FIELD OF THE INVENTION

The present invention relates to a clutch actuation system comprising a clutch pedal, a control system and an actuator operable to connect/disconnect a clutch.

PRIOR ART

Due to C0 ₂ -legislation and other factors there is an increasing share of vehicles equipped with start-stop systems. Today, these systems can offer full functionality only when they are combined with transmissions comprising a controllable clutch, as for example automatic transmissions (AT), dual clutch transmissions (DCT) and automatic manual transmissions (AMT). When installed in combination with a manual transmission there is no possibility to stop the internal combustion engine (ICE) in sailing conditions since there is no way to automatically disconnect the ICE from the wheels - hence, the vehicle will be retarded due to engine braking, unless fuel is wasted in order to compensate for the braking torque. As manual transmissions have a large market share there is a large fleet CO2 reduction and fuel economy improvement potential for a system that would solve this problem.

A known way of providing manual clutch vehicles with a start/stop system is to turn the engine off if the operator of the vehicle puts the gearbox in neutral position and releases the clutch. The engine will thereafter turn on when the clutch pedal is pressed down in order to put the gearbox in gear. Since the start/stop function is dependent on an operator action, there is, however, a clear risk that the start/stop function will not be used as often as would be possible.

For manual transmissions, another problem is clutch warranty costs due to misuse of the vehicle. Such misuse can for example be slipping the clutch for long periods of time or performing "idiot starts", i.e. revving the engine up to or close to full rpm and thereafter slip on the clutch until the vehicle has reached the desired speed. A system introducing a possibility for automatic override of the clutch control would have a potential to reduce these warranty costs as well as enable downsizing of the transmission since many of the extreme points in the load spectra could be avoided by automatic control.

Due to driveline downsizing, a trend towards engines having fewer cylinders and other factors, torsional vibrations is an increasing problem in the development of new vehicles. In the prior art, the solution for reducing torsional vibrations is often a damper in form of for example a dual mass flywheel. The drawback of such flywheels are that they are large and costly.

One known system giving the possibility of automatic override of the operator's clutch pedal movement is the Bosch "eClutch" system. This system comprises an electronic gauge connected to the clutch pedal and an electric actuator controlled by the gauge. Mostly, the actuator follows the gauge movement, but it is possible to override the systems, e.g. for sailing driving conditions and start/stop without the need for putting the gearshift in neutral.

Since the event of unintentionally releasing or applying the clutch can be very safety critical functional safety is a very important a very important consideration in the design of an automatic clutch control system. Such safety critical events can for example be unintended release of the clutch when the vehicle has stopped in an intersection for a red light. The release of the clutch could the cause the vehicle to inter the intersection and collide with crossing traffic.

It is the object of the present invention to provide a hydraulic actuation system for a clutch solving the above and other problems. It is also an object of the present invention to provide methods for controlling the hydraulic actuation such that the above problems are solved, or at least mitigated.

SUMMARY OF THE INVENTION

The above and other problems are solved, or at least mitigated, by a clutch actuation system comprising a control system comprising a hydraulic pump connected to an actuator via a controlled valve, wherein the controlled valve will be open when the clutch position is changed and closed once the clutch has reached the desired position such that pump can be stopped to save electrical energy.

In order to achieve the desired controllability, the controlled valve may be a solenoid valve.

Beneficially, the controlled valve may be a pilot controlled valve. By a pilot controlled valve, it may be possible to reduce the clutch actuating pressure by running the pump in a reverse direction.

In order to reduce the risk of system failure in the event of electrical failure, the clutch pedal may be hydraulically connected to the control system by a master cylinder in hydraulic connection with the control system. However, it may also be possible with a design wherein the clutch pedal is connected to a gauge and a pedal feel emulator. This is beneficial in that it reduces the need for costly hydraulic piping.

The system may also includes means for monitoring a current to a pump motor. The monitored current may be used for estimating a pressure signal usable for determining clutch position and thereby improve the functional safety of the system.

In order to provide for a cheaper, lighter and smaller system, the clutch actuation system may use transmission oil for actuation of the actuator.

In order to secure that the actuator does not change its actuating position when not desired, it may be of a type that is locked in its position once it has been actuated to its desired position. For such actuator designs, a low force spring may be connected to the actuator in order to avoid backlash in the clutch system. In order to reduce the force needed to connect/disconnect the clutch, the spring may be a spring with a spring constant equal to the inverse of the spring constant of a clutch spring.

In order to reduce noise vibration harshness, a small torque may be applied to the driveline from the clutch prior to releasing the clutch.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, the invention will be described with reference to the appended drawings, wherein:

Figs. 1-8 are schematic block diagrams showing the interrelationship between components comprised in embodiments of the invention.

DESCRIPTION OF EMBODIMENTS

All of the embodiments of the invention described below concern primarily hydraulic actuation systems, although some of the disclosed methods also may be used for the above disclosed eClutch system.

A hydraulic actuation system would be preferable since integration to the existing hydraulic clutch systems will be simplified. This applies especially to vehicle where some variants will have a clutch actuator for automatic control and some variants will have only the existing hydraulic manual clutch.

