Patent Application
20070102996
The subject invention relates to a hydraulic brake system for a trailer towed by a passenger car or light to medium duty truck where the hydraulic brake system is electronically controlled.
Light to medium duty vehicles, such as passenger cars, pick-up trucks, sport utility vehicles, etc., are often configured to pull trailers. These trailers are typically utility or work trailers but can include horse trailers and recreational trailers, such as campers, for example. These types of trailers typically include medium duty trailer brakes that are controlled by one of two different methods.
One method uses electronic control for actuating magnetic brakes at each trailer wheel. An electrical control signal is used to generate a magnetic brake actuation force. Another method uses hydraulic surge brake control to actuate hydraulic brakes. This is often referred to as a hydraulic over hydraulic system. During a braking event, a trailer tongue connection between the trailer and vehicle has a tendency to dive downwardly. Surge control recognizes this occurrence and utilizes hydraulic control to actuate the hydraulic brakes.
Each of these controls provides an effective method for stopping the trailer. However, neither method offers control for emergency stopping situations. In an emergency stopping situation a trailer has increased potential for jack-knifing or roll-over events. Further, neither method offers anti-lock control to prevent wheel lock-up under poor road conditions.
Thus, there is a need for a trailer brake system for light to medium duty vehicles that provides improved control for all stopping situations.
The subject invention provides a full power hydraulic brake system for a trailer that is controlled by an electronic control unit (ECU). The trailer brake system includes a power unit that maintains a desired level of fluid pressure in the brake system, and a brake control unit that applies trailer wheel brakes in response to a braking request. The trailer brake system optionally includes an anti-lock brake system (ABS) control unit to prevent wheel lock-up.
The power unit includes an electric motor that is controlled by the ECU. The electric motor drives a pump to maintain a desired pressure level in an accumulator. The pump supplies hydraulic fluid to the accumulator from a trailer supply reservoir. The pressure in the accumulator is monitored and controlled by the ECU by using a pressure transducer. A pressure limiting valve prevents over-pressure conditions.
The brake control unit includes a pressure transducer, an inlet valve that is normally closed, and an outlet valve that is normally open during non-braking. The ECU controls brake pressure in a closed loop circuit with the pressure transducer and the inlet and outlet valves. In response to a braking request, the outlet valve is closed and the inlet valve is pulsed open until an appropriate pressure is provided to a trailer wheel brake component.
The ABS control unit includes wheel speed sensors for a least a right side wheel and a left side wheel. The wheel speed sensors communicate speed data to the ECU. The ABS control unit includes inlet and outlet valves for each of the right and left side wheels. The inlet valves are normally open and the outlet valves are normally closed. The ECU generates a control signal based on the speed data to close the inlet valves and open the outlet valves as needed to prevent wheel lock-up.
The trailer brake system optionally includes a parking brake that is preferably a spring applied hydraulic release (SAHR) brake. A park brake valve assembly is fluidly connected to the accumulator. The park brake valve assembly applies pressure to the SALR brake to release the parking brake and releases pressure from the SAHR brake to apply the parking brake.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
A trailer brake system 20 generates an electric control signal ES that is used to hydraulically actuate the wheel brake member 18 in response to a braking request. Thus, the trailer brake system 20 provides an electric over hydraulic system for the trailer 12.
The trailer brake system 20 is shown in greater detail in
Pressure within the accumulator 30 is monitored and controlled by the ECU 34 by utilizing the pressure transducer 32. When pressure in the accumulator 30 falls below a predetermined minimum pressure or cut-in level, the ECU 34 generates a control signal S1 to actuate the electric motor 26 to drive the pump 28, which pumps fluid from the trailer supply reservoir 36 to the accumulator 30. A pressure limiting valve 38 prevents over-pressure situations, which could result in system damage.
The brake control unit 24 includes a pressure transducer 40, an inlet valve 42, and an outlet valve 44. The inlet valve 42 is normally closed and the outlet valve 44 is normally open during non-braking conditions. During a braking event, an electric voltage or current signal proportional to a requested brake pressure is used as an input to the ECU 34. The ECU 34 then controls brake pressure in a closed loop circuit with the pressure transducer 40 and the inlet 42 and outlet 44 valves. The ECU generates a control signal S2 such that the outlet valve 44 gets closed and the inlet valve 42 gets pulsed open until an appropriate pressure occurs in a brake circuit 46 at the wheel 16. To release the pressure, the inlet valve 42 is closed and the outlet valve 44 is opened.
