Abstract:
A fluid pump assembly for pumping hydraulic fluid through a controlled brake system includes a housing defining a pumping chamber. The chamber communicates with a hydraulic fluid circuit that operates the controlled brake system. A piston plunger is disposed within the chamber with a shaft affixed to the plunger. An electric coil is affixed to a casing having the shaft inserted therethrough. The coil is coaxially aligned with the shaft. The coil generates a magnetic field through an armature affixed to a distal end of the shaft disposed outside the chamber when receiving electrical current. The magnetic field draws the armature towards the casing for pumping hydraulic fluid from the chamber.

Description:
TECHNICAL FIELD 
     The subject invention relates generally to an improved precharge pump for use with a controlled brake system. 
     BACKGROUND OF THE INVENTION 
     Motor vehicle brakes that are interfaced with a controlled brake system are presently operated with hydraulic fluid. A master cylinder/booster distributes hydraulic fluid throughout the brake system as is well known in the art of hydraulic vehicle braking. Two separate feed lines transfer hydraulic fluid from the master cylinder to the driver&#39;s side and passenger&#39;s side brakes through a series of valves that are opened and closed by a controller. The controller determines which valves to open and close based on information obtained from sensors on the vehicle such as, for example, brake sensors, speed sensors, and yaw rate sensors. 
     The passenger&#39;s side and the driver&#39;s side hydraulic lines each include a main hydraulic pump for increasing hydraulic pressure in the hydraulic lines during a braking event. The appropriate valves either open or close depending upon whether a brake pedal is being depressed, or has been released. When the controller determines a controlled braking event is about to occur, it signals the main hydraulic pumps to rapidly increase pressure in the hydraulic lines for the valves to distribute hydraulic fluid to the appropriate brakes. However, the master cylinder alone has been found to be unable to supply enough hydraulic fluid to the main pumps to allow the main pumps to rapidly increase fluid pressure in the hydraulic lines. If the main pumps are not able to rapidly increase fluid pressure to the appropriate brakes, the effectiveness of the controlled brake system is significantly reduced. Therefore, a precharge pump is needed to rapidly supply additional hydraulic fluid to both the master cylinder and to the main pumps when signaled by the controller. 
     The precharge pump typically strokes one time when signaled by the controller that a controlled braking event is about to occur. This provides additional hydraulic fluid to the main pumps allowing the main pumps to rapidly increase fluid pressure to the valves. Complex gerotor or vane type pumps are often used for this type of application. These types of pumps have proven to be very costly and have not offered the reliability necessary to meet the requirements of the controlled brake assembly. Therefore, it would be desirable to introduce a low cost, mechanically simple pump to the controlled brake system for increasing the amount of hydraulic fluid to the main pumps to operate a controlled braking event. 
     SUMMARY OF THE INVENTION 
     The present invention is a precharge fluid pump for pumping hydraulic fluid through a controlled brake system. A housing defines a chamber that communicates with a hydraulic fluid circuit. A casing is fixedly attached to the housing and has an aperture aligned coaxially with the chamber. A piston includes a plunger slideably disposed within the chamber. A shaft is affixed to the plunger and has a distal end extending through the aperture. An armature is affixed to the distal end of the shaft. A coil is affixed to the casing and is arranged coaxially with the shaft. The coil generates a magnetic field through the armature when receiving an electrical current. The magnetic field draws the armature towards the casing driving the piston into the chamber for pumping hydraulic fluid. A spring biases the armature away from the casing in the absence of the magnetic field. 
