20076616(JSAE) 2007-32-0116(SAE)

Simplification of the Shift/Clutch Operations for the Formula SAE Vehicles (1) (1) (1) (2) Hiroshi ENOMOTO, Hironari MORITA, Yousuke FUKUNAGA and Naoki UOTA (1) (2) Kanazawa university and KADO corporation Copyright © 2007 Society of Automotive Engineers of Japan, Inc. and Copyright © 2007 SAE International The simplified shift/clutch operation system, KF-TOS-P, was driven by DC motors (DC12V driven) with a microprocessor. Two rotary sensors detected the positions of the shift lever and the clutch lever. In FSAE rules, the simple throttle-by-wire is prohibited and the engine speed was controlled by the drivers. The custom steering wheel, KF-SW07 as the human machine interface, was designed and manufactured with CFRP by VaRTM (Vacuum assisted Resin Transfer Modeling) method. The shift operation time of KF-TOS-P was half of the manual operation and the clutch engagement time of that was 25msec. KF-SW07 was 22.6% weight and 16.7% cost (calculated by FSAE rules) of the commercial steering wheel of the race use. Keywords Electric equipment, Steering Wheel, Shift/Clutch operations, Carbon Fiber Reinforced Plastic

1.

INTRODUCTION

Many FSAE cars use super-sport bike engines that have built-in manual transmissions. The drivers release the hand from the steering wheel when they control these transmissions. In FSAE rules, the students should be drivers and it is difficult to find well-trained students or to train them in circuits in Japan. Such amateur drivers cannot control well these hand-release transmission. As the FSAE car is a racing car, these transmission operating systems should satisfy many

trade-off parameters, light weight, easy-maintenance, easy-processing, tough-enough, low cost and so on. The related FSAE rules [1] are “3.5.1.3 Transmission and Drive”, “3.5.4.2 Throttle Actuation”. The “3.5.1.3 Transmission and Drive” rule say that we can use any transmission and any drive train. The “3.5.4.2 Throttle Actuation” rule say that we must use only mechanical throttle actuation system such as a cable and a rod system. The steering wheel is used as the human machine interface for the transmission control. The interface of the

This distance must be no more than 250mm. Front roll hoop

Steering wheel

Front roll hoop no lower than top of the steering wheel.

Figure 2

Figure 1 Schematic of the steering wheel and the shift/crutch handle for KF2006.

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The commercial steering wheel for KF2003 – KF2006. Weight: 473g

20076616(JSAE) 2007-32-0116(SAE) transmission control has two buttons for the up shift and for the down shift. The drivers could grasp the steering wheel with both hands during the races with the interfaces. The steering wheel shape and the location are defined in FSAE rules as “3.4.6.1 Circular Shape Required”, “3.3.4.3 Front Hoop”. The “3.4.6.1 Circular Shape Required” rule say that we must use steering wheel that have a continuous perimeter that is near circular or near oval. The steering wheels that have “H”, “Figure 9”, or cutout shape are not allowed. The “3.3.4.3 Front Hoop” rule determines the position relations of the steering wheel and front roll hoop. Figure 1 shows the schematic of these rules. The commercial steering wheel in Fig. 2 was used until 2006. The weight was 470g. It was difficult to process it to mount switches on. In this paper, the transmission control to simplify the operation was described. The system included the custom steering wheel, KF-SW07.

2.

