Patent Description:
Vehicles are typically provided with a number of paired rotational members which need to be selectively connected to each other in order to allow for a desired torque transfer between the respective members. For example, such members may be an input drive shaft and an output drive shaft, or an output shaft of an electrical motor and an associated drive train member.

Selective torque transfer between two rotational members is typically regulated by means of a clutch, and appropriate control of such clutch. The clutch may e.g. be a disc clutch or a dog clutch, having one side being connected to a rotational input shaft and a second side being connected to an output shaft which, upon closing of the clutch, is urged to rotate with the rotational input shaft.

Clutch control requires an actuator. Although various types exist on the market, there is an increasing demand for electrical actuators. An electrical actuator is typically operating against an elasticity; in case of a dog clutch the elasticity is provided by means of a return spring biasing the dog clutch towards an unconnected mode, and in case of a disc clutch the elasticity is provided by means of the intrinsic biasing of the individual discs. The elasticity ensures that no torque transfer is present when the drive current is zero. This configuration is due to safety reasons, preventing unintentional lock-up of the clutch. On the other hand, it is required to counteract the elasticity during clutch activation whereby high current must be supplied to the actuator during stationary torque transfer.

Document <CIT> discloses an isolating decoupler having a torsion spring having a first section having a major diameter and a second section having a minor diameter, the second section is disposed radially outboard of a wrap spring such that the second section moves radially inward to progressively clamp the wrap spring to a shaft during a load condition.

Further, in document <CIT> a double wrap spring with an inner winding region and an outer winding region, which regions are oppositely winded, is shown. The double wrap spring may be arranged in a rotation device between a shaft and a hollow hub to transfer rotation in one direction.

In order to reduce power consumption, but also to protect the electrical actuator from overheating, it is desired to bring down the stationary holding torque of the electrical actuator while still ensuring zero holding torque when there is no drive current. An improved electrical actuator is therefore required.

It is an object to provide an improved electrical actuator which can alleviate some of the problems of prior art. Also, it is an object to provide an electrical actuator which provides the desired operational functionality by means of a simple, robust, reliable, and cost-effective manner.

According to a first aspect, an electrical actuator is provided. The electrical actuator comprises an electric drive means and a drive member being rotationally driven upon activation of the electric drive means, an output member being rotationally connected to the drive member by means of a first one way spring clutch, and a second spring being connected to the output member and forming a one way clutch between the output member and a fixed tube forming part of a stationary housing. The electrical actuator further comprises a regulation cup being configured to engage with the second spring to disconnect the output member from the fixed tube. The second spring is maneuverable between an idle position in which the output member is connected to the fixed tube, and an open position in which the output member is disconnected from the fixed tube.

The drive member and the output member may be arranged coaxially.

The regulation cup may surround the drive member as well as the output member.

A first end of the first spring may be fixed to the output member, and a second end of the first spring may be fixed to the drive member as well as to the regulation cup.

The first spring may be configured to provide for an automatic return rotation of the output member when the second spring is maneuvered into its open position.

The regulation cup may have a circular end at the axial position of a radially protruding end of the second spring, and at least one axial edge being configured to push the end of the second spring upon rotation of the regulation cup.

The axial edge of the circular end may be formed by an interface between an axially longer portion of the circular end and an axially shorter portion of the circular end.

According to a second aspect, a clutch is provided. The clutch comprises an electrical actuator according to the first aspect.

The clutch may be provided with elastic properties arising from a return biasing feature of the clutch.

According to a third aspect, a vehicle is provided. The vehicle comprises at least one clutch according to the second aspect.

The invention will be described in further details below with reference to the accompanying drawings, in which:.

In <FIG> a vehicle <NUM> is shown schematically. The vehicle <NUM> has a front axle <NUM>, a rear axle <NUM>, and a propulsion unit <NUM> being connected to the front axle <NUM>, the rear axle <NUM>, or both. The vehicle <NUM> is provided with one or more clutches 9a-b. In the shown example a first clutch 9a is arranged at the rear axle <NUM> to allow for all wheel drive of the vehicle <NUM>. The first clutch 9a is for this purpose a disc clutch 9a being arranged at a rear axle differential <NUM>, and by activating the disc clutch 9a the rear axle <NUM> is receiving drive torque from the propulsion unit <NUM>.

The vehicle <NUM> of the shown example is also equipped with a second clutch 9b, here in the form of a dog clutch 9b arranged at the front axle <NUM> and configured to disconnect the rear axle <NUM> (as well as a cardan shaft <NUM>) from the drive train. When driving in two wheel drive mode, the dog clutch 9b is disconnected thereby reducing the rotating masses of the vehicle <NUM>. When four wheel drive mode is requested, the disc clutch 9a is activated to spin up the cardan shaft <NUM>, whereafter the dog clutch 9b is activated to connect the rear axle <NUM> to the propulsion unit <NUM> (via the dog clutch 9b and the disc clutch 9a).

At least one clutch 9a-b is regulated by means of an actuator <NUM>, which will be further described in the following. However, before turning to details of the electrical actuator <NUM> it should be noted that the exact configuration of the vehicle <NUM> shown in <FIG> is only for illustrative purposes. It should be readily understood that the vehicle <NUM> could in principle have any possible configuration, as long as there is at least one electrical actuator <NUM> arranged in conjunction with any suitable clutch 9a-b. Such examples include transfer cases, electric drive trains, torque vectoring systems, etc..

