POWER MEASUREMENT AND ROAD LOAD DATA ACQUISITION FOR SPEED EPACS

Transcription

1 POWER MEASUREMENT AND ROAD LOAD DATA ACQUISITION FOR SPEED EPACS Investigation regarding vehicle structure integrity for cycles designed to pedal of vehicle category L1e-B and ratio of auxiliary propulsion power and actual pedal power Refer to document COMMISSION DELEGATED REGULATION (EU) No 3/2014 of 24 October 2013 Dr. Eric Groß, Jorrid Lund, Christoph Petershagen, Anne Schröder Technische Universität Hamburg-Harburg Institut für Zuverlässigkeitstechnik Figure 1 / 15

2 Type approval ANNEX XIX of Regulation (EU) Nr. 168/2013 Requirements regarding vehicle structure integrity Vehicles of category L1e-A and cycles designed to pedal of vehicle category L1e-B shall be designed and constructed as to conform with all prescriptions regarding strength and construction of front forks and frames as encompassed in standard EN 14764:2005, specifying safety and performance requirements for the design, assembly, and testing of bicycles and subassemblies intended for use on public roads. Remark.: EN does not include Frame Fatigue test with horizontal forces Figure 2 / 15

3 Type approval REGULATIONS COMMISSION DELEGATED REGULATION (EU) No 3/2014 of 24 October 2013 supplementing Regulation (EU) No 168/2013 of the European Parliament and of the Council with regard to vehicle functional safety requirements for the approval of two- or three-wheel vehicles and quadricycles (11) The limitation to four of the ratio of auxiliary propulsion power and actual pedal power for cycles designed to pedal set out in Annex XIX should be subject to further scientific research and assessment. Upon availability of scientific data and statistics on vehicles placed on the market, the ratio four referred to above may be revisited in a future revision of this Regulation. Figure 3 / 15

4 Test vehicles and Metrology Test vehicle 1: Production Speed-EPAC Type/category: Citybike 500W back wheel hub motor (up to 40 km/h) Aluminum frame, hydraulic rim brakes Mass incl. battery 26 kg Test vehicle 2: Speed-EPAC-Prototype Type/category: Trekking bike 350W bottom bracket motor (up to 45 km/h) Fixed support ratios Pel/PPed from 2/1 to 6/1 Aluminum frame, hydraulic rim brakes Hub gear Mass incl. battery 26 kg Figure 4 / 15

5 Test vehicles and Metrology Test vehicle 3: Speed-EPAC-Prototype Type/category: Trekking bike 500W rear wheel hub motor (up to 45 km/h) Bang-bang control possible, 900W max Aluminum frame, suspension fork Hydraulic disc brakes Derailleur gears Mass incl. battery 28 kg Test vehicle 4: Production Speed-EPAC Type/category: Fun bike / commuter Back wheel hub motor (up to 45 km/h), no power specification from manufacturer Aluminum frame Hydraulic disc brakes Derailleur gears Mass incl. battery 23,8 kg Figure 5 / 15

6 Data acquisition Conditioning amplifier (strain gauges, current) Data logger (max. 16 channels, 4GB memory) Sample frequency 1 khz Buffering of data read out of data using digital interface Analysis-Software Load Data Power measurement Inductive current sensor for electric motor Strain gauges using full Wheatstone bridge Forces on crank measured by strain gauges on frame Loads on handlebar, front fork, frame and seat post rpm of crank to calculate human power Figure 6 / 15

7 Data acquisition Loads measured according to tests as defined in Standards ISO 4210 / EN / EN / pren Front fork horizontal Handlebar Seat post/saddle Pedal force Figure 7 / 15

8 Intended (normal) Use Definition: Service loads: Loads during normal use of the EPAC on typical tracks in combination with obtaining environmental conditions. Special events: Events with a low number of appearances that are part of the normal use and in general can not be affected by the rider. Test drivers: female and male 1,60 m to 1,86 m 55 kg to 98 kg Figure 8 / 15

