Trailer Electronic Braking System

The invention relates to a trailer electronic braking system for motor vehicles having a plurality of trailers.

In Australia and North America, vehicles consisting of a tractor unit and two or more trailers are commonly utilised and these are collectively termed "road trains". Road trains are not currently permitted in Western Europe due to weight limits on the size of vehicles but due to the environmental and cost advantages of road trains, it is likely that this will change.

In all these territories there are a large number of small engineering companies building trailers for various tractors employing compressed air operable brakes. Such trailer builders tend to specialize in specific vehicle types but to meet statutory requirements, it is a common feature that trailers are provided with means which control the braking force signaled from a towing tractor. These trailer braking systems are now invariably electronic braking systems having electronic control by an ECU. It is now routine that the electronic braking systems can incorporate features such as stability control. Stability control has proved to be a major safety enhancement.

Tractors are commonly provided with electronic stability control such as ESP®, which can generate an additional brake demand on the trailer but cannot provide full stability control on the trailer, only on the tractor. Trailers are therefore provided with roll stability control (RSP). Trailer Roll stability control monitors the lateral acceleration on the trailer as a build up of lateral acceleration leads to a roll over of the trailer as well as providing selective brake application and monitoring wheel speeds to detect any wheel lift which generates abnormal rotational speeds. The commonest roll over situations include where a driver steers rapidly in one direction and then back in the opposite direction, for example to avoid an obstruction on the motorway. In this situation, the ECU is able to make a predictive intervention to stabilize the vehicle by controlling the brake force at either an axle or individual wheel level. The other common roll over situation is where there is a slow build up of lateral acceleration on the trailer on, for example, a motorway exit, where a small

selective brake application to the inside (with respect to the curve) wheels may result in a large change in velocity. In this case, the ECU can apply a large brake effort to stabilise the vehicle.

Known RSP systems suffer from the problem that they cannot simply be extended to road trains as due to the increased size of the vehicle, it may take too long for the lateral acceleration signal to be measured, processed and the brake demand adjusted before the roll over event occurs. This will be particularly the case if the centre of gravity of the vehicle is towards the rear of the train.

The present invention therefore seeks to provide a trailer electronic braking system adapted to provide roll stability control for road trains.

According to the invention there is provided a trailer electronic braking system for motor vehicles having a plurality of trailers, the braking system comprising a braking device capable of generating brake force on an axle on each trailer, the brake force into the brake being controllable by a braking ECU on each trailer, communication means being provided so that the braking ECU on a first trailer and the braking ECU on a second trailer are able to communicate with one another, the respective braking ECU on the first and second trailer receiving an input from a respective sensor on the first and second trailer adapted to detect lateral acceleration and/or wheel speed, wherein, in the event that one of said sensors detects lateral acceleration and/or a wheel speed indicative of a loss of stability, the sensor generates a signal for actuating stability control, which signal is passed via the communication means to the braking ECU on the other trailer, so that the other trailer can actuate stability control.

Preferably, the communication means is a CAN bus or powerline carrier. Preferably, the sensor is a lateral acceleration sensor and/or two or more wheel speed sensors. Preferably, the sensor generates a signal only when the lateral acceleration detected exceeds a predetermined threshold. Preferably, if the sensor on the second trailer detects no lateral acceleration, the brake pressure is not increased. Alternatively, if the sensor of the second trailer detects no lateral acceleration the brake force is increased to a level intermediate to the force on the first trailer. Preferably the braking ECU monitors the wheel speed on its trailer, wherein stability control is

initiated as a function of whether the vehicle is braked or unbraked through a braking intervention by monitoring the rotational wheel speed behaviour. Preferably in a case of a braked vehicle, the brake force is lowered at the brake cylinder of the wheel on the inside of a turn and a stability control event initiated if the rotational speed of the wheel increases by less than a predetermined amount.

The invention advantageously improves vehicle stability control in a road train as the risk of braking the trailer individually can lead to instability in the other trailers on the road train thereby increasing the risk of roll over. The invention also advantageously decreases the time between lateral acceleration on the train being detected and stability control being initiated.

Exemplary embodiments of the invention will now be described in greater detail with reference to the drawings in which:

Fig. 1 shows a trailer electronic braking system;

Fig. 2 shows a schematic of a road train complying with ISO 11992;

Fig. 3 shows a schematic of a road train complying with J2497 SAE.

Figure 1 shows a trailer electronic braking system in which the utility vehicle trailer has a steerable front axle with front wheels 1, 2 and a rear axle with rear wheels 3, 4. Rotational wheel speed sensors 5-8 are in each case assigned to the front wheels 1, 2 and the rear wheels 3, 4, and are connected by way of electric lines 9-12 with an electropneumatic brake force control module 13 (EBS module) which is primarily assigned to the rear axle brakes. One brake 14-17 is in each case assigned to the front wheels 1, 2 and the rear wheels 3, 4, which brake 14-17 can be applied by means of brake cylinders 18, 19 of the front axle or spring-loaded brake cylinders 20, 21 of the rear axle.

The braking system of the trailer vehicle can be connected by way of three connections, specifically a pneumatic supply line connection 22, a pneumatic control line connection 23 and an electric control connection 24, with the braking system of a tractor or a further trailer.

The supply line connection 22 is connected by way of a return valve 25 and a parking valve 26 with an air brake reservoir 27. From the air brake reservoir 27, a pneumatic line 28, 31 leads to a supply input of the pressure control module 13 and ABS valve 32. In addition, a pneumatic line 29 branches off the parking valve 26 to the pressure control module 13. A pneumatic line 30 extending between the parking valve 26 and the air brake reservoir 27.

