First of all, lean control strategies can be divided into several groups, which we can call:

1/ Multiparametric

2/ Minimizing

3/ Proportional

4/ Rider superseded

Multiparametric lean controller, the first group, consists of several sensors that gather information about several vehicle motion parameters, use those information as input data in a previously defined function, and according to the output of the function - make a decision about what to do with the lean angle of the vehicle. For example, a multiparametric system would be the one that measures the vehicle velocity, position of the steering (in order to get the information about the curve) possibly some angular velocities of wheels and so on, and then leans the vehicle in appropriate position in order to provide a stable pass through the mentioned curve.

Minimizing lean control system would be a kind of system that measures just one parameter and leans the vehicle in a way that will minimize the measured value. That would be, for example a system that measures the offset of gravity/centrifugal resultant force from the line of CoG/contact patch, and leans the vehicle into a position where this offset will be minimized. That would be a system that measures only this one force, force N on the image bellow, and lean the vehicle in order to minimize it, as is shown in the picture. Note the position of the pendulum attached to the vehicle in the improper roll angle in the middle picture.

This picture shows three positions of a system. First, the lean with one curve radius and one velocity, than a higher velocity or smaller curve radius (or combination of both) with a lean angle that doesn't match this situation, so the lateral force occurs, which is shown as N and the rider will feel it as a force that drags him out of the curve. The sensors will detect this force and lean the vehicle in order to minimize it, what happened on the right picture, with increased roll angle. Vandenbrink Carver for example has a minimizing lean control system that minimizes the steering torque by leaning the vehicle.

Proportional lean control system would be the one where the maximum lean angle is determined henceforth. This angle can be determined out of the contact of the lowest parts of the engine with the ground or out of the extreme conditions that the tires can stand or in a simple word - extreme conditions. Sensors, which don't have to be different from the ones in the multiparametric class, but the difference is in the way the input data that came from sensors is being used. This system will calculate how far are the input data from the "extreme case" and then lean the vehicle proportionally away from the extreme lean.

Rider superseded lean control system would be the one where the rider (driver) has button or buttons that he uses to regulate the behavior of the lean regulation. Lean angle could be controlled with any of the systems mentioned above, with a difference which would contain an off/on button that could be used in order to cut the microcontroller (processor) off the valves on the hydraulic, what would immediately lock the vehicle in one position, just like the lean brake on Calleja prototype, only in this case the processor moves the vehicle into the position that the latest input data dictates right after this "lean brake" is released. The button could be also a turn type button with a potentiometer (like the volume button on CD player), and that button could regulate the influence that some parameter has over the lean angle, or it could control the maximum lean angle or what ever it could do if put between a sensor and the microcontroller Simply: choose the mode of the ride when the rider knows what ride is it going to be.

Now, we shall analyze the reactions of these systems in a situation where the vehicle is in motion situation that corresponds to motorcycling situation often described with terms like "accident" or "fall". Systems analyzed will be the multiparametric that considers velocity and steering position, minimizing that minimizes lateral force, and a proportional system that could be something like the multiparametric one. Situations analyzed will be rear end sliding, front end sliding, and both ends sliding, where we don't analyze values of yaw that come from tire slip angle but sliding like sliding where we look into the direction that we came from when it's over and we were lucky.

We will assume that rear end sliding is a situation that follows too fast pass through a curve. Every system has tilted the vehicle towards the curve center (approx..) and that point on, the rear wheel lost it's predictable contact with the ground. The rear end slides towards the outer edge of the curve which makes the vehicle rotate around a vertical axis. In order to try to maintain the motion direction through the curve, the rider might turn the front wheels into counter steer position and hope the sliding stops and the vehicle returns to the ideal path.