9 Data acquisition Overview of different road surfaces included in the measurement campaign Asphalt road and inner city traffic, paved trail (clinker) Cobblestone irregular (Belgian block) and moved regularly, dirt road Figure 9 / 15

10 Power measurement human power vs. electric assistance Max. assistance by 3.5 times the human power for mixed service for test bike 1 Approx. 500 W continous rated power as defined for this bike by design Time response : 1X+ 14 human power crank S-Pedelec Sparta Time (seconds) 21 : 1X+ 21 el. power motor S-Pedelec Sparta : 1X+ 22 Speed km/h S-Pedelec Sparta Figure 10 / 15

11 Power Measurement - Conclusion A limitation of the ratio of the added auxiliary propulsion power dependent on the actual pedal power is necessary to provide a safe handling for starting, during cornering or for low speed cruising. This proved to be a safety issue found during test drives with manipulated control for the electric motor. Without a limitation dangerous driving situations may occur due to too hard unintentional acceleration or the impossibility for slow speed riding. For the investigated s where the motor control is kept in original condition a maximum assistance in auxiliary propulsion power by factor of approx. 3.5 is found In many driving conditions, especially riding at constant speed, this factor (electric power / human power) is identified by measurements within the range of 1 to 2. These factors (maximum of 4, typically at 2) result in good handling and driving experience. For speeds between 30 to 40 km/h (cruise speed) for the driver a power requirement of W results meaning no exhaustion for the driver for longer periods. A limitation to a factor of 4 for the auxiliary power by electric assistance as scheduled in regulation (EU) No 3/2014 proved to be very reasonable. Figure 11 / 15

12 Load Data Front fork Load histories applied to components are irregular in nature, whereas fatigue test data are usually obtained from constant amplitude loading. Seat post Pedalling force Chain stay (stress) In order to use test data of irregular load histories for fatigue analysis, load cycles must be extracted. Handlebar left Best proven are counting techniques that take into account that for fatigue hysteresis effects are essential and therefore cycles between the highest peak and lowest valley in the spectrum are combined. Handlebar right Speed Motor current Most commonly used methods: rangemean-pair and rainflow counting Distance Figure 12 / 15

13 Example Fatigue Analysis - Rainflow Counting Extrapolation by multiplying of events Load spectrum spectrum pedalling pedalling forces forces measured measured distance distance of of km km extrapolatet to 1000 km Load 10000,0 Test load: 1000 N LC Woehler k=6,2 Woehler k=6,2 Max. load 17.7 km Max. load 17.7 kmkm Extrapolation 1000 Force [N] 1000,0 Calculation of Damage ratio 100,0 10,0 1,E+00 1,E+01 1,E+02 1,E+03 1,E+04 1,E+05 1,E+06 1,E+07 1,E+08 Number of cycles [-] Figure 13 / 15

14 Loads for dynamic ( cycles) and static tests of safety relevant components ±850 N 1) Changes compared to pren printed in bold 2) Values for standards EN resp. EN given in square brackets Figure 14 / 15

15 Load Data - Conclusion Due to increased speeds the loads caused by road excitation (surface roughness, potholes, cobblestones) in service for s are higher than for EPACs (250 W - 25 km / h). Demands acc. to EN are insufficient, but test methods according to EN 14764, EN 14766, pren or ISO 4210 with adopted loads are suitable. In normal driving conditions, loads are found only slightly higher than found for EPACs, but the "bandwidth" of loads is quite large influenced by the driver. Based on a sporty driving style of a driver of 95. percentile male the measurements lead to higher damage ratios most notably for front fork, handle bar and seat post. Since s are expected to a more frequent use (commuters) and longer driving distances, these should be taken into account for structural testing. For an intermixed route profile (mostly asphalt roads, partly cobblestones and rough or unpaved roads) the loads are below or comparable to that of mountain bicycles, so parts that are suitable for mountain bicycles according to Standard EN are sufficiently dimensioned for s. Figure 15 / 15