GB2246819A

GB2246819A - Vibration attenuator for a clutch hydraulic actuation system

Info

Publication number: GB2246819A
Application number: GB9017641A
Authority: GB
Inventors: Mervyn Brian Packer
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1990-08-11
Filing date: 1990-08-11
Publication date: 1992-02-12
Also published as: GB9017641D0

Abstract

A vibration attennuator for incorporation in a clutch hydraulic master/slave actuation system comprises a cast iron body 43 with an inlet port 47 and an outlet port 48. Two metal diaphragms 41, 42 are each connected to the two ports such that they can simultaneously follow vibrations transmitted through fluid in the system. <IMAGE>

Description

A CLUTCH HYDRAULIC ACTUATION SYSTEM This invention relates to clutch hydraulic actuation systems and more particularly for such systems used to operate the friction clutches of automobiles.

In clutch hydraulic actuation systems, the vibrations from the vehicle engine are transmitted back through th flywheel and clutch actuator into the hydraulic fluid and can be felt by the vehicle driver through the clutch pedal. In extreale circumstances these vibrations may even he audible to the driver.

In GB 156 27@9 it has been proposed by the present applicants, that these vibrations can be damped by the use of an attenuator having a sheet metal diaphragm which can follow the vibrations.

A problem has arisen with clutch actuation systems that operate at high pressure.

A conventional actuation system operates at about 4~ bars pressure during actuation of the clutch by the driver.

however stale systems require a pressure in the order of 7@ bar for operation. A vibration attenuator as disclosed in GB156 2789 does not operate at high pressure because the displacement of the diaphragm under the increased load will cause high levels of stress in the diaphragm, and reduce its fatigue life.

If the diaphragm is thickened to reduce the stress, this has the effect of reducing the volume displacement of the diaphragm and reduces its efficiency.

The present invention provides an adequate level of fluid displacement for attenuating the vibration in clutch hydraulic systems that operate at high pressure, while maintaining acceptable levels of stress in the diaphragm.

Accordingly there is provided a vibration attenuator for a clutch hydraulic system, said attenuator including a pair of boundary plates that form a boundary to the hydraulic system and which can both simultaneously follow vibrations transmitted through the fluid in the system to damp said vibrations.

Preferably the boundary plates are sheet metal plates, preferably steel, that are arranged opposite each other.

Also according to the invention there is provided a clutch hydraulic actuation system having a vibration attenuator means provided in the actuation system between the master cylinder piston and a slave cylindar, said attenuator means including a pair of boundary plates to the hydraulic system that can follow vibrations transmitted through the hydraulic fluid in the system and effect damping of the vibration.

The vibration will be described by way 0 example and with reference to the accozlpanying drawings in whinh:- Fig 1 is schemematic illustration of a vehicle engine, clutch and hydraulic actuation systems.

Fig 2 is the first embodiment of a vibration attenuator according to the invention.

Fig 3 is a second embodiment of an attenuator also according to the invention.

Fig 4 is yet another embodiment of an attenuator according to the invention.

Fig 1 illustrates an internal combustion engine 11 having a crankshaft 12 running in bearings 13. The rear end of the cranksheft has a flywheel 14 secured thereon which is mounted on a friction clutch 15. The clutch 15 may be operated through a release bearing 17 to control engagement of the engine 11 with the gear input shaft 16.

The release bearing 17 is movable by a lever 18 pivoted at 19 to the clutch bell housing or other structure. The lever 18 is mover via a push rod 32 which connects the piston 31 of a clutch slave cylinder 29 to the end of tlle cover 32.

The clutch slave cylinder 29 is operated from a driver controlled clutch pedal 21 pivoted at 22 to a chassis member and which acts through a push rod 23 to operate the piston 24 of a master cylinder 25.

The piston 24 is sealed in the master cylinder 25 by a seal 28 and can displace hydraulic fluid through an outlet tube 26 which is connected to the slave cylinder 29 via a clutch vibration actuator 27.

When the vehicle engine is running and the clutch is released, the master cylinder has been operated to cause the release bearing 17 to engage the friction clutch, there is a tendency for the release bearing to oscillate or vibrate in an axial direction. These oscillations may be due to vibration in the crankshaft and occur at certain engine speeds, The frequency of these vibrations is normally in the order of 308 Hz but may be as high as 188B Hz, or as low as l~~ Hz.

The purpose of the attenuator 27, connected to the slave cylinder 29 by the tube 28, is to damp out . these oscillations.

Now with reference to Fig 2 there is illustrated one embodiment of a clutch vibration attenuator 27 which is for clutch systems operating at a pressure of about 68 and 9Q bars in which a pair of diaphragms or boundary plates 41 are designed to be capable of following pressure vibration transmitted through the hydraulic fluid. The diaphragms 41 are capable of following the vibration by virtue of having low damping properties and a natural frequency which is above the frequency of the vibrations to be damped. The diaphragms 41 are of sheet metal, preferably steel and sit on a machined surface 42 surrounding a circular recess 46 in a cast iron body 73. The diaphragm 41 are held against the respective faces 46 by a retainer cap 44 which is Coraled around the body 43.Each diaphragm is sealed against the face 42 by a seal member 45, so that the recess 46 forms a sealed fluid chamber to which the respective diaphragm 41 forms a boundary. The boly 42 has an inlet port 47 and an outlet port 48 which each connect with the two recesss 46 through internal passageways, The ports 47 and 48 are utilised for connection with the clutch hydraulic system, so that the two diaphragms are connected in series within the hydraulic system, Preferably the attenuator will be arranged in the hydraulic system nearer to the master cylinder.

The two diaphragms allow the hydraulic system to expand sufficiently to overcome the full amplitude vibrations at high pressure of up to 70 bars.

In Fig 3, there is illustrated a vibration actuator in which the two diaphragms or boundary plates 141 arp operated in parallel. There is only a single inlet/outlet port 147 which is connected to the two recesses 146 by a single passageway through the body 143.

In a slight modification of the version shown in Fig 3 the two diaphragms can be operated in series by providing two ports 247, 248 each of which is connected to the two recesses 246.

Claims

1. A vibration attenuator for a clutch hydraulic system, said attenuator including a pair of boundary plates that form a boundary to the hydraulic system and which can both simultaneously follow vibrations transmitted through the fluid in the system and damp said vibration.

2. A vibration attenuator as claimed in Claim 1 wherein said bonding plates are arranged opposite each other.

3. A vibration attenuator as claimed in Claim 1 or laim 2 in which fluid enters and exits the attenuator through a single port.

4. A vibration attenuator as claimed in Claim 2 or Claim 3 where the fluid enters the attenuator through one port and exits through a second.

5. A vibration attenuator as claimed in any one of Claims 1 to 4 wherein boundary plates are sheet steel plates supported and sealed around the outer margin thereof to a body being a recess therinforming a boundary to a fluid member formed by said recess and with one face acted upon by the hydraulic fluid, and the other face being substantially pressure free.

6. A clutch hydraulic actuation system having a vibration attenuator means provided in the actuation system between a master cylinder piston and a slave cylinder, said attenuator means including a pair of boundary plates to the hydraulic system that can follow vibrations transmitted through the hydraulic fluid in the system and effect damping of the vibrations.

7. A clutch hydraulic attenuator system as claimed in Claim 4 wherein the attenuator means is located in the hydraulic system between the master cylinder and slave cylinder.

8. A clutch hydraulic attenuator system in which the two boundary plates of the attenuator means are connected through the hydraulic system in series.

9. A clutch hydraulic attenuator system in which the two boundary plates of the attenuator means are connected through the hydraulic system in parallel.