A Power on Demand Braking System

Technical Field

This invention concerns a power on demand (POD) braking system for a vehicle. The system has particular, but not exclusive, application in a braking system mounted on a towed vehicle and activated by electrical input from a towing vehicle.

Background Art

There are a number of braking systems available for towed vehicles. A simple system involves a mechanical override device (or surge brake) which is mounted on the tow coupling and comiected into the towed vehicle's hydraulic braking system. The surge brake telescopes when the towing vehicle decelerates in order to pressurize the hydraulic brakes in the towed vehicle.

Electric braking systems are also popular on trailers. An electrical connection is provided between the towing and towed vehicles to activate electric brakes on the towed vehicle when the brakes are applied on the towing vehicle.

Power on demand (POD) braking systems, use electrical signals from the towing vehicle to control hydraulic fluid pumps to activate and deactivate the brakes on the towed vehicle.

Summary of the Invention

According to the first aspect of the invention, there is provided a power on demand braking system, the system comprising: an electric motor to run a pump to pressurise hydraulic brake fluid and supply that pressure via a control manifold and a brake circuit to the vehicle's brake cylinders, wherein the pump comprises a piston which is driven to reciprocate in opposed cylinders, and valves on the cylinders' inlets and outlets are arranged to maintain brake fluid in the cylinders at positive pressure even when the pump is not running.

In a preferred embodiment, the electric motor may be a brushless DC motor. An advantage of incorporating a brushless DC motor is that is allows high starting torque which provides very fast pressure rise in the system. However, it should be appreciated that other types of electric motors may be used in this, or any embodiment.

In the preferred embodiment, the motor may provide output drive via an eccentric actuator. Optionally, the motor may provide output drive from an eccentrically rotating pin. The pump may comprise a cylinder block having opposed cylinders (cylinder heads) disposed at either ends thereof. The cylinder block and

heads are preferably injection moulded from a high grade plastic. Usable plastics include, but are not limited to, polyphenylene sulfide (PPS), marketed as Fortran, polyetheretherketone (Peek), polyetherimide (PEI), a glass-filled nylon, or combinations thereof. Plastic resins may include special additives, such as glass and carbon to enhance performance, reduce wear and lower thermal expansion.

In the preferred embodiment, the piston may comprise a pair of piston rods, respective first ends of which extend through opposing sides of a piston carrier yoke and engage a piston yoke slider for reciprocation of the piston in the cylinder heads. The piston yoke slider may engage the eccentric actuator which engages the motor's shaft, so that the eccentrically rotating motion of the actuator is efficiently converted into reciprocation of the piston. The motor's shaft may extend through the eccentric actuator. A projecting end of the motor's shaft may be retained by a retaining member or a fastening means, such as a screw, or the like. Fixed within each cylinder head may be a seal for guiding the piston rods. Preferably the seals are inert to the effects of the hydraulic brake fluid. Respective second ends of the piston rods may slidably engage the respective seal. The piston rods may be manufactured from cut lengths of centreless ground steel. A pump housing may house components of the pump. One or more of the pump housing, piston carrier yoke and slider may be manufactured from the same, or similar, high grade plastic as referred to above. In the preferred embodiment the system further comprises fluid reservoir in fluid communication with the inlet and outlet ports of each cylinder head.

In the preferred embodiment the pump may have fixed orifice in communication with the respective cylinder's outlets to receive pressurised hydraulic fluid for supply to the vehicle's brake cylinders. The control manifold may be arranged with respect to the pump's fixed orifice and the fluid reservoir. The control manifold may comprise a solenoid valve which is biased to cover a bleed port to prevent unrestricted return of brake fluid to the fluid reservoir at start up. Preferably the solenoid valve closes automatically when the system is not powered.

Preferably the system includes an electronic control unit comprising a control circuit to receive electrical input from a towing vehicle and process the electrical input to operate brakes on the towed vehicle. The control circuit may in the form of include a microprocessor. The microprocessor may be operable to process the electrical input to control/vary the speed of the motor. The microprocessor is preferably operable to process the electrical input to activate the solenoid valve and vary the speed of the motor to enable proportional braking pressure.

The control circuit preferably includes an accelerometer. The accelerometer may be, but not limited to, a single axis accelerometer, a two axis accelerometer or a three axis accelerometer. The microprocessor preferably processes the signal from the accelerometer together with operational parameters stored in memory to calculate a control signal to control the speed and torque of the electric motor. The effect of this is that the pressurised fluid output from the pump, and therefore the force, is applied to the towing vehicles brake callipers.

