It is well known that a single product may be provided with several electronic control systems for controlling its many different functions. For example, in an automotive vehicle, electronic control systems may be provided to control functions such as fuel injection and engine temperature monitoring and control. For critical functions, such as those which are critical to the safety of the vehicle, it is common for additional separate controllers to be provided as back-up systems in the event of failure. However, such back-up systems substantially increase the space required to house all of the control systems within the product, which is particularly disadvantageous in, for, example, automotive applications, where space is at a premium. In addition, the provision of separate back-up controllers substantially increases the cost of manufacture of the product. Due to the increasing use of electronic control systems, there is a requirement to achieve more cost-effective designs.

We have now devised an arrangement which eliminates the problems outlined above, while still maintaining the required level of safety and/or reliability.

In accordance with the present invention, there is provided a control unit comprising a first processing unit for monitoring and controlling the function of a first electronic control system, and a second processing unit for monitoring and controlling the function of a second electronic control system, at least one of the processing units having means for monitoring the operation of the other processing unit, means for detecting a fault in said other processing unit, and means for taking over the monitoring and controlling function of said other processing unit in the event of a fault being detected.

The use of two or more control processors eliminates the need for multiple separate controllers, thereby substantially reducing the overall cost and size of the complete control system. In a preferred embodiment, each processing unit monitors and controls the functions of more than one electronic control system.

Each processing unit preferably has an independent voltage supply, and even more preferably, voltage regulation means, thereby enabling the unit to function on a relatively wide range of voltages, e. g. up to 45 V DC.

The processing units are preferably formed on a printed circuit board (PCB) which may rest on a support or base carrier. In any event, the PCB is beneficially housed within an enclosure with a base, and a lid. Heat sinks for dissipating heat from the unit to the heat sinks and from the heat sinks to the atmosphere may also be provided.

The control unit beneficially includes an independent temperature monitor, preferably formed on the PCB, for monitoring the temperature of the control unit. The unit preferably also includes cooling means, e. g. a fan, which may be activated when the temperature of the unit reaches a predetermined temperature.

Each processing unit is preferably connected to at least one, and most preferably at least two, communication buses for communication with other parts of an overall control system, or other control systems.

One or both of the processing units may be provided with additional memory means, either for enhancing the software algorithm which determines the functions performed by the processing unit, or for recording test results, events and/or faults.

The control unit beneficially comprises one or more external connectors, e. g. power semiconductors.

The invention will now be described in a specific embodiment, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 is a perspective view of an exemplary embodiment of a control unit in accordance with the present invention, with a section of the cover omitted for clarity;

Figure 2 is a perspective view of the control unit of Figure 1 in an unassembled condition; Figure 3 is a perspective view of the base carrier which forms part of the control unit of Figure 1; Figure 4 is a perspective view of a heat sink which forms part of the control unit of Figure 1; Figure 5 is a schematic plan view of the printed circuit board, the base carrier and the heat sinks, forming part of the control unit of Figure 1; and Figure 6 is a schematic block diagram of the interconnection between and the operation of the central processing units included in the printed circuit board of Figure 5.

Referring to Figures 1 and 2 of the drawings, an exemplary control unit according to the invention comprises a base retainer 10, a base carrier 12, a printed circuit board (PCB) 14, two heat sinks 16, 18, and a lid assembly 20.

The PCB 14 rests on the base carrier 12, and the heat sinks 16,18, designed to dissipate heat from the control unit to the heat sinks and from the heat sinks to the atmosphere, are locked onto opposing sides of the base carrier 12, thereby retaining the PCB 14 in position on the base carrier 12, without any further fixing of the PCB 14 being required. The base retainer 10, which provides both

support and protection for the base carrier 12, is attached to the underside of the base carrier 12. The base retainer 10 is a cover plate constructed from an insulating material, having slots 40 formed in its surface to permit airflow. The base retainer may also include means for mounting the complete control unit on a surface. A lid assembly 20, formed of an insulating material and retaining a cooling fan 22, is fixed to the top of the base carrier 12 to cover and protect the PCB 14 and the base carrier 12.

Thus, the PCB 14 and the base carrier 12 are housed within an enclosure formed by the base retainer 10, the two heat sinks 16,18 and the lid assembly 20.