     By using a magnet field to draw a piston into a pumping chamber for pumping hydraulic fluid into the hydraulic fluid circuit reduces the cost of the precharge pump. Further, this concept reduces the amount of moving parts commonly needed in a precharge pump, which increases the dependability of the controlled brake system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
     FIG. 1 is a schematic view to the controlled braking system; 
     FIG. 2 is a sectional view of the inventive pump of the preferred embodiment; 
     FIG. 3 is a sectional view of an alternate embodiment of the inventive pump; 
     FIG. 4 is a sectional view of a further alternate embodiment of the inventive pump; 
     FIG. 5 is a sectional view of a still further alternate embodiment of the inventive pump. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a controlled brake assembly is generally shown at  10 . The controlled brake assembly  10  includes a master cylinder  12  that controls the distribution of hydraulic fluid throughout the assembly  10 . A driver&#39;s side feed line  14  delivers hydraulic fluid from the master cylinder  12  to the driver&#39;s side brakes  16 . A passenger&#39;s side feed line  18  delivers hydraulic fluid from the master cylinder  12  to the passenger&#39;s side brakes  20 . The driver&#39;s side of the assembly  10  generally mirrors the passenger&#39;s side of the assembly as is known in the art of vehicle braking. 
     The driver&#39;s side feed line  14  branches first to a closed valve line  22  and subsequently to an open valve line  24 . The closed valve line  22  includes a closed valve  26  biased in a closed position. The open valve line  24  includes an open valve  28  biased in an open position. 
     As is known in the art of hydraulic valving, each valve  26 ,  28  includes an electric coil  30  that communicates with a controller (not shown). A solenoid valve  32  is disposed within each of the valves  24 ,  26  and is actuated by the electric coil  30 . A spring  34  maintains the solenoid valve  32  in the biased direction, whether that is open or closed. Each of the valves discussed below includes the same elements and, therefore, will not be discussed in any further detail. 
     The open valve line  24  feeds each of the driver&#39;s side brakes  16  through an inlet valve  36 . Downstream from each inlet valve  36  is an outlet valve  38 . Each inlet valve  36  is biased in an open direction allowing the hydraulic fluid to pass through to each of the driver&#39;s side brakes  16 . Each outlet valve  38  is biased in a closed direction and, therefore, prevents the hydraulic fluid from bypassing the driver&#39;s side brakes  16  when the inlet valves  36  are biased in the open direction. Therefore, when the inlet valve  36  is open and the outlet valve  38  is closed, hydraulic fluid is delivered to the brake at a pressure high enough to actuate the brake  16 . 
     Each outlet valve  38  feeds into a main pump feed line  40 . A spring-loaded accumulator  42  is connected to the main pump feed line  40 . A driver&#39;s side main pump  44  is disposed in the main pump feed line  40 . The spring loaded accumulator  42  collects hydraulic fluid to provide additional hydraulic fluid to the driver&#39;s side pump  44  when needed. A pump piston  46  is disposed between the driver&#39;s side main pump  44  and the spring loaded accumulator  42 . The driver&#39;s side main pump  44  pumps hydraulic fluid via the piston  46  through a damping chamber  48  into a high pressure hydraulic line  50 . The high pressure hydraulic line  50  returns hydraulic fluid to each of the driver&#39;s side inlet valves  36 . A pump motor  52  powers the driver&#39;s side main pump  44 . 
     Referring now to the passenger&#39;s side, the passenger&#39;s side feed line  18  preferably includes a pressure sensor  54  in an open valve line  24 ′ that detects the pressure in the passenger&#39;s side feed line  18  derived from the pressure exerted on a brake pedal. The pressure sensor  54  can alternatively be located in the driver&#39;s side feed line  14 . The passenger&#39;s side brakes  20  utilize parallel apparatus as the driver&#39;s side apparatus as will be evident in the text below. 
     The passenger&#39;s side open valve line  24 ′ feeds each of the passenger&#39;s side brakes  20  through an inlet valve  36 ′. Downstream from the inlet valves  36 ′ are outlet valves  38 ′. The inlet valves  36 ′ are biased in an open direction allowing the hydraulic fluid to pass through to each of the passenger&#39;s side brakes  20 . The outlet valves  38 ′ are biased in a closed direction and therefore prevent the hydraulic fluid from bypassing the passenger&#39;s side brakes  20  when the inlet valves  36 ′ are biased in the open direction. 
