Case Studies in TRIZ: An Integrated Steering Shaft Lock for Motorcycles

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Yan-jie Mao* and Ching-huan Tseng**
Department of Mechanical Engineering, National Chiao-Tung University,
Hsinchu 30056, Taiwan, R.O.C.
Tel: 886-3-5712121 ext. 55155  Fax: 886-3-5717243

*              Graduate Student
**           Professor

Introduction

The steering shaft locks on most scooter motorcycles are designed separated from the saddle compartment locks, as shown in Figure 1. The steering shaft lock is in the front of motorcycle body under the handlebar and serves as the ignition switch and lock of steering shaft, while the saddle compartment  lock is in the back of the motorcycle body near the seat and  only provides the function of keeping the saddle secured.

Figure 1 - The separated handlebar and saddle locks of a traditional scooter motorcycle.
(The picture is used just for explaining, from Error! Bookmark not defined. )

Thus, before people can access anything inside the saddle compartment, they have to pull the key out from the steering shaft lock and plug it into the saddle lock to open it.  This operation  wastes  time.  Besides, it needs precise positioning for putting the key into the keyhole, which is difficult to do in the  dark of night.  Such design demonstrates not only the inconvenience of operation but also the opportunity to remove a  redundant lock device when  only one is needed.

Problem Clarification – Preliminary Design

To overcome the disadvantage described in the foregoing, designers may make some clarification over the problem in advance.  With referencing to Altshuller's 39 parameters of physical systems, the problem may be clarified as the following:

1. Decrease the waste of time to unlock the saddle compartment when accessing something inside it;

2. Retain or decrease the amount of substances of the new designed lock mechanism;

3. Retain or decrease the complexity of the new designed lock device.

Those requirements stated above can be restated in terms of Altshuller's Contradiction Matrix:

1. Improve the loss of time to unlock while deteriorating the amount of substances;

2. Improve the loss of time to unlock while increasing the complexity of the device.

For these technical contradictions, the Contradiction Matrix recommends corresponding principles to solve such kinds of conflicts, respectively:

Transformation of Properties – principle 35,
Accelerated Oxidation – principle 38,
Mechanical Vibration – principle 18,
Partial or Excessive Action – principle 16;

Universality – principle 6,
Pneumatic or Hydraulic Construction – principle 29.

As the designer consider the first comment of the latter group, the principle “Universality” suggests that:

An object can perform several functions; therefore, other elements can be removed.

By applying this suggestion, the designer may make a reasonable solution - combining the function of the saddle lock into that of steering shaft lock by eliminating the saddle lock unit.  As the saddle lock is removed, the rested saddle lockup hook mechanism, which grapples the saddle cover and keeps it secured, can be connected to the steering shaft lock unit with a cable.  Thus the hook can be operated via this cable by the steering shaft lock.  The connecting relation graph is shown in Error! Reference source not found..

Figure 2 - The saddle lockup hook mechanism is connected with the steering shaft lock via a cable.

Hence the main problem can be simplified into a design problem focusing on the steering shaft lock unit itself.  The whole problem is preliminary reduced.

Mechanical Restrictions

Before going toward the next design stage, the original restrictions of the steering shaft lock needs to be considered.  The emphasis will be on the controlling paths analysis.  The molding of the traditional steering shaft lock with ignition switch is shown in Error! Reference source not found..

Figure 3 - Molding of the traditional design of the steering shaft lock.

Two paths are arranged to control the power switch and steering shaft lock respectively:

1. OFF®ON: when the user turns the key, the lock core simply rotates the power switch off and on.  This operation won't cause the steering shaft to be locked;

2. OFF®LOCK: when the user wants to lock the steering shaft, he must "push" the key before turning it counterclockwise from the OFF position.  And the state of power switch will remain at OFF position during this operation.

Two functions located on the two paths separated by the OFF position won't interfere with each other in this traditional design.  For example, the driver would not ride the motorcycle with the lock at LOCK position, nor could he keep his motorcycle from being stolen with the lock at ON position when he leaves away.

Formulation of Technical Contradictions

However, joining the function of the saddle lock into the steering lock may cause overlaps of controlling paths - if the current state of power switch is changed while the driver is turning the key to open the saddle cover, this will cause inconvenience of use and confuse the driver.  Similarly, if the saddle cover is unlocked when switching the power, the safety problem while driving is achieved.  On the other hand, the increased number of functions on the locking device may bring out complexities of the mechanism.  Complicated organizations of the mechanisms will raise the manufacturing costs.

