In previous posts, we've seen more about rev matching and auto blippers which is very much used for our safety and for our motorbike's health. Always, all of us wants to ride at a constant speed without interruption for a longtime to feel the smoothness of the engine and just to ride peacefully. But in reality, it's less possible due to the road condition and the presence of heavy traffic. At that situation, we have to use brakes most often which increase the engine's RPM which is not good for health of the engine. To avoid this, we use to blip the throttle before leaving the clutch lever which results in gradual syncing of the both the engine and transmission speed. If we are not blipping the throttle, it may lead to control loss and locking of the rear wheel as we know. To avoid this, slipper clutch has been developed. We can able to see this slipper clutch in motorbikes like Bajaj Dominar 400 & 250, TVS Apache RTR 200 4V, Yamaha R15 V3 etc...
Let's assume that the engine is running at 2000 RPM. With the reduction ratio of 2:1 (when the gear A rotates 2 time, the gear B connected to the A will rotate 1 time), gearbox converts it into 1000 RPM and sends it to the rear wheel which means, the rear wheel is also running at 1000 RPM. Imagine suddenly any obstacle appears and you're downshifting the gears directly. Imagine the engine is at the same speed of 2000 RPM and due to downshifting, the reduction ratio at the gearbox now changes to 4:1. Due to this, engine wants the rear wheel to rotate at 500 RPM. But due to the presence of momentum at the rear wheel, it'll be running at more than 500 RPM for sure. When the engine tries to change the speed of the wheel suddenly, it changes the speed of the vehicle which results in locking of the rear wheel and lose in stability. The rear wheel which is running at higher speed than that of the gearbox will provide back power or back torque to the engine which is the reason for the engine to rev while downshifting. The function of the slipper clutch is to avoid these kind of problems.
The name itself tells the function of it. Slipper clutch refers to the action where the clutch slips when it experience any back torque from the rear wheel. Simply saying, it allows slight disengagement of clutch when the rear wheel is providing back torque. So, when the rear wheel is providing back torque, the clutch system should prevent the back torque reaching to the engine thereby avoiding the unnecessary increase in engine RPM. The clutch system should allow some slippage to help sync the speed gradually than suddenly.
As we know, engine's power will be transferred to the rear wheel via the clutch assembly and the transmission system. In the normal clutch assembly, steel and friction plates will be present in between the pressure plate and hub. Pressure plate is loaded by the spring which helps in keeping both the steel and friction plates always in contact. When we pull the clutch lever, this steel and friction plates will be disengaged. In the design of the slipper clutch, ramps will be present on both the hub as well as on the pressure plate. These ramps are designed in such a way to rotate in one direction freely and when the speed of the gearbox side is increased, this ramp will be helpful in disengaging the clutch plates thereby restricting the power flow.
When the engine is operating normally, speed of the engine is always higher than that of the gearbox side due to the presence of load. When you accelerate, steel and friction plates will be in contact thereby making way for the engine power to flow to the rear wheel via transmission. Imagine any sudden obstacle is appearing so that we are holding the clutch lever and downshifting. The moment when we leave the clutch lever, back torque from the wheel starts to transfer to the engine via the gearbox which raises the RPM. Here, slipper clutch comes to action.
As i said, at normal condition, engine's speed will be greater than the transmission speed. When the engine starts to receive back torque, the speed of the transmission side will become higher than that of the engine side which tries to increase the engine speed also. But, the ramp assembly present in the clutch avoids that. As you can see, ramp in the clutch assembly is designed in such a way that, when the engine speed is high, the ramp present in the hub goes and locks to the ramp present in the pressure plate thereby forcing it to rotate along with it.
Benefits
• Reduce engine braking
• Prevents rear wheel from locking up
• Maintains the health of the engine
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Let's assume that the engine is running at 2000 RPM. With the reduction ratio of 2:1 (when the gear A rotates 2 time, the gear B connected to the A will rotate 1 time), gearbox converts it into 1000 RPM and sends it to the rear wheel which means, the rear wheel is also running at 1000 RPM. Imagine suddenly any obstacle appears and you're downshifting the gears directly. Imagine the engine is at the same speed of 2000 RPM and due to downshifting, the reduction ratio at the gearbox now changes to 4:1. Due to this, engine wants the rear wheel to rotate at 500 RPM. But due to the presence of momentum at the rear wheel, it'll be running at more than 500 RPM for sure. When the engine tries to change the speed of the wheel suddenly, it changes the speed of the vehicle which results in locking of the rear wheel and lose in stability. The rear wheel which is running at higher speed than that of the gearbox will provide back power or back torque to the engine which is the reason for the engine to rev while downshifting. The function of the slipper clutch is to avoid these kind of problems.
The name itself tells the function of it. Slipper clutch refers to the action where the clutch slips when it experience any back torque from the rear wheel. Simply saying, it allows slight disengagement of clutch when the rear wheel is providing back torque. So, when the rear wheel is providing back torque, the clutch system should prevent the back torque reaching to the engine thereby avoiding the unnecessary increase in engine RPM. The clutch system should allow some slippage to help sync the speed gradually than suddenly.
As we know, engine's power will be transferred to the rear wheel via the clutch assembly and the transmission system. In the normal clutch assembly, steel and friction plates will be present in between the pressure plate and hub. Pressure plate is loaded by the spring which helps in keeping both the steel and friction plates always in contact. When we pull the clutch lever, this steel and friction plates will be disengaged. In the design of the slipper clutch, ramps will be present on both the hub as well as on the pressure plate. These ramps are designed in such a way to rotate in one direction freely and when the speed of the gearbox side is increased, this ramp will be helpful in disengaging the clutch plates thereby restricting the power flow.
When the engine is operating normally, speed of the engine is always higher than that of the gearbox side due to the presence of load. When you accelerate, steel and friction plates will be in contact thereby making way for the engine power to flow to the rear wheel via transmission. Imagine any sudden obstacle is appearing so that we are holding the clutch lever and downshifting. The moment when we leave the clutch lever, back torque from the wheel starts to transfer to the engine via the gearbox which raises the RPM. Here, slipper clutch comes to action.
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As i said, at normal condition, engine's speed will be greater than the transmission speed. When the engine starts to receive back torque, the speed of the transmission side will become higher than that of the engine side which tries to increase the engine speed also. But, the ramp assembly present in the clutch avoids that. As you can see, ramp in the clutch assembly is designed in such a way that, when the engine speed is high, the ramp present in the hub goes and locks to the ramp present in the pressure plate thereby forcing it to rotate along with it.
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When there's a back torque, engine speed will be low and transmission speed will be high. That is, the speed of the pressure plate will be higher than the speed of the hub. At this condition, the ramp can able to slip. Whenever the back torque tries to flow to the engine, this ramp slips and disengage the friction and steel plates thereby separating the engine and the transmission system. When the back torque is faded, automatically engine speed will become higher and the ramp present in the hub starts to pull the ramp in the pressure plate along with it thereby the clutch plates engages again making way for the flow of engine power. By this action, speed of the engine and the transmission system is synced gradually than suddenly which results in locking of the rear wheel as i said previously.
Benefits
• Reduce engine braking
• Prevents rear wheel from locking up
• Maintains the health of the engine
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