The ABS valve 32 is assigned jointly to both brake cylinders 18, 19 of the front axle and is connected with the brake cylinder 18 by way of a pneumatic line 33 and with the brake cylinder 19 by way of a pneumatic line 34. The ABS valve 32 has two electric control inputs which are connected by way of "one" electric line 35 shown here only schematically with the pressure control module 13.

Furthermore, the ABS valve 32 has a pneumatic control input 36 which is connected by way of a return valve 37 with the pneumatic control connection 23. The pneumatic control input 36 is also connected by way of a pneumatic control line 38 with a pneumatic control input of the pressure control module 13. The pressure control module 13 has an integrated pressure sensor (not shown) which measures the pressure in the pneumatic control line 38, that is, the control pressure present at the pneumatic control input 36 of the ABS valve, which control pressure is identical to the maximal pressure which can be controlled into the brake cylinders 18, 19.

The pressure control module 13 has pneumatic outputs 39 42 which are connected by way of assigned pneumatic lines with the spring brake cylinders 20 or 21.

Furthermore, pneumatic axle load sensors or air bellows 43 44 are provided at the rear axle and permit a determination of the axle load, particularly of the dynamic axle load during braking and starting. The axle load sensors 43 44 are connected by way of electric lines with the pressure control module 13 which is shown here only as an example by means of the electric line 55. Correspondingly, axle load sensors 45, 46 may be provided at the front axle. However, these axle load sensors 45,46 are not absolutely necessary.

To provide stability control a lateral acceleration sensor 50 is provided, which may also be integrated with a yaw sensor, and the output of the lateral acceleration sensor is fed to the pressure control module/ECU 13. Typically the lateral acceleration sensor 50 is integrated into the pressure control module/ECU 13. In the event that lateral acceleration on the trailer is detected, the pressure control module can provide for increased brake force at the front and/or rear axles. When the lateral acceleration sensor 50 detects lateral acceleration on the trailer in which it is installed, the sensor generates a signal setting the stability control to active.

With respect to the embodiment described to Figure 1, the ABS valve 32 may be replaced with an electro-pneumatic valve where the electric control line 35 consists of a communication means preferably CAN and an electric power source.

Figures 2 and 3 show schematically how the signals can be processed in a road train based on the International standard governing communications between tractors and trailers, ISOl 1992 and the US standard for governing communications between tractors and trailers J2497SAE.

Figure 2 shows schematically a tractor unit 100 connected to a first trailer 101, which in turn is connected to a second trailer 102. The tractor 100 is provided with a braking ECU 103 and the trailers 101 and 102 are provided with a braking ECU 13a and 13b, respectively, described in greater detail above. Pursuant to ISO 7638, a separate power line is provided along the length of the road train to provide power to the braking ECUs. Communication between the ECUs is via a CAN bus 105. In the event that the lateral acceleration sensor on the first trailer 101 detects lateral acceleration, a vehicle dynamic control signal setting the vehicle dynamic control (VDC) parameter to active is sent both ways on the CAN bus 105. If the lateral acceleration sensor on the second trailer 102 detects lateral accleration, the signal setting the VDC parameter to active is sent via the CAN bus 105 to the first trailer 101 and then to the tractor 100. The signal does not have to provide further information such as purpose. If the braking ECU 13a,b or 103 detects a VDC active parameter, stability control can be activated. The tractor 100 can therefore perform functions such as disabling cruise control and stopping the gearbox from downshifting when the brakes are applied.

Figure 3 shows schematically a road train using a powerline carrier in accordance with the SAE standard J2497 comprising a tractor 200, first trailer 201 and second trailer 202. The tractor 200 and first and second trailers are provided with respective braking ECU 203 and 13a,b but in this case the communication between the braking ECUs is via the powerline 204 rather than via a separate CAN bus. In this case the lateral acceleration sensors are adapted to provide a stability control actuation signal which is passed down the powerline to the adjacent trailer and to the tractor.

In both the embodiments described with respect to Figures 2 and 3, in the event that the lateral acceleration sensor 50 on only one of the trailers in the road train detects lateral acceleration or an RSP event, then by setting the stability control actuation signal to active, roll stability control can be actuated on both trailers. The stability control on one trailer is therefore actuatable based on information from the communication interface rather than from the sensors on that trailer.

In the event that lateral acceleration is detected in only one of the trailers independently of the order of the trailers in the road train, the effectiveness of the roll stability control intervention can be enhanced by modifying the thresholds on the roll stability control program of the unaffected trailer based on data from the affected trailer. In addition to the lateral acceleration, this data would include the wheel speeds and angles and yaw angle (if a yaw sensor is present). If the unaffected trailer detects no lateral acceleration and the wheel speed and angles are within acceptable predetermined limits, then the brake pressure in the unaffected trailer could be maintained, i.e. no additional braking effort applied or alternatively a reduced braking effort. The stability of the whole road train can therefore be improved with respect to the use of roll stability on a single trailer.

In the above description of a specific embodiment of the invention, it has been assumed that there is a separate lateral acceleration sensor installed on each of the trailers. However it is also possible to detect instability when two or more wheel speed sensors are installed on the same trailer. Although the system has been specifically described as relating to an electropneumatic brake system, it is equally applicable in a fully electric brake system.