WO2005036009A1

WO2005036009A1 - Clutches including a magneto-rheological fluid

Info

Publication number: WO2005036009A1
Application number: PCT/GB2004/004297
Authority: WO
Inventors: Jonathan Wheals; Andrew Turner; Keith Ramsay; James Michael Hey
Original assignee: Ricardo UK Ltd
Current assignee: Ricardo UK Ltd
Priority date: 2003-10-08
Filing date: 2004-10-08
Publication date: 2005-04-21
Anticipated expiration: 2006-04-08
Also published as: GB0413464D0; GB0323579D0

Abstract

A clutch for transmitting torque between two rotary shafts (6, 8) comprises a first clutch plate (2), which is opposed to a second clutch plate (4). The two clutch plates are accommodated within a housing (10) and define a gap. The interior of the housing accommodates a magneto-rheological fluid, at least some of which is within a gap. The clutch includes a first electromagnetic coil (26) which is so arranged that, when it is energised, it produces an electromagnetic field in the vicinity of the gap and causes the fluid to occupy the gap. The electromagnetic field causes the viscosity of the fluid to increase and thus in torque being transmitted between the two clutch plates. The clutch also includes a second electromagnetic coil (28) arranged so that when it is energised the fluid is caused to move out of the gap, whereby no torque is transmitted between the two clutch plates.

Description

CLUTCHES INCLUDING A MAGNETO-RHEOLOGICAL FLUID

The invention relates to clutches of the type including a magneto-rheological fluid and, more specifically, is concerned with a clutch for transmitting torque between two rotary shafts comprising a first rotary member which is opposed to a second rotary member, the two rotary members being accommodated within a housing and defining a gap, the interior of the housing accommodating a magneto-rheological fluid (MRF), the clutch including a first electromagnetic coil, which is operable to alter the viscosity of the MRF and thus to vary the torque transmitted between the two rotary members.

U.S. Patent No. 6032772 discloses a clutch or coupling of the type referred to above which is used to vary the power transmitted from an automotive engine to the cooling fan of the engine. The clutch or coupling disclosed in this document includes two relatively rotatable members, which are connected to the input and output, respectively, and define between them a shear gap in which an MRF is accommodated. An electromagnetic coil is arranged to produce an electromagnetic field in the region occupied by the MRF. When it is desired to transmit torque from the input to the output, electric power is supplied to the electromagnetic coil and the resulting electromagnetic field results, as is known, in an increase in the viscosity of the MRF. This increase in viscosity results in an increase in the torque transmitted between the input and the output. Appropriate adjustment of the electrical power supplied to the electromagnetic coil permits the mechanical power transmitted between the input and the output to be adjusted as desired. When no power is to be transmitted from the input to the output, no electrical power is supplied to the electromagnetic coil. However, MRF is inherently of relatively high viscosity and this means that an appreciable amount of torque is in fact transmitted to the output, even at those times when no output torque is required. This needless power consumption is inconvenient and degrades the overall efficiency of the engine. Furthermore, it means that the MRF is subjected to significant shear forces at all times when the engine is running, that is to say even when no torque is to be transmitted through the clutch, and this results in a reduction in the service life of the clutch because, as is known, MRF is subject to degradation and progressive destruction by the application of shear forces to it. The transmission of a certain amount of torque to the output in the construction disclosed in U.S. 6032772 is not itself a matter of particular concern, other than due to the fact that power is needlessly consumed, because the output shaft is only connected to a cooling fan, which is thus caused to rotate, if relatively slowly, even at those times when no cooling is required. However, an MRF clutch of the type disclosed in U.S. 6032772 would be inherently unsuitable for use as a propulsive power transmission clutch in a motor vehicle because it is necessary in such a vehicle that no torque is applied to the input of the gearbox at those times when a gear change is to be effected because gear changing is effectively impossible under the application of any significant torque.

It is therefore the object of the present invention to provide a clutch or coupling of the general type disclosed in U.S. 6032772 which may be controlled such that no torque is transmitted to the output at those times when no torque is required, thereby permitting the clutch to be used in the driveline of a vehicle. It is a further object of the invention to provide such a clutch in which the mechanical degradation to which the MRF is subjected is reduced to a minimum.

According to the present invention, a clutch for transmitting torque between two rotary shafts comprises a first rotary member, which is opposed to a second rotary member, the two rotary members being accommodated within a housing and defining a gap, the interior of the housing accommodating a magneto- rheological fluid (MRF), the clutch including first and second electromagnetic coils, the first electromagnetic coil being so arranged that, when it is energised, it produces an electromagnetic field in the vicinity of the said gap and the second electromagnetic coil being so arranged that when it is energised the MRF is caused to move substantially out of the said gap.

Thus the clutch in accordance with the present invention is similar in general terms to that disclosed in US 6032772 in that it includes two rotary members, e.g. clutch plates, which are accommodated within a housing and define a gap.