Operational parameters may comprise stored parameters. Stored parameters may comprise one or more of sensitivity (gain), boost, boost time, negative boost, override (brake assist) and road conditions.

The microprocessor preferably further receives input from a temperature sensor to enable temperature compensation of the accelerometer. The microprocessor may further receive input from a pressure transducer to monitor trailer brake pressure.

The microprocessor may receive electrical input from the vehicle's brake signal, a reversing lamp, driving headlamps, and an indicator lamp. The control circuit may be operable to output signals to control one or more visual indicators to indicate braking of the trailer, parking of trailer and direction of turn of the trailer (right and left indicators).

The system may further comprise a remote control unit to monitor the electronic control unit and/or remotely control the electronic control unit. Preferably the remote control unit comprises a control circuit having a microprocessor and a transceiver to facilitate remote communication between the remote control unit and the electronic control unit. The remote control unit is operable to communicate with the electronic control unit to vary one or more stored parameters. The remote control unit is further operable to enable the brakes' of the trailer to be locked down when the trailer is parked.

Advantageously the remote control unit may enable a driver of the vehicle to control and adjust the system in response to variations in, for example, road conditions.

In an optional embodiment, the electric motor may provide output drive from an eccentrically rotating pin. The pump may comprise a cylinder block and cylinder heads formed from solid blocks of aluminium or an aluminium alloy. A high grade plastic, as described in the previous embodiment may optionally be used. In such an embodiment, the piston may be a double-ended piston. A cut-out in the double ended piston may engage the eccentrically rotating pin of the motor, so that the eccentrically rotating motion of the pin is efficiently converted into reciprocating of the piston. The pump may be designed to be able to pump air, and so is able to purge itself of air.

The control manifold may be formed from a solid block of aluminium with various drillings to provide for the necessary fluid flows through it. A valve body within the control manifold covers a return port to prevent unrestricted return of brake fluid to a reservoir at start-up. As braking is applied, pressure on the pump side of a first check valve within the manifold increases rapidly so that a first check valve opens and supplies the pressure to the brake circuit and brakes. The first check valve closes when braking pressure is equalised in the brake circuit and manifold. Slight variations in pressure may be transmitted between the manifold and brake circuit at all times via an orifice arranged in parallel with the first check valve. When braking is reduced, or released, the higher pressure in the brake circuit than on the pump side drives the valve body to open the return port and relieve pressure from the brake circuit into the reservoir.

The use of such a control manifold is also able to provide a smooth braking operation and feathering of the brakes, even in reverse. The system can be applied to multiple axle trailers.

A breakaway controller may optionally be provided in the brake circuit. This may operate automatically in the event of the towed vehicle braking away from the towing vehicle to apply the brakes.

In this optional embodiment, the system may further comprise an electronic control unit and a remote control unit as described in relation to the preferred embodiment.

In either embodiment it is preferred that the system is a trailer mounted self contained system.

In at least one embodiment of the invention, when such a system is mounted in a towed vehicle it is able to provide an instant braking response to signals from the towing vehicle. Further, the system in accordance with the preferred embodiment is simple to install, compact, low maintenance, submersible and able to work in extreme environmental conditions.

In a further aspect the invention an electronic control unit for controlling operation of a power on demand braking system as described in relation to the first aspect of the invention, or any of its' embodiments.

Brief Description of the Drawings

Examples of the invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 is a pictorial view of a braking system for a towed vehicle in accordance with a first embodiment of the invention.

Fig. 2 is an exploded view of the braking system of Fig. 1.

Fig. 3 is an exploded view of an electric motor output assembly. Fig. 4 is an exploded view of a pump assembly.

Fig. 5 is an exploded view of a control manifold assembly.

Fig. 6 is a pictorial and x-ray view of a break away controller.

Fig. 7 is an exploded view of a braking system for a towed vehicle in accordance with a second embodiment of the invention. Fig. 8 is a sectional side view illustrating a reservoir and pump assembly of the braking system of Fig. 7.

Fig. 9 is a sectional side view illustrating a control manifold and control assembly of the braking system of Fig. 7.

Fig. 10 is a sectional plan view illustrating a control assembly of the braking system of Fig. 7.

Figs. 11 to 16 illustrate a third embodiment of the invention.

