Field of the Invention

This invention relates to a fluid flow control apparatus and a valve system, and more particularly, though not exclusively, to a valve system for providing a "limp-home" function to an Automated Manual Transmission (AMT), Double Clutch Transmission (DCT), Continuously Variable Transmission (CVT) or other transmission having a wet or dry clutch whereby a vehicle fitted with the transmission can be driven in the event of electrical power failure.

Background of the Invention

A recent wave of transmission inventions which incorporate wet (or dry) clutches have a common downfall in that, in the event of an electrical power failure, a "limp home" function is not available. The ability for a transmission to provide a "limp home" function, as has been provided already in a normal automatic transmission (ie. an automatic transmission having a torque converter - see Figure 5) is an inherent advantage in that it enables the driver to keep the vehicle mobile, with some loss of function, so as to be able to "limp home" to a location where the transmission can be diagnosed and repaired.

With new automated manual transmissions, friction launch devices, decouplers and wet start clutches, it has not been possible to incorporate a limp home function.

Preferred examples of the present invention seek to provide a valve system which enables the above devices to perform in a similar manner to a normal automatic transmission (ie. one with a torque converter) when electrical power to the transmission is lost. That is, to provide such devices with a "limp home" function which enables a vehicle propelled by way of the transmission to be driven to a location where the transmission can be diagnosed and repaired.

Summary of the Invention

In accordance with one aspect, there is provided a fluid flow control apparatus including a fluid supply line having a flow constrictor, the fluid flow control apparatus being adapted for receiving fluid at pressure from a pump driven by an engine, a section downstream of the constrictor being adapted for fluid communication with a clutch device, wherein the flow constrictor reduces pressure of fluid from the pump so that when the engine is at idle fluid downstream of the constrictor is at a pressure below an activation pressure required to engage the clutch device, and wherein the pressure of fluid downstream of the constrictor is able to be raised to the activation pressure by increasing engine speed.

Preferably, the fluid flow control apparatus is provided with a second flow constrictor downstream of the first flow constrictor, and said section downstream of the first constrictor is between the first constrictor and the second constrictor. More preferably, the second flow constrictor is upstream of an exhaust, and the second flow constrictor slows flow of fluid through the fluid flow control apparatus.

Preferably, the fluid flow control apparatus is in the form of a unitary device.

Preferably, the clutch device is operated by fluid via a first flow path when electrical power is available, and via the fluid flow control apparatus when electrical power is not available. More preferably, a valve automatically switches operation to the fluid flow control apparatus in response to a loss of electrical power.

In accordance with another aspect, there is provided a valve system for controlling engagement of a hydraulically actuated clutch device, the valve system including a valve and a fluid supply line, wherein the valve is movable between a normal condition in which engagement of the clutch device is controlled by way of an electrically powered control and a power-loss condition in which engagement of the clutch device is controlled by controlling pressure of fluid from said fluid supply line, wherein the pressure of fluid from said fluid supply line is controlled independently of the electrically powered control, and

wherein the valve is moved from the normal condition to the power-loss condition in response to loss of electrical power.

Preferably, fluid is fed to the fluid supply line by a pump, and pressure of fluid from said fluid supply line is controlled by controlling the pump. More preferably, the pressure of fluid from said fluid supply line is controlled by varying rotational speed of an input of the pump.

Even more preferably, the clutch device is for transmitting drive from an engine to a drive train of a vehicle, the pump is driven by the engine, and the pressure of fluid from said fluid supply line is controlled by increasing/decreasing engine speed.

Preferably, the fluid supply line includes a feed orifice for constricting fluid flow to the clutch device. More preferably, the valve system includes a bleed orifice for constricting fluid flow from the clutch device. Even more preferably, the feed orifice and bleed orifice are selected such that, when the engine is at idle the clutch device is disengaged and, when throttle of the engine is increased the clutch device engages progressively.

