GB2218758A

GB2218758A - Override control of centrifugally operated clutch

Info

Publication number: GB2218758A
Application number: GB8811690A
Authority: GB
Inventors: A E Lynes
Original assignee: Self Changing Gears Ltd
Current assignee: Self Changing Gears Ltd
Priority date: 1988-05-18
Filing date: 1988-05-18
Publication date: 1989-11-22
Also published as: GB8811690D0

Abstract

An override control consists of units 6-10 mounted into the clutch driving member at each location of the shoes causing clutch engagement by centrifugal action. Each unit consists of a piston 6 and enclosing cylinder 8, an extension of the piston being connected to the clutch shoe which provides the mass upon which the centrifugal force acts against spring restraint. The volume in the cylinder not occupied by the piston and its extension is filled with an electro-rheological fluid which becomes solid when an electric current is applied to it, so restraining the piston from movement. With the piston 6 held, the clutch shoe is prevented from moving under the action of centrifugal force so that clutch engagement can only take place when the electric current is switched off at the desired speed of engagement. <IMAGE>

Description

OVERRIDE CONTRA OF ENTRIFUGALLY OPERATED CLUTCH This invention relates to a system for controlled power transmission between a vehicle engine and a load imposed by the vehicle gearbox and in particular to a system including a clutch which engages the driven member by the action of centrifugal force upon weights within the clutch assembly.

The use of centrifugally operated clutches is well known as a power takeup device in many types of vehicles and may consist of shoes engaging within an annular drum or a series of plates clamped together by a lever system connected to weights affected by centrifugal force. Whichever system is considered the power transmitted and the speed at which this takes place is governed by the mass of the weights, the speed at which they rotate about the shaft centre and their radius of operation. Thus with a given coefficient of friction between the engaging surfaces the clutch will have a fixed relationship between power transmitted and input speed defined by the physical dimensions of the design.This characteristic is satisfactory over a wide field of operation but problems arise wnen it is desired to change the engaging speed without materially altering the physical dimensions of the clutch assembly.

An instance of this is when a turbo-charged engine replaces a normally aspirated unit and it is necessary to retain the same clutch assembly.

The turbo charged engine has a torque characteristic which requires a different clutch engagement pattern and it is an object of this invention to provide a control which over-rides the centrifugal operating force.

The invention consists of a piston within an enclosing cylinder, the piston having a shaft extension connecting with the operating mass of the centrifugal clutch. The cylinder is filled with a fluid having the property of becang a cement-like solid when a high voltage electrical current is applied to the fluid. The fluid, known as electro-rheological fluid, is a mixture of synthetic oil,water and microscopic polymer particles. Frrm the cylinder a terminal projects, connecting internally with the fluid and externally to the electrical power source. The power source may be a small battery pack as the current required is only approximately 2 milliamperes.Control of the power supply to the fluid is by an inter-connection with the engine/transmission management system so that the clutch may be held out of engagement as required by the prevailing vehicle operating conditions.

In order that the invention may be better understood a preferred embodiment will now be described with reference to the accompanying drawings in which : Figure 1 is a perspective view with a partial cross section of a centrifugal clutch embodying the present invention.

Figure 2 is a cross section through one of the centrifugally operated shoes in the non-driving condition.

Figure 3 is a cross section through one of the centrifugally operated shoes in the driving condition.

Referring to the drawings an override control unit is mounted into the clutch driving hub 1 at the radial centre of each shoe. In the example shown, six shoes are used but the invention may be applied to clutches with any number of shoes. Secured to each shoe is a moulded element 3 having high friction characteristics and which engage with the inner surface of the clutch driven member 4. Surrounding shoes are garter springs 5 which retain the shoes in contact with the hub until the centrifugal force overcomes the spring retaining force. Four garter springs are shown but any number may be used to give the required retaining force.

The piston 6 of the override control is connected to the plug 7, this latter being integral with the clutch shoe.The piston 6 operates within a cylinder formed in the control body 8 and a screwed cap 9 closes the cylinder. A terminal 10 is fitted to the screwed cap and insulated from the cap by a bush 11 and washer 12, these latter two items being made fram a non-conducting material. The terminal 10 is held in position by a nut 13 also retaining the connecting tag 14 to which is attached the wire carrying an electric current fron an outside source.

The space 15 which remains in the cylinder i.e. the cylinder volume unoccupied by the piston and its connecting rod is filled with an electrorheological fluid which as previously explained responds to a electric current applied through the terminal 10.

When the electric current is applied with the clutch in the condition shown by Figure 2, the fluid becomes a solid and prevents the shoe 2 from moving out of contact with the hub 1, when the centrifugal force created by the rotational speed of the hub is greater than the restraining force of the garter springs. Thus the speed at which the clutch may be engaged is determined by the engine/transmission management system which cuts off the electric current at the appropriate time.

When the current is switched off the electro-rheological fluid reverts instantly from the solid to a liquid state and the centrifugal force takes over to engage the clutch. Slots 16 in piston 6 allows the fluid to transfer from one side of the piston face to the other as the clutch engages or dis-engages. A sealing ring 17 on the piston rod prevents leakage of the fluid fran the cylinder. Figure 3 shows the clutch in the engaged condition.

Claims

1. An override control for the centrifugally operated clutch comprising an adaptor body Ssecured into the clutch driving member, the body having a cylindrical recess closed by a screwed cap at one end and a hole concentric with the recess, through the body at the other end.

2. An override control as claimed in Claim 1 wherein a piston slides in the cylinder provided in the body, the piston having an extension passing through the hole in the body.

3. An override control as claimed in Claims 1 and 2 wherein the extension of the piston is firmly affixed to the clutch shoe, said shoe being the mass providing the clutch clamping force when under centrifugal action

4. An override control as claimed in Claims 2 and 3 wherein the free space within the cylinder is filled with an electro rheological fluid which when acted upon by an electric current becones solid and thus arrests the piston fran movement and overrides the centrifugal force generated by the mass of the shoe and the speed of rotation.

5. An override control as claimed in Claim 4 wherein the cap closing the cylinder in the control body is provided with an insulated terminal to carry the electric current fran an outside source to the rheological fluid.

6. An override control substantially as described herein with reference to Figures 1, 2 and 3 of the acoompanying drawings.

7. An override control provided for each of the separate masses in a multiple shoe centrifugal clutch.