Fig. 11 is a schematic illustration of a braking system for a towed vehicle in accordance with a third embodiment of the invention.

Fig. 12 is a side elevation of a pump and piston assembly of the third embodiment.

Fig. 13 is a cross sectional view through A-A of Fig. 12.

Fig. 14 is a cross sectional view through B-B of Fig. 12.

Fig. 15 is a pictorial view of a piston yoke carrier and piston of the third embodiment. Fig. 16 is a pictorial view of a control manifold in the form of a solenoid valve of the third embodiment.

Fig. 17 is a cross sectional view through A-A of Fig. 16.

Fig. 18 is a graph illustrating the improved start-up characteristics relative to current state of the art pumps generally. Figs. 19 to 21 illustrate circuit diagrams of various components of the electronic control unit of at least the third embodiment of the system.

Best Modes of the Invention

Referring first to Figs. 1 and 2, power on demand braking system 10 is mounted on the trailer of a towed vehicle (not shown). It comprises an electric motor 20, a pump

30, an hydraulic fluid reservoir 40, a control manifold 50, a breakaway control

assembly located generally at 60 and an electronic control unit 70. Electrical input 80 from the towing vehicle is received to the electronic control unit 70 and processed to operate braking system 10, and control pressure variations in hydraulic fluid within brake circuit 90 to operate brakes on the towed vehicle. The electronic control unit 70 includes associated control circuitry.

Each of the parts of the assembly will now be described in turn: Referring to Fig. 3, the motor assembly 20 is seen to comprise: an electric motor 200, a mounting plate 202, a bell housing 204, a deep groove ball bearing 206 mounting in the bell housing, a crank 208 mounted on the output spindle 210 of electric motor 200 and riding in bearing 206, and an eccentrically mounted needle roller 212 extending out of bell housing 204. In use when motor 200 is activated by electrical control from the electrical control unit 70 the output spindle 210 rotates causing the crank 208 to rotate and the needle roller 212 to rotate eccentrically. The overall effect is to provide mechanical output in the form of an eccentrically rotating pin. Referring next to Fig. 4, pump assembly 30 comprises a cylinder block 300 on either side of which are mounted cylinder heads 302 and 304. Both the cylinder block and the cylinder heads are formed from solid blocks of aluminium. A horizontally arranged double headed piston 306 is mounted in the cylinder block 300 for horizontal reciprocation back and forth in the two cylinder heads 302 and 304. Two Teflon sleeves 308 and 310, which are inert to the effects of the hydraulic brake fluid, provide guides for the pistons as well as high pressure piston seals, stopping brake fluid from bypassing down the side of the piston. Each of the cylinder heads has a brake fluid input port, indicated at 312 and 314, and an output port, indicated at 316 and 318. The inlets 312 and 314 are directly connected to the hydraulic fluid reservoir 40. Check valves are provided at both inlet ports and both outlet ports, and the check valves at the outlet ports are designed to open at slightly higher pressures than the check valves at the inlet ports in order to maintain hydraulic braking fluid, at positive pressure, within the cylinder heads even when the pump is not running.

The double headed piston 306 includes a cut-out 320 that engages with a cross head 322 and needle roller bearing 324. The eccentrically mounted pin output 212 of the motor assembly engages in the roller bearing 324 so that eccentrically rotating motion of pin 212 is converted into horizontal reciprocation of the piston 306.

When the piston 320 has travelled to the left and entered cylinder head 304 it pumps any fluid within that cylinder out through outlet 318. At the same time it draws fluid into the right hand cylinder head 302 through inlet 312. As the piston reciprocates to the right it pumps the fluid out of the right hand cylinder head 302 via outlet port 316

while drawing fluid into the left hand cylinder head 304 through inlet 314. It can be seen that the piston 306 is driven in both directions. As a result the pump remains in a fully primed condition even when not in use, and is able to provide an instant start up response; that is the pump is essentially self-priming. The pump is designed to be able to pump air, and so is able to purge itself of air for instance when it is first commissioned, or recommissioned having been out of service.

Referring next to Fig. 5, the control manifold 50 is again formed from a solid block of aluminium with various drillings to provide for the necessary fluid flows through it.

On the rear face the control manifold block has two inlet ports (not shown) sealed in registration with the outlet ports 316 and 318 from the pump 30 to receive fluid into a first chamber within the manifold (not shown). On the front face a single outlet port 502 provides hydraulic brake fluid under pressure to the brake circuit 90, and receives braking fluid back from the brake circuit when the brakes are released.

