The present invention relates to an assist mechanism for assisting movement of an actuation device, particularly, but not exclusively, for use in clutch control systems.

EP 1722119 describes an assist mechanism for assisting the movement of a piston in a clutch actuation assembly for a motor vehicle. The piston is movable under hydraulic actuation and a spring element acts on the piston, e.g. to reduce the hydraulic force required to drive the piston.

It is an object of the invention to provide an improvement or alternative to the assist mechanism referred to above.

According to a first aspect of the invention, there is provided an assist mechanism for an actuation device, the assist mechanism including a spring element arranged for generating an assist force for the actuation device and a reaction element arranged to change the flexed shape of the spring element in order to change said assist force, wherein relative movement between the spring element and the reaction element brings about a change in flexed shape of the spring element, which produces a change in the assist force from the spring element, and wherein the assist mechanism configured to transfer the assist force from the spring element to a shaft intended to reciprocate along a linear thrust axis.

It will be understood that the assist force from the assist mechanism is dependent upon the shape and force characteristic of the spring element. The spring element is preferably of known shape and force characteristic, such that a predetermined change in the flexed shape of the spring element will result in a predetermined change in the assist force.

The spring element can be designed for specific applications. For example, the spring element may be designed for use in clutch applications, and so may be configured to compensate for kiss point sensitivity in a dry clutch. The spring element may include localised work hardening and/or areas of surface treatment (e.g. areas of nitride treatment), which are intended to influence the force characteristic of the spring element, e.g. to provide non-homogeneous spring characteristics.

In preferred embodiments, the assist mechanism is configured such that the spring element is supported in a first flexed shape when the reaction element is in a first position relative to the spring element, and is further configured such that a change in the relative position of the reaction element to the spring element from said first position causes a change in the flexed shape of the spring element from said first flexed shape.

The assist mechanism preferably includes a shaft intended to reciprocate along a linear thrust axis, wherein the change in the assist force resulting from relative movement between the spring element and reaction element is transferred to the shaft.

The spring element may be coupled for movement with the shaft and the reaction element is fixedly mounted on a grounded element located separate from the shaft to provide a grounded reaction against the spring element during movement of the shaft. In such embodiments, the spring element may be substantially bell-shaped and arranged coaxially with the thrust axis of the shaft. A plurality of reaction elements may be arranged to act on the spring element, e.g. one or more pairs of diametrically opposing reaction elements.

In other embodiments, the spring element is mounted on a grounded element and the reaction element is arranged for movement with the shaft. Again, spring element may be generally annular in relation to the shaft, and a plurality of reaction elements may be arranged on the shaft to act on the spring element, e.g. one or more pairs of diametrically opposing reaction elements.

In any of the embodiments, the assist mechanism may include a cam element against which the spring element is intended to deform under influence of the reaction element. Alternatively or in addition, one or more additional spring elements may be provided between the spring element and the reaction element, in order to modify the rate of change of assist force during deformation of the spring element.

The reaction element preferably includes a roller for contact with the spring element.

According to a second aspect of the invention there is provided a clutch control system including a clutch, an actuator arranged for opening or closing a clutch, and an assist mechanism provided in communication with the actuator for maintaining a clamp load at the clutch, wherein the assist mechanism includes a spring element and a reaction element arranged to act on the spring element, the spring element and reaction element configured such that relative movement between the spring element and driver brings about a change in the flexed shape of the spring element, in order to change in output force from the assist mechanism to the actuator.

The actuator preferably includes an output shaft intended to reciprocate along a linear thrust axis, for applying or releasing (dependent on the direction of movement of the shaft) force at the clutch, and the assist mechanism is intended to influence movement of said output shaft.

The assist mechanism in the second aspect of the invention may include any of the features of the assist mechanism from the first aspect of the invention.

It will be understood that the concept of an assist mechanism incorporating a spring element and a reaction element, configured such that relative movement between the spring element and reaction element brings about a change in the flexed shape of the spring element to change an output force from the assist mechanism is not limited in application to clutch control systems, but can be readily applied to other applications, e.g. for assisting movement of other force return devices in automotive and non- automotive applications.

According to another aspect of the invention, there is provided an actuation assembly having a movable output intended to reciprocate along a thrust axis, the actuation assembly incorporating an assist mechanism for assisting movement of the output along said thrust axis, wherein the assist mechanism includes a spring element arranged for generating an assist force for the output and a reaction element arranged to change the flexed shape of the spring element in order to change said assist force, and wherein the assist mechanism is configured such that relative movement between the spring element and the reaction element brings about a change in flexed shape of the spring element, thereby changing in the assist force from the spring element, wherein the assist mechanism is configured to transfer the assist force from the spring element to said output.

The spring element is preferably of known shape and force characteristic, such that a predetermined change in the flexed shape of the spring element will result in a predetermined change in the assist force.

Preferably, the assist mechanism is configured such that the spring element is supported in a first flexed shape when the reaction element is in a first position relative to the spring element, and is further configured such that a change in the relative position of the reaction element to the spring element from said first position causes a change in the flexed shape of the spring element from said first flexed shape.

Preferably, the spring element is coupled for movement with the output and the reaction element is fixedly mounted on a grounded element located separate from the output to provide a grounded reaction against the spring element during movement of the output.

