VEHICLE WHEEL ASSEMBLY COMPRISING A NON-PNEUMATIC TIRE

Abstract

The invention relates to a vehicle wheel assembly, comprising 1) a wheel rim (4) having two opposed circular rim flanges (5); 2) an outer tire (3) having two beads secured at the circular rim flanges (5); 3) a non-pneumatic inner tire (1) comprising expanded thermoplastic polyurethane (E-TPU), which inner tire (1) is enclosed by the outer tire (3) and the wheel rim (4); wherein the inner tire (1) in the assembly is in a compressed state S1, which state is compressed as compared to a relaxed state S2 when the inner tire (1) is not enclosed by the outer tire (3), the compression being such that the cross-sectional surface area SA of the inner tire (1), which area is perpendicular to the plane of the tire, is smaller in state S1 than in state S2.

Claims

1. Vehicle wheel assembly, comprising a wheel rim having two opposed circular rim flanges; an outer tire having two beads secured at the circular rim flanges; a non-pneumatic inner tire comprising expanded thermoplastic polyurethane (E-TPU), which inner tire is enclosed by the outer tire and the wheel rim; wherein the inner tire in the assembly is in a compressed state S1, which state is compressed as compared to a relaxed state S2 when the inner tire is not enclosed by the outer tire, the compression being such that the cross-sectional surface area SA of the inner tire, which area is perpendicular to the plane of the tire, is smaller in state S1 than in state S2.

2. Vehicle wheel assembly according to claim 1, wherein the inner tire when in the relaxed state S2, has a density in the range of 150-400 kg m.sup.3, in particular in the range of 200-300 kg m.sup.3.

3. Vehicle wheel assembly according to claim 1, wherein the SA in state S1 is 0.96 times or less the SA in state S2, in particular it is 0.90 times or less.

4. Vehicle wheel assembly according to claim 1, wherein the diameter DM.sub.S2 of the inner tire in state S2 is in the range of 30-40 mm, or wherein the surface area SA.sub.S2 of the inner tire in state S2 is in the range of 700-1250 mm.sup.2.

5. Vehicle wheel assembly according to claim 1, wherein the distance between the rim flanges is in the range of 16-26 mm.

6. Vehicle wheel assembly according to claim 1, wherein the inner tire and the outer tire are connected to each other.

7. Vehicle wheel assembly according to claim 1, wherein at at least part of the lateral faces of the outer tire in the assembly, the thickness is 0.75 mm or less, in particular 0.50 mm or less.

8. Vehicle comprising a vehicle wheel assembly according to claim 1, wherein the vehicle is selected from the group of bicycles, wheelchairs, electric bicycles, mobility scooters, scooters, motorcycles, cars, trucks, wheelbarrows, trolleys and hand trucks.

9. Method for preparing a vehicle wheel assembly according to claim 1, comprising providing 1) a wheel rim having two opposed circular rim flanges; 2) an outer tire having beads capable of being secured at the circular rim flanges of the wheel rim; 3) a non-pneumatic inner tire comprising expanded thermoplastic polyurethane; then pulling one of the beads of the outer tire over one of the rim flanges of the wheel rim; pressing the inner tire into the outer tire; finally pulling the second bead of the outer tire over the rim flange to form the wheel assembly of the invention.

10. Method according to claim 9, wherein the inner tire, before being pressed into the outer tire, is pre-compressed in a compression mold.

11. Method according to claim 9, wherein the inner tire, before being pressed into the outer tire, is made softer by exposing it so a pressure of less than 1 bar; followed by exposing it to atmospheric pressure.

Description

EXAMPLES

[0082] 1. Measuring the Rolling Resistance and Riding Comfort

[0083] 1.1. Materials and Methods

[0084] The wheel assemblies according to the invention were investigated by measuring their rolling resistance and driving comfort. The values were compared with those obtained when the same wheel assembly was provided with either a conventional pneumatic tire or a conventional non-pneumatic tire instead of the E-TPU tire.

[0085] The comparative pneumatic tire was tested when inflated to a pressure of 2.3 bar and the comparative non-pneumatic inner tire was made of polyurethane (PU). The outer tire was a standard 28 tire of a good quality (Schwalbe Energizer Plus) with a width of 40 mm (outer diameter), being an abundant tire in the Dutch bicycle market.

