Patent Application
20180178773
The present invention relates to vehicles and vehicle braking systems.
Conventional brake-by-wire braking systems normally utilize electrically powered systems to effect vehicle braking at brake cylinders. Such braking systems often include a mechanical back-up in which the master cylinder produces a limited deceleration potential dependent upon the physical configuration of the master cylinder.
In one aspect, the invention provides a vehicle brake system. The vehicle brake system includes a brake pedal operable to receive a user input force, a master cylinder operably coupled to the brake pedal to be actuated thereby, a brake cylinder selectively coupled to the master cylinder via a hydraulic circuit, an electronically-controlled pressure generating unit distinct from the master cylinder, and a controller operable to receive a signal indicative of the user input force to the brake pedal. In a first mode, the controller is operable to actuate the electronically-controlled pressure generating unit to apply hydraulic fluid pressure to the brake cylinder according to the signal. In a second mode, the master cylinder is operable to actuate the brake cylinder, and the controller is operable to actuate the electronically-controlled pressure generating unit to supplement the master cylinder and extend a fluid volume capacity of the master cylinder.
In another aspect, the invention provides a method of operating a vehicle brake system. The vehicle includes a hydraulically actuated brake cylinder. The vehicle brake system is operated in a primary brake-by-wire mode in which fluid is applied to the brake cylinder via an electronically-controlled pressure generating unit in response to depression of a brake pedal. A controller identifies that the vehicle brake system is inoperable in the primary brake-by-wire mode. Subsequent to identifying that the vehicle brake system is inoperable in the primary brake-by-wire mode, the vehicle brake system is operated in a back-up mode as follows when the brake pedal is depressed: a fluid path is opened between a master cylinder and the brake cylinder, thereby actuating the brake cylinder with the master cylinder, and the electronically-controlled pressure generating unit is actuated with the controller to extend a fluid volume capacity of the master cylinder.
In another aspect, the invention provides a vehicle brake system. The vehicle brake system includes a brake cylinder and a master cylinder operable to pressurize fluid in response to the input force. An electronically-controlled pressure generating unit is provided separate from the master cylinder and operable to selectively actuate the brake cylinder. A pedal feel simulator is operable to provide a reaction force in response to the input force. A controller is operable to actuate the electronically-controlled pressure generating unit in a brake-by-wire configuration and operable to transition the vehicle brake system from the brake-by-wire configuration to a back-up configuration. In the brake-by-wire configuration, the electronically-controlled pressure generating unit actuates the brake cylinder and the master cylinder provides pressurized fluid to the pedal feel simulator. In the back-up configuration, the master cylinder actuates the brake cylinder with a fluid addition provided by the electronically-controlled pressure generating unit to extend a fluid volume capacity of the master cylinder.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.
The brake system 10 includes two hydraulic circuits 18, 22, including a first hydraulic circuit 18 and a second hydraulic circuit 22. As shown in
As shown in
The first and second circuits 18, 22 are provided with master cylinder isolation valves 78, 82, respectively. The master cylinder isolation valves 78, 82 are two-position valves, operable to transition between an open position and a closed position. Alternatively, the valves 78, 82 may be proportional valves (e.g., controlled via pulse-width modulation) such that they provide a variable flow opening ranging from a closed position to a fully open position, including a plurality of intermediate positions therebetween. When the valves 78, 82 are in the closed position, the fluid from the master cylinder chambers 42A, 42B cannot reach the brake cylinders 38 and is therefore directed towards a pedal feel simulator 62.
The pedal feel simulator 62 is located downstream of the tandem master cylinder 42 and is fluidly connected to the first circuit 18. A pedal feel simulator control valve 66 is positioned between the pedal feel simulator 62 and the tandem master cylinder 42 to selectively open or close the fluid path between the same. When in fluid communication with the tandem master cylinder 42, the pedal feel simulator 62 provides a reaction force at the brake pedal 46 in response to the force provided by the pressurized hydraulic fluid to mimic the reaction force otherwise provided when the tandem master cylinder 42 communicates directly with the brake cylinders 38.
