Improved control system made it possible to reduce idle engine speed and extend the engine speed range where fuel is saved, thus enhancing fuel economy.

Fig.6 Crevice volume reduction and the effect on HC reduction

EGR flow rate is optimized by electronic control of the duty-solenoid valve as required for engine speed and load to achieve low emissions and low fuel consumption.

The evaporated fuel absorbed in the canister is sent to the engine via the solenoid valve to avoid gasoline volatilization. Fig. 7 shows the engine control systems. 

Fig. 7 Engine control system

LIGHTWEIGHT - KL engine became the lightest in their displacement classes among V6 engines by the implementation of several measures: using aluminum alloy for the cylinder blocks and auxiliary brackets; resinating the belt cover and airflow meter; utilizing a short stroke; integrating the inlet manifold and surge tank; and decreasing the exhaust manifold size.

EXCELLENT ACCELERATION AND TOP-END FEEL - To improve drive feeling, much effort was put into achieving excellent "acceleration and top-end feel." Fig. 8 shows a quantitative method that uses vehicle acceleration characteristics in which "response" and "acceleration" make up "acceleration feel"; and the area of further extension from the top of vehicle acceleration curve, makes up "top-end feel". (2) The object was to get smooth vehicle acceleration characteristics in the "response" area, powerful and linear vehicle acceleration in the "acceleration" area, and to keep high vehicle acceleration characteristics in "top-end feel" area. These objects were attained by ensuring high continuous torque characteristics in all engine speed ranges, reducing the inertia weight of rotating parts, and optimizing ignition timing. (Table 2)

High Continuous Torque Characteristics - Efforts were concentrated on the improvement of volumetric efficiency and the optimization of setting. The technical features incorporated in each area are shown in Table 3.

Fig. 8 Vehicle acceleration and top-end feel

Table 2 Techniques for improvement of acceleration and top-end feel
	Acceleration feel		Top-end feel
	Response	Acceleration
Torque improvement techniques	XX	XX	XX
DOHC 24valve	X	X	X
Short Stroke	X	X	X
Weight reduction of rotating parts	XX	X	X
Active IG timing control	XX

Fig.9 Volumetric efficiency calculated by intake air simulation

Table 3 Techniques for torque enhancement
	Engine speed
	Low	Mid	High
4-stage VRIS	X	X	X
Semi-dual exhaust system		X
Crank angle sensor			X
Trace knock control	X

To obtain high torque in all engine speeds, a multi-stage Variable Resonance Induction System(VRIS) was adopted in the intake system. In the VRIS, surge tanks in both banks were connected to each other by resonance tubes. The resonance induction generates high torque characteristics around the resonant frequency. The resonant frequency changes by changing the tube's length.(3) Each resonance tube of multi-stage VRIS has a switching valve, which are operated according to the engine speed and load. And the system of multi-stage VRIS changes the resonant frequency to use the effect of resonance charge in all engine speed ranges. In the K-series engines, to optimize the resonance effect with small packaging size, the length of each resonance tube was optimized by simulation research.(Fig. 9)

Because the switching valves are operated according to driving conditions, it is possible to utilize the different resonance tube characteristics, thus realizing smooth and high torque in all engine speed ranges. The structure of VRIS is shown in Fig. 10. Fig. 11 shows the valve drive controls and 4-stage VRIS torque characteristics in low, mid and high speed ranges.

Fig. 10 Construction of 4-stage VRIS	Fig. 11 Valve drive controls and 4-stage VRIS torque characteristics

Simulation was also utilized to optimize the exhaust system specifications, obtaining exhaust-pulse scavenging in the desired engine speed ranges as shown in Fig. 12.

By adopting the semi-dual exhaust system in which two exhaust pipes have almost the same length, torque was raised in the desired, mid speed range. ( Fig. 13)

Fig. 12 Volumetric efficiency calculated

Fig. 13 Effect of KL engine semi dual exhaust system	Fig. 14 Crank angle sensor

Fig. 15 Effect of crank angle sensor

Ignition control was optimized to raise torque in low and high engine speed ranges. First, to improve the control of ignition timing in the high speed range, a new direct crank-angle- detection method (crank-angle-sensor) was chosen over the conventional method, in which the angle was detected by a distributor attached to the camshaft. (Fig. 14) Fig. 15 shows the effect of the crank angle sensor on torque enhancement.