Preferably, the valve system includes a solenoid which automatically moves the valve from the normal condition to the power-loss condition in response to loss of electrical power.

Preferably, the clutch device is a friction clutch.

Brief Description of the Drawings

The invention is described, by way of non-limiting example only, with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic sketch of a valve system in accordance with a first example;

Figure 2 is a graph of fluid pressure versus current for the valve system of Figure 1;

Figure 3 is a diagrammatic sketch of an engine coupled to a friction device controlled by the valve system of Figure 1;

Figure 4 is a diagrammatic sketch of a valve system in accordance with an alternative example; and

Figure 5 is a diagrammatic sketch of an engine coupled to a typical existing automatic transmission having a torque converter.

Detailed Description

The valve system 10 shown in Figure 1 is for controlling engagement of a hydraulically actuated clutch device 12, and includes a valve 14 and a fluid flow control apparatus 15 having a fluid supply line 16 incorporating a pair of flow constrictors in the form of a feed orifice 38 and a bleed orifice 40. The valve 14 is movable between a normal condition (as shown) in which engagement of the clutch device 12 is controlled by way of an electrically powered control, and a power-loss condition in which engagement of the clutch device 12 is controlled by controlling pressure of fluid from the fluid supply line 16. The pressure of fluid from the fluid supply line 16 is controlled independently of the electrically powered control. Upon loss of electrical power, the valve 14 is moved from the normal condition to the power-loss condition so as to provide a limp home function.

For example, the clutch device 12 may form part of a transmission for transmitting drive from an engine of a vehicle to a drive train of the vehicle. Electrical power to the transmission may be lost by way of system failure or by default by a computer of the vehicle sensing a fault and switching off power to the transmission. In the case of the valve system 10 shown in Figure 1, loss of electrical power to the transmission will result in a solenoid 18 being denied electrical power. The solenoid 18 controls a line pressure regulator 20 which, in turn, controls pressure of hydraulic fluid in fluid line 22 which feeds the valve system 10.

Figure 2 shows a graph of pressure of fluid in the fluid line 22 downstream of the line pressure regulator 20 on the vertical axis, against current supplied to the solenoid 18 on the horizontal axis. The normal operating range is between the broken lines, as indicated by arrow 24 however, in the event of loss of electrical power, the current supplied to the solenoid 18 will drop below the normal operating range 24 such that pressure of fluid in the fluid line 22 will rise into the power-loss range, as represented in the graph by arrow 26. On loss of electrical power, the solenoid 18 also toggles the valve

14 to the power-loss condition so as to prevent flow from a clutch regulator valve 30 to the clutch device 12, and to enable flow from the fluid supply line 16 to the clutch device 12.

With reference to Figure 1, the valve 14 is shown in the normal condition and movement of the valve 14 to the power-loss condition will involve movement of the valve 14 to the right, as depicted by arrow 32. Movement of the valve 14 may also be controlled by way of a spring 34 which biases the valve 14 toward the normal condition.

When in the normal condition, engagement of the clutch device 12 is controlled by way of the clutch regulator valve 30, which in turn is controlled by way of a solenoid 36.

In the event of electrical power loss to the transmission, electrical power will also be lost to the solenoid 36 which, in the present example, is arranged to default to disabling passage of fluid through the clutch regulator valve 30.

Once the valve 14 is toggled to the power-loss condition, hydraulic fluid from the . clutch regulator valve 30 to the clutch device 12 is bypassed by the fluid supply line 16. Engagement of the clutch device 12 and, in particular control of slip of the clutch device 12, will instead by controlled by controlling pressure of fluid supplied by the fluid supply line 16 to the clutch device 12. More particularly, the amount of clutch pressure will depend on the pressure of fluid in the fluid supply line 16 between the feed orifice 38 and the bleed orifice 40. The feed orifice 38 reduces the fluid pressure to a level which is useable so as to selectively operate the clutch device 12 by varying fluid pressure provided by a pump 42 feeding the system 10.

