Technology

    It is well known that conventional tricycles possess excellent traction and stability across uneven road surfaces. In addition, tricycles are much less susceptible to the accident of falling inward and slipping outward during cornering. Two-wheeler riders need to maintain the balance of the entire vehicle. In contrast, conventional tricycle riders have a much smaller operational burden. Therefore, conventional tricycles possess excellent agility when running at a low speed, riders do not need to support a still vehicle, and the addition of payloads does not necessarily increase the difficulty in maneuvering or balancing the vehicles. However, the centrifugal force generated when making a turn with a traditional tricycle causes discomfort on the rider. The bulky body makes not only its appearance less desirable but also maneuvering in a constrained space very inconvenient. Hence, three-wheel tilters are occasionally seen on the market in an attempt to eliminate the above disadvantages.

    A type of tiltable tricycles utilizes two front wheels and a single rear wheel. The whole body of this type of tricycle can tilt. Steering a double-front-wheeled tricycle is never as easy as that of a classical single-front-wheeled bicycle. Since the entire vehicle can tilt to either side, the rider still needs to maintain the balance of the entire vehicle. For double-front-wheeled tricycles using a parallelogram tilting mechanism, the principle of parallelogram cannot be fully realized in practice, and therefore their tilt agility is not so good as that of classical bicycles.

    Another type of tiltable tricycles utilizes a single front wheel and two rear wheels. The front section of this type of tricycles can tilt, while the rear section is stationary, and the two sections are connected with a shaft. The shaft defines the axis of tilting and is located somewhere above the ground. When the front section leans toward one side, the above-the-ground axis of tilting also turns to that side (Figure. 1). As a result, tilting is coupled with turning the entire vehicle, which consumes energy. The turning leads to a change in the direction of travel even if steering is held straight. For a classical bicycle, the line connecting the two contact points between the two wheels and the ground functions like the hinge line of a door. Tilting a bicycle is as effortless as pushing a door. The line connecting the front contact point and the rear one can be described as a virtual axis of tilting. Under normal circumstances, the two wheel-ground contact points cannot shift sideways. Thus, the axis of tilting of a bicycle is on the ground, and tilting a bicycle neither consumes energy nor induces an unwanted change in the direction of travel. The ultimate agility and intuitive tilt dynamics are the classic advantages of bicycles. In contrast, the rider on a three-wheeler with the above-the-ground axis of tiling feels unexpected or weird response of the vehicle.

Figure 1: Coupling Effect of Above-the-ground Axis of Tilting

    The above-the-ground axis of tilting may also cause two hazardous phenomena that are inconsistent with our intuition about bicycles. Firstly, when riding on bumpy roads, the vertical motion of either rear wheel can cause the front section to be pushed sideways (Figure 2). The smaller the distance between the two rear wheels, the greater the lateral push. Since the front section is tiltable, even a small lateral force may be dangerous. Secondly, if the distance between the two rear wheels is inadequate or if the center of gravity of the rear section is too high, outward flipping may happen when a rider makes a turn with a supposedly appropriate leaning angle (Figure 3). Due to the above safety issues, all the tricycles on the market with the above-the-ground axis of tilting have an unwanted large rear width or small rear wheels. However, the width of such tricycles is not desirable for weaving through traffic or maneuvering under spatial constraint, and the two small rear wheels are not aesthetically appealing.

Figure 2: Lateral Push Resulting from Rise of Left Wheel Running over Obstacle

Figure 3: Rear Section May Flip Right When Turning Left with Appropriate Lean to Left

    The Leaning Control System (LCS) of the Naro Delta Vehicle (NDV) employs two parallel arc-shaped rails transversely mounted on the rear section of the NDV. The centers of both rails are located on the longitudinal midline of the stability triangular base, which is defined by the three wheel-ground contact points (Figure 4). The front section of the NDV is connected to the rear section with a sliding base that slides along the rails. Utilizing the high rigidity of the arch structure and a sufficient distance between the two rails, the simple LCS enables the front section to tilt about the midline on the ground, as the axis of tilting, against a minimum friction. In addition, the LCS can be equipped with a controller that automatically allows for or blocks tilting according to the speed of the vehicle. When the vehicle is at low speed or stationary, tilting is blocked and the NDV performs just like a conventional tricycle. Therefore, the NDV is agile at low speed and does not require physical support by riders when the vehicle is stationary.

Figure 4: Leaning Control System (LCS) of Naro Delta Vehicle (NDV)

    In summary, the NDV has the following complete set of advantages:

1. Enhanced high-speed safety: excellent traction, stability for running over obstacles/pits and for cornering (preventing falling inward and slipping outward)

2. Superb low-speed maneuverability and convenient rest: no touchdown of rider’s feet, elegant riding experience attributed to automatic locking/unlocking of the tilting front section

3. Burden reduced by allocating some payloads to the rear section

Due to the axis of tilting fixed on the ground and one single front wheel:

4. Retaining classic two-wheeler dynamics: agile and intuitive steering and leaning, immune to unpleasant coupling

5. Easy weaving through traffic and maneuvering under spatial constraint

6. Retaining the aesthetic width-to-wheel size ratio of bikes

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