METHOD

2. 1 Transmission operating A light-weight, small-size and high-quality transmission should be mounted on the FSAE racing car and many teams use the super-sports bike built-in transmissions. However, the drivers should control these transmissions manually shown in Table 1(a). For such amateur drivers or the weekend racers defined in FSAE rules, the quick and accurate operations are not easy because large acceleration occurs in accelerating, decelerating and cornering. From these facts, Kanazawa University Formula R&D used CVT (Continuously Variable Transmission) transmission to eliminate the hardness for KF2003, the first FSAE car that participated in the first FSAE Japan competition held in 2003. Our Kanazawa formula racing team has given the model code as KFxxxx to the successively developed racing vehicles. The four digit number xxxx signifies the year in which the team joined the race with those vehicles. For example, for the first participated year of 2003, the racing car is named as KF2003 and in the successive years the cars are named in the same manner. The CVT, built in the inline 2 cylinders 600cc engine which is commercially used for the scooter, was a little heavy and large and used dry belt. The dry belt could not transmit the high torque immediately and the disadvantages were not small in FSAE circuit events because the circuit had many tight corners and short straights. After deepest reflection, KF2004, developed in 2004, had the inline 4 cylinders 600cc engine for the competitive motorcycle use. The built-in transmission needed a manual operation that was usual in FSAE competitions. As the foot pedal controlled the clutch, KF2004 had three pedals and the left-hand lever to operate the shift. The shift/clutch operation

was almost same of the commercial car and was not difficult for these amateur drivers. However, the three-pedal interface was not good for the quick and accurate operation. The narrow spaces between the pedals caused mistakes to step not-intentional one or two pedals at once. The KF2005, that won 2005 FSAE Japan competition, used two-pedal system. The hand levers operated the shift/clutch in Fig. 3. The pull motion worked as the up-shift operation and the push motion worked as the down-shift one. In the push motion, the two levers moved sequentially and the clutch was released. The two feet were devoted to a single operation. Though the each operation was simplified in comparison with KF2004, drivers should have some practice to operate them smoothly. 2. 2

Semi-automatic transmission operating system Mechanical systems with links and wires were used to operate the manual transmissions. These systems should be allocated in a narrow space and the drivers should release the left hand from the steering wheel in the operation. It often caused miss-steering operations. KF-TOS-P, semi-automatic Transmission Operating System, was developed to simplify the operating and aimed to help the drivers. Switches mounted around the KF-SW07 controlled the shift/clutch with DC motors and the drivers did not release the hands for the operations. Table 1(b) shows the outline of the KF-TOS-P sequence. FSAE rules prohibit the throttle-by-wire. However, the most efficient device to control the engine speed is the electrical-controlled throttle. Though we can use the electrical-controlled throttle if the mechanical one is mounted together, KF-TOS-P gave up it in considering the cost, weight Front hoop

Steering wheel

Up Down

Shift lever Shift wire

Clutch lever Clutch wire

Figure 3

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Steering shaft

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The cockpit layout of KF2005.

20076616(JSAE) 2007-32-0116(SAE) Table 1

Outline of the shift sequence.

(a) Manual sequence Up

(b) Full-automatic sequence Up Down The accelerator kept pressed The accelerator kept released

Down

The micro computer read tachometer

Reading tachometer

Release the accelerator

Disengage the clutch by hand

The engine speed is over the threshold.

The engine speed is below the threshold.

Decreasing the engine speed

Disengage the clutch by an actuator

Press the accelerator Up-shift by hand

Increasing the engine speed

Down-shift by hand

Down-shift by DC motor

Release the accelerator Press the accelerator

Up-shift by DC motor

Engage the clutch by hand

Engage the clutch by an actuator

and the air-intake efficiency. The throttle operating by drivers controlled the engine speeds in shift operations. The engine and transmission for KF2004 and KF2005 uses a dog clutch. Though the drivers easily operate the up-shift operation with the dog clutch, the engagement time-lags and the engagement impacts in the down-shift operation stressed the drivers. A DC motor with PWM (Pulse Width Modulation) was used to control the partial clutch engagement in the down-shift operation. The manual up shift operation time was measured by throttle position sensor. The manual up shift operation time is time of an interval to release the accelerator. KF-TOS-P had rotary sensors and the operation times of the shift/clutch were measured with output of the sensor. The data logger (2kHz in sampling rate) was used.

