PBS decided to proceed with a detail design and development on this project in anticipation that a Sequential Shifter would have a potential application in a number of different race classes using the popular Webster/Hewland MK series gearboxes. The design objective was to develop a Shifter with the performance potential of an exotic computer controlled system and the simplicity, low cost, and reliability of the basic MK series gearbox. The success of this effort is reflected by the class winning performance of Travis Duder and Ben Beasley in the 1998 SCCA National Championship races at Mid Ohio in the Dsr and Csr Classes.

PRODUCT DESCRIPTION

The PBS Sequential Shifter uses a rachet mechanism, which rotates a drum to one of six equally spaced positions. Mechanical stops prevent the drum from rotating continuously so that once 5th gear is engaged the only way to get back to 1st, or neutral or any other gear is to step back through each gear in sequence. The six positions are neutral, 1st, 2nd, 3rd, 4th, and 5th. The drum has three circumferential grooves cut on its outer diameter. These grooves, (one for each shift fork), are shaped in the axial direction to move the shift forks to the desired axial position for each of the six detented drum positions.

The rachet is actuated by an external lever and is spring loaded to return to its center position after each shift. This resets the ratchet so that it is ready for the next shift, either up or down. The drum is held in position, when in gear or neutral, by a spring loaded ball bearing detent roller.

All three shift forks, 1st, 2nd/3rd, and 4th/5th are positioned on a single rail adjacent and parallel to the rotational axis of the drum. Each fork has a hardened steel pin which fits in one of the 3 grooves on the drum. There is no reverse provided. The drum and shift rail intersect the area normally occupied by the reverse idler gear. By eliminating reverse, 1st gear can be engaged by the same type of dog ring as 2nd/3rd and 4th/5th rather than the special 1st/rev slider gear used in the standard MK series gearbox. Also the 1st shift fork can be similar to the other two forks. The end result is that the 1st gear becomes truly a user-friendly racing gear, which can be engaged just as easily and quickly as the other 4 gears. In contrast the 1st gear in the standard 5 speed MK series gearbox is relatively awkward to use as a racing gear. The standard 1st/rev fork bends and wears rapidly if used as a racing gear. The elimination of reverse gear also reduces the cost of the Sequential Shifter kit and reduces maintenance cost and complexity.

A new cast aluminum bearing housing was designed and manufactured by PBS for the Sequential Shifter. This uses the standard rear pinion bearing and rear layshaft bearing. These are included with the PBS kit to minimize assembly required by the customer. The new bearing housing also incorporates a double row, ball bearing to support the rachet /drum mechanism.

Behind the bearing housing, an intermediate cover and a rear cover are mounted on studs. For the Formula Mazda, a wing mount is built into the intermediate cover. Also, a small cover is provided for access to the roller detent spring in the intermediate cover. This allows the user to shim up the detent spring if a stronger detent action is desired. For applications other than the Formula Mazda, the wing mount may be removed.

An extension of the Shifter drum protrudes through a seal into a boss on the rear cover. This extension has two flats, which drive a rotary switch. The switch mounts on the rear cover boss. A diode array is connected to the switch to drive a series of six (6) LED's for a display of Shifter position. A single red LED illuminates for neutral. A single amber LED illuminates for 1st gear. For 2nd gear a green LED illuminates in addition to the amber light. For 3rd through 5th additional green LED's illuminate for each higher gear.

The PBS Sequential Shifter kit replaces the standard MK series bearing carrier housing, rear cover, shift finger and shift rails and forks. It also eliminates the reverse idler and 1st/rev slider. The reverse driver gear is replaced by a spacer. The remaining parts are the same as standard MK series parts with the exception of the dogs on the gears and dog rings. For best performance it is recommended that every other dog is removed from both the gears and the dog rings. This leaves four dogs on each part and makes shifts quicker and more positive.

Up shifts, when moving, are easily accomplished without the clutch by momentary lifting of the throttle or by using an ignition interrupt. Down shifts may also be done without the clutch, but it is not recommended due to the difficulty of matching engine speed to the moving gearset. Using the clutch reduces wear on the parts and prevents breaking the rear tires loose under deceleration.

The PBS Sequential Shifter can be actuated in different ways to fit the particular application. The external lever requires a motion of plus and minus 1 inch of travel. This can be provided by a push-pull cable and a shift lever with a fore and aft motion, since the Shifter uses a full step to get neutral, the motion is the same for each shift either up or down into any gear, or into neutral. Neutral is located below 1st rather than ½ way in between 1st and 2nd as in most motorcycle based Shifters.

For the ultimate in reasonably priced high performance shifting, PBS can supply a complete steering wheel-mounted paddle switch assembly. This can actuate either an electric solenoid system or nitrogen driven piston assembly. In addition to the paddle switch assembly, these systems include an electrical interface box and a safety neutral interlock switch. The electrical interface box incorporates the diode matrix for the LED display and high quality relays to control the air valves or solenoids. The function of the safety neutral interlock switch is to prevent accidental shifting out of or into neutral in the pits or out on the track respectively.

Also included in the electrical interface box is an output 12-volt source, which can be used to power the ignition system. This 12 V source is turned off by a relay when the airvalve or solenoid actuator is activated to initiate an up shift. It is not disrupted during down shifts. Thus it works as a simple, but very effective, ignition interrupt for full throttle upshifts. The duration of the interrupt is controlled directly by the driver with the paddle switch.

The air Shifter system includes a small high-pressure air bottle, a pressure regulator, a solenoid operated air valve and a double acting air cylinder. These components can all be mounted on the transmission or they can be mounted remotely.

As another alternative, the Shifter can be actuated directly by 12V solenoids. Again these can be mounted on the transmission or they can be mounted remotely and a push-pull cable used to operate the Shifter. One of the primary advantages of the paddle switch operated Shifter is the fact that the driver can concentrate more on driving the car. Thus this system can be considered a safety feature as well as potentially improving performance. Considering that the complete PBS Sequential Shifter system is less expensive than many of the popular data logging systems used in many race cars, it would seem that the cost/benefit ratio is very positive for this system.

The basic design of the Shifter which includes neutral as a full step below 1st and has no reverse, coupled with the neutral safety interlock switch function, makes these steering wheel switch shift systems inherently simple, safe, and remarkably effective.