On the upper face the control manifold 50 has a number of ports which communicate directly with the hydraulic brake fluid reservoir 40 which is mounted directly above the control manifold and pump 30. Port 510 contains a pressure relief valve comprising a ball bearing 512, a spring 514 and hollow grub screw 516 to allow excess pressure to be released into the reservoir. Port 520 houses a pulsation accumulation piston 522 and spring 524 retained by retainer 526, which operate to reduce high frequency pressure fluctuations arising from the use of the pump 30. Port 530 is the return port to allow hydraulic fluid received from pump 30 to flow back to the reservoir. Orifice 532 in return port 530 maintains brake circuit pressure within the manifold. Port 535 is a dump port to allow hydraulic fluid returning from the back into the reservoir.

A dump valve 540 within the control manifold assembly ensures correct operation by moving under the influence of pressure across the manifold. At start up the pressure on the pump 30 side of dump valve 540 is greater than in the brake circuit 90 and valve 540 moves to cover the return passage port 535. At the same time pressure on the pump side of check valve 504 within the manifold increases as fluid is pumped into the manifold inlets and flows out to the reservoir via orifice 532 and return port 530. The pressure continues to increase, opening valve 504 and supplies the pressure to the brake circuit 90 via port 502. Ultimately pressure equalises, and check valve 504 then closes. Orifice 506 is arranged in parallel with valve 504 to transmit slight or slow pressure variations between the manifold and brake system when valve

504 is not open. Orifice 506 is very small and so prevents any remaining pulsations from entering the brake system.

When the brakes are applied the pressure on the pump side of check valve 504 within the manifold increases quickly as fluid is pumped into the manifold inlets. Since

5 orifice 506 is unable to transmit the pressure increase quickly, the pressure increases until valve 504 opens and supplies the pressure to the brake circuit 90 via port 502.

Ultimately pressure equalises, and valve 504 then closes.

When braking is reduced, or the brakes are released, the pump slows or stops and the higher pressure in the brake circuit than on the pump side closes valve 506 and 10 drives the dump valve 540 to open the dump port 535 and relieve pressure from the brake circuit into the reservoir. The equalisation requirement may be a small change in pressure as the brakes are feathered by the driver, or alternatively the pressure can be dumped entirely when the brakes are no longer required.

Referring finally to Fig. 6, the breakaway controller 60 comprises an inlet port

15 610 to receive pressure from the outlet port 502 of the control manifold assembly. It also has an outlet port 620 in communication with the brake circuit 90. In normal operation pressure received at inlet port 610 is provided at outlet port 620 to the brakes.

The breakaway controller comprises a drilled aluminium body 630, and a linear actuator 640 which in normal operation ensures an actuator rod 650 is correctly 0 positioned within the actuator control body 630 to ensure the operation described above. When the towed vehicle breaks away from the towing vehicle for any reason then the actuator operates under the control of the electronic control unit 70 to withdraw the rod 650 and ensure the brakes are applied.

Inside controller body 630 are a plunger 660 and plunger spring 662. The 5 plunger is spring loaded but retained in a depressed state against the spring by the rod

650. On the other side of rod 650 is a passageway which communicates with the inlet

610 and outlet 620. In the passageway between the inlet and outlet is a first check valve 664 which is actuated by a valve actuation pin 666. A further valve 668 is located on the far side of the connection with the outlet 620, and is also actuated by 0 valve actuation pin 666. Valve 668 accesses an accumulation chamber 670. A sliding piston 672 is located in the accumulation chamber 670 and behind the piston is a charge of nitrogen.

Whenever the trailer is plugged into a towing vehicle motor 20 will operate under the control of the electronic control unit 70 to run the motor at a predetermined 5 current in order to drive the pump 30 at a predetermined speed for a specified period of time to create the necessary pressure in the brake circuit and breakaway controller. As

the pressure increases within the break away controller body 630 valve 668 will open and the hydraulic braking fluid will depress cylinder 672. The charge of nitrogen behind cylinder 672 is pressurised until the nitrogen pressure is equal to the brake circuit pressure, at which point valve 668 closes. This valve will remain closed unless break away operation is required. Valve 668 has a higher cracking pressure than valve 664, and remains closed, while the valve actuator pin 666 maintains valve 664 open during normal operation.