With trace knock control, a single sensor between the engine V-banks detects small knocking, and the ignition timing is then set at a point just prior to the generation of the knocking in low speed ranges. In the conventional method, ignition timing was set in consideration of engine compression ratio and fuel octane number. (Fig. 16) The trace knock control optimizes ignition timing. And this optimizes engine potential, which in turn raises torque. (Fig. 17) 

Fig. 16 IG timing with/without trace knock control(T.K.C)	Fig. 17 Effect of trace knock control(T.K.C)

Fig. 18 Active IG timing control and its effect

Reduction of Inertia Weight of Rotating Parts - 24-valve DOHC short stroke was adopted as the basic specifications. Furthermore, the rotating inertia weight of the flywheel, crankshaft, and connecting rod was drastically lowered by making full use of Finite Element Method (FEM) analysis and acceleration response was greatly improved.

Optimization of Control - Ignition timing is actively controlled with crank angle sensor which detects changes in angular velocity of engine during acceleration; if vehicle vibration is generated, the timing is retarded, thus quickly converging vehicle acceleration value fluctuations which diminish acceleration feel, and improving acceleration in response area. (Fig. 18)

Because of the above new technologies and structure, KL engine can deliver the demanded torque characteristics and acceleration performance, while maintaining high and smooth acceleration characteristics.

PLEASANT ENGINE SOUND - Great efforts have been made not only to reduce engine vibration and noise levels but also to produce a more pleasant engine sound. To realize these objectives, engine development efforts were concentrated on the following two areas: 1) elimination of unpleasant rumbling sounds and 2) reduction of low-frequency sounds. Table 4shows the incorporated techniques and the objectives.

Fig. 19 Vibration characteristic of cylinder block

Table 4 Techniques for sound quality improvement
Technical menu	decrease of rumbling noise	decrease of low frequency noise
Lower block	X
No.4 journal widened up	X
Forged steel crankshaft	X
Lightweight piston & conn-rod	X	X
Increased transmission coupling rigidity		X

Elimination of Rumbling Noise - Unpleasant rumbling noises are often caused by crankshaft bending vibration due to flywheel face runout. This vibration is propagated through the cylinder block main bearing, block body, engine mount and vehicle body and results in an unpleasant rumbling interior noise. To reduce the noise, the engine mount's vibration level (inertance level), which responds to excitation in the cylinder, should be lowered.

Fig. 19 shows the engine mount vibration level when each cylinder is excited, the resonance mode increases the vibration level of the nonfundamental order components at which the unpleasant sound is often noticed. (4) To improve the flywheel resonance mode, that is, to reduce the inertance level and increase frequencies, cylinder block rigidity and crankshaft support rigidity of the main journal were increased. 

Fig. 20 Comparison of cylinder block rigidity

The vibration characteristics depends on dimensions and configurations, and the optimal configurations were studied through FEM analysis. As a result of the study, a two-piece cylinder block was employed to increase rigidity of both the cylinder block itself and its crankshaft supporting area. The cylinder block was divided into upper and lower sections at the crank center face and the lower block was given a ladder frame construction integrating the main-bearing cap and bearing beam. Fig. 20 shows a comparison of rigidity between the cast-iron cylinder block and the two-piece cylinder block employed in KL engine. The conventional cast-iron cylinder block was fitted with a bearing beam and a plate connecting the cylinder block skirts to increase the rigidity of the cylinder block itself. Generally, open-decked aluminum cylinder blocks give a lower rigidity than cast-iron blocks. Nevertheless, by adopting the new cylinder block construction, the natural frequency of the block itself was increased.