     The outlet valves  38 ′ feed into a main pump feed line  40 ′. A spring-loaded accumulator  42 ′ is connected to the main pump feed line  40 . A passenger&#39;s side main pump  44 ′ is disposed in the main pump feed line  40 ′. The spring loaded accumulator  42 ′ collects hydraulic fluid to provide additional hydraulic fluid to the passenger&#39;s side pump  44 ′ when needed. A pump piston  46 ′ is disposed between the passenger&#39;s side pump  44 ′ and the spring loaded accumulator  42 ′. The passenger&#39;s side main pump  44 ′ pumps hydraulic fluid through a damping chamber  48 ′ into a high pressure hydraulic line  50 ′. The high pressure hydraulic line  50 ′ returns hydraulic fluid to each of the driver&#39;s side inlet valves  36 ′. The pump motor  52  that powers the driver&#39;s side main pump  44  also powers the passenger&#39;s side main pump  44 ′. Therefore, when the inlet valve  36 ′ is open and the outlet valve  38 ′ is closed, hydraulic fluid is delivered to the brake at a pressure high enough to actuate the brake  20 . 
     An electromagnetic pump assembly  56  communicates with the passenger&#39;s side feed line  18 . The pump assembly  56  increases the hydraulic fluid pressure in the master cylinder  12  and in the hydraulic circuit in general. During a controlled braking event, the brakes  16 ,  20  are repeatedly actuated by the controller to prevent the loss of vehicle control. To obtain a rapid reaction time, the magnetic pump assembly  56  increases the supply of hydraulic fluid to the main pumps  44 ,  44 ′. Absent this additional pressure, the main pumps  44 ,  44 ′ could cavitate resulting in a response time that is inadequate to maintain control of the vehicle. The magnetic pump assembly  56  typically strokes one time when signaled by the controller that a controlled braking event is occurring. This single stroke provides enough hydraulic fluid pressure to both the master cylinder  12  and the passenger&#39;s side feed line  18  to supply an adequate amount of hydraulic fluid to both the driver&#39;s side main pump  44  and the passenger&#39;s side main pump  44 ′. Referring to FIG. 2, the magnetic pump assembly  56  includes a pump housing  58  that defines a pumping chamber  60 . A piston  62  is slidably retained in the pumping chamber  60 . A piston shaft  64  is affixed to the piston  62  and includes a distal shaft end  66  that telescopes out of the housing  58 . An armature  68  is affixed to the distal shaft end  66 . An electrical coil  70  is affixed to the housing coaxially with the piston shaft  64 . A spring  72  is disposed in the pumping chamber  60  and biases the armature  68  away from the housing  58 . An O-ring  74  encircles the piston  62  thereby sealing the piston  62  to the housing  58  for preventing hydraulic fluid from leaking past the piston  62  and out of the housing  58 . 
     Hydraulic fluid is pumped through an outlet check valve  76  in an outlet port  77  and into the passenger&#39;s side feed line  18  from the pumping chamber  60 . The outlet check valve  76  prevents hydraulic fluid from reentering the pumping chamber  60  from the passenger&#39;s side feed line  18 . Hydraulic fluid passes through an inlet check valve  78  in an inlet port  79  from a master cylinder reservoir  80  into the pumping chamber  60  when a vacuum is created in the pumping chamber  60  by the telescoping action of the piston  62 . The inlet check valve  78  prevents hydraulic fluid from leaving the pumping chamber  60  and reentering the master cylinder reservoir  80 . A pressure relief valve  82  in a pressure relief port  81  allows hydraulic fluid to pass from the pumping chamber  60  into the master cylinder reservoir  80  only if hydraulic pressure in the pumping chamber  60  reaches a critical level. Hydraulic fluid will be returned through the pressure relief valve  82  to the master cylinder reservoir  80  to prevent damaging the master cylinder  12  due to critically high levels of hydraulic pressure. Each of the valves  76 ,  78 ,  82  preferably include a ball  83  and spring  85  biasing the ball to close the port  77 ,  79 ,  81 . However, other types of check valves would be equally effective. 