An embodiment of an electrical actuator <NUM> is show in <FIG>. The electrical actuator <NUM> comprises an electric drive means <NUM>, e.g. a DC motor, a brushless DC motor, or a rotational solenoid. The electrical actuator <NUM> also has an output member <NUM> which is in connection with a clutch (not shown) through any suitable connection or gearing. As explained earlier, the clutch may e.g. be a dog clutch 9b or a disc clutch 9a. Importantly, the associated clutch 9a-b forms an elastic system, i.e. it is provided with a return biasing feature such that the output member <NUM> is subjected to a return force, as will be explained further below. Preferably, the clutch is configured such that rotation of the output member <NUM> will control actuation of the clutch.

The electric drive means <NUM> is connected to a drive member <NUM>, which is configured to rotate upon activation of the electric drive means <NUM>. With reference to the output member <NUM> the drive member <NUM> forms an input shaft. The drive member <NUM> is connected to the output member <NUM> by means of a return rotation spring <NUM> forming a one way clutch. The drive member <NUM> and the output member <NUM> are arranged coaxially, and having axial ends facing each other. The return rotation spring <NUM> is arranged around the outer circumference of the drive member <NUM> and the output member <NUM>. One end 28a of the return rotation spring <NUM> is secured to the output member <NUM>, for example by inserting the end 28a into a drilled radial hole of the output member <NUM>. The opposite end 28b of the return rotation spring <NUM> is securely attached to the drive member <NUM>, and to a thereto connected regulation cup <NUM>. The regulation cup <NUM> is thus rotationally secured to the drive member <NUM>.

When the electric drive means <NUM> is activated the drive member <NUM> will rotate, thus also causing the return rotation spring <NUM> to rotate. As one end 28a of the return rotation spring <NUM> is fixed to the output member <NUM>, the diameter of the return rotation spring <NUM> will decrease until it comes into contact with the external surfaces of the drive member <NUM> and the output member <NUM>. Consequently, rotation of the output member <NUM> is accomplished. This rotational motion of the output member <NUM> corresponds to the action of actuating the associated clutch, for example by compressing a spring or by urging discs towards each other.

The outer circumference of the output member <NUM> is also provided with a spring forming a one way spring clutch <NUM>. For this, the output member <NUM> is provided with a radial extension <NUM> onto which the spring <NUM> is arranged; the spring <NUM> is thereby arranged at a different radial, as well as axial position as compared to the return rotation spring <NUM>.

One end 32a of the spring <NUM> is rotationally fixed to the output member <NUM>, e.g. by means of inserting the end 32a into a drilled radial hole. The spring <NUM> is clamped around a fixed tube <NUM>, forming part of a stationary housing <NUM>. Hence, when the electric drive means <NUM> is activated rotation of the output member <NUM> will also allow the spring <NUM> to rotate around the fixed tube <NUM>.

When the desired rotation of the output member <NUM> is reached, i.e. when the associated clutch 9a-b is actuated in the desired manner, the current being supplied to the electric drive means <NUM> is significantly reduced, such as down to a level of <NUM>-<NUM> %, preferably <NUM> % compared to the current required during actuation. This corresponds to a so called holding position, in which the output member <NUM> of the actuator <NUM> is intended to retain its position obtained by rotation of the drive member <NUM>. This current is sufficient to drive the electric drive means <NUM> to keep the drive member <NUM> in position, while the provision of the spring <NUM> will prevent automatic return movement of the output member <NUM>. This is due to the fact that the friction between the spring <NUM> and the fixed tube <NUM> prevents automatic return rotation of the output member <NUM> relative the fixed tube <NUM>, whereby the spring <NUM> will accommodate the torque through the fixed tube <NUM>.

When actuation is completed the drive current is shut off, thus leading to zero torque supplied by the electric drive means <NUM>. The return rotation spring <NUM> will then be allowed to rotate the drive member <NUM> and the electric drive means <NUM> backwards, which also causes a corresponding rotational movement of the regulation cup <NUM>. The regulation cup <NUM> surrounds not only the drive member <NUM>, but also the output member <NUM> and extends as a sleeve surrounding these two members <NUM>, <NUM>. As already mentioned, one end 30a of the regulation cup <NUM> is rotationally fixed to the drive member <NUM>. The opposite end 30b has a circular shape, as illustrated in <FIG>. This circular end 30b has a portion of its circumference being axially cut off, such that a first portion 30c of the periphery of this end 30b has a somewhat greater axial length than another portion 30d of the periphery. The two portions 30c-d are arranged adjacent to each other and together forming the entire circular periphery, which means that two axial edges 30e are formed at the interface between the two portions 30c-d. The axial length and diameter of the circular end 30b of the regulation cup <NUM> is dimensioned such that an axial end 30e can come into contact with a radial protruding end 32b of the spring <NUM>.

As the regulation cup <NUM> rotates backwards the axial end 30e will eventually touch and push the radial end 32b of the spring <NUM>, causing its clutch functionality to open, whereby the output member <NUM> rotates backwards.

Claim 1:
An electrical actuator (<NUM>), comprising an electric drive means (<NUM>) and a drive member (<NUM>) being rotationally driven upon activation of the electric drive means (<NUM>), an output member (<NUM>) being rotationally connected to the drive member (<NUM>) by means of a first one way spring clutch (<NUM>), and a second spring (<NUM>) being connected to the output member (<NUM>) and forming a one way clutch between the output member (<NUM>) and a fixed tube (<NUM>) forming part of a stationary housing, wherein the electrical actuator (<NUM>) further comprises a regulation cup (<NUM>) being configured to engage with the second spring (<NUM>) to disconnect the output member (<NUM>) from the fixed tube (<NUM>), and characterized in that the second spring (<NUM>) is maneuverable between an idle position in which the output member (<NUM>) is connected to the fixed tube (<NUM>), and an open position in which the output member (<NUM>) is disconnected from the fixed tube (<NUM>).