The basic mechanical system behind the Browning transmission was invented in 1974 by Bruce W. Browning and developed by Bruce and his sons Marc, David, Paul and Chris. This unique shifter uses a hinged sprocket sector which can swing either out or in to guide the chain to the next sprocket. See Figure 1 and Figure 2.
The critical feature that differentiates the Browning from standard derailleur systems is the continuous gear/chain engagement during shifting, there is no skipping or grinding even under the heaviest loads. The transmission wil1 shift under any combination of speed, cadence and pedaling force. Shifts are smooth, fast and nearly silent. The chain stays fully in contact with the gear teeth during either up or down shifts. In contrast, even with the best standard derailleurs, on upshifts, the chain loses contact with the smaller sprocket before it is fully engaged on the large sprocket which often leads to grinding or skipping under heavy loads.
Another unique feature of the Browning transmission is that it is ideady suited for complete electric operation including computer controlled automatic shifting. This eliminates derailleur cables and cable adjustment. Although the Browning automatic transmission is not yet in mass production, it has been extensively tested in the field and the laboratory and it is now a fully functional design. Versions of the transmission have been produced in the past and orders can presently be placed for twospeed, three-speed, four-speed and twelve-speed transmissions.Another unique feature of the Browning transmission is that it is ideady suited for complete electric operation including computer controDed automatic shifting. This eliminates deraiDeur cables and cable adjustment. Although the Browning automatic transmission is not yet in mass production, it has been extensively tested in the field and the laboratory and it is now a fuDy functional design. Versions of the transmission have been produced in the past and orders can presently be placed for twospeed, three-speed, four-speed and twelve-speed transmissions.
In the early 1970's, Bruce and his sons formed a family research company to invent, research, prototype and sell ideas. Among these ideas was the concept of an automatic/electric bicycle transmission. For a short time in the early 1970's, Browning Arms marketed a bicycle as part of their sporting goods business. Under an agreement with Browning Arms, Bruce and his sons worked on an automatic bicycle transmission as part of this project. In 1977, Browning Arms closed their bicycle business, so Bruce and his sons continued to develop the transmission on their own. Since then it has undergone continuous change and improvement at the Browning Research. The company buildings are nestled in the woods, a half-hour ferry boat ride from Seattle, but about a century away in their idyllic surroundings.
During the 1980's, a two speed mechanical version of the Browning transmission was adapted for BMX racing. The essential elements of the present device were developed for this BMX transmission. In the late 1980's, a three speed ATB chainwheel was introduced which was later licensed exclusively to Suntour. The transmission was produced under the name "The Beast" Unfortunately, like many components companies which were under intense competitive pressure from Shimano, Suntour fell on hard times and the production of the ATB transmission was halted.
Research on a fully automatic, computer operated version of the Browning transmission continued. By 1990, two 12 speed prototypes were finished, one that was fully automatic, and one that used four electric push buttons (up and down for both front and back gears).
In May 1993, the Browning "Smart Bike" was completed. The development, which is still continuing, has been a cooperative effort among a team of 17 persons, including project management and mechanical design by Marc Browning, software development and mechanical design by David Browning, testing and product reliability by Paul Browning, general administration and legal affairs by Gloria Browning and mechanical design and guidance by Bruce Browning (see the photo). This makes the fifth generation of Brownings who have been involved in creating basic inventions. Their two decades of effort have again produced a truy superior system.
When starting from rest, one crank revolution will wake up the computer from its power-conserving sleep mode. Two front sensors use magnets and reed switches to feed pulses to the computer to determine the direction and rate of crank rotation. Two rear sensors are used to determine the wheel speed and the sprocket speed. By comparing the number of sensor pulses of the front crank with the freewheel sensor pulses, the computer can determine the current gear. After each shift, the computer updates the current gear. Using the wheel speed, the computer constantly searches for a "desired gear" that will allow the rider to maintain a preferred cadence. If the current gear is different from the desired gear, when the rider is pedaling forward, the computer will automatically shift toward the desired gear with no attention from the rider.
The rider can adjust the preferred cadence by pressing either the up or down button to shift to another gear. The computer remembers this selection and will choose gears, within the gears available, to maintain this new cadence.
I rode the Smart Bike for about 40 miles through a hilly region of Northern California. With steady riding, it shifted between 8 and 18 times per mile depending upon the terrain. This was much more than I usually shift, but the shifts were generally welcome. After the novelty had worn off, the shifting became essentially invisible, I forgot about it during the last part of the ride. At the beginning, when going up a long grade, I overrode the computer a few times to select a more comfortable gear, but later I seldom needed to do this.