The brake system 10 further includes an electronically-controlled pressure generating unit 70 separate from the tandem master cylinder 42. The pressure generating unit 70 provides a braking force to the brake cylinders 38 when the master cylinder isolation valves 78, 80 are in the closed position and may be mechanical, hydraulic, or mechatronic. The electronically-controlled pressure generating unit 70 has a greater fluid storage volume than the master cylinder 42 such that actuation of the pressure generating unit 70 is capable of displacing more fluid than the master cylinder 42. As shown, the pressure generating unit 70 is a motor-driven piston 70A. Alternatively, the pressure generating unit 70 may be, for example, a hydraulic accumulator or a pump. The pressure generating unit 70 produces a hydraulic pressure or output force proportional to a sensed input value. The input value may be the travel distance of the brake pedal 46 or pushrod 50, the input force provided by the user at the brake pedal 46, or the fluid pressure from the tandem master cylinder 42. Accordingly, various sensors (e.g., pedal force or travel sensor 74A, master cylinder pressure sensor 74B) measure the input value and relay the value to a controller 60. The pedal sensor 74A and the master cylinder pressure sensor 74B may be located on independent electrical circuits such that one may function as a back-up to the other. Collectively, the pedal sensor 74A and the master cylinder pressure sensor 74B can detect hard pedal issues based on a relationship between the measured fluid pressure and the force applied to or travel of the pedal 46. In turn, the pressure generating unit 70 is operated by the controller 60 to pressurize hydraulic fluid within the hydraulic circuits 18, 22 in proportion to the sensed input value.
The first and second circuits 18, 22 are further provided with pressure generating unit control valves 86, 90, respectively. The pressure generating control valves 86, 90 are two-position valves, operable to transition between an open position and a closed position. Alternatively, the valves 86, 90 may be proportional valves (e.g., controlled via pulse-width modulation) such that they provide a variable flow opening ranging from a closed position to a fully open position, including a plurality of intermediate positions therebetween. If the valves 86, 90 are in the closed position, the fluid from the pressure generating unit 70 cannot reach the brake cylinders 38.
Additional valves control the flow to and from each brake cylinder 38. Inlet valves 94 are proportional valves such that they provide a variable flow opening ranging from a closed position to a fully open position, including a plurality of intermediate positions therebetween to regulate the braking force at each brake cylinder 38 independently. Outlet valves 98 include a restrictive opening for selectively returning fluid from the brake cylinders 38 to the reservoir 58 and may, for example, assist with wheel anti-slip control.
The brake system 10 is operable in a primary mode or configuration for normal brake-by-wire operation. In the primary mode, the electronically-controlled pressure generating unit 70 provides a braking force to all of the brake cylinders 38, including those in the first and second subsets 38A, 38B of brake cylinders 38. The braking force is provided in proportion to a driver's request in the normal operation, where the tandem master cylinder 42 is isolated from the brake cylinders 38 by the isolation valves 78, 82. Such braking is illustrated in
In the primary mode, the user provides an input to the brake pedal 46, which translates the pushrod 50 and plunger 54, thereby moving fluid to the hydraulic circuits 18, 22. The pedal feel simulator control valve 66 is an open position. Therefore, as indicated by dotted lines 200, the fluid pressure supplied by the tandem master cylinder 42 is provided to the pedal feel simulator 62.
Concurrently, the pressure generating unit 70 is actuated by an output signal from the controller 60, in response to an input signal corresponding to the sensed value indicative of and proportional to the user input. The pedal travel (i.e., displacement of the brake pedal 46) is measured by the pedal travel sensor 74A and is transformed to a target piston pressure via the controller 60. The target piston pressure is associated with a specific pedal travel, for example, as shown in the graph of
In the primary mode, the pressure generating unit control valves 86, 90 are actuated to open positions. Therefore, as indicated by bolded lines 100 in
Once a user removes pressure from the brake pedal 46 (e.g., removes foot from the brake pedal), the controller 60 instructs the piston 70A to return to an un-actuated state and the fluid returns to the pressure generating unit 70 via the open control valves 86, 90. The control valves 86, 90 are then returned to the closed position once fluid pressures are equalized.