2. 3

Dimensions of hand The custom steering wheel, KF-SW07, shape should satisfy many requirements in section 2.4 and the hand specifications were measured. Members of 20 men, from 18 to 25 years old, cooperated with us. In many cases, middle, third and little fingers have an important role to grip. On the other hand, thumb works well to push switches. The thickness of the hand should be known to allocate the equipments or the instruments to be recognized easily. Five parameters were measured as shown in Fig. 4. • Length of the hand (Lhand) • Thickness of the hand (thand) • Length of thumb (Lthumb) • Length of little finger (Llittle) • Length of middle finger (Lmid) 2. 4

Lmid Lhand

Llittle

Lthumb thand

Figure 4

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Definition of the hand dimensions. (Left hand was used.)

Requirement to KF-SW07 The custom steering wheel, KF-SW07, was designed to satisfy the following requirements. These requirements were based on the commercial steering wheel. Req. 1. Tough enough. Req. 2. More than three button switches, that have 10mm in diameter and 10mm in thickness, should be mounted. Req. 3. Fine grip feeling. Req. 4. The rim or the drivers’ hands will never touch the drivers’ knee during lock-to-lock operation. Req. 5. Easy manufacturing. Req. 6. Light weight. Req. 7. Impressible. Req. 8. Low cost (if possible). The main parts of KF-SW07 are rim, hub and spoke. CFRP was used to satisfy Req. 1, 2 and 6. Four prototypes in Fig. 5 were manufactured with hard paper and were evaluated with a sensory evaluation. As the steering wheel is a rotating part, the CFRP

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20076616(JSAE) 2007-32-0116(SAE)

Case A

Case B

Case C

Case D Figure 5 Test pieces of the steering wheel. (unit: mm, manufactured with hard paper) Designed by Toshitsugu Hirose and Satoshi Kitayama

forming of KF-SW07 needs a high quality base. The VaRTM (Vacuum assisted Resin Transfer Modeling) method was used for the CFRP forming. The manufacturing cost was more than thousands dollars with a normal. 2. 5

The evils of one-hand operation The steering system of

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KF2006

adopted

a

rack-and-pinion but not the power assisted system with a hydraulic actuator/an electric actuator. The assisted systems will allow the drivers the easy one-hand operation of the steering. However, the following two reasons hindered to use the assisted systems. The first reason is that a power assisted steering system has heavyweight. The race cars should be lightweight to improve driving performance and such heavyweight parts

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20076616(JSAE) 2007-32-0116(SAE) Table 2

Joint angle in a comfortable driving position. Joint a1 a2 a3 a4 a5 a6

Angle [degree] 10 - 30 85 - 100 100 - 120 85 - 95 80 - 90 6 - 50

Table 3

Time sequence of clutch operation with KF-TOS-P.

Time

[msec] 0 236 480 500

0

1844

1062

2906

1087

2931

Start the clutch release (without PWM) Beginning of the clutch release Almost released Finish the clutch release Keep the clutch release Start of the clutch engagement (with PWM control) Beginning of the clutch engagement (a partial engagement) Finish of the clutch engagement

Table 4 Average [mm] Stand. Dev. [mm] S.D./Avg. [%] Maximum [mm] Minimum [mm] Figure 6

deg. +35.9

Figure 7

Lhand 183.6 11.3 6.2 210 171

thand 29.1 3.3 11.3 35 23

Lthumb 59.9 5.3 8.8 70 52

Llittle 61.5 5.4 8.8 75 50

Lmid 84.2 11.1 13.2 110 51

Driving position.

-35.9 d eg.

adjustable. These layouts and the adjustable systems made the drivers possible to keep comfortable driving positions without changing their postures. In the CAD model, the height of the driver reproduced 5th percentile and 90th percentile of the adult Japanese males, and the cockpit supports the most of the adult Japanese males. This design method was quoted by references [3]. The difference between "one-hand operation" and "two-hand operation" were evaluated with the following static steering test. The drivers rotate the steering wheel to the right and left target rotation angle, 35.9 deg. shown in Fig.7 on the standing vehicle as fast as possible in the duration. The output of the steering angle sensor was measured with a data logger (100Hz in sampling rate). The target rotation angle assumes the slalom run in the FSAE course.