David Browning, who developed the computer software, has solved some very difficult but fascinating problems. Today's common 24 speed road or mountain bikes, really only have 13 or 14 effective gears because of the close overlap between certain ratios. In contrast, the Browning Cross Bike that I rode had 12 gears, but they were in a neat progression, so all of them can be programmed into the computer software. The bike I rode had some of the shifts blocked out, leaving some fairly steep changes, but this can be modified in later versions of the software. The computer program allows the cadence to vary within a band width, so that the shifting will not "dither" (shift back and forth) when close to a shift point.
When a sector moves either out or in, it positively guides the chain to the next sprocket like a ramp on a freeway, or a railroad switch guiding a train from one rail to another. The sector provides a helical path for the chain to follow, and maintains positive contact during the switch. The shifts are therefore smooth and flawless. Shifts are timed so the swinging sectors can be moved without chain interference and they require very little force. At present a limited number of gear sizes have been made for the prototypes, but this selection can be expanded upon manufacture.
To assure the reliability of the shifting system, the Brownings have built testing machines that have subjected the transmission system components to thousands of hours of service under various loads while undergoing millions of cycles. Any failures have been analyzed with high speed videos and corrected, until the system is now superbly reliable.
A small control box is placed on the handle bar for easy finger tip operation. A toggle switch allows the rider to select either manual operation or automatic. In manual, two buttons allow the selection of either a higher or lower gear. The transmission will remain in this gear until the rider commands another shift. In automatic, pressing the buttons will cause a shift, but it will also cause the computer to readjust the preferred cadence for future automatic shifting.
There are other racing events where the automatic Browning transmission could prove invaluable. The UCI regulations permit gear shifts on the track for individual time trial races under article 49, Section III: "For track competitions, other than where the rider takes the track alone, (500m, kilometer TT Individual Pursuit and individual record attempts), derailleur gears and brakes shall be prohibited."
In track racing, in the individual time trial events such as the 1000 meter or the 4000 meter individual pursuit, cyclists must accelerate from a standing start and maintain speeds of from 33 to 38 mph for several laps of the track. Track racers currently use a fixed gear of about a 93 inches for the entire race. In these events, gear shifts might be advantageous because they could improve acceleration from a standing start.
Gear changers have been used in the past in international track racing. The kilo champion of Canada, Jocelyn Lovell used a two speed rear hub in the World Championships in the early 1980's. Lovell's system of drive chains on both sides of the rear axle was used by Gene Samuel of Trinidad in the 1992 Olympics to place 8th. Also in the 1992 Olympics, Adler Capelli used a derailleur gear shift in the 1000 meter time trial, and placed 5th. The Browning automatic transmission is technologically advanced compared to these earlier systems and can produce the same result in a cleaner, more efficient manner shifting by using a computer model along with available research data. In 1976, I used a 200 pound unbraked flywheel to measure the rate of acceleration of a sprinter from a standing start . The flywheel was driven from a stationary racing bicycle fixed to a stand. The flywheel speed was recorded using a light emitting diode and a fast strip chart recorder. The energy input to the flywheel could then be determined by calculating the kinetic energy of the flywheel. From this, I found the average crank torque as a function of time and other variables. Figure 6 shows the result. The rider, Mario Palombo, was a good sprinter but not nationally ranked.
Typically a kilo racer who can do 1000 meters in 1 minute 7 seconds can turn the first half lap in about 12 seconds, and his top speed is about 37 mph. From wind resistance data, and rolling resistance data from previous tests, a realistic estimate of the above coefficients for track racing with modern equipment would be A0 = .0022, A1 = .000029, and A2 = .00255.
Another differential equation gives the distance covered in a certain time:
Suppose we try a 14/19/24 tooth rear cluster with a single 48 tooth front chain ring and a 700C rear wheel. This would give gears of 91, 67 and 53 inches. With no shifts, using the 48/14 gear, the computed half lap time to 125 meters would be 12.08 seconds. If we try shifting when the crank RPM exceeds 100, using only one shift from 19 to 14, the computed time would be 11.53 seconds. Using one shift from 24 to 14, the time would be 11.47 seconds. Using two shifts from 24 to 19 to 14, the time would be 11.31 seconds.
So, the computation shows that the time for the first half lap might be improved by as much as 0.8 seconds by using an automatic shifter. Since the chain loads on the rear sprockets are enormous during the explosive starts in track racing, the Browning transmission would be ideal for this service. Even though the first half lap split time appears to favor shifting, it is still not certain whether the total race time would be lower or higher. However, the technique looks extremely promising and it merits extensive field testing.