Among the properties described above, the problem can be collected as follows:

1. Increase the productivity of the steering shaft lock since it is going to be designed multifunctional;

2. Improve the convenience and safety of use on the lock mechanism when it unlocks the saddle cover;

3. Retain or decrease the complexity of the lock device;

4. Retain or decrease the amount of substances of the lock device.

Again using Altshuller's TRIZ Contradiction Matrix Analysis, the refined contradiction problem can be transformed into the Contraction Matrix form:

1. Improve ease of use while deteriorating the complexity of the device;

2. Improve ease of use while increasing the amount of substances of the lock;

3. Improve the productivity while deteriorating the complexity of the device;

4. Improve the productivity while increasing the amount of substances of the lock.

In connection with these technical contradictions, the Contradiction Matrix recommends possible solutions as follows, respectively:

Changing the color – principle 32,
Copying – principle 26,
Equipotentiality – principle 12,
Transition into a New Dimension – principle 17;

Equipotentiality,
Transformation of Properties – principle 35;

Equipotentiality,
Transition into a New Dimension,
Replacement of Mechanical System – principle 28,
Mediator – principle 24;

Transformation of Properties,
Accelerated Oxidation – principle 38.

Note that both “Equipotentiality” and “New Dimension” appeared for 3 times each in the total recommended principles.  Consider the principle “Equipotentiality”, it suggests:

Change the conditions of the work in such a way that it will not require lifting of lowering an object.

And principle “Transition Into a New Dimension” suggests that:

Transition less dimensional movement, or placement, of objects into more dimensional.

Utilize multi-level composition of objects.

Incline an object, or place it on its side.

Utilize the opposite side of a given surface.

Project optical lines onto neighboring areas, or onto the reverse side, of an object.

According to these suggestions, it may get a conclusion that operations may be performed on the steering lock unit and would not need further works on other components or places would be an acceptable direction of new design.

Conceptual Design

Several companies in Taiwan R.O.C. have made some improvementsError! Reference source not found.]Error! Reference source not found.]Error! Reference source not found.].  One of the new designs is shown in Error! Reference source not found., which is from the patent communiqué applied by KYMCO, etcError! Reference source not found.].

Figure 4 - One sectional drawing in the patent communiqué.

For convenience of explanation, the molding of the steering shaft lock is extracted in Error! Reference source not found.a.  Error! Reference source not found.b shows the corresponding control paths of the multi-functional steering shaft lock represented in 3D graph.

(a) The molding of the lock;                      (b) 3D graph of controlling path.

Figure 5 - Property of the new designed steering shaft lock:

These two figures mean, for example, if the user wants to unlock the seat when he is currently at ON position, he must follow the control path “N®push®temporary location T₂®T₁” to open the seat.  However, if he wants to open the seat when at OFF position, he must follow the path “F®L.” Note that in this situation he cannot perform a “push” before turning the key.  That's because at the initial position of OFF, if a “push” is performed before the lock core is rotated counterclockwise, the “lock the steering shaft” function will be activated.

According to the design expressed above, the new steering shaft lock keeps its original functions well and simultaneously includes the function that a saddle cover lock originally provided.  The convenience of use is not deteriorated too much.  The problem is solved into an acceptable stage in this way.

Conclusions

During solving the problem in improving steering shaft locks of motorcycles, there are two design stages that need TRIZ Contradiction Matrix.  On the first stage, the TRIZ method helps to simplify and clarify the entire problem by finding the core sub-problem for designers to focus on.  Going through the latter design stage, once the target object is clearly defined, mechanical designers can figure out the core contradictions on the steering lock unit and solve them by using Altshuller's Contradiction Matrix. Requirements are satisfied on the new design with using TRIZ method.

References

[1]        G. Altshuller, Forty Principles TRIZ Keys to Technical Innovation, Technical Innovation Center, Inc., 1997.

[2]        J. Terninko, A. Zusman, B. Zlotin, STEP-by-STEP TRIZ: Creating Innovative Solution Concepts, St. Lucie Press, 1996.

[3]        Taiwan R.O.C. Patent No. 340,496, “An Improved Structure of the Motorcycle Main Lock Unit” (in Chinese) by Formosa Seiko Electronic Co., Ltd. (http://manufacture.com.tw/~jinkun/index.html) and Kwang-Yang Motor Co., Ltd. (http://www.kymco.com.tw/), 1998.

[4]        Taiwan R.O.C. Patent No. 302,866, “The Motorcycle Main Lock Mechanism That Can Control the Saddle Lock and Fuel Tank Lid Lock” (in Chinese) by Dong-yang-jian-chang Electronic Co., Ltd. (in Chinese) and Kwang-Yang Motor Col., Ltd., 1997.

[5]        Taiwan R.O.C. Patent No. 314,014, “A Central Controlled Lock Device” (in Chinese) by Sanyang Industry Co., Ltd. (http://www.sym.com.tw/), 1997.

Introducing the authors:

Yan-Jie Mao, who was born on 1974 at Kaohsiung in Taiwan, is a graduate student in NCTU. He is interested in mechanical design on bicycles and motorcycles. The further design of this integrated lock device is adopted by KWANG YANG MOTOR CO.,LTD, Taiwan.

Ching-Huan Tseng was born in 1955 at Hsinchu in Taiwan. He is a professor of Department of Mechanical Engineering at National Chiao Tung University, received his MS degree from Nation Cheng Kung University at Tainan, Taiwan, in 1980, and PH. D degree from University of Iowa at Iowa City in 1987. His current research interests are in design methodology and products design. The industrial products are included 2D & 3D cams, bicycle components, scroll and screw compressors, and etc.