The target rotation angle

could not be used. The second reason is that a position of the steering system is far from the center of gravity position of the vehicle and the inertia moment will be increased with the heavy system. The increased inertia moment will decrease the speed in turn. KF2006 adopts the cockpit in which the most of the adult Japanese males can operate in a comfortable driving position. The joint angle such as Tab.2 in a comfortable driving position was quoted from the references [2] and was evaluated with a sensory evaluation. The subjects were five adult males who had driven KF2005 or KF2006 and knew driving environment well. As a result of the sensory evaluation, drivers could operate comfortably at each joint angle shown in Tab.2 and the driving position was as figure 6. The seat, the steering wheel and the pedals were arranged to satisfy the angles in Tab.2. The angle of the steering wheel shaft and the pedal position were

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Dimensions of hand.

3. 3. 1

RESULTS

Shift/clutch operation The manual up shift operation time was 210msec. (7 frames) and that of KF-TOS-P was 110msec., about half of the manual operation. The DC motor speed was controlled by the current. There was room to increase the current and the operation time could be adjusted to the driving condition. The time history of the clutch operation with 0.5 duty ratio PWM was shown in Table 3. The clutch release time was defined by the DC motor power. The time for PWM preparation, 1344msec, was caused by the light microprocessor. A high-speed processor will make the time short. The partial clutch engagement was realized after 1062msec from the start of the clutch engagement.

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20076616(JSAE) 2007-32-0116(SAE) Knot of thumb Longest thumb Averaged thumb Shortest thumb

Thickness [mm]

100

80 Center of the wheel

60

40 Shift switch

20 170

Figure 9 Shift switch layout.

180

190 200 Length of hand [mm]

210

(a) Thickness vs. length of hand.

100

Length [mm]

80

60

40 thumb little middle

20 170

180

190 200 Length of hand [mm]

3. 3

210

(b) Length of fingers vs. that of hand. Figure 8 Relations between the hand specifications. 3. 2

Dimension of hand Though Fig. 8(a) shows that the thickness slightly decreases with the length of hand increase, the dependence is small enough to be ignored. The outer diameter of the commercial steering wheel satisfied the Req. 4 and the maximum outer diameter was the same. Figure 8(b) shows that the length of little finger was almost same of that of thumb and the middle finger was the longest. In order to grip well, the tip of the little finger should be the opposite side of the palm with the steering wheel rim between. The subjects measured these dimensions griped the pipes of various diameters with the little finger and felt

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fine-griped when the little finger touched the half of the circumference. As the shortest little finger was 50mm in Table 4, the circumstance of the KF-SW07 rim should be less than 100mm and the diameter of it was 25mm (78.5mm in circumstance) considering the manufacturing. The length of middle finger was the largest and increased with the length of hand increase. The switches will be allocated three methods, 1) tact switches on the steering wheel, 2) tact switches behind the steering wheel and 2) paddle switches around the steering shaft. The method 1 will operated with thumb. The methods 2 and 3 will operated with the forefinger or the middle finger. As the rudder angle of the FSAE car is not small, the drivers should control the wheel with large torque and should grip the rim tightly with three fingers, middle, third and little. As the result, the method 1 was used and the tack switches for the shift control were pushed with thumbs. Sensory evaluation of grip The case A in Figure 5 had good grip feel compared with the commercial one because of the spoke layout. However, thumb could not be stable and some drivers felt unease for slips. The case B in Figure 5 had the stable point for thumb and the unease feeling was decreased. However, the stiffness and the space for switch layout were not enough. While the case C in Figure 5 a little bulge put the drivers at ease, the processing of the base was difficult and costed much. The case D in Figure 5 had larger space for switches and decreased the cost of NC machined processing. The bulge such as rim of the case C will set with post processing. The bulge put the drivers at ease like the case C. 3. 3

Switch layout Figure 9 shows the tack switch layout. As most drivers set the center of hand on the centerline of the wheel, the thumb knot could be defined. The switches are allocated as the belly of thumb will touch even if the longest or the shortest had used it. This layout allows the drivers the two-hand operation.