     During operation, a controller (not shown) will receive information from both the pressure sensor  54  and other sensors (not shown) such as, for example, brake sensors, speed sensors, and yaw rate sensors. The controller will determine if a controlled braking event is about to occur. Subsequent to that determination, the electric coils  70  will be charged to create a magnetic flux path. The magnetic flux will draw the armature  68  towards the electric coil  70  driving the piston  62  into the pumping chamber  60 . The driving action increases hydraulic fluid pressure inside the pumping chamber  60  forcing hydraulic fluid out through the outlet check valve  76  towards both the master cylinder  12  and the passenger&#39;s side feed line  18 . The increased amount of hydraulic fluid in the assembly  10  will provide a sufficient amount of hydraulic fluid to the driver&#39;s and passenger&#39;s side main pumps  44 ,  44 ′ to actuate each of the brakes  16 ,  20  in a timely manner. Absent this additional hydraulic fluid, the main pumps  44 ,  44 ′ potentially will not have enough hydraulic fluid to actuate the brakes  16 ,  20  in a timely manner. Thus, the controlled braking assembly  10  would not provide an adequate amount of wheel control to prevent a loss of traction with the pavement. 
     An alternative embodiment for the magnetic pump assembly  56  is shown in FIG.  3 . The alternate magnetic pump assembly  56  draws fluid into the pumping chamber  60  through a bypass port  84  and a compensation port  86 . The bypass port  84  and the compensation port  86  merge to draw fluid from the master cylinder reservoir  80 . A lip seal  88  is disposed upon the end of the piston  62 . The lip seal  88  seals the bypass port  84  from the compensation port  86  when disposed therebetween. When the piston  62  is stroking into the pumping chamber  60 , hydraulic fluid will be pumped out of the pumping chamber  60  through the outlet check valve  76 . A small amount of hydraulic fluid will also be pumped into the bypass port  84  and flow through the compensation port  86  filling the space in the pumping chamber  60  defined by a groove  90  in the piston  62 . When the piston  62  stroke creates a vacuum in the pumping chamber  60 , and the lip seal  88  is disposed between the bypass port  84  and the compensation port  86 , hydraulic fluid will be drawn from the space created by the groove  90  through the compensation port  86  and into the pumping chamber  60  via the bypass port  84 . This insures that the pumping chamber  60  will maintain a prime and prevents the alternate pump assembly  56  from cavitating. 
     An additional alternate embodiment of the magnetic pump assembly  56  is shown in FIG.  4 . In this embodiment, the magnetic pump assembly  56  does not include any check valves and is therefore less costly than the other embodiments. A fluid passage  92  connects through the passenger&#39;s side feed line  18  to the master cylinder  12 . The stroking action of the piston  62  can both draw fluid from the master cylinder  12  and force fluid into the master cylinder  12  depending on the direction of the piston  62  stroke. In this embodiment, a single inward stroke of the piston  62  will increase fluid pressure in the master cylinder  12  and the passenger&#39;s side feed line  18 . No additional piston strokes are directed by the controller while the same controlled braking event is occurring. 
     A fourth alternate embodiment of the magnetic pump assembly  56  is shown in FIG.  5 . This embodiment includes a single inlet check valve  78  and a single outlet check valve  76 . As in the prior embodiments, hydraulic fluid is drawn through the inlet check valve  78  from the master cylinder reservoir  80 . Hydraulic fluid is pumped through the outlet check valve  76  into the passenger&#39;s side feed line  18  and through to the master cylinder  12  and the passenger&#39;s side feed line  14 . 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for convenience and are not to be in any way limiting, the invention may be practiced otherwise than as specifically described.