When the break away function is required the rod 650 is withdrawn under the control of signals from control electronics 70. Withdrawal of rod 650 allows the plunger 660 to advance under the pressure of spring 662. This closes valve 664 and pin 666 opens valve 668. This releases the pressure stored by the nitrogen in the accumulator 670 to the brake circuit via port 620. The pressure released from the accumulator causes the brakes to remain on until the rod 650 is again advanced.

The control circuit of the electronic control unit 70, is controlled by a microprocessor, and is operable to drive the motor 20 at variable speeds to produce a range of pressures available at the output of the pump 30. During use the brake light signal of the towing vehicle is used to trigger braking. An accelerometer in the form of a multi- axis accelerometer is used as an acceleration/deceleration sensor in the control circuit of the electronic control unit 70, and is able to detect acceleration/deceleration and gravitational forces in the vertical and horizontal planes (i.e. forward and reverse directions). This allows the POD braking system to detect that the vehicle is climbing or descending a hill and to adjust the braking algorithm, programmed into the microprocessor, accordingly. When the accelerometer detects deceleration of the car and trailer and the vehicle stop lamp is on, it is assumed that the trailer should brake proportionally with the car. When the trailer brakes are applied, this causes further deceleration of the vehicle and the trailer. The expected amount of deceleration caused by the trailer's brakes is subtracted from the total deceleration to determine the deceleration due to the vehicle's brakes and so the actual amount of trailer braking required. The control circuit of the electronic control unit 70 additionally monitors vehicle

'stop', 'park', 'left indicator' and 'right indicator' signals, and 'reverse' signals. The control circuit of the electronic control unit 70 is able to control the lamps on the trailer independently of the vehicle to visually indicate that the trailer is for instance, braking, or to indicate that the brakes have been engaged or disengaged as a result of the vehicle being parked. In addition, the control circuit of the electronic control unit 70 stores the following user definable towing values and operational parameters in flash memory:

Sensitivity, Boost, Boost time, Negative boost (reverse), an Override program, and Road conditions.

Sensitivity, otherwise referred to as gain, defines the proportion of braking effort applied to the towed vehicles brakes in response to the amount of deceleration measured. In effect it is used by the driver of the vehicle to adjust braking performance to suit the towing conditions. In this regard a higher level of gain is set when the towing load increases and a lower level of gain is set when the towing load decreases.

Boost enables the initial reaction of the system to increase rapidly (rapid build up in pressure) and is effective when the towing vehicles' brakes are initially applied. That is, when the towing vehicles' brakes are applied the towed vehicle is able to react responsively and lead the braking. The driver of the towing vehicle will be under the impression that the towed vehicle is in effect dragging, rather than pushing, the car.

The boost output is measurable as a function of time continues until a predetermined time has lapsed (boost time) or until a sensor monitoring the boost function outputs zero G's or when the towing vehicles' brakes are released. The predetermined time is dependent on the number of brake callipers.

Negative Boost applies when the towed vehicle is reversing and is used to decrease the braking performance. This will be useful in situations where the driver must feather the braking of the towed vehicle. There is no time associated with negative boost and the negative boost output continues until zero G's are output by the sensor or the brakes are released.

The ICC (as will be later referred to) will have a 'brake assist' or manual override button which allows the trailer's braking system to be applied independently of the towing vehicle's brakes. When pressed the trailer mounted electronics will output the selected brake assist/override program commanding independent braking force and ensure the trailer stop lights operate accordingly.

Road conditions may include various pre-programmed conditions such as 'dry road', 'wet road', 'unsealed road' and 'icy road'. Applying the brakes in less than ideal conditions may lead to locking up of trailer brakes and a drop in braking force as the wheels lose traction and skid. By altering braking conditions to take account of the road surface, it will possible to automatically optimise braking.

These values may be entered in the factory at the time of manufacture, or they may be entered or updated by the installer or distributor to take account of conditions and trailer setup and load. The braking level can be adjusted manually via a rotary shaft encoder control known to suit the weight of the trailer. The values can also be

adjusted by the end user if the load changes drastically or dash mounted control is required.

The control circuit's microprocessor uses the signal from the acceleration/deceleration sensor together with the stored towing value to calculate a 12V DC pulse width modulated control signal to drive electric motor 20 when braking is triggered. The use of stored towing values in the electronic control unit 70 enable the towing vehicle to be changed without having to change user settings.