This yaw motion will generate some additional lateral force towards the same side of the vehicle where the the previously minimized lateral force is directed. These two forces are not collinear, but the yaw-generated force can be projected on the measuring direction and eventually, the lean control system will lean the vehicle even more. In that way it will bring the rear motorcycle-wheel into a new position (roll) that will bring its consequences. Minimizing system such as the one on Carver should tend to straighten up the vehicle and tilt it to the other side since it relies on the steering, and leaning the vehicle in order to minimize the steering torque which should increase when turning the motorcycle steering into countersteer.

The multiparametric system that measures velocity, steering position and angle between the tilting and non tilting part of the vehicle (calculates the required angle and compares it to the existing and than takes action), as an example of this kind that is easiest to imagine, will behave in a different way. If the rider turns the steering in the "needed direction", the sensors will transmit that information to the microcontroller as entering another curve, and the system will tend to straighten up the vehicle by tilting it outwards the curve, helping in that way the centrifugal force to roll it over. System like the one on Jephcott Micro, that measures the centrifugal force and steering position and sets steering as a higher priority over the centrifugal force input, will also act in a wrong way in this situation.

Rider superseded system can be in the basics some of the aforementioned systems with the possibility for the driver to prevent the wrong reaction by preventing any reaction. In this case, rider would have the button to freeze some of the input data in a moment, and in that way "persuade" the microcontroller that, for example, turn to the other direction did not happen. The same "shut off" button could be used to bring the actuator in the position where hydraulics will not react, keeping in that way the lean angle constant until the crisis is over. Influencing the input data that the microcontroller receives from sensors could favourize one input over the other and in that way influence the vehicle behavior.

Front end sliding will have the similar effect only of a different sign. Front end sliding outwards will force the rider to steer more into the curve what will make the system that takes that information about the steering position tilt the vehicle more towards the center of the curve, while lateral force measuring sensor will send information about increase of the curve radius to the microcontroller which will "appropriately" straighten up the vehicle - all opposite from the case of rear end sliding.

Behavior of the proportional and rider superseded systems depends on what they are based on.

Apparently, selection of the lean control strategy that will work even in the crisis and abuse depends on the vehicle wheel layout and drive. Vehicle wheel layout induces mass distribution.

The image bellow shows the hydraulic lean controll system that consists of a half-gear, a rod-gear (email me about the correct name of that element, it is common in steering systems), hydraulic cylinder and valves on the hc. The axis of the half-gear is collinear with the pivot axis, and one of these elements (half-gear) must be fixed to one part of the vehicle (the non-tilting part for instance) an the hydraulic cylinder must be attached to the other part - the tilting part of the vehicle. Oil that goes into the hydraulic cylinder is distributed over the valves A and B, and the distribution is controlled by microcontroller. The image to the left shows oil distribution in the moment when the main body (tilting body of the vehicle) is about to straighten up while the roll angle decreases. The middle image shows position of the same mechanism in the moment when the main body that sstands straight up is about to lean to the side opposite from shown on the left image. The right image shows position of the system that it has when the vehicle is stabilized in lean what corresponds to the situation of passing through a curve with a constant radius with a constant velocity.

The image bellow shows distribution of oil under pressure to the chambers of the hydraulic cylinder which is a part of the lean control system. The triangle in circle represents the oil pump that permanently makes the oil circulate, while the microcontroler controled valves direct the flow into the desired chamber, according to the required lean angle or just in order to change it. The images are showing on the left oppened valves for piston motion in one direction, in the middle is the steady roll angle and oil running in circle, and to the right is the oil path for leaning to the other side. This system has 6 valves of which every one has a certain reliability (it is easy to calculate the system reliability once the elements are known), and in case of collapse of any one of them the system goes to broke. Specially if the vehicle is of the kind that is not self-stabile. So even if the rider gets the signal about the malfunction of the system, using only this hydraulics, without any locks elsewhere, the system might bring to an accident in the moment of breakdown.

The next image shows a system that is very similar in oil paths, only it has one actuator and a needle valve that distribute the oil to the hydraulic cylinder. The actuator should be doubled, one on each side of the needle valve, and only one should be enough for regular operation. The other one should get involved as a replacement in the moment the system registers the first one as non functioning.