A Pedestrian Unit for Hilly Country
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By L. J. COTTON, m.I.R.T.E.
Carrying Three-quarters Load, the Harbilt r-ton Battery-electric Chassis Performs Well on "The Commercial Motor " Test Course at Watford
OWERED by a 2 h.p. electric motor and having a robust transmission and frame, the rbilt 1-ton pedestrian-controlled battery-electric has earned a reputation for reliable retail delivery work in hilly territory. In works-truck form, it often has to withstand overloading, coupled with operation under difficult ground conditions.
The motor is a spigot-mounted, four-pole unit designed for lowvoltage traction operation. It is iittached to the final-drive unit and shares the trunnion suspension to the rear axle. The worm shaft is attached to the commutator and a helical gear is driven in conjunction with the worm wheel to effect a double reduction.
Tubular Backbone Frame A conventional, all-welded chassis frame having twin tubular backbone members is employed, and the driving wheels are fitted with internal expanding brake unit. There is a separate parking brake which complies with the legal requirements for road vehicles and, when applied, cuts off the current. thus safeguarding the electrical gear.
The operating switch is controlled by downward movement of the tiller and actuates a double contact switch with solenoid control. During the first stage of control a resistance is brought into. circuit. In the following stage the resistance circuit is by passed through a time-lagcontrolled direct contact.
The batteries are supported in crates outside the frame, behind the front wheels, the carriers being mounted on retractable runners Improvements in Performance The vehicle supplied for test was new and there were indications of initial stiffness in the transmission. Moreover, new uncycled batteries were supplied. Therefore the rang obtained during the tests on "The Commercial Motor" standard course at Watford would be improved with further discharging and charging of the batteries.
After weighing the complete vehicle unladen, the 75-per-cent. payload (15 cwt. of sand in bags) was added and initial readings were taken before starting the continuousrunning test. The hydrometer specific-gravity reading had to be compensated, because the electrolyte temperature was 20 degrees F. below optimum.
The initial stiffness of the chassis, together with the power absorbed in churning the oil in the axle, was
nmediately apparent in the meter !adings taken on the railway-siding ope, the average current flow being ;latively heavy. I found the m.p.h. speed on level ground a mfortable walking pace, but the :rvice brake was required on the 3wnhill slope of 1 in 25.
The first serious hillock, Balmoral oad, was the point where a decrease speed was noticeable. Here the .adient is 1 in 15. There was still .avy oil-churning at this point and noticed a slight increase of speed .iring the next circuit. The severest .imp on Devon Road was climbed )mfortably and the first circuit of 1 miles was completed in 551 mins. After recording the meter readgs, the second lap was started. here was a slight increase of speed )th on the level and when hillimbing—in fact, the second lap as run off in 531 mins, The meter adings suggested that there was A sufficient battery capacity to implete the third circuit, ha there as quite a large margin to exhaust :fore reaching the discharge point. There was no slackening of pace mg the Radlett Road during the ird lap, but the sharp fall in speed, tipled with a heavy voltage drop on
Balmoral Road, indicated an early stop. This happened a few yards short of the summit of the hill, the average amp -hr meter reading indicating that full battery discharge was still far off. This enforced stop could be attributed to the lack of battery cycling, because in the twomile return to the garage only slight external assistance was required.
According to the specific-gravity reading after allowing one hour for electrolyte diffusion, the battery was not exhausted to safe discharge point. Therefore, with a fully cycled battery, the potential range on this course, working to a 100-point drop in specific gravity from full charge. would be approximately nine miles After completing the reading procedure, the Harbilt was connected to the Davenset charging set and left to recuperate for the 60-stop-permile test the following day The power-supply meter was read before and after charging, and it required 4.9 units to restore the batteries to full capacity.
An initial one-mile continuous run was completed at the start of the delivery test, and then stops were made at approximately 30-yd. intervals. The vehicle started from rest on hills without harshness in the transmission, and the service brake proved adequate for stopping and holding the vehicle on the declines
I wouid prefer there to be a slightly greater distance between the tiller and chassis under certain conditions, because when holding the free running of the vehicle against the brake on declines, my heels made contact with the vehicle. This would not happen to a roundsman with a shorter stride The Harbilt again increased speed with further use during the second day and moved away from rest on Balmoral Road and Devon Road without fault during the first and second circuits. The total distance covered was then 6.2 miles, and as the meter readings indicated that the discharge point of the batteries would soon be reached, the trial was concluded at the garage.
Although the pace slackened during the final half-mile and the 'current consumption was on the increase, there were no involuntary stops and the vehicle reached the garage without assistance, the mileage at this point being 6.5.
The electrolyte specific-gravity drop, 84 points from full charge, indicated that with a fully cycled battery the rang,: for this type of work would be approximately 71 miles. Had the transmission corm. ponents been fully bedded down, there might have been a slightly better result.
The data panel showing meter readings of the stop-start test reveals that the hilly part of the course was covered during the second and third miles and between the fifth and sixth miles. Here, the current consumption increased by 50 per cent. compared with that on other parts of the course. Under more favourable conditions and with fewer stops per mile, it would be reasonable to expect a range of 9-10 miles per charge.