In Fig. 1 , a schematic view of an examplary embodiment of a hydraulic actuator system 100 that may be equipped according to the present invention is shown. This system comprises a clutch pedal P, which is hydraulically connected via a control system 110 and a master cylinder 115 to a slave cylinder 120, i.e. clutch actuator operable to connect/disconnect a clutch 130. The control system 1 10 may comprise components and or/ control methods according to the present invention.

The simplest form of a hydraulic actuator for the "System" below would be a rotary pump or other type of displacement pump/system. The master cylinder 115 and the control system 1 10 are in such embodiment both connected to a hydraulic reservoir 1 16. Using only a direct acting pump would however have the drawback that it would consume energy continuously when the system is pressurized. By adding a controllable valve to the system it can keep the pressure when the pump is turned off. To release the pressure the valve is opened. The valve can for example be controlled by a solenoid or a pilot pressure from the pump or by mechanical means.

Another embodiment of the present invention is shown in Fig. 2. Here, the master cylinder 1 15 of Fig. 1 has been replaced with a gauge 150, e.g. a position sensor and a pedal feel emulator providing a force feedback on the clutch pedal P resembling the force feedback of a manual clutch pedal.

As mentioned above, the system 110 of Figs. 1 and 2 may comprise pumps, hydraulic fluid reservoirs and different types of valves, such that the position of the slave cylinder, i.e. the clutch, can be controlled based on pedal position and/or automation requirements.

In a first embodiment of the invention, the system 110 includes means for monitoring a current to a pump motor such that the pump pressure may be estimated. This estimated pressure signal can be used as a redundant signal of the clutch lever position and thereby improve the functional safety of the system. As the pressure would rise when the slave cylinder reaches its end position the increase in motor current can be detected to offer better functional safety and clutch position information. As an alternative, a pressure sensor can be used for redundant position information.

In another embodiment of the invention, the system comprising pumps, and different types of valves uses the transmission oil for actuation of the slave cylinder, thereby eliminating the need for a separate reservoir for hydraulic fluid. By using the transmission oil for actuation of the slave cylinder, cost, weight and size of the system can be reduced.

In still another embodiment of the invention, shown in Fig. 3, the slave cylinder may be of a type that is locked in its position once it has been actuated to its desired position. In such a case, by adding a low force spring 160 to the slave cylinder piston the backlash in the lever system can be avoided thus leading to faster actuation times.

By adding a spring with a spring constant equal to the inverse of the spring constant of the clutch spring the clutch apply force can be completely or partially compensated and thus significantly reducing the required actuation force from the actuator.

In order to avoid unintentional movement of the clutch lever the actuation mechanism should be of a self-locking type, as for example a self-locking worm-gear or a hydraulic cylinder with controllable valve that prevents fluid from entering or exiting once the piston has reached the correct position.

To achieve a spring constant equal to the inverse of the clutch spring a system of springs and/or mechanism can be used.

In still another embodiment, which may be freely combined with the other embodiments disclosed herein, noise vibration harshness (NVH) from driveline rotational backlash in for example a "Race Start", a small torque can be applied to the driveline from the clutch prior to releasing the clutch. This small torque will then rotate the driveline until all rotational backlash has been "eaten up". The small torque can for example be applied as a pulse, ramp or continuously until the start has been performed.

To ensure correct function of the system and to maintain a good pedal feel in all situations an algorithm mapping the pedal position to the slave cylinder position can be used.

Below, some specific embodiments of the system comprised in the hydraulic actuator system according to the invention will be disclosed.

With reference to Fig. 4, a hydraulic pump 170 is connected to the slave cylinder 120 via a solenoid controlled valve V. The solenoid valve will be open when the clutch position is changed and once the clutch has reached the desired position the valve will be closed and the pump 170 can be stopped to save electrical energy. The system can also be modified to have a hydraulic connection to the pedal master cylinder 1 15. A valve or valve system 160 is then added to enable manual override of the system as well as emulate a good pedal feel by controlling the pressure to the pedal master cylinder. The valve or valve system 160 can for example be controlled by a pilot pressure or a solenoid.

In still another embodiment of the invention, shown in Fig. 5, the solenoid controlled valve V has been replaced with a pilot controlled valve PV. This is done in order to simplify the system - by using a pilot controlled valve, the slave cylinder may be emptied of hydraulic fluid if the pump 170 is run in the reverse direction.

In Figs. 6-8, different schematic layouts of hydraulic systems according to the invention are shown. Like references for like components as in Figs 1-5 are used in Figs. 6-8.

The control systems disclosed above and the system could also offer added functionality for the driver in the form of an automatic "Race start"-mode which by automatic control of the clutch would offer an optimized and fast start sequence without overloading the clutch and transmission. Another additional functionality that could be offered is automatic clutch control in specific driving scenarios as for example the stop and go traffic in a traffic jam.

An automatic control system for the clutch that could offer good controllability would give the possibility to introduce micro-slip over the clutch and thereby reduce the torsional vibrations without the need for an additional damper.

The system should be transparent for the driver and thus offer a normal clutch pedal feel in all situations.

The system will need to have a low energy consumption and limited peak power consumption.