[0086] The E-TPU of the inner tire was obtained from BASF under the name Infinergy. An inner tire of this material was obtained by processing globular beads of expanded TPU in a mould under steam pressure. The E-TPU had a density of approximately 250 kg m.sup.3.

[0087] In the assembly of the invention, an E-TPU inner tire with a circular cross-section of DM.sub.S2 of 37 mm (corresponding to an SA.sub.S2 of 1075 mm.sup.2) was placed in the outer tire of 40 mm width (outer diameter). The E-TPU inner tire was present in the outer tire under pressure (i.e. it was in a compressed state), such that the wheel assembly had an SA.sub.S1 of 850 mm.sup.2. Accordingly, the degree of compression C.sub.SA in the assembly was 0.79.

[0088] Measuring of the rolling resistance was performed by making use of the pendulum rolling resistance test as described in The world's most fuel efficient vehicle (ISBN-10: 3728131342).

[0089] The driving comfort of a bicycle comprising a wheel assembly of the invention was determined by measuring the vertical acceleration and deceleration of the bicycle in time when it rides over a certain trajectory. Therefore, an accelerometer was mounted on the bicycle. The acceleration values are indicative of the degree of vibration of the bicycle, and thus also of the comfort.

[0090] 1.2. Results

[0091] 1.2.1. Rolling Resistance

[0092] It was found that the rolling resistance coefficient of a wheel assembly of the invention was similar to that of an assembly comprising a pneumatic tire inflated to a pressure of 2.3 bar. In both cases a rolling resistance coefficient of 0.010 was found (which value was based on a measured 27.5 seconds of swinging of the pendulum).

[0093] 1.2.2. Comfort

[0094] During the particular ride, a set of 1060 data points was initially obtained. For aesthetic reasons and easy viewing, the representative 32 highest and lowest amplitudes were selected and plotted as a graph (FIG. 3). It appeared that the comfort of an assembly of the invention is similar to that of a pneumatic tire inflated to a pressure of 2.3 bar. This is demonstrated in FIG. 3, wherein the graphs of the E-TPU tire and the pneumatic tire have similar amplitudes. Further, the comfort provided by a E-TPU inner tire appeared to much higher than that provided by a conventional non-pneumatic PU tire, which is demonstrated by the much larger amplitudes in FIG. 3 in case of the non-pneumatic PU tire as compared to those of the E-TPU tire.

[0095] In addition to the visualization in FIG. 3, the degree of comfort of the three tires was also compared by calculating the average vertical acceleration of each tire by averaging the 1060 data points for each tire. This yielded an acceleration of 1.27 g for the E-TPU tire of the invention, an acceleration of 1.26 g for the 2.3 bar pneumatic tire, and an acceleration of 1.99 g for the non-pneumatic PU tire. This is line with the comfort measurements of the three tires as displayed in FIG. 3.

[0096] 2. Panel Test

[0097] A bicycle having in two of its wheels an assembly of the invention was used by a panel composed of 33 Dutch experienced bicycle riders. As a comparative, they also used a bicycle with conventional pneumatic wheel assemblies, inflated to a pressure of 2.3 bar. The two bicyles used in this panel test were essentially identical, except for the wheel assemblies. The pressure of 2.3 bar was chosen because this pressure gave vertical accelerations in the comfort measurements that were similar to those of the particular assembly of the invention (see section 1.2.2. of the Examples). In other words, with this pressure, a hardness of the tire is reached that is comparable to the hardness of the E-TPU containing tire.

[0098] The assemblies of the invention used in the bicycle were the same as those described under section 1.1. of the Examples. The bicycle riders were intercepted at a resting place on a busy Dutch bicycle route and asked to participate in the panel test.

[0099] The test was performed in a so-called double blind manner, i.e. neither the panel members nor the team of investigators responsible for the panel test knew which of the two bicycles contained the pneumatic inner tire or the E-TPU inner tire. In order to keep the bicycles visually identical, the bicycle with the assemblies of the invention was equipped with a fake air valve on each rim.

[0100] The form on which the panel members had to note their experiences contained 10 questions. Answering these questions required choosing the appropriate point of a Likert scale. The scale contained five choices: 1. Poor; 2. Fair; 3. Good; 4. Very good; 5. Excellent. The questions were the following:

1. How was your riding experience in general?
2. How was you riding experience on the flat (red) asphalt?
3. How was you riding experience on the brick road?
4. What is your opinion on the rolling resistance in general?
5. What is your opinion on the comfort on the brick road?
6. What is your opinion on the comfort during driving onto the curb?
7. What is your opinion on the comfort during driving off the curb?
8. What is your opinion on the driving behavior of the bicycle in the turns?
9. What is your opinion on the braking of the bicycle?
10. What is your opinion on the tension of the tires?