Referring to Figure 3 of the drawings, the base carrier 12 is constructed from an electrically insulating material and comprises a rectangular frame 24 with three flat support strips 26 spanning the opposing side walls of the frame 24, the support strips 26 being flush and formed integrally with the opposing side walls of the frame 24. When the control unit is assembled, the PCB 14 (Figure 2) rests on the support strips 26 of the base carrier 12.

The base carrier 12 is formed with raised sections 28 on opposing ends of the frame 24, each of the raised sections 28 housing a connector plate 30 consisting of several integrated connectors 32 comprising, for example, power semiconductors for retaining all electrical contacts.

Referring to Figure 4 of the drawings, each heat sink 16 comprises an elongated step-shaped body 34 which fits over

the outer edges of the base carrier. A heat dissipation zone 36 comprising an array of spaced fins 38 is formed on the external surface of the heat sink 16.

Referring to Figure 5 of the drawings, the PCB 14 is formed with a first central processing unit (CPU) 42 and a second CPU 44. Each CPU 42,44 has its own power supply and power regulation circuit 46,48, a memory expansion block 50,52, and two communications interfaces 54,56.

The PCB 14 also carries an independent temperature monitor 60 which monitors the temperature within the control unit.

When the temperature reaches a predetermined level, the monitor activates a cooling fan 22 (Figure 1) to ventilate the unit, thus reducing the internal ambient temperature.

In summary, the PCB 14 shown in Figure 5 has the following characteristics: -52 mixed analogue/digital inputs -4 communications interfaces -22 high current output -16 low current output -1 M Byte Flash memory -32K RAM memory -Smart power regulation enabling it to function on voltage ranges up to 45 V DC -Self monitoring temperature function for unit cooling an ventilating -Full onboard diagnostic function for each output

-Diagnostic monitoring between processing units -Signal switching and re-routing in the event of a fault in one of the CPU's -System monitoring and fault recording Referring to Figure 6 of the drawings, the manner of operation of an exemplary embodiment of a control unit according to the invention will now be described.

The control circuit is designed as two separate circuits, one including a CPU 42 programmed to monitor and control, for example, safety critical functions 66, such as engine temperature control in an automotive vehicle, and the other including a CPU 44 programmed to monitor and control, for example, non-safety critical functions 68. Each CPU 42,44 has an independent power supply 46,48, power regulation circuit 62,64, flash memory block 50,52 for memory expansion, and two communications buses for communication with other controllers or other parts of a control system.

The inputs and outputs of each CPU are connected together, as depicted by connections L1, L2, L3 and L4. Each CPU monitors the operation of the other by way of a dedicated fixed line and a communications bus, as depicted by L5 and L6. If one of the CPU's 42 detects a problem with the other CPU 44, the first CPU 42 takes control of the second CPU's 44 inputs and outputs (as depicted by the closing of switch S1), thereby effectively taking over its function, and switches off the defective second CPU's power regulation circuit 64 (depicted by the closing of switch

S2), thereby isolating the second CPU 44. By use of software algorithms, the control circuits can be configured to run any combination of signalling, including both digital and analogue inputs/outputs.

As stated above, each CPU 42, 44 is connected to a flash memory block 50,52 which can either be used to enhance the control algorithm which determines the functions performed by the CPU, or as a storage area for recording test results, faults, etc.

Specific advantages of the invention are as follows: (i) The control unit is completely programmable and re-programmable, making it exceptionally versatile, and eliminating the need to develop a new hardware design for each new control application.

(ii) The modular control unit and the fact that it is designed to work on a range of supply voltages permits standardisation of control systems generally.

(iii) Several control units can be linked together to form a multiple control system.

(iv) The control unit can re-route signals in the event of a fault being detected, thereby increasing safety and reliability of the overall control system.

(v) The control unit eliminates the need for duplicate or back-up control system, thereby reducing size and cost of the overall system.

The cost is further reduced because development and manufacturing time is also potentially reduced.

(vi) The control unit can record information as required for access at a later date, for maintenance or research purposes, for example.

(vii) The communications bus (es) allow remote access for system control, monitoring and the downloading of recorded information.

(viii) The control unit can accommodate a range of semiconductors to control various external functions.

It will be appreciated that, while the control unit of the present invention has been described particularly in relation to automotive applications, to which it is well suited, the present invention is suitable for controlling functions within many transportation, process and general control environments. It is in fact an object of the invention to provide an intelligent control unit which can be used for a range of different applications, simply by varying the software algorithms within the central processing units which determine the manner and method of control required.