Wow: The Secret Hidden in the Parameters (Part 1)

What does cam lift mean?

How does the valve overlap angle affect different models?

How do large reach and trajectory correspond to handling performance?

What is the difference between the ergonomic triangle setting of a sports car and a station wagon?

What do you mean by curb weight, net weight, payload, gross weight?

...

Concepts and operations,

parameters and performance,

What is the causal relationship between them?

Motorcycles speak plainly about industrial products, quantitative indicator data, using a variety of concepts and parameters to define and describe performance, such as forward angle, towing distance, wheelbase, ergonomic triangle, net weight and curb weight, valve overlap angle, cam lift, power, torque... However, motorcycles are also a tool for riders, requiring richer feedback and more experience for riders, and the data is too blunt, too cold, too difficult to understand. After all, what function are these motorcycle concepts used to describe? What kind of performance do these parameters correspond to? Let's explore the story behind the important concepts and parameters of motorcycles through "Car Talk".

Cam lift

In the engine, the driver of the camshaft components opens and closes the valves. The law of valve movement is directly related to the power performance and output characteristics of the engine, and the camshaft plays an absolute core role in the engine. Among them, the cam lift is the core component of the camshaft, representing the distance difference between the highest and lowest points relative to the center of the camshaft. Analogously, a cam is like a lift door opening: the larger the door opening, the stronger the ability to facilitate the flow of people in and out; similarly, the higher the cam lift, the stronger the ability of the oil and gas mixture to enter the engine and discharge exhaust gases from the engine.

The BMW R 1250 GS is a good example of the flexible use of cam lifts. From the previous generation of R 1200 GS to the latest generation of R 1250 GS, we can see from the name change that "boxer" has grown taller again. In fact, the bore and stroke of the liquid-cooled, dual overhead camshaft 8-valve horizontally opposed twin engine were modified from 101 mm x 73 mm to 102.5 mm x 76 mm. Correspondingly, the displacement has also increased, reaching 1254mL, 84mL more than the previous generation. Surprisingly, despite the increase in displacement, for the burly "boxer", only a little more, the effect of the increase in power exceeded expectations: the maximum power was increased to 100 kW (7750r/min), an increase of 8 kW; the maximum torque change was more significant, reaching 143 N·m (6250 r/min), an increase of 18 N·m!

Obviously, this is an unusual input-output ratio. In fact, the small increase in displacement is only a superficial phenomenon. What really makes this "boxer" more energetic and energetic is the use of a "secret weapon" - bmw motorcycles first introduced. Variable cam technology. The "boxers" still use a double overhead cam mechanism. But take a closer look and you'll find a hidden mystery, which is that a single intake valve is equipped with 2 cam servos! When the work speed is low, the servo is served by a cam with a smaller lift, which is fully combusted and improves the fuel economy ratio. Moreover, the power output at this time is relatively balanced, smooth, easy to control, suitable for slow speed through complex areas. At high speed, the cam servo with large lift is used to extract strong power and achieve violent acceleration, which is suitable for high-speed galloping.

BMW claims that variable cam technology achieves several advantages, not only reducing the "boxer" idle speed by 100 rpm, but also improving power output across the entire speed range. When the speed is as low as 2000r/min, this horizontally opposed twin-cylinder engine is already able to squeeze out 110N·m of strong torque; from 2000r/min to 8250r/min, the output torque is above 110N·m; between 3500r/mmin and 7750r/min, maintaining a high output state of 120N·m! As a result, the R 1250 GS is even more powerful, whether it's traversing complex areas at high speeds and low speeds on Yangguan Avenue, traveling with friends, or full of luggage, it makes riders start their adventures with confidence! It's also gratifying that despite the larger displacement and greater output of the new generation of "boxers", fuel consumption has dropped by 4%, both running faster and eating less!

Valve overlap angle

We know that each full duty cycle of a four-stroke engine consists of four strokes, which are intake, compression, power, and exhaust. Among them, in the intake stroke, the intake valve is opened, the exhaust valve is closed, and the oil and gas mixture enters the cylinder; in the exhaust stroke, the intake valve is closed and the exhaust valve is closed. The exhaust valve opens and the burned exhaust gases are discharged from the cylinder. Ideally, the intake and exhaust valves are opened and closed sequentially, i.e. they are not opened at the same time. However, in the actual operation of the engine, the opening of the intake and exhaust valves has a certain intersection point, and the degree of this intersection is usually expressed by the crankshaft angle, that is, the valve overlap angle. Theoretically, high-speed engines require more valve overlap angles. The larger the valve overlap angle of the high-speed and high-power engine.

Take the case of the Ducati Monster 1200. Monster has become a performance monster sought after by thousands of riders with its ultimate NK shape, strong personality, agile handling and comfortable riding experience. In 2020, Ducati launched the cooler and stronger Monster 1200, with stronger power output, more flexible sportsmanship, more sassy personality, and set off a black storm on the road!

The Monster 1200 is powerful and powered by the Ducati supercar's 1198cc engine. This L-shaped twin engine has a bore and stroke of 106mm × 67.9mm and a displacement of 1198mL. Of course, due to the different positioning, Ducati engineers made a deep modification of the power heart of the Monster 1200, and one of the cores was to adjust the valve overlap angle. This performance monster is positioned in the competition, requiring high speed and high power, so it uses a 41° valve overlap angle to ultimately squeeze the L2 engine potential. With a maximum power of 125 kW (9750 r/min) and a maximum torque of 131.4 N·m (8000 r/min), it is enough to compete with the Japanese juxtaposition four-cylinder supercar. The Monster 1200 is primarily positioned for road driving rather than track, considering the supercar 1198's power is too aggressive.

In order to improve the friendliness of the power, Ducati engineers reduced the valve overlap angle of the engine from the previous 41° to 11°. Correspondingly, the peak power has decreased, with a maximum power and maximum torque of 108 kW (9250 r/min) and 124 N·m (7750 r/min), respectively. Engines that reduce the valve overlap angle, while slightly reducing peak power, run more smoothly in the full speed range, are more powered at medium speeds, and are easier to drive on streets and highways. At the same time, Ducati's engineers have also made simultaneous improvements, such as injecting the position of the injector from the previous injection to the colder intake wall directly to the hotner intake valve, which increases fuel consumption. Excellent atomization effect; introduction of double spark plug ignition to achieve full combustion in a shorter time; built-in electronic control valve in the exhaust system, which automatically adjusts the opening degree according to the automatic adjustment of the opening degree, thereby optimizing the exhaust pressure in the full speed range. await. Therefore, the Power Heart of the Monster 1200 inherits the pedigree of the supercar, while the positioning of the NK street car is once again optimized for proofreading. Implement operations such as reducing the valve overlap angle to retain strong and practical torque and improve the driving pleasure on the road.

To be continued...

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