In the example shown, the inlet valve 42 supplies fluid pressure to the brake circuit 46 for a left wheel 16a and for a right wheel 16b positioned laterally opposite the left wheel 16a. The trailer 12 could also include additional axles and wheels that may or may not have brake circuits 46.
The trailer brake system 20 could optionally include an anti-lock brake system (ABS) control unit 50. The ABS control unit 50 includes an inlet valve 52, an outlet valve 54, and a wheel speed sensor 56 that is associated with each wheel 16. Any type of wheel speed sensor 56 could be used such as tone wheel configuration, for example. The wheel speed sensors 56 generate signals 58 that transmit wheel speed data to the ECU 34.
The inlet valve 52 is normally open and the outlet valve 54 is normally closed. During an ABS event, such as slippery or other types of poor road conditions, the wheel 16 has a tendency to lock-up. The ECU 34 generates a control signal S3 to open and close the inlet 52 and outlet 54 valves as needed to prevent wheel lock-up.
If the trailer 12 includes more than two wheels, each additional wheel may or may not be provided with an ABS feature. Preferably, at least one wheel per side (right and left sides) of the trailer 12 is provided with the ABS feature.
The trailer brake system 20 could also optionally include a parking brake 60. The parking brake 60 is preferably a spring applied hydraulic release (SAHR) brake that has a chamber 62 and spring member 64. A parking valve assembly 66 is fluidly connected to the chamber 62 and to the accumulator 30. The parking valve assembly 66 is a 3/2 way valve, which has an outlet port 68 in fluid communication with the chamber 62, a supply port 70 in fluid communication with the accumulator 30, and a release port 72 in fluid communication with the trailer supply reservoir 36.
The parking valve assembly 66 releases pressure from the chamber 62 via the release port 72 during a park brake request, such that the spring member 64 applies the parking brake 60. To release the parking brake 60, pressure is supplied through the supply port 70 to the outlet port 68, to the chamber 62.
The parking brake 60 could be located at each wheel 16 on the trailer 12, or could only be located at one wheel 16 depending on application requirements. Further, a short time parking brake function could be supplied without have to incorporate a parking brake 60 into the trailer brake system 20. To apply a short time park brake request, the brake circuit 46 at each wheel 16 gets applied with a specified amount of pressure like in a normal brake situation.
As shown in
The ECU 34 is electrically connected to the power unit 22, the brake control unit 24, and the ABS control unit 50. The ECU is connected at 88 to a vehicle battery (not shown) or other power source.
Optionally, the trailer brake system 20 could include a roll stability system (RSS) control and/or an electronic stability control (ESC) 90. For RSS, the trailer brake system 20 would use available data from the system described above to identify potential roll-over events. The ECU 34 would control braking as need to prevent roll-over.
For ESC, in addition to using the available data, an accelerometer 92 and a yaw rate sensor 94 are required. The trailer brake system 20 uses information from these sensors 92, 94 to identify potential unstable driving conditions, and the ECU 34 would then generate control signals to control braking as needed to improve stability.
Various system inputs and outputs are also communicated between the ECU 34 and the power unit 22, brake control unit 24, and the ABS control unit 50. The ECU 34 communicates a brake control output 120 to the inlet 42 and outlet 44 valves of the brake control unit 24. The brake control unit 24 communicates a brake pressure signal 122 from the pressure transducer 40 to the ECU 34. The ECU 34 communicates a brake control output 124 to the inlet 52 and outlet 54 valves of the ABS control unit 50.
The ECU 34 communicates a pump motor power request 130 to the electric motor 26 of the power unit 22. The power unit 22 communicates an accumulator pressure output 132 to the ECU 34 via the pressure transducer 32. The power unit 22 also communicates fluid level output 134 to the ECU 34.
The subject invention provides a hydraulic full power brake system for a trailer towed by a light to medium duty vehicle, which provides several advantages over prior systems. The hydraulic full power brake system is a compact unit that is self-contained and easily installed on a trailer. High braking forces are provided when needed. Further, precise and controlled pressure applications are also provided during emergency stopping conditions. This reduces premature wear and tear on brake components and prevents high mechanical stresses for towing bar and other associated hitch components. Also, by having precise control over braking, the occurrence of undesirable conditions, such as jack-knifing and roll over for example, are significantly reduced.
It should be understood that the subject system could be controlled in various different manners. A driver could manually actuate a hand brake, lever, or switch to generate a braking request. Preferably, a pressure transducer (not shown) is used to determine rear axle brake pressure at the towing vehicle. In this situation, the pressure transducer is connected within a brake line to a master cylinder on the vehicle. Optionally, a connection between the trailer and the vehicle can be monitored to determine when a braking request should be generated.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