A push button is provided to enable intentional removal of the trailer wiring plug from the towing vehicle without activating the brake away function. This feature may also serve as a theft deterrent.

Figs. 7 to 10 illustrate a power on demand braking system 10 for mounting on a towed vehicle in accordance with a second embodiment of the invention. In this embodiment, like numerals refer to like parts as previously referred to. The functioning of the braking system is the same as the embodiment illustrated in figures 1 to 6. However minor modifications have been made to the internal configuration of some of the components of the braking system 10. In particular, the reservoir 40, pump assembly 50, and breakaway circuitry 90 are enclosed within a general housing 701. A lid 703 encloses the housing 701. Moreover, with reference to the control manifold 50 illustrated in figure 5, port 510 which contained a pressure relief valve comprising a ball bearing 512, a spring 514 and a hollow grub screw has been discarded together with port 520, which housed a pulsation accumulation piston 522 and spring 524 retained by retainer 526.

Within the general housing 701 of the second embodiment, an N.O breakaway valve 702 and an N.C breakaway valve 704 are provided and are connected via breakaway inlet drilling 712 and control outlet circuit drilling 714 to the dump valve

540 and pulsation orifice 506 of the control manifold 50. A motor 710 is mounted to each N.O 702 and N.C valve 704.

On start-up, the device 10 operates at a predetermined pressure output for a period of time, typically between ten and thirty seconds. During this time both the N.O valve 702 and N.C. valve 704 are positioned in the open state. Prior to the period of time elapsing, the N.C valve 704 is repositioned to the closed state. In doing so a given volume of fluid under pressure is trapped in the breakaway accumulator 706.

Under normal operation, the N.O valve 702 remains in the open state and the

N.C valve 704 remains in the closed state. The pressure from the control circuit is free to flow to and from the brakes via the brake outlet 708.

Upon activation of the breakaway condition, the following sequence of events occurs: the pumping action of the device ceases, the N.O valve 702 closes, and the N.C valve 704 opens. In so doing, the brakes receive pressure from the breakaway accumulator 706, via the accumulator outlet 707, and fluid is unable to flow back through the control circuit.

To release the device 10 from a breakaway condition, electronics are operated such that the state of the valves 702, 704 are returned to their normal operation position. Additionally, when the device 10 is switched off without receiving the breakaway condition the N.C valve 704 is opened which allows accumulated pressure to flow back through the control circuit to the fluid reservoirs, thereby releasing all stored pressure from the system.

Figs. 11 to 17 illustrate a power on demand braking system 10 for mounting on a towed vehicle in accordance with a third, and preferable embodiment of the invention. In this embodiment, like numerals refer to like parts as previously referred to. The functioning of the braking system is the same as the embodiment illustrated in figures 1 to 6. However modifications have been made to certain system components as well as to the internal configuration of some of the components of the braking system 10.

As schematically illustrated in Fig 11, the POD braking system 10 comprises an electric motor 800, a pump 900, a hydraulic fluid reservoir 40, a control manifold 1000, and control electronics 70. Electrical input 80 from the towing vehicle is received to the electronic control unit 70 and processed to operate the braking system 10, and control pressure variations in hydraulic fluid within brake cylinders 90, having associated brake circuits, to operate brakes on the towed vehicle. The POD braking system 10 is a self contained, environmentally sealed, trailer mounted braking controller. Each of the parts of the assembly in accordance with the preferred embodiment will now be described in turn:

Referring to Figures 12, 13 and 14, the pump is powered by a brushless DC motor 800 which enables a high starting torque which results in a very fast pressure rise in the system. Because there are no brushes to wear out, the use of a brushless DC motor also has a virtually unlimited life expectancy. The motor's output shaft 802 engages with an eccentric actuator 810. The eccentric actuator 810 comprises an eccentric lobe 812 which engages with a needle roller bearer 814.