The interior of the housing accommodates MRF which is situated, when the clutch transmits torque, within the gap. An electromagnetic coil is arranged to produce an electromagnetic field in the vicinity of the gap and thus to alter the viscosity of the MRF in the gap. As the electromagnetic field strength is increased, the viscosity of the MRF in the gap increases and the torque transmitted between the two rotary members increases also. The electromagnetic field strength may be increased to a level at which the MRF in the gap becomes effectively solid and the two rotary members are thus effectively locked together and thus rotate at the same speed. However, the clutch in accordance with the invention also includes one or more second electromagnetic coils so arranged that, when energised, the MRF is caused to move substantially out of the said gap. Thus if the clutch is installed in the driveline of a motor vehicle and is thus used to selectively connect the engine output shaft to the gearbox input shaft and it is desired to change gear, the first electromagnetic coil is de-energised, whereby the viscosity of the MRF in the gap becomes relatively low. However, MRF, which typically comprises a relatively high viscosity liquid in which a large number of ferromagnetic particles are suspended, has a relatively high viscosity, even when it is not subjected to an electromagnetic field. This residual viscosity would result in the transmission of a not insignificant amount of torque to the output shaft and thus render gear changing effectively impossible. This is, however, overcome by the provision of the second electromagnetic coil because when it is energised it causes the MRF in the gap to move out of the gap. Torque transmission between the two clutch members then falls substantially to zero, thereby enabling the gear change to be effected. Once the gear change has been completed, the second electromagnetic coil is de-energised and the first coil is re-energised. The field produced by the first coil is configured to cause the MRF to move back into the gap, whereby torque can again be transmitted between the two clutch members.

When the second electromagnetic coil is energised, the MRF may be caused to move simply to a portion of the interior of the housing remote from the gap. However, the available volume of the interior of the housing is likely in practice to be very small and it is therefore convenient if the interior of the housing communicates with a reservoir and the electromagnetic coils are so arranged that when the second electromagnetic coil is energised at least a proportion of the MRF moves into the reservoir. In use, the first and second rotary members will be connected to input and output shafts, respectively, and the first and second magnetic coils will be connected to a source of electrical power via a controller. The controller will in practice be controlled by the engine management system with which most modern vehicles are now equipped.

In order to ensure that the desired amount of torque is transferred from one rotary member to the other, it is preferred that speed sensors are provided which are arranged to measure the speeds of the input and output shafts and are connected to the controller, which is arranged to control the electrical power supply to the first electromagnetic coil such that the difference between the two measured speeds reaches a predetermined value.

When it is desired to recommence the transmission of torque between the two rotary members, it is generally desirable that the viscosity of the MRF in the gap should not be increased too rapidly because if it were the clutch would be perceived by the driver to "snatch", that is to say to engage too rapidly, thereby resulting in jerky movement of the vehicle. It is therefore preferred that a torque sensor is provided, which is arranged to measure the torque transmitted by the output shaft and is connected to the controller, which is arranged to control the increase of electrical power supplied to the first electromagnetic coil such that the rate of rise of torque transmitted by the output shaft does not exceed a predetermined value.

Thus when it is desired to re-engage the clutch, for instance after a gear change operation, the controller is controlled, e.g. by the engine management system, to de-energise the second electromagnetic coil and to re-energise the first electro- magnetic coil. The rate of increase in the power supply to the first electromagnetic coil is controlled in response to the signal from the torque sensor to ensure that the rate of increase in the torque transmitted to the output shaft does not exceed a predetermined value and thus that the clutch does not produce a jerky gear change. The speed sensors will measure the speeds of the input and output shafts and the controller will compute the difference between them and once this difference has fallen to zero, which means that the two shafts are rotating at the same speed, the controller will ensure that there is no further increase in the power supply to the first electromagnetic coil because it is undesirable that the viscosity of the MRF should be increased to a value above that necessary to transmit the full torque from one rotary member to the other because this would result in unnecessary degradation of the MRF.

Further features and details of the invention will be apparent from the following description of one specific embodiment of automotive clutch in accordance with the present invention, which is given by way of example only with reference to the accompanying highly diagrammatic drawings, in which:

Figure 1 is a sectional view of one half of the clutch in the configuration in which it is transmitting torque; and

Figure 2 is a view similar to Figure 1 showing the clutch in the configuration in which it is transmitting no torque.

The clutch comprises two annular clutch plates 2 and 4, which are connected to rotate with an input shaft 6 and a coaxial output shaft 8, respectively. The two clutch discs are parallel and closely spaced and define between them a gap whose width is only a fraction of a millimetre. The clutch plates 2, 4 are accommodated within a housing 10. The majority of the clutch plates is constituted by non-ferromagnetic material, such as aluminium but their outer portions are constituted by a respective soft iron annular portion 12, 14 and the outer edges of these portions are in sliding contact with or spaced by only a very small distance from respective soft iron cheeks 16, 18 connected to the interior surfaces of the housing 10. The outer annular surface of the space within the housing 10 is constituted by an annular soft iron member 20, outside which is a further annular member 21 of non-ferromagnetic material, such as aluminium. The soft iron members 12, 14, 16, 18 and 20 define a small and substantially sealed enclosure 22 within the housing 10, into which the soft iron members 12 and 14 extend. This annular enclosure 22 is partially filled with MRF. Any MRF suitable for the particular application may be used but the fluid supplied by Liquids Research Limited under the designation MRHCCS4- B is suitable for this purpose. This comprises a thixotropic liquid with 80% of carbonyl iron particles by mass.