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20076616(JSAE) 2007-32-0116(SAE) 3. 4

45 two-hand one-hand Steering angle [degree]

Effect of the two-hand operation Figure 10 shows the value of the steering angle sensor in the Static steering test written in 2.5. Plus (+) is anticlockwise and minus (-) is clockwise. The angle resolution was 0.0288 degrees. The difference between steering angle vertex and the target angle was compared. The averaged difference of "two-hand operation" was 2.3297 degrees and that of "one-hand operation" was 3.1210 degrees. This shows that "two-hand operation" has more accurate than "one-hand operation". The test duration was 14 seconds and "two-hand operation" could steer 38 times. On the other hand, "one-hand operation" could steer only 36 times. This shows that "two-hand operation" is faster than "one-hand operation". These results show that "two-hand operation" surpass "one-hand operation" at the accuracy and the speed of the steering.

40

35.9 35

30 0

2

4

6 8 Time [sec]

10

12

14

(a) Anticlockwise DISCUSSION

4. 1 KF-TOS-P The shift operation time was short enough because the up shift operation time by DC motor was shorter than the up shift operation time by hand. On the other hand, the clutch engagement time was too long to mount on KF series. In this experiment, as the definition of the clutch release was detected by the end of the rotation, the partial engagement could not be controlled. The disengagement time, 250msec, was enough to develop the future seamless engagement. The adjustment of the actuator for clutch control is important. 4. 2 KF-SW07 The case D, adopted design, was 22.6% weight and 16.7% cost of the commercial one and satisfied the Req. 6 and 8. The thickness of KF-SW07 CFRP of 0.5mm contributed the weight and cost reduction. Few FSAE team in the world could design and manufacture the whole CFRP steering wheel and the Req. 7 was satisfied. While the steering action was smooth, the switch action made some stress for some drivers because the thumb should rise over the hub. Though the thumb works well beside the forefinger, some stress occurs on the thumb knot if the thumb moves far from the forefinger. To grip tight, it is better that the thumb works with the third and lithe fingers. Therefore, it is desirable that the switches operate by the forefinger or the middle finger. The paddle switch or the tack switch allocated behind the steering wheel should be considered.

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Steering angle [degree]

4.

-35 -35.9

-40

two-hand one-hand -45 0

2

4

6 8 Time [sec]

10

12

14

(b) Clockwise Figure 10 5.

Static steering test. CONCLUSION

The CFRP steering wheel with switches allocated in the center of the wheel to allow the two-hand operation, KF-SW07, was developed to improve the human-machine interface of the electrical shift/clutch operation system, KF-TOS-P. Sensory evaluations were used to evaluate grip of KF-SW07 and the difference between "one-hand operation" and "two-hand operation".

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20076616(JSAE) 2007-32-0116(SAE) 1) 2)

3)

KF-SW07 had good grip feel and much space to mount instruments and switches. KF-TOS-P had an advantage over the manual operation system on the past KF series in the shift operation time and the clutch engagement time. In FSAE vehicle, which could not have power steering system, the two-hand operation surpassed the one-hand operation at the operation speed by 5.3 % and the accuracy by 25.4 %.

ACKNOWLEDGEMENT As the operation cost includes the base processing in FSAE cost calculation, KF-SW07 was not expensive in spite of CFRP forming. However, the real cost is hundreds times of the cost. KF-SW07 could not come true without the supports of KADO Corporation and KINOSHITA SEISAKUSYO technically and financially. The authors gratefully acknowledge many of our colleagues who hove contributed to this work especially Mr. Noboru Hieda, research assistant of Kanazawa University Mechanical Systems Engineering, and the Kanazawa University Formula R&D team and Kanazawa University Administration. We wish to thank YAMAHA MOTOR to have sustained the presented work through many both parts and technical suggestions.

REFERENCES [1] [2]

[3]

2007 FORMULA SAE RULES, Society of Automotive Engineers, Inc., 2006 F. Picard, A. Wisner: “How can the physiologist contribute to the improvement of automobile seats”, SAE Technical Papers 610176, 1961 Kanazawa univ. Formula R&D Technical Report 2006, Kanazawa univ. Formula R&D, 2006

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