A rechargeable battery pack (not shown) provides a compact, high current capacity power source. In this example, a Li ion battery is used although any battery that minimises or substantially eliminates outgassing may be used. In addition, the

batteries are recharged via the parking signal lamp connection from the vehicle. The parking lamp signal also provides some of the power to drive the electronic controller 70. Power consumption is managed by the electronic controller's microprocessor to ensure that maximum power is available for braking. The microprocessor also shuts down all of the other circuits of the POD braking system when it is not in use to conserve battery power. The battery voltage and charging current as well as the motor voltage and current are measured to determine the remaining battery capacity and also to carefully control charging of the batteries. Battery charging is suspended during periods when the motor is running. Referring to Figures 13 and 15, the pump comprises a high grade plastics injection moulded pump housing 902. The use of a high grade plastic substantially reduces production costs and can also reduce the overall weight of pump. The pump housing 902 includes a cylinder block 904 on either side of which are mounted cylinder heads 906 and 908. Two seals 910, 912, which are inert to the effects of the hydraulic brake fluid, are mounted in bores of respective cylinder heads 906, 908 and provide guides for the horizontally arranged piston. The piston comprises two rods 914, 916 each of which are manufactured from cut lengths of centreless ground steel. Respective first ends of the piston rods are horizontally mounted within a piston yoke carrier 818 and engage a piston yoke slider 920 for horizontal reciprocation back and forth in the two cylinder heads 906 and 908. Respective first ends of the piston rods are retained with piston retaining pins 909. Respective second ends of the piston rods engage the respective seals 910, 912. The piston rods 914, 916 in effect "float" in the seals 910, 912. This feature is advantageous to the arrangement described in the earlier embodiments as it alleviates the requirement to produce an accurate cylinder bore which effectively enables the pump 900 to be more readily mass produced. The cylinder block 904 and cylinder heads 906, 908, the piston carrier yoke 918 and slider 920 are manufactured from the same, or similar, high grade plastics.

The shaft 802 of the motor passes through the piston yoke slider 920. The eccentrically rotating motion of the eccentric actuator 810 is efficiently converted into reciprocation of the piston rods 914, 916. The end of the shaft 802 is held by a bearing 804 which substantially prevents flexing of the shaft and improves the start-up characteristics of the pump. The improved start-up characteristics results in a significantly improved build up in pressure as a function of time compared with current state of the art pumps generally, as shown in the graph illustrated in figure 18.

The pump design of this embodiment additionally enhances the life of the piston seals 910, 912 as the full face contact of the eccentric actuator 810 with the ends of the piston rods 914, 916 provides a substantially axial force.

Each of the cylinder heads 906, 908 has a brake fluid inlet port 922, 924 and an outlet port 926, 928.

The inlet ports are directly connected to the hydraulic fluid reservoir 40. Check valves are provided at both inlet ports 922, 924 and both outlet ports 926, 928 and the check valves at the outlet ports 926, 928 are designed to open at higher pressures than the check valves at the inlet ports 922, 924 in order to maintain pressurised hydraulic braking fluid within the cylinder heads 906, 908 even when the pump 900 is not running. The pump 900 uses a fixed orifice 930 to allow fluid under pressure to be supplied via a control manifold 1000 to the vehicle's and a brake circuit 90, illustrated here as brake callipers.

When the piston rod 914 is driven to the left and entered cylinder head 906 it pumps any fluid within that cylinder head 906 out through outlet 928. At the same time it draws fluid into the right hand cylinder head 908 through inlet 922. As the piston reciprocates to the right it pumps the fluid out of the right hand cylinder head 908 via outlet port 926 while drawing fluid into the left hand cylinder head 906 through inlet 924. As with the earlier embodiments it can be seen that the piston is driven in both directions. The piston is centrally displaced a distance in the order of ± 1.25mm. As a result the pump remains in a fully primed condition even when not in use, and may be able to provide an instant start up response; that is the pump may be essentially self- priming.

Referring to Figs 16 and 17, the control manifold is in the form of a solenoid valve 1000. The solenoid valve 1000 comprises a solenoid 1002 and a valve generally designated by 1004. The valve 1004 is arranged to cover a bleed port 1006 to prevent unrestricted return of brake fluid to the reservoir 40 at start-up. This results in braking pressure to be rapidly increased during start-up and hydraulic expansion to be taken up.

The solenoid 1002 drives an armature guide 1010 which is connected to a screw 1012. The screw 1012 is situated within a needle roller bearing 1014. Attached to the screw

1012 is a plunger (needle) 1016 which punctures a check valve 1018. Opening of the solenoid valve 1000 is controlled by the electronic control unit 70 to allow proportional braking pressure by varying the motor speed and torque. Slight variations in pressure are able to be made to effect proportional braking by activating the bleed port 1006 and running the pump 900 at a rate which the pressure rise from the pump is greater than the pressure drop from the bleed port 1006.