The brake system 10 may transition from the primary mode to the secondary or back-up mode or configuration in response to a failure or malfunction of a component, such as one of the sensors 74A-74C (e.g., a missing signal from a sensor, a measurement outside a predetermined range, etc.), the simulator 62, or the simulator valve 66. For example, a failure of the simulator 62 or simulator valve 66 may prevent a proper pedal stroke, which may be identified by the controller 60 based on an increased pressure unassociated with an increased pedal travel. In response, the controller 60 sends a signal to transition the brake system 10 from the primary mode to the back-up mode.
However, the tandem master cylinder 42 contains a limited amount of fluid (i.e., the plungers 54 are only capable of a limited travel or translation within the tandem master cylinder 42). Because the system is primarily designed for brake-by-wire operation of the primary mode, the master cylinder volume may be quite small. Therefore, when the available fluid volume is spent and the plungers 54 bottom out, the tandem master cylinder 42 is not capable of providing any further increase in braking force. Although this technique has proven effective in practice to achieve minimum standards of deceleration in a back-up mode, further improvement in braking performance can be achieved with the layered back-up mode as described below.
Rather than cease operation of the pressure generating unit 70 and rely on mechanical back-up solely from the tandem master cylinder 42, the secondary mode can provide a layered braking actuation, utilizing fluid from the tandem master cylinder 42 in combination with a fluid supplement from the pressure generating unit 70. In the secondary mode, as shown in
In addition to the fluid supplied to the circuits 18,22 by the tandem master cylinder 42, the pressure generating unit 70 is actuated by the controller 60 and the control valves 86, 90 are opened to provide an additional quantity of fluid into the hydraulic circuits 18, 22, as indicated by dotted and bolded lines 300. With all of the isolation valves 78, 82 and control valves 86, 90 in open positions, the pressure generating unit 70 is in fluid communication with the brake cylinders 38 as well as the first and second master cylinder chambers 42A, 42B.
The controller 60 can actuate the pressure generating unit 70 to produce a fluid volume and/or fluid pressure value proportional to the user input to the brake pedal for addition to the hydraulic circuits 18, 22. The additional fluid is dependent upon the travel, force, or pressure measured by the sensors 74A, 74B. In other words, the pressure generating unit 70 is operated in a controlled manner to replicate or track proportionally with the input force of the driver to the brake pedal 46 as in the primary brake-by-wire mode. The layered back-up mode takes advantage of the pressure generating unit 70 to extend the ability beyond the fluid volume limitation inherent of the tandem master cylinder 42. The pressure generating unit 70, which provides brake-by-wire braking in the primary mode, functions as a volume booster for the master cylinder 42 in the back-up mode.
As the brake pedal 46 is depressed by an input force of a user, an increase in fluid volume from the pressure generating unit 70 is applied to displace the plungers 54 backwards and lift the brake pedal 46 against the user, providing additional stroke available to the user for increasing the manually-applied braking force. For example, the controller 60 may operate in a volume control mode to instruct the pressure generating unit 70 to displace a volume of fluid into the circuits 18, 22, the displaced volume dependent upon and proportional to the input force of the user. Once a user removes pressure from the brake pedal 46, the tandem master cylinder 42 returns to an un-actuated state and the controller 60 returns the piston 70A to an un-actuated state. The fluid in the circuits 18, 22 return to the pressure generating unit 70 via the open control valves 86, 90 and the tandem master cylinder 42 via the open isolation valves 78, 82.
In contrast to conventional back-up braking modes, the back-up braking mode illustrated in