Extending around the central portion of the annular soft iron member 20 is a primary electromagnetic coil 26. Also extending around the soft iron member 20 on either side of the coil 26 are two annular secondary electromagnetic coils 28. Extending from the enclosure 22 substantially through the soft iron member 20 in alignment with the secondary coils 28 is a plurality of bores or recesses 30, which together constitute an MRF reservoir.

The primary and secondary coils 26 are electrically connected to a controller 32, which is in turn connected to a source of electric power 34, typically the battery of the vehicle in which the clutch is installed. The controller 32 is also connected to a sensor 36 arranged to transmit to the controller a signal indicative of the speed of the input shaft 6. The controller 32 is also connected to a composite speed and torque sensor unit 38 which is arranged to transmit to the controller signals indicative of both the speed of the output shaft 8 and also the torque transmitted by it.

When the clutch is to transmit torque, the controller 32 energises the primary coil 26. This produces an electromagnetic field in the vicinity of the gap between the two soft iron members 12 and 14 and this field induces the MRF to move to and stay in the position indicated in Figure 1, that is to say in the gap between the two soft iron members 12 and 14 and annular regions adjacent these two members. The magnitude of the power supplied to the coil 26 is such that the viscosity of the MRF in the gap is increased to a level where it is semi- solid and the speed of the two clutch plates 2 and 4 and thus also of the input and output shafts 6 and 8 is therefore the same.

If it is desired to effect a change of gear in the gearbox to which the output shaft 8 is connected, it is essential that substantially no torque be transmitted to the output shaft 8. When this is to happen, the controller 32, under the control of the engine management system, switches off the power supply to the primary coil 26 and simultaneously switches on the power to the secondary coils 28. This results in the MRF vacating the position shown in Figure 1 and moving to the position shown in Figure 2. As shown in Figure 2, a proportion of the MRF enters the reservoir 30 and whilst it may all fit into this reservoir, this is not necessary and in the illustrated embodiment a proportion of it fits into the reservoir and the remainder occupies the radially outer region of the enclosure 22. However, as may be seen in Figure 2, all that MRF that was previously in the gap between the two members 12 and 14 has left this gap. No torque whatever is therefore now transmitted between the two clutch plates. The gear changing procedure may therefore now be effected without difficulty.

Once the gear changing procedure has been completed, the controller 32, under the control of the engine management system, de-energises the secondary coils 28 and re-energises the primary coil 26. The magnetic field produced by the coil 26 draws the MRF back to the position shown in Figure 1. The power supply to the coil 26 is initially relatively low and the viscosity of the MRF in the gap between the members 12 and 14 therefore reaches only an intermediate value. A certain proportion of the torque in the input shaft is therefore transmitted to the output shaft. The controller 32 is arranged to progressively increase the power supply to the coil 26 and the proportion of the torque that is transmitted to the output shaft 8 therefore increases progressively. However, the sensor 38 produces a signal indicative of the torque transmitted by the shaft 8 and this signal is transmitted to the controller 32 which ensures that the rate of increase in the supply of electrical power to the coil 26 does not result in the rate of increase in the torque transmitted by the shaft 8 exceeding a predetermined value. Starting from rest of the vehicle and changing gear are thus effected smoothly and without jerkiness. The speed of the shafts 6 and 8 are also measured by the sensors 36 and 38 and the difference between them computed by the controller 32 and once these two shafts are rotating at the same speed, the increase in electrical power supply to the coil 26 is stopped and the power supply is maintained at a constant level or reduced, as appropriate.

Claims

1. A clutch for transmitting torque between two rotary shafts comprising a first rotary member, which is opposed to a second rotary member, the two rotary members being accommodated within a housing and defining a gap, the interior of the housing accommodating a magneto-rheological fluid (MRF), the clutch including first and second electromagnetic coils, the first electromagnetic coil being so arranged that, when it is energised, it produces an electromagnetic field in the vicinity of the said gap and the second electromagnetic coil being so arranged that when it is energised the MRF is caused to move substantially out of the said gap.

2. A clutch as claimed in Claim 1 in which the interior of the housing communicates with a reservoir and the electromagnetic coils are so arranged that when the second electromagnetic coil is energised at least a proportion of the MRF moves into the reservoir.

3. A clutch as claimed in Claim 1 or Claim 2 in which the first and second rotary members are connected to input and output shafts, respectively, and the first and second magnetic coils are connected to a source of electrical power via a controller.

4. A clutch as claimed in Claim 3 in which speed sensors arranged to measure the speeds of the input and output shafts are connected to the controller, which is arranged to control the electrical power supply to the first electromagnetic coil such that the difference between the two measured speeds reaches a predetermined value.

5. A clutch as claimed in Claim 3 or 4 in which a torque sensor arranged to measure the torque transmitted by the output shaft is connected to the controller, which is arranged to control the rate of increase of electrical power supplied to the first electromagnetic coil such that the rate of rise of torque transmitted by the output shaft does not exceed a predetermined value.