Flexible joint mechanism for hub steering trikes

Abstract

A flexible joint unit 3 is incorporated into a hub-steering trike and allows a rear frame assembly 1, including the rear wheel, handlebars 6, and seat, to lean into corners relative to a front frame a

Description

This invention relates to a flexible joint that improves the stability, ride-ability and ease of manufacture of hub-steering tricycles. Background Cargo bikes, with electric assist and / or manual pedals, are being increasingly used to carry luggage on short journeys, therefore reducing our dependence on driving more polluting cars. A safe and stable way to carry loads on a trike is to mount the weight as low as possible, between two front wheels, with a third wheel at the back of the tricycle to provide a stable platform. Three-wheeled trikes cannot naturally lean into corners, without lifting one wheel off of the ground and without this ability to lean, the maximum safe cornering speed is significantly reduced. One solution to enable the rider to lean into the corners has been for trikes to use conventional bike steering, with both front wheels leaning into the corner inline with the rear wheel, unfortunately, this is expensive and limits the amount of space available for carrying cargo between the front wheels. Other solutions have been tried where bearings or pivots are used within the frame, between the front and rear wheels, to induce steering as the rider leans into corners but without much success. The most common solution for steering the two front wheels on vehicles hub-steering, as used on cars, recumbent and some sit on trikes, however, this still does not allow the rider to lean into corners because the two front and rear wheels are fixed within the same solid frame. This invention aims to provide one simple, flexible joint that will allow the rider of a tricycle to safely lean into corners, while not allowing the lean angle of the trike to have an influence on how the trike turns. The present invention relates to a new flexible joint for hub steering trikes that allows the main, rear frame assembly, including the rear wheel, seat, and handlebars can lean over relative to the front frame assembly, including the two steerable front wheels, which remain perpendicular to the ground. The present invention improves on the aforementioned prior art by making it possible for hub steering trikes to lean into corners safely. It also provides a single unit that combines the stable leaning axis that passes through a point on or close to where the rear wheel contacts the ground, spring return mechanism, increased cargo space, suspension, load indication, longitudinal load impact support and pre-tension adjustment. This invention will improve the stability, comfort, and cost-effectiveness of hub-steering trikes. Summary of the Invention The object of the present invention is to provide a single flexible joint unit that is simple to manufacture and provides all of the necessary features for a hub steering trike to be safe, stable, comfortable, and easy to ride. A unit assembly is proposed that will provide a flexible joint between the rear frame assembly, including the rear wheel, handlebars, and seat, and the front frame assembly, including the two, steered front wheels. The unit will allow the rider to lean into corners and therefore turn more safely at speed. The unit will allow the leaning axis, rotating joint to pass through the point where the rear wheel makes contact with the ground, therefore removing any side loads on the steering due to the rider leaning. The unit will allow the front frame area to be kept low, relative to the front wheels, therefore providing a large, low down, safe and stable, cargo space. The unit will provide a self-centring, spring return force operating around the rotating joint, that will return the rear frame assembly to an upright position when no external loads are applied. The unit’s self-centring forces will facilitate a much more stable experience for the rider. The unit will allow some vertical deflection between the front and rear frame assemblies to provide a little cushioning or suspension for the rider. The unit’s spring pre-compression rate can be changed to adapt the performance for different rider and / or luggage weights. The unit will hold the front and rear frame wheelbase dimension in the same relative position when axial loads or impacts are applied along the length of the trike. The unit’s vertical deflection will allow indicator marks to show when the trike has too high a load e.g. when rider plus cargo mass exceeds the trike’s design limit. The present invention allows a hub steering, leaning trike to overcome many of the complexities of existing cargo bikes / trikes and will provide more cost-effective, compact, cargo bike designs that can carry large loads, low to the ground, in a more safe and stable manner. Figure 1 shows a side view of the trike including the rear frame assembly 1 (complete with handlebars 6, seat 7, rear wheel 5) the front frame assembly 2 (complete with front wheels 4) the flexible joint unit 3 with an axis 0 pointing towards the bottom of the rear wheel 5. Figure 2 shows a front view of the trike including how the trike rear frame assembly leans (1 vs 1a) around the axis of the flexible joint unit 3. Figure 3 shows a top view of the trike including how the hub steering front wheel turns left 4a and right 4b. Figure 4 shows a simplified view of the flexible joint unit with arrow ‘A’ pointing to the end of the joint. Figure 5 shows a view on arrow A’. This end view of the flexible joint shows how the outer body 3a (attached to the rear frame assembly 1) can rotate relative to the inner body 3b (attached to the front frame assembly 2). Elastomeric balls 7 are held between the outer and inner bodies. The curved arrow shows how the outer body 3a rotates relative to the inner body 3b. The top half of the outer body may be clamped to the bottom half of the outer body by applying a force at ‘C’. Figure 6 shows a view section ‘BB’ in figure 5. This side view through the flexible joint shows the outer and inner bodies with rubber balls held between them, at the front and rear ends of the unit. Curved arrows indicate the direction of rotation of the outer and inner bodies when a vertical load is applied onto the trike. The dotted lines represent the angular movement that will be experienced within the flexible joint due to vertical loads. The longitudinal impact loads that may be felt by the trike are shown by arrows ‘FT and ‘F2’. Detailed Description of the Invention Lean angle rotary joint To enable the rider to lean the trike