More preferably, the spring element is substantially bell-shaped and arranged coaxially with the thrust axis of the output.

The output is preferably arranged to act on the spring element, for urging the spring element towards or away from the reaction element.

The spring element may be mounted on a grounded element with the reaction element arranged for movement with the output. A cam element may be provided against which the spring element is intended to deform under influence of the reaction element.

One or more additional spring elements may be provided between the spring element and the reaction element, in order to modify the rate of change of assist force during deformation of the spring element.

The reaction element may include a roller for contact with the spring element.

The output is preferably a shaft or piston arranged for movement along a preferably linear thrust axis.

Other aspects and preferred features of the invention will be readily apparent from the following description of preferred embodiments, made by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic cross-sectional side view through part of a clutch control system incorporating a spring biased assist mechanism in a first position;

Figure 2 is similar to Figure 1 and shows the assist mechanism in a second position; and

Figure 3 is similar to Figures 1 and 2 but includes a modified assist mechanism.

A clutch for a motor vehicle is indicated generally at 100 in Figure 1. A bi-directional actuator 102 is arranged for opening or closing the clutch 100. In this embodiment, the actuator 102 includes an output shaft 104 intended to reciprocate along a linear thrust axis 106, e.g. from left to right as viewed in Figure 1, for applying or releasing (dependent on the direction of movement of the shaft 104) force at the clutch 100.

An assist mechanism, indicated generally at 108, is provided in communication with the output shaft 104 of the actuator 102, e.g. for use in maintaining a clamp load at the clutch 100. The assist mechanism 108 includes a spring element 110 and a reaction element or driver 112, configured such that relative movement between the spring element 110 and driver 112 brings about a change in the flexed shape of the spring element 110. More particularly, it will be understood that the spring element 110 defines a particular flexed shape when the reaction element 112 is in a particular position relative to the spring element 110. However, a change in the relative position of the reaction element 112 to the spring element 110 will cause a change in the flexed shape of the spring element.

The spring element 110 is of known profile and force characteristic, and so a change in the flexed shape of the spring element 110 results in a change in the output force to the output shaft 104, dependent upon the profile and force characteristic of the spring element 110.

In the embodiment of Figure 1, the spring element 110 is arranged in direct communication with the output shaft 104 and the driver 112 is fixedly mounted on a grounded element 114 (e.g. a housing or casing) located separate from the shaft 104.

The spring element 110 is preferably bell-shaped and, more preferably, is arranged coaxially with the thrust axis 106 of the shaft 104, in order to balance working loads during movement of the shaft 104. Although shown with the end of the bell-shape located over one end of the shaft 104 in Figure 1, in other embodiments the shaft 104 may extend through an aperture (not shown) in the spring element 110, provided that the spring element 110 is suitably keyed or otherwise connected to the shaft 104 at or adjacent the point at which the shaft 104 passes through the spring element 110. The free end of the spring element 110 is constrained against axial movement relative to the shaft 104 by a stop member 116 extending radially from the shaft 104.

In use, the actuator 102 is operated to move the shaft 104 in a clutch closing direction along axis 106, e.g. as shown in Figure 2, in order to apply a clamp load to the clutch 100. Movement of the shaft 104 cause the spring 110 to be urged against the driver 112, which serves as a grounded reaction to movement of the spring element 110, resulting in a change in the flexed shape of the spring element 110. The change in flexed shape generates an assist force which is transferred to the output shaft 104 in the clutch apply direction, e.g. to reduce or overcome return forces generated by the clutch 100.

A cam element 118 may be provided on the output shaft 104, against which the spring 110 is intended to be flexed by said driver 112, during travel of the output shaft 104. The cam element 118 has a predetermined profile configured to impart specific loads for a given length of travel of the shaft 104, e.g. to modulate the assist force experienced by the output shaft 104 (beneficial for controlling slip of the clutch 100).

The embodiment of Figure 3 differs from the embodiments of Figures 1 and 2 in that the spring element 110 is mounted on the grounded element 114 and the driver 112 is mounted on the shaft 104. Otherwise, operation of the mechanism 108 is the same, i.e. travel of the shaft 104 causes the driver 112 to change the flexed shape of the spring element 110, which results in a change in the assist force from the spring element 110, dependent upon the profile and force characteristic of the spring element 110.

In the embodiment of Figure 3, the assist mechanism 108 is located upstream of actuator 102 (i.e. between the actuator 102 and the clutch 100), but may be arranged downstream of the actuator 102 as shown in Figures 1 and 2.

Contrary to Figures 1 to 3, the assist mechanism may be located independently of the shaft 104, e.g. as a separate mechanism incorporating a movable shaft intended to act on a free end of the shaft 104.

In each embodiment, the driver 112 preferably includes a roller 120 for contact with the spring element 110.

One or more additional spring elements (not shown) may be provided between the spring element 110 and the driver 112 or cam element 118, in order to modify the rate of change of feree output during deflexion of the spring element 110. The concept of an assist mechanism incorporating a spring element and a driver, configured such that relative movement between the spring element and driver brings about a change in the flexed shape of the spring element to change an output force from the assist mechanism is not limited in application to clutch control systems, but can be readily applied to other applications, e.g. for assisting movement of a force return device such as a piston (in automotive and non-automotive applications).