The unit may be locked down by deactivating the solenoid 1002 which closes the bleed port 1006. The bleed port 1006 closes automatically when the system is not powered. This allows braking pressure to be accumulated and held without constantly running the pump. This feature greatly reduces the amount of energy required to provide trailer braking in the event of breakaway of the trailer from the vehicle or when the trailer brakes are locked when the trailer is parked.

The POD braking system includes an electronic control unit 70 and rechargeable batteries. All the components necessary to provide effective independent control of trailer braking are contained within the POD braking system. An additional, separate component, an In Car Controller (ICC) is provided that allows the driver control and adjustment of the behaviour of the braking system and also allows the status of the POD braking system to be monitored. In the event that the communication link between the ICC and the POD braking system is broken, the POD braking system continues to independently manage trailer braking. Figures 19 to 21 represent circuit diagrams illustrating various components of the control circuit of the electronic control unit 70. With reference to these figures, the microprocessor is designated at 72, the brushless DC motor controller and solenoid valve drive at 74 and 76 respectively, the accelerometer at 78, radio communications transceiver for communicating with the ICC at 82, serial flash memory at 84, trailer light monitoring and control at 86 and the trailer breakaway sensing unit at 88. The power supply circuitry illustrates circuitry for power sharing 92, battery voltage monitoring 94, low voltage regulators 96, battery charging 98 and battery current monitoring 100.

The control circuit of the electronic control unit 70, as previously described, is microprocessor controlled. In addition, the microprocessor receives input from an internal temperature sensor that is used both to check that the POD braking system's internal temperature is within safe operating limits and also to allow temperature compensation of the accelerometer and other measurements. The microprocessor additionally receives input from a pressure transducer. The pressure transducer may be provided in the form of a variable resistance strain gauge to monitor trailer brake pressure.

The microprocessor has analogue inputs (accelerometer, temperature sensor, pressure transducer, battery voltage, motor current) and digital inputs (float switch for brake fluid level detection, towing values and operational inputs as previously described) and outputs (trailer brake lamp control, trailer park lamp control, right and left indicator lamp control, reverse lamp control and solenoid valve drive to release

brake pressure). An integrated radio transceiver integrated circuit is used to facilitate radio communication between the ICC and the POD.

The electronic control unit 70 allows motor speed and/or torque to be precisely and proportionally controlled with output at up to approximately 250W. This allows the hydraulic pump brake fluid pressure and so the braking force to be proportionally controlled. The pump motor 800 and electronic control unit 70 are able to be operated down to at least 5 V DC whilst maintaining operational braking pressure.

The control circuit of the electronic control unit 70 is designed as a single PCB construction with electronic components surface mounted on one side of the PCB. Heat from heat generating components is transferred to the back of the PCB via plated holes in the PCB. Power conducting circuit tracks are also located on the rear of the PCB. An aluminium plate heat sink that doubles as mounting bracket is pressed against the whole of the rear of the PCB and universally conducts heat away from tracks and components. This method of construction allows lower cost, automated, manufacture of the electronics and in a more compact form than would otherwise be possible.

The ICC may either be dashboard mounted, for instance plugged into and powered from the lighter or auxiliary power socket, on the vehicle console, or remotely operated over an appropriate radio frequency. Optionally the ICC could be powered by a rechargeable 3.6V Li-Ion battery or via the vehicles 12 V DC supply or a generic mains plug. Optionally, the ICC may communicate with the POD via data signals modulated onto the 12V power wiring of the towing vehicle, i.e. via powerline communications. This may be effected directly from the ICC via the towing vehicle's lighter or auxiliary power socket, through the towing vehicle's wiring loom and the trailer connector to the POD. As will be appreciated, the cable that is used for charging the ICC battery doubles as a communications lead.

Radio frequency circuitry built into the ICC enables communication between the ICC and the POD. In effect, the operational parameters/user defined towing values as previously described are able to be set from the ICC and sent to the POD braking system to vary the braking algorithm. The housing of the ICC has display screen which indicates the system status on a series of LEDs. Furthermore, the ICC functions to monitor and transmit input data from the rotary shaft encoder and emergency/manual braking switch. The ICC includes memory to store configuration information and log operational data. The ICC additionally communicates with an external PC for configuration and diagnostics.

Whilst embodiments have been described for connection to 12V DC systems it should be appreciated that they can readily be modified for connection to 24V DC systems.

The brakes, may be locked prior to disconnection of the towing vehicle and then remain locked until power from the vehicle is connected and the ICC releases the brakes.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.