[0101] At the end, the form contained a remark section, wherein the panel members could put additional remarks on their own discretion.

[0102] The answers of all 33 respondents on the questions are summarized in Table 1. Bicycle 1 has wheel assemblies of the invention and bicycle 2 has the conventional pneumatic wheel assemblies.

TABLE-US-00001 TABLE 1 Summary of the results of the panel test. Bicycle Poor Fair Good Very Good Excellent Q. 1 1 (E-TPU) 0 0 2 28 3 2 (pneum) 0 0 3 24 6 Q. 2 1 (E-TPU) 0 0 0 30 3 2 (pneum) 0 0 3 25 5 Q. 3 1 (E-TPU) 0 0 0 30 3 2 (pneum) 0 0 0 26 7 Q. 4 1 (E-TPU) 0 0 0 30 3 2 (pneum) 0 0 3 21 9 Q. 5 1 (E-TPU) 0 0 0 30 3 2 (pneum) 0 0 4 27 2 Q. 6 1 (E-TPU) 0 0 0 29 4 2 (pneum) 0 0 0 27 6 Q. 7 1 (E-TPU) 0 0 2 31 0 2 (pneum) 0 0 0 29 4 Q. 8 1 (E-TPU) 0 0 0 30 3 2 (pneum) 0 0 2 21 10 Q. 9 1 (E-TPU) 0 0 0 27 6 2 (pneum) 0 0 3 21 9 Q. 10 1 (E-TPU) 0 0 0 24 9 2 (pneum) 0 0 3 18 12

[0103] Questions 1-3 are directed to the riding experience, which is a catch-all of all factors that contribute to how a ride on the particular bicycle is perceived. In all three questions, the bicycle with wheel assemblies of the invention gives the same or a slightly poorer experience to the respondent than the comparative bicycle with pneumatic tires.

[0104] In question 4, the respondent is asked to give his opinion on the rolling resistance. The answers indicate that the perception of rolling resistance is substantially the same for both bicycles.

[0105] Questions 5-7 are directed to the comfort. A bicycle having assemblies of the invention was found to have a slightly better comfort on the brick road than a bicycle having pneumatic tires. On the other hand, ascending and descending the curbs is experienced as a bit more comfortable with a bicycle having pneumatic tires.

[0106] In questions 8 and 9, the respondent is asked to give his opinion on the bicycle's behavior in the turns and on the braking of the bicycles, respectively. The bicycle with assemblies of the invention and the comparative bicycle having pneumatic tires appear to have a similar performance in each of the two areas.

[0107] It is noted that the answers on question 10 confirm that the average bicycle rider is indeed used to an air pressure in the tire that is rather low (such as 2.3 bar). This is because 18 of the 33 members rate the pressure as very good, while 12 of them even rate it as excellent. No respondent awarded the relatively soft tension of the pneumatic tire with poor or fair.

[0108] In conclusion, questions 1-9 reveal that a bicycle with assemblies of the invention has a similar or slightly poorer performance than the comparative bicycle with pneumatic tires.

[0109] On some forms, the remark in the remark section contained the statement that there was in fact no difference noticed between both bicycles. This message was in much more cases also given orally by the respondents after completing the rides on both bicycles.

[0110] The total score of the two bicycles on all ten questions can be caught in one value by calculating the weighed sum of the choices on the Likart scale. These results are displayed in Table 2.

TABLE-US-00002 TABLE 2 Weighed sum of the results test and total score for both bicycles. Poor Fair Good Very Good Excellent Total score 1 (E-TPU) 1 0 = 0 2 0 = 0 3 4 = 12 4 298 = 1156 5 37 = 185 1353 2 (pneum.) 1 0 = 0 2 0 = 0 3 21 = 63 4 239 = 956 5 70 = 350 1369

[0111] Both scores differ by 1.3%, indicating that both bicycles have a similar performance. It is noted that the conventional bicycle has a larger spread in the choices, since it has 21 times been labeled as good and 70 times as excellent, whereas these values are 4 and 37, respectively, for the bicycle with wheel assemblies of the invention.