The advent of Drivematic, the automatic clutch system for standard transmission vehicles, brings down yet another barrier for the driver with a physical disability. Automatic transmissions have almost always been the only option for drivers with a disability affecting the lower extremities. This is based on the assumption that clutching and shifting, even if accomplished by the use of levers would force the driver to either leave the steering wheel unattended momentarily, or at very least to "thumb" the wheel while accomplishing some other function. Neither solution is acceptable from a safety or a liability standpoint.

The Drivematic is not an automatic clutch; it is an automatic clutch operating system using the vehicle's existing clutch pedal and linkage. When used in conjunction with properly configured brake and accelerator controls, the Drivematic system frees a disabled driver from the necessity of clutch operation, clearing the way for safe shifting and continuous steering wheel control in a wide variety of vehicles and equipment.

Designed in the spirit of parallel operation, the Drivematic changes from automatic to normal mode with the touch of a switch. Able-bodied drivers experience no change in feel or function, while drivers with disabilities ranging from leg amputation to paraplegia can easily switch to automatic mode to meet their driving needs.

At the heart of the system is a pneumatic servo, similar to a power brake booster unit. The servo uses the vacuum generated by the engine (or compressed air, in the case of a tractor trailer) to actuate a diaphragm which pulls the clutch pedal down via a heavy duty steel cable. It does this whenever the driver changes gear, and when the vehicle slows to a stop.

Crucial to the system is a special pressure-sensitive shift lever knob. Automatic operation of the clutch begins when the driver grasps the gearknob and starts to move the shift lever. The action is detected by a switch incorporated in the knob. The switch causes a valve to open which applies vacuum to the diaphragm, thereby developing a powerful suction to pull the pedal down and disengage the clutch. If the driver releases the knob without moving into gear, the clutch reengages.

However, if the driver shifts the lever to select a gear, a second switch in the shift lever position sensor tells the system that the vehicle is in gear, causing the clutch pedal to remain down.

The system now waits for the first movement of the accelerator pedal. When movement is detected, a third switch causes a precisely metered amount of ambient air through to the

chamber containing the diaphragm. At this stage, the clutch rises up to a point just below its engagement point.

Here, the electronics hand over control to the pneumatics and further movement of the clutch is governed by a rotary proportioning valve. The response of the clutch is in direct proportion to the action on the accelerator, both in acceleration and deceleration. Thus the clutch movement is made to correspond to the manner in which the vehicle is being driven, much the same as the instinctive reaction of an able-bodied driver.

Clutch operation when the vehicle is starting from stationary or coming to rest is achieved in a similar manner. When the vehicle is starting from stationary, the movement from neutral is detected as described above, but the clutch is not allowed to proceed to full engagement. As the vehicle moves off, the speed is monitored by the microprocessor. At a preset speed (in the region of 5-10 mph, adjustable on the microprocessor) , a bleed valve is engaged to ensure full release of the clutch. This adjustment can be tailored to suit the weight and torque characteristics of the particular vehicle. When the vehicle slows down, the same valve acts to disengage the clutch and prevent the engine from stalling.

The operation of the bleed valve occurs only at very low speeds, therefore at normal driving speeds the clutch remains engaged when the driver lifts his/her foot from the accelerator. This conserves the braking effect of the motor, a phenomenon which is central to maintaining the original "feel" of a manual transmission, and facilitating the transition to an automatic clutch. The operation of the bleed valve also permits relaxed, slow-speed crawling in heavy traffic.

* THIS WOULD GENERALLY BE DUE TO A LINKAGE PROBLEM RATHER THAN THE HARDNESS OF THE OEM CLUTCH