PAVAS RTZ

RTZ stands for Reduced Time Zone. These are sections of a Targa stage where the vehicle is required to spend a given time while greater than a minimum speed. The concept is to have a virtual chicane to restrict the vehicle's speed.

The Specifications

The typical parameters fo a RTZ are a distance of 400 meters and with a time duration of 20 seconds. Hence, to cross the RTZ in an optimum way, the average speed required is 20 meters/sec or 72 kph. A warning sign is located 200 meters from the start of the RTZ. A second sign indicates the start of the RTZ and a third sign shows the end location. If the time in the RTZ is less than 20 seconds or speed falls below the minimum speed time penalties are incurred.

The Method

The best method to cross an RTZ, based on loosing the minimum time, is to approach it as fast as possible and then brake hard so that the average speed is 72 kph; maintain that speed until the end of the RTZ. This is a difficult task but by adhering to it, time penalizes are not incurred. Other rally monitoring instrumentation, if fitted, provides a countdown time showing the time remaining in the RTZ.

One problem with this technique is that it puts a great load on the braking system and since the energy dissipated is proportional to the square of the speed, to converse the brakes, sensible to slow down before entering an RTZ.

The Setup

PAVAS provides a function to monitor operations in an RTZ. The first problem is to determine the start of the RTZ. This is achieved by pressing the Down in the Speed Alarms program. The is quite awkward and a separate optional activation button can be located on the gear stick. This designed to allow the driver, rather than the navigator, to initiate the RTZ procedure. This button is housed in a custom clamp which is tailored to the individual gear stick diameter.

The Method

Once the RTZ has been entered, PAVAS provides a beep tone to advise the driver that the RTZ calculations have commenced. PAVAS then calculates the instantaneous average speed from the distance and time taken. PAVAS uses the Null Guidance technique to advise the driver, so the initial tone is a high frequency, telling the driver to slow down. As he approaches within 10 kph of the required average speed, the tone changes to a series of beeps where the duration indicates how close the vehicle is to the average speed. Once the average speed is reached, the tone stops. If the vehicle falls below the average speed, a new tone sequence is generated with low frequency tone. If the vehicle reaches the minimum speed, a lower frequency tone is commenced which approximates a growl. The tones are designed to be easily distinguishable.

Once the vehicle is within five seconds on the end of the RTZ duration, PAVAS emits count down beeps at one per second. The allows the driver to judge when the time when he reaches the RTZ end sign. The RTZ mode ends after 20 seconds and PAVAS reverts to the Speed Alarms mode. Except for a Reset, there is no other way to terminate the RTZ function. The RTZ procedure is designed to minimize input from the crew.

The figure above shows actual data from a rally stage. The RTZ speed profile is shown between the between the dashed lines. The vehicle enters the RTZ zone and brakes hard. The little ripples to the left of the cursor are the gear changes. The average speed eventually falls below 72 kph and then the vehicle accelerates while leaving the RTZ.

2022-06-11