The bleed orifice 40 is provided downstream of a junction 41 feeding the clutch device 12 such that fluid is exhausted through the bleed orifice 40. The exhaust may be fed to a lubrication circuit as may be required to provide additional cooling in view of heat generated by clutch slippage. As well as having an effect on the pressure at junction 41 used for controlling the clutch device 12, the bleed orifice 40 also serves to slow flow of hydraulic fluid through the exhaust 43 thus reducing the need for a high volume pump to supply the valve system 10 with hydraulic fluid. The flow rates of the orifices 38 and 40 will be tuned along with a capacity of the pump 42 to achieve useable control of clutch engagement and disengagement.

For the purpose of illustration of the function of the feed orifice 38 and bleed orifice 40, Figure 3 shows a diagrammatic sketch of an engine 39 coupled to a friction clutch 12 controlled by pressure of fluid supplied from between a feed orifice 38 and a bleed orifice 40. A feed line 44 is branched from the fluid supply line 16 at a junction 41 between the orifices 38, 40. A valve 45 which defaults to an open condition in the event of electrical power failure is located along the feed line 44, and pressure fed by the feed line 44 to the friction clutch 12 controls engagement/disengagement and slippage of the clutch 12. As described with reference to Figure 1, the pressure of fluid in the feed line 44 may be controlled by varying pressure of fluid fed to the feed orifice 38, for example by adjusting throttle of the engine 39 where the supply pump 42 is driven by the engine 39.

In the inset of Figure 2, there is shown a sketched graph representing the change in fluid pressure as the fluid flows through the feed and bleed orifices 38, 40, for four different supply pressures 46, 48, 50, 52, corresponding to four speed positions of the engine 39. The sketched graph is aligned with the feed orifice 38 and bleed orifice 40 shown below the graph, in order to demonstrate the fluid pressures before the feed orifice 38, between the feed orifice 38 and the bleed orifice 40, and after the bleed orifice 40. The supply pressure 46a, 48a, 50a, 52a (ie. before the feed orifice 38) is indicative of the fluid pressure upstream of the feed orifice 38, and corresponds to the maximum pressure supplied by the line pressure regulator 20.

Because the bleed orifice 40 is open to exhaust, a demand is placed on the pump 42 thus causing supply pressure to drop, hence causing a low fluid pressure between the feed

orifice 38 and the bleed orifice 40 which is insufficient to engage the clutch device 12 at idle (see line 46 in the graph of Figure 2). Once output of the pump 42 is increased, for example by increasing the throttle of the engine 39 driving the pump 42, the pump flow arid pressure increases (see lines 48, 50 and 52 in the graph of Figure 2) and the clutch 12 begins to apply thus causing the engine to drive the transmission, and thus the vehicle. Accordingly, a limp home mode with controllable clutch slip is achieved.

Because of this slip, as mentioned above, it may be advantageous to allow the oil escaping from the orifice 40 to be dumped into a transmission lubricant circuit, thus providing additional lubrication flow to keep the clutch 12 lubricated and cool.

If a driver of the vehicle wishes to disengage the limp home function, he or she simply disengages the manual valve 28 by moving the gear selector device to a different position (for example "Neutral" or "Park"), or may simply reduce the throttle to prevent transmission of drive. The gear selector device may be in the form of, for example, a T- bar, column shift, push-button selector, or the like.

The limp-home function of the valve system 10 will be performed whenever electrical power is lost to the transmission with the gear selector in a "Drive" or "Reverse" range.

An alternative valve system 10 is shown in Figure 4, with like features being indicated with like reference numerals.

The above valve systems have been described by way of example only and modifications are possible within the scope of the invention. For example, in one form the fluid flow control apparatus 15 may be provided in a unitary solenoid type device which is connected to receive electrical power and which, in the absence of receiving electrical power, routes fluid flow through the fluid flow control apparatus 15 so as to activate the limp home function.