07-07-2014, 02:16 PM
The subaru hill holder system
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INTRODUCTION
Any device that prevents a car from rolling backward on a hill when the brake pedal is released can be called a hill holder. The earliest hill holders were used in horse-drawn carriages and early horseless carriages. They were often home-made or made by a local blacksmith. These early hill holders were little more than a heavy iron weight with a spike or other sharp end that could be quickly dropped behind a wheel when the need arose, preventing the vehicle from rolling backward.
Hill-Holder is a name for the mechanism invented by Wagner Electric and manufactured by Bendix Brake Company in South Bend, Indiana. Studebaker and many other carmakers offered the device as either optional or standard equipment for many years. It is a device that holds the brake until the clutch is at the friction point, making it easier to start up hills from a stop in manual transmission automobiles. It was first introduced in 1936 as an option for the Studebaker President. By 1937 the device, called "NoRoL" by Bendix, was available on Hudson, Nash and many other cars.
OBJECTIVES
The purpose of the hill holder is to keep the manual transmission car which is stopped facing uphill from rolling backwards during that time when the driver’s right foot moves from the brake pedal to the gas pedal while still holding the clutch pedal down with the left foot. The three necessary and sufficient conditions: uphill, clutch down, and not moving forward.
Technical Description:
When the clutch is depressed while the car is facing 3 degrees or more uphill and not moving forward, the hill holder actuates a one-way valve that retains the existing pressure (if any) in one of the two diagonal circuits of the brake system, allows increased pressure to be added, but prevents pressure from escaping until the clutch is released.
Operational characteristics:
The hill holder has no connection whatever to the transmission, so it functions in all gears, including neutral and reverse. As a result, the hill holder can kick in while backing down a driveway, as all three of the conditions may be satisfied in this situation. It takes a bit of experience to get comfortable with this - light application of brakes, coasting in neutral with the clutch up, etc.
Since the hill holder only retainsbrake system pressure and doesn’t addanypressure by itself, the Forester might begin to roll backwards if it had been stopped with just gentle brake pressure on a steep hill. The solution is simply to add more pressure to the system by pressing the brake pedal again, a bit harder.
It would be nice if the hill holder could provide a similar capability when one wanted to back up while facing downhill, but this fails to satisfy the uphill condition and will not work. The reason for this is that the gravity/inertia-based mechanism in the hill holder can't distinguish between a downhill orientation and a normal braking condition while traveling forward.
Advantages-
Hill-holder works best for those who are inexperienced with manual shift techniques, or in situations with heavy traffic in steep hilly conditions (as in San Francisco, or Duluth for example).
However the same technique can be accomplished by a driver through the use of the manual parking brake lever, coordinated with the braking, clutching, shifting and acceleration.
Disadvantages-
Cars equipped with a parking brake pedal are not suited for this manoeuver.