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An apron for a vehicle front end comprises a unitary plastic component having a front structure and a rear structure joined by an offset portion. The front and rear structures extend at rearward downward angles and in generally parallel directions, and the offset portion extends at a rearward upward

An apron for a vehicle front end comprises a unitary plastic component having a front structure and a rear structure joined by an offset portion. The front and rear structures extend at rearward downward angles and in generally parallel directions, and the offset portion extends at a rearward upward angle. The apron has a relatively constant vertical dimension, such that the angled structures define a wave-shaped envelope. Preferably, a horizontal plane extending from the tip of the front structure stays within the wave-shaped envelope, so that impact forces stay within the boundary in a manner providing improved impact strength and greater energy absorption during an impact. At the same time, the front structure provides a homogeneous structure that distributes local impact stresses uniformly and more widely into the rear structure, thus providing a more uniform impact resistance less sensitive to impact location.

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1. An apron for a vehicle front end under a primary bumper beam, comprising: a unitary molded component having a front structure and a rear structure joined by an offset portion, the front and rear structures extending at rearward downward angles, and the offset portion extending at a rearward upwar

1. An apron for a vehicle front end under a primary bumper beam, comprising: a unitary molded component having a front structure and a rear structure joined by an offset portion, the front and rear structures extending at rearward downward angles, and the offset portion extending at a rearward upward angle. 2. The apron defined in claim 1, wherein the rearward downward angles of the front and rear structures extend at a same downward angle. 3. The apron defined in claim 1, wherein the front structure, rear structure, and offset portion define a same vertical cross-sectional thickness dimension. 4. The apron defined in claim 1, wherein upper and lower surfaces of the apron define an envelope, and wherein lines extending horizontally from a front edge of the apron stay within the envelope. 5. The apron defined in claim 1, wherein: the rear structure defines adjacent channels extending in a fore-aft direction with adjacent channels being alternatingly upwardly and downwardly open;the front structure has a constant fore-aft depth and extending a full width of the rear structure and defining a non-linear front edge; andthe channels of the rear structure each form high and low force-generating locations when impacted, but the front structure distributes stress into the rear structure regardless of which channel is impacted. 6. An apron for a vehicle front end comprising: a unitary molded component having a front structure and a rear structure joined by an offset portion, the rear structure defining adjacent channels extending in a fore-aft direction with adjacent channels being alternatingly upwardly and downwardly open; the front structure having a constant fore-aft depth and extending a full width of the rear structure and defining a non-linear front edge; the channels of the rear structure each form high-impact-strength and low-impact-strength locations when impacted, but the front structure being configured to distribute stress uniformly into the rear section regardless of which location is impacted. 7. An apron for a vehicle front end under a primary bumper beam, comprising: a unitary molded component having a front structure and a rear structure joined by an offset portion the front and rear structures extending at rearward downward angles, and the offset portion extending at a rearward upward angle;wherein the front and rear structures and offset portion include upper and lower surfaces defining a boundary having a wave shape, and wherein the front structure defines a front edge with a tip that extends a full width of the front structure, and where lines extending horizontally rearward from the tip lie entirely within the boundary. 8. The apron defined in claim 7, wherein the lines define a horizontal plane. 9. An apron for a vehicle front end under a primary bumper beam, comprising: a unitary molded component having the front rear structures joined by an offset portion, the front structure and rear structures extending at rearward downward angles, and the offset portion extending at a rearward upward angle;wherein the front structure includes a front end having a lowest point and the rear structure includes a highest point, and wherein the offset includes material connecting the lowest point to the highest point, a step height being defined by the distance between the lowest point and the highest point, and wherein the rear structure includes columns having a beam vertical dimension; andwherein a ratio of the step height to beam vertical dimension is 125% to 300%. 10. The apron defined in claim 9, wherein the ratio is 150% to 300%. 11. The apron defined in claim 10, wherein the ratio is 200% to 300%. 12. An apron for a vehicle front end under a primary bumper beam, comprising: a unitary molded component having a front structure and a rear structure joined by an offset portion, the front and rear structures extending at rearward downward angles, and the offset portion extending at a rearward upward angle;wherein the front structure includes a front end with a tip and has a front fore-aft dimension; and wherein the apron has a total fore-aft dimension;wherein the front fore-aft dimension as a ratio with the total fore-aft dimension is within a range of between 5% and 75%. 13. The apron defined in claim 12, wherein the ratio is between 10% and 25%. 14. The apron defined in claim 12, wherein the ratio is between 60% and 75%. 15. A vehicle system comprising: a vehicle front end;a primary bumper system including a bumper reinforcement beam and a polymeric energy absorber on a face of the beam; andan apron extending generally horizontally and supported on the vehicle front end at a location spaced below the primary bumper system;the polymeric energy absorber and the apron having structure that, when impacted against a pedestrian leg, define force deflection curves having a same shape. 16. A vehicle system comprising: a vehicle front end;a primary bumper system including a bumper reinforcement beam and a polymeric energy absorber on a face of the beam; andan apron extending generally horizontally and supported on the vehicle front end at a location spaced below the primary bumper system;the polymeric energy absorber and the apron including faces defining a vertical structure where a pedestrian leg is impacted substantially simultaneously by both faces during an impact, and the apron, when impacted against the pedestrian leg, generates a force deflection curve that continues to rise during at least 90% of an impact stroke of at least 50 cm. 17. A method of designing a vehicle system comprising steps of: providing a vehicle front end including a primary bumper system with a bumper reinforcement beam and a polymeric energy absorber on a face of the beam, the energy absorber having a first force-deflection curve when impacted by a pedestrian-leg-simulating test device;designing an apron to have a second force-deflection curve that, when impacted by a pedestrian-leg-simulating test device, has a same shape as the first force-deflection curve;attaching the apron to the vehicle front end below the primary bumper system; andimpacting the polymeric energy absorber and the apron against a pedestrian-leg-simulating test device to determine leg injury characteristics.