleeve (not shown) which is pressed into the mounting bracket20. As the powertrain10rotates it will induce rotation of the bushing24relative to the mounting bracket20. This creates greater strain within a voided bushing24as compared to a solid bushing due to the reduced rubber and stiffness of the voided bushing24. As temperature of the voided bushing24rises the rubber softens thus enhancing the strain within the voided bushing further.

Bonding the bushing24into a sleeve (not shown) and pressing the sleeve into the mounting bracket20results in sleeve wear due to rotation of the sleeve relative to the mounting bracket20and can result in axial movement of the bushing24relative to the mounting bracket20under cornering load.

A solution to increased strain exhibited by a voided bushing is found inFIGS. 3, 4 and 5. The voided bushing24is pressed directly into a bearing34(FIG. 3) or self-aligning ball-bearing36(FIG. 4) or roller bearing38(FIG. 5). The voided bushing24is permitted to rotate freely relative to the mounting bracket20while being held in place by the bearing34,36,38. The bearing, in some embodiments, is a self-aligning ball bearing36, as illustrated inFIG. 4which permits certain rotation of the ball ring in both a first rotational orientation and a second rotational orientation relative to the ball bearing race.

In some embodiments, the voided bushing24is first pressed into a sleeve40. The sleeve40is then pressed into the bearing34,36,38.

In some embodiments the bearing42, as illustrated inFIG. 6, is provided with an outer surface coated with a vibration absorbent material44such as rubber.FIG. 6does not show a bushing pressed into the bearing42but it will be appreciated that either a voided bushing24or solid bushing could be used to mediate attachment of the mounting bracket20to the automotive powertrain10.

It will further be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined in the appended claims. In particular, reference to a voided bushing throughout the description is not intended to be limiting and those skilled in the art will appreciate that a solid bushing could be used in some applications of the invention.