FORMULA ONE TREND OF DESIGN

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FORMULA ONE TREND OF DESIGN

Clutch operation

WHEN the racing car had its engine at the front. with the gearbox and clutch between the driver’s feet it was a simple matter to provide the clutch operation by means of a pedal and cross-shaft. Putting the engine and gearbox behind the driver brought added complication to designers, for they had to devise ways of connecting the pedal at the front of the car to the clutch operating mechanism at the rear.

In today’s Formula One scene, with everyone following the same layout of driver/engine. gearbox it would be reasonable to suppose that all the designers follow the same method of clutch operation, but that is not so. There are three methods used, cable and mechanical leverage, hydraulic and ntechanical leverage, and fully hydraulic. The last-named is the most popular and came into being as a result of Lotus design detail on the Lotus 78. In that design the engine oil tank comprised a cast alloy component between the engine and gearbox with its front face bolting to the clutch housing on the rear of the Cosworth DFV engine, and the gearbox main-shaft ran through a tunnel cast into the oil tank. It was a logical development in the design stage to incorporate an hydraulic passageway in the casting and an hydraulic cylinder surrounding the drive-shaft tunnel. A piston could then act directly onto the clutch withdrawal thrust race, thus giving a much better actuation by applying equal pressure on a full 360 degrees rather than at three or four points by the conventional toggle-arms. MI that was then needed to connect the actuating piston to the pedal was an hydraulic line, with a master-cylinder and reservoir operated by the foot-pedal. This system was described as the co-axial clutch operation and was soon copied by most other designers who had studied the Lotus 78.

The master-cylinder with integral reservoir is mounted on the front bulkhead of the monocoque and is operated by a short push-rod from the foot Pedal; the hydraulic line runs back through the Monocoque to a union on the side of the casting between the engine and gearbox, which is the oil tank in most cases, and that is all that is involved. It is a very neat and functional system and it Parentees to push the clutch thrust race fairly and squarely. Today it is used by Lotus, Brabham, McLaren, ATS, Ensign, Fittipaldi, Williams, Arrows and Osella. Its only drawbacks seethe “feel” to the pedal, which some drivers do not like, and the inevitable failings of hydraulic Orstems, such as faulty master-cylinders, leaking unions, and faulty seals.

Tyrrell, Renault and Ligier eschew more .Ydraulics than are really necessary, by operating their clutches by the old-fashioned method of levers and cable. The foot pedal has a cable attached to It and this runs back through the toonocoque to the end of a lever protruding out through the clutch housing, this lever having its (fulcrum inside the housing and arranged so that ore-and-aft movement outside the housing Provides sufficent movement Inside, near to the fulcrum, to push the clutch thrust race forwards sufficiently. The pedal pressure required is designed into the length of the foot-pedal and the length of the operating arm. Renault and Ligier In a simple open cable, running freely from front Is rear, while Tyrrell uses a sophisticated aircraft enclosed cable.

The third method is to use an hydraulic line from the pedal to an external slave cylinder on the clutch housing frt,ev which unhurt push-rod operates a lever pivoted within. This system is used by Ferrari and Alfa Romeo and seems to combine the worst of both worlds, or the best, depending on your views on hydraulics and hydraulic “feel”. In both cases the operating lever rises vertically from the clutch thrust race, through an opening in the clutch housing, and the slave cylinder is externally mounted on top of the housing.

There are also individual variations on the method of operating the hydraulic master-cylinder from the foot-pedal, though there is total agreement on pivoting the pedal at thc bottom. There are three methods of connecting she push-rod to the pedal. The push-rod can have a forked end into which the pedal arm fits, with a pivot bolt (Ensign, Brabham), the pedal any can fork at its lower end, astride the push-rod (ATS) or the push-rod can be connected to the side of the pedal by a Rose or Heim spherical joint (Lotus, McLaren). When you read of a driver having clutch trouble, it is seldom the clutch itself, except in a case like Reutemann at Imola where he let the linings get overheated at the start, but is usually the mechanism that operates the clutch. It CM be a failure in the master-cylinder such as a sticking non-return valve or a leaking piston seal, or it can be similar problems inside the clutch housing in the co-axial slave cylinder. Although it might be said that the clutch failed, it is usually that the mechanism has failed and it has failed “safe”. In other words the clutch is fully home and gripping 100%, but the driver is unable to free it, so basso make his gear changes without using the clutch, which is not very difficult with a close-ratio 5-speed Hewland box. The only thing he must be careful of is to avoid a slide or spin which might stall the engine as it would mean he could not restart from rest. A driver will often say in loose paddock talk that “the clutch went on the first lap”. What he really means is that the operating mechanism failed, the clutch itself was perfectly all right otherwise he could not have continued. In a case where a driver holds his foot on the clutch pedal at the Milli for too long, the clutch linings can overheat so that when they are called upon to grip they fail. In a had case the linings will burn out completely and that is the end of the race, but if the overheating is not too bad a clever driver will bc careful with the power until the

linings have cooled off and grip effectively again. In such cases the original trouble is not clutch trouble but “cockpit” trouble and driver error. Must thoughtful drivers will snick into neutral as they approach thc final starting grid and only engage bottom gear when the red light comes on, thus avoiding any uneccessary strain on the clutch operating mechanism and minimum over-heating of the clutch plates. Some drivers are so concerned that they might not be able to engage bottom gear instantly that they come up to the line already in bottom gear with their left foot on the clutch pedal. If the operating mechanism is 100% and the clutch is totally fr., iris probably all right, but it is courting danger and imposing unnecessary strain on hard-worked components. If you are near the front of the grid you may have to wait thirty seconds for the back row to get in position before the red light comes on, and that could be crucial. When you next read of “clutch trouble” spare a thought that the trouble could lie anywhere from the driver’s foot at the front of the monocoque, to the clutch linings buried down between the engine and gearbox at the back of the car. —

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