For further reduction of flywheel face runout, the lower deck's No.4 journal near the flywheel was made wider than the other journals. In addition, a forged steel crankshaft was used to increase crankshaft bending rigidity. Fig. 21 shows the reduced inertance level and the increased frequency of flywheel resonance mode. By improving the vibration transmission structure, nonfundamental order components decreased from those of cast-iron block with the conventional construction. (Fig. 22)

Fig. 21 Improvement of crankshaft supporting rigidity

Fig. 22 Reduction of nonfundamental frequency level of KL engine

Reduction of Low-Frequency Noise - To reduce low-frequency noise, particular attention was paid to the second order components. To do this, powerplant bending (PPB) vibration and second-order inertia couple were reduced.

To reduce PPB vibration, coupling areas between the cylinder block and transmission should be made highly rigid. Transmission coupling rigidity was understood to be increased effectively by lengthening the cylinder block skirt and widening the coupling flange (cone flange). Fig. 23 shows the improvement effect of the above changes on in-line 4-cylinder engines' PPB vibration level calculated with FEM.

Fig. 23 MAZDA's basic concept for improvement power- plant bending (PPB) vibration  Based on these results, PPB vibration in the KL engine was reduced by adopting a cone flange with high rigidity as well as a longer skirt. Fig. 24shows the PPB natural frequency characteristics of the KL engine. PPB resonant frequency was increased to the point where no resonance was produced in the engine operating speed range (less than 7,500 rpm) - even with second-order excitation.

Fig. 24 PPB frequency characteristic of KL engine

To decrease second-order inertia couple, piston and connecting rod weight, which cause excitation, were reduced by making full use of FEM analysis. As shown in Fig. 25, the reciprocating inertial weight of the piston and connecting rod is lower than all the other reciprocating inertia weight with equal diameter. Because of the reduction of PPB vibration and second-order inertia couple, the KL engine reduces the second-order vibration level which causes most low-frequency noise.

Fig. 25 Comparison of reciprocating inertia weight

COMPACTNESS - To match the low hood & short nose vehicle style, the engine height, width and length were reduced. With a unique direct valve drive, combined with the adoption of a compact intake manifold and a compact cylinder block, the low hood could be realized. The valve drive system, as shown in Fig. 26, employs gears which directly engage each bank's intake and exhaust camshafts, and a timing belt attached to the rear bank's inner camshaft and the front bank's outer camshaft. This layout made it possible to reduce the height of the engine front as shown in Fig. 27. Also, this system, along with the adoption of a compact exhaust manifold, has reduced engine width. The combination of these design features gives KL engine the most compact packaging sizes in their displacement classes. 

Fig. 26 Valve train system	Fig. 27 Comparison of hood line

LONG LIFE AND MAINTENANCE-FREE - Efforts were made to extend the life of these engines and make them as maintenance-free as possible so that customers can be pleased with the vehicle's quality long after the initial driving period.

Long Life - The following achievements were made to ensure extended low engine oil consumption: Piston land volume and piston ring configuration were optimized through simulation analyses for stable ring behavior; and wear resistance of the cylinder liner was improved by the use of alloyed cast-iron.

The oil seal material (camshaft and crankshaft oil seals) was changed to fluorine to improve thermal resistance.

Maintenance-Free - Mazda's unique ventilation system comprises a PCV valve in the left bank and a forked ventilation hose connecting the air hose and both banks, providing the right bank a higher rate of air flow than the left bank (7:3). With this mechanism, fresh air flows in the crankcase and cylinder head cover effectively, thus ensuring stable oil characteristics.

A timing belt having STS-teeth and a hydraulic auto tensioner were designed as follows to have long-life quietness:

• Optimization was made on timing belt pitch, ejector force and leak-down time of the auto tensioner.

• H-NBR having high heat resistance and glass fiber having high bending resistance were used for the timing belt, realizing the reduction of belt width to 30mm while ensuring a satisfactorily long life.

The Hydraulic Lash Adjuster (HLA) has oil recirculation passages in its plunger to recycle the less-air-contaminated oil in the high-pressure chamber. This construction minimizes the influence of air-contaminated oil -- even in the engine-startup condition with high-air-contaminated oil -- resulting in improved quietness and the elimination of the need for valve clearance adjustment.