over while cornering (fig 2 items 1 vs 1a) a rotating joint (item 3) is provided to allow the rear frame assembly (item 1), including handlebars (item 6), seat (item 7), and rear wheel (item 5) to rotate relative to the front frame assembly (item 2) including the front wheels (item 4). The rotating joint (item 3) may be facilitated by several methods including, but not limited to elastomeric balls, elastomeric cord, or machined elastomeric blocks etc. Figure 5 shows an example of a flexible joint using rubber balls (item 7) that act as a torsion spring. This view on arrow ‘A’, shows an outer square body (item 3a) (attached to the rear frame assembly (item 1)) that retains the elastomeric balls against the inner square body (item 3b) (attached to the front frame assembly (item 2)) turned through 45 degrees. As the rider leans the rear frame assembly into a corner the outer body of the flexible joint (item 3a) will rotate against the elastomeric material (item 7), relative to the inner body (item 3b). Square body sections with four balls have been shown in this example but different shaped tubes with varying numbers or shaped elastomers may be used. The rear axis of the rotating joint shall be angled (Figure 4, angle 0), to pass through, or near to, the point at which the rear tyre (item 5) contacts the ground. Some offset, above or below the contact point, may be included to compensate for issues such as tyre sizes, tyre pressures, suspension, or to provide a small amount of bias to the steering etc. If the rotating joint axis passes significantly above or below the point at which the rear wheel’s contact the ground, the steering will experience turning forces due to side loads applied as the rider leans over. The flexible joint can be installed low down in the trike to allow the front frame assembly to be kept low. Keeping the flexible joint and front frame assembly low to the ground will allow a large cargo space with a safe, low-down centre of mass. On some trikes the inner body (item 3b) may attach to the front frame assembly (item 2) and outer bodies attach to the rear frame assemblies (item 1), rather than the other way around, as shown. Self-centring return spring When the rider’s rotational load on the flexible joint has been removed, the elastomeric material provides a self-centring force to return the joint to its normal condition (as shown by figure 5) and return the trike’s rear frame assembly to an upright position. The self-centring spring return force provided by the flexible joint unit will also make riding the trike feel much more stability and therefore make learning to ride the trike easier. Rider weight adjustment The flexible joint example, Figure 5, shows upper and lower, outside body channels when viewed on the end face, arrow A. The two channels can be secured together by applying a clamping force ‘C’ on the upper and lower flanges at both sides of the channels. Changing the clamping force will change the pre-compression in the elastomeric material and therefore the spring rate. Changing the spring rate will change the flexible joint spring return forces allowing different performances to be set for different riders weights etc. Cushioning suspension Figure 6 shows an example of a flexible joint, viewed from the side, section BB figure 5, with outer and inner bodies retaining the elastomeric balls at both ends of the unit. The circular balls have been shown for clarity but the flexible joint may be constructed in other ways including, but not limited to, rubber cord, blocks or plastic mouldings etc. As a vertical load is supported by the trike, or a bump in the road is transmitted through the wheels, the outer body 3a and inner 3b body will change angle relative to each other and the resulting compression of some of the elastomeric material will act like a damped spring. This movement will provide cushioning which acts similar to a bike’s suspension, therefore improving the rider’s comfort. The change in relative angles between the outer and inner bodies can also be used to indicate the total load that is being supported by the trike. Simple coloured areas with an indicator line can be used to identify when the total load is within or exceeds the safe design limit. Different lengths of elastomer or different element numbers may be used at different location within the flexible joint to provide different vertical and rotational spring rates. Axial load support The flexible joint shall retain the front and rear frame assemblies in the same relative longitudinal position to ensure the trike wheelbase does not change. When the front wheels receive an impact (F1), the outer and inner bodies (items 3a and 3b) may move slightly to absorb the shock but will return to their original positions to maintain the overall trike wheelbase dimension. Figure 6 shows an example of a flexible joint which includes small tabs designed to hold the elastomeric material in the same relative axial position relative to both inner and outer bodies. Force F1 may be applied to the unit for example when the front wheels hit a stone or curb. Force F2 may be applied to the unit for example due to changing drive loads or a rear wheel impacts.

Claims

1. A tricycle having two hub-steering front wheels and a single rear wheel, the tricycle having a front frame assembly carrying the front wheels and a rear frame carrying the rear wheel, a seat and a handlebar, wherein there is a flexible joint unit between the front frame and rear frame, the flexible joint unit comprising elastomeric material and defining a rotary lean axis, said rotary lean axis passing through a point close to where the rear wheel contacts the ground, the flexible joint allows the rear frame assembly to lean over while the front wheels remains perpendicular to the ground, and will automatically return the rear frame assembly to the upright position if no forces are acting on the rear frame assembly.

2. A tricycle with flexible joint according to claim 1, wherein the front frame assembly complete with flexible joint body are kept low to the ground e.g. below the axis of the front wheels, which may allow the cargo load to be carried more safely if the load forces act at a point below the front wheel axle height.

3. A vehicle with flexible joint according to claim 1, wherein the front and rear frames are fully supported in their longitudinal direction without the need to add additional bearings or thrust plates to maintain their relative positions, when the trike is subjected to a forward and / or backward load or impact, that is likely to occur while riding.

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